The Probert Encyclopaedia of Aircraft

TURBOPROP

A turboprop engine is a combination of propeller and jet engine. The main thrust comes from the propeller, with only a small proportion coming from the jet exhaust. A turboprop engine handles a larger airflow than other aircraft engines, and generally the largest thrust for any given rate of fuel consumption. At about 450 mph the efficiency of the propeller is seriously impaired, so turboprop engines are only suitable for lower speeds.
Research Turboprop