JET ENGINES
Turboprop Engine
Small airliners and most charter planes are powered by turboprops. A turboprop engine is a jet engine attached to a propeller with better propulsion efficiency than the turbojet. Rotation of the propeller develops a high thrust power with a low fuel consumption at low altitudes. There are mainly two exhaust streams. One is at high pressure generating a high velocity around the engine and the other is at a high temperature generating another high velocity internally. The total thrust is the sum of the two velocities (outlet velocity minus the inlet) times the very large rate of air flowing through each section. This engine is restricted to smaller aircraft with speeds below 500 miles per hour because of the aerodynamics along the propeller blades. Velocities across the blade increase from the hub to the tip. If flight speeds are too high, the velocities may go supersonic near the tip, separating the flow and shocks may form, decreasing effective air flow. The figure below illustrates the design of a turboprop engine.