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Using Graphs to Compare Lift Variables
Answers

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 Data Table

Variable
Description
Explanation
Angle of attack

A straight line at less than a 45o angle through 0,0. The lift and angle show + and - numbers.

The straight line shows a steady increase. If you double the angle, then you double the lift.

Thickness of airfoil

A slight upward curve.

The curve shows that as the thickness increases the lift also increases, but to a lesser degree.

At angle = 0.0, there is no line on the graph.

For a symmetric airfoil, a change in thickness will not change the lift.

Camber

A straight line at less than a 45o angle through 0,0 with lift being both + and -.

The straight line shows a steady increase.

 

Airspeed

An upward curve where the slope of the line increases with increased speed.

The upward curve shows that lift increases at a greater rate than the speed increases.

At angle = 0.0, there is no line.

For a symmetric airfoil, a change in airspeed does not create lift.

Altitude (density)

A downward curving line where the slope decreases with altitude.

As altitude increases the lift that results decreases; but the decrease lessens with altitude. ( As the altitude increases, the density of the air decreases. So lift decreases as density decreases.)

Area of airfoil surface

A straight line at a 45o angle through 0,0.

The lift increases at the same rate as the area.

Questions

  1. What does a graph with a straight line tell us about how the data changes? A graph with a straight line shows a steady increase (or decrease depending on the slope).
  2. What does an upward curve indicate on a graph? A graph with an upward curve has an increasing slope. So as the independent variable increases, the dependent variable increases, but at a greater rate.
  3. How does the data change if you have a line that curves downward on your graph? A downward curve shows a decrease at a varying rate.
  4. Which lift variables seem to change at a steady rate? Angle, camber, and area seem to increase at a steady rate.
  5. Which lift variables tend to change at an increasing rate? Decreasing rate? Airspeed increases at an increasing rate. Altitude decreases at a decreasing rate, while thickness increases at a decreasing rate.
 

Related Pages:
Standards
Activity
Worksheet
Lesson Index
Aerodynamics Index

 

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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Thu, Jun 12 04:47:14 PM EDT 2014

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