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As air flows over the top of an aerofoil the pressure drops. Compared to the high / normal pressures on the underside, a pressure gradient is formed with higher pressure further above the wing. You get:

less pressure = less particles = less density

This sketch summarizes what I know so far:

enter image description here

My questions are:

  • Does lower air density above the wing mean the air weighs less compared to the weight of the air underneath the wing? If the difference is negligible then it's OK, we can forget it.

  • What forces act on the air particles causing them to speed up?

123
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  • Its the shape on top of the wing. Lets refer to newtons law the second that states that if you have a straight line airspeed will not change, but on a jet or airliners wing it is slanted downwards which increases the airflow speed and results Iin a high pressure under the wing and a low pressure above the wing. Think of yyourself going down hill on your bike and you dont have to pedal to get down the hill, it has the same effect as going down a hill on your bike, gravity pushes down on the airflow making it go faster on top and slower on the bottom. – Ethan Aug 31 '15 at 18:57
  • is this right ??so the air particles speed up (due to gravitys downward pull) as they move arcoss towards the back of the wing due to the downwards slope of the rear of the wing as they speed up they are elastically pulled further apart this then cause less particles per unit vol in a given space and there for less localised pressure – 123 Aug 31 '15 at 19:08
  • thanks Ethan I think its starting to make more sense now !! – 123 Aug 31 '15 at 19:28
  • if your question is really of this kind I feel it should be better asked on physics.SE – Federico Aug 31 '15 at 19:37
  • Pressure is equivalent to static energy. But in lift, the inertial forces on the air molecules play an important part as well. Please read this answer and then let me know if there is still something unclear. – Peter Kämpf Aug 31 '15 at 20:26
  • Your welcome. Feel free to ask more questions. – Ethan Aug 31 '15 at 20:54
  • WHAT FORCES ACT ON THE AIR PARTICLE CAUSING IT TO SPEED UP

    IS IT GRAVITY PULLING IT DOWN ??

    OR IS IT THE CENTRIPITAL FORCE FROM THE CURVED RADIUS SHAPE OF WING ??

     – 123 Sep 01 '15 at 17:49
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    to me this is more and more about physics (and shouting won't achieve anything). – Federico Sep 01 '15 at 18:06
  • I didn't mean to type capitals – 123 Sep 01 '15 at 18:23
  • here is the question again – 123 Sep 01 '15 at 18:25
  • as it was meant to be typed originally it this correct?? the force that acts on the particle causing it to speed up over the top of wing Is as per rotational dynamics (a centripetal force acting towards the wings curved radius centre – 123 Sep 01 '15 at 18:26
  • as it was meant to be typed originally question to Ethan it this correct?? the force that acts on the particle causing it to speed up over the top of wing Is as per rotational dynamics (a centripetal force acting towards the wings curved radius centre this method would work for sails on yachts that have aerofiols perpendicular to gravity but still generate lift inorder to move forward – 123 Sep 01 '15 at 18:33

1 Answers1

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This is my understanding: A combination of the shape, angle of attack and movement of the wing creates high pressure on the front side of the wing and low pressure on the back side. By front and back I mean the part that is facing the oncoming air and the part that cannot "see" the oncoming air.

The low pressure is there because of this. This is the pressure difference which causes lift. Some lift also comes from the downdraft caused by air moving downwards at the trailing edge of the wing due to the angle of attack.

This article has a video that shows airflow over a wing. http://www.cam.ac.uk/research/news/how-wings-really-work

Philip Johnson
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    Uhhh... Newton's Third law requires that all lift exerted by the air on the wing is equal to the down force exerted by the wing on the air – DJohnM Aug 31 '15 at 21:48