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Ask us (almost) anything about our Wind Tunnel
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Alright, many of you may have heard that we (Specialized) launched an in house wind tunnel here at Morgan Hill last night. This being a relatively technical crowd, we wanted to open the door to questions and feedback. So ask away! Almost anything is fair game, from the tunnel, to our aero R&D process in general, to the people behind it. I want to be as open as possible, but there will be a few things that I unfortunately can't go into details about (e.g. financials of the project, details about the technical design of the force balance - we can chat specs and capability all day though!).

And just to answer a few of the big questions right off the bat:

What's the big deal and why did you do it?

The main thing everyone will think of when they see that we have built our own facility, is that we will now have quick turnaround times in the aero R&D process. Great for us, and hopefully indirectly great for our riders since it'll allow for more wild ideas to have a shot. But, that's just the one of the reasons we pulled the trigger. It'll allow us to do athlete testing (and not necessarily just at the world pro-level) much more effectively since we're no longer limited by time and we can customize the facility to be a better simulator of "real world" riding. But the biggest one (I think) is the outreach component. Since we can walk in and fire up the fans literally any time we want, we're able to connect with riders and help answer some of the big (or small!) aero questions. So I imagine being able to either come here on ST, or have some space where people can ask serious or silly aero questions and we go into the tunnel the next day and shoot a short video clip, answering that question with a test.

So what? Why do I care as a consumer since I can't directly buy a product here?

True, you can't directly buy anything since we're not selling tunnel time. But indirectly, the stuff that comes out of it will have the benefit of a basically unprecedented number of tunnel R&D hours (especially the stuff that gets 0 tunnel test time now). And the bigger part of it is what I alluded to above. We want this to be as much an outreach tool as it is an R&D tool. Aero in cycling is still relatively confusing and misunderstood - ok, maybe not as much with you guys on ST - but the vast majority of riders don't have a good grasp on why aero matters or what it can do for them. We want to be able to help educate and this will very much be a group-think exercise.

Isn't wind tunnel testing off the back already? Is it really that representative of the real world?

There's been a lot of discussion lately about tunnel testing being off the back since it's not that realistic, especially given the rise of on-track data tools. There's two things I want to address:

First, the neat thing about building and designing our own facility is that we can put in anything we want. We're not limited to basically putting a trainer into an existing tunnel and testing bikes that way. We have the freedom to build any apparatus that we feel will better simulate real-world riding. We're not the first here: F1 teams have been doing full course simulations for a particular track in the tunnel for a while now.

Second, aerodynamics is not something that you can effectively study with just one tool. Sure, you can get a pretty good idea with smart use of any one tool, but to get a complete picture you really need 3 big ones: CFD, on-road or field test data, and a controlled test environment in the tunnel. The on-road equipment allows us to determine "boundary conditions" for how to setup a test either in simulation or in the tunnel. It also allows us to double check that what we're seeing on the computer or in the tunnel is actually translating to riding your bike outside. CFD is a very powerful tool in the design space but to do it right and to use it for a full product design (and, trust me, it is *very* easy to do it wrong - there are a lot of virtual knobs to turn to setup a test) requires a lot of computational horsepower. This means that compromises will need to be made, in terms of how many and what dynamic riding effects to include. However, as a quick and dirty evaluation tool at the front end of the design cycle and a very precise, localized design optimization tool at the end of the design cycle, it cannot be beat. And that's where we get to the tunnel: everything in between is just better to do in a controlled lab environment. We can setup a test and be able to apply the same test conditions over and over again. That consistency is how we can make sure something we've changed is actually better.

(edited for typos)

----

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Last edited by: chrisyu: May 18, 13 21:32
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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What is the reported precision of the wind tunnel?
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Not so much a question, more an idea that I think would be super cool, and probably could help convince someone like myself to buy a nicer bike... this goes along with the stories of buying a VW in Germany. You go pick up your car from the factory, and kind of get to make a day out of it.

How about, if you buy an S-Works bike (or something of that nature), a couple hours of wind tunnel testing to optimize you is thrown in. You are paying a premium, sure, but its something you could offer that no other manufacturer can. Your LBS could have the bike shipped to the tunnel spec'ed out and pre-fit to your coordinates, and then you take a little trip there, spend a few hours with the tunnel, go over tech stuff, make changes, etc. Then, its shipped back to the LBS to pick up It could certainly get someone on the edge of upgrading from a Pro level to an S-Works.

I'm sure your dealers would love it, as it would mean extra time spent there. I would love to spend some time in a wind tunnel, if for no other reason that having the neat-o factor, but I would never spend the money on it. My .02 anyways....

Go Cyclones! In Hoc Signo Vinces. Twitter @Cise_Smash
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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story, and photo gallery, will be up on the home page in about 20 minutes. i have this question for you, chris, and it might not be something you can answer, but i think specialized has been nosing around the idea of a wind tunnel for awhile, and came close to buying a wind tunnel that came on the market several years ago. can you give me a chronology in the evolution of mike sinyard's interest in the and execution of a wind tunnel proximate to the design center at specialized?

Dan Empfield
aka Slowman
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hi
Thanks for this opportunity. I am lucky that my local bike store carries specialized.
My question is about helmets. At the age of 46 I am getting into olympic distance triathlons with the goal of being good at it by the time I am 50. Now, I have bought the shiv comp rival 2013 and have been giving it regular rides. What helmet should I get?
Is Specialized coming out with a semi-aero helmet, similar to the Giro air-attack? The true aero helmets seem too radical and niche for me and the typical road helmets not aero enough. My cycling position isnt ideal...I shift my hands...I tuck and then sit up and then may stand on the pedals briefly...I want a helmet that is light and usable daily.
Get in your wind tunnel and simulate an olympic bike ride with a few hills and hairpins and please tell me, for the age group competitive triathlete what is the best helmet?
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Re: Ask us (almost) anything about our Wind Tunnel [lorenzo7] [ In reply to ]
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lorenzo7 wrote:
Get in your wind tunnel and simulate an olympic bike ride with a few hills and hairpins and please tell me, for the age group competitive triathlete what is the best helmet?

Uhm....seriously?

John



Top notch coaching: Francois and Accelerate3 | Follow on Twitter: LifetimeAthlete |
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Alright, many of you may have heard that we (Specialized) launched an in house wind tunnel here at Morgan Hill last night. This being a relatively technical crowd, we wanted to open the door to questions and feedback. So ask away! Almost anything is fair game, from the tunnel, to our aero R&D process in general, to the people behind it. I want to be as open as possible, but there will be a few things that I unfortunately can't go into details about (e.g. financials of the project, details about the technical design of the force balance - we can chat specs and capability all day though!).

Thanks for the opportunity and for taking the time to post on Slowtwitch. This is an exciting move and decision for Specialized, I am looking forward to seeing its impacts on products and R&D overall.

Who at Specialized will be responsible for the prioritization of products that will make it to the tunnel? Is there a road map already? Will all bikes and components include some aero testing or will it be limited to specific models/lines/etc?

Thanks in advance

:)
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Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
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Slowman wrote:
story, and photo gallery, will be up on the home page in about 20 minutes. i have this question for you, chris, and it might not be something you can answer, but i think specialized has been nosing around the idea of a wind tunnel for awhile, and came close to buying a wind tunnel that came on the market several years ago. can you give me a chronology in the evolution of mike sinyard's interest in the and execution of a wind tunnel proximate to the design center at specialized?

If we are thinking of the same wind tunnel, then they made the right decision.

__________________________

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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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What test section size did Specialized choose?

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Re: Ask us (almost) anything about our Wind Tunnel [Devlin] [ In reply to ]
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Devlin wrote:
lorenzo7 wrote:
Get in your wind tunnel and simulate an olympic bike ride with a few hills and hairpins and please tell me, for the age group competitive triathlete what is the best helmet?


Uhm....seriously?

John

Sheer gold. Wow.

"One Line Robert"
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
----

All this effort to plan and build something in secret... why waste time on a wind tunnel when a Death Star is clearly what is needed (plus you guys would do a better job on the design)?

Seriously though, when does Specialized expect to realize it's first product that is directly impacted by having this facility?
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Re: Ask us (almost) anything about our Wind Tunnel [lorenzo7] [ In reply to ]
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lorenzo7 wrote:
Hi
Thanks for this opportunity. I am lucky that my local bike store carries specialized.
My question is about helmets. At the age of 46 I am getting into olympic distance triathlons with the goal of being good at it by the time I am 50. Now, I have bought the shiv comp rival 2013 and have been giving it regular rides. What helmet should I get?
Is Specialized coming out with a semi-aero helmet, similar to the Giro air-attack? The true aero helmets seem too radical and niche for me and the typical road helmets not aero enough. My cycling position isnt ideal...I shift my hands...I tuck and then sit up and then may stand on the pedals briefly...I want a helmet that is light and usable daily.
Get in your wind tunnel and simulate an olympic bike ride with a few hills and hairpins and please tell me, for the age group competitive triathlete what is the best helmet?

For what reason have you ruled out the conventional aero helmets on the market? There are so many options at the moment with a very wide variety of tail shapes, ranging from the very long (Specialized TT2, Kask K31, LG Superleggera, Giro Advantage, LAS Krono) to medium length (Lazer Tardiz, Bell Javelin, Giro Selector) to short (Rudy Project Wingspan), to non-existent (Kask Bambino, Giro Air Attack, LAS whateverit'scalled). I'm dubious that one of the existing helmets won't fundamentally meet your needs, but this is not to say that I'm not interested in seeing what Specialized can do.

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Re: Ask us (almost) anything about our Wind Tunnel [ZackCapets] [ In reply to ]
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it's massive, as tunnels go. there's pics on the home page. it's an interesting tunnel. open circuit. with a gallery for viewers, which i've never seen. you could either watch something being aero tested, or you could watch somebody being executed. it looks kind of like that room. plus, if you put the guy on the balance, you could execute him at various yaw angles, so that the spectators could see it from various points of view.

in all seriousness, tho, pretty cool tunnel.

Dan Empfield
aka Slowman
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Will you be testing a new aero version of your S-Works Epic 29er in there?

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Re: Ask us (almost) anything about our Wind Tunnel [morey000] [ In reply to ]
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Actually, if you read any of the press releases, they'll be testing everything from TT bikes to commuters and designing appropriately.

So no need for pink font. Or red. Or whatever that is you just used.

"One Line Robert"
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Re: Ask us (almost) anything about our Wind Tunnel [ZackCapets] [ In reply to ]
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Being fairly new to triathlon I havent tried on any of the aero helmets and I dont see them in the stores that I frequent. But, my impression is that they are heavier than road helmets, that they are hard to put on, that they are poorly ventilated and that their benefits are greatest when worn in a stable position at high bike speeds. I have seen posts that say that they should be worn only in triathlons and time trials and not for training rides...this greatly limits their usefulness to me.
When I see broadcasts of olympic distance triathlons I see road helmets and the odd semi-aero helmet. When I see photo galleries from ironman I see aero helmets.
So, given the way that I want to use my helmet I am curious if there is any benefit to a semi-aero helmet over a road helmet.
Living in a semi-rural area...I have one bike store within an hours drive and it carries Specialized. So, I am most interested in whether Specialized will be coming out with a semi-aero bike helmet. And, whether that helmet will have any benefits over a road helmet to me.
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
So what? Why do I care as a consumer since I can't directly buy a product here?

True, you can't directly buy anything since we're not selling tunnel time. But indirectly, the stuff that comes out of it will have the benefit of a basically unprecedented number of tunnel R&D hours (especially the stuff that gets 0 tunnel test time now). And the bigger part of it is what I alluded to above. We want this to be as much an outreach tool as it is an R&D tool. Aero in cycling is still relatively confusing and misunderstood - ok, maybe not as much with you guys on ST - but the vast majority of riders don't have a good grasp on why aero matters or what it can do for them. We want to be able to help educate and this will very much be a group-think exercise.

What I think might benefit the average consumer (i.e. the one that isn't buying the latest greatest superbike every year) is to go back to some of your older model years (Say the last 5 years) and test them with various wheels/aerobar/bento, etc., and offer value that way. That is something that would absolutely buy my brand loyalty, and probably that of many other age groupers who may only buy a bike once every few years.

I hate hashtags on forums, but #aeroiseverything and #gettingthemostoutofwhatyougot.

John



Top notch coaching: Francois and Accelerate3 | Follow on Twitter: LifetimeAthlete |
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Re: Ask us (almost) anything about our Wind Tunnel [wsrobert] [ In reply to ]
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wsrobert wrote:
Actually, if you read any of the press releases, they'll be testing everything from TT bikes to commuters and designing appropriately.

So no need for pink font. Or red. Or whatever that is you just used.

Sweet!! Finally a more aero expedition sport!!

_________________________________________________
When all is said and done. More is usually said than done
Ba Ba Booey

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Re: Ask us (almost) anything about our Wind Tunnel [Turd Ferguson] [ In reply to ]
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"I feel like I'm always late while trying to navigate to the grocery store. Do you have a more aero commuter bike?"

"One Line Robert"
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Can I come for a visit? Pleeeeease????? :-)

AndyF
bike geek
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hey guys, stoked to get so much response so quickly! I promise I'll get to everyone in a bit...I'm about to head out on course for the ATOC TT to do some last sec. wind data checks for our riders. Will be back in a few!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [lorenzo7] [ In reply to ]
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lorenzo7 wrote:
Being fairly new to triathlon I havent tried on any of the aero helmets and I dont see them in the stores that I frequent.
Many well-equipped bike shops, even those catering to triathletes, don't have a huge selection of aero helmets. My LBS, Inside-Out Sports, is an exception in that they do carry a substantial number for trying on and buying. Otherwise, I think most people would buy online.
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But, my impression is that they are heavier than road helmets, that they are hard to put on, that they are poorly ventilated and that their benefits are greatest when worn in a stable position at high bike speeds.
They are a bit heavier (typically ~350-400g vs. ~200-300g for a road helmet). Some people make a big deal out of this given that from a percentage standpoint there is a fairly large difference between the two, but in the absolute sense 100g is a minuscule amount of additional weight. I think more often than not those who report aero helmets causing some additional discomfort due to the weight would have been equally uncomfortable in a lighter road helmet, that is, it's the position more so than the weight that makes people uncomfortable. A wet ponytail adds more weight to a girl's head than an aero helmet does. As for putting it on, there are many that are quite easy to put on, as well as some that are not so easy. Generally, the larger the ear flaps on the helmet, the more difficult it will be to put it on and take it off. As with everything else, a bit of practice goes a long way. I have one of the most restrictive helmets on the market and it goes on in transition with ease. Regarding ventilation, you're generally correct, sometimes it makes a difference, sometimes it doesn't. Several manufacturers have come up with elegant solutions to the problem of overheating. I've never personally overheated as a result of my aero helmet being too hot, and I've done some extremely hot races.
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I have seen posts that say that they should be worn only in triathlons and time trials and not for training rides...this greatly limits their usefulness to me.
I suppose you could use it in training also. It's generally a race-day only option.
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When I see broadcasts of olympic distance triathlons I see road helmets and the odd semi-aero helmet. When I see photo galleries from ironman I see aero helmets.
So, given the way that I want to use my helmet I am curious if there is any benefit to a semi-aero helmet over a road helmet.
The right aero helmet will make you faster regardless of the distance at which you're racing. Bike speed and positioning play a greater role in the determination as to which helmet is the best for you. For all anyone knows one of these round-ish, tailless helmets you're calling "semi-aero" could be the fastest helmet for you. There are patterns to which helmets end up being fastest for which types of people, but the only way to know for sure is to test.

