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Re: Want unlimited wind tunnel testing? [desert dude] [ In reply to ]
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desert dude wrote:
Crashing isn't good for aerodynamics I'd guess.

Aerodynamics are unchanged as long as you stay in position, it's the rolling resistance that goes up exponentially.
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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Slowman wrote:
Jim@EROsports wrote:
Slowman wrote:
Jim@EROsports wrote:
That's correct, as far as I know it was never assembled after purchase; it's been crated since it was moved. What he bought it for would shock everyone. It cost him quite a bit more to move it, actually. The story behind how he even bought it is pretty interesting, too.

Before it went up for sale publicly, we looked at this, spoke to other industries, specifically the auto industry since many design facilities for the major manufactures are here in SoCal. There was interest, but not enough for us to take the chance.

This particular tunnel is a rolling road setup. It would take a decent investment just to create a platform for cycling, though it had just been updated before it was shut down, so the electronics were, at the time, state of the art.

Want to make money from a wind tunnel? Buy the San Diego tunnel and then sell it to the airport authority. They want that land so bad I bet you'd come out ahead on a quick flip!


but you have to admit, the rolling road motif does create an opportunity not available so far our testing.


My insurance agent would probably drop me at the very thought of it!

The are 3 tunnels that I know of for sale in the US alone at the moment. Know why? It's not a growth industry.


fine. i don't disagree with any of that. all i'm saying is, we never get bikes ridden in tunnels the way bikes are ridden on the road. here's one method that solves that. it's at least an interesting thought experiment!

The problem being, though...that the additional complexity required and data uncertainty resulting aren't "worth" the effort.

Non-"rolling road" test setups allow for data acquisition that results in being able to predict "real world" power demands to within 3% error, IIRC...so, to quote Chris Yu, "There's not enough juice for the squeeze" ;-)

http://bikeblather.blogspot.com/
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Re: Want unlimited wind tunnel testing? [ In reply to ]
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PAGING ED BAKER
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Re: Want unlimited wind tunnel testing? [Tom A.] [ In reply to ]
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Tom A. wrote:
Non-"rolling road" test setups allow for data acquisition that results in being able to predict "real world" power demands to within 3% error, IIRC...so, to quote Chris Yu, "There's not enough juice for the squeeze" ;-)

how would one know? how can you express that sort of confidence - 3 percent error - between a known process and an unknown process? that's the nature of unknowns.

maybe that's the limitation with tunnels. one limitation with the rolling road tunnel is that, unless that road is in a big turret, or unless the tunnel is on a big huge turret - when you were a kid did you every ride disneyland's carousel of progress? - you can't test a yaw.

Dan Empfield
aka Slowman
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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Slowman wrote:
Tom A. wrote:
Non-"rolling road" test setups allow for data acquisition that results in being able to predict "real world" power demands to within 3% error, IIRC...so, to quote Chris Yu, "There's not enough juice for the squeeze" ;-)


how would one know? how can you express that sort of confidence - 3 percent error - between a known process and an unknown process? that's the nature of unknowns.

maybe that's the limitation with tunnels. one limitation with the rolling road tunnel is that, unless that road is in a big turret, or unless the tunnel is on a big huge turret - when you were a kid did you every ride disneyland's carousel of progress? - you can't test a yaw.

The test of any theory is the quality of the predictions it makes, and using wind tunnel measured parameters you can make predictions that closely agree with performance in the real world.

Here's a different but clever approach; you can't do it on your own, but it's pretty damn neat. Plus, "ring of fire" is a great name.
https://www.mdpi.com/2504-3900/2/6/221
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Re: Want unlimited wind tunnel testing? [RChung] [ In reply to ]
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RChung wrote:
Slowman wrote:
Tom A. wrote:
Non-"rolling road" test setups allow for data acquisition that results in being able to predict "real world" power demands to within 3% error, IIRC...so, to quote Chris Yu, "There's not enough juice for the squeeze" ;-)


how would one know? how can you express that sort of confidence - 3 percent error - between a known process and an unknown process? that's the nature of unknowns.

maybe that's the limitation with tunnels. one limitation with the rolling road tunnel is that, unless that road is in a big turret, or unless the tunnel is on a big huge turret - when you were a kid did you every ride disneyland's carousel of progress? - you can't test a yaw.


The test of any theory is the quality of the predictions it makes, and using wind tunnel measured parameters you can make predictions that closely agree with performance in the real world.

