reservoir for the wet-sump system is either the
accessory gear case or a sump mounted to the
The dry-sump system is the most common. In
bottom of the accessory gear case. This system
the dry-sump lubrication system, a tank located
is similar to your car's engine. In the wet-sump
in the airframe or mounted on the engine holds
oil system, the gearbox provides space for foam-
the oil. This type of system carries a larger oil
ing and heat expansion because the oil level only
supply, and an oil cooler is usually included to
partly fills the casing. Deaerators, in the gearbox,
control temperature. The lubrication design of the
remove oil from the air and vent the air outside.
engine may use either an air-oil or a fuel-
The main disadvantages of a wet-sump system
oil cooler. The axial-flow engines keep their
are as follows:
comparatively small diameter through a stream-
lined design of the oil tank and oil cooler. A dry-
1. The oil supply is limited by the sump
sump oil system is shown in figure 5-2.
2. It is hard to cool the oil. Oil temperatures
The hot tank system stores oil in the tank
are higher because the oil is continuously sub-
jected to the engine temperature.
before it is cooled. The oil tank is an integral part
of the accessory drive case. The other parts
3. The system is not adaptable to unusual
include the main oil pump, pump pressure-
flight altitudes, since the oil supply would flood
regulating valve, and main oil filter (fig. 5-3).
Figure 5-3.--Hot tank oil system.