Abstract: An improved flight director go-around mode adjusts the collective stick position in a closed loop to increase lift to a desired value. If the engagement airspeed is below the maximum rate of climb airspeed, the airspeed is increased towards the maximum rate of climb airspeed at a moderate rate. When the maximum rate of climb airspeed is attained, or if the engagement airspeed is at least the maximum rate of climb airspeed, and the rate of climb is satisfactory, the airspeed is maintained. If the engagement airspeed is greater than the maximum rate of climb airspeed and the desired rate of climb is not achieved within ten seconds, the airspeed is decreased towards the maximum rate of climb airspeed. Heading or course is automatically maintained when go-around is engaged.

Abstract: An improved PBA shutdown monitor circuit senses collective pitch control position rate of change magnitude and inhibits PBA shutdown in response to the continuous presence of sensed magnitude within a range of selected collective pitch rate magnitudes bounded by a slow rate limit signal value and a fast rate limit signal value.

Abstract: In an aircraft automatic flight control system, automatic shutdown (42) of the roll axis thereof (FIG. 1) as a consequence of faults detected therein also provides automatic shutdown of the yaw axis thereof (180) in the same fashion as detection of faults in the yaw axis (171, 167) provides shutdown of the yaw axis. Coupling of the roll axis shutdown into the yaw axis shutdown allows determining which of three axes cause lighting of a single trim shutdown indicator by resetting the yaw shutdown register (145) and simultaneously resetting both the pitch and roll shutdown registers by means of a single cyclic pitch control switch. Automatic yaw trim outer loop and yaw inner loop stability systems are disclosed (FIG. 2).

Abstract: In an aircraft automatic flight control system having a reference parameter synchronizing system (70) operable in response to a trim release switch (44), an initial trim release period (139), on the order of a large fraction of a second (137) causes (217, 218) a relatively slow effect trim reference integrator (208, 211) time constant, for smooth transitions of any error signal, followed by a relatively fast (216) effective reference integrator time constant for close, rapid tracking of the reference signal with the actual aircraft parameter.

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, 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, 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 (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 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 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 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.

Abstract: Oscillations in helicopter attitude sustained by the aerodynamic response of the helicopter to an automatic flight control system which is responsive to an attitude sensor, are eliminated by band reject (notch) filtering of a control system stability command to the aircraft, derived from rate of changes of such attitude at a frequency related to the aircraft attitude oscillations induced by the rate-controlled stability compensation.

Abstract: An electrical circuit for allowing electrical power to be applied to the ctro-mechanical sensors of an automatic flight control system of an aircraft only when either the Engine Start switch or AFCS Engage switch is closed separately or simultaneously. Upon the closing of either one or both of the switches, a pair of latching relays are energized which in turn provide electric power to the electro-mechanical sensors.

Abstract: A helicopter having an automatic flight control system including an inner, stability loop is rendered less sensitive to short-term, inadvertent pilot inputs by applying a washed-out derivative of a stick position signal to the inner stability loop in a sense to countermand the pilot action. Using a washed-out signal countermands only short-term rapid stick motions, which may be induced by the pilot actively, but inadvertently, or inactively due to coupling between the pilot or the stick and motion of the fuselage, while permitting purposeful, long-term stick positions to have the full, intended effect.

Abstract: A bias actuator, such as an extensible link, in the longitudinal cyclic pitch channel of a helicopter is provided with inputs as a function of airspeed multiplied inversely with collective pitch, and as a function of the rate of change of collective pitch stick position, so as to enforce positive angle of attack and speed stability and positive static pitch trim gradient and to decouple collective pitch from the longitudinal cyclic pitch channel at cruise airspeeds, the invention compensates, inter alia, adverse control effects of tail stabilizer surfaces at cruise speeds. A pair of indicators display bias commands and actual bias responses.