Multi-Engine Mountings.
Several versions of the type of machine employing two or more engines, and which, by the way, is regarded as being the type most suitable for the commercial purposes of the future, are existent. The usual arrangement with the twin-engined machine is to support the engines between the planes on either side of the body, the bearers being mounted on a structure of struts, which also serve as interplane supports.
With regard to the flying-boat type of machine, a favourite practice is to mount the motor on the four struts supporting the centre section of the upper plane, which is braced by struts and wires from different points on the hull or body.
Although the modern aircraft engine is of greatly increased power, compared with the engine of the period 1912–1914, one does not find any great difference in the structural features of the mounting employed, and in view of the very diverse arrangements for mounting the same type of engine which now exist, there is need for greater uniformity. With regard to the materials employed, there is a very pronounced trend towards the greater use of wood, which circumstance is certainly at variance with the oft-portended approaching era of steel. As indicated in previous chapters, wood possesses remarkable powers of resistance to sudden shock, which, combined with its quality of absorbing vibration, renders it peculiarly suitable for the structure of the aeroplane, and despite its numerous defects, will undoubtedly continue in use until either the available supplies of suitable timber are exhausted, or until the production of a remarkably light alloy possessing high strength values.
CHAPTER XV.
ERECTION AND ALIGNMENT.
The accurate erection and alignment or truing up of the aeroplane, is a cogent factor in ensuring that the best performance is obtained, and it is almost platitudinous to emphasize the fact that a machine incorrectly aligned gives inferior results in flight, entails greater attention on the part of the pilot, and may possibly seriously interfere with the general stability of the aeroplane. The degree of precision attained in the manufacture of the various components is reflected in the ease or otherwise with which the complete assembly is aligned; indeed, accuracy of erection is impossible without the close observance of limits and general trueness in the production of the different parts. For this reason the erection of the principal components is surveyed as a necessary preliminary to a consideration of their assembly in the complete structure.