I hope I'm not coming across as bombastic, but I can't seem to make sense of this thing with a bird in flight in an aircraft being supported by the pressure on the floor. I ask these questions to explain this as much to myself as anyone else and enjoy this written conversation. Please excuse my ignorance in advance and I look forward to being convinced one way or the other.
404, your last post seems to support a rebuttal of your previous arguments.
Combine some sentences from the last posts...
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.
Substitute "bird" for "an aircraft or the rotor of a helicopter" and "aircraft" and read again.
Second, Oktas' quote:
Isn't it true that this particular helicopter is supported by air being accelerated...
Stop! Don't include "downwards", or "brought to rest by the ground or water."
Lift is produced by air being accelerated. The previously accelerated air is brought to rest or equilibrium by a variety of means, but most commonly with collisions with other molecules in the air, but it really doesn't matter how it is brought to rest for the sake of this conversation.
404, as Oktas pointed out, the swimming pool is not a good analogy. You've pointed out a very good example of bouyancy and not aerodynamic lift. That will work well for balloons in aircraft, but doesn't seem applicable here.
You've indicated earlier that when the bird takes off in the aircraft, its weight is still supported by the aircraft. On a vector diagram I can indicate this with a vector downward indicating aircraft weight and a vector downward representing bird weight. On the upper side of the diagram, I can indicate aircraft lift. The bird takes flight in the cabin. What do I do to indicate the Lift vector from the bird? How do I indicate it? Do I combine it with the Lift vector of the aircraft, or do I ignore it?
If some of the freight are birds in a large cage what do you think happens to their weight if they all become airborne? Their weight is now being supported by the air in the cabin instead of their perches which in turn is being supported by the floor of the aircraft.
I think this is slightly incorrrect. Please correct me if I am wrong, but shouldn't this read:
"Their weight is now supported by the birds accelerating the air in the cabin (albeit towards the floor via their wings) instead of their perches..." Even if there is a slight pressure buildup on the floor, it is going to be balanced by a slight pressure reduction elsewhere in the cabin.
BTW with the balloon in the car, accelrating the car will see the balloon move forward. Braking will move the balloon to the back. Why? The balloon is lighter then air. The air has momemetum and during acceleration will want to move towards the rear of the car. The balloon with less momentum will be forced forward and vice versa during braking. Fun to do with kids in the car.