Martin Bonner wrote:
On Oct 8, 9:16 am, Nige Danton wrote:
On Oct 8, 3:03 pm, Nige Danton wrote:

On Oct 8, 2:58 pm, Adrian wrote:
within any given class are likely to be fairly similar. As a rough rule
of thumb, increasing drag starts to come seriously into play from about
60mph upwards.
Drag cubes with velocity and so it may become important at speeds
lower than 60 mph.
My response would have been better phrased as "drag cubes with
velocity; are cars really so slippery that drag does not become
significant until 60mph?"

I *think* that the force exerted by drag goes as the /square/ of the
speed. That means the energy (and hence fuel consumption) per unit
distance will also go as the square. I suspect what you are thinking
of is that the /power/ (energy per unit time) is force * distance /
time which is force * speed, and hence the power used by drag goes as
the cube of speed.

I think we all agree. I have to often estimate drag in power terms in my
hobby*..and thats where the confusion came in.


* model aircraft,where someone always wants one that goes faster..which
ultimately becomes how much power you can cram in without the thing
needing a catapult or a mile of runway to get off the ground. Getting
beyond 200mph is pretty hard for a powered one (though jets are up
there), though the current unpowered speed record is about 300mph I
think. Don't ask how...google 'dynamic soaring' and take out a loan with
Northern Rock if interested.