R

Radius of action, or radius. The distance an airplane can fly and return to it's starting point.

Range. Maximum distance an aircraft can fly from takeoff until its fuel supply is exhausted.

Reaction engine. An engine, such as a. jet or rocket type, which derives thrust by its reaction to a substance ejected rearward.

Reciprocating engine. An engine which develops thrust by back-and-forth motion of pistons in cylinders to rotate a crankshaft.

Reduction gear. A gear assembly used to run a propeller or a rotor at a slower rate than the engine.

Relative wind. Flow of air with reference to an object passing through it.

Rendezvous. The meeting in flight of two or more aerospace vehicles at a planned time and place; also, the point in aerospace where the meeting occurs.

Rev, or rev up. To revolve or to increase the revolutions per minute of an engine.

Reversible-pitch propeller. A propeller whose blade angle can be changed to give reverse thrust for braking the airplane in landing.

Rocket. An engine which derives thrust from expulsion of hot gases and car- ries an oxidiser, making it independ- ent of atmosphere for combustion.

Roger. 1. A code word meaning "message received and understood." 2. An expression of agreement meaning "O. K." or "all right."

Roll. Rotation of an airplane about its longitudinal axis.

Run, or run up. To increase engine speed while the aircraft is standing still to check or to warm up the engine.