speed of the engine is equal to the rearward speed of the jet. It is
this low efficiency at takeoff and at low cruising speed (i.e., 400
mph) that makes the turbojet engine unsuitable for use in Army
aircraft. The propeller does not lack efficiency at low speed; the
reverse is true, in that efficiency falls off at high speed. The
result is to harness the jet engine's gas stream energy to drive a
propeller or helicopter rotor system, thereby taking advantage of the
best features of both.
Aircraft reciprocating engines operate on the fourstroke,
fiveevent principle. Four strokes of the piston, two up and two
down, are required to provide one power impulse to the crankshaft.
Five events take place during these four strokes: the intake,
compression, ignition, power, and exhaust events. These events must
take place in the cylinder in the sequence given for the engine to