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Living in a semi-rural area...I have one bike store within an hours drive and it carries Specialized. So, I am most interested in whether Specialized will be coming out with a semi-aero bike helmet. And, whether that helmet will have any benefits over a road helmet to me.

Reasonable.

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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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This is just cool!!!

It brings back memories of when I built my windtunnel (albeit much, much smaller and much less $$$) for my 8th grade science project to test drag coefficients of various shapes.

Of course, one of my goals was just to get out of class, since someone had to operate the tunnel during the science fair :)

Team Kiwami
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Re: Ask us (almost) anything about our Wind Tunnel [Nick_Barkley] [ In reply to ]
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Hey Nick,

I assume you mean precision of the force balance? For a controlled setup (e.g. not a human pedaling), we expect to see +/-2 gF over a 10s sample. In full disclosure, we are very close to that currently but have some tweaks to perform to nail the target. And of course, once you add in a human, the precision is dictated by how well the rider can hold a position...so the answer there is "it depends."

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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I know that you are hiring interns, but do you hire canadian interns (or only US)? I think this detail is not specified in your website and as a mechanical engineering student it would be awesome to work in the tunnel for a few months :)
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Re: Ask us (almost) anything about our Wind Tunnel [thepaul500] [ In reply to ]
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Great idea....believe me, the wheels are turning in everyone's heads. Not sure when and how we can accommodate something like that, but it would be cool. Failing that, at a minimum we can "give" people aero tidbits and information that may not be as sensitive to the particular rider (e.g. equipment setups) via videos or FAQ entries, etc...

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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I've always been curious where most of the cost of a high quality wind tunnel comes from.
ie. Is it from the large "tunnel" itself? Or R&D? Or from the "drag sensing equipment" or something else?
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Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
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Hey Dan,

Yeah, Specialized had been toying with the idea for the last 4 years or so (before my time with the company). There were times where it started rolling, then backed off again for one reason or another. The big requirements the entire time were: near our HQ and needed to be designed completely by us (allowing us to control every part of the process and the ability to modify or change things down the road).

About a year and a half ago, I joined the team and happened to come in at a time when the ball was rolling again. Around that time, (as you mention and Jordan knows well) a tunnel at Swift was decommissioned and offered at auction. We had some interest in re-purposing pieces of it (most notably the fan), but decided against mostly due to restriction on ultimate size. Pencil to paper started just about a year and a half ago and once we showed a viable design for the space that we had, Mike was all for it and pulled the trigger. Here we are now!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [lorenzo7] [ In reply to ]
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Hey, I think it's great that you're getting into the sport! It's never too late! You're already setup pretty well with that Shiv - as for the helmet, I hear your concerns and it's a common one that we've heard over and over again. All I can say is to stay tuned this summer....

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [neda] [ In reply to ]
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Yea, that's an interesting question. In a short span of time, we went from triage mode - figuring out which select group of products and prototypes got to have tunnel time - to the situation you've posed: figuring out how to prioritize what goes into it. For now, I'm juggling all the different groups and athletes to make sure everything hits the right timeline (in terms of product launches or important races for our athletes). There's literally a line at my desk internally looking for time to test - and I'm certainly not complaining! No limit or restriction on what will go in - anything flies. My new motto has become: "why not?"

Though we might need to put a cot in the control room...

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [ZackCapets] [ In reply to ]
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The cross-section is 16' wide by 10' tall. The cool part is that it's 30' long, which is unusually long for a tunnel this size. This was one of the original design targets (maximizing overall size of the test section) and knowing that we only needed to hit reasonable human speeds at the top end meant that we could get away with a lot without resorting to an insane fan power requirement.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Thanks for taking the time to answer, and for being candid. Best of luck with this, I am pretty sure that you'll need some rigorous and transparent triaging processes very soon, but in the mean time those people in line offer great "bribing" opportunities: ask for a king size cot ;)
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Re: Ask us (almost) anything about our Wind Tunnel [pick6] [ In reply to ]
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Haha, as cool as a Death Star would be, I'm an aero dork so the wind tunnel beats it in my book.

That's a good question - and honestly I'm not sure. We're obviously spending time in it on the big stuff like bikes, but we make a lot of other things that have faster design to production times that could make it out to market sooner after seeing time in the tunnel. I know, it's a bad answer but it's the best I can do.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [morey000] [ In reply to ]
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I know that's in pink (red?) but I don't think it's too far off. The top end XC racers are going so fast and races can be decided by so little - why not?

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Devlin] [ In reply to ]
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Hey John,

Yup, you hit the nail on the head. We will continue to design the fastest bikes that we can using the tunnel, but a huge secondary use is to do what you're suggesting. We can show riders how to best use what they have already and go over things that matter aerodynamically, and things that may not matter so much (and by how much). Of course, a lot of things are rider dependent, but other things may not be that sensitive. Bottom line is we want to have it as interactive as possible outside of our product R&D activities.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [wsrobert] [ In reply to ]
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You might be joking, but again - why not?

I'm sure you guys have seen those youtube videos of the commuters in Europe on the bike paths getting blown all over the place. Or those of you that commute - how much does it suck when you're trying to get home and you're riding right into a headwind? Aero matters. Even for commuters.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [AndyF] [ In reply to ]
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Oh Andy, you're definitely welcome. Let me know the next time you're in the Bay Area!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Oh Andy, you're definitely welcome. Let me know the next time you're in the Bay Area!


Yay!!! I'm going to Disneyland!!! ;-)

(I know, I know -- it's just an expression.)

AndyF
bike geek
Last edited by: AndyF: May 17, 13 15:34
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Re: Ask us (almost) anything about our Wind Tunnel [owtbac86] [ In reply to ]
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Haha, that is awesome...I did almost exactly the same thing. I had a small tunnel in my 7th grade science fair. Lots of straw cutting!!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Ossbr] [ In reply to ]
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Hey, good question. Honestly I don't know for sure, but I would just apply anyways and let our HR figure that out!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [AngrySaki] [ In reply to ]
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By far, the highest cost would typically come from the design (e.g. the man-hours to design the facility and run appropriate sims/calcs to verify the design). Usually you would contract that work out, but we were fortunate enough to have some world class experts consult with us from the beginning and between Mark Cote and I, we had enough tunnel background to hack something out ;-). As for the build itself, the cost is in the fans and balance equipment. Everything else is like constructing a building (albeit one with very precisely defined walls).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
The cross-section is 16' wide by 10' tall. The cool part is that it's 30' long, which is unusually long for a tunnel this size. This was one of the original design targets (maximizing overall size of the test section) and knowing that we only needed to hit reasonable human speeds at the top end meant that we could get away with a lot without resorting to an insane fan power requirement.

With it being that long will you do any multi bike interaction testing? In other words looking at how much benefit one gets at various draft distances and optimal drafting position (Direct vs V shape etc).
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hi Chris, I have some questions:

- Taking into account that you have developed the wind tunnel from scratch, why have you decided to go with rollers instead of a solution that represents better real world conditions (like a treadmill)? Some of the wind tunnels here in Europe have that type of equipment (Magny-Cours and Mercedes' one) and some manufacturers take a different approach to rear end design due to this. M.N. Godo said in one of his papers that ground modelisation was one of the limiting factors to achieve perfect WT-CFD correlation. Do you think that this can play a big role in correlation?

- Are you able to measure torque to spin (rotational drag)?

- Can you explain us your approach to WT pedalling tests? I know that M. Cote did some testing to know which static position of the legs gives the same average drag but this was limited to 0ş yaw and a bike model. Do you extrapolate those results for other yaws/bikes like Cervélo does or do you have a pedalling mannequin like Trek and Speedplay?

Thanks for your answers

http://cds-0.blogspot.com
Last edited by: Epic-o: May 17, 13 16:52
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hi Chris,

Maybe I'm asking some dumb questions so excuse my ignorance. How much space does the wind tunnel take in side that warehouse? Are there any plans to add other things inside that warehouse to complement the windtunnel? Would that be possible? Classrooms, road simulation testing? Rider testing and development I could see this as a real plus for the Specialized factory riders. Sorta an "All-in-One" Bike and Rider development facility.
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Hey Nick,

I assume you mean precision of the force balance? For a controlled setup (e.g. not a human pedaling), we expect to see +/-2 gF over a 10s sample. In full disclosure, we are very close to that currently but have some tweaks to perform to nail the target. And of course, once you add in a human, the precision is dictated by how well the rider can hold a position...so the answer there is "it depends."

Awesome. Thanks.
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Convenient how close you are to Ames too... :P

(My uncle is one of the windtunnel wizzes there)

The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important.

-Albert J. Nock
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Reasonable. Any idea on the power draw at 30mph? I'm assuming you went with variable speed fans rather than variable pitch?

__________________________

I tweet!

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Re: Ask us (almost) anything about our Wind Tunnel [LostNTransition] [ In reply to ]
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Absolutely. We wanted to be able to study all sorts of configurations - for team time trials, what's the optimal order for a set of riders - for mass start races, where in a pack is the best to be (and if/how the relative importance of each piece of aero equipment changes). So in summary, yes.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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Good questions! I'll answer below:


Epic-o wrote:
Hi Chris, I have some questions:

- Taking into account that you have developed the wind tunnel from scratch, why have you decided to go with rollers instead of a solution that represents better real world conditions (like a treadmill)? Some of the wind tunnels here in Europe have that type of equipment (Magny-Cours and Mercedes' one) and some manufacturers take a different approach to rear end design due to this. M.N. Godo said in one of his papers that ground modelisation was one of the limiting factors to achieve perfect WT-CFD correlation. Do you think that this can play a big role in correlation?

The beauty is we're free to put in any apparatus that best answers the question that we're trying to ask. For bike and equipment R&D, having a robust setup allows us to have very repeatable measurements which makes it easier to determine how/what we've changed. I've looked a bit at ground effect and for the vast majority of the bike/rider system (e.g. everything but the wheels), it's essentially a negligible impact. I believe the Godo study was on wheels. We looked at, but for now have avoided, a rolling road setup since it's just so hard to setup a test with the precision that we want...it's added complexity that does not necessarily gain us much. However, when we're talking about riders, we are very much interested in how to make the tunnel experience more representative of the real world riding. The trick is balancing that with high enough precision to still be useful. We have some ideas there...

Epic-o wrote:

- Are you able to measure torque to spin (rotational drag)?

Yup, we are getting setup to do so. The thing to remember though is any measurement of rotational drag in the tunnel will include rolling resistance (the so-called power-to-spin measurement will include rolling resistance and aerodynamic drag from rotation). So to tease out the aerodynamic drag component, we can measure the Crr in our test lab - or we can use the same tire and mounting load (normal force) for comparative studies.

Epic-o wrote:
- Can you explain us your approach to WT pedalling tests? I know that M. Cote did some testing to know which static position of the legs gives the same average drag but this was limited to 0ş yaw and a bike model. Do you extrapolate those results for other yaws/bikes like Cervélo does or do you have a pedalling mannequin like Trek and Speedplay?

Yea, Mark's study was enlightening, and we will continue to look at that at yaw. For R&D stuff, I still think that we need a setup that's as robust as possible so we can get the best possible precision. There's nothing worse than not knowing for sure whether you have something that's better or not just because the variability in the measurement is so high. If and when we find that we absolutely need a pedaling mannequin, that will happen. And cool side note: since it's our test section we can do stuff like: have a mannequin on a stinger separate from the balance - so we can swap out bikes and not worry about putting the mannequin back in exactly the same spot.

Epic-o wrote:
Thanks for your answers

No prob, anytime!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [King of Pain] [ In reply to ]
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King of Pain wrote:
Hi Chris,

Maybe I'm asking some dumb questions so excuse my ignorance. How much space does the wind tunnel take in side that warehouse? Are there any plans to add other things inside that warehouse to complement the windtunnel? Would that be possible? Classrooms, road simulation testing? Rider testing and development I could see this as a real plus for the Specialized factory riders. Sorta an "All-in-One" Bike and Rider development facility.

Not a dumb question at all. The tunnel is just over 100ft long. We've taken over essentially 1/3 of the floor space in that building and sectioned it off for the tunnel. We currently have one control room, but it was designed for an identical one on the opposite side of the test section. So as you've mentioned, we'll have more space for either a rider lounge, fit studio, or workshop, depending on what we're doing in the tunnel. We already have a locker room and showers in that area so we are setup to test riders comfortably. I like the "all-in-one bike and rider development faciltiy"...may need to steal that one!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Nick_Barkley] [ In reply to ]
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I forgot to mention that I'm using gF units since that's what everyone is familiar with (and honestly, it's more visceral...people can imagine what it feels like). Anyways, the number I quoted was for 50km/h...so scale appropriately for different speeds.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Derf] [ In reply to ]
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*Very* convenient in this case ;-)

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [ZackCapets] [ In reply to ]
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ZackCapets wrote:
Reasonable. Any idea on the power draw at 30mph? I'm assuming you went with variable speed fans rather than variable pitch?

Yup, that's correct. We're running variable speed fans rather than variable pitch to get the response time that we want. At 50km/h we're drawing roughly 100 kW total across the 6 fans.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hope the operations guys don't notice the hit to the electric bill and shut you down.... Ha ha.

100kW x 12hr per day x .15 $ per kW x 300 days a year is not a small bill.

I saw you've got plans for a solar panel.
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Aero test request!

Are you guys willing to release data on partners, even if they "lose" in the aero test?

If so...

Can you test the Flo disc/60 combo with conti 4000s 23mm vs zipp firecrest disc + 404 with zip tires?

Disc value opening tapped on both. Same skewer.

Do this on a s-works shiv please :).

*actually, any wheel combo testing with the shiv and venge would be appreciated. Change out tires too to hit the most popular ones and the 'aero' ones*

Also, please test bottle between the arm mounts on the shiv with the specialized carbon shiv aero bars.

CEO at TrainerRoad
Co-host of the Ask a Cycling Coach Podcast
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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As most of us STer's products are already tested in a rented wind tunnel, I am most excited by the potential for webinars. My question is will the tunnel be solely used for R&D of products or will it also be used as comparison amongst top brands for marketing purposes? If it will be used for comparison purposes, how do you plan on making it so no one can claim unfair testing protocol? Do you suspect product prices will drop since there is no longer the overhead of renting tunnel time?
Thanks,
Dave
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Re: Ask us (almost) anything about our Wind Tunnel [7401southwick] [ In reply to ]
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7401southwick wrote:
Hope the operations guys don't notice the hit to the electric bill and shut you down.... Ha ha.

100kW x 12hr per day x .15 $ per kW x 300 days a year is not a small bill.

I saw you've got plans for a solar panel.

