Why does air travel faster over a wing?

In summary, the air going over a wing travels faster than the air going underneath because of the downwards force applied on the air by the wing, resulting in a downwards acceleration of the air. This acceleration, combined with the wing's forward speed and effective angle of attack, increases the air's kinetic energy and decreases its pressure energy, resulting in lift. This is a more accurate explanation than the commonly believed notion of equal transit time.
  • #1
kidsmoker
88
0
Hi,
I was just wondering why the air going over a wing travels faster than the air going underneath? My teacher once said "because it has farther to travel" and I just accepted that at the time, but thinking about it now i don't really see why two adjacent air molecules that part company at the front of the wing should neccessarily meet up again on the opposite side. Is there a better explanation?

Thanks.
 
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  • #2
Well done for questioning it !
That model for how a wing works is wrong - but is believed by a large number of scientists and engineers who should know better.

This has a good explanation of a numberof the models: http://science.howstuffworks.com/airplane5.htm
 
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  • #3
If you're still in contact with your teacher, show him these pictures and ask how these pre-shuttle lifting bodies with flat tops and curved bottoms fly?

m2-f2 glider version:
m2-f2.jpg

m2-f3 rocket powered version (max speed mach 1.6):
m2-f3.jpg

Wings produce lift by applying a downwards force on the air, which responds with an equal and upwards force on the wing, following Netwons 3rd law of motion. The downwards force results in a downwards acceleration of air, and the air's reaction to this downwards acceleration is an upwards force on the wing.

You're correct in that equal transit time is wrong. With a conventional wing, the air above ends up displaced further behind the wing than the air below, but note that most of the acceleration and motion of the air is downwards (corresponding to lift), with only a small amount forwards (corresponding to drag).

How wings accelerate air downwards is a combination of foward speed and effective angle of attack (air is "deflected" downwards). The final result is a significant increase in kinetic energy of the air (1/2 m v2), which would normally require a lot of work done on the air, but most of this increase in kinetic energy is offset with a decrease in pressure energy, in a Bernoulli like transition. Wing's aren't 100% efficient, so there is some work done on the air and not all of the transition is Bernoulli like.
 
  • #4
Cool thanks for those. I've read the explanation on howstuffworks and i understand it better now.
 

What is lift on an airplane wing?

Lift is the upward force created by the motion of air over an airplane wing. It is one of the four main forces acting on an airplane during flight, along with weight, thrust, and drag.

How is lift created on an airplane wing?

Lift is created by the difference in air pressure above and below the wing. The shape of the wing, called an airfoil, is specifically designed to create this pressure difference when air flows over it at high speeds.

What factors affect the amount of lift on an airplane wing?

The amount of lift on an airplane wing is affected by the shape and size of the wing, the speed and angle of the airflow, the density of the air, and the angle of attack (the angle at which the wing meets the oncoming airflow).

How does lift help an airplane stay in the air?

When the lift force is greater than the weight of the airplane, the airplane is able to stay in the air. This is achieved by adjusting the speed, angle of attack, and other factors to maintain a balance between the four forces acting on the airplane.

Can lift be created in other ways besides using an airplane wing?

Yes, lift can also be created by using other airfoils, such as helicopter blades or sailboat sails. It can also be created by using engines to create thrust, as seen in vertical takeoff and landing aircraft.

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