United Technologies Corporation

Franklin A Tefft

Ronald E Barnum

Ricardo L Perez

Louis S Cotton

Don L Adams

Douglas H Clelford

Richard D Murphy

Lou S Cotton

Collective stick inputs are provided (18) to a high pass filter (24) when collective stick reversals in excess of a threshold collective authority rate (15%/sec) and in excess of a threshold frequency (3 stick reversals per second) are sensed. The output of the high pass filter (24) is scaled (26) and subtracted (14) from the collective inputs so as to effectively cancel the threshold stick reversals. Otherwise, if no stick reversals in excess of the threshold collective authority rate are sensed for a threshold time interval (5 seconds), the collective stick inputs are not provided to the high pass filter.

Preventing augmenting vertical load induced oscillations in a helicopter

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 longitudinal cyclic pitch channel of a helicopter has a negative pitch rate feedback bias added thereto when flying at higher speeds, thereby to stabilize the pitch axis against aft-load maneuvering instability and/or to induce a requirement for the pilot to provide a countermanding longitudinal cyclic pitch input through his cyclic pitch stick, the normal feed force of which provides an indication to him of the loading of the rotor as a consequence of undergoing pitch rate maneuvers.

Helicopter pitch rate feedback bias for pitch axis maneuvering stability

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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Killingworth, CT, United States of America

Franklin A Tefft