直升机教员手册 Helicopter Instructor’s Handbook
时间：2014-11-10 08:35来源：FAA 作者：直升机翻译 点击：次
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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Discuss with the student the phenomenon of a compressor stall (engine surges). Explain to the student how reducing the airflow might correct the condition. This is accomplished by activating the bleed air system, which vents excess pressure to the atmosphere and allows a larger volume of air to enter the compressor to unstall the compressor blades. Help the student understand the compressor air control system installed in the helicopter and explain the probable failure modes. If the inlet guide vanes fail closed or if a bleed air valve fails open, the pilot will notice much higher engine combustion temperatures at lower power settings with the maximum power available being very limited. If the guide vanes fail open or the bleed air valves fail closed, high power operations will probably be normal but compressor stalling and possible flameouts may occur as the power demand is reduced. Combustion Chamber The combustion chamber is where the fire takes place anytime the engine is running properly. An igniter plug connected to the combustion chamber ignites the fuel/air mixture only when starting the engine. If installed with an auto-relight, the igniter may attempt to automatically relight the fuel/air mixture in an engine flame-out condition. Discuss with the student what is done if the engine should flame out during flight. Altitude and time available should be mentioned as well. Turbine Discussions about the turbine need to be tailored to the specific helicopter that is being flown as each there are differences in how the two sections of the turbine are coupled to the drive line. For example, the Rolls-Royce (formerly Allison) (Bell JetRanger and BO-105), Lycoming engines (Astars), and Pratt and Whitney (BH-212) are free turbine engines with separate shafts for compressors and power turbines. Older Gazelle and Alouettes use a single-shaft turbine with a centrifugal clutch to allow starting, much like the older and often larger reciprocating-engine-powered helicopters. Turbines will always have the two sections of compression and combustion. What varies is how the sections are coupled to the drive line. Common in most helicopters now is the free turbine design, which uses one inner shaft from the combustion section turbine to drive the accessory gearbox, oil pump, fuel pump, starter/generator and the compressor to sustain the engine. This is typically called the N1(NG). A separate outer shaft around the inner shaft driven by the power output turbine wheel usually goes through the gearbox to be reduced in rpm and support the output drive shaft. This is typically called the N2 and is dedicated to driving the main rotor, tail rotor, drive system, and other accessories such as generators, alternators, and air conditioning (if installed). Help the student correlate possible emergencies, such as NR/NG overspeeds, to what is happening in the turbine and ensure that the student understand why the steps being taken for the emergency procedures help alleviate or control the problem so that they can safely land the helicopter. Memorizing emergency procedures is part of the beginning learning process for students, but the ultimate goal should be to help them recognize the onset of a system/component failure and then how to properly react to ensure a safe landing. Transmission System Explain to the student the purpose of the transmission system. It transfers the work done by the engine to the main rotor, tail rotor, and other components of the helicopter that rely on engine propulsion. Discuss the main components of the transmission and where they are located on the helicopter: 1. Main rotor transmission 2. Antitorque drive system 3. Clutch 4. Freewheeling unit 5. Rotor brake (if installed) Point out the location of the oil level sight gauge. Also, point out the location of chip detectors that are associated with the transmission and engine (if detectors are installed). Identify the location of the warning lights on the pilot’s instrument panel. Chip detectors give advance warning of possible excessive engine or transmission wear, which could prevent an impending failure. This early warning can also greatly reduce the cost of engine and transmission overhaul. The chip detectors illuminate warning light(s) when metal chips bridge the gap in the magnetic probe of the chip detector. NOTE: Some helicopters use chip detectors that have burn-off capability (fuzz burners). When a metal chip(s) bridge the gap in the magnetic probe a warning light is illuminated on the instrument panel. The chip(s) are automatically charged with an electrical current with the ability to eliminate most small particles. Main Rotor Transmission Explain to the student that the main rotor transmission is designed as a gear reduction, reducing engine power to rotor revolutions per minute (rpm). With a horizontally mounted engine, the transmission changes the axis of rotation from the horizontally mounted engine to the vertical axis of the rotor shaft. In many helicopters, the transmission also supports or carries the entire weight of the helicopter. Because of this, the transmission brackets should be checked on preflight for stability and condition. Explain to the student that the rotor rpm is kept at a predetermined setting during normal flight. During autorotation, the rotor rpm must be maintained by the pilot to continue a normal rate of descent. Remember, very low rotor rpm is unrecoverable as the blades will fold up and airflow will not increase the rpm. Discuss with the student that a high rotor rpm during autorotation increases the rate of descent. Low rotor rpm initially slows the rate of descent; however, if rpm is allowed to decrease excessively, the helicopter may fall almost vertically. Little or no collective is available at the bottom of the autorotation. Maintaining the autorotation rpm that is set by the helicopter manufacturer is important. Figure depicts various types of tachometer used to maintain/monitor the rotor rpm. |
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