Racer Ex 

Ayup. Played with some of that stuff on some flying machines.

Robbie ran my first tunnel session BTW.

What's happening here is what I've seen happen in engine technology...a sort of circle that revolves around the sun of limitations. I disagree with the comment that tunnel doesn't translate to the field in any case.

Nate552

Seen that all. Tunnels have the same sensors BTW. I said it before, and I'll say it again. Vaporware. Talk to me when I can get one.

Nate552

Found this kind of interesting. Why do you think the CdA of a flat plate, with material behind it (like a headtube, or handlebar) has the same CdA of flat plate by itself? Also, you're losing a bit of that accuracy you touted earlier.

RChung

What makes you think that there was any material behind the flat plate? The plate was attached to via a rod to hang out in the free air stream. Oh wait, you probably still don't get it so maybe I should be explicit: he tested with the rod both times but for one run the rod was bare and for the other the plate was attached.

The Cd of a flat plate is about 1.2, and 1.2 * .0025 is ....

Let me know if you need some help with that.

You figure out how I can get that wind tunnel time tomorrow on my budget? Cuz otherwise it's vaporware to me.

RChung

Cool. So Robbie knows his way around a wind tunnel and he obviously thinks an on-bike yaw meter has some value. Mike Giraud knows his way around a wind tunnel and he obviously thinks an on-bike yaw meter has some value.

Nate552

Wow, got a bit testy because I asked a question? Perhaps we shouldn't question any testing protocols and accept all results at face value? I apoligize for questioning any of the riders test results ( that you admit you couldn't validate).

Nate552

I think there is great potential value to these, but i dont think the devices are ready for consumers and have some potential flaws.

Racer Ex 

Mike's very good, in part because he's not at all dogmatic. New career path BTW. Hopefully A2 stays up.

On bike metering has value. But that value is limited from my perspective.

You try my suggestion? Just make sure you make factually accurate rather than threatening statements in the bank..."You're all going to die!" vs. "I'm going to kill you!" And make sure you have an account...demanding money in that case is OK.

Numerous flaws. Without some major improvements and the ability to do instantaneous calcs anything other than zero yaw is, at best, ball park. Even with those abilities I can't see how it's going to match the +/- of the tunnel beyond 0.

RChung

Nope, I wasn't testy with you. I was testy with me for overestimating you.

If you review this thread you'll see that I've been presenting data and test results, and giving caveats and clarifying nuance. That's cuz I was presuming that you could fill in the blanks. Evidently I was wrong, and rather than ask, "how did he mount the flat plate?" instead you ask "Why do you think the CdA of a flat plate, with material behind it (like a headtube, or handlebar) has the same CdA of flat plate by itself?"

The difference is that I assumed that you were smart enough to figure out that we had discussed how to mount it ahead of time and figured out how to mount it in an intelligent way while you couldn't imagine any other way to mount it except in a stupid way so you assumed we'd do it that way, too. Basically, we each projected our own level of intelligence onto the other.

Did you finish that 1.2 * .0025 calculation yet? Ordinarily I'd assume you were smart enough to solve that but now that I've seen the level of your argument I decided it might be safer to check. After that, compare it to the .003 m^2 estimated difference since you wrote "you're losing a bit of that accuracy you touted earlier." Just ask if you need help with that, too. (Hint: try subtraction).

Nate552

Sure, I could have asked the question better, for that I apologize. However, you never stated that you took any part in the tests, as in, monitoring them, checking protocol, etc. You stated "a guy I know who was doing some experiments with a short loop behind his housing development that went up a little slope around an athletic field." Now why would I assume that he was under supervision from you and was conducting the tests properly? Had you simply said, "I consulted with him on his testing as we came up with some solid procedures, etc" I wouldn't have questioned it because I know YOU know better. But I don't know HE knew better. Make sense? As for accuracy, you stated that the wind was "pretty consistent" and the estimates seemed "reasonable", but you couldn't validate them. That doesn't paint the picture of accuracy.
As for your CdA calculation, I wasn't going to respond because it is childish, but if you must.... First off, the Cd of a plate perpendicular to the wind is not 1.2, but closer to 2.0. Secondly, you didn't provide F, Da, or V. But, it's a silly sideshow to this conversation anyways.
It's obvious that you and I are going to not find an agreement on this, so I say we agree to disagree. So, lets move on to something we can be more civil about. I'd like to talk about why I have my concerns about field testing in the wind. Earlier, you mentioned using a Kestrel unit to measure yaw. Have you ever tried this? (Not being a smart**, seriously asking) If so, how successful were you at it, and were you able to confirm that the unit was providing accurate apparent wind angles? I ask because I have been involved in a wind tunnel experiment to create a device that would measure apparent wind angle on a cyclists while riding. In the picture below is me, during the experiment. I won't publicly disclose the results of the tests, or how the device was made/changed, etc but I will say this. You cannot simply stick an portable wind station on a pole in front of a cyclist and be done with it. There is a lot of "work" that would need to go into this. If you have tried this (and again, I'm seriously asking here), did you do any sort of calibration to confirm the wind angles / speed the device was giving you? If someone else was testing this, did they have a set of wind tunnel data to calibrate CdA to? (I know the guy in the valley you mentioned earlier didn't , but perhaps someone else did).

