5.2.3: Hydraulic system

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Hydraulic systems have been used since the early 30s and still nowadays play an important role in modern airliners. The basic function of the aircraft hydraulic system is to provide the required power to hydraulic consumers, such for instance: primary flight controls (ailerons, rudder, and elevator); secondary flight controls (flaps, slats, and spoilers); other systems, such landing gear system (extension and retraction, braking, steering, etc.), or door opening, etc.

The main advantages of hydraulic systems are:

relative low weight in comparison with the required force to apply; • simplicity in the installation;
low maintenance;
high efficiency with low losses, just due to liquid friction.

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Figure 5.17: Aircraft hydraulic system: aileron actuator and landing gear actuator.

The main components of a hydraulic system are:

a source of energy (any of the sources of the electrical system, i.e., engine driven alternator, APU, RAT);
a reservoir or tanks to store the hydraulic fluid;
a filter to maintain clean the hydraulic fluid;
a mean of storing energy such as an accumulator (high density fluid tank);
pipeline manifold (pipe or chamber branching into several openings);
pumps (engine driven or electric), pipes, and valves;
a mechanism for hydraulic oil cooling;
pressure and temperature sensors;
actuators (actuate mechanically on the device).