Originally Posted by aeronaut999
PS we would reach the same conclusions as I am suggesting, if we just considered in airplane in a closed box. Feel free to make the box as large as you want. Naturally there is a scale under the box. How does the airplanes weight get transmitted through the bottom of the box to the scale? By means of a nebulous pressure increase due to the kinetic stirring-up of the air by the wing, that is pressing equally on all sides of the box, pressing up on the top of the box just as hard as it is pressing down on the bottom of the box? That couldn't work. Or by means of the momentum of the downwash pushing down on the bottom of the box?
If the airplane pushes over into zero-G flight inside the box, does the box get lighter, as measured by the scale under the box? I say it does. Then the box gets heavier during the pull-out that follows.
Even in the static case the pressure in a box is not
equal on all sides.
There is more pressure on the bottom than the top because the pressure is higher there. Bernoulli explains this
It might be hard to visualise this with air, but it is clearly true if the box is filled with water.