FAA Powerplant Written Practice Test

What type of engine are most modern airliners fitted with to fly in the .8 mach speed range?

1. Piston engines

2. Turbojet engines

3. Turbofan engines

4. Rockets

The correct answer is: Turbofan engines

Most modern airliners are equipped with turbofan engines to operate efficiently within the .8 Mach speed range. Turbofan engines are designed with a large fan at the front, which allows them to generate significant thrust while also being fuel-efficient. This makes them particularly suitable for subsonic flight, where airliners typically operate. Turbofans produce thrust by mixing high-speed jet exhaust with slower-moving air from the fan, leading to a higher overall bypass ratio. This design contributes to a quieter operation and lower specific fuel consumption compared to turbojet engines, which are less efficient at subsonic speeds due to their design focus on producing maximum thrust at higher speeds. In comparison, piston engines are generally used for smaller aircraft and are not designed to achieve the speeds required for commercial airliners. Turbojet engines have largely been replaced by turbofans in commercial aviation due to their inefficiency at subsonic speeds and higher noise levels. Rockets, while capable of very high speeds, are suited for space travel and not typically used for commercial aviation scenarios. Thus, turbofan engines are the optimal choice for modern airliners flying in the typical range of .8 Mach.