3 ms·

Are you suggesting that if we have two planes of the same size and shape, the heavier one displaces more air? I can understand that objects floating on water f

Are you suggesting that if we have two planes of the same size and shape, the heavier one displaces more air? I can understand that objects floating on water follow that principle but that's because they are floating. Once fully suspended in water, I think the amount of water they displace is just their volume. Shouldn't it be likewise for aircrafts in the atmosphere?

mcguire 10y ago
To maintain level flight, a plane has to generate lift equal to its weight. It generates lift by forcing a mass of air down. More mass means more air disturbed.
- nf05papsjfVbc 10y ago
  Interesting. I never thought of it this way. Thanks for helping me see the missing part of the picture.
  - mcguire 10y ago
    When people explain flight through Bournoulli or whatever, they tend to forget Newton's basic laws, which really are the simplest way to understand flight. It won't make you an aerospace engineer, though.
- mzs 10y ago
  You are describing ground effect not lift.
  - mcguire 10y ago
    Note: I am not an aerospace engineer. Not quite. Outside of ground effect, a downward force is applied to the air mass around the aircraft, resulting in lift on the aircraft. IIUC, this results in compressed, high pressure air below the plane and low pressure air above it. The result of that is a pair of vortices roughly centered on the plane's wingtips. These vortices themselves are Somehow Important to the whole thing. Anyway, you can see the deal when a plane flies close to a cloud top.[1] In ground effect (i.e. the aircraft is flying within roughly one wingspan of the ground), the proximity of the ground blocks the formation of the wingtip vortices (?) and greatly enhances the efficiency of lift production (by some form of magic, AFAIK). [1] https://s-media-cache-ak0.pinimg.com/564x/1c/33/e2/1c33e2f2fa82b7bf4a86a1a67d32c2e3.jpg https://s-media-cache-ak0.pinimg.com/564x/1c/33/e2/1c33e2f2f...
    - mzs 10y ago
      You need to sum craft weight and lift when applying Newton's laws in figuring downward pressure, more lift -> less ground pressure across all craft weight.
- brian_cloutier 10y ago
  Ah, you're right, thanks for clarifying. My comment now looks pretty dumb, wish it didn't get so many upvotes.

mcguire 10y ago

To maintain level flight, a plane has to generate lift equal to its weight. It generates lift by forcing a mass of air down. More mass means more air disturbed.

nf05papsjfVbc 10y ago
Interesting. I never thought of it this way. Thanks for helping me see the missing part of the picture.
- mcguire 10y ago
  When people explain flight through Bournoulli or whatever, they tend to forget Newton's basic laws, which really are the simplest way to understand flight. It won't make you an aerospace engineer, though.
mzs 10y ago
You are describing ground effect not lift.
- mcguire 10y ago
  Note: I am not an aerospace engineer. Not quite. Outside of ground effect, a downward force is applied to the air mass around the aircraft, resulting in lift on the aircraft. IIUC, this results in compressed, high pressure air below the plane and low pressure air above it. The result of that is a pair of vortices roughly centered on the plane's wingtips. These vortices themselves are Somehow Important to the whole thing. Anyway, you can see the deal when a plane flies close to a cloud top.[1] In ground effect (i.e. the aircraft is flying within roughly one wingspan of the ground), the proximity of the ground blocks the formation of the wingtip vortices (?) and greatly enhances the efficiency of lift production (by some form of magic, AFAIK). [1] https://s-media-cache-ak0.pinimg.com/564x/1c/33/e2/1c33e2f2fa82b7bf4a86a1a67d32c2e3.jpg https://s-media-cache-ak0.pinimg.com/564x/1c/33/e2/1c33e2f2f...
  - mzs 10y ago
    You need to sum craft weight and lift when applying Newton's laws in figuring downward pressure, more lift -> less ground pressure across all craft weight.
brian_cloutier 10y ago
Ah, you're right, thanks for clarifying. My comment now looks pretty dumb, wish it didn't get so many upvotes.