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7. The relationship between varying power and attitude is so similar that the true reason for a deviation in airspeed, altitude, or heading is not always apparent. The heading or altitude can change without a corresponding change in attitude. Correct interpretation of information provided by the attitude indicator alone is often a difficult process. This demands correct interpretation of all control and performance instruments for stable co-ordinated flight.
PITCH ATTITUDE CONTROL
The performance instruments for pitch attitude control reference are:
1. Attitude Indicator (control)
The easiest method of visualizing the helicopter attitude, when using the attitude indicator, is to imagine the wings of the miniature aircraft as the rotor disc. The attitude indicator provides general pitch information and is used in conjunction with the other pitch instruments. In cruise flight, the rotor disc should be superimposed on the horizon bar. If the rotor disc rises above the horizon, the VSI and altimeter should confirm a climb, and the airspeed should decay. Small gains or losses of altitude, not exceeding 1.5 bar widths, are made by easing the nose up or down with cyclic. The performance should then be crosschecked against the other pitch instruments. If larger changes are required, power will likely have to be adjusted.
2. Altimeter
The altimeter provides indirect pitch information in cruise flight. Since the helicopter can ascend or descend in the cruise attitude, without an attitude change, the altimeter must be used in conjunction with the other pitch instruments. The altimeter is not a rate instrument and is of limited value if used in this capacity. Fixating on this instrument can lead to “chasing” and overcontrolling if it is used as the sole reference for pitch information.
3. Vertical Speed Indicator (VSI)
The VSI is essentially a trend instrument and should always be used in conjunction with the other pitch attitude instruments. In cruise, the needle indicates zero. Use the VSI together with the altimeter to correct deviations from level flight. Since there is a time lag associated with the VSI, fixating on this instrument can lead to “chasing” the indications, leading to a porpoising effect. Overcorrection leads to overcontrolling. To eliminate overcontrolling, neutralize the controls, allow the attitude to stabilize and readjust pitch attitude using the other pitch instruments.
4. Airspeed Indicator (ASI)
Airspeed is a function of power setting and attitude. In cruise, if the airspeed increases, pitch up. If it decreases, pitch down. Rapid changes in airspeed imply large changes of attitude; small changes represent small changes of attitude. An apparent lag may be observed when making attitude changes because it requires time to accelerate/decelerate. Departure from a constant airspeed due to an inadvertent attitude change results in an altitude change. For example, an increase in airspeed if the nose is low will lead to a decrease in altitude. Correcting the attitude will regain both the airspeed and the altitude.
BANK ATTITUDE CONTROL
The performance instruments used for bank control are:
1. Attitude Indicator
The rotor disc (miniature aircraft) on the attitude indicator displays changes in bank attitude. Banking is shown by the rotor disc assuming an angle in relation to the horizon bar and by the bank index pointer moving from the zero position to the angle of bank reference marks. Cyclic is used to tilt the rotor disc to the required angle of bank; the cyclic position has then to be maintained to hold the desired bank angle. The ball should remain centred during the turn. Small bank angles may not be readily detected on the attitude indicator, but can be determined by cross-reference to the heading indicator and turn and bank indicator or turn coordinator.
2. Heading Indicator
Although the heading indicator gives an immediate indication of turning, its primary purpose is to indicate heading, not bank angle. In co-ordinated flight, when the helicopter is banked, it turns. When the heading indicator shows a constant heading you are flying straight. Small bank angles show up as slow changes of heading; large changes as rapid heading changes. To correct an undesired turn, apply cyclic in the desired direction until the required heading is reached, maintaining co-ordinated flight with pedals. When initiating, or correcting a turn, use a bank angle less than the number of degrees off heading up to a maximum of a standard rate one turn.
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直升机飞行训练手册 HELICOPTER FLIGHT TRAINING MANUAL(58)
