TURBOPROP ENGINES AND PROPELLERS
After completing this chapter, you will be able to:
Recognize the principles of turboprop
Recognize power lever movement through the
operation and identify the major com-
alpha and beta ranges, and the effects of those
ponents of the turboprop engine.
movements on the propeller.
Identify the propeller designation system,
Recognize the procedures and cautions used
operating principles, and basic propeller parts.
in the removal, cleaning, and reinstallation of
Recognize propeller operating principles.
the propeller assembly and subassemblies.
more complicated and heavier than a turbojet
There are a variety of turboprop aircraft in
the Navy inventory. The C-130 Hercules, a cargo
engine of equal size and power. The turboprop
delivers more thrust at low subsonic airspeeds.
transport aircraft, is the workhorse of naval
This advantage decreases as flight speed increases.
aviation. The E-2 Hawkeye is the fleet's airborne
In normal cruising speed ranges, the propulsive
early warning aircraft. The C-2 Greyhound is a
fleet logistics support aircraft. The P-3 Orion is
efficiency of a turboprop decreases as speed
increases. In a turbojet, the propulsive efficiency
our fleet antisubmarine warfare (ASW) aircraft.
increases as speed increases. The ability of a
See figure 8-1.
propeller to accelerate a large mass of air at low
In this chapter, the T56 engine and the
airspeed results in the unusual high performance
54H60-77 model propeller are examples of a
of a turboprop during takeoff and climb. This
common turboshaft engine and propeller system.
low-speed performance also enables a turboprop
There are differences in the turboprop aircraft
aircraft to carry heavier payloads, making them
mentioned above, but the basic operation,
ideal cargo aircraft. At about Mach 1 airspeed,
assemblies, and maintenance are similar.
the turboprop engine can deliver more thrust than
The turboprop engine section of this chapter
the turbojet engine of the same gas turbine design.
discusses the operating principles, parts, and
For a given amount of thrust, the turboprop
systems unique to turboprop engines. After
engine requires a smaller gas turbine with lower
learning about the turboprop engine, we will
fuel consumption than the turbojet engine.
discuss propellers. The propeller section describes
The turboprop engine produces thrust in-
basic propeller parts, operating principles, and
directly through the propeller. A characteristic of
the turboprop is that changes in power do not
change engine speed. Changes in power change
the turbine inlet temperature (TIT). During flight,
the propeller maintains a constant 100-percent
engine speed. This speed is the design speed where
If the exhaust gases from the basic part of a
power and maximum efficiency is obtained.
turbojet rotates an additional turbine that drives
Changes in fuel flow affect power changes. An
a propeller through a speed-reducing system, it
increase in fuel flow causes an increase in turbine
is a turboprop engine. The aircraft turboprop is