A mounting strut for an aircraft engine suspended from a wing or from a side of an aircraft's fuselage must be capable of supporting the torque and axial loads generated by the engine, and in addition, isolate the fuselage and passenger section of the aircraft from shock and vibration produced by the engine. Several different approaches have been developed in the prior art to accomplish these functions. For example, a prior art assembly used for mounting turbine and low bypass turbo fan jet propulsion engines to an aircraft includes a shock absorbing mount structure attached either to the turbine casing or to the turbine and fan casing of the engine; a nacelle structure is then rigidly attached to the shock mounting structure. This approach requires that a relatively complex vibration shock mounting structure and seals be used to provide for the relative movement between the engine and the nacelle. In another approach, the engine is shock mounted within a relatively heavy load bearing nacelle structure, and the nacelle is rigidly attached to the fuselage by a strut.
A mounting arrangement developed for attaching a high bypass turbo fan jet engine to an aircraft fuselage is shown in U.S. Pat. No. 4,044,973. This engine mount uses dual beam structural yokes that extend around a portion of the periphery of the fan casing and are affixed to the fuselage. Both yokes are enclosed in an aerodynamic fairing and are attached to the turbo fan casing by elastomeric shock mounts.
None of the prior engine mounting designs is well adapted for use in mounting unducted fan (prop fan) engines to the aft sides of an aircraft fuselage. Prop fan engines must be mounted in a manner that permits large deflections between the engine and the supporting structure, so that low frequency vibrations caused by fan blade imbalance are isolated in the vertical, axial and lateral directions. In addition, since the center of gravity of the prop fan engine and nacelle assembly is near the extreme aft end of the supporting structure, the mount system must be capable of distributing the vertical, lateral and torque loads forward along the longitudinal length of the engine assembly. It is also desirable that the engine mount system has a relatively thin cross section. The supporting strut that extends between the fuselage and the prop fan engine should be lightweight and aerodynamic to avoid excessive drag. Prior art engine mounts do not permit sufficient decoupling of vertical, lateral and torque loads for use in mounting a prop fan engine, and would require a relatively heavy strut having an excessive cross-sectional thickness to carry the off-center loading characteristic of a prop fan engine.