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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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Hey all,

Not sure when the data's from, but I figured I'd add a couple of points that might or might not be useful.

1. Upturned verus flat hand holds on aerobar basebars: We designed, built, and tested both for Saxo when making the Shiv. We tested at 0 and -15 degrees. The flat hand hold bar on the fully built bike (-tare) was 502 gF at 0 degrees and 389 gF at -15 degrees. The angled hand holds were worse by 7 gF at 0 degrees (509 gF) and better at -15 degrees by 21 gF (368 gF).

We since have finished an extensive study at A2 testing the same exact control bike over 6 months of testing -- full yaw sweeps of the exact same bike tested ~1 month apart at the same tunnel, same protocol. At 0 degrees, the data over 6 months is within 9 gF. At -15 degrees, the data is within 35 gF (more vortex shedding, component of side force load cell, etc -- we should expect data at yaw to be worse than 0 deg).

So -- TAKEAWAY -- same shape, design of basebar with only the upturn changing, the drag difference is almost immeasurable. So, we've gone with the upturned hand holds as you simply don't crash when going down hills/hitting bumps! Confidence in handling with aero performance is key.


2. Note that the tare values at A2 are about 180 to 150 to 180 gF across -25 to 0 to 25 degrees.

3. Kestrel's Cervelo data seems high to me but the trends seem to indicate the same wheels were used between the Kestrel and the Cervelo. I'd assume tares have not been subtracted. Looks like bar spec could be significantly different though. I'll wait to hear more because the data's confusing to me too.

Thought the bar stuff might be interesting though.

Cheers,

Mark

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Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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In Reply To:
502 gF at 0 degrees and 389 gF at -15 degrees.

I'm still blown away by these reported numbers...

Anything you can share re. the UCI legality of the Shiv?
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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They're real. Still waiting to hear from the UCI but no matter what, we're planning to support the technology.

MC

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Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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In Reply To:
Still waiting to hear from the UCI but no matter what, we're planning to support the technology.

So assuming that the UCI doesn't rule the bike illegal, what would it take for somebody like me to lay their hands on one? :-)
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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Re: Kestrel Wind tunnel data [jackmott] [ In reply to ]
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You realize that can be done by virtually anyone with just a bit of ingenuity and a few hundred hours to spare, right?

Chris
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Re: Kestrel Wind tunnel data [chicanery] [ In reply to ]
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In Reply To:
You realize that can be done by virtually anyone with just a bit of ingenuity and a few hundred hours to spare, right?

It's not just about making something that /looks/ aero!
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Re: Kestrel Wind tunnel data [zebragonzo] [ In reply to ]
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Yeah, shaping a nose cone is SO complicated. No reason not to do the CFD and publish the shape yourself.

Chris
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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In Reply To:
In Reply To:
They're real. Still waiting to hear from the UCI but no matter what, we're planning to support the technology.

So assuming that the UCI doesn't rule the bike illegal, what would it take for somebody like me to lay their hands on one? :-)

Assuming they do anyway...and since you're planning on supporting the technology...either way, what would it take for somebody like me to lay their hands on one? :-)


BTW, you were supposed to respond "They're real...and they're SPECTACULAR!" :-)

http://bikeblather.blogspot.com/
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Re: Kestrel Wind tunnel data [Tom A.] [ In reply to ]
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Does this mean I need to sell my P3C? But I really like it!

Nevertheless, I always wonder how much wind tunnel data is "massaged" by the manufacturer to make their bike look better. I guess I'm a little skeptical about everything lately...
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Re: Kestrel Wind tunnel data [djarecke] [ In reply to ]
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The first Shivs will be available this spring. The nosecone was a very non-trivial development that actually did take a lot of CFD, layup, design, manufacturing time, and really only works well aerodynamically if there's no gap between the stem and the HT.

But I didn't come on here to hi-jack the thread -- just to make a note about the data and some basebar aero. I'm glad to see Kestrel kickin' out some new product and doing these studies throughout their development. Anyone with the company that can give us all a bit more info on the data, protocol, etc, please share.

Cheers,

MC

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Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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In Reply To:
In Reply To:
502 gF at 0 degrees and 389 gF at -15 degrees.

I'm still blown away by these reported numbers...

Anything you can share re. the UCI legality of the Shiv?
Andy- why are you blown away from data from... A2... i thought you ripped me a new one for being an early tester there- and saying they had a really nice facility? Looks like Specialized is camping out there, along with Kestrel, Blue, Columbia, etc... :)
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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I am curious about this concept. I realize that the MOST will be gained with a level top tube/stem interface, but is it really all that poor for a standard bolt on stem to lengthen the leading edge a bit? My testing (not exactly a wind tunnel) has shown that it's very awesome (though I don't know how much better it could be) despite not being level.

Thanks for any input.

Chris
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Re: Kestrel Wind tunnel data [chicanery] [ In reply to ]
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I don't think I understand the question. Is a stem being in line with the top tube good or the stem lengthening the airfoil section of the HT? Are you asking on of these?

MC

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Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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In Reply To:
The nosecone was a very non-trivial development that actually did take a lot of CFD, layup, design, manufacturing time, and really only works well aerodynamically if there's no gap between the stem and the HT.

Does the nosecone not need to pass the credit-card test?
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Re: Kestrel Wind tunnel data [mlinenb] [ In reply to ]
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In Reply To:
In Reply To:
In Reply To:
502 gF at 0 degrees and 389 gF at -15 degrees.

I'm still blown away by these reported numbers...

