Quote:
Originally Posted by SteveP
Maybe you mean something different by "fineness ratio" than I understand it to mean, so perhaps you should provide a short definition. Mine is "width/length" (or, for a cylinder, diameter/length). I therefore don't understand how lowering a car can alter its fineness ratio.
Also, would you be so kind as to expand on your comment that "Since road vehicles all suffer from the "mirroring" effect of the ground,anything which can be done to increase fineness-ratio is a shoe-in for lower drag". What does fineness ratio have to do with the ground effect? I could see it if you were *narrowing* the car, but lowering it doesn't do that.
Thanks,
--Steve
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SteveP, tried to post a reply a while back,guess it got lost in the cyber netherworld.Here's second attempt.The fineness ratio is defined by the vehicles length,divided by it's height.It's very much like the aspect ratio of a wing,if you take the vehicle height to be the "thickness" and length of the vehicle to be the "chord".5.5-1 is considered the ultimate for a vehicle in ground-effect,as it respects the relationship between reduced profile drag,and skin friction.With respect to the "mirroring",its the phenomena which effects bodies close to the ground,which effectively doubles the height of the vehicle,as if it was placed on a mirror,and the air was striking the real AND the reflected image.If you look at very early windtunnel photographs for car testing,you will see model cars joined at the wheels,one upright,one inverted,in the test-section of the tunnel.Cars that look very "swoopy" on the ground look very "blunt" to the air,and to get the efficiency of a 2.75:1 fuselage form in free air,a car body must have a 5.5:1 L/H ratio.