Sage-Tips

How efficient are turboprop engines?

Compared to turbofans, turboprops are most efficient at flight speeds below 725 km/h (450 mph; 390 knots) because the jet velocity of the propeller (and exhaust) is relatively low. Modern turboprop airliners operate at nearly the same speed as small regional jet airliners but burn two-thirds of the fuel per passenger.

Are turbo props more efficient?

The turboprop engine is more fuel efficient especially at low altitudes and lower air speeds. The main disadvantage of turboprop engines is that they lose the ability to make thrust at high speeds because the propellor blade tips begin to go transonic at high RPM reducing their efficiency.

How fast does a turbo prop spin?

The high pressure compressor and turbines of an airliner engine will run at above ten thousand RPM, while the propeller of a large turboprop engine wants to run at about 1700 to 2200 RPM, and in case of the NK-12 of the Tu-95 the propellers run at only 750 RPM.

What is the maximum speed of a prop fan engine?

Propellers lose efficiency as aircraft speed increases, so turboprops are normally not used on high-speed aircraft above Mach 0.6-0.7. However, propfan engines, which are very similar to turboprop engines, can cruise at flight speeds approaching Mach 0.75.

Why are turboprops more efficient than turbofan engines?

At medium and low altitudes, the turboprops are more efficient engines. Since all flights start and end at low altitudes, the high altitude cruise segment needs to be long enough for the turbofan engine to offset it’s disadvantage during start and landing.

How high can turboprops fly?

As a result, most turboprops are limited to Mach 0.5 to 0.6, and altitudes in the 35,000 foot range, with a handful of turboprops reaching the Mach 0.7 and 40,000 feet. These aircraft use complex propeller designs and massive engines; but still operated well below the Mach 0.9+ and 50,000 foot altitudes turbofans are capable of achieving.

Why do turboprops use constant-speed propellers?

To maintain propeller efficiency across a wide range of airspeeds, turboprops use constant-speed (variable-pitch) propellers. The blades of a constant-speed propeller increase pitch as aircraft speed increases. Another benefit of this type of propeller is that it can also be used to generate reverse thrust to reduce stopping distance on the runway.