Explain the basics of an aeroplane's Fuel and Hydraulic systems?

Answer 1

Large Commericial Jet ===

Fuel Most large commericial jets operate on diesel fuel. The fuel is distributed over several fuel tanks distributed within the wings and the center fuselage. The Fuel Control system is a computer that helps the flight crew distribute the fuel in order to maintain the aircraft center of gravity and attitude for a safe flight. There are fuel probes in each fuel tank and most larger aircraft use more than one probe to determine the exact quantity of fuel in each tank.

Each engine will have a fuel controller that provides the correct amount of fuel for the power setting and also adjust controls on the engine to obtain maximum efficiency of burn. For example, the stators on some engine are adjusted to improve the flow through the various turbine stages.

Hydraulics - Most of the aircraft mechanical controls are powered by hydraulic pressure. (Aircraft in the future may rely less and less on hydraulics and more on electrical control.) Since the hydraulics are the "blood line" of the aircraft, it is important to ensure that the lines are safe from damage and leaks. Therefore, most aircraft have 2 or 3 redundant hydraulic systems. Usually the flight controls are powered by 2 redundant systems so that the loss of one hydraulic system will not cause that flight control to be inoperative.

Each hydraulic system has a Reservoir which collects all returned fluid and filters it. The fluid leaves the reservoir and is routed to the Hydraulic Pumps mounted on the engines. The pump sends the fluid throughout all the lines out to each hydraulic component and then back to the reservoir. Most aircraft operate at 3000 psi pressure. Some military aircraft and commericial aircraft such as the Airbus A380 provides pressure at 5000 psi. The advantage of this is smaller hydraulic lines to save weight.

The Hydraulic Components that are powered by the hydraulics are usually simple linear actuators. Some may be rotary actuators or hydraulic latches.

The Landing Gears are retracted and extended by hydraulic actuators. The fluid inside the landing gear that allows the strut to absorb the shock of the landing is NOT related to the aircraft hydraulics. The shock strut is a closed system which uses a slightly different type of fluid. The hydraulics does provide power to a Brake Valve that is controlled by the brake pedals in the cockpit. The Brake Valve sends pressure to the Brakesthrough a manifold that is controlled by the anti-skid braking system. Each brake on the aircraft is powered by 2 separate braking systems from two separate hydraulic sources. So, if one hydraulic system fails, then the other hydraulic system can still operate the brakes.

The DC10 that crashed in Sioux City, Iowa, had a triple failure of all three of its hydraulic systems. The engine on the tail experienced a catastropic failure and pieces of turbine blades cut hydraulic lines that were routed to the tail of the aircraft. The aircraft lost all hydraulics. It had not control of any flight surfaces. The landing gear can be extended by free-fall. The only controls it had were throttle to the engines.

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