
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 d_{w} 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 d_{t} 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.
 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?
 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.)
 Explain why the
tail lift force is different in Problems 1 and 2 while the wing lift
force is the same.
 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.)
 If the movement
of the cg causes the airplane to become unbalanced, what do you think
the pilot will do to regain balance?
 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.)