Here's a different but clever approach; you can't do it on your own, but it's pretty damn neat. Plus, "ring of fire" is a great name.
https://www.mdpi.com/2504-3900/2/6/221

does this test prove out the validity of a wind tunnel test using a bike fixed in an upright position? or does this test prove that a bike in that fixed upright position is demonstrably identical, minus a meaningless variance, to a bike ridden freely in a wind tunnel? were the latter possible?

Dan Empfield
aka Slowman
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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Slowman wrote:
RChung wrote:

The test of any theory is the quality of the predictions it makes, and using wind tunnel measured parameters you can make predictions that closely agree with performance in the real world.

Here's a different but clever approach; you can't do it on your own, but it's pretty damn neat. Plus, "ring of fire" is a great name.
https://www.mdpi.com/2504-3900/2/6/221


does this test prove out the validity of a wind tunnel test using a bike fixed in an upright position? or does this test prove that a bike in that fixed upright position is demonstrably identical, minus a meaningless variance, to a bike ridden freely in a wind tunnel? were the latter possible?


Well, both field-tested and wind-tunnel-tested parameters do a good job predicting performance in the real world, and field-derived parameters agree with wind-tunnel-derived parameters.

That is, they give you the same results, and the same predictions. Wind tunnel measurement is faster and easier (but more expensive), and you can do controlled yaw. You can do observed yaw in field tests but you obviously can't do controlled yaw. If I weren't so poor and if my time weren't worth so little I'd've never figured out a way to do field tests.
Last edited by: RChung: Apr 18, 19 16:07
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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Slowman wrote:
Tom A. wrote:
Non-"rolling road" test setups allow for data acquisition that results in being able to predict "real world" power demands to within 3% error, IIRC...so, to quote Chris Yu, "There's not enough juice for the squeeze" ;-)


how would one know? how can you express that sort of confidence - 3 percent error - between a known process and an unknown process? that's the nature of unknowns.

Ummm...you use a mathematical model to predict real world times based on observed inputs (i.e. ambient conditions, course elevation profile, power output, etc.) based on tunnel-derived CdA and compare them to actual performance times? Pretty much "Best Bike Split" and the like (public, or cycling team proprietary models). As I recall, those models (using stationary mounted wind tunnel data as an input) can predict what the time should be for the observed conditions and power to within a few %.

I'll defer to what Josh had to say in the marathon "Comprehensive wheel study..." thread:

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As Robert and Tom pointed out, the current tunnel protocols have succeeded in producing CdA graphs that can be used to predict real world event times within a few %. I have no doubt that we are collectively still missing some terms from our equation, but the reality is that what we are missing must be orders of magnitude smaller than what we already know and likely have more of an effect on handling or other factors which are not captured in pure watts/velocity/time calculations. Again though, if our current models are giving us predictions accurate within a few %, then we have to believe that whatever we are missing at most represents those few % and nothing more on the drag/power side of the equation and if there is any significance it would be more in the handling equation.

https://forum.slowtwitch.com/...ost=6779847#p6779847

http://bikeblather.blogspot.com/
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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Tunnels and velodrome have both been good predictors of time, so have proven results. Both, though, can also be poor predictors of time depending on how well the tests are completed. In the tunnel, many fall into the trap of testing a position that just isn't sustainable in the real world. On the velodrome, it can be the opposite, athletes tend to keep their head higher than they would outdoors looking for the next corner.

This is where field testing comes in, no? Aero sticks will fill this void (if one wants to refer to it as a void), and we've shown the results are quite good predictors of time in the past few months with the one we're using. You need to include yaw, though, and I don't think there's one available to the general public that measures yaw...yet. It's good to be me. ;-)

Jim Manton / ERO Sports
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Re: Want unlimited wind tunnel testing? [Jim@EROsports] [ In reply to ]
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Jim@EROsports wrote:
It's good to be me. ;-)
You know, my life has turned out way better than I thought or deserve, but sometimes I do feel slightly jealous of others.
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Re: Want unlimited wind tunnel testing? [Jim@EROsports] [ In reply to ]
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Jim@EROsports wrote:
Tunnels and velodrome have both been good predictors of time, so have proven results. Both, though, can also be poor predictors of time depending on how well the tests are completed. In the tunnel, many fall into the trap of testing a position that just isn't sustainable in the real world. On the velodrome, it can be the opposite, athletes tend to keep their head higher than they would outdoors looking for the next corner.

