Using Graphs to Compare Lift Variables Activity

---

If so instructed by your teacher, print out a worksheet page for these problems

This activity involves using the graphs created by FoilSim for each of six variables to compare their effect on the lift of an airfoil. We will analyze the graphs produced by each of the following variables compared to the lift produced: airspeed, angle of attack, area of the airfoil,altitude, thickness of the airfoil,and camber of the airfoil.

Start FoilSim. Set up the graph plotter on the upper right side of the screen by clicking on the blue "Graphics" button (On Version 1.4 of FoilSim II this button has been changed to a red on white "Plots" button).

1. A selection of available plots now appears in the upper right screen. Let's plot the lift versus the angle of attack. Click on the red on white "Angle" button and a graph will appear in the top righthand corner. This graph shows how the lift changes as the angle of attack increases or decreases. Analyze the graph by describing how the line is shaped and explaining what the shape of the line means to the change in lift. Enter your answers in a hard copy of the data table shown at the bottom of the page.

2. Click the "Graphics" (or "Plots") button again. This time plot lift versus the thickness of the airfoil. Click on the "Thickness" button and a graph will appear that compares the change in thickness of the airfoil to the resulting effect on lift. What do you notice about the graph?

Set the angle to 0.0 and explain what happens to the graph.

Now, analyze the graph and fill in the data table.

3. Push the red "Reset" button and then the "Graphics" (or "Plots") button. Plot the lift versus camber. Compare the changes in camber and the resulting change in lift. Analyze and record the data.

4. Click the "Graphics" (or "Plots") button again. This time plot lift verus airspeed. Explain what happens when the graph appears.

Change the angle to 0.0 and look at the graph again. What do you notice? Why?

5. Push the red "Reset" button and then the "Graphics" (or "Plots") button. Plot lift versus altitude and notice the graph that appears. Remember that when we examine altitude we are actually comparing the density of the air in that part of the atmosphere. It is a good idea to keep this in mind while analyzing the graph. Analyze your altitude graph and enter data in the data table.

6. Click the "Graphics" (or "Plots") button again. The final variable is the area of the airfoil surface. Plot the lift versus wing area and analyze and record the data represented by the graph.

Questions:

1. What does a graph with a straight line tell us about how the data changes?

    

2. What does an upward curve indicate on a graph?

    

3. How does the data change if you have a line that curves downward on your graph?

    

4. Which lift variables seem to change at a steady rate?

    

5. Which lift variables tend to change at an increasing rate? Decreasing rate?