Haha, fortunately our operations guys are awesome and yes, we're looking at ways to partially or fully offset the fan power draw so we can claim to also be the greenest wind tunnel! But in seriousness, it's not a small amount but that number equates to just a handful of test days if we were to travel to another tunnel to do a test (accounting for rental, travel and shipping costs - not to mention engineer time away from the office).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Nate Pearson] [ In reply to ]
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Nate Pearson wrote:
Aero test request!

Are you guys willing to release data on partners, even if they "lose" in the aero test?

If so...

Can you test the Flo disc/60 combo with conti 4000s 23mm vs zipp firecrest disc + 404 with zip tires?

Disc value opening tapped on both. Same skewer.

Do this on a s-works shiv please :).

*actually, any wheel combo testing with the shiv and venge would be appreciated. Change out tires too to hit the most popular ones and the 'aero' ones*

Also, please test bottle between the arm mounts on the shiv with the specialized carbon shiv aero bars.


You got it...well I can't promise every single combination (because we do have to buy our test samples!) but we will try things that are either in popular use or make sense and show you all what comes out. Yes, we run into the possibility of something testing faster than what we make - in that case I hope to be able to argue why we may still have the most beneficial or advantageous setup overall, but if not, hey at least we learned something!

Edited to add: We want to get all this out to you guys asap but we have a queue of stuff we need to get to (like I said, everyone here at HQ is waiting to test something). I'll keep the ST crowd posted when we start doing the fun stuff...

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Last edited by: chrisyu: May 17, 13 23:06
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Re: Ask us (almost) anything about our Wind Tunnel [number114] [ In reply to ]
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number114 wrote:
As most of us STer's products are already tested in a rented wind tunnel, I am most excited by the potential for webinars. My question is will the tunnel be solely used for R&D of products or will it also be used as comparison amongst top brands for marketing purposes? If it will be used for comparison purposes, how do you plan on making it so no one can claim unfair testing protocol? Do you suspect product prices will drop since there is no longer the overhead of renting tunnel time?
Thanks,
Dave

That's a good question. To be honest, I'm not sure how the product marketing will happen. Up until now, for aero products, it's been a graph or two with the product release. We can brainstorm on what would be more effective for you guys. Maybe we do a video documenting a test? Either way, tunnel testing is becoming more and more common - many magazine reviews are even including test data (Velonews, Tour Mag.). So I'm sure there will still be independent data out there.

As for the product prices dropping - I'm definitely the wrong person to ask about that one! But it's likely a question of how much more can we do for the same R&D dollars as before rather than how much we can save.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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This is great guys...keep 'em coming! I know Mark (MITaerobike) has been running back and forth like crazy the last couple of weeks but he promises to come on to answer questions as well!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Crazy Idea: aero crank arms

Does the shape of the crank arm have any affect on drag while pedaling at multiple yaw angles?

Crazy Idea: aero shoe

Why do I have to put shoe covers on to make my shoe aero? I can't do that in a tri (but shoe covers save time).

We need some type of shoe with the ratchet in the heel (maybe entry point is in the heel too). The rest if the shoe should be really aero/smooth.

Crazy idea: big fat shiv seat posts

Seems like there would be a lot of crazy air around your seat post while pedaling. Can you dramatically change the shape of the seat post so that it decreases drag while pedaling?

Simple idea: aero center pull brakes

This one should be easy(ier)

CEO at TrainerRoad
Co-host of the Ask a Cycling Coach Podcast
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Re: Ask us (almost) anything about our Wind Tunnel [Nate Pearson] [ In reply to ]
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I've used shoe covers for an IM. Pre put on ver the cleat then just pulled ver the heal. Probably took 4 seconds if that. Although there are some very aero shoes out there, ie Giro Empire, but I'd tape over the laces.

Styrrell
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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What air speeds are available to you for testing? I ask this because everything that I've read that you and other companies post is ~30mph, this isn't really indicative of your average triathlete's speed.
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Do you plan to set up a PIV system (DEHS or similar)?

http://cds-0.blogspot.com
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Re: Ask us (almost) anything about our Wind Tunnel [Nate Pearson] [ In reply to ]
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Nate Pearson wrote:
Crazy Idea: aero crank arms

Does the shape of the crank arm have any affect on drag while pedaling at multiple yaw angles?

Crazy Idea: aero shoe

Why do I have to put shoe covers on to make my shoe aero? I can't do that in a tri (but shoe covers save time).

We need some type of shoe with the ratchet in the heel (maybe entry point is in the heel too). The rest if the shoe should be really aero/smooth.

Crazy idea: big fat shiv seat posts

Seems like there would be a lot of crazy air around your seat post while pedaling. Can you dramatically change the shape of the seat post so that it decreases drag while pedaling?

Simple idea: aero center pull brakes

This one should be easy(ier)

Nice...that's a good list of ideas! Can't give away everything that we're looking at, but I will say that looking at crank arm shape is one of the reasons why you need a dedicated balance with high precision - at the tunnels we have gone to, any changes we studied have been within the noise. On the topic of shoe covers - there are actually shoes out there that test fast without them (you would be hard pressed to find a cover that made the shoe faster). The new S-Works road is one of them...

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chris948] [ In reply to ]
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chris948 wrote:
What air speeds are available to you for testing? I ask this because everything that I've read that you and other companies post is ~30mph, this isn't really indicative of your average triathlete's speed.


Yea, 30mph or ~50km/h has been the standard. And really, scientifically speaking, it's perfectly valid. In the speed range of any cyclist, the flow doesn't qualitatively change - the forces just scale with velocity (actually velocity squared). So by testing at a higher speed you get a cleaner signal since you're higher off the noise floor. Also, in most tunnels 50km/h is about the min. that you can go. Anyways, we can run our tunnel reliably from 10km/h up to 100 km/h (at the low end, the balance needs to have super high resolution and be ultra precise to tease out any changes).

Edit to add: To directly answer your question, we will run tests at lower and more typically attainable speeds to demonstrate what I pointed out above (heck, maybe I'm completely wrong and there's some crazy flow phenomenon that happens...wouldn't be the first time).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Last edited by: chrisyu: May 18, 13 9:35
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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Epic-o wrote:
Do you plan to set up a PIV system (DEHS or similar)?

Yeah, good visualization techniques will definitely be a part of the process. We have a high freq., multi-component pitot that we can use to do velocity and pressure mapping and will be looking at PIV systems as well as other high speed flow field viz systems. It's all a question of whether the juice is worth the squeeze - for example, simple micro tufting is still a really powerful and cheap tool.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chris948] [ In reply to ]
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Hey all,

I've been dormant on this site for a while....well now you know why. Chris, myself, and the team here has been jamming on this windy hallway for a while now. I'll do my best to be present for questions but between Chris and I, we'll make sure we're available.

On this question:

What air speeds are available to you for testing? I ask this because everything that I've read that you and other companies post is ~30mph, this isn't really indicative of your average triathlete's speed.

We can test at all speeds from ~5-60 mph with fairly good data, but within the cyclist airflow regime, generally testing at 30 mph doesn't mean that we're only considering this speed. We capture wind speed (truly, dynamic pressure) and use drag measurements to calculate the riders coefficient of drag (or more detailed, their Cd * Frontal Area).

We run at 30 mph, as many people do for these tests, because the forces on the balance are a bit higher at the higher speeds (versus testing at 20 mph) and we can get better measurements. Then we use the coefficients and calculate what the drag or power req'd to overcome that drag would be at say, 18 mph or 24 mph, etc.

We'll of course be looking at running true speeds in the tunnel for an athlete as the wind will feel more realistic. Many are surprised what 30 mph feels like until you're sitting in the tube and catching all of that air!

Goal is to make this real -- so it feels and relates to cycling.

Mark

--
Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Last question, I promise

- I know that the industry standard is testing with a wheel rotation speed that matches the WT speed (bike-air relative speed) but have you analysed the effect of wheel rotational speed in both wheel and induced drag? Once you set your yaw and WT speed, there is an "infinity" of real world wind directions and bike speeds (and obviously wheel rotational speed) that can produce that yaw so even if you are in the same Re regime, the different rotational speed can modify the system drag.

http://cds-0.blogspot.com
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Re: Ask us (almost) anything about our Wind Tunnel [MITaerobike] [ In reply to ]
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MITaerobike wrote:
Many are surprised what 30 mph feels like until you're sitting in the tube and catching all of that air!

Thanks! I ride a sportbike, so very aware.
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Awesome! I have an sworks road on order already :)

CEO at TrainerRoad
Co-host of the Ask a Cycling Coach Podcast
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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You guys need to start aero.specialized.com. Make it a blog dedicated to the wind tunnel and aero testing. Like you said before, show the results even if you aren't the fastest. Educate me as a rider why this stuff matters and what to look for. You'd create a bond between the company and the consumer. Your marketing department should be all over this :).

For the CFD stuff you mentioned that specialized uses its own servers for this. Why did you guys go that way instead of aws it azure. Looks like you can spin up some huge aws servers working in parallel on cfd.

That might reduce the time it takes to do your cfd modeling and save some money. If you already have the servers though its a hard sell to management.

CEO at TrainerRoad
Co-host of the Ask a Cycling Coach Podcast
Last edited by: Nate Pearson: May 18, 13 13:50
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Re: Ask us (almost) anything about our Wind Tunnel [Nate Pearson] [ In reply to ]
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Nate Pearson wrote:
You guys need to start aero.specialized.com. Make it a blog dedicated to the wind tunnel and aero testing.

THIS
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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You said that building a test section with a large cross section was easy(er) because of the low speeds. My question is why soooo big? It seems that it wouldn't be so hard to test everything in a tunnel half that size. The only thing I can think of is analyzing longer test subjects (Like a TTT mentioned above).

___________________
"TRIATHLON ISN'T ACTUALLY THAT HARD OF A SPORT" -ALISTAIR
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Re: Ask us (almost) anything about our Wind Tunnel [C_Sousa] [ In reply to ]
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The largest issue we've had with other tunnels testing bikes has been blockage at higher yaws. A tunnel should only have 5-6% blockage in frontal area to represent good freestream velocity without accelerating air flowing around the test subject.

So at 16' x 10', we have a tunnel x-sec of 160 sq ft. Our splitter plate takes up about 16 sq ft of that, so we're at 144 sq ft of testable area. 5% is about 7 sq ft so you actually do need a pretty big tunnel to do good athlete testing at yaw.

We also want the ability to test a bunch of other stuff too, so a big tunnel is great for future crazy ideas. Honestly, I've been pretty obsessed with the idea of getting some wing suits this week...just ask Chris!

--
Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Ask us (almost) anything about our Wind Tunnel [MITaerobike] [ In reply to ]
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I should add, the tunnel size discussion is one reason among many that makes the A2 tunnel awesome for bike testing.

Mark

--
Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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So I think there are a couple of questions here:

If wheels spinning versus not spinning matters
yes, there is a difference so we generally test with wheels spinning

Have we separated drag from the frame and wheels?
We do this in CFD and have the ability to do this with our new facility but haven't done it before.

How do we study the infinite yaw combos due to wind on the road and the rider's speed?
We capture CdA's for a full yaw sweep and then can go back and simulate any details per what we measure on the road using our DAQ system.

Mark

--
Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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Epic-o wrote:
Last question, I promise

- I know that the industry standard is testing with a wheel rotation speed that matches the WT speed (bike-air relative speed) but have you analysed the effect of wheel rotational speed in both wheel and induced drag? Once you set your yaw and WT speed, there is an "infinity" of real world wind directions and bike speeds (and obviously wheel rotational speed) that can produce that yaw so even if you are in the same Re regime, the different rotational speed can modify the system drag.

Mark hit on this already, but you bring up a good point. We do have the ability to vary wheel speed relative to wind speed and can definitely see doing some extensive studies - at the extreme cases I would not be surprised if we find something interesting.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Nate Pearson] [ In reply to ]
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Nate Pearson wrote:
You guys need to start aero.specialized.com. Make it a blog dedicated to the wind tunnel and aero testing. Like you said before, show the results even if you aren't the fastest. Educate me as a rider why this stuff matters and what to look for. You'd create a bond between the company and the consumer. Your marketing department should be all over this :).

For the CFD stuff you mentioned that specialized uses its own servers for this. Why did you guys go that way instead of aws it azure. Looks like you can spin up some huge aws servers working in parallel on cfd.

That might reduce the time it takes to do your cfd modeling and save some money. If you already have the servers though its a hard sell to management.

On the "blog": Good idea ;-)

CFD: Yea, that is potentially something that we'd do, depending on the problem. As it stands, we do a lot of verification and validation stuff between design R&D runs and those cases aren't as time pressing so we can just have them sit in queue on our server (rather than paying for CPU-hours on the cloud).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Nate Pearson wrote:
You guys need to start aero.specialized.com. Make it a blog dedicated to the wind tunnel and aero testing. Like you said before, show the results even if you aren't the fastest. Educate me as a rider why this stuff matters and what to look for. You'd create a bond between the company and the consumer. Your marketing department should be all over this :).

For the CFD stuff you mentioned that specialized uses its own servers for this. Why did you guys go that way instead of aws it azure. Looks like you can spin up some huge aws servers working in parallel on cfd.

That might reduce the time it takes to do your cfd modeling and save some money. If you already have the servers though its a hard sell to management.


On the "blog": Good idea ;-)

CFD: Yea, that is potentially something that we'd do, depending on the problem. As it stands, we do a lot of verification and validation stuff between design R&D runs and those cases aren't as time pressing so we can just have them sit in queue on our server (rather than paying for CPU-hours on the cloud).

A few comments/observations:

aero.specialized.com is a fabulous idea for maintaining a central information source. Please do it.

Second: I appreciate it when you quote the post you are responding to as above. As this thread gets longer, it gets/will get more difficult to remember what post you (Chris & Mark) are responding to.

Next: Please, talk down to me. It might be helpful for those of us that aren't enginerds and don't speak your language to have a glossary of the terms and acronyms you use so casually.

Finally, thank you for sharing this super cool project with us.


________________________________________________
DFL >> DNF >> DNS
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Re: Ask us (almost) anything about our Wind Tunnel [InspectorGadget] [ In reply to ]
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For me anyway a company that posts all the data good and bad is a company I would trust and buy from them even if something might be a little slower in the tunnel. I think marketing guys forget that trust is big when we are spending or considering spending thousands of dollars. I think it does more harm to you when a company tests, marketing puts out they tested better (but don't put out the data) and then an independent person tests and find it is basically not true except in a very narrow instance.
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Re: Ask us (almost) anything about our Wind Tunnel [InspectorGadget] [ In reply to ]
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Thanks for the comments and feedback! It's good to have a reminder to keep the jargon to a min - it's easy to forget sometimes.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
I forgot to mention that I'm using gF units since that's what everyone is familiar with (and honestly, it's more visceral...people can imagine what it feels like). Anyways, the number I quoted was for 50km/h...so scale appropriately for different speeds.

