Mxsmanic wrote in
:

writes:

If the vertical postion of an aircraft is constant, i.e. straight and
level flight, the first derivative of the vertical position is zero
and hence the second derivative is also zero.

Gravity is constantly trying to accelerate an aircraft downwards;
something else has to compensate for this, or it will descend.

An aircraft in straight and level flight is not accelerated.

Because a force is being applied to it that exactly counters gravity.
Whence comes this force?




From somewhere that's waaaaay beyond you , obviously.


Bertie