A glider is a special kind of aircraft that has no engine.
Paper airplanes are the most obvious example, but gliders come a wide
range of sizes. Toy gliders, made of balsa wood or styrofoam, are an excellent
way for students to study the basics of
aerodynamics.
The Wright brothers perfected the design of the first airplane and
gained piloting experience through a series of
glider flights.
These aircraft were similar to modern **hang-gliders** and were
launched by running off a hill.

If a glider is in a **steady**
(constant velocity and no acceleration) descent, it loses altitude as
it travels. The glider's flight path is a simple straight line,
shown as the inclined red line in the figure. The flight path
intersects the ground at an angle "a" called the **glide angle**.
If we know the distance flown and the altitude change, we can
calculate the glide angle using trigonometry.
The tangent (tan) of the glide angle (a) is equal to the change in height (h)
divided by the distance flown (d).

If the glider is flown at a specified glide angle, the
trigonometric equation can be solved to determine how far the glider
can fly for a given change in altitude.
Notice that if the glide angle is small, the aircraft can fly a long distance
for a small change in altitude.
Conversely, if the glide is large
it can travel only a short distance for a given change in
altitude. We can think of the **glide angle** as a measure of the
flying efficiency of the glider. On
another page, we will show that the glide
angle is inversely related to the
lift to drag ratio. The smaller the glide angle,
the higher the lift to drag ratio.

Go to...

- Beginner's Guide Home Page

*byTom
Benson
Please send suggestions/corrections to: benson@grc.nasa.gov *