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Old 02-17-10, 02:21 PM   #1
acortez
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Cheap Wind Tunnel?

So my gf sent me this video of Lance riding his TT bike. She thought it was cool because it looked like he had a bunch of streamers placed on him. I think they are using it to gather cheap data similar to a wind tunnel. Not the ideal situation but this may work. You could import the video into some software and then do some analysis on how the white streamers are behaving with a change in position. Anyone seen this done? Discuss.

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Old 02-17-10, 02:24 PM   #2
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how about "real world conditions" in place of "cheap wind tunnel".

I don't know, but have a feeling, that Lance and his crew are not short of funds for some tunnel time.

oh, and 217.
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Old 02-17-10, 02:25 PM   #3
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it's a shame that LA can't afford a wind tunnel
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Old 02-17-10, 02:41 PM   #4
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I understand that they are not short on funding. I thought maybe someone has seen/done this before. If not it would be interesting to see.
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Old 02-17-10, 02:44 PM   #5
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Hold off on the 217 for now. We've discussed TT equipment and setups many times. I don't care who the rider is, look at what they are doing from a technical perspective and learn a little something.

If you're doing serious TT work, I think you'd be well served in spending some time doing this. It's very cool, cheap and accessible to any of us. This is just little pieces of yarn held on with tape. You can see what the air is doing as it flows.

Specifically look at how long they've kept the air attached down his back. It makes it a long way down his back before separating and causing the yarn pieces to go chaotic. I bet there are some big gains in playing with position and helmets to keep the flow attached down the back as long as possible. Having the air that hits your arms relatively controlled will also be an important area to look at.

This is a good find, acortez, well done.
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Old 02-17-10, 02:45 PM   #6
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I understand that they are not short on funding. I thought maybe someone has seen/done this before. If not it would be interesting to see.
It's common to do on racecars, even when the car has been thoroughly tested in a tunnel. There are aspects of 'the real world' that are very difficult to replicate.
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Old 02-17-10, 02:50 PM   #7
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Hold off on the 217 for now.
it was tongue-in-cheek
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Old 02-17-10, 02:51 PM   #8
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Again, I don't particularly care about the rider. The information on this clip concerning position is pretty interesting.

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Old 02-17-10, 02:52 PM   #9
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it was tongue-in-cheek

copy that....duh.
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Old 02-17-10, 03:02 PM   #10
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Hope it helps someone. Maybe if I can get going in TT's I will try this and make a post.
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Old 02-17-10, 03:13 PM   #11
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Last year I speculated that position was really the key factor in the difference between LA and Contador on time trials. There is a substantial weight difference between the two of them (and I still think LA might have more raw power). I'd be interested to see how he fares with a considerably more aggressive position.
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Old 02-17-10, 07:13 PM   #12
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So my gf sent me this video of Lance riding his TT bike. She thought it was cool because it looked like he had a bunch of streamers placed on him. I think they are using it to gather cheap data similar to a wind tunnel. Not the ideal situation but this may work. You could import the video into some software and then do some analysis on how the white streamers are behaving with a change in position. Anyone seen this done? Discuss.
While I appreciate your desire to do analysis about drag, etc, I don't think you can discern anything usable from this. Essentially, all you can see from this video are areas of turbulence. And, these area's are not a secret. Again, not to burst bubbles, but what are you hoping to discern from analysis of tufts other than areas of turbulence? Are you hoping to be able to tell how a tuft behaves differently because of a position change? There is not any software out there that can do that, nor can video reveal that. While it's interesting to see, I don't see how it can be a tool used to make aerodynamic decisions.
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Old 02-17-10, 08:33 PM   #13
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while I agree that you can't make descisions based on the tuft flow, you CAN quickly start focusing on areas that need work, rather than guessing in the tunnel. Go out, do some positions, and find out where the problems lie. Then take that to a tunnel and correct them.
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Old 02-17-10, 08:52 PM   #14
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provided that you have a crew to film you.
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Old 02-17-10, 09:15 PM   #15
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Or a friend with a point and shoot camera.
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Old 02-17-10, 09:45 PM   #16
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While I appreciate your desire to do analysis about drag, etc, I don't think you can discern anything usable from this. Essentially, all you can see from this video are areas of turbulence. And, these area's are not a secret. Again, not to burst bubbles, but what are you hoping to discern from analysis of tufts other than areas of turbulence? Are you hoping to be able to tell how a tuft behaves differently because of a position change? There is not any software out there that can do that, nor can video reveal that. While it's interesting to see, I don't see how it can be a tool used to make aerodynamic decisions.
Hmmm...I *politely* disagree with this. If you used this method while having somebody film you (it could even be a teammate or another rider...), all you need to see is which tufts are staying aero, and which aren't. Then, adjust your position and film again (on the same stretch of road, in the same conditions, of course). Compare the two, and see if your new adjustments are more aero or not.
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Old 02-17-10, 09:47 PM   #17
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While I appreciate your desire to do analysis about drag, etc, I don't think you can discern anything usable from this. Essentially, all you can see from this video are areas of turbulence. [...] While it's interesting to see, I don't see how it can be a tool used to make aerodynamic decisions.
Experts use flow visualization all the time. Tufts, smoke, and CFD all help do that. It doesn't always tell you what to do but it can tell you where to focus. That can be pretty useful.
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Old 02-18-10, 12:06 AM   #18
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While I appreciate your desire to do analysis about drag, etc, I don't think you can discern anything usable from this. Essentially, all you can see from this video are areas of turbulence. And, these area's are not a secret. Again, not to burst bubbles, but what are you hoping to discern from analysis of tufts other than areas of turbulence? Are you hoping to be able to tell how a tuft behaves differently because of a position change? There is not any software out there that can do that, nor can video reveal that. While it's interesting to see, I don't see how it can be a tool used to make aerodynamic decisions.

