Part of Aircraft (3)

Part of Aircraft (3)

SPOILER

Spoilers are small, hinged plates on the top
portion of wings. Spoilers can be used to
slow an aircraft, or to make an aircraft
descend, if they are deployed on both wings.
Spoilers can also be used to generate a rolling
motion for an aircraft, if they are deployed on
only one wing. This slide shows what
happens when the pilot only deflects the
spoiler on the right wing.

1. Spoilers Deployed on Both Wings

When the pilot activates the spoilers, the
plates flip up into the air stream. The flow
over the wing is disturbed by the spoiler, the
drag of the wing is increased, and the lift is
decreased. Spoilers can be used to “dump” lift
and make the airplane descend; or they can be
used to slow the airplane down as it prepares
to land. When the airplane lands on the
runway, the pilot usually brings up the
spoilers to kill the lift, keep the plane on the
ground, and make the brakes work more
efficiently. The friction force between the tires
and the runway depends on the “normal”
force, which is the weight minus the lift. The
lower the lift, the better the brakes work. The
additional drag of the spoilers also slows the
plane down.

2. Spoiler Deployed on Only One Wing

A single spoiler is 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 curve.
If the airplane’s right wing spoiler
is deployed, while the left wing spoiler is
stored flat against the wing surface. The
flow over the right wing will be disturbed by
the spoiler, the drag of this wing will be
increased, and the lift will decrease relative to
the left wing. The lift force (F) is applied at
the center of pressure of the segment of the
wing containing the spoiler. This location is
some distance (L) from the aircraft center of
gravity which creates a torque
T = F * L
about the center of gravity. The net torque
causes the aircraft to rotate about its center
of gravity. The resulting motion will roll the
aircraft to the right (clockwise) as viewed
from the rear. If the pilot reverses the spoiler
deflections (right spoiler flat and left spoiler
up) the aircraft will roll in the opposite
direction. 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.