Direct-drive control of aircraft stability augmentation

According to one embodiment, a stability augmentation system includes a master linkage, a stability augmentation motor, and three linkages. A first linkage is coupled to the master linkage and operable to receive movements representative of pilot commands from a pilot command system. A second linkage is coupled between the stability augmentation motor and the master linkage and operable to receive movements representative of augmentation commands from the stability augmentation motor. A third linkage is coupled to the master linkage and operable to transmit movements representative of blade position commands to a blade control system in response to the movements representative of pilot commands and the movements representative of augmentation commands.

TECHNICAL FIELD

This invention relates generally to aircraft stability and control augmentation systems, and more particularly, to a direct-drive control of aircraft stability augmentation.

BACKGROUND

A rotorcraft may include one or more rotor systems. One example of a rotorcraft rotor system is a main rotor system. A main rotor system may generate aerodynamic lift to support the weight of the rotorcraft in flight and thrust to counteract aerodynamic drag and move the rotorcraft in forward flight. Another example of a rotorcraft rotor system is a tail rotor system. A tail rotor system may generate thrust in the same direction as the main rotor system's rotation to counter the torque effect created by the main rotor system. A rotor system may include one or more devices to rotate, deflect, and/or adjust rotor blades.

SUMMARY

Particular embodiments of the present disclosure may provide one or more technical advantages. A technical advantage of one embodiment may include the capability to provide stability augmentation in an aircraft. A technical advantage of one embodiment may also include the capability to reduce jam-type failure modes in a stability augmentation system. A technical advantage of one embodiment may also include the capability to reduce the weight and size of a stability augmentation system. A technical advantage of one embodiment may also include the capability to eliminate gearboxes from a stability augmentation system.

Certain embodiments of the present disclosure may include some, all, or none of the above advantages. One or more other technical advantages may be readily apparent to those skilled in the art from the figures, descriptions, and claims included herein.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1shows a rotorcraft100according to one example configuration. Rotorcraft100features a rotor system110, blades120, a fuselage130, a landing gear140, and an empennage150. Rotor system110may rotate blades120. Rotor system110may include a control system for selectively controlling the pitch of each blade120in order to selectively control direction, thrust, and lift of rotorcraft100. Fuselage130represents the body of rotorcraft100and may be coupled to rotor system110such that rotor system110and blades120may move fuselage130through the air. Landing gear140supports rotorcraft100when rotorcraft100is landing and/or when rotorcraft100is at rest on the ground. Empennage150represents the tail section of the aircraft and features components of a rotor system110and blades120′. Blades120′ may provide thrust in the same direction as the rotation of blades120so as to counter the torque effect created by rotor system110and blades120. Teachings of certain embodiments relating to rotor systems described herein may apply to rotor system110and/or other rotor systems, such as other tilt rotor and helicopter rotor systems. It should also be appreciated that teachings from rotorcraft100may apply to aircraft other than rotorcraft, such as airplanes and unmanned aircraft, to name a few examples.

FIG. 2shows rotor system110and blades120ofFIG. 1according to one example configuration. In the example configuration ofFIG. 2, rotor system110features a power train112, a hub114, a swashplate116, and pitch links118. In some examples, rotor system110may include more or fewer components. For example, FIG.2does not show components such as a gearbox, a swash plate, drive links, drive levers, and other components that may be incorporated.

Power train112features a power source112aand a drive shaft112b. Power source112a, drive shaft112b, and hub114are mechanical components for transmitting torque and/or rotation. Power train112may include a variety of components, including an engine, a transmission, and differentials. In operation, drive shaft112breceives torque or rotational energy from power source112aand rotates hub114. Rotation of rotor hub114causes blades120to rotate about drive shaft112b.

Swashplate116translates rotorcraft flight control input into motion of blades120. Because blades120are typically spinning when the rotorcraft is in flight, swashplate116may transmit flight control input from the non-rotating fuselage to the hub114, blades120, and/or components coupling hub114to blades120(e.g., grips and pitch horns). References in this description to coupling between a pitch link and a hub may also include, but are not limited to, coupling between a pitch link and a blade or components coupling a hub to a blade.

In operation, according to one example embodiment, translating the non-rotating swashplate ring116aalong the axis of drive shaft112bcauses the pitch links118to move up or down. This changes the pitch angle of all blades120equally, increasing or decreasing the thrust of the rotor and causing the aircraft to ascend or descend. Tilting the non-rotating swashplate ring116acauses the rotating swashplate116bto tilt, moving the pitch links118up and down cyclically as they rotate with the drive shaft. This tilts the thrust vector of the rotor, causing rotorcraft100to translate horizontally following the direction the swashplate is tilted.

In some examples, a stability augmentation system may be provided to the stabilize the movement of flight-control devices such as swashplate116. In general, the inherent stability and response behavior of many modern aircraft flight-control systems may tend towards low damping or even instability. A stability augmentation system may add damping to a flight-control system to increase stability.

FIG. 3shows a stability augmentation system200according to one example embodiment. System200features a master linkage210; linkages212,214, and216; a stability augmentation motor220; a control valve230; and a hydraulic actuator240. Teachings of certain embodiments also recognize that system200may include more, fewer, or different components. As one example,FIG. 3does not show components that may mechanically and/or hydraulically link the swashplate116ofFIG. 2to the hydraulic actuator240ofFIG. 3.

