Aircraft Hydraulic System Components & Function

Have you ever wondered how an enormous aircraft effortlessly raises the landing gear it uses, turns along its runway, or manages their flight areas? The answer lies in a complex web of pumps, pipes, and actuators which is the hydraulic system of the aircraft.

Instead of being just a convenience, hydraulics are silent machines which provide the massive power accuracy, precision, and reliability crucial for safe and effective flight. Without these even the most sophisticated aircraft could be nothing more than the glider.

What is an Aircraft Hydraulic System?

In essence the aircraft hydraulics system can be described as a closed loop system that utilizes an incompressible liquid (hydraulic fluid) under pressure to transfer energy. The underlying principle that is known by the name of Pascal's Law, states that the pressure applied to a closed fluid is transmitted without diminishing. The result is that a tiny force applied to a tiny area to produce a massive force across the larger area.

Imagine it as the plane's nervous and muscular system..

Key Components and Their Vital Functions

Let's take a look at the most important elements to make it work:

1. Hydraulic Fluid: The Lifeblood

function: This is the medium used to transmit power. Fluids for aircraft hydraulics are specially designed synthetic liquids, usually either purple or red, made to:

• It is incompressible at high pressure.

• Operate in extreme temperatures.

• Refrain from corrosion and foaming.

• Help to provide Lubrication for moving parts.

• Fireproof properties.

2. Hydraulic Pumps: The Heartbeat

Funktion: These generate the pressure and flow within the system.

• Engine-Driven pumps (EDP): The main source directly powered by engines of the aircraft.

• Electric Motor Pumps (EMP): Provide backup power to ground operations or emergency situations.

• PTUs (Power Transfer Units (PTU): Importantly, they move hydraulic power between one unit to the next (e.g. for example, from the green system to the yellow-colored system) with no mixing of the fluids. This is often you can hear an clear "barking" sound that is heard on the surface!

3. Reservoirs: The Storage Tanks

function: Stores the hydraulic fluid.

• They compensate for fluid volume changes due to thermal expansion/contraction.

• They have filters that ensure that the fluid is clean.

• Certain pumps have been under pressure (often through bleeding in air) for steady flow of air to the pumps and to prevent the cavitation (formation by the formation of bubbles in air).

4. Accumulators: The Shock Absorbers & Surge Tanks

function: These are gas-charged (typically nitrogen) units that

• Conserve hydraulic energy during times that are not in high demand.

• Reduce the pressure of surges (like an absorber for shocks).

• It is important to provide backup power in the event that the main pump is not working.

• Compensation for leaks that are small in the system.

5. Filters: The Purity Guardians

function: Crucial for system endurance.

• Eliminate the contaminants (metal particles dirt, degradation products, etc.) in the water to avoid damage to valves, pumps and actuators.

6. Selector/Control Valves: The Traffic Cops

function: Direct the flow of hydraulic fluid to the desired actuators.

• They're usually controlled by electricity (solenoid valves) and allow fluid to either retract or extend an element (e.g. the landing gear down or up).

7. Actuators (Cylinders & Motors): The Muscles

Funktion: Convert hydraulic pressure into mechanical motion.

• Hydraulic Cylinders: Linear actuators that push or pull components (e.g., landing gear extension/retraction, flap deployment, braking).

• Hydraulic Motors Motors that rotate that spin parts (e.g. motors that power high-lift devices or thrust reversers such as slats).

8. Lines, Hoses, and Fittings: The Arteries & Veins

function: Connect all the components, and transmit liquid throughout the plane.

• Made of high-strength material (e.g. titanium, stainless steel or specially-designed flexible hoses) to withstand extreme temperatures and pressures.

Where is Hydraulic Power Used on an Aircraft?

Aircraft hydraulic systems support many vital tasks:

• Flight Controls Ailerons and elevators and rudders. Also, spoilers, rudders flaps, and slats that allow the pilot to control the plane.

• Landing gear: Extension and retract as well as steering of the nose wheel.

• Brakes Pressuring the brakes of the wheel to stop it.

• Thrust Reversers Utilizing the mechanism to slow down the aircraft following landing.

• Cargo Doors & Ramps: Opening and closing doors that are heavy

Why Hydraulics Over Electric or Mechanical?

While modern aircraft incorporate more electric systems, hydraulics remain indispensable due to:

• Immense Power: Unmatched force generation for heavy loads (e.g., landing gear, large flight surfaces).

• Fine Control allows for extremely precise and precise movements.

• Redundancy and Reliability Aircraft generally include multiple hydraulic systems independent of each other (e.g. Green Blue, Yellow, or Red Systems for Airbus) Airbus) in order to make sure that failure of one system does not affect vital functions.

• Simple force transmission: It's easier to transfer high force over long distances using fluid rather than complex mechanical linkages, or powerful electric motors.