直升機(jī)教員手冊(cè) Helicopter Instructor’s Handbook
時(shí)間：2014-11-10 08:35來(lái)源：FAA 作者：直升機(jī)翻譯 點(diǎn)擊：次
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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Hydraulics Hydraulic systems vary slightly with different helicopter designs. Pilots must understand the system on the specific helicopter that is being flown. Not all helicopters rely on hydraulic assist for the control inputs, and smaller helicopters usually do not use hydraulics in an effort to keep total weight of the airframe down. Larger helicopters (light to heavy) incorporate hydraulics to overcome high control forces. The discussion should begin with showing the student the manufacturer’s hydraulic schematic and indicating where the pressure and return lines are located. Walk through the entire hydraulic system, showing the student the location of components and explain what the basic functions are of each component. Hydraulic System Components Always refer to the proper Rotorcraft Flight Manual for the specific hydraulic system that the helicopter is equipped with. The following is a list of hydraulic system components and their functions with which the student should be familiar. Hydraulic reservoir—The reservoir has three lines: overboard scupper drain, systems return line, and the pump supply line. The pump supply line uses both gravity feed and pump suction to keep the hydraulic pump supplied with fluid. The reservoir may be pressurized to prevent cavitations for helicopters that are capable of higher altitudes and to ensure positive control pressure. The hydraulic reservoir is usually located higher than the hydraulic pump to ensure adequate fluid gravity flow to the pump and is mounted on a bracket, which is located near the transmission. A window is provided on the cowling for inspection of the sight glass. A sight glass is provided to determine when the reservoir needs servicing. Normal fluid level is indicated when hydraulic fluid completely fills sight glass or on some helicopters, is filled to a set level on the sight glass. Hydraulic pump—provides the pressure to operate the servos and the entire system pressure is regulated by the pump via the pressure line. If the pump is driven off the transmission and it fails, there is usually a shear shaft which breaks to allow the transmission to keep rotating so that the helicopter can be landed safely. Other systems drive the pump from the engine. An engine failure will also include a hydraulic failure. The pilot must understand the system on the specific helicopter being flown. Quick disconnects—usually seen from the cabin roof and need to be checked for security. What is important is that the student understands how to ensure that the quick disconnect fittings are fully seated and locked together. The quick disconnects located on the pressure side are where fluid flows through from the hydraulic pump. On the return side, the quick disconnect is the last component through which the fluid flows before returning to the hydraulic reservoir. These components allow maintenance to isolate the hydraulic reservoir and pump from the hydraulic system. Filter bypass indicator—the pressure and return filters both have a pressure indicator that should be checked during preflight. When the indicator is in the reset position, it will be flush and not seen. An extended red indicator indicates an impending filter stoppage. The system is also affected by low temperature, pressure surges and excessive vibration. The red indicator pops out when a set differential pressure across the filter is exceeded. The difference in pressure is not the same for all helicopters; therefore, instructors should teach students what the pressure differentials are for the helicopter being flown. Once the red indicator pops it will remain extended until it is reset manually. Refer the student the proper Rotorcraft Flight Manual for reset procedures. Bypass check valve—the helicopter is equipped with a bypass system and there is an obstruction in the filter causing a pressure differential (the differential point will be different for each hydraulic system), the bypass valve will open and allow unfiltered fluid to flow directly to the reservoir. This feature allows the pilot to safely land the helicopter with the hydraulic system still working. Relief valve—part of the hydraulic system, and located between the pressure and return portions of the hydraulic system. The unit protects the system from overpressurization in the event of a hydraulic pump malfunction. Solenoid valve—designed to provide pressure to the system when it is deenergized. The solenoid valve is de-energized when the HYD SYS switch is in the HYD SYS position or in the event of loss of electrical power to the valve. Placing the HYD SYS switch to the OFF position will energize the valve and pump pressure will be blocked with the system pressure connected back to the reservoir. Hydraulic system switch—located inside the cockpit. When the hydraulic switch is placed in the HYD SYSTEM position, the solenoid is deenergized. The solenoid is then energized when the hydraulic switch is placed in the OFF position. This system is a “fail safe” system which requires power to disable. Therefore, pulling the circuit breaker for the hydraulics might restore the system if it happens to be an electrical control problem. If the hydraulics have failed, it is most important for the hydraulics to be switched off to ensure the hydraulic system does not come back online when large control forces are being applied. A gross over controlling situation could result which could lead to damaging the helicopter. Pressure manifold—a distribution point that permits hydraulic pressure to evenly flow to all actuators. Pressure switch—the switch opens if the hydraulic pressure ever becomes low. The pilot should see an indication in the cockpit that the hydraulic pressure is low. External check valves—prevent reverse flow of the hydraulic fluid from the actuator when pressure is lost. The return line check valve permits the return fluid from the directional control actuator to flow out of the actuator, and then pack into the inlet port. When hydraulic pressure is lost, this type of design permits the directional control actuator to remain full of fluid and prevents feedback forces in the flight controls. |
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