Materials.
Wood, on account of its property of absorbing vibration, is particularly well suited for the construction of the engine mounting, and one finds examples of its use in a variety of ways. Perhaps the most common form is that in which a bearer of ash or spruce, channelled out between the fastening-down bolt holes for lightness, is attached to steel brackets which in turn are bolted to the various fuselage members. A development of this method consists of mounting the bearers on either multi-ply formers of wood, or built-up wood brackets stiffened with a three-ply covering on each side, and both of these arrangements are being extensively used. Sheet steel is used for the mountings of various machines, but it does not possess the characteristic of absorbing vibration. In some instances one finds that the engine has been specifically designed to be supported on bearers of the tubular variety, in either steel or duralumin; but here again rigidity is difficult of attainment. Although the use of welding, that is to any extent, is not advisable in the construction of the engine mounting, one finds this process very extensively used for the mountings of some modern machines. In one particular instance, the tubular bearers are supported from the steel tube fuselage by various tubes, the whole structure being welded, and although every joint successfully survived a smash which resulted in a considerable bending and distortion of the fuselage, its use does not engender a sense of security or reliability.