Shaft Engines Turboprop, Turboshaft, and Propfan

Abstract

This chapter handles shaft-based aero engines. In Chap. 4 piston engines were analyzed while this chapter completes the family tree of shaft engines. Turboprop, turboshaft, and propfan engines are thoroughly analyzed. This engine family is concerned with output power rather than the thrust force. Thus specific power and powers specific fuel consumption are derived.

A short historical review for manufacturers of each engine is first given. Next, thermodynamic analysis of the operating cycle is given.

Turboprop engines power many bush, commuter, and heavy transport aircrafts flying at moderate subsonic speeds. Both single and double spool are examined. The engine is composed of two main parts, namely, gas turbine and propeller. Gearbox couples the propeller to the driving turbine. The exhaust gases leave the engine at very low speeds, and thus its share in power generated is around 15 %. The propeller develops the great share of power.

Turboshaft engines are employed in most helicopters, maritime applications, as well as some race cars. In both applications planetary gearbox is mostly used. Exhaust gases leave turboshaft engines at nearly zero speeds.

Propfan engines use a gas generator to drive an unshielded propeller like a turboprop, with a large number of short, highly twisted blades, similar to the fan of a turbofan engine. Propfan engines have the highest propulsive efficiency among all air-breathing engines including shaft-based, ram-based, and turbine-based engines.