Image map page header with links listed at bottom of page Link to Internet Access Research Link to Aeronautic Educational Resources Link to Educator Resources Link to Glenn Learning Technologies Homepage Link to Icing Research Tunnel Virtual Tour
Left side image map with list of links located at bottom of page Link to Aeronautics Lessons and Activities Link to Videoconferences with the U.K. Link to Engine Sim General Information and Free Java Software Link to Foil Sim Problem Sets Link to ModelRocketSim Link to Engine Sim Problem Sets Link to Propulsion General Information and Free Java Software Link to Propulsion General Information and Free Java Software Link to Free Software Link to Aerodynamics Problem Sets Link to Wind Tunnel Web Pages Link to Aeronauts 2000 Link to Foil Sim General Information and Free Java Software Link to Aerodynamics General Information and Free Java Software Link to Beginner's Guide to Aeronautics
Trimmed Aircraft Problems
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.)
Please send any comments to:
Curator: Tom.Benson@grc.nasa.gov
Responsible Official: Kathy.Zona@grc.nasa.gov