Originally Posted by
Nate552
Sure, I could have asked the question better, for that I apologize.
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.
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?
Sure. The right way to ask was "how was the plate mounted?"
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.
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.
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.
http://www.grc.nasa.gov/WWW/K-12/airplane/shaped.html
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 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.
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?
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.