Page 156 - Understanding Flight

CH05_Anderson 7/25/01 8:58 AM Page 143

Airplane Propulsion 143

Fig. 5.21. The engine of a Boeing 777.

5.22 shows an example of a corporate turboprop airplane. A pro-
peller cannot be directly attached to this shaft from the turbines
because it turns at too high a speed. So a gearbox or reduction gear
is used to reduce the rotation speed to the propeller. At lower flight
speeds the propeller is more efficient than the fanjet. Since it has a
larger diameter, it gets its thrust from accelerating more air at a low
speed. This we know is the most efficient way to get propulsion.
Propellers become less efficient at high speeds because the effects
of compressibility, which will be covered in the next chapter, are
introduced. Special propellers have been designed to operate at
these higher speeds but have not seen use except on experimental
aircraft.
Turboprops are used on smaller commuter aircraft and have
found a growing market in smaller aircraft. They have also found a
growing use in the general-aviation and corporate airplane
Henry Ford tried to be a leader
market. Their big advantage is that they are able to produce
in airplane manufacturing. In
greater power than the equivalent piston-driven engine with
1927, the Ford Tri-motor became
much less noise and maintenance. Turboprop engines are
the first successful commercial
much lighter than piston engines of the same power but are
airplane.
also more expensive.