The word “hydraulics” is derived from the Greek word for water and originally referred to the study of the behavior of water at rest and in motion. Today, the term has been expanded to include the behavior of all liquids, including hydraulic fluid. Hydraulic systems have long been used in aviation. Early aircraft incorporated simple hydraulic brake systems, but as aircraft design evolved and became more sophisticated, hydraulic power systems were developed to operate many aircraft components.
Hydraulic systems provide a reliable means of transmitting power to operate aircraft components. Landing gear, flaps, flight control surfaces, and braking systems commonly rely on hydraulic power. The complexity of these systems varies widely depending on the aircraft. Small aircraft may use hydraulic fluid only for brake operation, while large transport aircraft employ highly complex hydraulic systems designed to operate numerous subsystems simultaneously.
To ensure reliability and redundancy, large aircraft often use multiple hydraulic subsystems. Each subsystem typically includes a pump, reservoir, accumulator, heat exchanger, filters, and control valves. Operating pressures vary significantly, ranging from a few hundred pounds per square inch (psi) in small aircraft and rotorcraft to as high as 5,000 psi in modern large transport aircraft.
Hydraulic systems offer several advantages for aircraft power transmission. They provide high power with relatively lightweight components, allow flexible installation throughout the aircraft structure, and require relatively simple maintenance. Because hydraulic fluid transmits force efficiently, these systems operate with minimal energy loss, making them highly effective for operating critical aircraft mechanisms.
Aircraft Hydraulic and Pneumatic Systems Series
1. Hydraulic Fluids
Learn about the fluids used in aircraft hydraulic systems and their essential properties.
View Topic →2. Types of Hydraulic Fluids
Explore different hydraulic fluid types and their specific applications in aircraft systems.
View Topic →3. Basic and Hydraulic Power Systems
Understand the fundamentals of hydraulic systems and how they operate in aircraft.
View Topic →4. Hydraulic System Components
An overview of major components used in aircraft hydraulic systems.
View Topic →5. Hydraulic Filters
Learn how filters protect hydraulic systems from contamination and damage.
View Topic →6. Hydraulic Pumps
Explore the different types of pumps used to generate hydraulic pressure.
View Topic →7. Hydraulic Valves
Understand how valves control the direction, pressure, and flow of hydraulic fluid.
View Topic →8. Hydraulic Accumulators
Learn how accumulators store hydraulic energy and stabilize system pressure.
View Topic →9. Heat Exchangers
Explore how hydraulic heat exchangers regulate fluid temperature.
View Topic →10. Hydraulic Actuators
Understand actuators and how they convert hydraulic energy into mechanical motion.
View Topic →11. Power Transfer Unit (PTU)
Learn how PTUs transfer hydraulic power between aircraft systems.
View Topic →12. Ram Air Turbine & Hydraulic Motor-Driven Generator
Explore emergency power devices used to supply hydraulic or electrical power.
View Topic →13. Hydraulic Seals
Understand the importance of seals in preventing hydraulic leaks and maintaining pressure.
View Topic →14. Large Aircraft Hydraulic Systems
An overview of complex hydraulic systems used in large transport aircraft.
View Topic →15. Aircraft Pneumatic Systems
Learn about pneumatic systems and their applications in aircraft operations.
View Topic →