Patent Description:
The present disclosure generally relates to aircraft flight control systems, and more particularly, to rotorcraft fly-by-wire (FBW) control laws. In particular embodiments, the present disclosure relates to a system and method for automating an offshore approach for a rotorcraft.

A rotorcraft may include one or more rotor systems including one or more main rotor systems. A main rotor system generates aerodynamic lift to support the weight of the rotorcraft in flight and thrust to 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.

An example of a prior art system which may be used with a rotorcraft is disclosed in <CIT>. This document discloses a system and method to facilitate approach of a VTOL aircraft to an offshore facility. The method includes inputting a waypoint for a landing platform of an offshore facility into an aircraft module, inputting an offset distance from the landing platform into the aircraft module, inputting a minimum descent height into an aircraft module, and inputting a final approach inbound course toward the landing platform into the aircraft module.

An example of a prior art aircraft system is disclosed in <CIT>. This document discloses a system for determining an instrument approach procedure for an aircraft comprises a database system containing terrain data and obstacle data, an input device onboard the aircraft for selecting a target position, a display device onboard the aircraft for displaying information to the pilot, and a processor onboard the aircraft. The processor determines, on the basis of the selected target position, a final approach path segment and a missed approach path segment. The final approach path segment begins at a final approach waypoint and ends at a missed approach point for deciding whether the aircraft may continue to a landing position on the ground or a missed approach procedure is started. The missed approach path segment begins at the missed approach point and ends at a higher altitude. A memory contains obstacle clearance surface data, on the basis of which, for each of the final approach path segment and the missed approach path segment, an obstacle clearance surface is defined that extends at a pre-determined orientation and at a pre-determined distance below said path segment. The processor determines an obstacle clearance altitude (OCA) for the instrument approach procedure as the lowest altitude at which any obstacle identified by the terrain data and obstacle data in the database system does not penetrate the obstacle clearance surfaces in the final approach path segment and the missed approach path segment. The system is configured to display the obstacle clearance altitude (OCA) on the display device.

A prior art example of a method of facilitating the approach to a platform by an aircraft is disclosed in <CIT>. In the method, the value of a required position integrity performance (RNP) is determined for a localization system. During an approach stage, this position integrity performance (RNP) is compared with a position integrity radius (HPL) resulting from the use of a GNSS localization system, and an alert is generated if the position integrity radius (HPL) is greater than the position integrity performance (RNP).

A prior art example of a procedure for facilitating the approach to a platform with an aircraft is disclosed in <CIT>. The procedure includes a construction stage for a database that includes, for each stored platform, attributes that include at least one platform identifier, the coordinates of the platform, a landing height of a landing zone of the platform, and the radius of a circle within which the platform is inscribed. During a parameterization stage, the target platform to be reached is determined, along with a course to be followed and a height parameter relative to a minimum decision altitude. During a construction stage, the position of an initial approach fix is determined, along with the position of a final approach fix, an offset point, and a decision point, in response to the information and in response to the attributes.

Advisory Circular number <NUM>-80C of the US Federal Aviation Administration ("Approval of Offshore Standard Approach Procedures, Airborne Radar Approaches, and Helicopter En Route Descent Areas") provides guidance for instrument operations to offshore landing facilities. The document includes application and procedures to show an alternate means authorized by the Federal Aviation Administration (FAA) for compliance with the regulations contained in Title <NUM> of the Code of Federal Regulations (<NUM> CFR) part <NUM>, which address instrument approach requirements. Specifically, the document provides guidance for obtaining approval for Offshore Standard Approach Procedures (OSAP), Airborne Radar Approaches (ARA), and Helicopter En Route Descent Areas (HEDA). The document retains the ARA, parallel offset OSAP, Delta <NUM>° OSAP and the HEDA along with Global Positioning System (GPS) navigation for the OSAP and HEDA operations contained in Advisory Circular number <NUM>-80B.

In accordance with an embodiment, a rotorcraft according to claim <NUM> is provided.

The scope of the invention is set out in the appended independent claims. Optional features are provided in the dependent claims.

Illustrative embodiments of the system and method of the present disclosure are described below. In the interest of clarity, all features of an actual implementation may not be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Reference may be made herein to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as "above," "below," "upper," "lower," or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.

<FIG> illustrates a rotorcraft <NUM> according to a representative embodiment. The rotorcraft <NUM> includes a rotor system <NUM>, main rotor blades <NUM>, a fuselage <NUM>, landing gear <NUM>, and a tail boom <NUM>. The rotor system <NUM> may rotate the main rotor blades <NUM>. The rotor system <NUM> may include a control system for selectively controlling a pitch of each of the main rotor blades <NUM> to selectively control the direction, thrust, and lift of the rotorcraft <NUM>. The fuselage <NUM> comprises the body of the rotorcraft <NUM> and may be coupled to the rotor system <NUM> such that the rotor system <NUM> and the main rotor blades <NUM> move the fuselage <NUM> through the air in flight. The landing gear <NUM> supports the rotorcraft <NUM> during landing or when the rotorcraft <NUM> is at rest on the ground. The tail boom <NUM> represents the rear section of the rotorcraft <NUM> and has components of the rotor system <NUM> and tail rotor blades <NUM>'. The tail rotor blades <NUM>' counter torque effect created by the rotor system <NUM> and the main rotor blades <NUM>. Teachings of certain embodiments relating to rotor systems described herein may apply to the rotor system <NUM> or other rotor systems (e.g., tilt rotorcraft, tandem rotorcraft, or other helicopter rotor systems). It should also be appreciated that representative embodiments of the rotorcraft <NUM> may apply to aircraft other than rotorcraft, such as airplanes, unmanned aircraft, or the like.

A pilot may manipulate one or more pilot flight controls to achieve controlled aerodynamic flight. Inputs provided by the pilot to the pilot flight controls may be transmitted mechanically or electronically (for example, via a fly-by-wire system) to flight control devices. The flight control devices may include devices operable to change flight characteristics of the aircraft. Representative flight control devices may include a control system operable to change a configuration of the main rotor blades <NUM> or the tail rotor blades <NUM>'.

In some embodiments, the rotorcraft <NUM> may include a flight control system (FCS) and a flight control computer (FCC). The FCC is in electrical communication with the FCS and the FCC controls the FCS. Inputs from the pilot are sent to the FCC and the FCC controls the FCS based on the pilot inputs, control laws, other logic, and the like.

<FIG> illustrates a cockpit configuration <NUM> of the rotorcraft <NUM> according to a representative embodiment. The rotorcraft <NUM> may include, e.g., three sets of pilot flight controls (e.g., cyclic control assemblies <NUM>, collective control assemblies <NUM>, and pedal assemblies <NUM>). In accordance with a representative embodiment, a pilot and a co-pilot (both of which may be referred to as a "pilot" for purposes of discussion herein) may each be provided with an individual pilot flight control assembly comprising a cyclic control assembly <NUM>, a collective control assembly <NUM>, and a pedal assembly <NUM>.

In general, the cyclic pilot flight controls may allow a pilot to impart cyclic configurations to the main rotor blades <NUM>. Varied cyclic configurations of the main rotor blades <NUM> may cause the rotorcraft <NUM> to tilt in a direction specified by the pilot. For tilting forward and back (pitch) or tilting side-to-side (roll), the angle of attack of the main rotor blades <NUM> may be altered with cyclic periodicity during the rotation of the rotor system <NUM>, thereby creating variable amounts of lift at varied points in the rotation cycle. Alteration of the cyclic configuration of the main rotor blades <NUM> may be accomplished by an input from the cyclic control assembly <NUM>.

The collective pilot flight controls may allow a pilot to impart collective configurations (e.g., collective blade pitch) to the main rotor blades <NUM>. Collective configurations of the main rotor blades <NUM> may change the overall lift produced by the main rotor blades <NUM>. For increasing or decreasing the overall lift in the main rotor blades <NUM>, the angle of attack for all of the main rotor blades <NUM> may be collectively altered by equal amounts and at the same time, resulting in ascent, descent, acceleration, or deceleration. Alteration of the collective configuration of the main rotor blades <NUM> may be accomplished by input from the collective control assembly <NUM>.

