Abstract: An improved apparatus for automatic deceleration of a helicopter to substantially zero air speed from a glide slope descent. Parameters available in a typical helicopter automatic flight control system, such as vertical speed, glide slope error, longitudinal acceleration, and pitch attitude are blended together in a manner as to approximate helicopter ground speed which is then used in a control law computation to decelerate the helicopter to a near hover speed as the vehicle approaches a preset altitude minimum.

Abstract: A full time three-cue (roll control, pitch control and collective control) for helicopters flight director and/or autopilot wherein the collective control cue is automatically activated when airspeed is below a predetermined low value or above such value when path errors naturally or manually produced, or airspeed errors exceed predetermined values in magnitude or time.

Abstract: During a transition of a VTOL aircraft such as a helicopter, from one altitude held without its ground effect zone to another to be held within its ground effect zone, or vice versa, a collective stick position synchronizer which can memorize the proper trim condition at the previous altitude in conjunction with the stick force sensor out-of-detent logic and a low vertical speed sensor, together constituting a ground effect zone detector, is used to drive the collective stick trim actuator in a direction which relieves any force being exerted by the pilot in order to maintain the new commanded altitude.

Abstract: An altitude preselect apparatus for use with or incorporation into an automatic flight control system combines the incremental altitude signal from a pneumatic encoding altimeter with a vertical speed computation to generate a smooth, continuous instantaneous altitude signal. A vertical speed reference signal is generated to control the vertical flight path of the aircraft when the instantaneous altitude reaches a prescribed proximity to a desired flying altitude which is manually selected by the pilot. The apparatus initiates a capture sequence to hold the aircraft at the desired altitude once it is reached.

Abstract: A stability augmentation system utilizing a limited authority series actuator has an adaptive washout circuit which automatically reduces the effective washout system washout time constant as a function of attitude error or series actuator displacement. For small errors and for disturbances due to gusting winds, the system washout time constants are slow, thus providing good stability. For large errors the circuit smoothly reduces the time constants to keep the series actuators from saturating.

Abstract: A hybrid analog/digital autopilot utilizing analog inner loops in each control axis of the aircraft and a digital processor for providing outer loop commands and inner loop gain augmentation commands to the inner loops. The command from the processor to each inner loop is buffered by an adaptive rate limit circuit that initially transmits high frequency commands and over a predetermined time interval limits the command rate to a safe low value. Alternatively, the adaptive rate limit buffer transmits the high frequency command up to a predetermined attitude limit and thereafter transmits a command limited to a low safe rate.

Abstract: An aircraft automatic yaw stabilization system with heading hold and manual command override capability provides circuit means responsive to the manual commands for suppressing heading transients in commmanding a heading change and in the ultimate capture of a desired heading.

Abstract: The invention provides improvements whereby the stall current of an actuator servo loop is limited without adversely affecting actuator speed or servo loop dynamics by supplying variable current limits. Full high current capacity is allowed in dynamic situations, but a desirably severe current limit is imposed in the event of a long term stall of the actuator. A simple and inexpensive modification of the servo loop permits the improvement with no limitation of the maximum slew rate and no adverse effects on the large and small amplitude frequency response.

Abstract: An apparatus for extracting signals, proportional to data relative to a given variable, from two data modulated signals which mutually define the variable. Each signal is followed-up with a linear integrate/clamp circuit, the outputs of which are cross multiplied with the input signals. The multiplier output signals are summed and appropriately shaped to provide an output signal that is proportional to the desired angular rate.