1.12.
ADVANTAGES OF TURBINE ENGINES
Keeping in mind the basic theory of turbine engines, compare
the advantages and disadvantages of the turbine engine with the
piston or reciprocating engine. The advantages are covered in the
subparagraphs below, and disadvantages are discussed in paragraph
1.13.
a. Powertoweight ratio. Turbine engines have a higher
powertoweight ratio than reciprocating engines. An example of this
is the T55Ll11. It weighs approximately 650 pounds and delivers 3,
750 shaft horsepower. The powertoweight ratio for this engine is
5.60 shp per pound, where the average reciprocating engine has a
powertoweight ratio of approximately .67 shp per pound.
b. Less maintenance. Maintenance per hour of operation is
especially important in military operations. Turbine engines require
less maintenance per flying hour than reciprocating engines generally
do. As an aircraft maintenance officer, this advantage will appeal
to you because of a greater aircraft availability and lower
maintenance hour to flying hour ratio. The turbine engine also has
fewer moving parts than a reciprocating engine; this is also an
advantage over the reciprocating engine.
c. Less drag. Because of the design, the turbine engine has
a smaller frontal area than the reciprocating engine. A
reciprocating engine requires a large frontal area which causes a
great deal of drag on the aircraft. Turbine engines are more
streamlined in design, causing less drag. Figure 1.6 shows one of
the two nacelles that contain reciprocating engines in the old CH37
cargo helicopter. Figure 1.7 shows the smaller frontal area of the
turbine engines that power the CH47 Chinook helicopter. Because of
this, the engine nacelles are more streamlined in design, causing
less drag.
d. Cold weather starting. The turbine engine does not
require any oil dilution or preheating of the engine before starting.
Also, once started, the reciprocating engine takes a long time to
warm up to operating temperatures, whereas the turbine engine starts
readily and is up to operating temperature immediately.
e. Low oil consumption. The turbine engine, in general, has
a lower rate of oil consumption than the reciprocating engine. The
turbine engine does not require the oil reservoir capacity to be as
large as the reciprocating engine's; because of this, a weight and
economy factor is an additional advantage.
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