Flight Control Hydraulics Flashcards
General
Contains 2 identical systems that work in parallel in operation but hydraulically separated
Operate at 3000psi indicated but are reduced to 1500 psi for lower boost and AFCs actuators
4 upper boost actuators (3000psi), 4 dual stick boost actuators (1500psi), 3 dual AFCS links (1500psi)
Accumulators for pressure surges in system and stored hydraulic power for peak loads, hydraulics reservoirs and return lines pressurized to prevent pump cavitation
Emergency hydraulic system provides hydraulic system pressure through no. 1 hydraulic system should normal system plumbing pressure fall below 2800psi
System Operation
Pump pressurizes fluid from 2950 to 3000psi
Pump solenoid valve installed on each pump reduces system pressure on pumps during APU starts, when valve is energized, system pressure drops to 475-525psi to unload AGB on which pumps are mounted to help utility hydraulic pressure bring APU motor/pump to speed
From pump pressurized fluid passes through check valve to FLIGHT CONTROL MANIFOLD, where it passes through a filter within manifold. Manifold contains pressure relief valve, solenoid operated boost control valve, pressure transmitter port, pressure switch port, and accumulator port
When de energized, boost control manifold valve directs fluid to flight control ACTUATING CYLINDERS. Energizing control valve routes pump output back to reservoir tank. If pump malfunction causes overpressurization the relief valve will open (3500-4050psi)
25 in accumulator connected to accumulator port on manifold, act as surge damper to absorb surges in pressure line
Downstream from manifold fluid passes through check valve to aft upper control actuating cylinders. Fluid also passes through filter and check valves to forward cylinders. Check valves prevent fluid from draining when system not running
Pressure is reduced to 1500psi as fluid passes through PRESSURE CONTROL MODULE. PCM distribute fluid to lower stick boost actuators and AFCS extensible links
AFCS solenoid axis shutoff valves for pitch, roll, and yaw are within PCM. When energized open the valve directs fluid to e link, de energizing solenoid valve closes it and causes pressure ports of e link to connect to system return
Locking piston in e link forces it to become rigid without hydraulic pressure supplied to it
Return fluid from upper and lower stick boost actuators passes return filter on way to tank, check valves prevent reverse flow and system contamination
When system is depressurized, electrical contacts in each pressure switch (installed on flight control manifold) complete the circuit to HYD PRESS annunciator. Another contact opens opposite system boost control valve circuit, which prevents system solenoid from being energized to BOOST OFF position when other system is depressurized. If helicopter were operating with one boost system OFF and other operating system were to fail, pressure switch will automatically change over control to other system.
Reservoir Tanks
Each tank contains filler cap/filter assembly, fluid level indicator, suction port, return port, scupper drain, and pneumatic system connection
Holds 5.25 us quarts
Each tank is pressurized to 20-25psi by P2 bleed air from No. 2 engine through air pressure regulator. Regulator filters, regulates, and distributes billed air to both reservoirs
Return fluid form actuating cylinders is recycled through reservoir return ports
Pneumatic System
Provides air pressure for hydraulic tanks. P2 bleed air from port on No. 2 engine directed through filter and check valve to air pressure regulator valve. Regulator valve limits air pressure on top of tank, contains WATER DRAIN BUTTON to remove condensation and relieve air pressure from system
Fluid under pressure prevents pump cavitation and air from being sucked into system.
Pumps
Variable delivery constant pressure nine piston pump (x2)
No. 1 pump mounted above No. 1 generator, No. 2 pump above No. 2 generator
Each pump driven by AGB when APU or rotors operating
During APU start, No. 2 systems pump compensator solenoid is energized if there is less than 2000 psi in No. 1 system. Energizing the solenoid reduces pump output pressure. No. 1 pump compensator solenoid is also energized during an APU start, therefore reducing pump output pressure if both generator main contractors are not energized and there is less than 2000 psi in No. 2 system
Flight Control Manifold
Contains an internal filter, chamber with high pressure relief valve, solenoid operated boost control valve, pressure transmitter port, pressure switch port, and accumulator port
When de energized manifold boost control valve directs fluid to actuated components of the system. Energizing boost control valve cuts off pump pressure supply at valve and connects all downstream pressure lines and components to return passages
If pump malfunctions and causes system to overpressurize, pressure relief valve opens at 3500 to 4150 psi pressure.
