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All About Aircraft Hydraulic Systems

Hydraulic systems are a common and often essential element of modern aviation design, such equipment serving to provide the necessary power to operate various aircraft components. While many aircraft have long relied on mechanical and pneumatic systems for actuation, the importance of aircraft hydraulic systems lies in their ability to provide high power and reliability while being lightweight and compact. In this blog, we will explore the general makeup of aircraft hydraulic systems and how they are used in flight operations.

What Are Aircraft Hydraulic Systems?

In their most basic form, hydraulic systems are simply apparatuses that harness the properties of compressed fluids to transmit power. When featured on an aircraft, hydraulics promote efficient actuation and operation of various aircraft parts, including landing gear, brakes, and flight control surfaces. These systems rely on hydraulic pumps and other assembly components to generate pressure, that of which is then used to move fluid through hydraulic lines to various parts of the aircraft.

When it comes to the specific makeup of an aircraft hydraulic system, the exact parts and components present may vary based on the type of aircraft and its specific application. Nevertheless, there are a number of parts that are considered fundamental to aircraft hydraulic systems, and these include:

  1. Hydraulic Reservoirs: The hydraulic reservoir stores the hydraulic fluids used to transmit power throughout systems. Typically, the size of the reservoir will be based on the size of the aircraft itself. For optimization, the reservoir will not hold more fluid than is necessary for operations, and bleed air may be used for pressurization to avoid any risk of hydraulic pump cavitation.
  2. Hydraulic Pumps: The hydraulic pumps of a hydraulic system are what generate pressure within the assembly. These pumps are most commonly engine-driven or electrically-driven, though other types do exist. For example, manual hydraulic pumps are common on light aircraft for expanding and retracting flaps and wheel brakes, and other aircraft may feature pneumatic pumps.
  3. Hydraulic Lines: In order for hydraulic fluids to be transmitted from the pumps to other various aircraft parts, hydraulic lines are used. These lines often vary in construction, some being rigid metal lines while other aircraft utilize flexible materials.
  4. Hydraulic Actuators: In order for the pressure of fluids to be harnessed for work to be carried out, hydraulic actuators are necessary. These devices convert hydraulic pressure into mechanical force, allowing for landing gear, brakes, and flight control systems to be moved as necessary.
  5. Hydraulic Valves: The valves of an aircraft hydraulic system can often be considered some of the most pivotal parts of operations, serving as the components that control the flow of hydraulic fluids throughout the entire system. Depending on the section of the hydraulic system and the processes being carried out, there are a number of valves that may be present. Generally, some of the most notable types include shut-off valves, control valves, and pressure relief valves.

How Are Aircraft Hydraulic Systems Used for Flight Operations?

While we have provided a brief overview of the most common elements of a typical aircraft hydraulic system, it is important to know how they actually carry out their operations for various aircraft parts. One of the most important uses of the hydraulic system is to operate flight control surfaces, those of which manage the aircraft’s attitude and direction of flight. These surfaces include ailerons, elevators, and the rudder.

The ailerons of the aircraft are situated on the trailing edge of the wings, and they allow a pilot to control roll motion. When a pilot moves the control column situated in the cockpit to the right, the aileron on the right wing will move up, while the one on the left will move down. The opposite occurs when the control column is moved left, and this process allows for lift to be created for rolling. With the aircraft hydraulic system, ailerons can be adjusted with ease while not requiring much physical exertion from the pilot.

The same general process is true for other flight control surfaces as well, the hydraulic system permitting easy management and control from the cockpit. While the forces provided by hydraulics are powerful, such systems are also highly reliable and efficient, furthering their overall benefit for flight operations. Nevertheless, hydraulic systems can fail, so many aircraft utilize redundant features to guarantee safety.

For example, multiple pressure sources may be used to maintain fluid pressure, meaning that a manual pump or other device may be present alongside more typical electric pumps. While these redundant systems can be used in the instance of a failure, they also offer increased capability when extra pressure is required. Devices known as Ram Air Turbines (RAT) are also common backups, and they can offer electrical power for various operations to be carried out.

Aircraft Hydraulic System Maintenance

Like most other aircraft parts or systems, all hydraulic components and assemblies must be inspected and maintained on a regular basis to ensure safety and operational efficiency. The frequency of carrying out inspections and maintenance will depend on the type of aircraft, its usage, and manufacturer recommendations. Most often, aircraft hydraulic systems are inspected during routine maintenance checks, and maintenance personnel will look for contamination, leaks, physical damage, or other problems. When any issue is detected, repairs or replacements will be made to ensure that the system is functioning correctly.


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June 22, 2022

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