14 ms·

Actually, it is "pushes-flow-down-so-goes-up". You remember? Action requires opposite and equal reaction? Plane is (mostly) not a rocket and so to be able to

Actually, it is "pushes-flow-down-so-goes-up". You remember? Action requires opposite and equal reaction? Plane is (mostly) not a rocket and so to be able to fly it has to act on something and the only something up there is air. If the plane is being lifted it means a bunch of air needs to be pushed/dragged down. Helicopter is a better way to visualize it. Now, in a plane, once that air is pushed/dragged down it immediately starts doing funky things like vortices and so on, but at least initially the air is being pushed/dragged down. I write "pushed/dragged down" because the air is deflected on both sides of the wing. On the low pressure side of the wing (hopefully for most people this is the upper side) it is being deflected by creating low pressure in a laminar flow. If that laminar low pressure flow state is lost and instead we get turbulences, those turbulences are really bad at inducing the air to go down. We say that "it has stalled". EDIT: The only way for something to stay up is to push off something. When you stay on the ground you push off the ground but when you are up there you have to push something else even to just stay at an altitude. Wings, turbines, rocket engines, propellers, barn doors, these are just different ways to accomplish the same task -- push air (and very infrequently some other material) downwards. A plane is different from a rocket in that the material is mostly air (and very tiny amount of fuel) and main mechanism of pushing it are wings and air breathing engines/turbines. Some planes can have so much power that their main pushing mechanism is engine exhaust and additional air sped up by the turbine. But most planes have engines that do not produce anywhere near what is needed to stay up this way. These planes use the engines to push (mostly) forward (there is slight downwards vector due to engine exhaust being in line with the plane body but AoA positive). These planes rely on air stream being deflected downwards as seen by the plane to be economical.

lordnacho 5y ago
No, this is wrong. First of all, rockets are no exception. Just throwing things backwards will make the object fall to the ground, no matter how hard it pushes. It is indeed the air that pushes the wing up, but you have to ask yourself why the wing would need to be shaped in a certain way if it's merely deflection. If it was that, you could just have flat boards at an angle and be done with it. Vorticity has to come into the explanation, and explains both the points further up.
- ColinWright 5y ago
  You can have 'planes with wings that are "flat boards at an angle." You're right that it's not "merely deflection", but the reason you give here is not conclusive. PS: I've tried replying to you by email so we can coordinate our efforts, but I don't seem to have been able to deduce your email from your profile. If you want to contact me, my email is in my profile. Update: A second attempt may have succeeded.
  - deleted 5y ago
    [deleted]
  - deleted 5y ago
    [deleted]
- bbojan 5y ago
  The wing doesn't need to be shaped a special way to produce lift. In fact, a flat board can produce lift. The special shape is just an optimization, ie. cambered wings are more efficient/stall at higher angles of attack.
- choeger 5y ago
  According to the NASA site, the theory is not wrong but incomplete as it ignores the dynamics on the upper wing. This means, you probably could build a plane with this theory but would be surprised by the amount of lift you get.
- trashtester 5y ago
  Imilcin is precisely right. Rockets are an exception, in that they work perfectly well in a vacuum, where a propellar would do nothing. Rockets are easiest understood by concervation of momentum. In the case of a rocket, this is for the combined momentum of the rocket and the spent fuel/exhaust. The rocket "trows" the exhaust backward with a momentum exactly opposite to the momentum gained by the rocket. A wing or the propellar. They accelerate the aircraft by "throwing" air in some direction, with a momentum per unit of timemass equal to the acceleration they cause. (In order to maintain their altitude, this acceleration must counteract the "gravitational acceleration", g of 9.81m/s^2) This all follows from Newton's laws, where "Force" is the time derivative of momentum F=(dp/dt)=ma => a=(dp/dt)/m. With conservation of momentum for the aircraft + air, one gets: (dp_aircraft/dt) + (dp_air/dt) = m_aircraft * -9.81 m/s^2 If dp_aircraft/dt = 0 (level flight), then: dp_air/dt = -m_aircraft * 9.81 m/s^2 In other words, lift is generated by accelerating air in the opposite direction of the lift. Airodynamic theory, including Bernoulli and Navier-Stokes equations only serve to explain _how_ the wings accelerate the air down.

lordnacho 5y ago

No, this is wrong. First of all, rockets are no exception. Just throwing things backwards will make the object fall to the ground, no matter how hard it pushes. It is indeed the air that pushes the wing up, but you have to ask yourself why the wing would need to be shaped in a certain way if it's merely deflection. If it was that, you could just have flat boards at an angle and be done with it. Vorticity has to come into the explanation, and explains both the points further up.

ColinWright 5y ago
You can have 'planes with wings that are "flat boards at an angle." You're right that it's not "merely deflection", but the reason you give here is not conclusive. PS: I've tried replying to you by email so we can coordinate our efforts, but I don't seem to have been able to deduce your email from your profile. If you want to contact me, my email is in my profile. Update: A second attempt may have succeeded.
- deleted 5y ago
  [deleted]
- deleted 5y ago
  [deleted]
bbojan 5y ago
The wing doesn't need to be shaped a special way to produce lift. In fact, a flat board can produce lift. The special shape is just an optimization, ie. cambered wings are more efficient/stall at higher angles of attack.
choeger 5y ago
According to the NASA site, the theory is not wrong but incomplete as it ignores the dynamics on the upper wing. This means, you probably could build a plane with this theory but would be surprised by the amount of lift you get.
trashtester 5y ago
Imilcin is precisely right. Rockets are an exception, in that they work perfectly well in a vacuum, where a propellar would do nothing. Rockets are easiest understood by concervation of momentum. In the case of a rocket, this is for the combined momentum of the rocket and the spent fuel/exhaust. The rocket "trows" the exhaust backward with a momentum exactly opposite to the momentum gained by the rocket. A wing or the propellar. They accelerate the aircraft by "throwing" air in some direction, with a momentum per unit of timemass equal to the acceleration they cause. (In order to maintain their altitude, this acceleration must counteract the "gravitational acceleration", g of 9.81m/s^2) This all follows from Newton's laws, where "Force" is the time derivative of momentum F=(dp/dt)=ma => a=(dp/dt)/m. With conservation of momentum for the aircraft + air, one gets: (dp_aircraft/dt) + (dp_air/dt) = m_aircraft * -9.81 m/s^2 If dp_aircraft/dt = 0 (level flight), then: dp_air/dt = -m_aircraft * 9.81 m/s^2 In other words, lift is generated by accelerating air in the opposite direction of the lift. Airodynamic theory, including Bernoulli and Navier-Stokes equations only serve to explain _how_ the wings accelerate the air down.