直升機(jī)教員手冊 Helicopter Instructor’s Handbook
時(shí)間：2014-11-10 08:35來源：FAA 作者：直升機(jī)翻譯 點(diǎn)擊：次
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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. Refer to Chapter 10 of the Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25) for a detailed explanation of density altitude as it relates to aircraft performance and Chapter 3 for more information on the structure of our atmosphere. Weight The student should possess a basic understanding of the aerodynamics of weight opposing lift. As the weight of the helicopter increases, the power required to produce lift also must increase. The instructor should use the helicopter’s performance charts in the relevant Pilot’s Operating Handbook (POH) to demonstrate minimum and maximum weight configurations and how that correlates to required power with a given set of environmental conditions. A beneficial technique is to show various power/torque requirements at graduated weight and altitude increments, culminating with high gross weight/high altitude condition. This demonstrates the additional power required as weight and/or density altitude increase. Validation of this exercise can be accomplished using similar data in performance charts while flying at various weights and altitudes and noting the corresponding torque values, or using fuel weight at various stages of the flight. As fuel (i.e., weight) is burned off, power requirements decrease. This gives the student a practical application of his planning. Loads The strength of the helicopter is measured by the total load the rotor blades are capable of carrying without causing permanent damage. The load imposed upon the rotor blades depends largely on the type of flight. The blades must support not only the weight of the helicopter and its contents (gross weight), but also the additional loads imposed during maneuvers. In straight-and-level flight, the rotor blades support a weight equal to the helicopter and its contents. So long as the helicopter is moving at a constant altitude and airspeed in a straight line, the load on the blades remains constant. When the helicopter assumes a curved flightpath—all types of turns (except hovering turns utilizing pedals only), flares, and pullouts from dives—the actual load on the blades is much greater because of the centrifugal force produced by the curved flight. This additional load results in the development of much greater stresses on the rotor blades. Load Factor The load factor is the actual load on the rotor blades at any time, divided by the normal load or gross weight (weight of the helicopter and its contents). Any time a helicopter flies in a curved flightpath, the load supported by the rotor blades is greater than the total weight of the helicopter. The tighter the curved flightpath, that is, the steeper the bank, or the more rapid the flare or pullout from a dive, the greater the load supported by the rotor; therefore, the greater the load factor. The load factor and, hence, apparent gross weight increase is relatively small in banks up to 30°. Even so, under the right set of adverse circumstances, such as high-density altitude, gusty air, high gross weight, and poor pilot technique, sufficient power may not be available to maintain altitude and airspeed. Above 30° of bank, the apparent increase in gross weight soars. At 30° of bank, the apparent increase is only 16 percent, but at 60°, it is 100 percent. If the weight of the helicopter is 1,600 pounds, the weight supported by the rotor in a 30° bank at a constant altitude would be 1,856 pounds (1,600 + 256). In a 60° bank, it would be 3,200 pounds; and in an 80° bank, it would be almost six times as much or 8,000 pounds. One additional cause of large load factors is rough or turbulent air. The severe vertical gusts produced by turbulence can cause a sudden increase in angle of attack, resulting in increased rotor blade loads that are resisted by the inertia of the helicopter. To be certificated by the Federal Aviation Administration (FAA), each helicopter must have a maximum permissible limit load factor that should not be exceeded. As a pilot, you should have the basic information necessary to fly a helicopter safely within its structural limitations. Be familiar with the situations in which the load factor may approach maximum and avoid them. If you meet such situations inadvertently, you must know the proper technique. Wind Much like density altitude, awareness of the wind’s influence plays a large part in performance planning. To avoid the potential for wind-induced incidents, the student must understand the impact of wind on the handling of the aircraft, as well as performance planning. One simple demonstration can be conducted while completing hover checks. Caution must be taken not to jeopardize controllability while performing this demonstration. In some cases, the instructor may need to fly so the student can focus more on the engine instruments. Position the aircraft into the wind, note the power required, then conduct pedal turns at 90° increments. At each subsequent heading change, note the variation in power required and difficulty in maintaining heading control. Depending on the wind velocity, moderate to sizable increases in power will be noticed. This will facilitate understanding of the impact that directional wind has on power requirements and the importance of wind direction awareness. Additionally, this demonstrates to the student the changes in power required by the tail rotor to overcome the tendency of the aircraft to weather vane into the wind. A comparison of hover power into the wind versus with a tail wind is very effect in demonstrating this flight characteristic. In gusty wind conditions, it is also important to note the momentary spikes in torque while attempting to maintain a stationary hover. Discussing the impact of wind on translational lift best illustrates contrasting effects of a takeoff or landing into a headwind or with a tailwind. If, in a no-wind situation, translational lift occurs when airspeed reaches approximately 16 to 24 knots, then the impact of directional wind will increase or decrease that range. Noting this, the student can see the advantage of using the headwind to more quickly depart the vortices caused by in ground effect conditions. Conversely, the student will understand that a prolonged in-ground-effect condition (and the need for greater power) exists during a takeoff with a tailwind conditions, because the aircraft must accelerate more to outrun the wind and pass through translational lift. |
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