Master linkage210and linkages212,214, and216may be constructed from any suitable material. In some embodiments, master linkage210and linkages212,214, and216may be considered rigid, and the connections between the linkages may be considered joints.

In the example ofFIG. 3, the joint between master linkage210and linkage214may operate as an adjustable fulcrum. In this manner, control input205may cause the joint between master linkage210and linkage212to rotate about the joint between master linkage210and linkage212. The joint between master linkage210and linkage216may move in response to this rotation, causing linkage216to move. The position of the joint between master linkage210and linkage214is adjustable by motor220. For example, motor220may reposition linkage214such that the joint between master linkage210and linkage214moves to a different position.

Stability augmentation motor220moves linkage214. In some embodiments, stability augmentation motor220may be a torque motor. In some embodiments, stability augmentation motor220may provide a substantially constant torque over a limited range. In the example ofFIG. 3, motor220is shown as a rotary motor, but embodiments of system200may also include a linear motor. In some embodiments, system200may include two or more stability augmentation motors220. For example, a fourth linkage may couple a second motor to master linkage210proximate to the joint between master linkage210and linkage214. In this and other examples, the torque provided by two or more motors may be mechanically summed at master linkage210.

Control valve230and hydraulic actuator240, in combination, may convert movements of linkage216into a control output245. In the example ofFIG. 3, control valve230includes a spool235that is coupled to linkage216. Moving spool235may open and close passages within control valve230which, in turn, may change the hydraulic pressures within hydraulic actuator240. A change in hydraulic output pressure by hydraulic actuator240may represent one example of a control output245. The control output245may move an aircraft control device (e.g., swashplate116). For example, control output245may represent a change in hydraulic pressure by hydraulic actuator240, which may cause swashplate116to change position.

In operation, according to one example embodiment, stability augmentation motor220repositions linkage214to provide stability augmentation to system200. For example, the aircraft control device associated with control output245may tend toward low damping or even instability. In this example, low damping or instability may cause hydraulic actuator240to oscillate or vibrate, which may result in spool235and linkage216oscillating or vibrating as well. Without motor220and linkage214, oscillations and vibrations in linkage216could cause linkage212to oscillate and vibrate. In a mechanical flight control system, oscillations and vibrations in linkage212could cause the pilot control stick to oscillate and vibrate. Motor220, however, may reduce or even eliminate pilot control stick oscillations and vibrations by moving linkage214to counteract oscillations and vibrations in linkage216. For example, if linkage216moves master linkage210, motor220could move linkage214in such a manner so as to keep the joint between master linkage210and linkage212in approximately the same position. Thus in this example, motor220and linkage214may provide stability augmentation to system200by counteracting the oscillations and vibrations in linkage216.

Teachings of certain embodiments recognize that master linkage210may act as a “summing” linkage by mechanically summing inputs from linkage212and linkages214and providing the summed mechanical output to linkage216. For example, linkage212may provide a mechanical input to linkage216through master linkage210, but linkage214may be moved so as to add to or subtract from this mechanical input. If the mechanical input from linkage212would result in linkage216moving a certain distance in a certain direction, for example, moving linkage214may change the distance that linkage216moves and/or change the direction in which linkage216moves.

In some circumstances, linkage216may oscillate or vibrate at a high frequency. In this example, teachings of certain embodiments recognize that motor220may oscillate linkage214at a sufficiently high frequency so as to counteract the oscillations of linkage216. Teachings of certain embodiments recognize that a limited-angle torque motor may provide torque with sufficient control, precision, and bandwidth so as to counteract the oscillations of linkage216. Teachings of certain embodiments recognize that motor220may provide sufficient torque without the use of gearboxes and other devices designed to multiple the torque output. Such gearboxes may add complexity and weight and may limit the ability of motor220to control the position of linkage214.

Teachings of certain embodiments recognize that system200may continue to operate even if motor220fails. In particular, the pilot may continue to control the aircraft even if motor220fails. If motor220stops operating, for example, linkage214may become fixed by motor220while still allowing master linkage210and linkages212and216to move. In this example, the pilot control stick may oscillate and vibrate, but the pilot would still have the ability to control the aircraft control devices.

In the example ofFIGS. 1-3, the aircraft control device in communication with hydraulic actuator240is a rotor flight control device such as swashplate116. Teachings of certain embodiments recognize, however, that system200may operate with a variety of flight control devices on a variety of aircraft. As one non-limiting example, system200may provide stability augmentation for aileron, flap, and/or rudder controls on an airplane.

In some embodiments, motor220may be controlled and/or monitored by a flight control computer. For example, a flight control computer may instruct motor220on how to move linkage214so as to counteract the oscillations of linkage216.

FIG. 4shows a method300of controlling and monitoring motor220according to one example embodiment. At step310, a command input is received. In one example, this command input may be provided by a flight control computer. The command input may specify, for example, an output position of motor220, which is mechanically related to the position of linkage214. At step320, the current position of motor220is measured. At step330, the current position of motor220is compared with the command input position. At step340, motor220is instructed to move its output position to the command position.

During operation, motor220may be subject to various vibrations and other movements. Accordingly, teachings of certain embodiments recognize the capability to periodically remeasure the output position of motor220and adjust the output position if it does not match the command position. Accordingly, after step340, method300may return to step320even if no new command input is received. If a new command input specifying a new command position is received, then method300may return to step310.

Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order.

Although several embodiments have been illustrated and described in detail, it will be recognized that substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the appended claims.