and formed, by welding, into a cylinder. Two
scavenged oil path. There are two types. Both
bosses, located on the horizontal center plane, are
types have magnetized contact points to collect
provided for oil inlet and outlet connections. This
metal particles. When enough metal particles
type of cooler acts as an inlet air duct; therefore,
collect on the magnetized contacts, one type
a cooling effect occurs when the engine is
completes a circuit between the contacts. This
illuminates a warning light in the cockpit, advising
operating. The cooling capacity of each of the oil
the pilot of metal contamination. This indicates
cooler assemblies also depends upon the amount
that one of the engine gears, bearings, or other
of air allowed to pass through the cooler. Some
metal parts might have failed. The other chip
aircraft use a controllable oil cooler door, which
restricts the opening of the oil cooler exit duct.
detector gives no cockpit indication. It is removed
and inspected at regular intervals for metal
particles.
FUEL-OIL COOLERS.-- The fuel-oil cooler
or heat exchanger (fig. 5-13) cools the hot oil and
Oil Coolers
preheats the fuel for combustion. Fuel flow to the
engine must pass through the heat exchanger.
Oil coolers reduce the temperature of the oil
However, a thermostatic valve controls the oil
through either an air-oil or a fuel-oil type cooler.
flow, so the oil may bypass the cooler if no cooling
These coolers keep the temperature of the oil
is needed. The fuel-oil heat exchanger consists of
within the proper range.
a series of joined tubes with an inlet and an outlet
port. The oil enters the inlet port, moves around
AIR-OIL COOLER.-- The air-oil type cooler
the fuel tubes, and goes out the oil outlet port.
(fig. 5-12) is installed at the entry end of the engine
as an integral part of the engine. This type of
The heat-exchanger type of cooler has the
advantage of allowing the engine to keep its small
cooler is usually an aircraft part conforming to
frontal area. Since the cooler is flat and mounted
the inlet duct design of the airframe. This
cooler is made of rectangular-sectioned aluminum
on the bottom side of the engine, it offers little
tubing, spirally wound between two end flanges
drag. This type of cooler is an engine part.
Figure 5-12.-Air-oil type of oil cooler.
5-14
