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. . Evaluate the area to determine the most advantageous takeoff location and direction. Maximum Performance Takeoff Maximum performance takeoff is practiced to simulate a takeoff from a confined area with a climb over an obstacle. Normally, it is begun from the ground with the collective raised to obtain maximum power while the pitch attitude is adjusted to establish a near vertical climb to clear an obstacle. Height of obstacle permitting, at an altitude of about 50 feet, the nose is lowered gently to accelerate to normal climb speed, attaining efficiency of ETL. The pilot should always be watching the rotor disk in the climb and the distance between the rotor disk and the obstructions should not narrow. If the rotor disk is not clearing the obstruction, then the helicopter, which is suspended under the rotor disk, will not clear the obstructions as well. This is an early indication to abort the takeoff and to possibly try another position. Some penetration of the crosshatched or shaded areas of the height/velocity diagram may be unavoidable during this maneuver. Stress to the student that the lowest climb angle possible should be used, both to improve climb performance and to minimize the time in the restricted area of the high/velocity diagram. Instructional Points Before attempting a maximum performance takeoff, bring the helicopter to hover and determine the excess power available by noting the difference between the power available and the power required to hover. Under certain conditions, there may not be sufficient power available to complete the maneuver. Also perform a balance and flight control check and note the position of the cyclic. Explain to the student the aerodynamic advantages of initiating this maneuver from the ground. That is, an in-ground-effect (IGE) hover requires less power due to: . The reduced induce flow through the rotor disk (resulting from the displacement of induced airflow by the ground). . The lift vector increases (using a lesser blade angle for the same amount of lift). . Because the surface area disperses the airflow outward, the blade tip vortices are reduced resulting in larger portions of the blade producing lift. This discussion helps the student understand the need to use the maximum power available, while IGE, to establish a climb over the obstacle. Explain the practice of selecting go/no-go criteria, both from a performance planning aspect and as a reference point along the flightpath. If, upon reaching this predetermined point, a climb has not been established that allows clearance over the obstacle within power/rotor limits, abort the maneuver. Have the student establish a proposed flightpath that maintains rotor and skid/wheel clearance along the entire flightpath. It is crucial that the student understand that at any time it appears that the maneuver cannot be completed (due to lack of available power or other limitations) or that the obstacle cannot be cleared, the student can abort the maneuver. Descending rearward along the same flightpath is a viable option. It cannot be stressed enough that pulling more power may cause rotor RPM droop with horrendous consequences. Have the student position the helicopter into the wind and return the helicopter to the surface. Normally, this maneuver is initiated from the surface. [Figure 11-1] After checking the area for obstacles and other aircraft, select reference points along the takeoff path to maintain ground track. Consider alternate routes in case the maneuver cannot be completed. Begin the takeoff by getting the helicopter light on the skids/landing gear. At this time, have the student pause and neutralize all aircraft movement. The student should then slowly increase the collective (to allow the engine to 5 4 3 2 1 Figure 11-1.Maximum performance takeoff. achieve and maintain full power) and position the cyclic so the helicopter leaves the ground in a 40-knot attitude. This is approximately the same attitude as when the helicopter is light on the skids/landing gear. Continue to increase the collective slowly until reaching the maximum power available. Ensure the student is aware that the large collective movement requires a substantial corresponding antitorque pedal input to maintain heading. During the maneuver, use the cyclic as necessary to control movement toward the desired flightpath and climb angle. An alternate method is a vertical climb with allowing a vertical abort back down whereas the 40 knot attitude lift off requires aborting with backwards flight. If the 40 knot attitude takeoff is chosen, some landmark should be selected as a reference in the case of an aborted takeoff to ensure the tailrotor is not backed into an obstruction. Maintaining rotor revolutions per minute (rpm) at its maximum is vital. A rotor droop and/or decrease in power causes the aircraft to descend. Maintain these inputs until the helicopter clears the obstacle or until reaching 50 feet for demonstration purposes. Then, establish a normal climb attitude and reduce power. Reinforce to the student that smooth, coordinated inputs coupled with precise control allow the helicopter to attain its maximum performance. Maximum performance takeoff in most light helicopters require operation within the crosshatched or shaded areas of the height/velocity curve. An engine failure while operating within the shaded area may not allow enough time for the critical transition from powered flight to autorotation. Check engine condition by monitoring the engine instruments and apply maximum power smoothly and slowly in order to prevent exceeding the engine limitations. Common Student Difficulties Coordination Power, pitch attitude, and directional control are all essential when performing a smooth transition from the surface to a maximum performance climb. The student must set power smoothly, yet promptly, to the maximum allowable manifold pressure while maintaining maximum rpm. Proper pitch attitude must be established to ensure the helicopter accelerates to the desired climb speed as it gains altitude. The student should avoid abrupt or uncoordinated control application. |
推荐内容
热点内容
