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
|
To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Airspeed A common problem for students when doing a maximum performance takeoff is finding the proper airspeed for the maneuver. A steep climb coupled with a low airspeed could result in insufficient power to take off. This may result in low rpm followed by sinking and a possible hard landing or landing in the trees. Neither option is desirable. The other extreme is accelerating to an airspeed higher than necessary, resulting in a takeoff profile that is not steep enough. Revisit the positive effects of ETL on power requirements while stressing the importance of maintaining clearance along the departure path. The increased rotor efficiency of passing through ETL should be achieved as soon as possible to reduce power requirements. Running/Rolling Takeoff A running takeoff, while not normally used, is practiced to simulate conditions that could exist as a result of high density altitude and/or a high gross weight. The student must be aware of the performance characteristics of the helicopter and the techniques to be used if sufficient power is not available to permit hovering in ground effect. While conducting performance planning, have the student calculate power for a series of weights at 3 feet and check loading versus performance for that particular helicopter. Use this power-to-weight ratio, if feasible, in scenario-driven lesson plans utilizing increased gross weights. During the flight, validate the calculations and demonstrate to the student that power required to hover can be used to conduct running/ rolling takeoffs. From a hover, accelerate the helicopter forward along the ground, until ETL permits a takeoff. Instructors should point out that, during this maneuver, altitude should remain constant until ETL is reached and the student should not lift up and down on the collective, which could cause the skids to touch the ground. Instructional Points Demonstrate the following to the student: . For helicopters equipped with skids, it may be better to practice running takeoffs on a hard surface runway instead of a grassy field. There is less probability of catching a skid, which could lead to dynamic rollover. In addition, check the condition of the skid shoes before and after practicing running takeoffs and landing. . To begin the maneuver, align the helicopter to the takeoff path. [Figure 11-2] Next, increase the throttle to obtain takeoff rpm (if applicable) and smoothly increase the collective until the helicopter becomes light on the skids for landing gear. . Move the cyclic slightly forward of the neutral hovering position and apply additional collective to start the forward movement. To simulate a reduced power condition during practice, use one to two inches/pounds of torque less power than required to hover. Do not apply any forward cyclic to start the forward motion until simulated maximum power has been applied. Applying forward cyclic before maximum available power is obtained may cause the helicopter to dig into the ground, requiring even more power to break free. . Maintain a straight ground track with lateral cyclic and heading with antitorque pedals until a climb is established. As ETL is gained, the helicopter becomes airborne in a fairly level attitude with little or no pitching. . Maintain an altitude to take advantage of ground effect and allow the airspeed to increase toward normal climb speed. Then, follow a climb profile that takes the helicopter through the clear area of the height/ velocity diagram. During practice maneuvers, after climbing to an altitude of 50 feet, establish the normal climb power setting and attitude. Common Student Difficulties RPM It takes self-discipline to keep from raising the collective when the helicopter is about to become airborne. Emphasize to the student that increasing collective above the maximum available power may only result in a loss of rpm, producing a loss of lift, rather than an increase. This can be demonstrated in a hover by raising the collective while reducing throttle to maintain manifold pressure or torque pressure. Attitude Control It initially requires more forward cyclic control to accelerate the helicopter on the ground, against the resistance of the skids/landing gear, than it does to maintain the slightly nose-down attitude required for acceleration in the air. As effective translational lift is gained, the tendency may be to hold the attitude and climb too rapidly. However, lowering the nose too much after becoming airborne may result in the helicopter settling back to the surface. Once airborne, the helicopter should be held in ground effect until climb speed is reached. Wind Explain to the student that the greater the headwind component, the easier it is to get the helicopter off the ground when power is limited. All available means should be exercised to determine wind direction accurately before attempting the takeoff. In a crosswind, cyclic must be applied into the wind to keep the ground track parallel. Maintain this attitude even after leaving the ground. Only after climb speed is reached and the climb has begun, should the helicopter be crabbed into the wind. Rapid Deceleration or Quick Stop A rapid deceleration, or quick stop, is used to decelerate from forward flight to a hover. The objective of a rapid deceleration or quick stop is to lose airspeed rapidly while maintaining a constant heading, ensuring adequate tail rotor to ground clearance at all times. Quick stops are practiced to improve coordination and to increase proficiency in maneuvering a helicopter. As the student gains coordination and proficiency in the maneuver, conduct the maneuver with a crosswind. From previous discussion of aerodynamics, the student should realize that downwind decelerations or quick stops are not recommended and that every effort should be made to avoid them. Instructional Points During initial training, always perform this maneuver into the wind. As discussed above, once the student has demonstrated sound coordination and proficiency, conduct training with crosswinds. It is essential that the student begin crosswind training with light wind velocities. [Figure 11-3] For the instructor, it is important to know that the maneuver is conducted in IGE and just above ETL, which facilitate recovery. |
推荐内容
热点内容
