FAA Powerplant Written Practice Test

What type of mounts are typically used on reciprocating engines to reduce vibration?

1. Rigid Mounts

2. Dyna-focal Mounts

3. Rubber Shock Mounts

4. Spring Mounted Supports

The correct answer is: Rubber Shock Mounts

Rubber shock mounts are commonly used on reciprocating engines to effectively dampen vibrations that can occur during operation. These mounts are designed to absorb and isolate the vibrations produced by the engine, minimizing the transmission of these vibrations to the airframe and consequently enhancing comfort and structural integrity. The inherent flexibility of rubber allows it to deform under load, which helps to absorb energy and reduce the amplitude of vibrations. In contrast, rigid mounts provide little to no vibration isolation, as they are designed to hold the engine in a fixed position without allowing any movement. This rigidity can lead to higher vibration transmission into the airframe. Dyna-focal mounts are engineered to provide some level of vibration isolation, but they are also critical in aligning the engine concerning the aircraft structure to maintain proper operational dynamics. While they do help, they do not provide the level of vibration dampening as effectively as rubber shock mounts. Spring mounted supports can also provide some level of absorption of vibrations, but they are generally more suited for larger engines or specific applications where large motions or displacements are expected. For typical use in reciprocating engines, rubber shock mounts remain the preferred choice due to their optimal balance of vibration damping, weight, and simplicity in design.