incorrect


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Old 02-18-10, 12:17 AM   #19
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incorrect

Can't get the attachment to work....can you try again? I'd like to see what it is.
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Old 02-18-10, 02:18 AM   #20
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Again, I don't particularly care about the rider. The information on this clip concerning position is pretty interesting.
It's a shame they don't have the streamers in both positions. We could see if we could see a difference.
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Old 02-18-10, 04:24 AM   #21
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Great devices for determining laminar air flow.
Cheap and funny looking indeed, this technology is used by sailors at the highest level.
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Old 02-18-10, 06:14 AM   #22
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while I agree that you can't make descisions based on the tuft flow, you CAN quickly start focusing on areas that need work, rather than guessing in the tunnel. Go out, do some positions, and find out where the problems lie. Then take that to a tunnel and correct them.
I agree. I should have been more specific in my statement, sorry. You can see area's of turbulence, and large changes can probably be seen. When I was typing that last night I was picturing all the effort that this would take (making/buying the jersey, finding someone to film you, studying the videos ) and trying to make a helmet choice from it, or trying to decide if lowering your stem 1 cm is faster. Small changes, like narrowing your elbows would be tough to see. The visualization of the airflow and turbulence would be nice to see, so you can focus on an area, I agree, I just don't see it being a complete substitute for a wind tunnel.
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Old 02-18-10, 11:00 AM   #23
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Really, the trick to the whole deal is knowing what 'good' airflow looks like. Once you have that figured out, you can duplicate it. Luckily, because of this video, we have an example of 'good' airflow.

I'd say getting the air to stay attatched (laminar is not the correct term, that's something completely different) as far as possible on the back is going to be a big trick. The longer it stays attached, the less of a separation bubble you're going to have and the less pressure drag you're going to have. Humans in general are not particularly aerodynamic beings. We evolved walking at 3 mph, so there wasn't much advantage to bird-like shapes. Having said that, there is going to be better and worse ways of positioning, and this is a good way of beginning to figure it out.

It's certainly not a substitute for a wind tunnel, but it would be a good precursor and/or sanity check. Flow-Viz stuff is very common to do because it makes it possible to wrap our brains around something that is invisible. Couple this type of work with one of those aero power meters, and you're getting closer to doing real wind-tunnel work without a wind-tunnel.
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Old 02-18-10, 12:42 PM   #24
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I'd say getting the air to stay attatched [...] as far as possible on the back is going to be a big trick. [...] Flow-Viz stuff is very common to do because it makes it possible to wrap our brains around something that is invisible.
Many people seem to think that "aero" is something that happens at the front of the rider/bike and not at the back so they focus on the "A" part of CdA and rarely think about the "Cd" part.
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Old 02-18-10, 01:14 PM   #25
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I wonder what value strings + coastdown test would carry.
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