This is where field testing comes in, no? Aero sticks will fill this void (if one wants to refer to it as a void), and we've shown the results are quite good predictors of time in the past few months with the one we're using. You need to include yaw, though, and I don't think there's one available to the general public that measures yaw...yet. It's good to be me. ;-)

i guess i'm a pretty bad explainer of my query. i'm comfortable with wind tunnels. i'm comfortable with field testing. i'm comfortable that there's agreement among the models. i'm not casting doubt on the validity of wind tunnels. but if i could *wheel* this back to the point i made: a tunnel using a rolling road *might* teach us something we aren't getting from what we now have. no well funded tunnels were made for bikes. they're made for subsonic airplanes, or 200mph cars, and those vehicles don't shuck and jive the way we do on bicycles. we've been hacking these tunnels with our own contrivances that give us pretty good guesses. i'm not complaining. i'd just like to see a bike & rider mimicking their movements on the road in a tunnel. wouldn't you?

Dan Empfield
aka Slowman
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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I get that, but I would argue that's what we're getting outdoors now with the aero sticks. Measuring people as they ride outdoors...true real world. You could put people on a rolling road in a tunnel, but I doubt they'd ride the way they do outdoors.

I'm guessing (truly guessing but with a little data) that what we're actually going to learn is that some of the nuances we pick up in controlled environments aren't really going to be measurable outdoors. Air tumbles, it doesn't flow nice and straight for us. Some of the finite details aren't likely to matter, at least as much, outdoors. So, that small percentage we've been "missing" that Tom was referring to, just might not be there to measure after all. Maybe. Don't quote me just yet!

Jim Manton / ERO Sports
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Re: Want unlimited wind tunnel testing? [Jim@EROsports] [ In reply to ]
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Jim@EROsports wrote:
I get that, but I would argue that's what we're getting outdoors now with the aero sticks.

i know. that's why i like what you're doing with aero sticks.

Dan Empfield
aka Slowman
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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Slowman wrote:
Jim@EROsports wrote:
Tunnels and velodrome have both been good predictors of time, so have proven results. Both, though, can also be poor predictors of time depending on how well the tests are completed. In the tunnel, many fall into the trap of testing a position that just isn't sustainable in the real world. On the velodrome, it can be the opposite, athletes tend to keep their head higher than they would outdoors looking for the next corner.

This is where field testing comes in, no? Aero sticks will fill this void (if one wants to refer to it as a void), and we've shown the results are quite good predictors of time in the past few months with the one we're using. You need to include yaw, though, and I don't think there's one available to the general public that measures yaw...yet. It's good to be me. ;-)


i guess i'm a pretty bad explainer of my query. i'm comfortable with wind tunnels. i'm comfortable with field testing. i'm comfortable that there's agreement among the models. i'm not casting doubt on the validity of wind tunnels. but if i could *wheel* this back to the point i made: a tunnel using a rolling road *might* teach us something we aren't getting from what we now have. no well funded tunnels were made for bikes. they're made for subsonic airplanes, or 200mph cars, and those vehicles don't shuck and jive the way we do on bicycles. we've been hacking these tunnels with our own contrivances that give us pretty good guesses. i'm not complaining. i'd just like to see a bike & rider mimicking their movements on the road in a tunnel. wouldn't you?

I would think the movement of the bike and rider is going to be both very specific to individual riders and inconsistent even for an individual depending on effort level, fatigue, terrain & road conditions, weather conditions, perception of danger, etc. Surely that would make test data from a free riding athlete in a tunnel pretty impossible to usefully analyse?

I hadn't even considered the idea of using a tunnel with a rolling road in this way, and I don't think it's what I would do.
The purpose of a rolling road is normally to eliminate the tunnel boundary layer to more accurately model movement of an object through still air. In normal testing, the idea is the bike stays still and the air flows around it to simulate the relative movement of the two. However out on the road, in still air, the road and air are not moving relative to each other so there is no wind velocity gradient (ground boundary layer). The bottom of the wheel has the same impinging airflow as the top of the rider's head. That's not the case when it's windy and it's not the case in a tunnel without a rolling road. Different wind tunnels have different boundary layer characteristics. For most testing you want a uniform airflow, but you also don't mount your test piece on the floor of the tunnel. It's mounted in the middle of the tunnel where the airflow interacts least with the surfaces of the tunnel. For testing of entire ground based vehicles, it's necessary to test in proximity to a plane representing a road. You may still want uniform airflow to represent movement through still air, or you may want a gradient to represent the ground boundary layer. A rolling road allows you to model the relative movement of an object and a surface (e.g. a bike moving on a road surface). There are various set-ups and devices sometimes used to manipulate the tunnel's BL to produce or eliminate the BL immediately upstream of the test section.
I've never seen any of this mentioned in bicycle related tunnel test discussions. That may be because it's not considered, or because there's a conventional setup considered to be the standard and assumed for all cycling tunnel testing. Or I just missed it (I admit I don't usually spend much time on tunnel testing discussions).

