Aircraft that use
propellers as their prime propulsion device constitute a historically important subset of aircraft, despite inherent limitations to their speed. Aircraft powered by piston engines get virtually all of their thrust from the propeller driven by the engine. A few piston engined aircraft derive some thrust from the engine's exhaust gases, and there are certain hybrid types like the
Motorjet that use a piston engine to drive the compressor of a jet engine, which supplies the primary thrust (although some types also have a propeller powered by the piston engine for low speed efficiency). All aircraft prior to
World War II (except for a tiny number of early
jet aircraft and
rocket aircraft) used
piston engines to drive propellers, so all
Flight airspeed records prior to 1944 were necessarily set by propeller-driven aircraft. Rapid advances in first
liquid-fueled rocket engine-powered aircraft – with
a record set in October 1941 by a German example — and
axial-flow jet engine technology during World War II meant that no propeller-driven aircraft would ever again hold an absolute air speed record. Shock wave formation in propeller-driven aircraft at speeds near
sonic conditions, impose limits not encountered in
jet aircraft. Jet engines, particularly
turbojets, are a type of
gas turbine configured such that most of the work available results from the thrust of the hot exhaust gases. Turbofans, both the
high-bypass versions used in all modern commercial
jetliners, and the low-bypass versions in most modern military aircraft, produce a combination of jet thrust from the exhaust of burnt fuel, and air thrust from what amounts to an internal propeller. High-bypass turbofan engines achieve most of their thrust from a fan driving air backwards through the engine casing, and driven by a gas turbine, which also contributes jet thrust via its exhaust. The two are in one large engine casing with the fan (propeller) at the front and the jet engine behind, with both turbine exhaust and fan-driven air exiting the rear of the engine casing.
Turboprop engines are similar, but use an external propeller rather than an internal fan (propeller) inside an engine casing. The hot exhaust gas from a turboprop engine gives a small amount of thrust, however the propeller is the main source of thrust. ==Turboprops==