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Robert Bronson asked the Naked Scientists: Hello, I have just found your podcasts this year and love your show. I have noticed, however, that on several occasions your team has described the flight of airplanes as being caused by the air pushing up on the wings. It was always explained to me that airplanes fly due to lift created by the vacuum caused on the top of the wing because of the curvature of the wing. I was told that it was similar physics to why sailboats work. Which is the correct answer?RobertSeattle, WAWhat do you think?
Very little lift is directly caused by low pressure (the air pulling the wing up)
Quote from: Roy Dale on 27/03/2011 19:22:08Very little lift is directly caused by low pressure (the air pulling the wing up) Strictly speaking, there is no "pulling" on the surface of the wing; there is only pushing. There is a pressure difference between the surfaces of the wing, and the high pressure side (the lower surface) exerts a greater force on the wing than the lower pressure side (the upper surface) exerts. The difference is the lift force.
It directs the air downwards giving you a lift.
That too Geezer, But how about it?Will the airplane take off?
Quote from: yor_on on 28/03/2011 06:46:35It directs the air downwards giving you a lift.Not necessarily Yoron. An aerofoil can produce lift even with a zero degree angle of attack. In that situation, the lift is produced because the air flow across the top surface of the aerofoil is faster than the air flow across the bottom surface. This results in greater air pressure on the bottom surface than on the top, which creates an upward force on the wing.
The reason an airfoil can produce lift in the upward direction at zero angle of attack is because it diverts air downward as a result of its shape like I said before. One of the airfoil shapes that generates the most lift at zero angle of attack is the under cambered wing. The distance over the top of the under cambered wing is close to the distance under the bottom. The only thing better that shaping the top of the wing to divert the air downward is shaping the bottom to do the same. Burnulies effect requires the motion of the air stream but the relative airflow that causes lift does not. Take an airplane that is flying through the air, the air that is generating its aerodynamic force is made up of still air. This air is not moving over the wing the wing is moving through the air. For this air to experience low pressure as a result of its increased speed it has to increase its speed. In order for it to increase speed it has to have speed. The way the wing sets this still air in motion is by pulling on it and pushing on it (measured in pressure). Some pull is from viscosity. After this air has been set in motion its pressure may go down but it would not be in motion unless the wing pushed or pulled on it, and the air pushed and pulled back causing pressure. You dont have to wonder what came first the chicken or the egg or in this case the pressure or the motion of the air.