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An accurate level turn entry requires that the helicopter be flying straight and level as accurately as possible, prior to entering the turn. Any error made before entering the turn is likely to be exaggerated as the turn develops. The same principle applies to turns while descending or climbing.
In making an accurate turn, the trained pilot co-ordinates the movement of all three controls so that the entry, the sustained turn, and recovery is made in one apparently simultaneous movement. Cyclic controls bank and pitch attitude, the collective controls altitude and the pedals prevent yaw.
To execute a turn from straight and level flight:
1. make sure the helicopter is in accurate straight and level flight;
2. look out for other aircraft;
3. roll the helicopter gently to the desired bank attitude with lateral cyclic, maintain this attitude, and at the same time;
4. use appropriate pedal pressure to control any tendency for the helicopter to yaw;
5. use cyclic to maintain the correct attitude in relation to the horizon; and
6. maintain the lookout.
In a gentle turn, the position of the nose in relation to the horizon, which is the visual reference for pitch attitude, will remain relatively the same as in straight and level flight. However, as the angle of bank is increased, the attitude of the disc must be altered by backward pressure on the cyclic. This is to compensate for the added load factor imposed by centrifugal force as the turn steepens. The loss in airspeed, or the need for an increase in collective to maintain airspeed, becomes more apparent as the angle of bank increases.
As the helicopter settles into an accurate turn in co-ordinated flight:
1. the nose will move steadily around the horizon, neither rising nor falling;
2. the airspeed will be constant;
3. the turn indicator will show a constant rate of turn;
4. the ball will be centred in its glass tube;
5. the altimeter will be steady, and
6. you should repeatedly check the attitude instruments and maintain a good lookout.
One common fault when entering turns is excessive use of the pedals. This fault can be corrected quickly or completely prevented, if you remember right from the outset not to apply pedal unless it is necessary to control yaw. Normally you may need only a small pedal input into the turn.
To recover from a turn onto a pre-selected heading:
1. look out for other aircraft;
2. anticipate the desired heading by approximately 10 degrees;
3. roll the helicopter to level flight with lateral cyclic, and at the same time;
4. use appropriate pedal pressure to control yaw;
5. select correct attitude with cyclic; and
6. maintain the new heading and look out.
Climbing and descending turns are executed like level turns except that instead of maintaining a constant altitude, a constant climb or descent is maintained. The control inputs to enter, maintain, and recover from the turn are the basically the same as in level turns. Initially, climbing and descending turns will be entered from normal straight climbs and descents and the recovery made back to straight climbing or descending flight, to enable you to experience and readily observe the difference in pitch attitude necessary to maintain the desired airspeed. As you gain proficiency, these turns will be entered directly from straight and level flight, and recovery made directly back to straight and level flight.
STANDARD RATE TURNS
The standard rate turn is a turn at the rate of 3 degrees per second. The rate at which a helicopter turns is determined by airspeed and angle of bank. At a given airspeed a specific angle of bank will provide a certain rate of turn. A simple way to estimate the angle of bank required for a standard rate turn at a given airspeed is to take 10% of the airspeed (mph) and add 5 to the quotient or add 7 to the quotient if the airspeed is in nautical miles (kt). For example, at 100 mph, (10 + 5) = 15 degrees of bank; at 80 kt, (8+7)= 15 degrees of bank.
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直升机飞行训练手册 HELICOPTER FLIGHT TRAINING MANUAL(16)
