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. Lateral CG is often plotted against the longitudinal CG. [Figure 7-12] In this case, –1.6 is plotted against 93.8, which was the longitudinal CG determined in the previous problem. The intersection of the two lines falls well within the lateral CG envelope. Instructor Tips . Review all the terms associated with weight and balance with the student. . Review the sample weight and balance problems with the student. . Ensure that the student understands weight and balance must remain within limits after all loading, unloading, refueling, and fuel consumption. . Ensure that the student understands current and forecast environmental conditions affect the performance of the aircraft, thereby affecting weight and loading limitations. . Review and practice with the student the actual weight and balance forms for the helicopter to be flown. . Ensure the student understands the charts by using weights and/or balances that may put the helicopter in an out-of-weight or out-of-balance condition. . The more the student works the weight and balance figures, the more proficient the student will become at computing weight and balance. [Figure 7-13] Chapter Summary This chapter explained how to introduce weight and balance to the student, how to read the charts necessary for computing weight and balance of the helicopter, and definitions of common terms associated with weight and balance. Factors Affecting Performance Instructors should ensure the student has a firm grasp on the four major factors affecting helicopter performance: density altitude, weight, loads, and wind. Emphasis must be placed on the importance of proper and thorough performance planning prior to each flight. Density Altitude The instructor should convey to the student the need for a comprehensive knowledge of density altitude. The student must understand what combinations of high elevations, low atmospheric pressure, high temperatures, and high humidity directly impact density altitude and its affect on helicopter performance. Explain that density altitude is pressure altitude corrected for nonstandard temperature. High density altitude refers to thin air while low density altitude refers to dense air. [Figure 8-1] Air density is affected by changes in altitude, temperature, and humidity. Conditions that result in a high density altitude are high elevations, low atmospheric pressures, high temperatures, high humidity, or some combination of these factors. Lower elevations, high atmospheric pressure, low temperatures, and low humidity are more indicative of low density altitude. A' B B' Low temp High pressureStandard atmosphere Using the building block concept, explain the factors that may increase or decrease density altitude. The predominant factors are atmospheric pressure, altitude, temperature, and moisture. Use examples of each factor’s impact on the performance planning used for the aircraft to be flown. Stressing the impact that each factor has on density altitude leads to a greater awareness of the student to these ambient conditions. The lift equation is an effective tool that can be used to show the affect of an increase or decrease of density altitude on aircraft performance. Lift = coefficient of lift x density x velocity2x lifting surface area 2 Once the student has a clear understanding of how density altitude affects helicopter performance, you can advance to actual flight demonstrations and hands-on practice. The instructor can set artificial limitations on the amount of available torque or temperature to simulate operations in environments that cause actual reductions in power margins. While this provides a demonstration to the student, it is not a substitute for actual conditions. The instructor could ask the student to determine performance for a maneuver, such as OGE hover, for a low or field elevation, and then for one at a much higher altitude normally found in the area of flight. Then, the instructor could discuss Equivalent density altitude A Equivalent density altitude High temp Low pressure Figure 8-1.Three atmospheres are illustrated. The Standard Atmosphere (29.92 "Hg and 15 °C) is shown in the middle in gray. A less dense atmosphere (A) (lower pressure and/or higher temperature) is shown on the right in red. A denser atmosphere (B) (higher pressure and/or colder temperature) is illustrated on the left in blue. the difference with the student and ask the student to describe the practical response differences of the helicopter in the two situations. The instructor may be able to simulate higher elevation power of the helicopter performance by artificially limiting the power the student can use (e.g., limit the manifold pressure or torque to be used). However, the instructor cannot limit the lift and efficiency of the rotor system. The instructor must ensure the student understands the lack of fidelity of the simulation and the hazards awaiting the pilot at high density altitudes, such as lower VNE, less antitorque available, less lift from the rotor system, slower engine response, and higher collective pitch settings for cruise and hovering. If the student makes errors during the simulated high-altitude practice, the increased power is still there, whereas the power is simply not there at actual higher altitudes. At higher altitudes, helicopters do not have the margins of performance necessary to correct errors in planning or judgment. Due to the retreating blade stall characteristic of helicopters, increasing altitudes yield no performance improvements over 5,000 feet to 6,000 feet depending on the design and powerplant(s). Therefore, when operating in higher terrain, any altitude gains above takeoff elevation usually results in decreasing performance. By the very nature of a helicopter, a pilot must be versed in the performance limitations imposed by the change in the environment. The pilot must understand the limitations of increased altitudes and plan accordingly. Therefore, the instructor must include that planning in the syllabus. |
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