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. Roll attitude can be determined by using the tip-path plane or a canopy crossbar and its relation to the natural horizon. Prominent objects on the ground should be used for heading reference. This encourages the student to look outside instead of concentrating too much on the instruments. While the student is gaining proficiency in straight-and-level flight, power is usually not adjusted once it is set, in order to maintain the desired cruise power. Instructional Points It is important that the student learn to recognize the correct attitude for various flight maneuvers. The attitude of the helicopter usually indicates the rate of acceleration or deceleration of the helicopter and the airspeed, and is controlled by the cyclic. Altitude is primarily controlled by the use of the collective. To maintain forward flight, the rotor tip-path plane must be tilted forward to obtain the necessary horizontal thrust component from the main rotor. This usually results in an initially nose-low attitude. Due to the horizontal stabilizer, once the helicopter stabilizes in flight, the helicopter’s fuselage will tend to return to a neutral, level attitude. The attitude of the helicopter should not be confused with the position of the rotor disk relative to the horizon. The lower the nose rotor disk is, the greater the power is that is required to maintain altitude, and the higher the resulting airspeeds. Conversely, the greater the power used, the lower the rotor disk must be to maintain at altitude. Since the helicopter is suspended beneath the rotor system, the angle of attack of the wings is not determined by the airframe’s pitch as in an airplane. The horizontal stabilizer streamlines the helicopter airframe for reduced drag by applying more down force as airspeed increases, thereby raising the nose to a level (or almost level) cruising attitude. Show the student, while in straight-and-level flight, any increase in the collective also increases the airspeed and altitude, due to an increase in lift and thrust. A decrease in the collective while holding airspeed constant causes a helicopter to descend. A change in the collective requires a coordinated change of the throttle to maintain a constant rpm. (In this handbook, all throttle discussions refer to helicopters without a governor or correllator.) Additionally, the antitorque pedals need to be adjusted to maintain heading and keep the helicopter in longitudinal trim. To increase airspeed in straight-and-level flight, instruct the student to apply forward pressure on the cyclic and raise the collective as necessary to maintain altitude. To decrease airspeed, the student needs to apply rearward pressure on the cyclic and lower the collective as necessary to maintain altitude. The student should be guided to notice the yawing resulting from the changing of the torque and airflows over the vertical stabilizer as equipped, and make sufficient changes to maintain the heading and trim. Once the student has maintained a specific altitude and airspeed with little deviation, point out that the helicopter’s altitude and airspeed remain constant with a constant power setting. Small adjustments may be required to compensate for turbulence, but ensure the student uses outside references and does not focus on instruments alone. Assess the position of the rotor disk relative to the natural horizon. The attitude of the helicopter due to the influence of the horizontal stabilizer will approximate a consistent “level attitude” when not accelerating or decelerating. Also, heading is easier to maintain if the student at some point looks outside in line with the intended flightpath. Looking outside fulfills another very important task—scanning for other traffic and obstructions. To prevent overcontrolling, teach control pressures and not movements. This is especially true in the first few lessons when the student is concentrating on control input and how the helicopter reacts. Common Student Difficulties Visualizing Attitude The forward seating position and the excellent visibility in most helicopters may make it difficult for a student to visualize the attitude of the helicopter. It is important that the instructor provide all the assistance possible to ensure the student can determine an attitude by some visual reference. Instructors usually develop different methods of teaching attitude references. Overcontrolling Two factors contribute to overcontrolling the helicopter, the most common difficulty for the beginning student. First, the student fails to notice attitude deviation until it becomes rather large. Second, in the attempt to recover to level attitude, too much control is applied because a student is not prepared for the helicopter’s quick response to control inputs. Generally, the beginning student does not know when to remove a control input and usually holds it until after the required attitude is passed. This results in an overshoot, followed by another large control application, another overshoot, and so on. Explain that controls are operated by pressure rather than movement, and it is not necessary to return immediately to the level attitude. As soon as the student understands these two items and loses the sense of urgency, overcontrolling diminishes. It is also helpful to remind a student that when a deviation from the desired attitude is noticed, the proper technique is to first stop the deviation, then make a smooth correction to return to the original attitude. Trim To reduce control pressures in helicopters with electric trim, it is imperative to have the helicopter properly trimmed before the student takes control, otherwise the term control pressure is meaningless. When the helicopter is out of trim, some control pressure must be held just to maintain the desired attitude and any instruction to relax control pressure can only lead to confusion. If the helicopter has an electric trim (especially the “coolie hat” type), the student should be shown how it functions before starting the engine and turning the blades. If installed, have the student use the trim and remind him or her to always trim the pressures off. The on/ off type (force trim) is often of less value and very often just left off by experienced pilots as a personal preference. When trim is mentioned in this handbook, it is in reference to the antitorque trim of the helicopter unless otherwise indicated. |
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