A glider is a special kind of
aircraft
that has no engine.
There are many different types of gliders.
Paper airplanes
are the simplest gliders to build and fly.
Balsa wood or styrofoam toy gliders are an inexpensive
vehicle for students to
have fun
while learning the basics of
aerodynamics.
Hang-gliders are piloted aircraft having
cloth wings and minimal structure. Some hang-gliders
look like piloted
kites,
while others resemble maneuverable parachutes.
Sailplanes are piloted gliders that
have standard aircraft parts, construction, and
flight control systems, but no engine.
The
Space Shuttle
returns to earth as a glider; the rocket engines are used only
during liftoff.
Even the Wright Brothers
gained piloting experience through a series of
glider flights
from 1900 to 1903.
In flight, a glider has
three forces
acting on it
as compared to the
four forces
that act on a powered aircraft.
Both types of aircraft are subjected to the forces of
lift,
drag, and
weight.
The powered aircraft has an engine that generates
thrust, while the glider has
no thrust.
In order for a glider to fly, it must generate lift
to oppose its weight. To
generate
lift, a glider must move through the air.
The motion of a
glider through the air also generates drag. In a powered aircraft, the
thrust
from the engine opposes drag, but a glider has no
engine to generate thrust. With the
drag unopposed,
a glider quickly slows down until it can no longer
generate enough lift to oppose the weight, and it then falls to earth.
So how does a glider generate the velocity needed for
flight?
For paper airplanes and balsa gliders, the aircraft is given an initial
velocity by throwing the aircraft. Some larger balsa gliders employ a
catapult made from rubber bands and a tow line to provide velocity and
some initial altitude. Hang-glider pilots often run and jump off the side of a
hill or cliff to get going. Some hang-gliders and most sailplanes are
towed aloft by a powered aircraft and then cut loose to begin the glide.
The powered aircraft that pulls the glider aloft gives the glider a
certain amount of potential energy.
The glider can
trade the potential energy difference from a higher altitude to a
lower altitude to produce kinetic energy, which means velocity.
Gliders are always descending
relative to the air in
which they are flying.
How do gliders stay aloft for hours if they constantly
descend?
The answer is that they are designed to be very
efficient, to descend very slowly. If the pilot can locate a
pocket of air that is rising faster than the glider is descending,
the glider can actually gain altitude, increasing its potential
energy. Pockets of rising air are called
updrafts. Updrafts are found when a wind blowing at a hill or
mountain has to rise to climb over it.
Updrafts can also be found over dark
land masses that
absorb heat
from the sun.
The heat from the ground warms the surrounding air, which
causes the air to rise. Rising pockets of hot air are called
thermals. Large gliding birds, such as owls and hawks, are
often seen circling inside a thermal to gain altitude without
flapping their wings. Gliders do exactly the same thing.
Activities:
Guided Tours
-
Forces on a Glider:
-
Gliding Flight:
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