Anti-torque pilot flight controls may allow a pilot to change the amount of anti-torque force applied to the rotorcraft <NUM>. The tail rotor blades <NUM>' may operate to counter torque created by the rotor system <NUM> and the main rotor blades <NUM>. The anti-torque pilot flight controls may change the amount of anti-torque force applied to change a heading (yaw) of the rotorcraft <NUM>. For example, providing anti-torque force greater than the torque effect created by the rotor system <NUM> and the main rotor blades <NUM> may cause the rotorcraft <NUM> to rotate in a first direction, whereas providing anti-torque force less than the torque effect created by the rotor system <NUM> and the main rotor blades <NUM> may cause the rotorcraft <NUM> to rotate in a second direction opposite the first direction. In some embodiments, the anti-torque pilot flight controls may change the amount of anti-torque force applied by changing the pitch of the tail rotor blades <NUM>', thereby increasing or reducing the thrust produced by the tail rotor blades <NUM>' and causing the nose of the rotorcraft <NUM> to yaw in a direction corresponding to the application of input from the pedal assembly <NUM>.

In other embodiments, the rotorcraft <NUM> may include additional or different anti-torque devices, such as a rudder or a no-tail-rotor (NOTAR) anti-torque device. Conjunctive or alternative anti-torque embodiments may be operable to change an amount of anti-torque force provided by such additional or different anti-torque device or system.

In some embodiments, the cyclic control assembly <NUM>, the collective control assembly <NUM>, and the pedal assemblies <NUM> may be used in a fly-by-wire (FBW) system. In an example as representatively illustrated in <FIG>, each cyclic control assembly <NUM> is located to the right of a pilot seat, each collective control assembly <NUM> is located to the left of the pilot seat, and each pedal assembly <NUM> is located in front of the pilot seat. In other embodiments, the cyclic control assemblies <NUM>, the collective control assemblies <NUM>, and the pedal assemblies <NUM> may be disposed in any suitable location of a cockpit configuration.

In some embodiments, the cyclic control assembly <NUM>, the collective control assembly <NUM>, and the pedal assemblies <NUM> may be in mechanical communication with trim assemblies that convert mechanical inputs into FBW system flight control commands. These trim assemblies may include, among other items, measurement devices for measuring mechanical inputs (e.g., measuring or otherwise determining input position) and trim motors for back-driving center positions of the cyclic control assembly <NUM>, the collective control assembly <NUM>, or the pedal assemblies <NUM>.

For example, <FIG> representatively illustrates an installation of two cyclic control assemblies <NUM> and two collective control assemblies <NUM> according to an embodiment. In this example, the cyclic control assemblies <NUM> and the collective control assemblies <NUM> are coupled to three integrated trim assemblies: two cyclic trim assemblies <NUM> and a collective trim assembly <NUM>. One of the cyclic trim assemblies <NUM> manages left/right cyclic tilting movements (e.g., roll) and the other cyclic trim assembly <NUM> manages front/back cyclic tilting movements (e.g., pitch).

The cyclic trim assemblies <NUM> and the collective trim assembly <NUM> are operable to receive and measure mechanical communications of cyclic and collective motions from a pilot. In a representative aspect, the cyclic trim assemblies <NUM> and the collective trim assembly <NUM> may embody components of an FBW flight control system, and measurements from the cyclic trim assemblies <NUM> and the collective trim assembly <NUM> may be sent to the flight control computer (FCC) operable to instruct the rotor system <NUM> to change a position or configuration of the main rotor blades <NUM> based on received or otherwise determined measurements. For example, the FCC may be in communication with actuators or other devices operable to change the pitch or position of the main rotor blades <NUM>.

<FIG> representatively illustrates an installation of pedal assemblies <NUM> in accordance with an embodiment. Two pedal assemblies <NUM> are coupled to an anti-torque trim assembly <NUM>. Pedal linkages are in mechanical communication, e.g., via a rocker arm and pedal adjustment linkages. The rocker arm is operable to rotate about a point of rotation such that pushing in one pedal causes the pedal adjustment linkage to rotate the rocker arm, which in turn causes the pedal adjustment linkage to push out the other pedal in a corresponding opposite direction.

Rotating the rocker arm also causes a trim linkage to reposition a mechanical input associated with the anti-torque trim assembly <NUM>. In this manner, the pilot can mechanically communicate anti-torque commands to the anti-torque trim assembly <NUM> by moving the pedals. Furthermore, trim linkages couple adjacent pedal assemblies <NUM> together such that pilot pedals and co-pilot pedals are in mechanical communication.

<FIG>, <FIG>, and <FIG> illustrate the trim assemblies (i.e., the cyclic trim assemblies <NUM>, the collective control assembly <NUM>, and the anti-torque trim assembly <NUM>) of <FIG> and <FIG> according to a representative embodiment. <FIG> shows one of the cyclic trim assemblies <NUM> according to an embodiment, <FIG> shows the collective trim assembly <NUM> according to an embodiment, and <FIG> shows the anti-torque trim assembly <NUM> according to an embodiment.

<FIG> representatively illustrates an embodiment of a cyclic trim assembly <NUM> having a trim motor <NUM>, a clutch <NUM>, a run-down damper <NUM>, first position measurement devices <NUM>, a gradient spring <NUM>, a damper <NUM>, a shear device <NUM>, second position measurement devices <NUM>, mechanical stop devices <NUM>, and an output shaft <NUM>. Although the output shaft <NUM> may be described as a single shaft, it will be appreciated that the output shaft <NUM> may have multiple components. For example, the output shaft <NUM> may include two shafts separated by the gradient spring <NUM>. In another example, the output shaft <NUM> may have a single shaft with a torsion spring attached thereto.

In operation, according to an embodiment, the output shaft <NUM> and the cyclic control assemblies <NUM> are in mechanical communication such that movement of a pilot control assembly (PCA) grip results in movement of the output shaft <NUM>, and movement of the output shaft <NUM> likewise results in movement of the PCA grip. Movement of the output shaft <NUM> may be measured or otherwise determined by the first position measurement devices <NUM> and the second position measurement devices <NUM>. The measurements from the first position measurement devices <NUM> and the second position measurement devices <NUM> may be used to instruct the rotor system <NUM> to change the position of the main rotor blades <NUM>.

The cyclic trim assembly <NUM> may operate in three modes of operation. In a first mode of operation, the clutch <NUM> is engaged and the trim motor <NUM> drives the output shaft <NUM>. This first mode of operation may represent, for example, operation of the cyclic trim assembly <NUM> during auto-pilot operations. In this example, the trim motor <NUM> may drive movement of the output shaft <NUM> to drive movement of the PCA grip of the cyclic control assembly <NUM>. The first position measurement devices <NUM> and the second measurement devices <NUM> may also measure how the trim motor <NUM> drives the output shaft <NUM> and communicate these measurements to the rotor system <NUM>.

In a second mode of operation, the clutch <NUM> is disengaged and the pilot drives the output shaft <NUM> by way of the cyclic control assembly <NUM>. In this example, the pilot changes the position of the output shaft <NUM>, which may be measured by the first position measurement devices <NUM> and the second measurement devices <NUM>. The first position measurement devices <NUM> and the second measurement devices <NUM> may measure how the pilot drives the output shaft <NUM> and communicate these measurements to the rotor system <NUM>.

In a third mode of operation, the clutch <NUM> is engaged and the trim motor <NUM> holds its output arm at a trim position to provide a ground point for the output shaft <NUM>. In this example, the pilot may change the position of the output shaft <NUM> about the trim position set by the trim motor <NUM>. When the pilot releases the PCA grip, the PCA grip may move to the trim position corresponding to the position established by the trim motor <NUM>. In some embodiments, the first and third modes of operations may be combined such that the trim motor <NUM> moves the trim position during operation.

Thus, trim motor the <NUM> may provide cyclic force (or trim) to the cyclic control assembly <NUM> through the output shaft <NUM>. In an embodiment, the trim motor <NUM> may be a <NUM>-volt DC permanent magnet motor. In operation, the trim motor <NUM> may provide an artificial-force feel (or "force feedback") for the flight control system (FCS) about an anchor point (or "detent"). The clutch <NUM> provides a mechanism for engaging and disengaging the trim motor <NUM>.

