Oktas8
Don’t get confused by the downward force of air from a helicopters rotors or the downward air rush from the birds wings. It isn’t relevant and has no effect on the weight or the CofG of the aircraft. Let’s take the same pool that I used in my previous thread. That same swimmer now has a set of fins on and uses them to try and propel him/herself vertically straight up out of the water. Of course this swimmer can only get to the surface of the water and then basically becomes stationary but is still exerting considerable energy. There is a large downwash of water from the fins that hits the bottom of the pool. What do you think happens to the weight of the pool and its CofG? Simple, nothing. It’s an equal and opposite reaction in a closed environment. The Earth is also a closed environment.
They don't displace a weight of air equal to their own weight, so there will be a pressure pulse under an aircraft. Stand under a 747 flying at 20' and you'll detect it, but perhaps the pressure pulse under aircraft flying at 500'+ is too spread out to be easily detected.
The force produced by the wing of an aircraft or the rotor of a helicopter (lift) in level flight is equal to or very close to the weight of that aircraft. The downward force of the air and increase in the air pressure just under this aircraft again isn’t relevant. What one must ask is does the weight of the earth, if it could be measured change? Again the answer is no.