Changing Lift

Changing Lift

Lift can be increased in three ways. Pilots should understand each method so they can apply it in the air. While in the final flare to land, for example, lift is increased by increasing AOA. In slow flight, lift is increased by increasing airspeed. These methods for generating lift are not isolated: far from it. Good airmanship often involves changing lift in multiple ways at once.

Lesson Notes

Airplanes are flown by constantly adjusting the forces acting on the airplane. How do we change these forces? Generally speaking, there are three ways:

• AOA
• Changing wing shape (flaps, leading edge devices)
• Airspeed

There is a widely-distributed, but incorrect theory on lift that pilots should be aware of, because they will likely be told of it at some point: It’s called the equal transit time theory. It states that air molecules move across both sides of the wing in the same amount of time, so that molecules will “meet together” at the backend of the wing.

Studies have demonstrated this is not the case. See the visualization below:

Additional Resources

• Venturi Handout
• AOA Handout

Review Questions

• What 3 ways can a pilot change lift?
• How does a pilot change the AOA?
• What wing shape generally generates more lift for a given airspeed/AOA? What generates less?
• Why does a higher airspeed create more lift?
• What flight control most directly is used to change the AOA?
• There is a limit to how much lift can be increased by changing the AOA. What is this limit called?
• If an airplane with a symmetrical airfoil has a 0° AOA, what will be its flight path? Will this change with an increase in airspeed?
• Are elevator position and AOA directly linked? Are elevator force and AOA directly linked?