<FIG> shows an embodiment of a collective trim assembly <NUM> having a trim motor <NUM>, a planetary gear set <NUM>, variable friction devices <NUM>, resolvers <NUM>, a shear device <NUM>, position measurement devices <NUM>, mechanical stop devices <NUM>, and an output shaft <NUM>. The output shaft <NUM> may be coupled to various linkages. Although the output shaft <NUM> may be described as a single shaft, it will be appreciated that the output shaft <NUM> may comprise multiple components or pieces.

The output shaft <NUM> and the collective control assemblies <NUM> are in mechanical communication such that movement of a PCA grip of the collective control results in movement of the output shaft <NUM>, and movement of the output shaft <NUM> likewise results in movement of the PCA grip of the collective control. Movement of the output shaft <NUM> may be measured or otherwise determined by the position measurement devices <NUM>. Measurements from the measurement devices <NUM> may be used to instruct the rotor system <NUM>, e.g., as to how to change the position of the main rotor blades <NUM>.

The collective trim assembly <NUM> may operate in three modes of operation. In a first mode of operation, the variable friction devices <NUM> are engaged and the trim motor <NUM> drives the output shaft <NUM>. This first mode of operation may represent, for example, operation of the collective trim assembly <NUM> during auto-pilot operations. In this example, the trim motor <NUM> may drive movement of the output shaft <NUM> to drive movement of the PCA grip of the collective control assembly <NUM>. The position measurement devices <NUM> may also measure how the trim motor <NUM> drives the output shaft <NUM> and communicate these measurements to the rotor system <NUM>.

In a second mode of operation, the variable friction devices <NUM> are disengaged and the pilot drives the output shaft <NUM> by way of the collective control assembly <NUM>. In this example, the pilot changes the position of the output shaft <NUM>, which may be measured or otherwise determined by the position measurement devices <NUM>. The position measurement devices <NUM> may measure or otherwise determine how the pilot drives the output shaft <NUM> and communicate these measurements to the rotor system <NUM>.

In a third mode of operation, the variable friction devices <NUM> are engaged and the trim motor <NUM> holds its output arm at a trim position to provide a ground point for the output shaft <NUM>. In this example, the pilot may change the position of the output shaft <NUM> about the trim position set by the trim motor <NUM>. When the pilot releases the PCA grip, the PCA grip may move to the trim position corresponding to the position established by the trim motor <NUM>. In some embodiments, the first and third modes of operations may be combined such that the trim motor <NUM> moves the trim position during operation.

Thus, the trim motor <NUM> may provide collective force (trim) to the collective control assembly <NUM> through the output shaft <NUM>. In one example embodiment, the trim motor <NUM> may be a <NUM> volt DC permanent magnet motor. In operation, the trim motor <NUM> may provide an artificial force feel for the FCS about an anchor point. The variable friction devices <NUM> provide a mechanism for engaging and disengaging the trim motor <NUM>.

<FIG> shows an embodiment of an anti-torque trim assembly <NUM> having a gradient spring <NUM>, a damper <NUM>, a shear device <NUM>, position measurement devices <NUM>, mechanical stop devices <NUM>, and an output shaft <NUM>. Although the output shaft <NUM> may be described as a single shaft, it will be appreciated that the output shaft <NUM> may comprise multiple pieces or components.

In operation, according to an embodiment, the output shaft <NUM> and the pedal assemblies <NUM> are in mechanical communication such that movement of the pedals results in movement of the output shaft <NUM>, and movement of the output shaft <NUM> likewise results in movement of the pedals. Movement of the output shaft <NUM> may be measured or otherwise determined by the position measurement devices <NUM>. Measurements from the measurement devices <NUM> may be used to instruct the rotor system <NUM>, e.g., as to how to change the pitch of the tail rotor blades <NUM>' (or how to change the operation of an alternative anti-torque device or system).

Although the cyclic control assembly <NUM>, the collective control assembly <NUM>, and the pedal assemblies <NUM> may generally control the cyclic, collective, and anti-torque movements of the rotorcraft <NUM> respectively, generally, aircraft dynamics may result in a coupling of aircraft motions (or flight characteristics). As an example, inputting a change in lateral cyclic into the cyclic control assembly <NUM> may result in a change in the pitch moment of the rotorcraft <NUM>. This change in the pitch moment may occur even if no longitudinal cyclic input is provided to the cyclic control assembly <NUM>. Rather, this change in the pitch moment would be the result of aircraft dynamics. In such an example, a pilot may apply a counteracting longitudinal cyclic input to compensate for the change in pitch moment. Accordingly, coupling of aircraft flight characteristics generally increases pilot workload.

Different aircrafts may be associated with different couplings of aircraft motions. For example, a rotorcraft with a canted tail rotor may be associated with a high level of coupling due to the "lift" generated by the canted tail rotor combined with normal coupling of yaw motion to collective pitch and coupling of cyclic inputs of conventional single-rotor rotorcraft. In such an example, feedback loops may not be sufficient to compensate for this coupling because feedback loops do not engage until after the coupled response occurs.

Accordingly, rotorcraft fly-by-wire systems described herein recognize the capability to augment flight control commands with feed-forward control cross-feeds that anticipate inherent coupling of aircraft motions. <FIG> shows a fly-by-wire cross-feed arrangement <NUM>. As shown in <FIG>, the cross-feed arrangement <NUM> has five inputs: a collective axis input <NUM>, a longitudinal cyclic axis input <NUM>, a lateral cyclic axis input <NUM>, a pedal axis input <NUM>, and an inner loop input <NUM>. Examples of the inner loop input <NUM> will be discussed later with regard to description of <FIG>.

As representatively illustrated in <FIG>, each input may be cross-fed to a different axis. In some examples, high-pass filters (e.g., a first high-pass filter <NUM>, a second high-pass filter <NUM>, a third high-pass filter <NUM>, a fourth high-pass filter <NUM>, and a fifth high-pass filter <NUM>) may be used to filter cross-feed signals by allowing high-frequency signals to pass, but attenuating frequencies lower than a cut-off frequency. Fixed gains are applied to the inputs before passing the inputs through the high-pass filters. The cross-feed signals may then be passed through a limiter (e.g., a first limiter <NUM>, a second limiter <NUM>, a third limiter <NUM>, or a fourth limiter <NUM>) to an actuator position converter <NUM>, which processes the signals and converts them into instructions for one or more actuators <NUM>. Each of the actuators <NUM> may represent any device that provides flight control inputs to a flight control device. Examples of the actuators <NUM> may include, but are not limited to, a swashplate actuator, a pitch-link actuator, an on-blade actuator, or the like.

The example of <FIG> has five representative cross-feeds. A first cross-feed <NUM> is a lateral cyclic to longitudinal cyclic cross-feed based on providing longitudinal cyclic to cancel the pitch moment generated by a change in the lateral cyclic. A second cross-feed <NUM> is a longitudinal cyclic to lateral cyclic cross-feed based on providing lateral cyclic to cancel the roll moment generated by a change in the longitudinal cyclic. A third cross-feed <NUM> is a pedal axis (e.g., tail rotor collective) to longitudinal cyclic cross-feed based on providing longitudinal cyclic to cancel the pitch moment of the tail rotor collective. A fourth cross-feed <NUM> is a tail rotor collective to lateral cyclic cross-feed based on providing lateral cyclic to cancel the roll moment of, e.g., the tail rotor collective. A fifth cross-feed <NUM> is a main rotor collective to tail rotor collective cross- feed based on providing tail rotor collective to cancel the yaw moment of the main rotor collective.

Although <FIG> is representatively illustrated with five cross-feeds, more, fewer, or different cross-feed arrangements may be utilized. In general, cross-feeds may be utilized whenever a pilot provides a command to change a first flight characteristic, where changing the first flight characteristic would result in an expected change to a second flight characteristic. The cross-feed may result in an instruction to change a first operating condition of the FCS in response to a received pilot command, and an instruction to change a second operating condition in response to the expected change to the second flight characteristic. This second instruction could at least partially offset, counteract, or otherwise address the expected change to the second flight characteristic.