It was refreshing for me to see that the CFME wind tunnel in Geneva reported results in a proper force value, i.e. newtons :-)

It was actually pretty easy to figure out power requirements in my head since I know that 40 kph is ~11m/s ;-)

BTW, IMHO wind tunnels really should report values in terms of CdA. That's actually item of interest, no? Plus, it's easily used for different conditions of air velocity and density. No need to "qualify" test speed, etc.

It's cool to see that you guys put this together. I'm jealous :-)

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [chris948] [ In reply to ]
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chris948 wrote:
What air speeds are available to you for testing? I ask this because everything that I've read that you and other companies post is ~30mph, this isn't really indicative of your average triathlete's speed.

See? This is why results should be reported in terms of CdA. No more having to explain why tests taken at 30mph can scale to 20-ish mph...

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [MITaerobike] [ In reply to ]
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MITaerobike wrote:
The largest issue we've had with other tunnels testing bikes has been blockage at higher yaws. A tunnel should only have 5-6% blockage in frontal area to represent good freestream velocity without accelerating air flowing around the test subject.

So at 16' x 10', we have a tunnel x-sec of 160 sq ft. Our splitter plate takes up about 16 sq ft of that, so we're at 144 sq ft of testable area. 5% is about 7 sq ft so you actually do need a pretty big tunnel to do good athlete testing at yaw.

We also want the ability to test a bunch of other stuff too, so a big tunnel is great for future crazy ideas. Honestly, I've been pretty obsessed with the idea of getting some wing suits this week...just ask Chris!

Mark, speaking of the tunnel X-section, what's the contraction ratio of the inlet section?

Also, could you describe how the inlet is in relation to "the outside world"? How do you guys prevent/minimize ambient wind from skewing the tunnel flow? Have you mapped out the flow field in the test section yet?

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
chrisyu wrote:
I forgot to mention that I'm using gF units since that's what everyone is familiar with (and honestly, it's more visceral...people can imagine what it feels like). Anyways, the number I quoted was for 50km/h...so scale appropriately for different speeds.


It was refreshing for me to see that the CFME wind tunnel in Geneva reported results in a proper force value, i.e. newtons :-)

It was actually pretty easy to figure out power requirements in my head since I know that 40 kph is ~11m/s ;-)

BTW, IMHO wind tunnels really should report values in terms of CdA. That's actually item of interest, no? Plus, it's easily used for different conditions of air velocity and density. No need to "qualify" test speed, etc.

It's cool to see that you guys put this together. I'm jealous :-)

Hi Tom, yes I am on board with you on the units. Internally, we do everything in coefficients but going back to what I was mentioning before, gF is pretty entrenched and it really does connect better with the average consumer. Anyways, we will report both to appease all =). (and hey, at least we're better than the aerospace industry where everything is typically in lbs-force).

You're pretty close to us, we'll have to get you a tour sometime...

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:

Hi Tom, yes I am on board with you on the units. Internally, we do everything in coefficients but going back to what I was mentioning before, gF is pretty entrenched and it really does connect better with the average consumer. Anyways, we will report both to appease all =). (and hey, at least we're better than the aerospace industry where everything is typically in lbs-force).

At least lbs are actually a force ;-)

Yeah, I know that reporting results in grams is pretty entrenched...but, if there's ever going to be a change, SOMEBODY has to start it, right?


chrisyu wrote:
You're pretty close to us, we'll have to get you a tour sometime...

That would be fun!

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
MITaerobike wrote:
The largest issue we've had with other tunnels testing bikes has been blockage at higher yaws. A tunnel should only have 5-6% blockage in frontal area to represent good freestream velocity without accelerating air flowing around the test subject.

So at 16' x 10', we have a tunnel x-sec of 160 sq ft. Our splitter plate takes up about 16 sq ft of that, so we're at 144 sq ft of testable area. 5% is about 7 sq ft so you actually do need a pretty big tunnel to do good athlete testing at yaw.

We also want the ability to test a bunch of other stuff too, so a big tunnel is great for future crazy ideas. Honestly, I've been pretty obsessed with the idea of getting some wing suits this week...just ask Chris!


Mark, speaking of the tunnel X-section, what's the contraction ratio of the inlet section?

Also, could you describe how the inlet is in relation to "the outside world"? How do you guys prevent/minimize ambient wind from skewing the tunnel flow? Have you mapped out the flow field in the test section yet?

The contraction ratio is 4:1. We had a lot of back and forth in the early design balancing either maximizing contraction ratio or test section size (can't do both given the space we had). After some simulations and consulting with our team of tunnel experts, we came to the conclusion that 4:1 would be sufficient for the speeds that we're running.

The tunnel is completely indoors and sits inside a completely sectioned off area of the building. So "ambient" is still all internal. We have a couple of stages of "flow cleaning" at the beginning of the inlet (honeycomb and wire mesh). We have done a round of mapping in the test section and I'm about to do a second round with a different (fancier) probe. Flow uniformity is quite good across the cross-section but, as you can imagine, is quite sensitive to what is outside the tunnel....which is why it's important to have a controlled space for it to sit in.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [InspectorGadget] [ In reply to ]
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InspectorGadget wrote:
[
Next: Please, talk down to me. It might be helpful for those of us that aren't enginerds and don't speak your language to have a glossary of the terms and acronyms you use so casually.

Quick tip...if you want someone to simplify things for you, it's probably not a good idea to refer to them in a somewhat derogatory manner ;-)

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
The contraction ratio is 4:1. We had a lot of back and forth in the early design balancing either maximizing contraction ratio or test section size (can't do both given the space we had). After some simulations and consulting with our team of tunnel experts, we came to the conclusion that 4:1 would be sufficient for the speeds that we're running.

The tunnel is completely indoors and sits inside a completely sectioned off area of the building. So "ambient" is still all internal. We have a couple of stages of "flow cleaning" at the beginning of the inlet (honeycomb and wire mesh). We have done a round of mapping in the test section and I'm about to do a second round with a different (fancier) probe. Flow uniformity is quite good across the cross-section but, as you can imagine, is quite sensitive to what is outside the tunnel....which is why it's important to have a controlled space for it to sit in.

Hmmm...so, in reality it's actually a "closed circuit" design? I'm imagining that the air flowing out of the exit eventually makes it's way back around to the inlet, no?

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
InspectorGadget wrote:
[
Next: Please, talk down to me. It might be helpful for those of us that aren't enginerds and don't speak your language to have a glossary of the terms and acronyms you use so casually.


Quick tip...if you want someone to simplify things for you, it's probably not a good idea to refer to them in a somewhat derogatory manner ;-)

That's ok, I took it as a compliment ;-)

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
chrisyu wrote:

The contraction ratio is 4:1. We had a lot of back and forth in the early design balancing either maximizing contraction ratio or test section size (can't do both given the space we had). After some simulations and consulting with our team of tunnel experts, we came to the conclusion that 4:1 would be sufficient for the speeds that we're running.

The tunnel is completely indoors and sits inside a completely sectioned off area of the building. So "ambient" is still all internal. We have a couple of stages of "flow cleaning" at the beginning of the inlet (honeycomb and wire mesh). We have done a round of mapping in the test section and I'm about to do a second round with a different (fancier) probe. Flow uniformity is quite good across the cross-section but, as you can imagine, is quite sensitive to what is outside the tunnel....which is why it's important to have a controlled space for it to sit in.


Hmmm...so, in reality it's actually a "closed circuit" design? I'm imagining that the air flowing out of the exit eventually makes it's way back around to the inlet, no?

Yes, technically speaking it's "closed." It's not a recirculating tunnel in the traditional sense but yes the exit flow eventually makes it back into the inlet.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Tom A. wrote:
chrisyu wrote:

The contraction ratio is 4:1. We had a lot of back and forth in the early design balancing either maximizing contraction ratio or test section size (can't do both given the space we had). After some simulations and consulting with our team of tunnel experts, we came to the conclusion that 4:1 would be sufficient for the speeds that we're running.

The tunnel is completely indoors and sits inside a completely sectioned off area of the building. So "ambient" is still all internal. We have a couple of stages of "flow cleaning" at the beginning of the inlet (honeycomb and wire mesh). We have done a round of mapping in the test section and I'm about to do a second round with a different (fancier) probe. Flow uniformity is quite good across the cross-section but, as you can imagine, is quite sensitive to what is outside the tunnel....which is why it's important to have a controlled space for it to sit in.


Hmmm...so, in reality it's actually a "closed circuit" design? I'm imagining that the air flowing out of the exit eventually makes it's way back around to the inlet, no?


Yes, technically speaking it's "closed." It's not a recirculating tunnel in the traditional sense but yes the exit flow eventually makes it back into the inlet.

Is there any "tuning" of the return paths?

I only ask this because I just got back from a trip to the CFME university wind tunnel in Geneva, and they referred to their tunnel as being "closed circuit", even though it isn't laid out as a traditional "racetrack" type configuration. Instead, the contraction, test, fan, and diffuser sections are centered in a section of what was originally intended to be a railroad tunnel, and there are "caps" at either end of the tunnel that split and redirect the flow back and around between the test section and the tunnel walls. Here's a plan view of that tunnel and an internal pic to better illustrate what I mean:


http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Chris-
Are you guys doing anything in particular to alleviate the ground interaction differences with the real world or has that proven to not be anything significant for bicycles? I see you had a raised test section, but didn't know if you installed a trip strip or a suction system.

Also you said earlier that the precision of the balance is approaching 2gf, but what has the repeatability of the tunnel itself proven to be? And have you done any comparison tests with existing tunnels (i.e. LSWT, or the smaller A2)?
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Yes and no. We found that the building volume around the tunnel was high enough that we didn't need to have "caps" or turning vanes at either end to guide airflow back around. We did think about doing this if necessary, but so far haven't found it to be an issue. One thing that we did tune was balancing external blockage to make sure we had symmetric return flow on either side of the tunnel. That's one of the reasons why our design has two control rooms - to keep everything symmetric outside of the tunnel. However, we haven't built the second control room yet (but the design relies on its presence), so we are using large wooden crates to re-create the blockage that additional control room would have.

Fun fact: flow uniformity inside the test section was pretty sensitive to the location of those crates.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Yes and no. We found that the building volume around the tunnel was high enough that we didn't need to have "caps" or turning vanes at either end to guide airflow back around. We did think about doing this if necessary, but so far haven't found it to be an issue. One thing that we did tune was balancing external blockage to make sure we had symmetric return flow on either side of the tunnel. That's one of the reasons why our design has two control rooms - to keep everything symmetric outside of the tunnel. However, we haven't built the second control room yet (but the design relies on its presence), so we are using large wooden crates to re-create the blockage that additional control room would have.

Fun fact: flow uniformity inside the test section was pretty sensitive to the location of those crates.

Interesting...yeah, I didn't think to ask some questions about the asymmetric design of the "returns" of the Geneva tunnel at the time. However, I did see a scale model of the whole facility that the director of the tunnel told me was used in a hydrodynamic tank to better visualize the flow patterns in the facility.

BTW, I thought you'd get a kick out of this (if you haven't seen it already), but in a paper on low speed wind tunnels by Mehta and Bradshaw (http://navier.stanford.edu/.../LowSpeedTunnels.pdf) they have this quote: "...remember that an open-circuit tunnel in a room is really a closed-circuit design with a poorly designed return leg." ;-)

Of course, as you probably know, they then go on to describe all the ways to make a high performing open circuit tunnel :-)

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Tom A. wrote:
InspectorGadget wrote:
[
Next: Please, talk down to me. It might be helpful for those of us that aren't enginerds and don't speak your language to have a glossary of the terms and acronyms you use so casually.


Quick tip...if you want someone to simplify things for you, it's probably not a good idea to refer to them in a somewhat derogatory manner ;-)


That's ok, I took it as a compliment ;-)
. Great!

Absent a smilie, I meant it with the utmost respect. And more than a touch of job envy.


________________________________________________
DFL >> DNF >> DNS
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Re: Ask us (almost) anything about our Wind Tunnel [pyrahna] [ In reply to ]
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pyrahna wrote:
Chris-

Are you guys doing anything in particular to alleviate the ground interaction differences with the real world or has that proven to not be anything significant for bicycles? I see you had a raised test section, but didn't know if you installed a trip strip or a suction system.

Also you said earlier that the precision of the balance is approaching 2gf, but what has the repeatability of the tunnel itself proven to be? And have you done any comparison tests with existing tunnels (i.e. LSWT, or the smaller A2)?


I'll hop in here:

Are you guys doing anything in particular to alleviate the ground interaction differences with the real world or has that proven to not be anything significant for bicycles? I see you had a raised test section, but didn't know if you installed a trip strip or a suction system.
From both Chris and my past experience testing here, generally the ground affects aren't that big for a bicycle. Our splitter plate spans the whole test section width and works well to slice off the boundary layer coming up the inlet bell. This doesn't mean we won't add or modify systems in the future, but we've found the simplicity of this system is very nice and robust.

To clarify for someone new to this piece -- wind sticks to the walls, floor, ceiling of the tunnel and slows down close to these surfaces. As it moves up into the tunnel, through the inlet bell, 3-6" of dirty, slow air can build up. We don't want that, so we effectively "split" this and let this bad air go under the floor by the bike and let nice clean air hit the bike and rider.

We made this nice and wide so it's easy for a cyclist to ride right into the tunnel without having to step awkwardly on the table if we had a raised circle or something like that. Nice and easy since we were able to design from scratch.



Also you said earlier that the precision of the balance is approaching 2gf, but what has the repeatability of the tunnel itself proven to be? And have you done any comparison tests with existing tunnels (i.e. LSWT, or the smaller A2)?
Not sure if we're talking wind or force measurements here. I assume balance but reply if not.

The balance is going through continuous improvement. We're really good right now after beginning testing about 1 month ago but aren't done yet. Precision of a tunnel comes down to a few things:

1. Precision of the balance. Based on load cells or strain gages used and how good all of the linkages and flextures are.
2. How long and fast the sample is taken. Ideally a shorter sample - ~5-10 secs at a high frequency for a point is preferable to having to average for 20-60 seconds. Often this averaging is to average large scale wind disturbances, not just balance stuff.
3. How robust the balance is to outside mechanical vibrations -- like a wheel spinning or an athlete pedaling...really tricky stuff.
4. Electrical noise. Can be a bigger issue than most would expect.

Balance accuracy comes down to the above plus some other stuff:

1. The protocol of how data is taken, the software is setup, etc. Pretty critical to do a Wind Off Zero (WOZ) or a wind off load cell tare before testing.
2. How robust the bike fixture is to repeatably removing and remounting a bike. We check this bike testing THE SAME EXACT BIKE all the time...lots of bad data comes from a bad bike fixture.

A2 has really good accuracy and precision. About as good as anywhere I've tested. In fact, I had a Transition (control bike) that was tested there every month for 14 months straight and got incredibly good data. Around +/- 7 gF in a 95% confidence interval for +/- 10 deg of yaw at 50 kph over 14 months of testing. At higher yaw, the repeatability isn't as good since the bike is shedding vorticies all over the place and the data is less stable.

I've only tested at SD LSWT once so it's not fair for me to quote their data.

