直升机飞行训练手册 HELICOPTER FLIGHT TRAINING MANUAL(24)

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1. select a suitable approach angle, although it is difficult to visualize initially, an angle of  6 to 8 degrees can be considered a standard approach;
2. initiate the approach by reducing collective, keep straight with pedal, apply aft cyclic to begin a reduction in the airspeed and to maintain a level attitude; the helicopter will begin to descend;
3. use the collective to maintain the desired approach angle. Use the cyclic to maintain the apparent groundspeed at a walking pace;
4. as you approach the ground and speed is reducing through approximately 15 to 20 mph, anticipate the need for an increase in collective as translational lift is lost; this requirement will not be as great if there is a strong wind. As you raise the collective, the nose will pitch up, correct with cyclic;
5. bring the helicopter to the hover over the selected spot, avoid flaring to reduce the groundspeed to zero; if you have been constantly reducing both height and speed during the transition, a flare should not be necessary; and
6. prevent yaw or drift, as you establish your hover, through the use of pedal and cyclic as appropriate.

 
Figure 12-3: Transition to Hover 
OVERSHOOTING FROM THE TRANSITION TO THE HOVER
On occasion, it may be necessary to carry out an overshoot from the transition to the hover; this is also a valuable co-ordination exercise. To perform this manoeuvre:
1. after checking the traffic, increase collective to set climb power;
2. at the same time, adjust the attitude to the climb with forward cyclic. Depending on your type of helicopter and its approach speed, there may be no difference between the approach and the climb speeds, and therefore little or no required attitude change; and 
3. prevent yaw with pedals.
EXERCISE 13 - AUTOROTATIONS 2 (LANDINGS)
In Exercise 7, you learned how to enter autorotative flight and establish the descent at the minimum rate of descent speed for your helicopter type. You also learned that the helicopter is fully manoeuvrable in autorotation and that turns can be made just as in powered flight. In this exercise, you will learn how to carry out the landing from an autorotational descent in a safe and effective manner.
In addition, you will learn how to perform a “power recovery” in the event that the “full-on” landing may be unsafe due to aircraft performance, inappropriate landing area, a lack of suitable wind or a high-density altitude. The power recovery may be performed to either the hover, or the hover-taxi and is a good coordination exercise and should be practised when it is not possible to perform full-on autorotations. “Power recovery” autorotation is not a substitute for the full-on autorotation. It is essential to practise full-on autorotations to become safe and competent.
In preparation for this exercise, perform the pre-entry H.A.S.E.L. checks that were learned in Exercise 7.
After completing the pre-entry checks, manoeuvre the helicopter to a position, which will allow the safe completion of the full-on autorotation. When in position, smoothly lower the collective and roll the throttle to idle. Adjust the cyclic to acquire the minimum rate of descent speed and remember to compensate both for the yawing and the nose-down pitching moments that occur when the collective and throttle are reduced. During the descent, further adjustment to the cyclic and the collective may be necessary to maintain both the desired speed and the Rotor RPM within limits.
At approximately 50 to 100 feet, depending on the type, a flare is initiated. The purpose  of this manoeuvre is threefold: to reduce forward speed, rate of descent, and increase  Rotor RPM. Commence the flare by applying aft cyclic, keeping straight with pedals. Your instructor will demonstrate to you the effects of applying too much aft cyclic; this will usually result in a climb. Conversely, little flare will not reduce efficiently the forward speed and the rate of descent. In this case, the landing speed will be much greater than desirable, giving the possibility of damaging the helicopter during a fast ground run or the possibility of the helicopter striking its tail.
　
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