How an Aeroplane Works

New Zealand Herald, Volume LXXVII, Issue 23618, 30 March 1940, Page 5 (Supplement)

How an Aeroplane Works

Mr. Frank Coiton has written for the "Schoolmaster" an article on "The Aeroplane—How It Works." It is dosigned to help teachers in their explanations to boys and girls, but we quote it because we are sure that many "grown ups" will be interested, too. EFOEE describing the action |~j of the wings and motor of an aeroplane there is one point that must be fully appreciated ; that is, that air under certain conditions can behave quite differently from still air, so differently that we must think about it a little. "Seeing an aeroplane rise for the first time makes one wonder how such a heavy vehicle can leave the ground and fly through a medium that seems so unsubstantial. No such wonder is expressed when one sees a yacht under sail, because we are familiar with its motive power, the wind. Both aeroplane and yacht, however, depend upon the action of air in compression and rarefaction. Let us examine the propertics of air under these conditions. If the outlet hole of a garden syringe is sealed and the plunger is depressed we compress the air enclosed within the barrel, and find that the plunger tends to resist the movement made to push it down. Motor and Wings "Now if we withdraw the plunger we find that as soon as the air begins to rarefy the plunger again resists movement, it is pulled into the syringe. For our purpose we can say that coinpressed air 'pushes' and rarefied air 'pulls,' and we shall see how these forces lift the aeroplane. "The most important parts of the aeroplane are its motor and wings. The motor pulls the wings and, of course, the rest of the aeroplane through the air, and it is the action of the air upon the wings that lifts the aeroplane. "The motor drives the propeller, or, to give it its more correct name, the 'airscrew,' and this is very similar in action to a woodscrew. When a woodscrew is driven with a screwdriver every turn of the screw causes it to enter farther into the wood. Similarly, the airscrew moves forward through tho air, because it is indeed a screw. "The thread on the woodscrew is set at a slight angle, and this angle determines the 'pitch' of the screw. The pitch is the distance moved forward by the screw during each revolution, and in wood this can easily be measured as the distance between two adjacent threads. The blades of the airscrew are algo set at an angle; this angle similarly determines the pitch of the airscrew.

"This is, however, difficult to measure in air, as there is a certain amount of 'slip' or lost movement. So that wo see that the rapidly revolving airscrew moves through the air and carries the rest of the aeroplane along with it. "The wings are affixed to the body, or 'fuselage,' of the aeroplane at a

slight angle, the front, or 'leading,' edges being slightly higher than the rear, or 'trailing,' edges. As the wing rushes forward, the leading edge meets the air and splits it into two streams, one over tho wing and the other underneath it.

"Because of the angle at which the wings are set the air passing beneath the wings is compressed, having to occupy a smaller space. That passing over the wing must occupv a larger space, and to do this it must become less dense, or rarefied. Method of Control "We therefore have compressed air beneath the wing and rarefied air above it, and from our knowledge of air under these conditions we can understand that the compressed air 'pushes' the wing upwards and the rarefied air 'pulls' it upwards, so lifting the wings and the aeroplane. It is of interest to note that the greater part of the lift is done by tho upper surface of the wing. "Apart from the regulation of the motor speed it is necessary, of course, to steer the aeroplane, and this is done by tho ailerons, elevator and rudder. "Although each has a separate duty to perform, it must be appreciated that the movement of any one of them has an effect on the others. "The ailerons are movable portions of the wings capable of being raised or lowered by means of the 'joystick.' Their movement alters the section of the wings, and by working in opposite directions, one 011 each wing, cause the aeroplane to tilt sideways, or 'bank.' In turning right or loft they are used in combination with the rudder, which directs the 'plane just as the rudder on a ship directs the ship.

"The rudder is connected to the rudder bar, which is foot-operated. Just as the rudder steers the aeroplane right and left, so does tho elevator causo the aeroplane to climb or descend; in fact, the rudder and elevator change places when the aeroplane is flying on its side and the elevator is used as a rudder, and vice versa.

"Even a. small aeroplane must carry a number of instruments to enable the pilot to feel sure that the engine is working correctly, and to keep to a planned course without danger. Oil and petrol gauges show the oil pressure in the engine and the quantity of petrol in the fuel tank, and a revolution counter shows tho speed of the engine.

"11l the centre of the dash hoard is the air speed indicator, and this must not he confused with a. speedometer in the normal sense, as the pilot must make various allowances for head and following winds. Height above sea-level is shown on the altimeter; more modern 'planes have an instrument to show the height of the aeroplane above the land directly beneath. "On Even Keel" "The level is a- modification of the ordinary spirit level and serves the same purpose, showing whether the 'plane is 011 an even keel or otherwise; it also helps the pilot to control the ailerons when banking for a turn. Directly in front of the joystick, which controls ailerons and elevator, is the compass by which the ship is held to its course. The engine speed is regulated by the throttle lexers situated on the left of the cockpit. "In multi-cngined aeroplanes and flying boats there are many more necessary instruments, as well as wireless transmitting and receiving equipment."