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. Additionally, stress the need to increase throttle and join the engine and rotor tachometer needles with the collective in the down position. The power or throttle should be increased to engage the clutch or have the rotor and engine together at about 100 feet AGL. If the throttle is increased too much or too fast, an engine overspeed can occur; if the throttle is increased too little or too slowly in proportion to the increase in collective pitch, a loss of rotor rpm results. Coordinate upward collective pitch control with an increase in the throttle to join the needles at operating rpm. Ensure the student understands the increase of throttle and collective pitch must be accomplished properly. If a power recovery is to be made, slowly increase the engine rpm during the descent to avoid the rapid application of throttle for the recovery. If the student is at all apprehensive about autorotations, be prepared for him or her to either overcontrol or freeze on the controls. One technique of teaching autorotations is to use power-on glides that replicate the autorotational profile, terminating to a hover or with a slight ground run, if permissible. By using this technique, a new instructor can get the feel for the power required and subsequent yaw that occurs during the flare and landing. An instructor should never let the student exceed aircraft limits or the instructor’s ability to recover the helicopter. As a teaching technique in many helicopters, a minimum of power can be used for the landing to offer a preview of a full autorotative touchdown. Basically, this offers more cushion and allows a quicker but very controlled touchdown. Having the engine engaged prior to the flare allows the engine to accelerate throughout the flare to produce hover power. The instructor should remember the power recovery is actually a very precise maneuver, requiring the most control movement of almost any maneuver in very little time, and the student is required to transition from power-off flight to almost maximum power in a hover. Because so much is happening so quickly, anything the instructor can do to allow more time for the student to perceive all of the actions that must occur in that brief time period gives large returns for the training. Power Failure in a Hover, With Instructional Points Whether instructing or evaluating, performing a power failure at a hover is another high accident rate maneuver. The following are some of the common mistakes made by instructors. The first is site selection. Ensure the surface area is a flat, smooth, and hard surface. Students initially tend to have a difficult time accounting for translating tendency. This, in turn, most often causes lateral drift. If conducting this maneuver on a sloping surface, one or more of several phenomena may occur, from dynamic rollover to damaged skid gear. The same can be said for soft or uneven surfaces, as the skid gear may stick, causing a pivot point. Selecting the proper entry height is also imperative. Often, initiating this maneuver from higher than the prescribed entry altitude may cause the student to prematurely apply collective to arrest the rate of descent for landing, leaving the aircraft at little or no available rpm while not yet on the ground. At higher entry heights, a tendency is to attempt to lower the collective to build available inertia or keep the rotor rpm up. Loss of power at a hover with the normal high power setting always results in a rapid rotor rpm decay. Review of the H/V chart almost always indicates that there is insufficient power to allow a safe, uneventful landing if the hover height is too high. However the student does it, if the hover height is too high, a hard landing results from a power or driveline failure. There simply is not enough potential energy in the rotor system alone to cushion the landing. This should not be shown to students as it requires a great amount of experience and special training to accomplish successfully. Ensure the student understands a power failure can occur at any time. Hovering autorotations are practiced to develop the automatic response and coordination required to maintain heading and cushion the landing following an engine failure at a hover. Explain to the student that power failures at a hover may occur during either of the two modes of flight: hovering flight in ground effect (IGE) and hovering flight out of ground effect (OGE). Refer to the RFM to generate discussion of the procedures to be used for each instance. Stress to the student that for power failures at a hover while IGE, the collective is not lowered, but held in place until approximately 1 foot AGL when collective pitch is increased to cushion the landing. Explain that when hovering OGE, operations usually fall in the hashmarked area of the height-velocity diagram, which may require lowering the collective and adding forward cyclic in attempt to land the helicopter. As previously mentioned, emphasize the importance of minimizing sideward or rearward drift during the maneuver to reduce the possibility of dynamic rollover or other damage to the helicopter. It is best to debrief the student after each maneuver. Review the maneuvers with the student and point out what was done correctly, and what was not. When discussing errors, point out to the student why they happened and what could be done to correct or prevent them. When a student is continuously having difficulty with a particular maneuver, the instructor must find a way to help the student understand what is happening. Helping the student pinpoint exactly what they are doing wrong, and how to help the student learn to avoid these errors is what the instructor should focus on. This permits the student to immediately take corrective action on the next repetition. Take time to talk about the hazards of excessive nose low takeoffs, exposure to the hazard area of the height/velocity chart, and the dangers of dynamic rollover. Discussing these hazards while performing this maneuver reinforces the need to carefully choose correct flight techniques and profiles. |
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