Patent Description:
Flight control systems for aircraft provides variable tactile feel for manually controlled mechanical members in charge of a flight control member, for instance, a lever actuated by the pilot.

The following different types of trim systems are known in the state of the art:.

In passive systems a feel force is used to control the forces that pilot operates during operation, i.e., systems that include a feel actuator. Therefore, a manual control member has an end manually operable by the pilot of the aircraft and a passive spring-damper component linked to the manual control member.

Thus, the trim actuator is used to transmit a sensation of forces to the pilot in response to the pivoting maneuvers that the pilot operates via the manual control member. The actuator is typically redundant in design, i.e., with more than one rod.

According to the above, the actuator has two main functionalities, the capability of positioning the zero-load of sensation of forces feel and providing the pilot with the artificial tactile feeling of maneuvering stick force by the capability to keep the target position to provide the required feel forces.

The spring in series with the actuator allows the feel force to be composed by the forces of the spring. The zero-load of the feel actuator is centered and controlled by the trim actuator based on a mechanical translation of the spring in series with the actuator as previously explained.

According to the above, in order to keep the target position of the actuator, the mechanical design defines an irreversible characteristic of the actuator that is able to avoid the motion of the actuator under the maximum operating external load applied by the manual control member. This characteristics could be achieved by friction, brake, or mechanical stop. Thus, the motion of the actuator is only possible from the electrical motor.

The zero-load centering compensation could be performed by pilot manual operation, or it could be performed by a computer controller that is able to operate the trim actuator depending on flight conditions. This controller is in charge of operating the trim electrical motor.

When the centering operation is performed by a computer, the system requires a control-monitor computing device for safety reasons. The monitor computing device validates and allows the operation calculated or performed by the control computing system. Any discrepancy detected by the monitor computing device, or loss of one computing device, will not validate the operation of the control system avoiding the zero-load trim operation.

As the trim actuator is irreversible, external electrical failures that causes unintended motion of motor could cause an "uncountered trim runaway" failure, i.e., and the actuator is fully retracted or extended. In this case, the pilot capability for maneuverability aircraft is reduced. <CIT> discloses an artificial force feel generating device for generation of an artificial feeling of force on an inceptor of a vehicle control system.

<CIT> discloses control systems in general and, more particularly, control systems for aircraft.

The active trim system of a flight control system of an aircraft object of the invention is adapted for transmitting a tactile feeling or sensation of forces to a pilot of the aircraft through a manual control member in response to a manoeuvre of the flight control member.

The active trim system object of the invention comprises:.

Parallel is understood in this invention as everywhere equally distant, i.e., the elastic deformation means and the rod of the reversible actuator are equally distant along their length.

Stiffness is the extent to which an object resists deformation in response to an applied force. Said stiffness is provided by the reversible actuator and the elastic deformation means to the intermediate linkage member and hence to the manual control member.

Reversible actuator means that is movable by the motor and also by the motion of the manual control member, therefore the pilot may exert a force that moves the reversible actuator.

Thus, one of the objectives of this invention is to implement a redundant control system able to control the feel forces with an active systems. The claimed arrangement allows the feel forces to be composed of the sum of the forces of the elastic deformation means and also the added forces of the parallel reversible actuator.

In normal operation, i.e., without any failure, this system is configured to operate the motor of the reversible actuator in the same way as in the state of the art in order to minimize the differences of control demands. Therefore, the controller is able to control actively the feel forces. The trim actuator is able to both position the zero-load force according to the flight conditions and in addition provide an added virtual stiffness of the tactile feel forces.

The known series architecture of the state of the art is a system that feel loads are composed only of the stiffness of the elastic deformation means whose centered mechanical position is positioned by the actuator. To the contrary, the parallel architecture object of the invention is a system in which feel loads are composed of the added forces of the elastic deformation means and the parallel reversible actuator. This allows to modify not only the zero position but also the stiffness provided by the elastic deformation means with the additional stiffness provided by the reversible actuator to better adapt to the flight conditions.

The parallel reversible actuator could add loads in both directions in order to modify the zero-load and the stiffness of spring to achieve the feel force required for operation. The above active trim system is able to actively control the tactile feeling operation of flight control system in order to add, increase or reduce, feel forces to the spring forces to achieve the forces required according to the flight conditions.

Thus, the system object of the invention implements a redundant control system able to control the tactile feel forces with an active and reversible mechanism wherein the pilot could operate the total control of positioning.

To complete the description and to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate preferred embodiments of the invention. The drawings comprise the following figures.

<FIG> discloses series trim system according to the state of the art. The trim system comprises:.

The elastic deformation means (<NUM>), and the irreversible actuator (<NUM>) are mechanically linked to the rotatable lever arm (<NUM>) at one of their ends. They are specifically joined to the rotatable lever arm (<NUM>). The other end of the elastic deformation means (<NUM>) is in connection with the manual control member (<NUM>) and the other end of the reversible actuator (<NUM>) is joined to an aircraft structure.

<FIG> discloses an embodiment of the object of the invention. The active trim system comprises:.

In the shown embodiment, the reversible actuator (<NUM>) is redundant as it comprises two reversible actuator (<NUM>) with two motors (<NUM>) and two rods (<NUM>).

In the shown embodiment, the elastic deformation means (<NUM>), and the reversible actuator (<NUM>) are joined to the intermediate linkage member (<NUM>) at one of their ends. They are joined to an aircraft structure at their other end. An end of the manual control member (<NUM>) is joined to the intermediate linkage member (<NUM>).