Mark

--
Mark Cote
MITAerobike
Specialized Bicycle Components
Last edited by: MITaerobike: May 19, 13 19:44
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Re: Ask us (almost) anything about our Wind Tunnel [pyrahna] [ In reply to ]
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pyrahna wrote:
Chris-
Are you guys doing anything in particular to alleviate the ground interaction differences with the real world or has that proven to not be anything significant for bicycles? I see you had a raised test section, but didn't know if you installed a trip strip or a suction system.

Also you said earlier that the precision of the balance is approaching 2gf, but what has the repeatability of the tunnel itself proven to be? And have you done any comparison tests with existing tunnels (i.e. LSWT, or the smaller A2)?


Edit: I replied to this before even seeing Mark's reply above. So everything he said too!

Hi, so far everything that I've seen suggests that "rolling road" effects are pretty insignificant except maybe in wheels/tires (and even then, it likely will not change rank order when doing comparisons of one design vs. another). However, that is definitely on the list to look at more closely. As I was mentioning earlier, it's a balance of including the effects that matter and keeping the test apparatus as simple/clean as possible to reduce sources of uncertainty.

When I referred to the 2 gF figure (at 50km/h on a std. day) that's the target resolution and repeatability (in layman's terms, we want to be able to reliably and repeatably measure differences of 2 gF). At the facilities that I've been to, we typically get between 5-10 gF depending on the test setup.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Last edited by: chrisyu: May 19, 13 21:30
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
chrisyu wrote:
Yes and no. We found that the building volume around the tunnel was high enough that we didn't need to have "caps" or turning vanes at either end to guide airflow back around. We did think about doing this if necessary, but so far haven't found it to be an issue. One thing that we did tune was balancing external blockage to make sure we had symmetric return flow on either side of the tunnel. That's one of the reasons why our design has two control rooms - to keep everything symmetric outside of the tunnel. However, we haven't built the second control room yet (but the design relies on its presence), so we are using large wooden crates to re-create the blockage that additional control room would have.

Fun fact: flow uniformity inside the test section was pretty sensitive to the location of those crates.


Interesting...yeah, I didn't think to ask some questions about the asymmetric design of the "returns" of the Geneva tunnel at the time. However, I did see a scale model of the whole facility that the director of the tunnel told me was used in a hydrodynamic tank to better visualize the flow patterns in the facility.

BTW, I thought you'd get a kick out of this (if you haven't seen it already), but in a paper on low speed wind tunnels by Mehta and Bradshaw (http://navier.stanford.edu/.../LowSpeedTunnels.pdf) they have this quote: "...remember that an open-circuit tunnel in a room is really a closed-circuit design with a poorly designed return leg." ;-)

Of course, as you probably know, they then go on to describe all the ways to make a high performing open circuit tunnel :-)

Yup, we're very familiar with Rabi's and Prof. Bradshaw's excellent papers and articles on WT design. I know you were just poking with the comment on the open circuit design - but after evaluating the pros and cons of open vs. closed circuit designs, we prioritized having a larger test section for the same floor space (especially given our relatively low operating speeds).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:

Yup, we're very familiar with Rabi's and Prof. Bradshaw's excellent papers and articles on WT design. I know you were just poking with the comment on the open circuit design - but after evaluating the pros and cons of open vs. closed circuit designs, we prioritized having a larger test section for the same floor space (especially given our relatively low operating speeds).

Think of it as more of a "gentle nudge/wink" ;-)

The fact that you put the crates in place to mimic the yet to be constructed twin control room points to the fact that your return leg isn't exactly "poorly designed" :-)

Lots of REALLY good stuff comes out of open-circuit designed tunnels.

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Quote:
When I referred to the 2 gF figure (at 50km/h on a std. day) that's the target resolution and repeatability (in layman's terms, we want to be able to reliably and repeatably measure differences of 2 gF). At the facilities that I've been to, we typically get between 5-10 gF depending on the test setup.

Sorry I assumed you meant that the balance by itself was accurate to 2 gF. i.e. with a calibration rig or some known masses, not with the tunnel on and measuring the drag on something.

I have to admit, whatever you have done to get that level of consistency is pretty impressive.
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Re: Ask us (almost) anything about our Wind Tunnel [MITaerobike] [ In reply to ]
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In reference to the wind tunnel comparison I was curious if you had done back to back testing with the same bike in multiple tunnels and compared the results. In the auto racing world when ever a new tunnel came online the manufacturers would do a comparison test to the tunnel that was considered the "gold std." (for the mfg. I was privy to it was Lockheed in Atlanta) and compared the outputs for a given car. For instance the most dramatic differences I ever saw was front downforce for the Chrysler tunnel was reported to be a couple counts different than Lockheed due to the vertical return and how they did the laminar tripping in the Chrysler tunnel vs. the horizontal return at Lockheed. I was just curious with the emphasis on the test area size whether the data in your tunnel trended in one way at high yaws vs. data taken at the little A2, or whether the data mirrored each other pretty well across all the yaw angles.
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Re: Ask us (almost) anything about our Wind Tunnel [pyrahna] [ In reply to ]
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That's a cool tidbit about the Chrysler/Lockheed tunnel comparison! Yea, I would imagine for performance cars especially, how ground effect is modeled is pretty important. We don't have enough data yet that I would be comfortable claiming seeing different yaw trends (and furthermore directly attributing that to blockage differences). Also, as far as cycling tunnels go A2 is actually pretty good in that regard which is why we tested there. It's the smaller aeronautical tunnels that I would be more wary about.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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How much of the wind tunnel project was developed or learned from the relationship with McLaren? Will you guys share data with each other and review together? How does this affect the ongoing relationship with them in future? Besides the aero testing and technical know how, I know they also helped with the carbon lay-up on the McLaren Venge. Will this turn into more of a technical materials relationship since you are taking the aero testing in house?
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Re: Ask us (almost) anything about our Wind Tunnel [mile2424] [ In reply to ]
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mile2424 wrote:
How much of the wind tunnel project was developed or learned from the relationship with McLaren? Will you guys share data with each other and review together? How does this affect the ongoing relationship with them in future? Besides the aero testing and technical know how, I know they also helped with the carbon lay-up on the McLaren Venge. Will this turn into more of a technical materials relationship since you are taking the aero testing in house?

We currently have a bunch of projects going on with McLaren, from composites to dynamics & vibrations. We'll continue to work on aero etc with them. The only thing that changes now is that we have a tunnel here and some more CFD and on-road tools. With McLaren, it's as much or more about their engineers and technologists as it is their tools. The relationship with McLaren is as strong as ever and we're all pumped on the next big things coming!

Mark

--
Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hey Chris

I have always been curious about calibration of strain guages. Is that something you have to do before each new measurement or set up? Is there some kind of NIST traceability for that?

Thanks,
Mike
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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I just wonder how much of the inconsistencies between data sets of different manufacturers is based on different tunnels used. For instance the Mavic data showing different high yaw data for Zipp wheels than Zipp shows. It is possible that it is due to testing protocol differences, different equipment choices, but some of it may be a coloring of the data by the tunnel that is being used. I was hoping you guys had done some of the leg work to figure out the differences to try and help us all piece different information together into a coherent picture.


I have no experience with the small A2 tunnel, but from my limited experiences with the tunnel next door they are a class act and are constantly trying to improve the usefulness of the tunnel as a tool.
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Re: Ask us (almost) anything about our Wind Tunnel [TriMike] [ In reply to ]
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TriMike wrote:
Hey Chris

I have always been curious about calibration of strain guages. Is that something you have to do before each new measurement or set up? Is there some kind of NIST traceability for that?

Thanks,
Mike

Yea, it's actually kind of like using a power meter. We zero the readings periodically during a test. For calibration (e.g. finding the slope relationship between applied force and voltage output of the sensors), we will do that when anything on the balance apparatus itself changes. It's pretty stable otherwise. We will also verify the cal regularly. We perform the cal with NIST weights but everything on the balance end is custom in house.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [pyrahna] [ In reply to ]
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pyrahna wrote:
I just wonder how much of the inconsistencies between data sets of different manufacturers is based on different tunnels used. For instance the Mavic data showing different high yaw data for Zipp wheels than Zipp shows. It is possible that it is due to testing protocol differences, different equipment choices, but some of it may be a coloring of the data by the tunnel that is being used. I was hoping you guys had done some of the leg work to figure out the differences to try and help us all piece different information together into a coherent picture.


I have no experience with the small A2 tunnel, but from my limited experiences with the tunnel next door they are a class act and are constantly trying to improve the usefulness of the tunnel as a tool.

Yea, the guys at A2 and Aerodyne are definitely class acts. I think you're right about the different tunnel facilities playing some role in seeing slightly different data from different sources. It'll be interesting to explore further but that may require some collaborative effort at other facilities (after all, we built the tunnel so we wouldn't have to travel anymore!).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Nate Pearson] [ In reply to ]
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Hello Nate and All,

"Why do I have to put shoe covers on to make my shoe aero? I can't do that in a tri (but shoe covers save time).

We need some type of shoe with the ratchet in the heel (maybe entry point is in the heel too). The rest if the shoe should be really aero/smooth."

Suggest that you must consider shoe/cleat/pedal combination as an aero unit ..... not just the shoe.

http://forum.slowtwitch.com/...post=4558598#4558598



Showing smooth pedal retraction (like aircraft wheels) into shoe body

Covers not required for View-Speed Aero modified shoes (although a smooth top shoe like the Bont works best) and you can run on the shoes.

Saves 40 seconds per hour San Diego LWST = saves 4 min in 6 hour race.

Available .................. now.

Cheers,

Neal

+1 mph Faster
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Re: Ask us (almost) anything about our Wind Tunnel [Aspo] [ In reply to ]
Quote | Reply
Aspo wrote:
Nate Pearson wrote:
You guys need to start aero.specialized.com. Make it a blog dedicated to the wind tunnel and aero testing.

THIS


Nothing builds trust like the truth. Hopefully, you are the fastest most of the time. When you aren't, say so. That way when you are, people listen. The truth in a marketing driven, spin infested space would be refreshing.
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
chrisyu wrote:

The contraction ratio is 4:1. We had a lot of back and forth in the early design balancing either maximizing contraction ratio or test section size (can't do both given the space we had). After some simulations and consulting with our team of tunnel experts, we came to the conclusion that 4:1 would be sufficient for the speeds that we're running.

The tunnel is completely indoors and sits inside a completely sectioned off area of the building. So "ambient" is still all internal. We have a couple of stages of "flow cleaning" at the beginning of the inlet (honeycomb and wire mesh). We have done a round of mapping in the test section and I'm about to do a second round with a different (fancier) probe. Flow uniformity is quite good across the cross-section but, as you can imagine, is quite sensitive to what is outside the tunnel....which is why it's important to have a controlled space for it to sit in.


Hmmm...so, in reality it's actually a "closed circuit" design? I'm imagining that the air flowing out of the exit eventually makes it's way back around to the inlet, no?

More or less. If you stand in the warehouse room that holds the A2 tunnel you can actually feel a fairly strong breeze blowing opposite the direction of the tunnel flow. Enclosing an "open return" tunnel has advantages, particularly for testing humans (better control of environmental conditions), but I have to believe there's a fairly substantial efficiency gain too. A2's power requirements at bike testing speeds are LOW--under 50hp//37kw as I recall. Granted, they have a smaller TS, but I think the enclosure of the tunnel plays a small part.

__________________________

I tweet!

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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hey everyone, sorry for the last second notice but we will be hosting a live Q&A session with video this afternoon from 4-5pm PST. Chuck Teixeira and I will be answering questions this time around. We'll do the same on Thurs but at 9am PST (I believe) with Mark Cote and Chris D'Aluisio online.

Link: http://www.specialized.com/...ws/latest-news/16025

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:

The fact that you put the crates in place to mimic the yet to be constructed twin control room points to the fact that your return leg isn't exactly "poorly designed" :-)

Lots of REALLY good stuff comes out of open-circuit designed tunnels.


I'm reminded me of a quote that said something like: all wind tunnels are closed loop. The difference is only the degree of efficiency of the return path. :-)

AndyF
bike geek
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
Quote | Reply
chrisyu wrote:
When I referred to the 2 gF figure (at 50km/h on a std. day) that's the target resolution and repeatability (in layman's terms, we want to be able to reliably and repeatably measure differences of 2 gF). At the facilities that I've been to, we typically get between 5-10 gF depending on the test setup.

You're hoping for 2 gF for the bike alone? And you've been seeing 5-10 gF for the bike alone, or for the bike+rider, at these other facilities?

The best I've seen from a field test (with bike+rider, of course) would have been in the ballpark of 5-10 gF at 14 m/s.
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Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
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Hi Robert,

That's correct, the target is 2 gF for no (live) rider and we have typically seen 5-10 gF at other facilities, again with no (live) rider. A really good/steady rider will get us numbers in the same range but a poor one can be a lot worse so the window is pretty big once you factor that in. As you know, the same is true for field testing - which as you point out requires a rider! So for R&D stuff, it may take a bit longer to hone in on the effect of a design change due to the additional variable. Not saying it can't be done, just using the different tools for different pieces of the puzzle.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
Quote | Reply
RChung wrote:
chrisyu wrote:

When I referred to the 2 gF figure (at 50km/h on a std. day) that's the target resolution and repeatability (in layman's terms, we want to be able to reliably and repeatably measure differences of 2 gF). At the facilities that I've been to, we typically get between 5-10 gF depending on the test setup.


You're hoping for 2 gF for the bike alone? And you've been seeing 5-10 gF for the bike alone, or for the bike+rider, at these other facilities?

The best I've seen from a field test (with bike+rider, of course) would have been in the ballpark of 5-10 gF at 14 m/s.

Are you talking about me again? :-)

http://bikeblather.blogspot.com/
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:
RChung wrote:
chrisyu wrote:

When I referred to the 2 gF figure (at 50km/h on a std. day) that's the target resolution and repeatability (in layman's terms, we want to be able to reliably and repeatably measure differences of 2 gF). At the facilities that I've been to, we typically get between 5-10 gF depending on the test setup.


You're hoping for 2 gF for the bike alone? And you've been seeing 5-10 gF for the bike alone, or for the bike+rider, at these other facilities?

The best I've seen from a field test (with bike+rider, of course) would have been in the ballpark of 5-10 gF at 14 m/s.


Are you talking about me again? :-)

Well, Chris said:
Quote:
A really good/steady rider will get us numbers in the same range

so, yeah, I'm talking about you, damn you.
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
Quote | Reply
RChung wrote:
Tom A. wrote:

Are you talking about me again? :-)


Well, Chris said:
Quote:
A really good/steady rider will get us numbers in the same range


so, yeah, I'm talking about you, damn you.

:-) It's getting warmer here in the mornings and is getting into prime field testing season...I think I'll be stopping by the local craft store to procure some "standard shapes" to help calibrate my new half-pipe venue (as AC calls it, the "Tom Compton Challenge")...

BTW, and I don't recall if this was brought up earlier, but as you well know, one of the "advantages" of field testing is that the "power to rotate" of the wheels is included in the overall demand.

