I’m much more comfortable field testing on a windless day on an outdoor track. With some very sophisticated measuring devices (some pieces of string attached to my handlebars), I know I’m incorporating some segments up to 8 to maybe 10 degrees.
FWIW, that is the approach that Kyle et al. used as well - only difference (I assume) being that they strapped a small video camera to the bike so as to continuously record the data.
Somewhat (but not entirely) as an aside, this is also how they measured precisely how much the handlebars/front wheel swing back and forth even when riding in a straight line.
well, in my effort to give you a new signature, I’ll simply ask ‘who ever thought that field-testing at zero yaw was a good idea?’
Ummm…I dunno, but I recall that these guys seemed to think that field testing matched up with wind tunnel results fairly well:
Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291.
Actually, Jim’s more recent paper would be a more appropriate reference, because we didn’t present data for the back-calculated CdA in the above publication.
In any case, when it comes to establishing the utility of the field test approach, demonstrating that you can precisely and accurately estimate CdA from such data (provided you have the necessary raw data…which in the above study, included measurements of wind speed and direction) is only a necessary, but not a sufficient, condition.
at what yaw angles do field tests and wind tunnel results ‘match up fairly well’?
The answer is “at all yaw angles we tested” (which means at least up to 15 deg). Allow me to explain:
In our study, we used a cup anemometer set next to the taxiway to measure wind speed at 1 m off the ground. On average, the wind was blowing at 2-2.5 m/s, with (IIRC) a maximum gust of 3.6 m/s. Wind direction was obtained by radioing the airport control tower immediately after each run, and averaged 220-225 deg (compass heading). The taxiway itself was oriented along a line running from 340 to 160 deg (or 160 to 340 deg when runs were made in the other direction). This information, along with the actual speed of the cyclist (which ranged from ~5 to ~13 m/s) was used to calculate the yaw angle experienced by each rider during each run, which in turn was used to determine the appropriate wind-tunnel-derived CdA (which was measured out to 15 deg of yaw) to calculate the expected power.
I’m definitely closing the gap…have I mentioned the power levels I’ve been maintaining in some TT intervals lately?
Finally got some PowerCranks, eh?
Besides…since you don’t even HAVE a TT bike right now
That’s right, I don’t - and I can’t really afford one, either, so unless somebody wants to sponsor me, I won’t.
(as far as I know anyway…have you put the order in for the P4 yet?), I’m fairly sure I could give you a pretty good “run for your money” with you riding whatever is left in your “quiver”
Well, the situation is not that bad…we still have my wife’s P2T (if I wanted to go the fixie route again), and a friend has graciously offered to loan me his Tiemeyer. Alternatively, I could just be a cheapass and set up my Soloist as a TT bike and use it.
I kinda like the idea of the P2K vs. P2T “mano a mano”…and also the idea of the “showdown at Moriarty Corral” with Sheriff Murphy officiating
That does sound like fun - loser pays for the winner’s trip?
I’m not as far off as you might think
Congratulations on the improvement - we should expect to see you nip-and-tuck with Kevin Metcalfe now, eh?
Ummm…probably not :-\
Hey, if you can’t get close to Kevin I don’t think you’re going to be able to beat me (despite last year’s equipment troubles I believe that I’m still batting .500 against him at master nationals).
Hey, if you can’t get close to Kevin I don’t think you’re going to be able to beat me (despite last year’s equipment troubles I believe that I’m still batting .500 against him at master nationals).
Well…to be completely honest, I don’t know…especially since I haven’t “officially” produced the power values I’m currently training at in a real TT “pedaling in anger” and I’ve never gone against him (or you) in an event…plus, for sporting events my style is more “under-promise and over-deliver” rather than trash-talkin’…know what I mean?
