I still need to find an equation for the following restated problem: Suppose a full-size glider passes 10 feet over my head at high speed. No doubt I will feel the downward air pressure caused by the angle of attack of the undersides of the wings. But if the same glider flies over me at a distance of one mile, I will not feel any effect at all. So obviously there is a diminishing strength of the downward air pressure that eventually lessens to a point where I cannot physically detect it. Therefore, is there an equation that, with all relevant criteria being inputted, such as air temp, air density, wing speed, wing characteristics, wing angle of attack, etc., can allow me to at least approximate how far I must be below a passing wing to be unable to detect its downward pressure wave?

  • $\begingroup$ Your question seems to be related to the recent question "Over how large an area does an airplane in flight increase the pressure on the ground underneath it?" ( physics.stackexchange.com/questions/402033/… ) Never got a clear answer on it, though. $\endgroup$ – Samuel Weir May 21 '18 at 20:07

I know of no explicit equation of the sort you seek, but here is a useful estimate which may be of help.

A pilot who is flying her airplane in for a landing on a runway will notice that the proximity of the ground beneath the plane begins to affect the flow of air over the wings on her plane when the plane is within one or two wingspans above the runway. This is called "ground effect" (see wikipedia) and it corresponds to the height at which a "bubble" of air pressure gets entrained between the runway and the underside of the wing, which means that if you were standing under the plane as it flew over you at that height, you would definitely feel a sudden whoosh of air in your face as it passed over you.

There are a number of skilled aerodynamicists on the aviation stack exchange who may be able to furnish equations for ground effect, so you might want to pull this post and move it over there.


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