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What Is the Role of an Aircraft’s Hydraulic System?

With several tons of equipment constantly moving on an aircraft, it is a true feat of engineering that passengers experience a smooth flight. Aircraft accomplish this impressive undertaking with the aid of hydraulics, which is an efficient and easy way to transfer great amounts of force through a system. In this blog, we will discuss how hydraulic system in aircraft works to support smooth and safe operation.

Hydraulic systems were first described by the French physicist Blaise Pascal when he was completing his survey of fluid dynamics. He postulated that a closed system could be created in which pressure could be evenly distributed to all the walls of a container. In his famous eponymous equation, Pascal's principle, he proved that F1/A1=F2/A2. According to this principle, you could compress fluid in a closed system with minimal force and distribute a great amount of force at the other end of the system.

Engineers realized that they could harness the power of Pascal's principle early on in aviation history. In fact, some of the earliest braking systems on airplanes functioned using hydraulic systems. With the advent of commercial airline travel came newer performance demands that were met by implementing hydraulic systems to control nearly every movable part of the aircraft. Today's hydraulic systems consist of several components, including the reservoir, pipes, pumps, valves, fuses, actuators, and more.

The reservoir holds the hydraulic fluid and protects it from contamination. Most fluids used in modern aviation systems reare made from mineral oil because of its incompressible nature and biodegradability. Once the fluid has left the reservoir, it travels to other parts of the aircraft through hydraulic pipes, which are unique in their ability to withstand high and continuous pressure. Next, pumps accomplish the critical job of pushing on the fluid with a desired amount of force. Additionally, the complex network of valves in a hydraulic system performs several tasks, including controlling the amount of fluid in the system, preventing backflow, and stopping the fluid from moving in an emergency. Finally, filters are strategically placed at several spots in the hydraulic system and remove any potential contaminants in the fluid that could cause damage.

Since hydraulic systems are subject to immense pressure and periods of extreme temperatures, the fluid chosen must have several distinctive physical properties:

  1. It must have a high temperature of ignition. If a leak in the hydraulic system were to occur and the fluid was not ignition retardant, a potentially devastating fire could ensue.
  2. Hydraulic fluid should also have a high viscosity index, meaning it can flow easily over a wide temperature spectrum from very cold to extremely hot.
  3. Properly chosen hydraulic fluid should be able to lubricate the various components it comes into contact with while also protecting them from corrosion.
  4. Since hydraulic fluid also acts as a coolant, it must be able to absorb heat from the various components it passes.

Like all aircraft systems, hydraulics are built with a level of redundancy in case of failure. The first level of redundancy is that each hydraulic system is equipped with several pumps, with most containing both manual and electric pumps. Using this configuration, a certain hydraulic system may rely on a manual pump for the majority of the flight but can readily use the electric pump during periods where additional pressure is needed. In systems where an electric pump is the primary pressure source, a backup pump or ram air turbine will also be mechanically linked in case the electrical systems are lost. Additionally, multiple hydraulic systems are connected to the same flight control surfaces so that pilots can maintain control of the aircraft even if one system fails.

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