Representative embodiments appreciate that applying cross-feeds to "decouple" an aircraft having coupled flight dynamics may reduce pilot workload by automatically applying cross-feed commands without pilot intervention. For example, in some embodiments, applying decoupling cross-feeds may reduce or eliminate the need for a pilot to apply commands through pilot controls that are intended to at least partially offset coupled motions of the aircraft. In some circumstances, the FCS may apply cross-feed inputs faster than a pilot could manually. For example, the cross-feeds may anticipate (and therefore more quickly address) inherently coupled aircraft motions or flight characteristics.

The cyclic control assembly <NUM> may be configured to operate as a displacement-trim device such that movements of the longitudinal stick correlate to the position of the swashplate. In such an example, applying cross-feeds to anticipate inherent coupling of aircraft motions may result in the stick position failing to accurately represent a position of the swashplate, unless or until the trim motor back-drives the pilot control device to match swashplate position. Continuously driving the stick, especially at high frequency due to aircraft dynamics, however, may increase the workload of the pilot trim system and may increase pilot fatigue by transferring transient motions of the swashplate to the pilot's hand and forcing the pilot's hand to follow the stick as the swashplate moves.

Accordingly, teachings of representative embodiments recognize capabilities to wash out cross-feeds over short periods of time such that a displacement-trim flight control device substantially reflects the position of the swashplate during steady-state flight, but does not reflect the position of the swashplate during short transient periods. For example, the trim motor may drive the stick in certain conditions (e.g., during auto-pilot-controlled flight or establishing a new trim position), but the FCC may be configured to not command the trim motor to move the pilot control stick in response to application of the cross-feed. In some embodiments, the FCC may be configured to command the motor to move the pilot control stick based on positions of the swashplate during steady-state conditions, and may be configured to not command the motor to move the pilot control stick during transitory conditions.

The wash-out time period may be less than about ten seconds (e.g., about <NUM>-<NUM> seconds). In some embodiments, a wash-out time period begins when the cross-feed is first applied. In other embodiments, a wash-out time period begins after the aircraft returns to steady-state. In some embodiments, the aircraft returns to a same steady-state condition as existing before the cross-feed was applied. In other embodiments, a new steady-state condition may be established after the cross-feed is applied.

Elements of the cross-feed arrangement <NUM> may be implemented at least partially by one or more computer systems <NUM>. All, some, or none of the components of the cross-feed arrangement <NUM> may be located on or near an aircraft, such as the rotorcraft <NUM>.

Users <NUM> may access the cross-feed arrangement <NUM> through the computer systems <NUM>. For example, in some embodiments, the users <NUM> may provide flight control inputs that may be processed using a computer system <NUM>. The users <NUM> may include any individual, group of individuals, entity, machine, or mechanism that interacts with computer systems <NUM>. Examples of the users <NUM> include, but are not limited to, a pilot, a copilot, a service person, an engineer, a technician, a contractor, an agent, an employee, or the like.

The computer system <NUM> may include processors <NUM>, input/output devices <NUM>, network interfaces <NUM>, and a memory <NUM>. In other embodiments, the computer system <NUM> may include more, less, or other components. The computer system <NUM> may be operable to perform one or more operations of various embodiments. Although representatively illustrated embodiments illustrate one example of a computer system <NUM> that may be used, other embodiments may utilize computers other than the computer system <NUM>. Other embodiments may employ multiple computer systems <NUM> or other computers networked together in one or more public or private computer networks, such as one or more networks <NUM>.

The processors <NUM> represent devices operable to execute logic contained within a computer-readable medium. Examples of the processor <NUM> include one or more microprocessors, one or more applications, virtual machines, or other logic. The computer system <NUM> may include one or multiple processors <NUM>.

The input/output devices <NUM> may include any device or interface operable to enable communication between the computer system <NUM> and external components, including communication with a user or another system. Examples of the input/output devices <NUM> may include, but are not limited to, a mouse, a keyboard, a display, a printer, or the like.

The network interfaces <NUM> may be operable to facilitate communication between the computer system <NUM> and another element of a network, such as other computer systems <NUM>. The network interfaces <NUM> (e.g., a communications link) may connect to any number or combination of wired or wireless networks suitable for data transmission, including transmission of communications.

The memory <NUM> represents any suitable storage mechanism and may store any data for use by the computer system <NUM>. The memory <NUM> may comprise one or more tangible, computer-readable, or computer-executable storage medium. In some embodiments, the memory <NUM> stores logic <NUM>. The logic <NUM> facilitates the operation of the computer system <NUM>. The logic <NUM> may include hardware, software, or other logic. The logic <NUM> may be encoded in one or more tangible, non-transitory media and may perform operations when executed by a computer. The logic <NUM> may include a computer program, software, computer executable instructions, or instructions capable of being executed by computer system <NUM>.

Various communications within the computer system <NUM> or between components of the computer system <NUM> may occur across a network, such as the network <NUM>. The network <NUM> may represent any number and combination of networks suitable for data transmission. The network <NUM> may, for example, communicate internet protocol packets, frame relay frames, asynchronous transfer mode cells, or other suitable data between network addresses. Although representatively illustrated embodiments show one network <NUM>, other embodiments may include more or fewer networks <NUM>. Not all elements comprising various network embodiments may communicate via a network. Representative aspects and implementations will appreciate that communications over a network is one example of a mechanism for communicating between parties, and that any suitable mechanism may be used.

<FIG> representatively illustrates a three-loop FCS <NUM> according to an embodiment. Like the cross-feed arrangement <NUM> of <FIG>, elements of the three-loop FCS <NUM> may be implemented at least partially by one or more computer systems <NUM>. All, some, or none of the components of the three-loop FCS <NUM> may be located on or near an aircraft such as a rotorcraft <NUM>.

The three-loop FCS <NUM> of <FIG> has a pilot input <NUM>, an outer loop <NUM>, a rate (middle) loop <NUM>, an inner loop <NUM>, a decoupler <NUM>, and aircraft equipment <NUM>. Examples of the inner loop <NUM> and the decoupler <NUM> may include, but are not limited to, the cross-feed arrangement <NUM> and the inner loop <NUM> of <FIG>. Representative examples of the aircraft equipment <NUM> may include, but are not limited to, the actuator position converter <NUM> and the actuators <NUM> of <FIG>.

In the example of <FIG>, a three-loop design separates the inner stabilization and rate feedback loops from outer guidance and tracking loops. The control law structure primarily assigns the overall stabilization task to the inner loop <NUM>. Next, the middle loop <NUM> provides rate augmentation. The outer loop <NUM> focuses on guidance and tracking tasks. Since the inner loop <NUM> and the rate loop <NUM> provide most of the stabilization, less control effort is required at the outer loop level. As representatively illustrated in <FIG>, a switch <NUM> is provided to turn the third-loop flight augmentation on and off.

In some embodiments, the inner loop and the rate loop include a set of gains and filters applied to the roll/pitch/yaw <NUM>-axis rate gyro and the acceleration feedback sensors. Both the inner loop and the rate loop may stay active, independent of various outer loop hold modes. The outer loop <NUM> may include cascaded layers of loops, including an attitude loop, a speed loop, a position loop, a vertical speed loop, an altitude loop, and a heading loop.

The sum of the inner loop <NUM>, the rate loop <NUM>, and the outer loop <NUM> are applied to the decoupler <NUM>. The decoupler <NUM> approximately decouples the <NUM>-axes (pitch, roll, yaw, and collective pitch (vertical)) such that, for example, forward longitudinal stick input does not require the pilot to push the stick diagonally for manual deconvolution. Similarly, as collective pull increases torque and results in an increased anti-torque requirement, the decoupler <NUM> may provide both the necessary pedal and a portion of cyclic (e.g., if the rotorcraft <NUM> has a canted tail rotor) to counter the increased torque. In accordance with representative embodiments, the decoupling of plural flight characteristics allows for a control-law -automated, -mediated, or at least -assisted change in the pitch angle, the roll angle, the yaw rate, or the collective pitch angle, e.g., attending the performance of an approach maneuver (e.g., an offshore approach).

