United Technologies Corporation

Ronald E Barnum

Franklin A Tefft

Ricardo L Perez

Louis S Cotton

The pitch and roll channels of the stability augmentation system (inner loop) of a helicopter automatic flight control system are utilized to provide positional and attitude stability at low speeds and hover, and to reduce the attitude effects of wind gusts during essentially level, forward flight at cruise speeds. In the longitudinal or pitch channel, true longitudinal acceleration is summed with washed-out vertical gyro pitch in level flight below 60 knots, and washed-out vertical gyro pitch is used alone above 60 knots; in the lateral or roll channel, true lateral acceleration is summed with vertical gyro roll at speeds below 60 knots in essentially level flight, and vertical gyro roll is inputted alone above 60 knots whenever the heading hold logic has not been disengaged (indicating a roll has not been commanded to perfect a turn); thereby to provide positional and attitude stability at low speeds, and to provide attitude stability at cruise speeds.

Helicopter hover stability and cruise gust effect alleviation

The yaw channel of a helicopter, which includes a yaw servo having a yaw trim valve operable to automatically hold heading, and at cruise speeds alternatively operable to provide controlled yaw for coordinated turns, which is normally disengaged by switches located on the pedals, is selectively allowed to remain engaged at cruise speeds so that if the pilot induces commands in yaw by means of the pedals, the pedal linkage must be forced against the position of the trim piston established by the heading hold or coordinated turn input commands to the yaw trim valve, thereby giving the pilot pedal force feel as a consequence of the resilient connection to the trim piston, which provides an indication to the pilot of the amount of side slip he is creating, thereby to avoid destructive overloading of the tail rotor.

Helicopter pedal feel force proportional to side slip

The automatic heading retention mode of operation of a flight control system for a rotary wing aircraft is discontinued and reestablished through the use of logic circuitry responsive to the bank angle of the aircraft and to the force applied to a control stick by the pilot. When the bank angle of the aircraft exceeds a preselected minimum and the lateral force applied to the cyclic pitch stick also exceeds a predetermined minimum the logic circuit operates to isolate the heading hold control from heading error signals and the heading retention mode of operation is automatically resumed when both of the bank angle and stick force fall below the preselected minimum levels. The invention may also encompass the application to the control mechanism of signals which will cause the aircraft to perform coordinated turns above a preselected minimum airspeed.

Automatic heading synchronization control system

To prevent inadvertent ground contact of the tail of a helicopter during a landing operation without providing a continuous warning signal for normal landings the altitude and attitude signals are scaled such that when they are equal and opposite in voltage and phase compared to a ground contact curve the comparator will energize a relay for actuating a pilot warning signal. A rate of descent signal biases the altitude signal upward varying in proportion to rate of descent as to enable the pilot to have sufficient warning time to take corrective action.

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Trumbull, CT, United States of America

Ronald E Barnum