parts that the pilot adjusts to increase
the size of the wing surface. This
changes the amount of force made by
the wing. Ailerons are hinged parts that
the pilot moves to turn the airplane.
The rear of the plane is called the tail.
The horizontal stabilizer is a part of the
54 Airplane BRITANNICA STUDENT ENCYCLOPEDIA
tail that often looks like a small wing. It
prevents the plane from pitching, or
bucking up and down. The elevator is
hinged to the horizontal stabilizer. It
raises or lowers the nose, or front end, of
the plane. The vertical stabilizer often
looks like a fin. It prevents the aircraft
from yawing, or swinging from side to
side. The rudder is connected to the
vertical stabilizer. It controls side-to-side
movement.
The landing gear consists of rubber tires
and shock-absorbing devices. Most
planes have two main wheels or sets of
wheels and another wheel to support the
tail. Some planes have wheels that fold
up when the plane is in the air.
Power System
A plane’s power system includes one or
more engines and sometimes propellers.
The two main types of engines are
reciprocating engines and jet engines. A
BRITANNICA STUDENT ENCYCLOPEDIA Airplane 55
reciprocating, or piston, engine turns a
propeller. The turning of the propeller
provides most of the power to move the
plane forward. Reciprocating engines
are usually found on smaller airplanes.
A jet engine moves a plane forward by
shooting exhaust gases out the back. Jet
engines are common on large
commercial planes and military aircraft.
Some small planes have a turboprop
engine, which is a jet engine that turns
a propeller.
Flight Controls and Instruments
Flight controls help a pilot to regulate
the movement and position of an airplane.
The control wheel or stick is used
to adjust the elevator and the ailerons.
Foot pedals allow the pilot to control the
rudder. A throttle controls the engine
power. The pilot also controls the wing
flaps and slats.
Flight instruments are used for navigation,
checking engine performance, and
monitoring other equipment. In addition
to these instruments, there are a
variety of indicators that monitor the
engines and other parts of the plane’s
mechanical and electrical systems.
How Airplanes Fly
The science of flight is called aerodynamics.
Four main aerodynamic forces
act on an airplane in flight. They are
called drag, thrust, gravity (or weight),
and lift.
As a plane flies, the air slows it down.
This is the effect of drag. To overcome
drag a plane needs the forward-moving
force of thrust. Thrust is produced by
the plane’s engines or propellers.
An airplane is heavier than air. It will fall
to the ground under the influence of
gravity unless lift is applied. The plane’s
wings are able to produce the necessary
lift because of their shape. The upper
surface is curved, while the lower surface
is flat. To get past the curved surface, the
air that flows over the wing has to go
farther—and therefore faster—than the
air that flows under it. This creates a
difference in air pressure between the
upper and lower surfaces as the plane
moves forward. The air underneath is
under greater pressure and therefore
pushes the wing up. The faster the air
flows past the wings, the greater the lift.
For this reason, an airplane takes off
most easily when it faces the wind.
Pilots use flaps and slats to change the
amount of lift. Lowering the flaps
increases the curved surface of the wing,
which provides more lift for takeoff.
Slats also increase lift by allowing air to
flow more smoothly over the wing. Rais-
A plane with turboprop engine uses both jet
power and propellers. Turboprop engines
are used only in small planes.
56 Airplane BRITANNICA STUDENT ENCYCLOPEDIA
ing the flaps reduces lift, which slows
down the plane for landing.
History
Before humans took to the air in airplanes,
they flew in lighter-than-air
craft. In 1783 the Montgolfier brothers
of France made the first balloon that
could carry people high into the air.
Their balloon rose because they filled it
with hot air, which is lighter than
unheated air.
The 1800s saw much experimentation
in both lighter-than-air and heavierthan-
air craft. Several people worked
with gliders to establish the principles of
airplane design. Gliders are similar to
airplanes but they have no motor. Once
they are launched, they move through
the air as a plane does.
Early Aviation
On December 17, 1903, in Kitty Hawk,
North Carolina, Orville andWilbur
Wright made the first flight in an
engine-powered airplane. TheWright
brothers had experimented with gliders.
They chose the North Carolina coast for
their testing because of its strong winds.
Their first plane flight, with Orville
piloting, lasted 12 seconds and covered
120 feet (37 meters). By 1905 the
Wright brothers had improved their
plane to the point that it could fly 24
miles (39 kilometers) in 38 minutes.
During WorldWar I (1914–18) airplanes
began to change the nature of
war. Planes were first used to observe the
enemy from the air. Eventually countries
discovered that they could use planes for
dropping bombs. Pilots also learned to
shoot at each other in the sky.