<FIG> illustrates a flow diagram of a method <NUM> for landing a rotorcraft <NUM> on an offshore target according to some embodiments. The method <NUM> is an offshore standard approach procedure (OSAP). In block <NUM>, a pilot of the rotorcraft <NUM> enters approach data into a flight management system (FMS) of the rotorcraft <NUM>. The approach data include the location of the offshore target, the direction of approach, the type of approach to be made, and the minimum altitude for a missed approach point (MAP). Some of the approach data are automatically populated. For example, the FMS may include default settings for the approach type and the minimum altitude for the MAP. The FMS also determines the approach direction based on a detected wind direction. Thus, the pilot may only be required to enter the location of the offshore target. The pilot may enter the approach data into the FMS at any time during a flight, or even before a flight.

The direction of approach is based on the wind direction and wind speed at the target location. The direction of approach is set such that the rotorcraft <NUM> approaches the offshore target from the upwind direction. The rotorcraft <NUM> includes systems for detecting the wind direction and wind speed at the rotorcraft <NUM>. The FMS may set the direction of approach automatically based on the wind direction and wind speed detected by the rotorcraft <NUM>. However, in some cases, the wind direction and wind speed at the target location may be different from the wind direction and wind speed at the rotorcraft <NUM>. Thus, the pilot may enter the wind direction and wind speed at the offshore target. The type of approach may be one of a Delta <NUM>°OSAP or a parallel offset OSAP, the details of each of which will be discussed in detail below. The minimum MAP altitude may be set to a minimum value, such as about <NUM> (<NUM> feet), by default. However, the pilot may increase the minimum altitude above the default value. For example, if the offshore target is unusually high, the pilot may increase the minimum MAP altitude.

In block <NUM>, the FMS determines the location of the MAP based on the pilot's inputs. In block <NUM>, the pilot inputs a command to engage the approach. The pilot inputs the command to engage the approach into a flight director (FD) in the rotorcraft <NUM>. In block <NUM>, the FMS sets waypoints between the current location of the rotorcraft <NUM> and the MAP. The FMS may automatically calculate a flight path based on the current location of the rotorcraft <NUM> and the approach data input by the pilot. The FMS then sets waypoints along the flight path to fly to the MAP. If the MAP is located on the opposite side of the offshore target as the rotorcraft <NUM>, the FMS may set the waypoints such that the rotorcraft flies over the offshore target and performs a teardrop turn to approach the MAP from the correct direction. The waypoints may include an offshore initial approach fix (OSIAF), an offshore final approach fix (OSFAF), an offshore decision point altitude (OSDPA), a minimum descent altitude (MDA), and the MAP. In some embodiments, the FMS may calculate the OSIAF, the OSFAF, and the OSDPA based on the approach data and the location of the rotorcraft <NUM>, while the MDA and the MAP may be set based on the approach data alone. When the Delta <NUM>°OSAP is selected, the waypoints may further include an offshore Delta <NUM>° turning point (OS30P). The FD flies to each waypoint and transition to the next waypoint based on the location of the rotorcraft <NUM>.

In block <NUM>, the FD provides controls to the FCS to fly the rotorcraft <NUM> to the MAP. In block <NUM>, the pilot determines whether visual contact is made with the offshore target. If the pilot makes visual contact with the offshore target, the method <NUM> proceeds to block <NUM> and the pilot takes control of the rotorcraft <NUM> in order to land the rotorcraft on the offshore target. The pilot may take control of the rotorcraft <NUM> at any point along the offshore approach. For example, the pilot may take control of the rotorcraft <NUM> after the rotorcraft <NUM> has flown to the OSIAF once visual contact with the offshore target has been made.

In block <NUM>, if the rotorcraft reaches the MAP or the pilot presses a go-around (GA) button, the FD controls the FCS to engage in a go-around procedure (discussed in greater detail below). After the go-around procedure is completed, the pilot may choose to abort the OSAP in block <NUM> if visual contact with the offshore target has not been made; return to block <NUM> and alter the approach data input into the FMS; return to block <NUM> and attempt to engage another approach; or return to block <NUM> and continue to attempt to make visual contact with the offshore target.

<FIG> illustrate flight approach path <NUM> including a plurality of waypoints set by the FMS for a Delta <NUM>° approach to an offshore target <NUM>. <FIG> illustrates the plurality of waypoints from a top-down view and <FIG> illustrates the altitudes of the plurality of waypoints. The waypoints include an OSIAF <NUM>, an OSFAF <NUM>, an OSDPA <NUM>, an MDA <NUM>, an OS30P <NUM>, and an MAP <NUM>. The OSIAF <NUM> may be located a distance of <NUM>,<NUM> (<NUM> nautical miles (NMN)) from the offshore target at an altitude of between about <NUM> (<NUM> ft) MSL and about <NUM> (<NUM>,<NUM> ft) MSL, such as about <NUM> (<NUM>,<NUM> ft) MSL. The OSIAF <NUM> may have a minimum altitude value, such as about <NUM> (<NUM> ft) MSL. The altitude of the OSIAF <NUM> may be input by the pilot in block <NUM> of the method <NUM>. The OSFAF <NUM> may be located a distance <NUM>,<NUM> (<NUM>) from the offshore target at an altitude of <NUM> (<NUM> ft) MSL. The OSFAF <NUM> may not be input or altered by the pilot. The OSDPA <NUM> may be located a distance <NUM>, <NUM> (<NUM>) from the offshore target at an altitude of <NUM> (<NUM> ft) MSL. The OSDPA <NUM> may not be input or altered by the pilot. The MDA <NUM> may be located a distance of less than <NUM>,<NUM> (<NUM>) from the offshore target at an altitude of at least <NUM> (<NUM> ft) radio altimeter (RA) or <NUM> (<NUM> ft) MSL if the rotorcraft <NUM> does not include an operable RA. The altitude of the MDA <NUM> may be raised by the pilot, but may not be lowered below <NUM> (<NUM> ft) RA or <NUM> (<NUM> ft) MSL. In some embodiments, the pilot may raise the MDA <NUM> altitude if the offshore target <NUM> is unusually high. The OS30P <NUM> and the MAP <NUM> may be located distances of <NUM> and <NUM>,<NUM> (<NUM> and <NUM>) from the offshore target <NUM>, respectively. The altitude of the OS30P <NUM> and the MAP <NUM> may be the same as the altitude of the MDA <NUM>.

As illustrated in <FIG>, the rotorcraft <NUM> may fly directly towards the offshore target <NUM> from the OSIAF <NUM> to the OS30P <NUM>. Once the rotorcraft <NUM> reaches the OS30P <NUM>, the rotorcraft may turn at an angle of <NUM> degrees to proceed to the MAP <NUM>. Although <FIG> illustrates a left-hand turn at the OS30P <NUM>, the rotorcraft <NUM> may alternatively make a right-hand turn at the OS30P <NUM> to proceed to the MAP <NUM> (not separately illustrated). The pilot may input a Delta <NUM>° left approach or a Delta <NUM>° right approach at block <NUM> of the method <NUM> to make a left-hand turn or a right-hand turn at the OS30P <NUM>, respectively, depending on personal preferences.

The FCS flies the rotorcraft <NUM> to the offshore target <NUM> by flying to each of the waypoints, the OSIAF <NUM>, the OSFAF <NUM>, the OSDPA <NUM>, the MDA <NUM>, the OS30P <NUM>, and the MAP <NUM> in order. Upon reaching the OSFAF <NUM>, the rotorcraft <NUM> may decelerate to a ground speed of less than <NUM>/h (<NUM> knots) or a ground speed of less than <NUM>/h (<NUM> knots). The rotorcraft <NUM> may further decelerate to a ground speed of less than (<NUM> knots) upon reaching the MDA <NUM>, before reaching the OS30P <NUM>.

If the pilot does not make visual contact with the offshore target <NUM> by the time the rotorcraft reaches the MAP <NUM>, or the pilot presses the GA button, the FCS engages in a go-around procedure. The go-around procedure includes flying the rotorcraft <NUM> to a first point <NUM> in the Delta <NUM>° heading and climbing to an altitude of <NUM> (<NUM> ft) The rotorcraft <NUM> then executes a climbing turn towards the offshore target <NUM> and climbs to an altitude of <NUM> (<NUM> ft) MSL at a second point <NUM>. If there is a missed approach, the pilot may attempt to alter the approach data, engage another approach, continue to attempt to make visual contact with the offshore target, or abort the OSAP.

