It’s a question that many people ask, especially those new to private aviation: What is the difference between a turboprop and a jet?
In technical terms, it all comes down to the engine. Which type of engine does the aircraft have? In a turboprop (short for turbo propeller) engine, the gases produced by the output of the turbine engine drive a propeller, which in turn generates the aircraft’s power. If it has a jet engine, the exhaust gases generate a direct power called ‘thrust’.
Visually you can see the difference if you look at them side-by-side on a runway: The turboprop will have obvious propellers on the outside of the aircraft. But it’s certainly not true to say that propeller aircraft are slow or inferior to a jet.
There are many types of flight when turboprop aircraft are ideal, such as short and regional flights. They are more fuel-efficient and therefore more cost-effective than a jet aircraft. They can also be very high tech and fast. The Beechcraft King Air is best example of this – the world’s most successful turboprop can seat between 7 and 11 people in different configurations, and many have a VIP interior to rival luxury jets.
What are the advantages of a turboprop aircraft?
What are the advantages of a jet aircraft?
More power and speed
Less engine noise
There are a number of different turbine based engines that all fall into the general category of jet engines. They all use the same fuel which is mostly diesel oil. Indeed diesel engines will run very happily on jet fuel. Turbojet engines (the first type of jets in general use) operate exclusively by compressing air, adding burning fuel, and using turbines to turn the compressor blades. This was a revolutionary "External combustion" engine which changed aviation forever. They burn prodigious quantities of fuel to produce huge levels of thrust.
Fan jet engines take the turbojet concept and add blades that push air around the outside of the engine to generate more thrust. They are more efficient than straight turbojet engines and have, for the most part, completely replaced turbojet engines in aviation use.
Turboprop engines (AKA turboshaft engines) use the same basic turbine arrangement as a turbojet engine but are optimized to generate torque on a central shaft instead of maximizing thrust generated by the air/fuel flow in the engine. The shaft is connect to an otherwise normal propeller to provide most of the thrust to make an aircraft fly. In the case of helicopters the same type of engine is used to turn the main rotors and provide lift. These engines produce generally less power than fan jet engines but are much more efficient while producing this lower level of power. Airplanes powered with turboprop engines go significantly faster than planes with propellers powered by reciprocating engines but not as fast as pure jet aircraft. Operating costs for turboprop planes are often one tenth the costs for turbojet powered planes.
Turboprop airplanes are generally used for shorter length flights than pure jets. They are efficient at lower altitudes and lower airspeeds than pure jets. They are generally smaller in terms of seats and cargo capacity but have a wide range of sizes from a few seats to perhaps a hundred. Turboprops also can operate from shorter runways than pure jets with similar payload capacities. That means they are ideal for some military applications where the C-130 has been a work horse for many decades.
Today nearly all helicopters are powered by turboshaft engines. They provide more power than can be generated by reciprocating engines of similar weight. These are the ideal engines to use for larger helicopters.