Bob Molholm, age 11, of Manhattan, Kan., for his question:
WHAT MAKES A GLIDER STAY IN THE AIR?
A glider is an aircraft that looks like an airplane but doesn't have an engine. Both gliders and airplanes stay in the air by flying fast enough for the pressure of the air moving around their wings to produce an upward force.
An airplane's engine or propellers provide a thrust that gives the plane enough speed to take off and fly. But a glider doesn't have power, so it must depend on other means for flight.
A glider is usually launched by being towed into the air by an airplane and then released. Level flight cannot be sustained without a motor so a glider pilot must keep the nose of his aircraft pointed just below the horizon and glide downward through the air.
As a glider is being pointed downward, the force of gravity produces the speed necessary for the glider to remain the air.
Gliders can soar upward, even though they are always pointed slightly downward. They can gain altitude rapidly by flying in air currents that rise faster than the plane sinks.
Most gliders have wings, body and a tail assembly. These three parts have streamlined designs that enable a glider to knife through the air with just a minimum amount of drag, or air resistance.
Reduction of drag gives a glider a high glide ratio. Glide ratio is the relationship between forward and downward motion. A typical glider used for recreation has a glide ratio of about 25. This means that for every mile of altitude lost, it can fly 25 times as far forward.
A high performance glider has a glide ratio of 30 or more. A glider made for competition flying may have a glide ratio or more than 40.
Narrow wings on a glider help to reduce the drag at the glider's wing tips.
The body, or fuselage, of a glider extends from the nose to the tail and gradually narrows toward the rear. In some gliders, the canopy covering the cockpit follows the lines of the fuselage so smoothly that the pilot must lie back while flying.
Gliders are usually made of materials that can be sanded to a smooth finish, such as aluminum, fiberglass or wood.
A glider's tail assembly, or empennage, consists of a horizontal stabilizer and elevator and a vertical fin and rudder. The elevator is hinged to the stabilizer and is raised or lowered by the pilot by means of a control stick in the cockpit. The pilot moves the rudder to the right or left by means of pedals.