<FIG> illustrate flight approach path <NUM> including a plurality of waypoints set by the FMS for a parallel offset approach to an offshore target <NUM>. <FIG> illustrates the plurality of waypoints from a top-down view and <FIG> illustrates the altitudes of the plurality of waypoints. The waypoints include an OSIAF <NUM>, an OSFAF <NUM>, an OSDPA <NUM>, an MDA <NUM>, and an MAP <NUM>. The OSIAF <NUM> may be located a distance of <NUM>,<NUM> (<NUM> nautical miles (NM)) from the offshore target at an altitude of between about <NUM> (<NUM>,<NUM> ft) MSL and about <NUM> (<NUM>,<NUM> ft) MSL, such as about <NUM> (<NUM>,<NUM> ft) ft MSL. The OSIAF <NUM> may have a minimum altitude value, such as about <NUM> (<NUM> ft) MSL. The altitude of the OSIAF <NUM> may be input by the pilot in block <NUM> of the method <NUM>. The OSFAF <NUM> may be located a distance <NUM>,<NUM> (<NUM>) from the offshore target at an altitude of <NUM> (<NUM> ft) MSL. The OSFAF <NUM> may not be input or altered by the pilot. The OSDPA <NUM> may be located a distance <NUM>,<NUM> (<NUM>) from the offshore target at an altitude of <NUM> (<NUM> ft) MSL. The OSDPA <NUM> may not be input or altered by the pilot. The MDA <NUM> may be located a distance of less than <NUM>,<NUM> (<NUM>) from the offshore target at an altitude of at least <NUM> (<NUM> ft) radio altimeter (RA) or <NUM> (<NUM> ft) MSL if the rotorcraft <NUM> does not include an operable RA. The altitude of the MDA <NUM> may be raised by the pilot, but may not be lowered below <NUM> (<NUM> ft) RA or <NUM> (<NUM> ft) MSL. In some embodiments, the pilot may raise the MDA <NUM> altitude if the offshore target <NUM> is unusually high. The MAP <NUM> may be located a distance of <NUM>,<NUM> (<NUM>) from the offshore target <NUM>.

As illustrated in <FIG>, the FMS may set the waypoints for the parallel offset approach such that the rotorcraft flies along a path parallel to a direct path <NUM> to the offshore target <NUM>. The flight path set by the FMS may be offset from the direct path <NUM> by <NUM>,<NUM> (<NUM>). The FMS may set the flight path for the parallel offset approach on either the left side of the offshore target <NUM> or the right side of the offshore target <NUM>, depending on the pilot's input in block <NUM> of the method <NUM>. More specifically, the pilot may input an offset left approach or an offset right approach into the FMS in block <NUM>. The pilot may choose a right-hand approach or a left-hand approach based on personal preferences.

The FCS flies the rotorcraft <NUM> to the offshore target <NUM> by flying to each of the waypoints, the OSIAF <NUM>, the OSFAF <NUM>, the OSDPA <NUM>, the MDA <NUM>, and the MAP <NUM> in order. Upon reaching the OSFAF <NUM>, the rotorcraft <NUM> may decelerate to a ground speed of less than <NUM>/h (<NUM> knots) or a ground speed of less than <NUM>/h (<NUM> knots). The rotorcraft <NUM> may further decelerate to a ground speed of less than <NUM>/h (<NUM> knots) upon reaching the MDA <NUM>.

If the pilot does not make visual contact with the offshore target <NUM> by the time the rotorcraft reaches the MAP <NUM>, or the pilot presses the GA button, the FCS engages in a go-around procedure. The go-around procedure includes flying the rotorcraft <NUM> to a first point <NUM> in the parallel offset heading and climbing to an altitude of <NUM> (<NUM> ft) MSL. The rotorcraft <NUM> then executes a climbing turn towards the offshore target <NUM> and climbs to an altitude of <NUM> (<NUM> ft) MSL at a second point <NUM>. If there is a missed approach, the pilot may attempt to alter the approach data, engage another approach, continue to attempt to make visual contact with the offshore target, or abort the OSAP.

<FIG> illustrates OSAP logic <NUM> that may be implemented by the FMS and the FCS of the rotorcraft <NUM>. Pilot command data <NUM> (e.g., commands from the cyclic control assembly <NUM>, the collective control assembly <NUM>, and the pedal assembly <NUM>) and sensor data <NUM> (e.g., flight data obtained from sensors on the rotorcraft <NUM> or received by the rotorcraft <NUM>) are provided to the OSAP logic block <NUM>. The output of the OSAP logic block <NUM> corresponds to data indicating which phase of the OSAP the rotorcraft <NUM> is currently engaging in. The OSAP logic block <NUM> provides the approach phase data to a longitudinal control block <NUM>, a lateral control block <NUM>, and a collective control block <NUM>. The OSAP logic block <NUM> may further output data indicating which longitudinal mode, lateral mode, and vertical mode the rotorcraft <NUM> is currently engaging in. The OSAP logic block <NUM> provides the longitudinal mode data to the longitudinal control block <NUM>, the lateral mode data to the lateral control block <NUM>, and the vertical mode data to the collective control block <NUM>.

The longitudinal control block <NUM> operates on approach phase data from the OSAP logic block <NUM>, longitudinal mode data from the OSAP logic block <NUM>, and flight data from the sensor data <NUM> in order to produce a pitch command <NUM>. In a representative embodiment, the pitch command <NUM> is provided by the FMS to the FCS for implementation to affect an increase or decrease in pitch angle attending performance of a component pitch motion of the OSAP maneuver.

The lateral control block <NUM> operates on approach phase data from the OSAP logic block <NUM>, lateral mode data from the OSAP logic block <NUM>, and flight data from the sensor data <NUM> in order to produce a roll command <NUM>. In a representative embodiment, the roll command <NUM> is provided by the FMS to the FCS for implementation to affect an increase or decrease in roll angle or yaw rate attending performance of a component roll motion of the OSAP maneuver.

The collective control block <NUM> operates on approach phase data from the OSAP logic block <NUM>, vertical mode data from the OSAP logic block <NUM>, and flight data from the sensor data <NUM> in order to produce a collective command <NUM>. In a representative embodiment, the collective command <NUM> is provided by the FMS to the FCS for implementation to affect an increase or decrease in collective rate attending performance of a component collective motion of the OSAP maneuver.

<FIG> illustrates collective mode logic <NUM> that may be implemented by the FMS and the FCS of the rotorcraft <NUM>. Approach phase data <NUM> (indicating which phase of the OSAP the rotorcraft <NUM> is currently engaging in) and flight data <NUM> (including sensor data obtained from sensors on the rotorcraft <NUM> or received by the rotorcraft <NUM>) are provided to a barometric altitude hold mode block <NUM>, a radio altitude hold mode block <NUM>, a flight path tracking mode block <NUM>, and a level-off mode block <NUM>. A collective multiport switch <NUM> is configured to allow selection of a collective mode <NUM> from a barometric altitude hold mode, a radio altitude hold mode, a flight path tracking mode, or a level-off mode to produce a collective command <NUM>. The collective command <NUM> is provided by the FMS to the FCS for implementation to affect an increase or decrease in collective pitch attending performance of a component collective motion of the OSAP maneuver corresponding to the mode selected by the collective multiport switch <NUM>.

<FIG> illustrates lateral mode logic <NUM> that may be implemented by the FMS and the FCS of the rotorcraft <NUM>. Approach phase data <NUM> (indicating which phase of the OSAP the rotorcraft <NUM> is currently engaging in) and flight data <NUM> (including sensor data obtained from sensors on the rotorcraft <NUM> or received by the rotorcraft <NUM>) are provided to a heading/ground tracking mode block <NUM>, a course tracking mode block <NUM>. A lateral multiport switch <NUM> is configured to allow selection of a lateral mode <NUM> from a heading/ground track mode or a course tracking mode in order to produce a lateral command <NUM>. In some embodiments, the lateral command <NUM> is provided by the FMS to the FCS for implementation to affect an increase or decrease in roll angle or yaw rate attending performance of a component lateral motion of the OSAP maneuver corresponding to the mode selected by the lateral multiport switch <NUM>.

