6 - Engines and transmissions

Abstract

This chapter focuses on the choice of power plant in a helicopter, along with the operating principles of piston and turbine engines and associated transmissions. The power source of a conventional helicopter must be able to drive a shaft, and have reasonable weight and fuel consumption in relation to the power delivered. All internal combustion engines work by burning fuel in air. This raises the temperature, causing expansion that can do work. In practice, more power can be obtained if the air is compressed before the fuel burns. The turbine engine has dominated the helicopter power plant market for some time. Piston engines do not provide uniform torque because of the power impulses when each cylinder fires, and it is necessary to have some flexibility in the transmission to even out the power delivery. As helicopters become larger, heavier, and faster, the forces necessary to control the rotor head become too great for the pilot to manage reasonably, and some form of power operation is necessary. If stability augmentation or autopilot functions are required, powered controls will also be needed so that the control information can fly the machine.