FLIGHT 



32C1 



FL-IGHT 



FLIGHT: IN THEORY AND PRACTICE 



J. Laurence Pritchard, Editor, The Aeronautical Journal 



In this article are described the main underlying principles that 



have made possible the conquest of the air. For the history of flight 



and aviation consult Aeronautics. See also Aeroplane; Airship; 



and the articles on the various types of machine 



particular angle at which the wings 

 are set. If the speed of the aero- 

 plane is increased, then the angle of 

 the wings must be altered to satisfy 

 this principle. The curved wing 

 has the great advantage over the 

 flat wing that its resistance is 

 Though for many centuries freedom to alter the shape of its relatively much smaller at the 

 attempts have been made to dis- wings as the bird has. In place of usual flying speeds, 

 cover the principles of flight, it was flapping wings we find the airscrew, There is one important aspect of 

 not till Langley in America made and a vertical fin and rudder for mechanical flight which is rela- 

 his experiments on a scientific basis steerage and control purposes, not tively unimportant in bird flight, 

 in 1890-1900 that any real ad- observable in the bird. But the and that is flying at great heights. 



aeroplane has flown to a 

 eight of 5 m., and the conditions 



An aeroplane flies as a result of of flight at such a height, where the 



through the air at a certain angle, the support given to it by its mercury stands at 10 ins. instead 

 and at a certain speed. He an- wings when the latter are being of 30 ins., are very different from 



driven through the air. As the those on the ground. Here another 

 aeroplane moves forward, the principle is enunciated, namely at 



vance was made. Langley showed principles of bird flight and human An 

 that a flat plate of material could flight remain identical. heis 



be made to support itself if forced 



nounced that a weight of 750 Ib. 

 could be lifted by an engine of 25 



h.p. The experiments of Lilienthal wings, owing to their curved shape, the same altitude and speed of 



drive downwards flight of the aeroplane the air force 



the air through is proportional to the air density, 



which they pass. The problem is further complicated 



Galled by Lord by the fact that the power of an 



Rayleigh the engine decreases more rapidly than 



" sacrificial " prin- the density of the atmosphere, 

 ciple, this prin- The general laws of flight are 



ciple of flight is an simple, but their detailed applica- 



expression of the cations often present insuperable 



fact that if you do theoretical difficulties which can 



not want to fall only be solved by experiment on 



yourself you must model or full-sized aeroplanes. In 



make something steady horizontal flight the lifting 



else fall. It is the force on the wings is equal to the 



constant falling of total weight of the aeroplane, in 



Flight. Diagram of the forces acting on an aeroplane 

 in horizontal flight. T, the thrust of the propeller ; 

 L, the lift on the wings ; W, the weight of the aeroplane ; 

 D, the resistance or drag ; and P, the force on the tail 

 plane to maintain equilibrium 



and others added that curved sur- the air, as it were, which gives climbing flight it is greater, and in 

 faces were better than flat ones for that support necessary for flight to diving flight it is less. These are 

 flying purposes. 



the aeroplane. Exactly how the air simple laws, but to calculate 



Air resists the rapid passage of is made to move downwards by the exactly how much greater the 



any body through it, and this re- curved wings of an aeroplane is a lifting force is under certain con- 



sistance is proportionately less, matter of experiment, the theo- ditions, in order to find out how 



compared with lifting-power, in retical solution of the problem being fast an aeroplane will climb, is not 



beyond the power of present-day nearly so simple. The calculations 



mathematics. 



certain curved surfaces than n 

 flat surfaces. But though the sur- 

 face was discovered, the next step 



are complicated by the varying 

 It was early discovered that the density of the atmosphere and 



forward, that of the discovery of air is forced downwards in a way consequent varying efficiency of the 

 the engine which could force it depending upon the angle at which engine. The solution of these corn- 

 through the air at the necessary the wings are set 



speed, remained in abeyance till to the air, and 

 the invention of the petrol engine, also the speed at 



which they are 



though Sir Hiram Maxim actually 



lifted 10,000 Ib. off the ground, forced through the 



using a steam engine. With the air. With the 



advent of the internal combustion wings set at any 



engine and the experiments result- particular angle it 



ing in the present-day curved or was found that 



cambered wing, flying became the lifting power 



possible. increases as the 



The study of the flight of birds square of the 



has had a marked result on the speed. But with 



ultimate methods of flight adopted the increase of 



by man, with certain differences speed there natur- 



largely due to mechanical difficul- ally comes in- 



ties. The aeroplane has its wings crease of resist - 



and balancing tail, and a certain ance to forward 



motion, requiring increased plications depends upon a very 

 engine power to overcome it, large number of experiments car- 

 and, therefore, increased ried out in the wind tunnels at the 

 weight, so complicating the National Physical Laboratory, and 

 problem. The principle which practical flying experiments at the 

 may be stated here is that in Royal Aircraft Establishment and 

 any given aeroplane there is at Martlesham, as well as corre- 

 only one speed of flying for a sponding experiments in America, 



Flight. Diagram showing how the stream of air is 

 deflected by the curved wing, shown in section in 

 black, of an aeroplane. The air is forced downwards 

 at the rear or trailing edge of the wing, and a partial 

 vacuum is created above the wing with increased pres- 

 sure below it, so making it lift 



Flight. Diagram representing the difference 

 of air flow past a round body and a stream- 

 line body 



IK 4 



