The applied science of hydraulics has been a part of human ingenuity since ancient times. From irrigation to dams, humans have established the utilization of the forces of water pressure for applications such as transmission, generation, and control of power. In the realm of aviation, the aircraft hydraulic system has been an integral facet of aircraft in-flight functions since the 1920’s. Over time, the uses of hydraulic power and aircraft hydraulic system components have steadily increased due to their cost-effectiveness, reliability, and capabilities. In this blog, we will discuss the basics of the aircraft hydraulic system, what components they help power, as well as their advantages.
The aircraft hydraulic system, as with all hydraulic systems, follows the science of Pascal’s law. This law states that with a confined, incompressible fluid, if pressure is changed at any point, the change is also reflected throughout the rest of the fluid. Pascal’s law describes the idea of power transfer through compressed liquids that are used for aircraft systems. To put it in perspective, when the pilot activates a flight control device or actuator, such as disc brakes, pumps begin to exert pressure on the compressed hydraulic liquids. This pressure is then transferred to pistons which squeeze the brake discs together to slow down the rotation of the wheels. When the opposite effect is desired, pressure can be released from the system, allowing pressure to return to previous levels.
The first aircraft hydraulic system components featured on aircraft were the brakes and landing gear during the 1920’s and 1930’s. Over the next decade, hydraulic systems began to be used for other components, such as wing flaps and other flight control surfaces. In the 1960’s, capabilities of the aircraft hydraulic system increased with the introduction of variable displacement piston pumps which allowed for an increase or decrease of fluid output depending on the needs of the system. This is compared to fixed displacement piston pumps which only move a specific amount of fluid. Gear pumps are another type of hydraulic pump, allowing for fixed displacement within low pressure systems. To power these various types of pumps, the aircraft can use manual, engine driven, electric, pneumatic, hydraulic, or ram air turbine power.
To reap the benefits of hydraulic system components, motors or cylinders use the pressurized liquids for conducting mechanical processes. A hydraulic motor is a device that uses fluid pressure to create rotation, angular displacement, and torque. Aircraft systems that utilize the hydraulic motor include flaps, trims, and other components. The hydraulic cylinder, on the other hand, utilizes hydraulic forces to create a single directional force that can be reversed. Hydraulic cylinders within an aircraft hydraulic system aid with the control of landing gear, cargo bay doors, and various flight control surfaces.
Altogether, there are many advantages of hydraulic system powered components. Aircraft hydraulic system components are very reliable, cheap to install, and very dependable for efficient operation and control. Due to their simplistic properties of operation, there are not many moving parts within a hydraulic system, lessening the amount of possible mechanical failures. As compared to similar systems, such as pneumatic and electric systems, hydraulics present less of a risk for fires and other damages. Hydraulics also have the benefit of incompressibility, which is a problem that pneumatic systems may face. Vegetable, mineral, and synthetic type fluids are the standards for hydraulic systems, each having their own properties and benefits. Lastly, hydraulics are very efficient and quick acting, allowing for commands to be actuated quickly and precisely, increasing reliability and safety of systems.
Despite the advantages and benefits that hydraulic systems bring for aircraft, they are still prone to failures and issues, creating the need to be regularly inspected and maintained. Over time during use, hydraulic systems can begin to overheat, surpassing their maximum operating temperatures and must be cooled or deenergized. Systems may also lose their pressure if there is a failure of a pump, or fluid is lost. This can result in systems and controls not functioning, and thus hydraulic pressure should always be checked and maintained to ensure safe operation. Lastly, contamination of the hydraulic fluids could occur if servicing is not conducted regularly for the system, or a component undergoes failure. Contamination poses the risk of damage and failure of a hydraulic system if left unchecked. Ensuring that your aircraft hydraulic system components are regularly maintained is always the best way to keep them operating with great efficiency.
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