Applied Science 851 



which he flies with his map. This is the simplest and most 

 accurate, but can only be used when the atmosphere is clear and 

 the ground beneath visible. The second method is to work out 

 the correct compass bearing before starting a flight, and then 

 proceed solely by means of compass guidance until the destina- 

 tion is reached. Unfortunately the currents of air tend to make 

 an aeroplane drift out of its course, so that the pilot flying on a 

 cempass course has occasionally to check his position by compar- 

 ing his map and the ground. The third and most up-to-date- 

 method is by wireless direction finding, by means of which signals 

 are sent out when requested by the pilot from one or more 

 ground stations and the direction of the currents marked by the 

 pilot on the map; the point where these lines intersect is his 

 position at the time. 



One serious problem which confronts the man who is likely 

 to use a private aeroplane is the question of aerodrome accommo- 

 dation. An aerodrome large enough to accommodate all types 

 of aircraft must have a minimum area of about sixty acres. 

 Needless to say, each man cannot have his own aerodrome, but 

 it is suggested that each village will have its own landing-ground 

 and that the users of private aeroplanes will proceed to the aero- 

 drome when they wish to fly. 



How an Aeroplane Flies 



The method by which an aeroplane flies is very similar to 

 that which maintains a kite in the air. A kite is pulled against 

 the wind by a string to get air pressure, the wind tending to 

 blow the kite away and the string to hold it back. The result 

 is that as long as the wind and the pull remain constant 

 the kite tends to rise. In an aeroplane the "string" which pulls 

 the kite is replaced by an air-screw. With a kite, if the 

 centre of the pressure is altered, it dips and swerves. In an 

 aeroplane a similar thing happens, causing the aeroplane to be 

 "bumped." Birds have this trouble also. Rooks landing 



