旋翼機飛行手冊 ROTORCRAFT FLYING HANDBOOK

時間：2011-04-05 11:32來源：藍(lán)天飛行翻譯 作者：航空 點擊：次

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An impending hydraulic failure can be recognized by a grinding or howling noise from the pump or actuators, increased control forces and feedback, and limited control movement. The corrective action required is stated in detail in the appropriate rotorcraft flight manual. However, in most cases, airspeed needs to be reduced in order to reduce control forces. The hydraulic switch and circuit breaker should be checked and recycled. If hydraulic power is not restored, make a shallow approach to a running or roll-on landing. This technique is used because it requires less control force and pilot workload. Additionally, the hydraulic system should be disabled, by either pulling the circuit breaker and/or placing the switch in the off position. The reason for this is to prevent an inadvertent restoration of hydraulic power, which may lead to overcontrolling near the ground.
In those helicopters where the control forces are so high that they cannot be moved without hydraulic assistance, two or more independent hydraulic systems may be installed. Some helicopters use hydraulic accumulators to store pressure that can be used for a short time while in an emergency if the hydraulic pump fails. This gives you enough time to land the helicopter with normal control.
GOVERNOR FAILURE
Governors automatically adjust engine power to maintain rotor r.p.m. when the collective pitch is changed. If the governor fails, any change in collective pitch requires you to manually adjust the throttle to maintain correct r.p.m. In the event of a high side governor failure, the engine and rotor r.p.m. try to increase above the normal range. If the r.p.m. cannot be reduced and controlled with the throttle, close the throttle and enter an autorotation. If the governor fails on the low side, normal r.p.m. may not be attainable, even if the throttle is manually controlled. In this case, the collective has to be lowered to maintain r.p.m. A running or roll-on landing may be performed if the engine can maintain sufficient rotor r.p.m. If there is insufficient power, enter an autorotation.
ABNORMAL VIBRATIONS
With the many rotating parts found in helicopters, some vibration is inherent. You need to understand the cause and effect of helicopter vibrations because abnormal vibrations cause premature component wear and may even result in structural failure. With experience, you learn what vibrations are normal versus those that are abnormal and can then decide whether continued flight is safe or not. Helicopter vibrations are categorized into low, medium, or high frequency.
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LOW FREQUENCY VIBRATIONS
Low frequency vibrations (100-500 cycles per minute) usually originate from the main rotor system. The vibration may be felt through the controls, the airframe, or a combination of both. Furthermore, the vibration may have a definite direction of push or thrust. It may be vertical, lateral, horizontal, or even a combination. Normally, the direction of the vibration can be determined by concentrating on the feel of the vibration, which may push you up and down, backwards and forwards, or from side to side. The direction of the vibration and whether it is felt in the controls or the airframe is an important means for the mechanic to troubleshoot the source. Some possible causes could be that the main rotor blades are out of track or balance, damaged blades, worn bearings, dampers out of adjustment, or worn parts.

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