How Do They Fly? – an intuitive look into lift generation and flight stability

Have you ever wondered why the flight attendants of a half empty airliner talk people into moving to the front half of the plane? Have you ever wondered why a flying wing can fly without a tail or why the stability of some of these flying wing can be controlled only by computer? Or why a 12 pack stored in at the back of a Cessna can make the plane unstable… It all has to do with two momentums that act on a plane, a positive aerodynamic pitch momentum and a negative gravitation momentum which need to balance each other during the flight.

This article has 5 Comments

  1. I never heard the first quote before :-). That’s so true.

  2. I observed a huge change in my understanding and capacity of solving problems. I am talking huge. I am trying to convey this in here. Cheers, George

  3. It all goes like this: wedge = deflects air down (both top and bottom of the wing), changes impulse of air particles down. By Newton’s 3rd law the same but opposite impulse is experienced by the wing. Newton 2nd law: impulse change => acceleration => force => lift. Of course the sape makes a huge diference (1-2 orders of magnitude in efficiency) but that is a secondary effect – later on that one. All you said it’s true but about that, later… There is some Bernoully there also but it’s not the main factor.

  4. OK George

    Maybe Einstein was on your side with attributed quotes such as
    “The only thing that interferes with my learning is my education” and the one I believe in, “Everything should be made as simple as possible, but no simpler.”

    For me, insight and understanding count for everything; learning and memory provide poor substitutes – although they may offer a few shortcuts.

  5. Point of correction: In a number of cases you have used ‘momentum’ (mass x velocity) where I think you mean ‘moment’ (force x distance).

    Point for discussion: I am not an aerodynamicist but I suspect the ‘wedge effect’ you offer as an aid to visualising aerodynamic lift is not as distinct from the Bernoulli effect as you suggest. The bedroom door will generate lift so the force on the underside is greater than that on the topside. On a streamline this, in turn, tells you that the velocity on the underside is lower and that there is circulation about the door, so one would expect to see vortices created. Even a particle model such as your bat and flow of ping pong balls would have the bat decreasing the momentum of the ping pong balls it strikes.

    The shape of the aerofoil also has an effect but I think your point is that the effect is not essential to the understanding of lift as an aerodynamic force.

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