Abstract: In an automatic flight control system, failure of dual inner loop actuators (12, 13) to track position (22, 23) within a permissible tolerance (182) of each other will cause automatic shut down (185, 190) of an outer loop actuator (37) which is responsive (61) to the same proportional signals (54, 55) as are the inner loop actuators. The invention is disclosed in a system in which automatic flight control positioning of the control surfaces of the aircraft is through a fast, limited authority inner loop, the authority of which is centered by repositioning of the outer loop.

Abstract: An aircraft automatic flight control system having a roll channel (FIG. 1), a yaw outer loop trim system (bottom of FIG. 2) and a yaw stability inner loop (top of FIG. 2) provides proportional (129) and integral (114) lateral acceleration inputs to the yaw trim system (106, 93) during coordinated turns, and provides proportional (130) and lagged (131) roll rate inputs to the trim system to provide initial coordination to the turns.

Abstract: In an aircraft automatic flight control system, proportional commands (54, 55) provided to fast, limited authority inner loop actuators (12, 13) are integrated (41), and when the integrator output indicates that the inner loop actuators 12, 13 have been driven a certain percentage of their authority, a comparator (130, 132) activates a pulse generator (137, 138) to provide timed excitation of an actuator (150), thereby to position the aircraft control system outer loop by a commensurate increment. Driving the actuator for a longer time than the desired pulse width is detected (165-169) and causes automatic shutdown (190) of the actuator. Resetting the integrator at the start of each pulse (162, 104), and pulse-controlled gating of the pulse circuits (172, 135, 136) allow sensing of authority transitions which occur within a pulse, and permit a subsequent pulse in response thereto.

Abstract: In an aircraft automatic flight control system, a flight path controlling, full authority outer loop actuator (37) operated in response to the integral (41) of commands thereto, is shutdown (111, 113-115) in response to the sensing (31, 32) of force on the related pilot control member (27). After removal of force (118), the outer loop is continued to be shut down for a time interval (119) to allow the aircraft to resettle toward the trim point before building up error in the integrator, unless high input demand (122) is indicated.

Abstract: In an aircraft automatic flight control system (FIG. 4) the application of force to a control member (35R, FIG. 5) forces (222, 216, 217, 212, 213) the flight path controlling, full authority outer loop to be disengaged. Once disengaged by force, the outer loop remains disengaged (224) until force is removed (225) and a signal indicates (226) a need to reestablish the outer loop. Reestablishment may be indicated by beeping (228) or by the controlled attitude (54R, 55R) being restored to within a predetermined level (230).

Abstract: In a helicopter automatic flight control system having both automatic pitch attitude retention (70, 71) and automatic airspeed hold (84) and responsive both to pitch attitude error (206) and integrated (241) airspeed error (230), saturation of either the attitude error or integrated airspeed error circuitry is avoided by sensing (171) integrated airspeed error buildup to a threshold magnitude (which may be a significant fraction of the instantaneous authority of the automatic flight control system), and causing (169, 167) automatic slewing of the pitch attitude reference signal toward the current pitch attitude and reduction of the integrated airspeed error. In a disclosed embodiment, the correction of attitude reference and reduction of airspeed error is effected by utilizing an equal effective time constant (220, 221; 258, 259) for both actions over the same period of time (170, 168, 175).

Abstract: An aircraft automatic flight control system includes a pair of fast, limited authority inner loop actuators (12, 13) responsive to signals (52-55) indicative of aircraft attitude (68, 69) or other flight parameters such as airspeed (84), the inner loop being recentered by an outer loop actuator (37) responsive to attitude or other aircraft parameter-indicating signals (54, 55). Commands (40) applied to the outer loop are applied in a lagged fashion (58, 59) in opposite direction so as to drive the inner loop actuators (12, 13) back toward the center of their authority. The rate of response of the outer loop (FIG. 2, FIG. 5) is adaptive in dependence upon airspeed (93, 96, 212, 213) and in response to magnitude of inner loop input (101, FIG. 2). An integral gain (41), pulsed (39), open loop drive of the outer loop actuator (37) and outer loop automatic shutdown (38) are disclosed.

Abstract: In an aircraft automatic flight control system (FIG. 1) beeping of the reference voltage in attitude synchronizing and beeping circuits (70, FIG. 4; 70R, FIG. 6) is inhibited (196, 201; 278, 282) in response to proportional commands (54, 55; 54R, 55R) in excess of a predetermined magnitude (183-186, 283-286). Beeping is inhibited only in the direction of the high proportional command, but not in the other direction. In a dual system (FIG. 1) pitch attitude beeping is inhibited only if both channels of the system have excessive proportional commands (195, 200, FIG. 3) whereas roll attitude beeping is inhibited if either channel has excessive proportional command (294, 295).

Abstract: In an aircraft automatic flight control system (FIG. 1) having an airspeed controller (84), the engagement of the airspeed control function (244, FIG. 4 ) is initiated (123, FIG. 2 ) only in response to airspeed being greater than a 45 knot threshold (88). But once the speed threshold is attained, should the pilot override the airspeed control by applying force (35, 109) to the pitch attitude controller, airspeed engagement is retained (122) until a small airspeed error (126) indicates that the system has substantially regained the reference airspeed.

Abstract: In an aircraft automatic flight control system (FIG. 1) having pitch attitude synchronizing and beeping circuits 70-71 and airspeed control circuits 84, trimming of airspeed (233, 165) is achieved by beeping (104) or releasing trim (45) to adjust the pitch attitude synchronizer reference (208), causing the airspeed reference (232) to be synchronized (233, 165) for 25 seconds (156), unless the pilot applies force to the longitudinal axis (31, 32, 35) of the cyclic pitch stick (27), which causes (160, 156) termination of airspeed synchronizing.

Abstract: The engagement (83) of a flight director (82) that provides automatic steering by roll angle of an aircraft which includes an automatic yaw trim system (FIG. 2) that will automatically coordinate turns induced by the flight director establishes (155, 157, 138) a heading hold disengagement mode which is maintained even if the flight director becomes disengaged (160) until the aircraft roll attitude is indicated as being nearly level (163). Exemplary roll channel (FIG. 1) and yaw channel (FIG. 2 ) of an automatic flight control system which may incorporate the invention are disclosed.

Abstract: In an automatic flight control system (FIG. 1) an airspeed control engage function (84) is automatically engaged (136, FIG. 2; 244, FIG. 4) in response to airspeed above a threshold magnitude, such as 45 knots (88, FIG. 2) and will remain engaged (subject to a fault condition, 135) until the airspeed command (75) reaches a predetermined, insignificant magnitude (132). An airspeed error integrator 241 which accommodates the difference between a reference attitude and an attitude required for a reference airspeed, does not react to large airspeed errors as a consequence of pilot maneuvering due to pilot force on the control stick (35, 109) opening the input (252, FIG. 4) to the airspeed error integrator.