There are numerous hydraulic systems implemented in aircraft for providing safety and comfort for occupants. Wheel brakes, autopilot system, landing gear, gun turrets, etc., are critical hydraulic aircraft applications. For delivering maximum functionality, most of the components used are lightweight. Therefore, the aircraft hydraulic system for any application will vary depending on the aircraft size and application complexity. The benefit of hydraulics includes the generation of high pressure or power using the minimum volume of fluid. Also, maximum safety and comparatively fewer maintenance requirements are other features of the hydraulic system.
Every hydraulic system will include different hydraulic components integrated and here mentioned are the significant components in aircraft hydraulic systems.
Hydraulic Fluid: Compared with that of industrial fluids, the aircraft hydraulic fluids are relatively thin, and the fluid temperature will range between -65° to 275° F. In this mentioned temperature range, most of the mineral oils or water will freeze or boil. MIL-H-5606, MIL-H-83282, Skydrol™, MIL-H-87257, and Hyjet™ are some commonly used aircraft hydraulic fluids. The preferred properties of aircraft fluid include high flash point, lubricant properties, low freezing point, high boiling point, adequate viscosity, anti-corrosiveness, and thermal capacity/conductivity. If these fluid properties are not maintained properly, it can cause serious threats to system performance.
Hydraulic Pump: The aircraft hydraulic system can be operated at a pressure ranging from 3000 to 5000 psi. The hydraulic pumps are used for pressurizing the fluid from the reservoir. Gear pumps, fixed displacement piston pump, and variable displacement piston pump are usually used in aircraft. With a gear pump, a fixed volume of fluid will be transferred in every rotation. Manual, electric, engine driven, ram air turbine(RAT), pneumatic, or hydraulic are the different power sources for operating this hydraulic pump.
Hydraulic Cylinders: Hydraulic cylinder, also known as a linear hydraulic actuator, is used to apply reversible force. Depending on the applied hydraulic pressure, the piston rod will move linearly within a cylindrical barrel. The hydraulic cylinder working will be based on the pilot’s control inputs.
Hydraulic Motor: Hydraulic motor can convert hydraulic pressure into rotational motion and powerful torque. This mechanical device is used to drive jackscrews.
Hydraulic Plumbing: The aircraft hydraulic plumbing system will include different components that help for facilitating the flow of hydraulic fluid throughout the system. Aircraft hydraulic circuits are mostly open-loop, and the plumping circuit will manage all task starting from drawing fluid from a reservoir and then returning it to the reservoir. Reservoir, hydraulic fuses, control valves, shut off valves, accumulators, pressure relief valves, etc., will be located in the plumbing circuit.
All the above mentioned are the essential hydraulic components in aircraft hydraulic system. But, except these, there are other components like heat exchangers, seals, fittings, and more to control the generated heat and prevent contamination and leakages.