As the holiday season approaches, millions of people are preparing to travel by air to visit family and friends. During this busy travel period, the safety of airline passengers depends significantly on the proper functioning of essential equipment like hydraulics systems on aircraft. Aerospace hydraulics play a vital yet often overlooked role in ensuring safe and reliable holiday air travel.
Critical functions of aircraft hydraulics
Hydraulics utilize pressurized fluids to transmit power on aircraft and are used to operate key components, such as the following:
- Landing Gear - Hydraulics extend and retract the landing gears and power braking systems to enable safe takeoffs and landings.
- Wing Flaps - Hydraulics adjust the flaps on wings to provide extra lift at slower speeds needed for takeoff and landing.
- Hydraulic Pumps
- Gear Pumps - Meshing gears are used in gear pumps to move fluid. Because gear pumps move a set volume of fluid with each rotation, they are classified as fixed displacement type pumps. Gear pumps are often not appropriate for high pressure applications; however, they can be ideal for low pressure systems, typically less than 1500 psi.
- Variable Displacement Piston Pumps - are typically found on large aircraft. A variable displacement pump converts mechanical energy to fluid power. The amount of fluid pumped per revolution of the input shaft is the displacement, which can be adjusted while the pump is running. The pump is vital for increasing or decreasing the fluid output to compensate for changes in the system's demand, allowing virtually continuous system pressure.
- Fixed Displacement Piston Pumps - pressurize the fluid with a piston which moves in a cylinder, moving a precise quantity of fluid with each stroke.
- Hydraulic Cylinders and Motors
- Hydraulic Cylinders, also known as hydraulic actuators or linear hydraulic motors, are mechanical devices which deliver a reversible force in a single direction. They are cylinder barrels that incorporate a piston connected to a piston rod which uses hydraulic pressure to alternate direction. Hydraulic cylinders are used for movement of flight control surfaces, cargo door operation and the dependable extension and retraction of landing gear.
- Hydraulic Motors - use mechanical force to transform hydraulic pressure and flow into torque, rotation or angular displacement. There are many kinds of hydraulic motors, including radial piston, vane and gear motors. Hydraulic motors are primarily utilized in aircraft to operate jackscrews to power flaps, vertically extend landing gear and operate stabilizer trim used prior to takeoff for achieving optimal elevation of the craft.
Typical aircraft hydraulic systems draw fluid from a reservoir in an "open loop" configuration to pressurize the system for powering various components before the fluid is returned to the reservoir.
A typical commercial airliner has multiple independent hydraulic systems for redundancy in case one system fails. It's crucial to have numerous actuators powered by various hydraulic systems on each surface to guarantee that control won't be lost in the event of a hydraulic system failure. Three independent hydraulic systems are frequently used to power the flight control surfaces of commercial aircraft. Two of those systems can fail without affecting control of the aircraft because of the architecture of the control surface.
Rigorous maintenance and testing
With millions of holiday travelers in the air this season, even a seemingly minor hydraulic failure can lead to flight delays or cancellations, as well as danger to passengers and crew. That's why the FAA requires airlines and ground support crews to conduct rigorous maintenance checks and testing procedures to verify all hydraulic systems are functioning optimally.
Teams meticulously inspect hydraulic fluid levels, pumps, accumulators, valves, filters and lines for any leaks, contaminants, or other issues. Catching minor problems pre-flight avoids more significant issues mid-flight.
Aviation hydraulic systems need routine maintenance to prevent leaks, safeguard against in-flight pressure loss and ensure maximum system operation. Inadequate system maintenance can result in catastrophic failure, which can be expensive and even life threatening.
Essential for safe skies
As friends and families go to airports this holiday season, few pause to consider the critical role hydraulics systems play in enabling safe and reliable air transportation. Yet it is the unseen, often unsung components like aircraft hydraulics that will be working diligently behind the scenes around the globe to ensure holiday travelers arrive safely at their destinations.
Behind all the reunions, embraces and joyful airport scenes are the tireless efforts of ground support maintenance crews inspecting and servicing these complex hydraulics systems. It is thanks to their expertise and commitment, as well as the reliability of the technology itself, that air travel remains one of the safest, most efficient ways for us all to reconnect this holiday season. When familiarizing ourselves with flight safety statistics or marveling at aerial views from airplane windows, we would do well to spare a grateful thought for the hydraulic systems quietly making it all possible.