Momentum
A better way to look at lift in this system is to introduce momentum. The momentum of an object is defined as its mass times velocity. Let’s assume that the air in a given location in the sky is before the plane reaches it. In other words, the particles of air are not moving in any one particular direction (no wind). Once the airfoil cuts through the air, it moves the air, giving it velocity. (Note that this is a transfer of energy from the plane to the air, and this is one of the reasons why a plane needs engine power to maintain lift). In order for a wing to create more lift, it can either direct more air downwards (hence increasing the mass of the diverted air) or increase the downward velocity of the air. Either of these would increase the lift force. How might a wing divert more air or increase the velocity of the downwash to generate more lift? This is where angle of attack and the velocity of the plane come into play. |
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