DISCOVERY 



309 



stability, and — most important of all — economy in 

 operation and upkeep. This has naturally meant a 

 considerable change in the attitude of mind of those who 

 had during five years of war become accustomed to 

 attack the problem of design from the point of view of 

 fighting requirements. 



For some time after civil flying became permissible in 

 the summer of 1919, the vast majority of machines used 

 were war-types roughly adapted for passenger-carr^^ng, 

 by the enlargement, for instance, of the observer's 

 cockpit to take two passengers, with the addition of a 

 hinged cover to pro\-ide protection from the weather. 

 This could not last for long, as it was obviously bad 

 •economy to employ an engine of 350 h. p. or more to 

 carry two passengers. Actually the first machine de- 

 signed specially for commercial work was a biplane 

 produced by the British Aerial Transport Company and 

 known as the " B.A.T. F.K.26"type. It was fitted 

 with a 375 h.p. Rolls-Royce engine and carried four pas- 

 sengers in a comfortable cabin immediately behind the 

 engine, the pilot sitting in a cockpit in the upper part of 

 the fuselage towards the tail. The advantage of this 

 arrangement, which was followed for a time by other 

 •designers, was that it provided a comparatively easy 

 solution of a somewhat difficult problem. It will be 

 obvious, on a little reflection, that the fore-and-aft 

 balance of an aeroplane may be very considerably 

 affected by a variation in the weight carried at different 

 points along the length. This difficulty can be over- 

 come to some extent by altering the setting of the angle 

 of the tail plane so as to change the attitude at which 

 the machine will fly. At the same time it is clear that 

 the difference between the weight of a cabin when 

 empty and when containing a full complement of four 

 passengers (weighing altogether about 800 lbs.) must 

 considerably affect the pilot's power of control. This 

 problem is solved if such passenger accommodation can 

 be concentrated at the centre of gravity (or position of 

 fore-and-aft balance) of the machine ; and that is 

 the reason for the placing of the cabin in the B.A.T. 

 machine at this point, with the pilot far back to balance 

 the weight of the engine in front. Another important 

 feature of this machine was that the control move- 

 ments of the pilot's lever were transferred to the ele- 

 vators and rudder by means of rods in place of the usual 

 cable. An interesting commentary on this innovation, 

 which has not been followed to any great extent, 

 occurs in the report of the Committee on Safety and 

 Economy in Commercial Fhnng, appointed by the 

 Royal Aeronautical Society last year, which called atten- 

 tion to the fact that the renewal of frayed control cables 

 was found to be one of the heaviest items in the upkeep 

 of commercial aeroplanes. The disadvantage of having 

 the pilot so far towards the rear of the machine is that 

 his view on coming down to land is obscured by the 



cabin in front of him. Accordingly this practice, which 

 was widely adopted at one time, has gradually been 

 abandoned, and most of the latest types have the pilot's 

 seat as near as possible to the nose of the machine in 

 order that he may have the best possible view in all 

 directions. Experience and careful attention to detail 

 design has rendered it possible for this to be done and 

 still to retain the passenger accommodation compara- 

 tively close to the centre of gravity ; although it is 

 sometimes necessary to provide ballast where there is 

 not a full complement of passengers. It is interesting 

 to note, here, that many of the two-seater observation 

 machines used during the war were almost uncontrol- 

 lable if the observer's cockpit — which was situated in 

 rear of that of the pilot — were empty, unless the place 

 was filled by a bag of ballast. WTien this was not done, 

 the machine tended to get its nose down (owing to the 



riG. I.— DU H.WILL-^XD MOXOPI,.\NE- 

 Showiug absence of bracing wires owing to cantilever construction. 



weight of the engine not being counteracted) into a 

 dive from which it could not be pulled out. 



The main difficulty which had to be faced by the 

 commercial aeroplane designer was the production of a 

 machine which would carry an economic load of passen- 

 gers — which was found to be not less than six or 

 eight — with a reasonable engine-power. At first there 

 was nothing between the converted single-engined war- 

 type referred to above capable of carrying a couple 

 of passengers, and the big twin-engined ex-bombing 

 machine, which had its fuselage made into a cabin to 

 accommodate ten or a dozen travellers. In the one 

 case the horse-power was usually 350-375, while in the 

 latter it totalled 700-750. We have already seen how 

 the B.A.T. machine doubled the earning capacity of 

 the first type. Further progress in this direction was 

 much assisted through the production by the Napier 

 Motor Company of their 450 h.p. " Lion " engine, 

 which is at the present time almost a standard fitting 

 in British commercial machines. This made a con- 

 siderable advance on any engine that had existed 



