no, lift uses the mass of the air it displaces. It doesn't matter if the lift is generated up or down. The mass of air being diverted is what generates the lift, you are not "pushing down on the atmosphere, adding to its weight."

What keeps a plane in flight is not the air pushing on the ground, it is the mass of air diverted over the airfoil. Even ground effect flight is not pushing on the ground, it is *pulling* on the mass of air above it. After the plane goes overhead, the downward momentum of the air continues, but it hasn't changed the mass of the atmosphere, it has only imparted acceleration to a small part of it. A plane flying straight up or straight down, according to your model, would lose all control, because it can't push against the ground or the weight of air above it. If there were no gravity, yet somehow a dense body of air, a plane could still navigate through it, because it operates on the mass of air acted upon by the wing.

 

Sorry, I'm done flying in circles today.

 

If there were no gravity, then your plane wouldn't need wings.

 

[QUOTE=mikegarrison,Dec 8 2005, 10:27 AM] This is where we get into interesting but futile territory. We all agree that lower static pressure on the top of the wing creates lift. We all agree that higher velocity above the wing creates lower static pressure.

But if you look at the wing from the side, higher velocity above is exactly the same thing as adding a circulation to the air around the wing. This is the same as saying

 

it would need control surfaces, however, which we would call "wings" due to the resemblance to the larger counterparts on ancient Earth relics called "aeroplanes."
The point is, you could use lift to control the craft, even in the absence of gravity.

 

It's funny that you're handle is "no_really".

No, really.

When it sounds like someone really knows what they're talking about, it's usually a good idea to tread carefully and ask questions humbly, not outright declare them wrong.

And the atmosphere, as a system, must impart this acceleration onto something else. I think that's the way to say it.

 

True. But what keeps the air for dispersing? At 14 psi, if you transport a volume of air into interstellar space by itself, it'll fade into a low-density cloud extremly quickly (think about cracking open a fully charged SCUBA tank) and be rather useless for control surfaces. Unless, of course, you hold the air in some sort of giant container. In which case the "pushes against the Earth" scenario still holds - any air acted on by a plane flying around would ultimate be exerting force upon the insides on said container.

 

 

ever heard of the sun? Big ball of gas that hasn't dispersed yet? Obviously, you cannot have mass without gravity, so the whole "globe of air without gravity" was not intended to model a realistic environment. It was to make obvious that a wing does not act upon the ground, or the atmosphere as a whole, to generate lift. Air is compressible, so any force exerted by your hand is easily dissipated over distance. You cannot knock down a house of cards in China by waving your hands vigorously in Utah, or even Japan.

One or more persons appear to be suggesting that lift is dependent on exerting force against the ground, which is quite untrue. Of course a moving airfoil is going to create a disturbance in the area around it, I don't know why anyone would think otherwise. Suggesting a scale on the ground would register the weight of a jumbojet passing 10 miles above is ludicrous, and easily disproved. A very sensitive barometer might detect this air disturbance, but I seriously doubt it. It would be more likely to detect the sound of the engines than the force of the air passing over the wings. Hell, even in water, which is much more resistant to compression than air, a massive shock wave from an undersea landslide will dissipate, why would one believe a disturbance in air wouldn't?

next you people will be suggesting we kill all butterflies, as they cause hurricanes :/

 

if i push against the ground, does that force go all the way to the center of the earth? If it distributes around the outside like an arch then where does the force I exert stop?