Why are many transport planes still propelled by old propellers?

Although these modern propeller planes still use traditional propellers, they are completely different from the old piston propeller planes before World War II. These propellers are not driven by reciprocating piston engine, but are all out-and-out turbine engines, which are much more powerful than the old-fashioned star piston aero-engines, and the power-to-weight ratio is much higher than the old-fashioned aero-engines, and it also has a special name called turboprop engine.

The turboprop engine is born out of the turbojet engine used in jet aircraft, but all the power generated by combustion is used to drive the power turbine to do work, and the propeller is driven by the gearbox.

Compared with jet engines, turboprop engines have many advantages. First of all, this kind of engine has high energy utilization rate and much less fuel consumption than jet engine. Secondly, this kind of engine has great pulling force, especially on the ground and at low altitude, and its propulsion force far exceeds that of jet engine. Another point is that this kind of engine can be equipped with an adjustable pitch propeller to achieve the effect of freely changing thrust or even reverse thrust, which is much more flexible than ordinary jet engines.

One advantage of turboprop engine is that it is not easy to swallow birds and inhale ground debris when working.

The obvious disadvantages of this kind of engine are slow flight speed and poor high altitude performance. As we all know, with the increase of altitude, the air will become thinner and thinner, and the efficiency of propeller running in thin air will decrease rapidly, which is one of the main reasons why planes on hump routes always crash during World War II. The air is too thin, and the working efficiency of the propeller is greatly reduced. If the plane wants to fly higher, it has to increase the power of the engine desperately. However, the engine power of those old transport planes in World War II was limited, and the high-altitude performance of the piston engine itself was also poor. In addition, the plane was desperately loaded with materials during the war, so that it was seriously overloaded and the flying height dropped more seriously. The plane was forced to hover in the Himalayas, and it was easy to crash when encountering some crosswinds and protruding peaks. After a general understanding of the performance characteristics, advantages and disadvantages of turboprop engines, it is not difficult to understand the designer's painstaking efforts by looking back at those turboprop conveyors.