The hydraulic system of the aircraft
The hydraulic system is designed for aircraft control systems and mechanisms that are responsible for the safety of the flight. On modern aircraft hydraulic system is of great importance, there has been widespread use of hydraulic drives control surfaces. The durability, survivability and reliability of hydraulic system ensures the perfection of construction aggregates, a multiple redundant hydraulic drive as a source of energy, automation control, control of the crew.
The use of hydraulic actuators on the aircraft caused by the relatively small size and dimensions, low inertia and a large speed actuators. The hydraulic unit has a mass and size of $ 10% the size and weight of the electrical machine of the same power and purpose.
The hydraulic system used to control the rudders and stabilizers, landing gear extension and retraction subsidence-takeoff mechanization, other consumers.
The disadvantage of the hydraulic system of the aircraft is a relatively large mass of the working fluid, piping and assemblies, their work depending on the ambient temperature of the space. Damage conduits and assemblies, because of which the sealing is lost, can cause liquid discharge, and then - the hydraulic system failure.
In most aircraft hydraulic working fluid is hydraulic aviation oil AMG-10. In many ways, the nature of the system depends on the properties of the liquid.
It is neutral to steel and duralumin, and the viscosity varies insignificantly in temperature. Fire becomes liquid when reaching 120 ° C temperature. In IL-86 aircraft use explosion-proof non-combustible fluid through DALY-4 mineral oils, which can withstand temperatures of up to 200 ° C.
Most often used on airplanes hydraulic driven aircraft engines, air or electric driven pump having a variable flow structure.
The operating principle of the hydraulic system of the aircraft
The hydraulic system of the aircraft consists of two parts:
Pressure source network - designed for energy storage, the creation of the working pressure, the distribution of consumers and the placement of reserve fluid, pressure control within the system;
Consumer Network - consists of components, each of which is designed to launch a specific mechanism.
For example, the hydraulic system of modern aircraft hydraulic fluid feeds:
drives mechanization of the wing and the aircraft control system;
network landing gear-cleaning;
mechanisms of rotation of the wheels the front desk;
Control Network rear and front gruzolyukom;
wiper control network;
wheel braking network.
To many consumers energy comes simultaneously from multiple hydraulic systems. Failure of one hydraulic consumer is no problem continuing to feed other resources.
Control surfaces on the aircraft are controlled by the maximum possible number of installed systems, and responsible consumers (landing gear, flaps, etc.) - a minimum of 2 hydraulic systems. Those consumers who are only in the position of the aircraft on the ground, controlled by a hydraulic system.
Each hydraulic system has, besides the main pumps, redundant power supplies. The latter are represented torque converter, turbo-way electric plants and pumping stations.
torque converters Purpose is to create pressure in the hydraulic system failure during the main pump or engine failure, using the energy of the adjacent hydraulic system. wherein the transmission power from one hydraulic system to another without going transition of the working fluid.
Torque converter - a backup unit, which consists of two motor-pumps unregulated.
The converter of each pump motor is connected to its hydraulic system, fluid between them is not contacted. During operation, the torque converter is one of the motor-pump operates as a motor and drives the second motor-pump that creates the fluid pressure in the fuel system.
Role turbopump units is to establish a fluid pressure during the aircraft flight in case of failure of the engine system and for a certain operation consumer hydraulic system of the aircraft when parked on the ground with the engines turned off. Turbopump system - is a hydraulic pump which is driven by an air turbine operation. Compressed air installation is taken from one of the aircraft engines and APU. Pumping stations are electric emergency source of pressure during flight and nourish consumers during maintenance of the aircraft on the ground.
In order to prevent cavitation at the pump suction line is pressurized. To this end, the hydraulic tank drain system is connected to the aircraft engine compressor, is connected to the air-conditioning system or connected thereto booster pumping stations.
Most aircraft used as the main hydraulic system with variable displacement pumps. It increases the pressure due to axial rotary plunger pumps. Sensitive components of the pump automatically responds to changing pressures in the hydraulic system and servo through the variable capacity pump plunger stroke, the position of the swash plate. Almost constantly pump is capable of producing over the wide range of pressures. After reaching a certain pressure value close to the working hydraulic system, triggered automatic movement, and the pump capacity is reduced to the minimum necessary for cooling and lubrication. fluid cooling is performed in the radiator.
When the fluid pressure is reduced, automatic switch on the pump at full pitch. If the automatic device is not operating, the pump starts to operate with maximum efficiency when the reduction valve into the tank is discharged excess liquid.
The advantage of the hydraulic system with variable displacement pump is smooth discharge pumps, which reduces water hammer.
Working hydraulic pumps of constant performance is similar to the operation of the hydraulic system with variable displacement pump that can also be sent by 2-x highways:
pipe, feeding consumers;
highway connecting the high-pressure line, and hydraulic tank.
Unlike systems with variable capacity pumps it is that the fluid can move simultaneously in two directions.
When charging the accumulator or the consumer fluid from the pump through the automatic discharge and filter goes on to consumers and the battery charging. When the pressure is increased to a working value of the limit switches working fluid in the discharge drain line machine.
The main disadvantage of hydraulic pumps of constant capacity-necessity always to work with the unloading machine. Such systems are short-lived, because of repeated shutdowns connections pumps there are additional variations.
In addition to using the unloading machine, there are other schemes to connect pumps constant performance. They are used mostly in hydraulic emergency.
Power actuators in fluid pressure changes in technology are divided into:
actuators that convert fluid pressure to the piston movement in the cylinder;
actuators, which convert the pressure energy of the rotor during rotation.
The first is called the hydraulic cylinders, the second - gidrorotorami.
Motors - rotary-piston pump, which is suitable for high-pressure fluid.
Accumulator - spherical or cylindrical container. Its internal cavity is divided into parts of rubber-elastic membrane or a free-piston. The upper chamber filled with nitrogen accumulator, connected to the lower pressurizing highway.
working fluid pressure displaces the piston downward and compresses the nitrogen accumulating energy. Energy consumption occurs during the expansion of nitrogen when the liquid is ejected from the system accumulator.
Functions of the accumulator:
reduction in fluid pressure fluctuations caused by the operation of hydraulic actuators, switchgear, unloading machine, pump;
transient increase in initial power system when the hydraulic drive;
failure of the pump operates as an emergency power source.
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