<FIG> illustrates longitudinal mode logic <NUM> that may be implemented by the FMS and the FCS of the rotorcraft <NUM>. Approach phase data <NUM> (indicating which phase of the OSAP the rotorcraft <NUM> is currently engaging in) and flight data <NUM> (including sensor data obtained from sensors on the rotorcraft <NUM> or received by the rotorcraft <NUM>) are provided to an airspeed control mode block <NUM>, a decelerate mode block <NUM>, and a groundspeed control mode block <NUM>. A longitudinal multiport switch <NUM> is configured to allow selection of a longitudinal mode <NUM> from an airspeed control mode, a decelerate mode, or a groundspeed control mode to produce a longitudinal command <NUM>. In some embodiments, the longitudinal command <NUM> is provided by the FMS to the FCS for implementation to affect an increase or decrease in pitch attending performance of a component longitudinal motion of the OSAP maneuver corresponding to the mode selected by the longitudinal multiport switch <NUM>.

<FIG> illustrates a forward velocity airspeed control component <NUM> of the OSAP maneuver that may be implemented by the FMS and the FCS of the rotorcraft <NUM>. In an embodiment as representatively illustrated in <FIG>, the FMS and FCS may be configured to engage a forward velocity airspeed control component <NUM> of an approach-to-hover maneuver. The approach phase data <NUM> and the flight data <NUM> may be provided to the airspeed control mode block <NUM>. The airspeed control mode block <NUM> provides a target airspeed output to an airspeed control comparator <NUM>. The longitudinal multiport switch <NUM> provides mode-selected airspeed flight data to the airspeed control comparator <NUM>. The airspeed control comparator <NUM> determines a vector difference between the mode-selected airspeed flight data and the desired or computed forward velocity for the then-current approach phase. For example, the absolute value (or magnitude) of the difference between the sensed airspeed and the desired forward velocity is determined, as well as the sign (or direction) of the difference (e.g., positive indicating acceleration to achieve the desired forward velocity, negative indicating deceleration to achieve the desired forward velocity). The output of the airspeed control comparator <NUM> is provided to an airspeed control gain stage <NUM>, where K indicates a desired acceleration or deceleration. The output from the airspeed control gain stage <NUM> is provided as the longitudinal command <NUM>. In accordance some embodiments, the longitudinal command <NUM> is provided by the FMS to the FCS for implementation to affect an increase or decrease in pitch attending performance of a component longitudinal motion of the OSAP maneuver corresponding to the selection of the airspeed control mode.

<FIG> illustrates a forward velocity decelerate component <NUM> of the OSAP maneuver that may be implemented by the FMS and the FCS of the rotorcraft <NUM>. The approach phase data <NUM> and the flight data <NUM> may be provided to the decelerate mode block <NUM>. The decelerate mode block <NUM> provides target airspeed output to a decelerate comparator <NUM>. The longitudinal multiport switch <NUM> provides mode-selected airspeed flight data to the decelerate comparator <NUM>. The decelerate comparator <NUM> determines a vector difference between the mode-selected airspeed flight data and the desired or computed forward velocity for the then-current approach phase. For example, the absolute value (or magnitude) of the difference between the sensed airspeed and the desired forward velocity is determined, as well as the sign (or direction) of the difference (e.g., positive indicating acceleration to achieve the desired forward velocity, negative indicating deceleration to achieve the desired forward velocity). The output of the decelerate comparator <NUM> is provided to a decelerate gain stage <NUM>, where K indicates a desired acceleration or deceleration. The output from the decelerate gain stage <NUM> is provided as the longitudinal command <NUM>. The longitudinal command <NUM> may be provided by the FMS to the FCS for implementation to affect an increase or decrease in pitch attending performance of a component longitudinal motion of the OSAP maneuver corresponding to the selection of the decelerate mode.

<FIG> illustrates a forward velocity groundspeed control component <NUM> of the OSAP maneuver that may be implemented by the FMS and the FCS of the rotorcraft <NUM>. The approach phase data <NUM> and the flight data <NUM> may be provided to the groundspeed control mode block <NUM>. The groundspeed control mode block <NUM> provides target airspeed output to a groundspeed control comparator <NUM>. The longitudinal multiport switch <NUM> provides mode-selected groundspeed flight data to the groundspeed control comparator <NUM>. The groundspeed control comparator <NUM> determines a vector difference between the mode-selected groundspeed flight data and the desired or computed forward velocity for the then-current approach phase. For example, the absolute value (or magnitude) of the difference between the sensed groundspeed and the desired forward velocity is determined, as well as the sign (or direction) of the difference (e.g., positive indicating acceleration to achieve the desired forward velocity, negative indicating deceleration to achieve the desired forward velocity). The output of the groundspeed control comparator <NUM> is provided to a groundspeed control gain stage <NUM>, where K indicates a desired acceleration or deceleration. The output from the groundspeed control gain stage <NUM> is provided as the longitudinal command <NUM>. The longitudinal command <NUM> may be provided by the FMS to the FCS for implementation to affect an increase or decrease in pitch attending performance of a component longitudinal motion of the OSAP maneuver corresponding to the selection of the groundspeed control mode.

<FIG> illustrates a method <NUM> for performing an OSAP in accordance with a representative embodiment. The method <NUM> begins <NUM> with an optional step <NUM> of pre-processing. The optional pre-processing of step <NUM> may include control laws performing various adjustments preliminary to (or during some portion of) the operation of the rotorcraft <NUM> in a first operating condition <NUM> of the FCS. The method <NUM> further includes a step <NUM> of the FMS receiving a pilot command for a target location. In response to receiving the pilot command for the target location, the method <NUM> further includes a step <NUM> of the FMS designating a missed approach point (MAP). The method <NUM> further includes a step <NUM> of the FMS determining waypoints in a flight path to approach the MAP. After the FMS determines waypoints in the flight path to approach the MAP, the method <NUM> further includes a step <NUM> of the FD/FCC receiving a pilot command to engage in an approach maneuver. In response to the pilot command to engage in the approach maneuver, the method <NUM> further includes a step <NUM> of the rotorcraft <NUM> flying to the MAP. The FD instructs the FCS to alter conditions of the rotor system <NUM> in order to fly the rotorcraft <NUM> to the MAP along the flight path. In response to the FD/FCC engaging in the approach maneuver and the rotorcraft <NUM> flying to the MAP, the method <NUM> further includes a step <NUM> of the FCS transitioning to a second operating condition (or a series or sequence of second operating conditions) of the FCS, wherein the second operating condition (or series of the same) is operable to reduce the airspeed and to reduce the altitude attending the rotorcraft <NUM> approaching the MAP (e.g., <NUM> feet over the marked target location). The method <NUM> further includes a step <NUM> of optional post-processing. In some embodiments, the optional post-processing <NUM> may include control laws performing various adjustments during or after the operation of the rotorcraft <NUM> in the first operating condition of the FCS. The method <NUM> also includes a step <NUM> of the rotorcraft <NUM> hovering over the marked target location of the MAP.

<FIG> illustrates a method <NUM> for implementing an automated-, mediated-, or at least assisted-OSAP maneuver. The method <NUM> begins <NUM> with a step <NUM> of operating the FCS of the rotorcraft <NUM> in an initial operating condition. The initial operating condition may be any condition of operating the FCS (e.g., generally regarded as a stable operating condition). For example, the initial operating condition may correspond to the rotorcraft <NUM> engaging in forward flight at a relatively constant, nonzero velocity. Step <NUM> represents optional pre-processing that the FMS may engage in (or be engaged in) preliminary to the FMS receiving a pilot command to engage an OSAP maneuver in step <NUM>. For example, the optional pre-processing <NUM> may include control laws performing various adjustments during the operation of the rotorcraft <NUM> in the initial operating condition <NUM>. After a pilot command to engage in an OSAP maneuver is received in step <NUM>, the FMS determines (in step <NUM>) a pitch angle, a roll angle, a yaw rate, or a collective pitch angle for turning the rotorcraft <NUM> into a downwind path to begin the OSAP maneuver. In step <NUM>, the FMS determines a pitch angle, a roll angle, a yaw rate, or a collective pitch angle for implementation in performance of the OSAP maneuver. Thereafter the FCS is transitioned to an interim operating condition in step <NUM> (e.g., the interim operating condition corresponding to a component portion of the RTT maneuver for returning the rotorcraft <NUM> to an MAP). Thereafter, the OSAP maneuver processing is looped <NUM> to iteratively or sequentially determine pitch angles, roll angles, yaw rates, or collective pitch angles for implementation in performance of subsequent phases of the OSAP maneuver. Steps <NUM> and <NUM> are looped <NUM> until cancellation of the OSAP maneuver by the pilot in step <NUM>, or reaching the target location in step <NUM>. If the target location is reach, the rotorcraft <NUM> is placed in a hover above the target location in step <NUM>. If the pilot optionally cancels the OSAP maneuver, the rotorcraft <NUM> may be optionally returned to the initial operating condition existing prior to the engagement of the OSAP maneuver. The FMS may engage the optional post-processing in step <NUM>. For example, the optional post-processing <NUM> may include control laws performing various automated control functions.

