orifice which provides the proper oil flow at all engine operating
speeds. The oil is supplied from the oil pressure pump through
tubing and internal passageways to the spray jets, where the oil is
sprayed on the bearing surfaces.
Gas turbine engine oil systems perform three major functions.
They clean and reduce friction, and they cool and dissipate heat.
They also clean the engine interior through the use of oil filters
and strainers. Because much of the aircraft powerplant consists of
one metal surface sliding or rolling over another. Friction causes
heating of parts, excessive wearing, and useless expenditure of
tanks, pressure pumps, scavenger pumps, filter, oil coolers, and
spray oil jets. The system most widely used on turbine engines is
the dry sump lubrication system which uses a separate or external oil
tank, located near the engine.
The two kinds of pumps are pressure pumps and scavenge pumps,
the first to put oil into the system, and the second to collect oil
from the system. Filters remove foreign matter from the oil, and
either a fuel oilcooler or an air cooler takes the heat out of it.
Oil is sprayed on the bearing surface by spray jets.
Gas turbine ignition systems fall into three general types:
first, the induction type, that produces high tension voltage by
conventional induction coils; second, the capacitor type that causes
ignition by means of high energy and very high temperature sparks
produced by a condenser discharge; and a third type of ignition
system, not widely adopted, that uses a glow plug.
Most ignition systems used on Army aircraft are of the high
energy capacitor type. This system has been accepted for gas turbine
engines because it produces high voltage and an exceptionally hot
spark, and the high voltage covers a large area.
The tachometer is one of the cockpit instruments described
briefly in this section. Others are indicating systems for torque,
engine oil pressure, engine oil temperature, exhaust gas temperature,
and fuel pressure.