In order to fly a helicopter by reference to the instruments, you should know the approximate power settings required for your particular helicopter in various load configurations and flight conditions.  Trim, in helicopters, refers to the use of the cyclic center- ing button, if the helicopter is so equipped, to relieve all possible cyclic pressures. Trim also refers to the use of pedal adjustment to center the ball of the turn indicator. Pedal trim is required during all power changes. The proper adjustment of collective pitch and cyclic friction helps you relax during instrument flight. Friction should be adjusted to minimize overcontrol- ling and to prevent creeping, but not applied to such a degree that control movement is limited. In addition, many helicopters equipped for instrument flight con- tain stability augmentation systems or an autopilot to help relieve pilot workload. Controlling the helicopter is the result of accurately interpreting the flight instruments and translating these readings into correct control responses. Aircraft control involves adjustment to pitch, bank, power, and trim in order to achieve a desired flight path.  Pitch attitude control is controlling the movement of the helicopter about its lateral axis. After interpreting the helicopter’s pitch attitude by reference to the pitch instruments (attitude indicator, altimeter, airspeed indi- cator, and vertical speed indicator), cyclic control adjustments are made to affect the desired pitch atti- tude. In this chapter, the pitch attitudes illustrated are approximate and will vary with different helicopters. Bank attitude control is controlling the angle made by the lateral tilt of the rotor and the natural horizon, or, the movement of the helicopter about its longitudinal axis. After interpreting the helicopter’s bank instru- ments (attitude indicator, heading indicator, and turn indicator), cyclic control adjustments are made to attain the desired bank attitude. Straight-and-level unaccelerated flight consists of maintaining the desired altitude, heading, airspeed, and pedal trim. The pitch attitude of a helicopter is the angular relation of its longitudinal axis and the natural horizon. If avail- able, the attitude indicator is used to establish the desired pitch attitude. In level flight, pitch attitude varies with airspeed and center of gravity. At a constant altitude and a stabilized airspeed, the pitch attitude is approximately level. [Figure 12-11] Power control is the application of collective pitch with corresponding throttle control, where applicable. In straight-and-level flight, changes of collective pitch are made to correct for altitude deviations if the error is more than 100 feet, or the airspeed is off by more than 10 knots. If the error is less than that amount, use a slight cyclic climb or descent. 12-7 Figure 12-11. The flight instruments for pitch control are the airspeed indicator, attitude indicator, altimeter, and vertical speed indicator. STRAIGHT-AND-LEVEL FLIGHT PITCH CONTROL AIRCRAFT CONTROL PITCH CONTR PITC H C O NTROL OL