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. The loss of ETL occurs higher in a steep approach, requiring an increase in the collective to prevent settling, and more forward cyclic to achieve the proper rate of closure. For training, terminate the approach at hovering altitude above the intended landing point with zero groundspeed. If power has been properly applied during the final portion of the approach, very little additional power is required in the hover. The instructor should remind the student of ground effect as the helicopter gets closer to the surface. This effect on a well executed approach increases lift and allows the helicopter to glide to a halt over the landing point. Common Student Difficulties Students frequently attempt to dive toward the selected touchdown point when they seem to be overshooting it. This only builds speed and moves the helicopter farther forward. Frequently, the next move is to lower the collective, which does accomplish a loss of altitude, but also results in a high rate of descent. Conversely, when undershooting, it is a natural tendency to raise the nose in an attempt to maintain altitude. This leads to collective corrections, which could lead to settling with power, or in the case of large collective increases, leads to rotor droop, engine overspeeds, or loss of tail rotor thrust. The student should be taught to regulate the steepness of the approach path with collective and use the cyclic to control the airspeed. Near the landing area, the collective should be increased to slow the rate of descent so the transition to a hover is accomplished as smoothly as possible. Constant reminders to use the imaginary approach path from the landing gear to 3 feet above the intended landing point helps the student to not chase the landing point. It must be stressed to the student pilot that, if the approach is unstable, it is best to conduct a go-around prior to descending below the obstacles. Once below the obstacles, the required power to conduct a climb out may not be available. If after several attempts, the angle is too steep or environmental conditions dictate, have the student select another landing. Shallow Approach and Running/Roll-On Landing The objective in a running landing is to maintain a sufficient forward speed to take advantage of translational lift until touchdown. As in the running takeoff, power should be limited to less than that required to hover. A shallow final approach should be used to maintain a low rate of descent. Since the helicopter is sliding or rolling to a stop during this maneuver, the landing area must be smooth and long enough to accomplish this task. [Figure 11-6] 5° Descent 1 2 34 Figure 11-6. Shallow approach and running landing. It may become useful to the student to practice these approaches for the purpose of relating conditions where minimal powered approaches are required, such as fixed or loss of tail rotor control or mechanically induced engine underspeeds. Additionally, under certain whiteout or brownout conditions, shallow approaches can be made to keep the aircraft ahead of the obscurants, allowing the pilot to see the landing area. Extreme caution should be used when conducting this technique. The landing area must be smooth, and precise heading control must be maintained to avoid the possibility of dynamic rollover. In any case, do not rapidly lower the collective after touchdown. Smooth reduction of collective prevents a rapid stop that could result in damage to the aircraft or injury to the crew. Instructional Points For helicopters equipped with skids, it may be better to practice running landings on a hard surface runway instead of on a grassy field because there is less probability of catching a skid, which can lead to dynamic rollover. In addition, check the condition of the skid shoes before and after practicing running takeoffs and landings. A shallow approach is initiated in the same manner as the normal approach except that the student intercepts the final approach path at a shallower angle (approximately 5° or less). The required power to maintain this shallow angle is more than that required for a normal approach but less than that needed to land due to increased ground effect and partial translational lift, depending on the wind. As the collective is lowered, maintain heading with proper antitorque pressure and rpm with the throttle. Maintain approach airspeed until the apparent rate of closure appears to be increasing, then began to slow the helicopter with aft cyclic. As in normal and steep approaches, the primary control for the angle and rate of descent is the collective, while the cyclic primarily controls the groundspeed. However, there must be a coordination of all the controls for the maneuver to be accomplished successfully. The instructor should remind the student that with any aft cyclic movement, any collective control increase is also increasing the aft cyclic adding more negative thrust, which can slow the helicopter too quickly. The student should always remember the cyclic’s effects are affected by the amount of total thrust selected by the collective. The helicopter should arrive at the point of touchdown at, or slightly above, ETL. Since ETL diminishes rapidly at low airspeed, the deceleration must be coordinated smoothly with not too much aft cyclic applied, while keeping enough lift to prevent the helicopter from abruptly ballooning upward, or worse, allow the rotor blades to contact the tail boom if the landing is too harsh. Just prior to touchdown, place the helicopter in a level attitude with the cyclic, and maintain heading with the antitorque pedals. Use the cyclic to keep the heading and ground track identical. Allow the helicopter to descend gently to the surface in a straight-and-level attitude, cushioning the landing with the collective. After surface contact, move the cyclic slightly forward to ensure clearance between tail boom and the rotor disk. Use the cyclic to maintain the surface track. In most cases, hold the collective stationery until the helicopter stops. However, if more braking action is required, lower the collective slightly. Keep in mind that due to the increased ground friction when the collective is lowered, the helicopter’s nose might pitch forward. Exercise caution not to correct this pitching movement with aft cyclic, this movement could result in main rotor contact with the tail boom. During the landing, maintain normal rpm with the throttle and directional control with the antitorque pedals. |
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