Accumulator is connected to manifold port, and acts as surge damper to absorb pressure surges in pressure line
Pressure Control Module
Contains pressure reducer which reduces fluid pressure to 1500psi for stock boost actuator and AFCS e link
Reduced pressure from control module is directed to stick boost actuator manifolds that the stick boost actuators are mounted on.
Within pressure control module are 3 normally closed solenoid valves for AFCS single axis shutoff
Pivoting Dual Actuating Cylinder
Consists of:
- 2 cylinders
- 2 pistons
- Control assembly fabricated to a single unit
Pivoting actuator pivots about its dual mounting lugs during operation of controls
Split pilot valve is located on paper movable portion. When it is displaced it moves the dual pistons. Movable assembly consists of split plot assemblies attached together but controlled from one mechanical push rod input. Pilot valves are jam proof with mechanical jam indicator for each valve
Swiveling Actuating Cylinder
Mounted by a spherical dry ball type bearing on mount between cylinders. The swiveling actuator swivels about its single mounting lug during operation of controls
Split pilot valve is on upper movable portion, movements of connecting link displace pilot valve, causing pistons to move. Pilot valves are jam proof with mechanical jam indicators for each valve
AFCS Control Module Solenoid Valve
Energized open causes solenoid valve to direct pressurized fluid to extensible links. De energizing AFCS control module stops pressurized fluid at valve and connects pressure ports of e links to system return lines
AFCS Dual Extensible Link
3 links for pitch, roll, and yaw located between the lower stick boost actuators and first stage flight control mixing linkages
Each actuator is controlled by its own pilot valve and each valve responds to electrical signals developed by the AFCS
Each link is rendered inop or operable by hydraulic pressure or lack thereof, selecting ON AFCS channel allows fluid to pass from pressure control manifold into pressure port of e link plot valve, while simultaneously hydraulic pressure will lift underside of locking piston, allowing e link to move
Dual Stick Boost (Lower Control) Actuator
Pitch, roll, and yaw are identical, collective is different because control valve allows greater movement of control input before actuator movement occurs
Jam proof pilot valves are fitted prevent flying hazard of controls seizing in the even of freezing or contamination occurs
Each valve consists of a landed slide operate inside a ported tube, tube is normally hel in position by spring, and landed valve moves inside tube. Blockage of landed valve which causes friction sufficient to stop movement will overcome spring force and cause landed valve and tube to move as one. Ports of tube now take over job of directing fluid to appropriate side of piston. In this event movement of the tube will duct pressure fluid to a jam indicator pop out button which indicates failure of normal system.
Backup Flight Hydraulic System
Mounted on top left side of aux gear casing on forward end of aft transmission. Pump works when rotors are engaged. Output of pump (2800 psi) flows through normally open solenoid valve to check valve. This valve is normally kept closed because No. 1 system pressure is greater and prevents valve from opening.
Pressure switch installed on output pressure line fo backup pump, if pump pressure falls below 2000 psi the pressure switch contacts close and EMERG HYD FAIL light comes on
When EMER HYD TEST switch is placed to TEST electrical power is applied to No. 1 flight boost pump solenoid valve which releases hydraulic pressure, when pressure drops below 2800 psi backup hydraulic pump immediately takes over and maintains 2800 psi
Thermal Switch
Thermal switches activate when excessive temp in each system return line is reached, when temp closes the thermal switch contacts, a relay energizes and respective SYS HOT light comes on on overhead console.
When either SYS 1 HOT, SYS 2 HOT, OR UTIL HOT illuminate on overhead panel, HYD OVER TEMP light illuminates on annunciator panel
