Model Aircraft Glossary

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Hand-Launch

To start a model in flight by releasing it or throwing it from the hand.

Hang Angle

The angular difference between the longitudinal reference line through the fuselage centre and the level horizon when the (rotary wing) model is suspended by the rotor centre.

Heading Hold

This describes a type of Gyro which senses rotation, and maintains direction. This is accomplished by sensing the rate of motion, and the time of motion, then compensating for the distance. While this sounds complicated, the effect is that if you have the model dialed in, and point the nose north, with a heading hold gyro on the yaw axis the model will continue to face north until you command it to yaw.

Height Velocity Diagram

The combinations of altitude and airspeed from which structural damage to the helicopter will occur in case of a power failure. Also called the dead man′s curve.

Helicopter

An aircraft that can rise or descend vertically, by means of large overhead power-driven rotor or rotors.

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High Lift Wing

A wing designed to produce a greater lifting force than a conventional wing. This is often achieved at the penalty of drag.

Hinge

There are many ways of constructing a hinge for the ailerons, rudder and elevator control surfaces. A number of the different methods are described here along with the pro's and con's of each.

Hingeless Rotor

A rotor with no mechanical hinges.

History of Flight

See: Chronology of Flight.

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Horizontal Stabilizer

The horizontal tail surface at the back of the fuselage (more commonly called an elevator) which provides aerodynamic pitch stability to the airplane.

Horsepower Loading

The ratio of gross wieght to horsepower, obtained by dividing the total weight by the engine′s horsepower rating.

Hovering in Ground Effect

Maintaining a fixed position over a spot on the surface that compresses a cushion of high - density air between the main rotor and the surface and thus increases the lift produced by the main rotor. Normally the main rotor must be within one - half rotor diameter to the surface in order to produce an efficient ground effect.

Hovering Out of Ground Effect

Maintaining a fixed position over a spot on the surface at some altitude above the surface at which no additional lift is obtained from ground effect.

Hunting

The tendency of a blade, due to coriolis effect, to seek a position ahead of or behind that would be determined by centrifugal force alone.

Hypersonic

Speeds above mach 6.

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Hypervelocity

A range of speed that is about 12 times or more the speed of sound in air.

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