Chris or Mark, can you go into detail about how you guys plan to measure that value consistently and include it in your measurements?

http://bikeblather.blogspot.com/
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:

:-) It's getting warmer here in the mornings and is getting into prime field testing season...I think I'll be stopping by the local craft store to procure some "standard shapes" to help calibrate my new half-pipe venue (as AC calls it, the "Tom Compton Challenge")...
An alternative is to re-visit the "delta mass" experiment. Since a Newton is a Newton, hold your CdA constant and run with empty vs. half-full water bottle (~200 or 250 ml or so, depending on what the Crr is). That should also be a difference in drag of ~0.1 N. If you can detect that amount of difference in rolling drag you ought to be able to detect that amount of difference in aero drag.

Quote:
BTW, and I don't recall if this was brought up earlier, but as you well know, one of the "advantages" of field testing is that the "power to rotate" of the wheels is included in the overall demand.

Chris or Mark, can you go into detail about how you guys plan to measure that value consistently and include it in your measurements?
I don't know whether that's an advantage or a disadvantage -- I just think of these sorts of differences as characteristics of each particular method. But it is something I'd like to know, too.
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
Quote | Reply
RChung wrote:
Tom A. wrote:


:-) It's getting warmer here in the mornings and is getting into prime field testing season...I think I'll be stopping by the local craft store to procure some "standard shapes" to help calibrate my new half-pipe venue (as AC calls it, the "Tom Compton Challenge")...

An alternative is to re-visit the "delta mass" experiment. Since a Newton is a Newton, hold your CdA constant and run with empty vs. half-full water bottle (~200 or 250 ml or so, depending on what the Crr is). That should also be a difference in drag of ~0.1 N. If you can detect that amount of difference in rolling drag you ought to be able to detect that amount of difference in aero drag.

Good idea. Even better would be if I'd have someone there who would change the water level unbeknownst to me so that when I analyzed the runs I wouldn't know ahead of time which was which ;-)

http://bikeblather.blogspot.com/
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:
RChung wrote:

An alternative is to re-visit the "delta mass" experiment. Since a Newton is a Newton, hold your CdA constant and run with empty vs. half-full water bottle (~200 or 250 ml or so, depending on what the Crr is). That should also be a difference in drag of ~0.1 N. If you can detect that amount of difference in rolling drag you ought to be able to detect that amount of difference in aero drag.

Good idea. Even better would be if I'd have someone there who would change the water level unbeknownst to me so that when I analyzed the runs I wouldn't know ahead of time which was which ;-)
Ah, yes. That was a funny critique.

You needn't actually only put 200 ml of water in the bottle. You can put any mass in there (as long as you weigh it; how about something dense like krugerrands?) and see how closely the measured change in drag force matches the known change in mass. That's your standard and you won't have to worry about standard "shapes." Much cleaner experiment. You'd maybe want to change the test protocol into a hill climb and then compare the VE profiles.
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:

BTW, and I don't recall if this was brought up earlier, but as you well know, one of the "advantages" of field testing is that the "power to rotate" of the wheels is included in the overall demand.

Chris or Mark, can you go into detail about how you guys plan to measure that value consistently and include it in your measurements?


Initially, we'll be measuring the electrical power that the drum motors are drawing. That, along with the motor efficiency tables, should get us pretty close. However, if that doesn't look like it's hacking it, we've designed the apparatus so that we can insert some rotary torque cells in the drive system. We'll also have load cells to measure the normal force applied to the tire. As I had mentioned earlier, this measurement will include rolling resistance on our smooth (and small diameter) drum so to tease out rotational aerodynamic drag, we'll need to either use the same tire and pressure and do comparative tests or measure Crr using a lab fixture with a similar drum (and subtract that value out from the total power-to-spin number measured in the tunnel).

Edit: I just realized you may have also been referring to how we plan on reporting it....well, good question. How would you like to see it? A total drag curve including everything? 2 separate curves, 1 including all and another including just the translational or rotational drag components?

And as Robert mentions, the different tools each have different strengths - the tunnel allows us to isolate the effects of different parts of the bike/rider system a bit easier (and going to the extreme, in CFD we can isolate drag contribution from different sub-components). Imagine having different parts (e.g. wheels or mannequin) on an isolated stinger so we still get the aerodynamic flow contribution but we can include or exclude its force contribution. So say we make a change to a wheel and the overall drag reading decreases by X amount. Is that X all from the wheel change or is it now interacting differently with the frame or rider and we're getting some benefit there? (or in an extreme case, maybe the wheel is actually higher in drag but the frame/rider has benefited enough to compensate).

Sorry I'm rambling now and shouldn't spill all the beans ;-)...

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Last edited by: chrisyu: May 22, 13 14:00
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
Quote | Reply
"Yes, technically speaking it's "closed.""

i don't see how you can describe this tunnel as such. this would mean that every open circuit tunnel indoors is really a closed circuit tunnel, and the only real open circuit tunnels are non-recirculating tunnels that are outdoors. is that what you're saying, or am i misunderstanding? not that i think it matters, because of everything you do to condition and straighten the air.


Dan Empfield
aka Slowman
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Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
Quote | Reply
Slowman wrote:
"Yes, technically speaking it's "closed.""

i don't see how you can describe this tunnel as such. this would mean that every open circuit tunnel indoors is really a closed circuit tunnel...


That's exactly what he means...otherwise, there would be no need to place shipping boxes in the future "2nd control room" location to minimize the flow asymmetry he mentioned happens without it ;-)


Slowman wrote:
...and the only real open circuit tunnels are non-recirculating tunnels that are outdoors.

According to Andy F's quote above, even those could be considered "closed circuit" :-)

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
"That's exactly what he means"

again, i don't think it matters in the end. but, it had been my understanding that open and closed circuit were terms of art and that by any definition this is an open circuit tunnel, aka open return tunnel, with open circuit and open return being synonyms.


Dan Empfield
aka Slowman
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
Quote | Reply
chrisyu wrote:

Initially, we'll be measuring the electrical power that the drum motors are drawing. That, along with the motor efficiency tables, should get us pretty close. However, if that doesn't look like it's hacking it, we've designed the apparatus so that we can insert some rotary torque cells in the drive system. We'll also have load cells to measure the normal force applied to the tire. As I had mentioned earlier, this measurement will include rolling resistance on our smooth (and small diameter) drum so to tease out rotational aerodynamic drag, we'll need to either use the same tire and pressure and do comparative tests or measure Crr using a lab fixture with a similar drum (and subtract that value out from the total power-to-spin number measured in the tunnel).

Yeah, having the tire Crr in there is a confounder...but, seeing as how the drums would need to be mounted on the balance, you really only need just enough pressure on the tire to prevent slipping, so that should help minimize any Crr effects. On the front that shouldn't be a huge issue...doing so on the rear, especially if the rear drum is applying a pedaling resistance, might be problematic. I guess that's why Mavic mentioned they'd be building an electric brake into a Comete disc...although I haven't completely thought through exactly how that would work...


chrisyu wrote:
Edit: I just realized you may have also been referring to how we plan on reporting it....well, good question. How would you like to see it? A total drag curve including everything? 2 separate curves, 1 including all and another including just the translational or rotational drag components?

How about all 3? Translational only, rotational (while subjected to translational air flow), and combined. All in newtons, of course ;-)

http://bikeblather.blogspot.com/
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
Quote | Reply
Slowman wrote:
"That's exactly what he means"

again, i don't think it matters in the end. but, it had been my understanding that open and closed circuit were terms of art and that by any definition this is an open circuit tunnel, aka open return tunnel, with open circuit and open return being synonyms.

See post #96 above...from the guys who basically have "written the book" on low speed wind tunnel design (emphasis added by me):

"...remember that an open-circuit tunnel in a room is really a closed-circuit design with a poorly designed return leg." ;-)

http://bikeblather.blogspot.com/
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
Quote | Reply
Slowman wrote:
"That's exactly what he means"

again, i don't think it matters in the end. but, it had been my understanding that open and closed circuit were terms of art and that by any definition this is an open circuit tunnel, aka open return tunnel, with open circuit and open return being synonyms.

Hi Dan,

Yup, it's a question of semantics...traditionally when discussing wind tunnel design, an open-return tunnel is a tube in a space (indoors or outdoors) and a closed-return tunnel is a continuous tube (e.g. the exhaust is continuously and directly connected to the inlet). However, as Tom and others have pointed out, strictly speaking every tunnel is in reality a "closed-return"; it's just a matter of how much control you have over the return path (ranging from a warehouse space to the entire planet's atmosphere). With a "open-return" tunnel sitting outside, if you run it long enough eventually the same air molecule of air will go through again =).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
Quote | Reply
Slowman wrote:
"Yes, technically speaking it's "closed.""

i don't see how you can describe this tunnel as such. this would mean that every open circuit tunnel indoors is really a closed circuit tunnel, and the only real open circuit tunnels are non-recirculating tunnels that are outdoors. is that what you're saying, or am i misunderstanding? not that i think it matters, because of everything you do to condition and straighten the air.


It's a matter of the area and design of the return. There are fully sealed closed-loop designs where the static pressure inside the tunnel is vastly different from outside the test section, there are closed-loop designs that are open to atmopheric pressure, and then there are non-recirculating designs. By virtue of the fact that Specialized tunnel and A2 are located inside warehouses, they do recirculate to a certain extent, but through an area an order of magnitude larger than the test section itself, so the return flow speed is reduced to an order of magnitude below the test section speed also. It's still an open design, but it's smart for bike testing. For one thing, closed loop designs take up substantially more space--double or even triple the footprint of a tunnel like A2 or Specialized. They're substantially more expensive because there's more of everything--more roof overhead, more wood, more paint, more design work, more flow correction materials, etc. Flow visualization media tend to junk up the tunnel walls too, forcing extra cleaning work. As sort of a final concern you have heating--our 3x4 closed-loop, vented tunnel would heat up from room ambient 72 to 80+ at Q=10psf (around 60mph maybe) within 10 minutes. A tunnel with more area, lower flow velocity, and larger vents would probably not suffer this effect as much. Enclosing a tunnel for bike testing also has the benefit of not freezing the rider as a blowdown tunnel with an outdoor inlet would. I'm a bit curious how A2 fares in the summer, with temps here in the 90's and 25-50hp of waste heat generation, but for the winter it's comfy.

__________________________

I tweet!

Last edited by: ZackCapets: May 22, 13 14:37
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:
Yeah, having the tire Crr in there is a confounder...but, seeing as how the drums would need to be mounted on the balance, you really only need just enough pressure on the tire to prevent slipping, so that should help minimize any Crr effects. On the front that shouldn't be a huge issue...doing so on the rear, especially if the rear drum is applying a pedaling resistance, might be problematic. I guess that's why Mavic mentioned they'd be building an electric brake into a Comete disc...although I haven't completely thought through exactly how that would work...

...

How about all 3? Translational only, rotational (while subjected to translational air flow), and combined. All in newtons, of course ;-)

Yup, good points on the Crr measurement. We'll definitely spend a bit of time playing with it to determine the most robust way of extracting the data.

All 3 huh? Ok, I think we can do that. Newtons though....that's pushing it! (just kidding...it's not too hard to convince me to use the "correct" units)

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
Quote | Reply
chrisyu wrote:
Slowman wrote:
"That's exactly what he means"

again, i don't think it matters in the end. but, it had been my understanding that open and closed circuit were terms of art and that by any definition this is an open circuit tunnel, aka open return tunnel, with open circuit and open return being synonyms.


Hi Dan,

Yup, it's a question of semantics...traditionally when discussing wind tunnel design, an open-return tunnel is a tube in a space (indoors or outdoors) and a closed-return tunnel is a continuous tube (e.g. the exhaust is continuously and directly connected to the inlet). However, as Tom and others have pointed out, strictly speaking every tunnel is in reality a "closed-return"; it's just a matter of how much control you have over the return path (ranging from a warehouse space to the entire planet's atmosphere). With a "open-return" tunnel sitting outside, if you run it long enough eventually the same air molecule of air will go through again =).

Right...and it's also why, even though they refer to their tunnel as "closed circuit", the CFME wind tunnel in Geneva is actually closer in design to what is usually called "open circuit", like the A2 and Specialized tunnels, than it is to a traditional closed-circuit design like the San Diego LSWT.

Semantics aside, it's really all a matter of understanding the pluses and minuses of each configuration and doing whatever is necessary to get good data out of the test section :-)

http://bikeblather.blogspot.com/
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
Quote | Reply
chrisyu wrote:

All 3 huh? Ok, I think we can do that. Newtons though....that's pushing it! (just kidding...it's not too hard to convince me to use the "correct" units)


Yeah, my thought is that you'd need to keep the "translational only" plots around (at least for a while, since that's what folks are used to seeing - pretty much the same reason you gave for reporting in gF for drag), but obviously the combined plot is really where the rubber meets the road (pun-ny analogy intended ;-)

Then, also having the rotational drag plot would also help to put that into perspective for folks...as in how much it can vary, both between setups and across yaw, and how much of the total drag it contributes. The "power to rotate" being as large as 15-30% of translational drag that Mavic quotes is nothing to sneeze at...

Of course, ultimately it would mean coming up with a way to combine the aerodynamic drag with the rolling resistance drag to create an overall "resistance to forward motion plot", sort of like what I've done with the combined aero drag + Crr plots I've put up on my blog.

http://bikeblather.blogspot.com/
Last edited by: Tom A.: May 22, 13 14:54
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:

How about all 3? Translational only, rotational (while subjected to translational air flow), and combined. All in newtons, of course ;-)

I would advice against using Newtons for the rotational drag for the same reason that rolling resistance shouldn't be given as a force. They both are moments so please use N·m

Translational drag, spin moment and total power can be a good combination. And you should give data about the effect of wheel angular velocity in both translation drag and spin moment for additional points ;-)

http://cds-0.blogspot.com
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:
Yeah, having the tire Crr in there is a confounder...but, seeing as how the drums would need to be mounted on the balance, you really only need just enough pressure on the tire to prevent slipping, so that should help minimize any Crr effects. On the front that shouldn't be a huge issue...doing so on the rear, especially if the rear drum is applying a pedaling resistance, might be problematic. I guess that's why Mavic mentioned they'd be building an electric brake into a Comete disc...although I haven't completely thought through exactly how that would work...

There is a way to do it. You have to set up the resistance of the electric brake to a value high enough to prevent wheel acceleration. Knowing rider power and power dissipated in rolling resistance, you can calculate power to spin as the difference between rider power and the sum of rolling resistance and braking power

http://cds-0.blogspot.com
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
Quote | Reply
Epic-o wrote:
Tom A. wrote:


How about all 3? Translational only, rotational (while subjected to translational air flow), and combined. All in newtons, of course ;-)


I would advice against using Newtons for the rotational drag for the same reason that rolling resistance shouldn't be given as a force. They both are moments so please use N·m

Translational drag, spin moment and total power can be a good combination. And you should give data about the effect of wheel angular velocity in both translation drag and spin moment for additional points ;-)

Well, technically that moment is the result of a difference in force of compression in the leading and trailing sections of the contact patch ;-)

I don't have any problem with resolving the moment into a force at the contact patch...after all, that's what the rider "feels" as a resistance. In fact, it's why some folks confuse high Crr with high mass...and one can think of changes in Crr as being analogous to changes road grade.

