We are now going to explore some of the factors that affect the lift of a wing. We will be using the input sliders and boxes located at the lower left and will be watching the output scale marked "Lift" at the bottom on the left. In this lesson we will be most interested in answering the question, "What changes the lift of a wing?." If you have been playing with FoilSim, it will now be necessary to set the inputs to some initial conditions.
Click the Reset button to set the following conditions:
Airspeed = 100 mph
Altitude = 0 feet
Angle = 0 degrees
Thickness = 0.5
Camber = 0
Area = 1.0 sq ft
WHAT IS THE VALUE OF THE LIFT?
Increase the speed to 150.
WHAT HAPPENS TO THE LIFT?
Increase the Thickness to 0.7 and the Area to
10.
WHAT HAPPENS TO THE LIFT?
OK - let's change the Angle of attack to
10 degrees.
WHAT HAPPENS TO THE LIFT?
-->
A symmetric
airfoil inclined to the incoming
flow will generate lift. <--
You don't need a
curved airfoil to generate lift!!
Increase the Angle to 15 degrees.
--> Increasing the angle of attack will increase the amount of lift. <--
Let's decrease the Thickness to 0.05. This will approximate a flat plate.
--> Decreasing the thickness will decrease the amount of lift. <--
--> But a flat plate at angle of attack will generate a lot of lift. <--
Let's do a little experiment with this flat plate!
Suppose we had the door to our house which is about 7 feet by 4 feet = 28 square feet. (Set the Area = 28) And suppose we were in a tornado which generates a wind of 150 mph. (Set Airspeed = 150) And suppose the door was inclined to the wind at only 10 degrees. (Set Angle = 10)
HOW MUCH FORCE IS GENERATED ON THE DOOR?
Suppose, instead of a 28 square foot door we had a 4 by 8 sheet of plywood. (Area = 32)
HOW MUCH FORCE IS GENERATED ON THE SHEET?
--> Increasing the area will increase the amount of lift. <--
Well, back to airfoils. Let's look at an airplane problem.
Let's set the Thickness to 0.5, and the wing Area to 180 square feet (6 ft. chord and 30 ft. wing span). At 150 miles per hour and 10 degrees Angle of attack, this will generate 12,640 pounds of Lift. This will easily lift a 10,000 pound airplane off the ground.
Let's see what happens at 25,000 feet Altitude.
IS THERE ENOUGH LIFT GENERATED TO KEEP OUR PLANE FLYING?
--> Increasing the altitude will decrease the lift. <--
What can we do ?
Let's increase our Airspeed to 200 mph.
IS THERE ENOUGH LIFT GENERATED TO KEEP OUR PLANE FLYING?
--> Increasing the airspeed will increase the lift. <--
Well, we've changed all the input conditions except the camber (or curvature) of the airfoil so let's set the Camber = 0.2.
--> Increasing the camber will increase the lift. <--
Let's check these results at a different set of conditions. Set Airspeed = 100, Altitude = 0, Camber = 0, then change to Camber = 0.2
--> Lift appears to be a very strong function of the airfoil camber. <--
(As an engineer, when you see a result that you weren't expecting, it's a good idea to repeat the experiment!)
In this lesson we have seen the effects of various shape and flow factors on the lift of a wing. So far, we have just taken a qualitative look. In the next lesson we're going to be carefully comparing results to find quantitative (numerical) results.
Let's summarize what we've learned:
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How Lift Changes