What Are Aircraft Hydraulic Actuators?

To operate heavy, flight-pertinent machinery such as landing gear and main steam system valves, aircraft rely on the hydraulic system. With a hydraulic system, a small volume of fluids may be utilized to transfer high amounts of pressure and force. This is due to the incompressibility of fluids, allowing for force to be equally transferred throughout the fluid as according to Pascal’s law of hydraulics. For hydraulics to be successfully operated, they require the use of aircraft actuators.

Actuators, in their most basic form, are components that are used to move and control a system. In regards to the aircraft fluid system, actuators are used to turn fluid pressure into a mechanical force, providing linear motion for a mechanism or object. Although there are a variety of aircraft hydraulic actuator parts available, the piston type proves to be the most common. Piston aircraft actuators typically consist of a piston, cylinder, spring, stem, and hydraulic supply and return line. Within the cylinder of the actuator, the piston may move vertically, and it divides the cylinder into two sections. In one section, hydraulic oil is kept, connecting to the hydraulic supply and return line. In the upper section, the spring is placed.

With the supply and return line, hydraulic fluids are supplied to the chamber, and the stem is then used to transmit piston motion to the valve. When there is no pressure within the cylinder, the valve is held closed by the spring. As fluid begins to enter the cylinder, the spring is forced to compress, opening the valve as pressure increases. The opposite is true as well, as when fluids exit the system, the spring’s force overtakes that of the fluid pressure and closes the valve. To control opening and closing to a needed degree, the amount of fluid within aircraft hydraulic actuator parts may be adjusted.

As compared to pneumatic actuators, which are also common to many aircraft, hydraulic aircraft actuators present various advantages and disadvantages. As compared to pneumatic actuators, hydraulic actuators benefit high force applications much better. This is due to the fact that hydraulic actuators provide for 25 times the produced force of a pneumatic cylinder that is the same size. Actuators are also capable of holding specific force and torque constants even while more fluid is not supplied to the cylinder. Lastly, hydraulic aircraft pipes and motors may be placed farther away from operational areas due to a minimal loss in power.

Despite their advantages, hydraulic actuators are surpassed by the pneumatic actuator in some other facets. For one, hydraulics have the chance of leaking fluids, thus resulting in a decrease in efficiency. With leaking, damages may occur to nearby components as well. Hydraulic actuators also require more parts, thus increasing their complexity and sometimes maintenance needs. Lastly, hydraulic systems are heavier than pneumatic systems due to their fluid and construction. Nevertheless, their immense power remains very beneficial for many aircraft for important operations that require high amounts of force.


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