Originally Posted by acoggan
Well that depends on where you test, now doesn't it?
(I picked my "natural wind tunnel" because it is nicely aligned with the prevailing wind in that immediate vicinity...indeed, it has to be, because it is just that, i.e., a tunnel through the trees.)
Ah, clever. Crap -- I wish I'd thought of that! :-)
Yes, I guess there are a lot of cases where it might be possible to use the natural terrain to "shape" the wind. I find any kind of wind difficult to manage, but my test venues are quite open to wild yaw variations.
Headwinds, btw, tend to give you a virtual elevation that's too high by a factor of:
h = 0.5 * CdA * rho * v * ( v+w)^2 * T / ( m * g ) ,
v = ground speed
h = the virtual additional height
w = the headwind
T = time spent riding at the given headwind
Example: CdA = 0.300, rho = 1.2, v = 10 m/s, w = 5 m/s, m = 80kg, T= 10 s
gives us a virtual elevation height of:
h = 1.72m
In other words, 10s into a 5m/s headwind gives you a false virtual elevation of 1.72m.
I've used this with a bad file, some historical wind date, and Google Earth to estimate the CdA for Tony O'Keeffe ( TONY O'KEEFFE - TRIATHLETE - HOME
). I don't have an error estimate for this approach, though. I'm just saying that sometimes, you have to get creative.