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. When hovering backwards, the helicopter is tilted so the tail is low to the ground. Therefore, maintain a slightly higher than normal hovering altitude. To stop the rearward movement, apply forward cyclic and hold it until the helicopter stops. As the motion stops, return the cyclic to the neutral position. Also, as in the case of forward flight and sideward flight, use opposite cyclic to level the helicopter and let it drift to a stop. Common Student Difficulties Speed Control The student may not realize that it takes a steeper pitch attitude to start the helicopter moving than it does to continue motion at a steady speed. If the nose is not moved down slightly as the desired rearward speed is attained, the helicopter continues to accelerate. Note: Acceleration and force are vectors. In Newton’s second law of motion, the direction of the force vector is the same as the direction of the acceleration vector. In other words, an object with a certain velocity maintains that velocity unless a force acts on it to cause an acceleration (that is, a change in the velocity). If the pitch attitude is not returned to a neutral (non-accelerating or decelerating) attitude, stabilization of the speed and velocity cannot occur. Heading The faster the helicopter travels rearward, the greater the tendency for the nose of the helicopter to swing around toward the direction of flight. With the tail directly into the relative wind, there is little tendency for it to weathervane, but if the relative wind is a little bit on one side, the tail tends to continue to the downwind side. The resulting heading correction requires a fairly large pedal input, which may cause an overshoot to the other side, and the process must be repeated with opposite pedal input. Speed must be reduced to regain control. During preflight, show the student which surface areas of the helicopter are affected by relative wind from different directions (what is causing the weathervane). Discuss how you need to overcome the effects of the wind during different directions of hover (forward, rearward, sideward). Landing From a Hover The helicopter is stabilized in a hover directly over the intended landing spot, then gently lowered onto the ground. It should not drift in any direction at the point of touchdown. The instructor should remind the student pilot of the flight control changes that must occur during this seemingly simple task. As the helicopter begins to settle onto the surface, all of the flight controls must be manipulated simultaneously and in coordination to achieve a smooth landing. When choosing a landing area for the student to practice landing from a hover, instructors should keep in mind that certain conditions usually dictate a landing directly to the ground with little or no hover. For example, dust, sand, or snow landings are very difficult and should not be attempted until the student has shown considerable proficiency with takeoffs and landings. These types of landings are discussed in Chapter 12, Helicopter Emergencies. Landing in a grassy field or in a spot with puddles of water can also cause problems for flight students. The grass or water motion presents a false picture of helicopter movement to the new pilot and causes them to incorrectly respond when attempting to land. Instructional Points The student should be instructed to look outside and ahead of the helicopter. Focusing on the ground through the chin bubble leads to overcontrolling and makes it difficult to land on the desired spot. Always keep the rpm within limits. This allows for quick transition back to hover if the landing is not suitable. Never allow the helicopter to settle on the ground, which might occur if the throttle is reduced below the rpm limits. To prevent overspeed, the correct technique requires simultaneously lowering the collective and reducing the throttle. Do not abruptly lower the collective once ground contact is made. First, ensure the ground is sufficiently stable to support the helicopter. This requires a slow and deliberate lowering of the collective. The cyclic may be moved in a small circular motion to determine that the helicopter is firmly on the ground before lowering the collective fully. Once the helicopter is firmly on the ground, the collective should be lowered completely. Landing a helicopter requires the same attention as takeoffs to a hover. Point out which skid/gear will contact the surface first and why. What control inputs will be applied to stop sliding (moving forward)? Forward or aft cyclic may be required during the landing to maintain the position. How is excessive slope recognized before the tilt is too much to overcome? Common Student Difficulties Attitude Control The closer the helicopter comes to the ground, the more likely it is for the student to focus on a point almost directly beneath the helicopter. As the helicopter descends, ground effect tends to increase, thereby creating a greater workload for the pilot to maintain coordination of all the flight controls until the helicopter is on the surface. Without proper attitude technique, the student may overcontrol when the helicopter begins to drift, and the situation may go from bad to worse. The student must be taught to look far in front of the helicopter and then gently lower it until the touchdown is felt, not seen. Remind the student that most likely one side of the landing gear contacts the surface before the other due to winds or translating tendency. Due to loading and winds, the front or the rear of the landing gear may touchdown first depending on the hovering attitude of that helicopter. In any event, as the landing gear first touches down, cyclic and pedal corrections are continually necessary to maintain heading and position until the remainder of the landing gear is firmly on the surface. RPM Control During the landing, rotor rpm tends to increase due to the effects of increased ground effect and decreased collective pitch. During touchdown, for those helicopters not equipped with a governor, the throttle may need to be reduced to avoid an overspeed. |
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