4 ms·

Euler equations explain the lift, but it can be still hard to grok. Newton’s Laws of Motion gives the clearest correct explanation: If the wing stays in the ai

by nabla9 5y ago

Euler equations explain the lift, but it can be still hard to grok. Newton’s Laws of Motion gives the clearest correct explanation: If the wing stays in the air, there must be a force that is equal but opposite to the gravity. If you divide the air around the wing into equal mass chunks of air (not equal volume) and visualize the velocity and acceleration of each chunk, you get very informative picture of where and when of the lift. If the wing stays in the air, air around the wing must be accelerating downwards.

VBprogrammer 5y ago
Expanding on that, the downwash theory is the easiest to understand in my opinion. If you think about the flow of water over the back of a spoon then imagine increasing the amount of the water flow and the size of the spoon until you could eventually feel the force pulling your hand opposite the direction the water is deflected.
- bbojan 5y ago
  You don't have to imagine, simply put a spoon sideways against a flow of water from the faucet and you can instantly feel a pull.
wbeaty 5y ago
In 2D airfoil diagrams, first the parcels approach horizontally. Then they are mysteriously accelerated upwards. Then the airfoil accelerates them downwards. Then behind the airfoil, they're mysteriously accelerated upwards again, so they depart horizontally, for zero net acceleration applied to each parcel. As a whole, air around the wing ISN'T accelerating downwards. As long as we ignore the "mysterious" part, or try to sweep it under the rug, our explanations won't satisfy. A complete explanation must include the ground surface ...and then we discover that we're actually explaining a kind of "venturi effect," where the ground is a part of the system, and those mysterious accelerations before and behind the airfoil are caused by interaction with the ground. This is a "big AHA!" situation: a 2D airfoil can only explain ground-effect flight, where the Newtonian force-pair is located between ground and the airfoil, so no net downward acceleration of air exists. (In other words, if we erase the ground from our diagram, we've just violated Newton's 3rd law.) A 2D airfoil diagram without the ground surface ...that's a sort of "inertial drive," where the upward force on the airfoil has no corresponding down-force (it does not give a net downward acceleration to the air as a whole.) Easy to fix. Just add the ground surface back in. And then confront the fact that this is a venturi, and not an explanation of flight.

by nabla9 5y ago

VBprogrammer 5y ago

Expanding on that, the downwash theory is the easiest to understand in my opinion. If you think about the flow of water over the back of a spoon then imagine increasing the amount of the water flow and the size of the spoon until you could eventually feel the force pulling your hand opposite the direction the water is deflected.

bbojan 5y ago
You don't have to imagine, simply put a spoon sideways against a flow of water from the faucet and you can instantly feel a pull.

wbeaty 5y ago

In 2D airfoil diagrams, first the parcels approach horizontally. Then they are mysteriously accelerated upwards. Then the airfoil accelerates them downwards. Then behind the airfoil, they're mysteriously accelerated upwards again, so they depart horizontally, for zero net acceleration applied to each parcel. As a whole, air around the wing ISN'T accelerating downwards. As long as we ignore the "mysterious" part, or try to sweep it under the rug, our explanations won't satisfy. A complete explanation must include the ground surface ...and then we discover that we're actually explaining a kind of "venturi effect," where the ground is a part of the system, and those mysterious accelerations before and behind the airfoil are caused by interaction with the ground. This is a "big AHA!" situation: a 2D airfoil can only explain ground-effect flight, where the Newtonian force-pair is located between ground and the airfoil, so no net downward acceleration of air exists. (In other words, if we erase the ground from our diagram, we've just violated Newton's 3rd law.) A 2D airfoil diagram without the ground surface ...that's a sort of "inertial drive," where the upward force on the airfoil has no corresponding down-force (it does not give a net downward acceleration to the air as a whole.) Easy to fix. Just add the ground surface back in. And then confront the fact that this is a venturi, and not an explanation of flight.