Aircraft Systems

the combustion chamber. The combustion chamber contains of the turboprop engine is normally available in the altitude the fuel inlet and igniter for combustion. The expanding range of 25,000 feet to the tropopause. [Figure 7-24] air drives a turbine, which is connected by a shaft to the compressor, sustaining engine operation. The accelerated Turbofan exhaust gases from the engine provide thrust. This is a basic Turbofans were developed to combine some of the best application of compressing air, igniting the fuel-air mixture, features of the turbojet and the turboprop. Turbofan engines producing power to self-sustain the engine operation, and are designed to create additional thrust by diverting a exhaust for propulsion. [Figure 7-23] secondary airflow around the combustion chamber. The turbofan bypass air generates increased thrust, cools the Turbojet engines are limited in range and endurance. They engine, and aids in exhaust noise suppression. This provides are also slow to respond to throttle applications at slow turbojet-type cruise speed and lower fuel consumption. compressor speeds. The inlet air that passes through a turbofan engine is usually Turboprop divided into two separate streams of air. One stream passes A turboprop engine is a turbine engine that drives a propeller through the engine core, while a second stream bypasses the through a reduction gear. The exhaust gases drive a power engine core. It is this bypass stream of air that is responsible turbine connected by a shaft that drives the reduction gear for the term “bypass engine.” A turbofan’s bypass ratio refers assembly. Reduction gearing is necessary in turboprop to the ratio of the mass airflow that passes through the fan engines because optimum propeller performance is achieved divided by the mass airflow that passes through the engine at much slower speeds than the engine’s operating rpm. core. [Figure 7-25] Turboprop engines are a compromise between turbojet engines and reciprocating powerplants. Turboprop engines Turboshaft are most efficient at speeds between 250 and 400 mph and The fourth common type of jet engine is the turboshaft. altitudes between 18,000 and 30,000 feet. They also perform [Figure 7-26] It delivers power to a shaft that drives well at the slow airspeeds required for takeoff and landing and something other than a propeller. The biggest difference are fuel efficient. The minimum specific fuel consumption between a turbojet and turboshaft engine is that on a Fuel injector Turbine Inlet Hot gases Compressor Combustion chamber Nozzle Figure 7-23. Turbojet engine. Gear box Compressor Combustion chamber Inlet Exhaust Prop Fuel injector Turbine Figure 7-24. Turboprop engine. 7-21