TLDR?
Okay, what I'm getting at is this:
I'd expect the bike to be mounted rigidly on a rolling road for the purpose of more accurate airflow modelling.
I don't see a convincing reason to try using it like a cycling treadmill to achieve more accurate modelling of rider movement.


How do you measure drag for a bike moving freely on a rolling road anyway?
You couldn't directly measure it, so what do you gain over field testing?
Last edited by: Ai_1: Apr 19, 19 1:33
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Re: Want unlimited wind tunnel testing? [Jim@EROsports] [ In reply to ]
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....one Chris Boardman seems to have made a nice business from building a wind tunnel in the UK. So why is it not possible in the US?

https://www.boardmanbikes.com/...kages/aero-packages/
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Re: Want unlimited wind tunnel testing? [Ai_1] [ In reply to ]
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Ai_1 wrote:
How do you measure drag for a bike moving freely on a rolling road anyway?
Presumably with a power meter.

Quote:
You couldn't directly measure it, so what do you gain over field testing?
You might be able to validate flow field for CFD.
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Re: Want unlimited wind tunnel testing? [CG99] [ In reply to ]
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CG99 wrote:
....one Chris Boardman seems to have made a nice business from building a wind tunnel in the UK. So why is it not possible in the US?

https://www.boardmanbikes.com/...kages/aero-packages/

You need to consider the market and geography. The UK isn't a huge place and there are probably as many racing cyclists there as there are in the US. Even if the number is half, that's still massive. Also there is a huge TT scene there. Everyone time trials. In the UK that's how you get into racing bikes. Here there are very limited number of TT's. Most cyclists in the US don't have a dedicated TT bike.

Triathletes, which is mainly our market with AeroCamp, generally are more interested in the latest shiny bit than actually doing something to make themselves faster. One hour of guided time in the wind tunnel is around $600, also the same price as a Ceramic Speed pulley system. There are almost infinitely more fancy pulleys in the transitions than those who have been to test their aerodynamics.

The problem, I think, is this. People will spend money on shiny things that promise meager gains because it is something that is tangible they can show off. Aero Testing, on the other hand, can potentially net massive savings. The only thing one has to show for it is some pictures on social media and much faster bike splits. Let's face it, that's just not a cool as carbon fiber.



Heath Dotson
HD Coaching:Website |Twitter: 140 Characters or Less|Facebook:Follow us on Facebook
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Re: Want unlimited wind tunnel testing? [desert dude] [ In reply to ]
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desert dude wrote:
I think you're probably still going to have to figure out a way to stabilize the triathlete. Otherwise you're going to see a lot of athletes crashing.
Crashing isn't good for aerodynamics I'd guess.

I once got a tour of the rolling road wind tunnel in Charlotte that nascar, indy and other race teams use. It's pretty damn cool. The rolling road part of that tunnel costs > $250k. That's just the belt the cars are on when testing. In the summer they can't test after 1 or 2 pm bc they'll brown out the surrounding neighborhoods

They would be such overkill for bike testing. One of the biggest challenges is that they are designed for cars that produce down force by creating an area of low pressure under the car. So this belt is being sucked up with hundreds of pounds of force. But it can't deflect up, because the road doesn't (or at least any meaningful amount). So if the belt deflects, it ruins the data because it affects the results. So you have to design this belt that has to move very quickly to simulate the speed of the road and also somehow not deflect under this huge load. One of the solutions is to actually suck it on the other side to keep it from moving up. this also means it must be air tight, so this suction does not affect the measurement up top. Then all sorts of designs to make sure that the proper boundary layer forms on the belt before the model. There are just a handful of rolling road tunnels in the world, I think less than 30. So very niche product that requires serious engineering really drives up the price.

They are just so over engineered for bike where you don't care about that boundary layer.
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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Slowman wrote:
Jim@EROsports wrote:
Tunnels and velodrome have both been good predictors of time, so have proven results. Both, though, can also be poor predictors of time depending on how well the tests are completed. In the tunnel, many fall into the trap of testing a position that just isn't sustainable in the real world. On the velodrome, it can be the opposite, athletes tend to keep their head higher than they would outdoors looking for the next corner.

