Birds inverted, no different, as the air displacement is still supported by the cabin (in the perfectly sealed environment)
Birds in an open helicopter, same deal as the mesh aviary as opposed to a sealed one - a change in weight if the birds landed because it is now supporting weight it wasnt before (due to the air inside not being supported by the helicopter - read: non-sealed environment)
Think about a flying elephant landing on a small boat. It will certainly experience weight it wasnt supporting before because of no sealed environment.
Plane in the terminal velocity dive - It is at a constant velocity, so acceleration is zero (F=ma). Therefore zero
net force - the air resistance force is equal and opposite to the force due to gravity.
But the
pilot will still be experiencing acceleration due to gravity while climbing up to the tail so will experience the same forces as if climbing on the ground.
Thats what I think anyway. Thanks to this discussion, i understand the sealed factor a bit more.
...Disco
You beat me to it 404! Thanks for your help mate
Thanks also to swh's great analogy!