GB561940A - Improvements in or relating to flexible mounting systems applicable to mounting engines in aircraft - Google Patents

Abstract

561,940. Aircraft engine mountings. HIRST; A. J. July 27, 1942, No. 10490. [Class 4] A flexible mounting for an aircraft engine or other body subject to vibration and comprising a cantilever structure adapted to engage the body by elastic devices at two longitudinally spaced points on each side of its central vertical plane is characterised in that the elastic devices for the forward supports provide high stiffness in the vertical direction and low stiffness longitudinally, whereas the elastic devices for the rear supports provide high stiffness longiiudinally and low stiffness transversely of the mounting. The principal loads are thus taken substantially in the direction of high stiffness and produce little deflection while a high degree of flexibility is. provided for pitching and yawing movements. The mounting shown, for an in-line aircraft engine comprises a pair of triangulated structures ABCDF, A<1>B<1>C<1>D<1>F<1>, secured to the aircraft structure at CD, C<1>D<1>. The lines CD, C<1>D<1> may be vertical or may, as shown, be inclined. Elastic supports for the engine are provided at A, B, A<1>, B<1>. Those at A, A<1> may comprise inner and outer metal bushes vulcanized to a mass of rubber between them and connected respectively to the engine and to the structures ACD, A<1>C<1>D<1> so that low stiffness is provided in the longitudinal direction AB, A<1>B<1>, and high stiffness in transverse directions, while the supports at B, B<1> may each comprise a disc embedded in rubber in a cylindrical casing, spindles secured to the casing and to the disc being connected to the engine and to the structures ACD, A<1>C<1>D<1>. The supports B, B<1> have high stiffness in the direction of the axes of the spindles and low stiffness in directions transverse thereto and these axes are arranged in the plane containing the point of application H of the propeller thrust and the supports as shown in Fig. 3 and also converge inwardly so as to intersect at or near the centre of gravity G of the engine. The centre of gravity is arranged as near as possible to the vertical plane through the supports A, A<1>. Sufficient flexibility to allow of pitching and yawing which take place about horizontal and vertical axes through the centre of gravity G is thus provided for. Vertical weight and inertia loads are carried almost entirely on the supports A, A<1> and thus give rise to only small deflections. The propeller thrust at H is balanced by forces Q, R in the vertical planes through AB, A<1>B<1> and thus in directions of high stiffness. Side inertia loads act through the centre of gravity G and are balanced mainly, by forces along the lines from G to the supports B, B<1> and thus substantially in the direction of high stiffness. The torque reaction gives rise to vertical loads in opposite directions and these are taken mainly by the supports A, A<1> since the supports B, B<1> are highly flexible in this direction. If the lines CD, C<1>D<1> are inclined in opposite directions as shown these vertical loads apply moments acting in the same direction to the structures ACD, A<1>C<1>D<1> and apply a horizontal transverse force to the engine and this is counteracted mainly by forces taken by the supports B, B<1> substantially in the direction of high stiffness thereof. The mounting may be reversed to accommodate an inverted in-line engine and it may be cross-braced in plan, in which case the supports A, A<1> may be such as to provide high stiffness only in a vertical direction and low stiffness in all directions in a horizontal plane. The supports A, A<1> may give complete longitudinal freedom and may for this purpose comprise links or sliding joints.