直升机飞行训练手册 HELICOPTER FLIGHT TRAINING MANUAL(23)

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1. flapback;
2. translational lift;
3. dissymmetry of lift; and
4. the height/velocity diagram for your helicopter type.
The manoeuvres that are employed to accelerate the helicopter from the hover to forward flight, and decelerate it from forward flight to the hover, are known as transitions. In fact all accelerations or decelerations of the helicopter in any direction as a result of cyclic change are transitions.
During this exercise, you concentrate on performing smooth and accurate transitions. The ability to perform accurate transitions is important in the working environment of the helicopter pilot.
Remember to carry out a careful lookout during this exercise and to perform a clearing turn prior to each takeoff. Do this by turning 90 degrees right or left and observing that the approach area is clear of other aircraft.
TRANSITION TO THE CLIMB
Begin the transition to the climb from a steady into-wind hover at normal hover height  (Fig 12-1): 
1. make the clearing turn to ensure that both approach and departure paths are clear;
2. ease the cyclic forward to initiate forward movement, and as you have tilted the disc thereby decreasing the vertical component of lift;
3. increase collective sufficiently to maintain your height and to prevent the helicopter from sinking;
4. apply additional forward cyclic to prevent the occurrence of flapback as a result of lift dissymmetry;
5. as effective translational lift is achieved, the helicopter begins to climb, smoothly apply climb power and set the best rate of climb speed’s attitude; and
6. prevent yaw throughout the manoeuvre with pedals.

 
Figure 12-1: Transition to Forward Flight
 
As effective translational lift is achieved the nose will tend to rise and the helicopter will  want to climb. Remember to stay within the take-off corridor of the Height/Velocity diagram. Forward cyclic may be required to prevent the helicopter from climbing into the “Avoid” curve. In winds of approximately 15 mph or more, flapback will not be encountered as the helicopter is already experiencing translational lift (Fig 12-2).
 

 
Figure 12-2: Height/Velocity diagram showing “Avoid” areas for a typical light, single-engine helicopter 
 
During this exercise, your instructor will demonstrate the effects of flapback if it is not compensated for with additional forward cyclic during the transition.
 
 
TRANSITION FROM STRAIGHT AND LEVEL FLIGHT TO HOVER 
This transition is the standard type of approach to a hover or to a landing that will be utilised throughout your training and your career. (Fig 12-3)
The manoeuvre requires that you combine two separate actions in a co-ordinated procedure to achieve:
1. height reduction; and
2. speed reduction.
HEIGHT REDUCTION
The height of the helicopter has to be reduced from the approach altitude, (this may be circuit height, cruise altitude or whatever altitude you are flying at), to hover height above ground. Ideally this is a constant angle, straight-line type of approach, which can be made with little change of attitude and gradual changes in power.
SPEED REDUCTION
The approach speed must be progressively reduced to zero groundspeed as you arrive at  the hover. Since different approach angles or wind conditions will cause the airspeed to vary, refer to groundspeed, and not airspeed as indicated on your instruments. A good guide for approaching the touchdown point is to fly so that the helicopter appears to be moving across the ground at a walking pace. If you are able to maintain this visual perspective, your groundspeed will be constantly reducing throughout the transition to the hover.
To begin the transition to the hover, after ensuring the approach path and the landing zone are clear of other traffic, set the helicopter up straight and level, into wind, at a specific height and airspeed. For training purposes a minimum of 300 feet is desirable, with speed appropriate to type:
　
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