RChung

Cool. I think people who read my stuff can see that when I'm asked a straight up question then I give a straight up answer, and when I'm asked a snarky question then I'm pretty capable of bringing it on. But, I have a short memory so once people start asking straight up questions again I don't carry a grudge.

Sure. The right way to ask was "how was the plate mounted?"

I agree. If you follow this stuff, I don't usually mention his findings because they weren't validated -- however, in this instance, I wasn't being asked about specific findings but rather how one might go about doing a yaw test in the absence of a yaw sensor. So I discussed the general approach *and then I added that the results hadn't been validated.* You won't hear that kind of admission from someone who's an uncritical advocate of something: I try to make sure that people understand the limitations of the things that have been tried.

https://www.grc.nasa.gov/WWW/K-12/airplane/shaped.html

I haven't done this, no. Andy Coggan has done this and I believe he's reported that the direction is less precise than the wind speed (that's not hard to believe; others who have tested the Kestrel units also say this). That's why I mentioned (as part of my full disclosure that you won't get from most people) that the guy who was doing this wasn't relying on the Kestrel to give him direction, only speed; and that he was doing this up and around an athletic field; and what the terrain looked like. And that's why I describe his results as "reasonable but not validated." Of course, to tease out small deltas in yaw you need pretty high wind speeds so the pressure differential is big enough to measure; when the wind speed is low the wind angle is both harder to measure and, thankfully, less important. That's about the only nice thing about yaw measurement: the situations when it's hardest to measure are also the situations when it's least important.

Um, I can't say, other than that you're exactly right and the correct way to do this would include exactly the kinds of calibration you're talking about.

What I can say is that I have a day job that I like, I'm not selling anything, I haven't invested any money in any device, I wish the best of luck to anyone who's attempting to make any similar device, I haven't charged anyone any money for anything I've done on this, everything I've written on this is either in the public domain or licensed under Creative Commons, people often ask me to look at something and I answer as best I can, and that I've received a really nice bottle of wine and a free dinner for this stuff -- and that makes me happy. [Edit:] My wife thinks I'm nuts and she says if I charged for this I could afford to visit a wind tunnel.

echappist

wow, a treasure trove of info here. Too bad it's so info-dense it'll take me a few reads to process everything.

Thanks Nate, RX, and RChung

Nate552

Sorry, I used a book marked site that I just pulled up as I was typing that.
https://www.cyclingpowermodels.com/Cy...odynamics.aspx

AC is right. Those Kestrel Units are remarkably unstable when it comes to direction. And I agree with the rest of this.


I've always been a fan of VE, and have done quite a bit of it myself. I've even gotten good enough that I was able to validate a VE helmet test almost spot on with a test at the tunnel (0 yaw). I recommend it to everyone who comes up to me and asks "Hey, which is faster, X or Y?" I'll even give them a detailed explanation of how to do Bowl Testing,( my preferred method of VE testing.) Of course, I always tell them that it's only part of the story, but it's a great start to it, and can give you some insight into what's working and what isn't. So, for that, thanks for bringing it to the cycling community. And like you, I have a day job, and don't make a living doing work at the tunnel, I do it because it's interesting and fun. And like you, my wife thinks I'm nuts for taking days and days of vacation to run around trying to learn about this stuff.

Nate552

I thought it was just going to be us 3 yammering on for days in here.

waterrockets 

Well, it's being absorbed...

RChung

My condolences. You know, you'll never get a refund on those four minutes of your life.

Racer Ex 

Not true.

Say he does 5 TT's a year and this information yields a 2 minute improvement per TT.

That's 10 minutes so he nets out 6.

His family will get 4 of those but he's still 2 minutes up. I'm frankly surprised you didn't see that.

So Nate...ask me about trying to get to 53 off the axle when you have a BB that's 3cm taller. It's a bit...bent over. So we're settling.

RChung

I just ran across this thread from 9 years ago. I'd completely forgotten about it, but I think it held up pretty well.

burnthesheep

I have been less than impressed at the sensor offerings and prices.

I did bite on a $20 bluetooth anemometer I can then toss the data on top of my VE data to work with a more “real” airspeed.

Hermes

Welcome back RChung Many of the posters in this thread are no longer active. It may be fun to start a new aero thread or continue this one as we have new TT riders such as burnthesheep, TMonk , and wktmeow to name a few.

ridethecliche

What's held up?

Your being testy? 😁😁😁😁

Glad you're a regular again!