[net.bicycle] Bike Tech - mistake in the wind article?

neal@druxv.UUCP (Neal D. McBurnett) (07/10/84)

I agree that Bike Tech is an interesting publication, and I recommend it,
but it seems to me that the article on the effects of wind is really butchered.

The author says that the net effect of a slight tail wind can slow you
down!  For example, he claims that a wind with a true heading of 100 degrees
off of your direction of motion will slow you down if it has a true
strength of 1.5 times your true velocity.  As I see it, your drag is
determined only by your forward velocity and the component of the true
wind which is in the direction of your motion: cos alpha.

I think his mistake starts with equation 3.  He says drag is proportional to
	w^2 cos beta
where w is the magnitude of the apparent wind velocity, and beta is the angle
of the apparent wind (apparent wind = true wind plus bicycle-induced wind).

I say that eq. 3 should read
	(w cos beta) ^ 2
or, equivalently,
	(u + (v cos alpha)) ^ 2
where u is bicycle ground velocity, and v is true wind speed.

This makes all the rest of his equations and figures needlessly complicated
and counter-intuitive.
What do you think?
-Neal McBurnett, ihnp4!druny!neal, DR x4852