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Aviation History
1915
1915 - 0090.PDF
THE AIRCRAFT MANUFACTURING CO.'S NEW GUN-CARRYING BIPLANE. PROBABLY no other type of aeroplane presents greater difficulties and more complex problems to be solved than does the propeller or " pusher " type, and when a new machine of this class is produced one may be per fectly certain that the reason for its appearance is not that the design of a pusher offers a short cut to success, but' that there is a demand existing for a machine of this type for special purposes. The reasons which make the design of a propeller biplane a matter of great difficulty may not be immediately apparent, but they are very real, and some may be briefly referred to. In the first place, there is a question of side areas which must be carefully proportioned if spiral instability is to be avoided. A very deep nacelle, while possessing the advantage of pro tecting the occupants against the rush of air, and at the same time giving a better stream-line, necessitates larger vertical surface in the tail-fin and rudder. Large vertical surfaces for a given weight again necessitate very careful arrangement of these surfaces in relation to the centre of gravity, which latter must of course also be in its proper keep them from overheating, and this arrangement will partly spoil the stream-line form of the nacelle. Owing to the proximity of the tail planes to the propeller in an engine-behind machine, the effect of the slip stream on the former is a factor that cannot be neglected, and for which allowances must be made in the design and position of the tail planes. In our photographs is seen the new biplane designed by Mr. G. de Havilland, and built by the Aircraft Manu facturing Co., Ltd., which is an attempt to produce an aeroplane capable of being used as a fighting machine carrying a gun, and at the same time being reasonably stable and sufficiently fast to meet the requirements of the military authorities. Whether Mr. de Havilland has com pletely achieved his object the trials will show, but there can be no doubt that as an experiment the new machine gives promise of great possibilities. During its preliminary trials Mr. de Havilland flew it repeatedly with his hands off the controls, and when he did a turn, the machine automatically banked to the right degree for the speed Side view of the Aircraft Co.'s new biplane. 'Flight" Copyright position relatively to the main planes. Again, the shape of the nacelle enters very considerably into the question, as a nacelle having curved sides would obviously not have the same effect in a relative side-wind as one with per fectly flat sides of the same projected side area. By making the nacelle low the side area may be reduced, but then the difficulty enters of providing the necessary clearance between the ground and the pro peller, if the latter is to be kept of the desired diameter. This difficulty can, of course, be overcome by lengthening the struts of the under-carriage, but practical considera tions put a limit to the length it is advisable to make these members if extra head resistance and a " stilty " chassis are to be avoided. The arrangement of the engine in the rear of the nacelle is another problem which has to be dealt with. In order to make the nacelle of good stream-line form it should taper towards the rear, but where an air-cooled engine is used provision must at-the same time be made for at least a portion of the cylinders to receive the necessary amount of draught to and the radius of the curve. Thus there seems little doubt that the stability of the new biplane is all that can be desired in a machine that does not lay claim to being absolutely inherently stable. As regards speed, this has not been definitely deter mined yet, as the propeller fitted during the preliminary trials was not quite suitable, allowing the 70 h.p. Renault engine to run at much higher revolutions than those for which it is designed. Even under those unfavourable con ditions the machine showed a speed of over 70 m.p.h. as registered on the speed indicator, so that there is every reason to believe that when a suitable propeller has been fitted this figure will be considerably exceeded. This is distinctly good, especially as the machine was originally designed for an engine of 80 h.p. When landing the speed appeared to us to be quite low for so substantial a machine, although the designer did not at any time attempt to land it at its absolute minimum speed. In its general appearance the new gun-carrier is of very pleasing lines, and, as one expects from a firm of so 90
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