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
Quote | Reply
Tom A. wrote:
Epic-o wrote:
Tom A. wrote:


How about all 3? Translational only, rotational (while subjected to translational air flow), and combined. All in newtons, of course ;-)


I would advice against using Newtons for the rotational drag for the same reason that rolling resistance shouldn't be given as a force. They both are moments so please use N·m

Translational drag, spin moment and total power can be a good combination. And you should give data about the effect of wheel angular velocity in both translation drag and spin moment for additional points ;-)


Well, technically that moment is the result of a difference in force of compression in the leading and trailing sections of the contact patch ;-)

I don't have any problem with resolving the moment into a force at the contact patch...after all, that's what the rider "feels" as a resistance. In fact, it's why some folks confuse high Crr with high mass...and one can think of changes in Crr as being analogous to changes road grade.


We are getting deep into dynamics here but technically a force at the contact patch doesn't dissipate power due to the RWS condition ;-). That force brought to the wheel axe is the force that is tipically defined as rolling resistance force. Due to the definition of Crr (the ratio between the shift of the center of pressure in the contact patch and the rolling radius), both powers are the same

http://cds-0.blogspot.com
Last edited by: Epic-o: May 22, 13 16:06
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
Initially, we'll be measuring the electrical power that the drum motors are drawing. That, along with the motor efficiency tables, should get us pretty close.

Okay, I admit I'm lost. This is almost surely because I've never been to a full-size wind tunnel testing full-size bikes (hint hint) but doesn't that mean you're going to have confounding with the wheel and drum bearings, and the tire/drum interface? If your drum and drum motor are attached to the balance surface why do you have to worry about the power the drum motors are drawing, or their efficiency?
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
Quote | Reply
RChung wrote:
chrisyu wrote:

Initially, we'll be measuring the electrical power that the drum motors are drawing. That, along with the motor efficiency tables, should get us pretty close.


Okay, I admit I'm lost. This is almost surely because I've never been to a full-size wind tunnel testing full-size bikes (hint hint) but doesn't that mean you're going to have confounding with the wheel and drum bearings, and the tire/drum interface? If your drum and drum motor are attached to the balance surface why do you have to worry about the power the drum motors are drawing, or their efficiency?

You can know how much power you are using to drive the drum but you don't know how much of that power goes to the wheel, so you need to know the efficiency. Knowing that the wheel turns at constant velocity and power dissipated due to rolling resistance, you can calculate power to spin

http://cds-0.blogspot.com
Quote Reply
Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
Quote | Reply
RChung wrote:
chrisyu wrote:

Initially, we'll be measuring the electrical power that the drum motors are drawing. That, along with the motor efficiency tables, should get us pretty close.


Okay, I admit I'm lost. This is almost surely because I've never been to a full-size wind tunnel testing full-size bikes (hint hint) but doesn't that mean you're going to have confounding with the wheel and drum bearings, and the tire/drum interface? If your drum and drum motor are attached to the balance surface why do you have to worry about the power the drum motors are drawing, or their efficiency?


Hi Robert,

Epic-O basically hit it above. You're right that we'll also be measuring rolling resistance (tire/drum interface) and bearing drag on the drums, but that's pretty hard to avoid. But basically, we measure how much power it takes to turn the drum (and thus the tire and wheel) at a constant speed. Then if we want to extract out rotational aerodynamic drag, we need to know Crr to take out that contribution from the measurement.

By the way, you're also pretty local so you'll have to stop by for a tour sometime too!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
Last edited by: chrisyu: May 22, 13 16:41
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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For everyone following along, I know we're really into the nitty gritty here (which is awesome) but please (please!!) don't be scared away. No questions too basic or simple!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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Epic-o wrote:
RChung wrote:
chrisyu wrote:

Initially, we'll be measuring the electrical power that the drum motors are drawing. That, along with the motor efficiency tables, should get us pretty close.


Okay, I admit I'm lost. This is almost surely because I've never been to a full-size wind tunnel testing full-size bikes (hint hint) but doesn't that mean you're going to have confounding with the wheel and drum bearings, and the tire/drum interface? If your drum and drum motor are attached to the balance surface why do you have to worry about the power the drum motors are drawing, or their efficiency?


You can know how much power you are using to drive the drum but you don't know how much of that power goes to the wheel, so you need to know the efficiency. Knowing that the wheel turns at constant velocity and power dissipated due to rolling resistance, you can calculate power to spin

Right, but why would that be better than measuring the difference in forces between a stationary wheel and a wheel rotating at airspeed? Wouldn't that difference be the net effect of the rotation, both from the wheel but also any downstream effect on the frame? (I'm sure the reason is sensible -- it's just that because I'm only familiar with field testing I just get the net effect anyway).
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Hi Chris,

Do you have any comparison data on your new Roval wheels with other brands?

Thanks,
Alex
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Chris- 2 questions:

1. Have you done much research into how a reduced q factor would reduce drag on the cyclist? Obree and Ekimov both used narrow q bikes to great success and recently a British fellow did a study that efficiency of the rider was slightly higher with low q values. Seems like alot of cranksets have ridiculosly high q factors, and there is almost no way to get a narrow one without going back to square taper.

2. Have you shown boundary layer trip strips to be very helpful (on rider, bike or helmet) ?

Thanks,
BJ
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Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
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You have to enforce wheel velocity using a drum to get something meaningful (if not drag won't be constant). To make the wheel rotate at airspeed you need to raise the bike to avoid contact (if there is contact, the angular velocity would be very low) with the WT ground but the wheel would accelerate until infinity and the direction of spin is wheel-dependent

The only possible way to avoid acceleration is to reduce the normal load on the wheel to equilibrate rolling resistance moment and power to spin for the desired wheel velocity but this is very complex and would need special wind tunnel fixtures. This could work for the H3 but not for the rest of wheels

With field testing you get a mixed CdA-moment coefficent so when manufacturers start to give power to spin values, it can become a source of error that hasn't been taken into account until now

http://cds-0.blogspot.com
Last edited by: Epic-o: May 22, 13 17:44
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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Epic-o wrote:
You have to enforce wheel velocity using a drum to get something meaningful (if not drag won't be constant). The only way to make the wheel rotate at airspeed is to raise the bike to avoid contact (if there is contact, the angular velocity would be very low) with the WT ground but the wheel would accelerate until infinity and the direction of spin is wheel-dependent

The only way to do that is to reduce the normal load on the wheel to equilibrate rolling resistance moment and power to spin for the desired wheel velocity but this is very complex and would need special wind tunnel fixtures.

With field testing you get a mixed CdA-moment coefficent so when manufacturers start to give power to spin values, it can become a source of error that hasn't been taken into account until now

Oh, I completely understand the wheel has to be driven to match airspeed. What I don't quite understand is why you have to monitor the power drawn by the drum motors and their efficiency (and the bearing losses) in order to get the "power to rotate." Why can't you do it backwards by measuring the drag difference between rotating and non-rotating wheels. What does measuring the power at the motor (and its efficiency and the losses in the bearings) tell you that you don't get the other way?
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Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
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RChung wrote:
Why can't you do it backwards by measuring the drag difference between rotating and non-rotating wheels. What does measuring the power at the motor (and its efficiency and the losses in the bearings) tell you that you don't get the other way?

With your proposed method you can only calculate the differences in translational drag. You don't get any info about the power to rotate

http://cds-0.blogspot.com
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Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
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Slowman wrote:
"That's exactly what he means"

again, i don't think it matters in the end. but, it had been my understanding that open and closed circuit were terms of art and that by any definition this is an open circuit tunnel, aka open return tunnel, with open circuit and open return being synonyms.

Air molecules don't know the name you've given the path, as they try to return to the low-pressure zone you call the inlet. Even in what humans call "closed loop" return paths, the air molecules sometimes double-back a little bit. Really, they don't care -- they'll eventually get back around the merry-go-round.

AndyF
bike geek
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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Epic-o wrote:
RChung wrote:
Why can't you do it backwards by measuring the drag difference between rotating and non-rotating wheels. What does measuring the power at the motor (and its efficiency and the losses in the bearings) tell you that you don't get the other way?


With your proposed method you can only calculate the differences in translational drag. You don't get any info about the power to rotate

Forgive me, I'm used to field tests so this is not something I'm used to thinking about. I'm sure you're right but I'm still confused. If you hold the wheel fixed then don't you get the translational aero piece, and then if you drive the wheel at airspeed don't you get the total aero drag from the whole thing? Then isn't the difference due to the aero bit due to rotation, and it excludes the bearing losses?
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Re: Ask us (almost) anything about our Wind Tunnel [AndyF] [ In reply to ]
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"Air molecules don't know the name you've given the path"

no argument there. nevertheless, i know the name, even if the molecule does not.


Dan Empfield
aka Slowman
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Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
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Slowman wrote:
"Air molecules don't know the name you've given the path"

no argument there. nevertheless, i know the name, even if the molecule does not.


Maybe, but it's a continuum from being fully open to fully closed. Naturally, the monotonicity and linearity of the fan speed / tunnel airspeed relation is related to the number of flow regimes the air flow goes through on the return path, as you ramp up the fan speed. In a more open return path, you might also need a bigger motor on those fans.

AndyF
bike geek
Last edited by: AndyF: May 22, 13 18:08
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:
For everyone following along, I know we're really into the nitty gritty here (which is awesome) but please (please!!) don't be scared away. No questions too basic or simple!

It is awesome! Educational, too (I'm learning). I hope people aren't scared away by the fine details, but I also hope that by answering these questions everyone understands what a statement Specialized is making here. They hired the right people, built the tunnel the way they should, and now they've opened themselves up for questioning by some very smart people in the field. To borrow an often-used phrase from the Bay area - it's a commitment to excellence.

I'm excited for you guys; you're kids in a candy store, I'm sure, and I can't wait to see what comes out of Morgan Hill in the future. I can already picture one of you waking up in the middle of the night with an idea, and then running over to the tunnel to test the next morning. BTW, with all the testing we're doing down here at ERO, I can tell you guys that some of the lowest CdA's we've seen from geared bikes have come from athletes on the Shiv TT! Great bike.

Jim Manton / ERO Sports
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Re: Ask us (almost) anything about our Wind Tunnel [AndyF] [ In reply to ]
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i don't think these guys care too much whether it's an open or closed circuit tunnel, or whether they think it is, or whether we think it is. as i said originally, it doesn't matter to me. the tunnel type doesn't matter to me as long as it works. words and definitions, however, do mean things to me. hence my question.

i'm confident specialized has made itself a tool that will move the ball forward in product design. how this translates to new and better products we will see. this isn't the last we'll be writing about this wind tunnel in particular and wind tunnels in general.

Dan Empfield
aka Slowman
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Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
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Slowman wrote:
i don't think these guys care too much whether it's an open or closed circuit tunnel, or whether they think it is, or whether we think it is. as i said originally, it doesn't matter to me. the tunnel type doesn't matter to me as long as it works. words and definitions, however, do mean things to me. hence my question.

i'm confident specialized has made itself a tool that will move the ball forward in product design. how this translates to new and better products we will see. this isn't the last we'll be writing about this wind tunnel in particular and wind tunnels in general.

Oh, I certainly agree with you on that. They've really anted up, and made a clear statement that they're committed to making better bikes. No argument there.

And I don't care about open/closed either.

AndyF
bike geek
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Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
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RChung wrote:
Forgive me, I'm used to field tests so this is not something I'm used to thinking about. I'm sure you're right but I'm still confused. If you hold the wheel fixed then don't you get the translational aero piece, and then if you drive the wheel at airspeed don't you get the total aero drag from the whole thing? Then isn't the difference due to the aero bit due to rotation, and it excludes the bearing losses?


No worries :). I will do the real world equivalence, maybe that way you understand it better.

If you want to ride at constant speed to have to compensate the translational drag and the moment that tries to reduce the angular velocity of the wheel and, consequently, the speed of the bicycle. As you can see, there are two sources of dissipation. Traditional WT calculate the power associated to the first source (for a given wheel rotational speed) but not the power associated to the second one so you are understimating total power dissipation.

As I've said, this is a source of error for WT-field test correlation

http://cds-0.blogspot.com
Last edited by: Epic-o: May 22, 13 18:29
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Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
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RChung wrote:
Epic-o wrote:
RChung wrote:
Why can't you do it backwards by measuring the drag difference between rotating and non-rotating wheels. What does measuring the power at the motor (and its efficiency and the losses in the bearings) tell you that you don't get the other way?


With your proposed method you can only calculate the differences in translational drag. You don't get any info about the power to rotate


Forgive me, I'm used to field tests so this is not something I'm used to thinking about. I'm sure you're right but I'm still confused. If you hold the wheel fixed then don't you get the translational aero piece, and then if you drive the wheel at airspeed don't you get the total aero drag from the whole thing? Then isn't the difference due to the aero bit due to rotation, and it excludes the bearing losses?

Hi Robert,

I think I know what you're asking...but I could be completely off (like I said before, wouldn't be the first time!!). Take this scenario: We have a wheel mounted on the force balance and it's spinning. We then completely cover it with a shroud that's not touching the force balance at all (say we hang it from the ceiling). The wheel inside is still spinning, but since no airflow is hitting it, our force balance will show a zero (translational) drag reading. However, power is still required to spin the wheel inside the box (power that would have to be expended by the rider). The different setups we've mentioned are to measure that power (and in particular the aerodynamic drag work generated by spinning the spokes and rim).

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [alexZA] [ In reply to ]
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alexZA wrote:
Hi Chris,

Do you have any comparison data on your new Roval wheels with other brands?

Thanks,
Alex

Let me try to dig up something for you in the morning. That project was underway when I joined, so I'll have to go into our archives.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Thanks Chris
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Re: Ask us (almost) anything about our Wind Tunnel [J7] [ In reply to ]
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J7 wrote:
Chris- 2 questions:

1. Have you done much research into how a reduced q factor would reduce drag on the cyclist? Obree and Ekimov both used narrow q bikes to great success and recently a British fellow did a study that efficiency of the rider was slightly higher with low q values. Seems like alot of cranksets have ridiculosly high q factors, and there is almost no way to get a narrow one without going back to square taper.

2. Have you shown boundary layer trip strips to be very helpful (on rider, bike or helmet) ?

Thanks,
BJ

Hi BJ,

Good questions!

1. To be honest, not too much because there are so many other variables here. Since a rider still needs to pedal the thing, we need to remember that changing stance width will likely affect leg position (knee tracking) which could have as big or bigger impact on drag as the width change at the pedals. And that's not even accounting for any power loss or gain from the change in fit.

2. I won't go into details, but we're looking at all ways of reducing drag. For cycling flow regimes there are certain cases (for you aero-geeks out there: there's certain parts of the bikes that are in the transitional Re regime) where a trip may work. The complicated part is: cycling is pretty dynamic relative to something like a plane (in cruise state, a plane doesn't really move around that much!) so having a trip that works most of the time is not as easy as it may seem.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Jim@EROsports] [ In reply to ]
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Jim@EROsports wrote:
chrisyu wrote:
For everyone following along, I know we're really into the nitty gritty here (which is awesome) but please (please!!) don't be scared away. No questions too basic or simple!


