Anti‐Vibration Mounting of Aircraft Power Plants: An Analysis of the Problems Associated with Turbojet, Turbo‐Propeller and Reciprocating Engines

Early aircraft engines were usually bolted direct to the aircraft structure and no attempt was made to prevent the vibrations which they set up from being transmitted to the airframe. With increasing engine powers and the use of larger airscrews these vibrations eventually become of sufficient magnitude in some cases to cause annoyance to the occupants of the aircraft and also failure by fatigue of parts of the structure. Various attempts were made both to analyse the source of the vibrations with a view to eliminating them or reducing them to an acceptable magnitude. Where this was not possible attempts were made to isolate the disturbances from the airframe and its occupants. This paper presents the basic theory of vibration isolation and gives an account of the various sources of vibration met with in reciprocating, turbo‐propeller and pure‐jet installations. The loads acting on the engine during various conditions of flight are then examined as a knowledge of these is required in order to determine the strength of the supporting units. Various practical engine mounting configurations are then considered which will give vibration isolation together with adequate support of the engine under all conditions of flight. Some account is given of the properties of rubber and the design and testing of rubber vibration isolators, and some installation problems are examined. Finally, the complete programme of testing an installation both on the test‐bed and inflight to evaluate the degree of vibration isolation achieved is described, together with various criteria of acceptability both from a structural and physiological standpoint. A bibliography covering the various sections is included.