Applied Science 



is as follows. Though types vary in themselves all work on the 

 four-stroke or Otto cycle principle. The action of the engine 

 is divided into four operations, each operation occupying one 

 stroke of the piston. The first stroke sucks a mixture of petrol 

 gas and air into the cylinder, the second compresses the gas as 

 the piston moves up the cylinder. Just before the compression 

 is at its greatest, an electric spark, produced by a magneto, or 

 batteries, and conducted to the cylinder through a sparking plug, 

 explodes the compressed gas, and the expansion of the burnt 

 gas forces the piston down the cylinder again, the energy being 

 transmitted to a fly-wheel which keeps the revolutions regular. 

 The fourth action of the piston expels the burnt gas from the 

 cylinder. At the fifth stroke the cycle of operations recom- 

 mences. These strokes are called, in the order given above, the 

 induction or sucking-in stroke, the compression stroke, the igni- 

 tion or power-stroke, and the exhaust stroke. Aero-engines are 

 of three main types, stationary, radial, and rotating cylinder, gen- 

 erally called rotary. 



In rising, a pilot opens out his engine until the aeroplane 

 is moving across the ground at a sufficient speed ; he then gently 

 draws the control lever in towards him, and in so doing moves 

 the elevator which causes the aeroplane to rise into the air. 

 When sufficient height has been attained, a slight movement for- 

 ward of the control lever causes the aeroplane to flatten out and 

 fly on an even keel. When turning, the pilot simultaneously 

 presses his foot on the rudder bar, thus moving over the rudder, 

 and at the same time moves the control lever in the same direc- 

 tion. This movement of the control lever operates the ailerons 

 or wing-flaps, so that the aeroplane tilts up slightly on one wing- 

 tip, and is therefore able to turn more easily and more safely 

 than if it made a flat turn with the rudder alone. When the 

 turn has been made, the operations are reversed and the aero- 

 plane again brought on an even keel. To descend, the pilot 

 throttles back the engine, simultaneously pushing forward the 