<FIG> illustrates a method <NUM> providing further detail of the step <NUM> (see <FIG>) of transitioning the FCS to an interim operating condition. The method <NUM> includes an optional pre-processing step <NUM>. The optional pre-processing step <NUM> may include the same, similar, or different elements or steps as the optional pre-processing step <NUM> of <FIG>. In step <NUM>, the FMS makes a change to a first flight characteristic. In step <NUM>, the FMS changes a prior operating condition of the FCS to a subsequent operating condition of the FCS in correspondence to, in congruence with, or otherwise appreciating, an expected change in a second flight characteristic inherently-coupled to, or convolved with, the first flight characteristic (as previously discussed) in order to counteract or otherwise address the expected change in the second flight characteristic (e.g., main rotor tilt engagement to affect a roll maneuver may require modification of collective pitch). Thereafter optional post-processing may be performed in step <NUM>. The optional post-processing step <NUM> may identically include or find correspondence to same, similar, or different elements as the optional post-processing step <NUM> of <FIG>. For example, some or all of the optional post-processing of step <NUM> may be a subset of the optional post-processing step <NUM> of <FIG>.

<FIG> illustrates a logic diagram of control logic <NUM> for engaging an OSAP in the FMS. In block <NUM>, the OSAP is not active. In block <NUM>, the rotorcraft <NUM> may be operating in a first operating condition, such as forward flight at an airspeed of greater than <NUM>/h (<NUM> knots). In block <NUM>, the pilot of the rotorcraft <NUM> presses an OSAP button, and the OSAP is armed. In block <NUM>, the FMS captures a course. The FMS determines the rotorcraft <NUM>'s current location and approach data indicating an offshore target location, an approach direction, an approach type, and a minimum approach altitude. The FMS then sets waypoints between the current location of the rotorcraft <NUM> and a missed approach point (MAP) located a distance from the offshore target location.

Once the course is set and the OSAP has been engaged, the FMS commands the FCS to engage in the OSAP and the FMS tracks the course of the OSAP in block <NUM>. In block <NUM>, the FMS of the rotorcraft <NUM> tracks the course of the rotorcraft in the OSAP. The FMS may gather data from various sensors on the rotorcraft <NUM> and may also receive data from outside the rotorcraft <NUM> to track the position of the rotorcraft <NUM>.

The control logic <NUM> further includes a speed control block <NUM> and a vertical control <NUM>. In block <NUM>, the rotorcraft <NUM> engages in an airspeed (ASPD) hold mode in which the rotorcraft moves to an offshore initial approach fix. Once the rotorcraft <NUM> reaches the offshore initial approach fix (OSIAF), the rotorcraft <NUM> decelerates to Vy in block <NUM>. Vy is the optimal climbing speed for the rotorcraft <NUM> and may, in some embodiments, be about <NUM>/h (<NUM> knots). The rotorcraft <NUM> then continues forward holding the forward velocity Vy in block <NUM> until the rotorcraft <NUM> reaches the minimum descent altitude (MDA). The rotorcraft <NUM> then decelerates to Vtoss in block <NUM> after reaching the MDA. Vtoss may be the safety takeoff speed for the rotorcraft <NUM> and, in some embodiments, may be about <NUM>/h (<NUM> knots).

The FMS holds the altitude of the rotorcraft <NUM> in block <NUM> until the rotorcraft <NUM> reaches the OSIAF. In some embodiments, the initial altitude of the rotorcraft <NUM> may be about <NUM> (<NUM> ft) MSL or about <NUM> (<NUM> ft) MSL. Once the rotorcraft <NUM> reaches the OSIAF, the rotorcraft <NUM> engages a glidepath in block <NUM> to decrease the altitude of the rotorcraft <NUM> to the MDA, which may be about <NUM> (<NUM> ft) MSL. The rotorcraft <NUM> then levels off at the MDA in block <NUM> and holds the MDA in block <NUM>.

<FIG> illustrates an optional mode logic block <NUM>. In some embodiments, the optional mode logic block <NUM> may be included in the OSAP logic <NUM> of <FIG>. Pilot command data <NUM> (e.g., commands from the cyclic control assembly <NUM>, the collective control assembly <NUM>, and the pedal assembly <NUM>) and sensor data <NUM> (e.g., flight data obtained from sensors on the rotorcraft <NUM> or received by the rotorcraft <NUM>) are provided to the optional mode logic block <NUM>. The output of the optional mode logic block <NUM> corresponds to data indicating the approach phase, the lateral mode, the longitudinal mode, and the vertical mode that are currently set in the rotorcraft <NUM>. The optional mode logic block <NUM> provides the approach phase date to the longitudinal control block <NUM>, the lateral control block <NUM>, and the collective control block <NUM> of <FIG>. The optional mode logic block <NUM> further provides the lateral mode data to the lateral control block <NUM>, the longitudinal mode data to the longitudinal control block <NUM>, and the vertical mode data to the collective control block <NUM> of <FIG>.

The OSAP may be used to aid pilots in flying to an offshore target. A pilot is able to fly the rotorcraft <NUM> to an offshore target by only providing the location of the offshore target, or by providing a combination of the location of the offshore target and any of an approach direction, an approach type, and a minimum altitude for a missed approach point. The FMS automatically generates waypoints between the rotorcraft <NUM>'s current location and the missed approach point, thus the pilot does not have to calculate these waypoints.

Claim 1:
A rotorcraft (<NUM>) comprising:
a rotor system (<NUM>) comprising a plurality of blades (<NUM>);
a flight director (FD) operable to receive commands from a pilot (<NUM>);
a wind sensor;
a collective multiport switch (<NUM>);
a flight control system (FCS), the flight control system operable to control flight of the rotorcraft by changing an operating condition of the rotor system; and
a flight management system (FMS) in signal communication with a control assembly and the FCS, the FMS being operable to:
receive, from a pilot via a pilot input into said FMS, approach parameters that include at least an offshore target location;
automatically populate a plurality of approach parameters, the plurality of approach parameters including an approach type, an approach direction based on a detected wind direction from the wind sensor, and a minimum altitude for a missed approach point (MAP);
generate a missed approach point (MAP) based on the target location and the plurality of approach parameters;
after the flight director receives a pilot command to engage in an approach maneuver within an offshore standard approach procedure (OSAP),
generating a plurality of waypoints between a current location of the rotorcraft and the MAP (<NUM>) in response to receiving the offshore target location and populating the plurality of approach parameters;
wherein the flight director is operable to:
receive, after the MAP is generated, the command to engage in the approach maneuver;
and, in response to the command to engage in the approach maneuver, instruct the FCS to fly to the MAP along a flight path comprising the plurality of waypoints, wherein instructing the FCS to fly to the MAP comprises providing at least a collective command generated by the FMS according to approach phase data indicating which phase of the OSAP the rotorcraft (<NUM>) is currently engaging, and generated according to pilot command data (<NUM>) and/or sensor data (<NUM>), and further according to a collective mode selected through the collective multiport switch; and
a go-around button (GA) in signal communication with the FCS, wherein the FCS is operable to engage in a go-around procedure in response to the go-around button being engaged.