This page is intended for college, high school, or middle school students.
For younger students, a simpler explanation of the information on this page is
available on the Kid's Page.
for a description of flight control, or
for a discussion of airplane parts.
Ailerons can be used to generate a
rolling motion for an aircraft.
Ailerons are small hinged sections on the outboard
portion of a wing.
Ailerons usually work in opposition: as the
right aileron is deflected upward, the left is deflected downward,
and vice versa.
This slide shows what happens when the pilot deflects the right aileron
upwards and the left aileron downwards.
The ailerons are used to bank the aircraft; to cause one wing tip to move
up and the other wing tip to move down.
The banking creates an unbalanced side force component of the
large wing lift force
which causes the aircraft's flight path to
(Airplanes turn because of banking created by the ailerons, not because
The ailerons work by changing the effective shape of the airfoil
of the outer portion of the wing.
As described on the shape effects slide,
changing the angle of deflection at the rear of an airfoil will
change the amount of lift generated by the foil. With greater
downward deflection, the lift will increase in the upward direction.
Notice on this slide that the aileron on the left wing, as viewed
from the rear of the aircraft, is deflected down. The aileron on the
right wing is deflected up. Therefore, the lift on the left wing is
increased, while the lift on the right wing is decreased.
For both wings,
the lift force (Fr or Fl) of the wing section through the aileron
is applied at the
of the section which is
some distance (L) from the aircraft
center of gravity. This creates a
T = F * L
about the center of gravity.
If the forces (and distances) are equal there is no net torque on the
aircraft. But if the forces are unequal, there is a net torque and the aircraft
about its center of gravity.
For the conditions shown in the figure, the resulting motion
will roll the aircraft to the right (clockwise) as viewed from
the rear. If the pilot reverses the aileron deflections (right
aileron down, left aileron up) the aircraft will roll in the
We have chosen to name the left wing and right wing
based on a view from the back of the aircraft towards
the nose, because
that is the direction in which the pilot is looking.
[You can also test the roll effect yourself using a paper airplane.
Just cut some control tabs into the rear of both wings. Bend one tab
up and the other down, and you will see the airplane roll when it is
flown. The roll will be in the direction of the tab that is pulled
up. The same thing will work on a simple wooden glider. The tabs can
be yellow stick-ums or tape attached to the wings.]
When you travel on an airliner, watch
the wings during turns. The pilot rolls the aircraft in the direction
of the turn. You will probably be surprised at how little deflection
is necessary to bank (roll) a large airliner. But be warned that
there is a possible source of confusion on some airliners. We have
been talking here about rolling the aircraft by using a pair of
ailerons at the very trailing edge of both wings to increase or
decrease the lift of each wing. On some airliners, the aircraft is
rolled by killing the lift on only one wing at a time. A plate,
called a spoiler, is raised between the
leading and trailing edges of the wing. This effectively changes the
shape of the airfoil, disrupts the flow over the wing, and causes a
section of the wing to decrease its lift. This produces an unbalanced
force with the other wing, which causes the roll. Airliners use
spoilers because spoilers can react more quickly than ailerons and
require less force to activate, but they always decrease the total
amount of lift for the aircraft. It's an interesting trade! You can
tell whether an airliner is using spoilers or ailerons by noticing
where the moving part is located. At the trailing edge, it's an
aileron; between the leading and trailing edges, it's a spoiler. (Now
you can dazzle the person sitting next to you on the plane!)
You can view a short
of "Orville and Wilbur Wright" explaining how wing warping
was used to roll their aircraft. The movie file can
be saved to your computer and viewed as a Podcast on your podcast player.
Parts of an Airplane:
Aircraft Roll Motion:
- Beginner's Guide Home Page