About Turbo Prop Aircraft
The propeller is coupled to the turbine through a reduction gear that converts the high RPM, low torque output to low RPM, high torque. The Turbo Prop itself is normally a constant speed (variable pitch) type similar to that used with larger reciprocating aircraft engines. Turboprop engines are generally used on small subsonic aircraft, but some aircraft outfitted with turboprops have cruising speeds in excess of 575 mph. Turbo Prop aircraft are most efficient at flight speeds below 450 mph because the jet velocity of the propeller is relatively low. The most common application of turboprop engines in civilian aviation is in small commuter aircraft, where their greater power and reliability than reciprocating engines offsets their higher initial cost and fuel consumption. Turboprop airliners now operate at near the same speed as small turbofan-powered aircraft but burn two-thirds of the fuel per passenger. However, compared to a turbojet (which can fly at high altitude for enhanced speed and fuel efficiency) a propeller aircraft has a much lower ceiling. Turboprop-powered aircraft have become popular for bush airplanes such as the Cessna Caravan and Quest Kodiak as jet fuel is easier to obtain in remote areas than is aviation-grade gasoline (avgas).