Anything you can share re. the UCI legality of the Shiv?
Andy- why are you blown away

Because of how low the numbers are. If correct, somebody on a Shiv would have a massive advantage over everybody else.

In Reply To:
from data from... A2... i thought you ripped me a new one for being an early tester there- and saying they had a really nice facility?

If you are referring to this thread:

http://forum.slowtwitch.com/...post=1676566#1676566

then I would say that your memory is quite faulty.
Last edited by: Andrew Coggan: Oct 9, 09 7:54
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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The question is "how effective is the nosecone when it's NOT even with the head tube?" and/or "Is it worth having a nosecone when it's NOT even with the head tube?".

Chris
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Re: Kestrel Wind tunnel data [chicanery] [ In reply to ]
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Gotcha -- well there are things you can do to make a leading edge system like a bayonet work but it's pretty hard as the airflow trips across the gap. If the width of your leading edge piece is wider than your HT, then your wake region begins, you get some reattachment but not much at the Reynolds numbers we're working with.

Re number on at HT at 30 mph is still only 50,000 max -- so no F1 tricks will work here. I do think that a nose cone with a gap could still be more effective than not but it's not nearly as effective as a properly shaped wing/sail/airfoil.

And from our side, no about the credit card rule -- only applies to frame members in front of wheels (i.e. ST). Look at Look/Felt/Trek -- same thing with their fork/stems.

MC

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Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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What if there is no gap? On my front water bottle design, the carbon extends all the way to the head tube, but is flexible to allow normal steerage to occur. Also, the bladder is setup to bulge out the sides to 1.1x the width of the HT at 1/3 of the overall length of water bottle + head/downtube interface. Unfortunately on a Softride, the trailing edge of that section is not that well designed.

Link here

Chris
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Re: Kestrel Wind tunnel data [chicanery] [ In reply to ]
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That looks gooooood...nice work! Yeah, that should work and will definitely help in a big way. Will it buldge out more than this when full? It looks like a pretty gentle shape so I'd expect airflow attachment on the downwind side up to and maybe past 10 degrees (just an estimate). If it buldges out any more, you'll probably be better in crosswind but a bit worse head on. Looks like a beautiful execution though. I would expect an execution like this to save 50ish grams of drag over a bare bike) at 30 mph from +/- 10 degrees, maybe more.

Hope I get to see it in person! Are you an engineer or just a very very good tinkerer?

Good luck with the TT and Tri-ing,

Mark

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Mark Cote
MITAerobike
Specialized Bicycle Components
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Re: Kestrel Wind tunnel data [MITaerobike] [ In reply to ]
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Thank you for the kind words, Mark - really means a lot coming from ShivMan (I really do think you should go by that from now on - maybe even get a nice lycra TT suit with the Specialized logo and some other cool effects). The bulge is "tunable" as the sides are only a single layer thick at the 1/3 point and I have a couple of "skeleton" pieces that hold the bulge in the correct position when the bladder starts getting empty. There are a few different setups I can run depending on weather and length of the course...anywhere from 24oz to 48oz. I have a Kestrel 4500 weather meter that I use on course with some custom Google maps based software I've built to calculate average yaw on course. It's also legal for USAT events according to all of the rules I have been able to find - but only barely.

I am actually a software engineer, but my family is in cabinetry/carpentry and auto mechanics so I've been building random stuff for as long as I can remember. I really appreciate your input here.

Chris
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Re: Kestrel Wind tunnel data [Andrew Coggan] [ In reply to ]
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Dangit, now I'm a hijacker too...


With 150-180g of tare drag "left off" I don't see any reason to doubt the Shiv #'s are real. I'm just wondering if the Shiv's lead would still seem massive when you add that drag back in...which I think you'd have to do if massiveness is judged in the context of data like Cervelo's. I point to their oft-posted/quoted drag comparison charts in this example because for the P3C and TTX, tested at the same facility (LSWT in this case), we and Cervelo get similar #s @0deg and at least stay in the same ballpark as yaw increases. We don't subtract out tare drag (never mind 150-180g worth) to arrive at our comparison #s...so I'm guessing it's still there in theirs too.


Let's play the game and say it's not...and let's also say LSWT's tare drag is probably in the same ballpark as A2's. Could you come up with 150-180g more drag via setups, sure...but given what you know - or suspect - about how folks like Cervelo do their testing, do you really think they're going to set their own bikes up in a manner that's 150-180g worse than it really has to be?




Carl

Carl Matson
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Re: Kestrel Wind tunnel data [chicanery] [ In reply to ]
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122 posts and counting on a thread that is nothing but speculation until the actual paper comes out. Perhaps I'll ask steve about it today. A chart is just a chart.... until you know how the chart was arrived we are all just spouting hot air.

36 kona qualifiers 2006-'23 - 3 Kona Podiums - 4 OA IM AG wins - 5 IM AG wins - 18 70.3 AG wins
I ka nana no a 'ike -- by observing, one learns | Kulia i ka nu'u -- strive for excellence
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Re: Kestrel Wind tunnel data [jmhtx] [ In reply to ]
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So Trek and Specialized has chimed in.

If Gerard would comment, I'm certain he would say he was glad to finish second in yet another manufacturer's wind tunnel data.

No comment from Kestrel, yet. I know there a little event in Kona, but....

Suffer Well.
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Re: Kestrel Wind tunnel data [MarkyV] [ In reply to ]
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Right. I see no reason why Steven can't just pop on here and dispel the assumptions and rumors we've made. Perhaps he's busy in the tunnel at A2 right now, or trying to get the 4000 under some pros in Kona, but a quick note would let us all sleep a little easier tonight.

Chris
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