It is awesome! Educational, too (I'm learning). I hope people aren't scared away by the fine details, but I also hope that by answering these questions everyone understands what a statement Specialized is making here. They hired the right people, built the tunnel the way they should, and now they've opened themselves up for questioning by some very smart people in the field. To borrow an often-used phrase from the Bay area - it's a commitment to excellence.

I'm excited for you guys; you're kids in a candy store, I'm sure, and I can't wait to see what comes out of Morgan Hill in the future. I can already picture one of you waking up in the middle of the night with an idea, and then running over to the tunnel to test the next morning. BTW, with all the testing we're doing down here at ERO, I can tell you guys that some of the lowest CdA's we've seen from geared bikes have come from athletes on the Shiv TT! Great bike.

Hi Jim,

Thanks! We appreciate it. The stuff you guys are doing down there with ERO has been fun to watch. I'm all for bringing aero to the masses!

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:

I think I know what you're asking...but I could be completely off (like I said before, wouldn't be the first time!!). Take this scenario: We have a wheel mounted on the force balance and it's spinning. We then completely cover it with a shroud that's not touching the force balance at all (say we hang it from the ceiling). The wheel inside is still spinning, but since no airflow is hitting it, our force balance will show a zero (translational) drag reading. However, power is still required to spin the wheel inside the box (power that would have to be expended by the rider). The different setups we've mentioned are to measure that power (and in particular the aerodynamic drag work generated by spinning the spokes and rim).

...and, the really interesting thing (to me, at least) is if and how that rotational power requirement changes when the shroud is dropped in place :-)

Thinking about this some more, I think what Robert is getting at is that since the motor is mounted to the balance plate, wouldn't there be a reaction moment measurable on the plate from spinning the wheel? It's a 6-axis balance, right (measuring an orthogonal set of axes and the moments about them)?

Here's another scenario with just a wheel mounted to the balance. With no wind blowing and wheel stationary, the balance is tared and measures zero about all 6 axes of measurement. Now, start the wheel spinning...wouldn't there be a moment measured about the transverse axis? That should be resolvable into a "moment to spin", wouldn't it?

So...then if the above is true, wouldn't one be able to compare the measurements between wheels stationary and spinning while the wind tunnel is on to back out a power to rotate just from the balance readings alone? Granted, it would still be lumping in tire rolling resistance and bearing drag, but that's the case with the other approach as well...but, at least you wouldn't have to worry about motor efficiency.

Like I said, just "thinking out loud" here...and it's late, so I might be totally stuffing this ;-)

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
chrisyu wrote:

I think I know what you're asking...but I could be completely off (like I said before, wouldn't be the first time!!). Take this scenario: We have a wheel mounted on the force balance and it's spinning. We then completely cover it with a shroud that's not touching the force balance at all (say we hang it from the ceiling). The wheel inside is still spinning, but since no airflow is hitting it, our force balance will show a zero (translational) drag reading. However, power is still required to spin the wheel inside the box (power that would have to be expended by the rider). The different setups we've mentioned are to measure that power (and in particular the aerodynamic drag work generated by spinning the spokes and rim).


...and, the really interesting thing (to me, at least) is if and how that rotational power requirement changes when the shroud is dropped in place :-)

Thinking about this some more, I think what Robert is getting at is that since the motor is mounted to the balance plate, wouldn't there be a reaction moment measurable on the plate from spinning the wheel? It's a 6-axis balance, right (measuring an orthogonal set of axes and the moments about them)?

Here's another scenario with just a wheel mounted to the balance. With no wind blowing and wheel stationary, the balance is tared and measures zero about all 6 axes of measurement. Now, start the wheel spinning...wouldn't there be a moment measured about the transverse axis? That should be resolvable into a "moment to spin", wouldn't it?

So...then if the above is true, wouldn't one be able to compare the measurements between wheels stationary and spinning while the wind tunnel is on to back out a power to rotate just from the balance readings alone? Granted, it would still be lumping in tire rolling resistance and bearing drag, but that's the case with the other approach as well...but, at least you wouldn't have to worry about motor efficiency.

Like I said, just "thinking out loud" here...and it's late, so I might be totally stuffing this ;-)

Nope, you're absolutely right. With a 6 component balance, you'd be able to back out power to spin with measured moments. We actually contemplated doing this early on but decided to build a 3 component balance for several reasons but the big ones were: it's tough (really tough) to make a robust and precise balance with that many components. We need a balance that people can walk and ride on (sometimes slip and fall on!) which can also then measure down to +/- 2 gF. I've used a few 6 component balances before and they are all pretty delicate instruments. The other reason is, once you get into combining several moment components, there are a lot of places for error to creep in. It's not that much of a pain to just measure it directly, so that's the path we took.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Tom A. wrote:

Thinking about this some more, I think what Robert is getting at is that since the motor is mounted to the balance plate, wouldn't there be a reaction moment measurable on the plate from spinning the wheel? It's a 6-axis balance, right (measuring an orthogonal set of axes and the moments about them)?

Here's another scenario with just a wheel mounted to the balance. With no wind blowing and wheel stationary, the balance is tared and measures zero about all 6 axes of measurement. Now, start the wheel spinning...wouldn't there be a moment measured about the transverse axis? That should be resolvable into a "moment to spin", wouldn't it?

So...then if the above is true, wouldn't one be able to compare the measurements between wheels stationary and spinning while the wind tunnel is on to back out a power to rotate just from the balance readings alone? Granted, it would still be lumping in tire rolling resistance and bearing drag, but that's the case with the other approach as well...but, at least you wouldn't have to worry about motor efficiency.

Like I said, just "thinking out loud" here...and it's late, so I might be totally stuffing this ;-)


Yes, this is what I meant.

chrisyu wrote:

Nope, you're absolutely right. With a 6 component balance, you'd be able to back out power to spin with measured moments. We actually contemplated doing this early on but decided to build a 3 component balance for several reasons but the big ones were: it's tough (really tough) to make a robust and precise balance with that many components. We need a balance that people can walk and ride on (sometimes slip and fall on!) which can also then measure down to +/- 2 gF. I've used a few 6 component balances before and they are all pretty delicate instruments. The other reason is, once you get into combining several moment components, there are a lot of places for error to creep in. It's not that much of a pain to just measure it directly, so that's the path we took.


Chris: Thanks. Yes, this answers my original confusion. My intuition was telling me it would have worked, but it sounds like you're saying that although my intuition was right in a theoretical sense, the demands of the application meant that in a practical sense the errors would have been big. This is cool, and I've learned something. It gives me more reason to come down sometime and look at your tunnel.
Last edited by: RChung: May 22, 13 22:49
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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I've read through just about all of this thread and maybe I've missed it but:

What are you using to quantify air speed in the test section? Kiel probes, Hot wires, Vanes, nozzels, something else?

Are you calculating to a standard condition to compare results from different days? (Air density)

Thanks

jaretj
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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I assume you guys will be building a icing wind tunnel next? Because I swear that a better shaped fork on a commuter bike could reduce the ice build up on my legs.


A couple more serious thoughts.

Since it is an "open" design, how much did cleaning the tunnel affect the design? You guys mention using it for more than just road racing bikes, so would you have the capability to simulate rain? It may be possible to design better fenders that not keep you and the drivetrain cleaner, but also with less drag.

Does your scale have the ability to determine where the center of lift for a bike/rider system is? Obviously your scales measure drag of bike/rider and may even measure the side load that is perpendicular to the drag force during yaw. Does the location of the force matter? Is closer to the rear wheel more stable? Or is CFD just a better place to look at this?

I know that ERO has found some interesting things when they have the riders actually riding around a velodrome and I assume you guys have also with your box. This can be due to a rider changing their position or moving slightly differently when they are actually riding compared to being in a tunnel. Have you considered a scale that constrains the rider less than normal, to "force" them to make the same sort of tweaks you would see actually riding? Something like a very clever set of rollers?
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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"we need to remember that changing stance width will likely affect leg position (knee tracking) which could have as big or bigger impact on drag as the width change at the pedals"

that is an exceptionally good statement from someone whose specialty is not, to my knowledge, bike fit. only the very best bike fitters would know to answer that question the way you just answered it.


Dan Empfield
aka Slowman
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Re: Ask us (almost) anything about our Wind Tunnel [RChung] [ In reply to ]
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Yea, I had a hunch that's what you were getting at but wasn't sure. Would love to have you over sometime.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [jaretj] [ In reply to ]
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jaretj wrote:
I've read through just about all of this thread and maybe I've missed it but:

What are you using to quantify air speed in the test section? Kiel probes, Hot wires, Vanes, nozzels, something else?

Are you calculating to a standard condition to compare results from different days? (Air density)

Thanks

jaretj

Hi Jaret,

We directly measure it using a pitot over the center of the test section (actually just upstream of center). Our uniformity is good enough (and blockage low enough) that we are getting good correlation between the installed pitot and a separate high speed, multi-component pitot placed at the apparatus location (which we can move anywhere else in the tunnel).

All our data is either normalized to coefficients, or if we show forces, those are normalized to a standard day so we can compare day-to-day.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chaparral] [ In reply to ]
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chaparral wrote:
Since it is an "open" design, how much did cleaning the tunnel affect the design? You guys mention using it for more than just road racing bikes, so would you have the capability to simulate rain? It may be possible to design better fenders that not keep you and the drivetrain cleaner, but also with less drag.

Yup, absolutely. Even without the environmental tests, the flow conditioning screens at the inlet will accumulate dust over time, which we will need to clean (just a fact of life with any wind tunnel). It's important to do this regularly since dust will typically accumulate non-uniformly on the screens (e.g. more at the bottom than the top) which would affect flow uniformity in the test section.

chaparral wrote:
Does your scale have the ability to determine where the center of lift for a bike/rider system is? Obviously your scales measure drag of bike/rider and may even measure the side load that is perpendicular to the drag force during yaw. Does the location of the force matter? Is closer to the rear wheel more stable? Or is CFD just a better place to look at this?

I think you're referring to side force when you say "lift"? Our balance is 3-components, meaning we can measure drag, side force, and yaw-moment. So we can determine yaw-center on the bike/rider system. It'll definitely be interesting to see the impact of shifting that center back and forth.

chaparral wrote:
I know that ERO has found some interesting things when they have the riders actually riding around a velodrome and I assume you guys have also with your box. This can be due to a rider changing their position or moving slightly differently when they are actually riding compared to being in a tunnel. Have you considered a scale that constrains the rider less than normal, to "force" them to make the same sort of tweaks you would see actually riding? Something like a very clever set of rollers?

Oh yea, the goal (at least for athlete testing) is to make it as dynamic as possible. We're looking into all sorts of ways to include realistic riding dynamics into the tunnel fixtures. But as I had mentioned before, there is definitely a trade-off in repeatability of the measurements. And as you point out, field testing is great for real world validation.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [Slowman] [ In reply to ]
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Slowman wrote:
"we need to remember that changing stance width will likely affect leg position (knee tracking) which could have as big or bigger impact on drag as the width change at the pedals"

that is an exceptionally good statement from someone whose specialty is not, to my knowledge, bike fit. only the very best bike fitters would know to answer that question the way you just answered it.

Thanks Dan. I'm not a bike fitter but I've worked alongside some very good ones here...enough to see that stuff like this matters a lot.

Chris Yu
Applied Technology
Specialized Bicycle Components
@chrisyuinc
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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Thanks, I was just curious. I have a lot of experience in measuring airflow but not much in wind tunnel applications.

jaretj
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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chrisyu wrote:

All our data is either normalized to coefficients...

Translation: You work with results in terms of CdA...as it should be. Nice. :-)

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [chrisyu] [ In reply to ]
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What do you think about this?. Taken from Giant's FB:

Giant Bicycles

Congratulations on a beautiful wind tunnel, @iamspecialized . How about you put it to a true test by accepting Giant’s challenge to test our Propel Advanced SL 0 against your Venge S-Works Di2? Let’s see which bike truly is the most aero….once and for all. You pick the time, we’ll bring our bike. Do you accept? #aeroiseverything #ridelife #giantbicycles


http://cds-0.blogspot.com
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Re: Ask us (almost) anything about our Wind Tunnel [Epic-o] [ In reply to ]
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I think that lacks a bit of class. I do not own any Specialized bike nor have I ever done so. I do have a Giant Cross bike and love it, but this kind of call out reminds me a bit of some dude showing up at the wedding of Tom and Susan and yelling out loud "Congrats on that pending wedding Susan. How about I show you my penis, and Tom needs to do the same. Let's see which penis truly is bigger.....once and for all. So Susan, you pick the time. I bring the penis."
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Re: Ask us (almost) anything about our Wind Tunnel [Herbert] [ In reply to ]
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Herbert wrote:
I think that lacks a bit of class. I do not own any Specialized bike nor have I ever done so. I do have a Giant Cross bike and love it, but this kind of call out reminds me a bit of some dude showing up at the wedding of Tom and Susan and yelling out loud "Congrats on that pending wedding Susan. How about I show you my penis, and Tom needs to do the same. Let's see which penis truly is bigger.....once and for all. So Susan, you pick the time. I bring the penis."

Easy to make a mistake with social media. Bet there are some people over at Giant who are none too thrilled that was posted. Besides, careful what you wish for, right? Ol' Tom might be might be hung like a horse. ;-)

Jim Manton / ERO Sports
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Tom A. wrote:
chrisyu wrote:

All our data is either normalized to coefficients...


Translation: You work with results in terms of CdA...as it should be. Nice. :-)

Data should only be in CdA's unless converting to true forces or power to overcome. A lot of the confusion in aero over the years has been due to gF talked about and then it's unclear if that's at 30 mph, 40 kph, 10 m/s... too many units.

We use CdA (m^2) here and talk deltas as non-dimensionalized percentages. We're working to make sure we're consistent here and hope to do a better job publishing data to the world in the future. Room for improvement for sure.

Mark

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Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Ask us (almost) anything about our Wind Tunnel [MITaerobike] [ In reply to ]
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If you then tell me that your Z coordinate is positive in the up direction you will be my hero (the old aerospace std. of z is negative up has infected too many disciplines including automotive).
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Re: Ask us (almost) anything about our Wind Tunnel [pyrahna] [ In reply to ]
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pyrahna wrote:
If you then tell me that your Z coordinate is positive in the up direction you will be my hero (the old aerospace std. of z is negative up has infected too many disciplines including automotive).

But, then they would have to swap + and - yaw ;-)

http://bikeblather.blogspot.com/
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Re: Ask us (almost) anything about our Wind Tunnel [Tom A.] [ In reply to ]
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Until the main focus of testing bikes in a wind tunnel is aerodynamic lift it makes the most sense to make Z + up. No one, to my knowledge, does it and it is a personal pet peeve. But as a professor once told me, the benefit of being an engineer is being able to define the coordinate system you choose to work in, what he failed to explain was you would be haunted by previous engineers decisions for the entirety of your career:)
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Re: Ask us (almost) anything about our Wind Tunnel [Ossbr] [ In reply to ]
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I'd be intereste in that too!
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