This is where field testing comes in, no? Aero sticks will fill this void (if one wants to refer to it as a void), and we've shown the results are quite good predictors of time in the past few months with the one we're using. You need to include yaw, though, and I don't think there's one available to the general public that measures yaw...yet. It's good to be me. ;-)

i guess i'm a pretty bad explainer of my query. i'm comfortable with wind tunnels. i'm comfortable with field testing. i'm comfortable that there's agreement among the models. i'm not casting doubt on the validity of wind tunnels. but if i could *wheel* this back to the point i made: a tunnel using a rolling road *might* teach us something we aren't getting from what we now have. no well funded tunnels were made for bikes. they're made for subsonic airplanes, or 200mph cars, and those vehicles don't shuck and jive the way we do on bicycles. we've been hacking these tunnels with our own contrivances that give us pretty good guesses. i'm not complaining. i'd just like to see a bike & rider mimicking their movements on the road in a tunnel. wouldn't you?

The Hambini wheel test thread comes to my mind when I read this ... until the thread derailed a bit...

I guess that should be pink.
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Re: Want unlimited wind tunnel testing? [Leanmeanmachine] [ In reply to ]
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Sounds like the old joke on how to make a small fortune in the bike biz, start out with a big fortune and buy a wind tunnel. Looks like it would take over a $million to get it covered and up and running. With staff and fixed costs how many $1000 tests would have to sell to break even? A lot. Steve Hed was a brilliant guy, if he couldn't get it going not sure I know who could unless it was one of the Walton boys. That would be chump change for them.
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Re: Want unlimited wind tunnel testing? [Ex-cyclist] [ In reply to ]
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Ex-cyclist wrote:
CG99 wrote:
....one Chris Boardman seems to have made a nice business from building a wind tunnel in the UK. So why is it not possible in the US?

https://www.boardmanbikes.com/...kages/aero-packages/


You need to consider the market and geography. The UK isn't a huge place and there are probably as many racing cyclists there as there are in the US. Even if the number is half, that's still massive. Also there is a huge TT scene there. Everyone time trials. In the UK that's how you get into racing bikes. Here there are very limited number of TT's. Most cyclists in the US don't have a dedicated TT bike.

Triathletes, which is mainly our market with AeroCamp, generally are more interested in the latest shiny bit than actually doing something to make themselves faster. One hour of guided time in the wind tunnel is around $600, also the same price as a Ceramic Speed pulley system. There are almost infinitely more fancy pulleys in the transitions than those who have been to test their aerodynamics.

The problem, I think, is this. People will spend money on shiny things that promise meager gains because it is something that is tangible they can show off. Aero Testing, on the other hand, can potentially net massive savings. The only thing one has to show for it is some pictures on social media and much faster bike splits. Let's face it, that's just not a cool as carbon fiber.

It's like I just heard this on the way to work? Good to hear you on the TT podcast!
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Re: Want unlimited wind tunnel testing? [Slowman] [ In reply to ]
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So we spent 3 years trying to develop a completely new method of tunnel testing when I was at Zipp, by using the ARC tunnel here in Indy which is the sister tunnel to the Mercedes tunnel in England and is rolling road.

The key to remember about the rolling road is that you essentially cannot touch it.. the models have to hover just above it, or touch it with almost not force as the frictional increases involved with touching it are very large. Models tested in tunnels like this are held by a 'sting' which is an aero arm extending from the ceiling and containing the balance.

We pretty quickly learned that while rolling road seems amazing, it has big issues for testing with riders and pretty big issues when testing equipment only.

Out of this, Michael Hall at Zipp conceived and then we developed an amazing tunnel concept that we had quoted for construction in 2010 by the same team who built the ARC and SRAM determined it was just too expensive.. the problem with this sort of thing is sort of similar to helmet safety or chronograph accuracy.. selling somebody on something that costs 5-10x for much higher accuracy is really hard, almost impossible unless you have unlimited funds. In the end, we should have pitched a much cheaper tunnel that was primarily focused on low operating cost and marketing focus, as specialized built this tunnel a few years later and it is still considered the standard for the industry despite considerable shortcomings.. but few people really care about those.

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
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Last edited by: joshatsilca: Apr 22, 19 4:47
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Re: Want unlimited wind tunnel testing? [Nazgul350r] [ In reply to ]
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Thanks, Mark is a great guy. It was good timing for sure. Glad you enjoyed my ramblings.



Heath Dotson
HD Coaching:Website |Twitter: 140 Characters or Less|Facebook:Follow us on Facebook
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