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Trimmed Aircraft Activity
If so instructed by your teacher, print out a worksheet page for these problems.


Suppose an airplane has a center of pressure on the wings that provides a wing lift force of W. The force W is located a distance dw from the airplane's center of gravity (cg). The center of pressure on the tail provides a lift force of T. The force T is located a distance dt from the airplane's center of gravity (cg). The lift force W will always be positive, which indicates an upward force. However, the lift force T can be positive for some airplanes (upward force) and negative (downward force) for other airplanes.

The plane is traveling to the left; the tail is on the right.
  1. An airplane has a wing lift of 30,000 lbs. which is centered 20 feet to the right of the cg. The tail lift is centered 100 feet to the right of the cg. How much force must the tail lift supply in order to keep the plane from rotating? Is this force upward or downward?

  2. Continuing with Problem 1, suppose the lift force is located 20 feet to the left of the cg. How much force must the tail lift supply in order to keep the plane from rotating ? Is this force upward or downward?

    (Hint: Distances measured to the right of the cg are positive while distances to the left are negative.)

  3. Explain why the tail lift force is different in Problems 1 and 2 while the wing lift force is the same.

  4. Consider Problem 1 again. Suppose the fuel tanks become significantly lighter after a long flight. This causes the cg to move toward the front of the plane (to the left). Will a change in the position of the cg of 10 feet to the left affect the previously trimmed (balanced) airplane? (Mathematically support your answer.)
     
  5. If the movement of the cg causes the airplane to become unbalanced, what do you think the pilot will do to regain balance?

  6. Consider Problem 2 again. Suppose the same thing that happened in Problem 4 happens in Problem 2. Will a change in the position of the cg of 10 feet to the left affect the previously trimmed (balanced) airplane? (Mathematically support your answer.)

Related Pages:
Standards
Worksheet
Lesson Index
Aerodynamics Index

 

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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Thu, Jun 12 04:46:36 PM EDT 2014

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