In an embodiment, in case of failure of the active trim system, the controller is configured to disconnect the motor (<NUM>) such that the reversible actuator (<NUM>) is movable only by the motion of the manual control member (<NUM>) so that the tactile feeling transmitted to the manual control member (<NUM>) comes only from the elastic deformation means (<NUM>).

Thus, the embodiment avoids any runaway of feel force trim actuator (<NUM>) as it is based on a reversible system. In case of failure of the actuator (<NUM>), an electrical disconnection is performed and therefore the parallel added forces are removed. The reversible actuator (<NUM>) is disconnected automatically with the computer or manually by pilot action.

It has the advantage that the pilot could continue the operation of the flight control system with just the feel forces composed of only the elastic deformation means (<NUM>). Any runaway or not controlled operation of the actuator (<NUM>) is avoided by electrical disconnection. This will produce that the tactile feel force will be only of the passive elastic deformation means (<NUM>) without the actuation of the parallel reversible actuator (<NUM>). Thus, a fixed feel elastic element provides a fixed force gradient when the trim actuator (<NUM>) is disengaged. It has to be noted that the elastic deformation means (<NUM>) is a mechanical system that depends neither on a computer nor on electrical supply.

Thus, the system object of the invention implements a redundant control system able to control the tactile feel forces with an active and reversible mechanism wherein the pilot could operate the total control of positioning even in a situation of an uncountered runaway of feel actuator (<NUM>). Although it may imply an over-workload for the pilot, he/she can operate the flight control element through the manual control member (<NUM>).

In an embodiment, in a failure, the forces will be centered to a certain position pre-defined by operation requirement, i.e., to a pre-set zero-load position.

Due to safety reasons, the auto trim operation performed by a computer requires a control/monitor computing system. A monitor computing device validates and allows the operation calculated/performed by the control computing device. Any discrepancy detected by the monitor computing device, or loss of one computing device will not validate the operation of the control device and the operation is not allowed. This control operation crosscheck performed by the monitor computing device allows to avoid any failure, mainly a runaway failure, of trim actuator (<NUM>). As the actuator (<NUM>) of the device object of the invention is reversible that means that in case of any failure or unintended operation the monitor device will switch-off the reversible actuator (<NUM>), as previously explained, but still keeping the operation with the elastic deformation means (<NUM>) feel forces.

In addition, the tactile feel trim actuator (<NUM>) is designed to introduce a maximum force, even in case of failure, lower than the maximum force that pilot can apply to the manual control member (<NUM>) for a long period of time so that the pilot is able to manipulate the manual control member (<NUM>) by himself to control the aircraft.

In an embodiment, the intermediate linkage member (<NUM>) comprises a sensor for measuring the displacement of the elastic deformation means (<NUM>) that is the input force of the pilot since the position of the irreversible actuator (<NUM>) is already known.

<FIG> discloses a representation of reversible actuator (<NUM>) and passive spring system (<NUM>) performances.

As previously stated, the operation of feel forces is based on the force of two components, the spring that provides zero-load and stiffness feel and the parallel reversible actuator (<NUM>) that provides an added stiffness. The parallel reversible actuator (<NUM>) adds forces to the spring in both direction, as they are placed in parallel, by controlling a close loop current whose target is the operating feel force target. The parallel reversible actuator (<NUM>) mechanically deforms the spring to sum or subtract forces.

As can be seen in <FIG>, according to the performance of the parallel reversible actuator (<NUM>), the mechanical dead-zone or hysteresis of the spring mechanics can be corrected by adding or subtracting the required forces of the spring stiffness in order to obtain a continuous curve along the complete stroke of the actuator (<NUM>).

The system object of the invention with a parallel reversible actuator is able to introduce an offset in the spring position in order to vary the zero-force position of the spring according to flight conditions.

In addition, the feel stiffness, force-stroke slope of spring, could be controlled by adding/removing force with the parallel reversible actuator (<NUM>) in order to, for instance, increase the stiffness at high speed or reduced it at low speed.

Claim 1:
Active trim system of a flight control system for an aircraft, for transmitting a tactile feeling to a pilot of the aircraft in response to a manoeuvre, the active trim system comprising:
- a manual control member (<NUM>) for operating the flight control system and for transmitting the tactile feeling to the pilot, and
- an elastic deformation means (<NUM>) having a longitudinal axis,
wherein the active trim system further comprises:
- a reversible actuator (<NUM>) comprising a rod (<NUM>) and a motor (<NUM>), the rod (<NUM>) of the reversible actuator (<NUM>) being located parallel to the elastic deformation means (<NUM>) and being lineally displaceable in the direction of the longitudinal axis of the elastic deformation means (<NUM>), the reversible actuator (<NUM>) being movable by the motor (<NUM>) and by the motion of the manual control member (<NUM>),
- an intermediate linkage member (<NUM>) mechanically linked to the manual control member (<NUM>), located between:
- the manual control member (<NUM>), and
- the elastic deformation means (<NUM>) and the reversible actuator (<NUM>),
- a controller in connection with the motor (<NUM>) of the reversible actuator (<NUM>) and configured to provide stiffness against a displacement of the intermediate linkage member (<NUM>) by the manual control member (<NUM>), characterised in that the intermediate linkage member is lineally displaceable in the direction of the longitudinal axis of the elastic deformation means (<NUM>) by the motion of the manual control member and/or of the reversible actuator and in that the controller is also configured to move the reversible actuator (<NUM>) and in turn the elastic deformation means (<NUM>) to a predetermined zero position.