Quote:
Originally Posted by NeilBlanchard
Hmmm, I missed that part of the discussion, I guess. It is odd to think that the air is "bumped" out of the way and has a spring affect? One would think that a given volume moves out of the way a given distance, and then moves back.
There must be a repelling force between the molecules in the air that is acting as a spring. So, it is not just the static volume of air that gets displaced, but rather the speed and shape of the front that has a lot to do with it.
So, then the shape of the front does have an indirect affect on drag -- blunt front ends "punch" the air harder, and may *improve* the air flow on the trailing side, by creating higher pressure? But at high(er) speeds, this leading pressure wave becomes critical, and the front must be pointy to split the air, rather than "punch" it?
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I think 'spring' is a pretty good analogy in this perverted sense.The atmosphere is a valve-lifter and spring pushing against a camshaft,or breaker block in an old distributor.
There is a rpm at which the spring is unable to close the valve or maintain contact between the breaker-points rubbing block and distributor cam,and you'll have 'float.'
If the body of a car's aft-body drops off too suddenly,the air 'spring' of the atmosphere will be unable to prevent 'float' resulting in separation.