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Wing Shape Investigations
Answers
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An airfoil is the shape of a wing or blade (of a propeller, rotor or turbine) or
sail as seen in cross-section.
FoilSim is a computer program that
lets you investigate how an aircraft wing produces lift by changing the values
of different factors that affect lift.
Here are some exercises using FoilSim that will help you understand airfoils better.
Start the
FoilSim
program.
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Camber, in aerospace engineering, is the asymmetry between the top and the
bottom curves of an airfoil in cross-section.
Click the Reset button in FoilSim. Then set:
Angle-deg ( Angle of attack ) to 0.0
Camber-%c to 0.0
Notice how Lift is zero. Increase the angle of attack to some positive value.
Is there lift now? This proves you don’t need the wing to be curved to make lift!
Increasing the angle of attack
generates lift for the symmetric airfoil.
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Now set the thickness ( Thick-%crd) to 0.0. Do you get positive lift?
A flat plate makes lift !
Even with zero thickness (a flat plate),
increasing the angle of attack generates lift.
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Does making a curved airfoil help increase the lift?
What do real wings on planes look like?
Curving the airfoil will generate more lift at a given
angle of attack than a flat plate. Real wings have some degree of camber.
The greater the camber, the greater the drag; real wing shapes are the result of a
trade bewteen lift and drag.
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Click the Reset button again. From the Input menu select Flight Test.
Increase the speed from 100 mph to 200 mph. Does the lift double? What does it do?
Doubling the speed quadruples the lift.
Lift depends on the square of the velocity.
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Leave the speed at 200 mph. Increase the Altitude slowly.
What happens to the lift? Let’s say the plane needs 2000 lbs of lift to stay aloft.
At what altitude will the airfoil not be generating enough left to keep the plane aloft?
This is the flight ceiling. It is the highest altitude you can fly with this wing.
Lift decreases with altitude because it depends on the air density.
Air density decreases with altitude. Value of the ceiling altitude varies with wing design.
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Click the Reset button again. Adjust the thickness of the airfoil (Thick-%crd).
What happens to the lift? Does changing the thickness have a big effect on the lift?
Lift varies only slightly with airfoil thickness, for
the thin airfoils developed in FoilSim.
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Click the Reset button again. If you make the camber negative
what happens to the lift? Can you think of a situation where it would be good to
have negative lift?
Negative camber produces negative lift at small angles of attack.
Negative lift is used by race cars to increase traction. The wings at the rear of NASCAR and
Indy cars produce negative lift.
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