Flight Line Supplement

Question 1

Primary function of the stabilator?

Answer 1

The primary function of the stabilator is the longitudinal control of the aircraft.

Question 2

To achieve this longitudinal control the stabilator is programmed to its optimum angle to provide the following functions: (SCALP)

Answer 2

STREAMLINE or Align stabilator to main rotor downwash in low speed flight to minimize nose-up attitude resulting from downwash. (30 KIAS and below to minimize nose-up attitudes from the main rotor downwash on the stabilator)

COLLECTIVE COUPLING to minimize pitch attitude excursions due to collective inputs from the pilot. Collective position sensors detect pilot collective displacement and program the stabilator a corresponding amount to counteract the pitch changes. This coupling begins at 30 KIAS.

ANGLE of incidence decrease with increased airspeed to improve static stability. (programs up with increased airspeed)

LATERAL Sideslip to Pitch Coupling to reduce susceptibility to gusts. This feature compensates for downwash on the stabilator and tail rotor efficiency. In forward flight, the downwash on the retreating side of the rotor system is weaker than the downwash on the advancing side. If a right sideslip is entered (left pedal applied), the stabilator encounters increased downwash and the nose tends to pitch up, therefore the stabilator programs down to prevent the nose up attitude. A right sideslip condition also results in increased induced flow through the tail rotor and a corresponding decrease in the amount of lift provided by the tail rotor. In a left sideslip (right pedal applied), the stabilator is positioned in a reduced downwash area, causing the nose to pitch down. The stabilator programs trailing edge up to prevent the nose from pitching down. A left sideslip condition also results in decreased induced flow through the tail rotor and a corresponding increase in the amount of lift provided by the tail rotor.

PITCH rate feedback to improve dynamic stability. The rate of pitch attitude change of the helicopter is sensed and used to position the stabilator to help dampen pitch excursions during gusty wind conditions. A sudden pitch up due to gusts would cause the stabilator to be programmed trailing edge down a small amount to induce a nose-down pitch to dampen the initial reaction.