# US 10,766,613 B2 · System and method for rotorcraft-weight-on-wheels flight state transition control

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- Number: US 10,766,613 B2
- Document ID: US10766613B2
- Status: Granted
- Kind: B2
- Application number: 15/940,184
- Filed: 2018-03-29
- Published: 2019-05-30
- Granted: 2020-09-08
- Earliest claimed: 2017-11-28
- Assignees: Textron Innovations Inc.
- Applicants: Textron Innovations Inc.
- Inventors: Jillian Samantha Alfred; Monica Sibello; Robert Earl Worsham, II
- Web page: https://patentgrep.com/patent/US10766613B2

## CPC

- B64C 27/00: Rotorcraft; Rotors peculiar thereto
- B64C 27/57: automatic or condition responsive, e.g. responsive to rotor speed, torque or thrust
- B64C 13/503: {Fly-by-Wire}
- B64C 19/00: Aircraft control not otherwise provided for
- B64C 25/00: Alighting gear (air-cushion alighting gear B60V3/08)
- B64D 45/04: Landing aids; Safety measures to prevent collision with earth's surface
- G05D 1/102: {specially adapted for vertical take-off of aircraft}
- B64C 25/34: wheeled type, e.g. multi-wheeled bogies
- B64C 2025/325: {specially adapted for helicopters}
- B64C: AEROPLANES; HELICOPTERS
- B64D: EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
- G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES

## Abstract

A rotorcraft having a plurality of wheels, each wheel configured to receive weight of the rotorcraft when in contact with a landing surface, a plurality of wheel sensors, each wheel sensor associated with a respective wheel and having circuitry configured to generate a wheel on ground (WOG) signal indicating that the respective wheel is in contact with the landing surface, and a flight control computer (FCC) in signal communication with the plurality of wheel sensors, the FCC operable to execute a first hold loop having a first integrator and providing first control augmentation of a rotorcraft flight system, the FCC further operable to freeze the first integrator according to a number of WOG signals received from the plurality of wheel sensors, the FCC further operable to generate a first control signal according to a first value provided by the first integrator while the first integrator is frozen.

## Claims

### Claim 1

A rotorcraft, comprising:
a plurality of wheels, each wheel of the plurality of wheels configured to receive weight of the rotorcraft when in contact with a landing surface;
a plurality of wheel sensors, each wheel sensor of the plurality of wheel sensors associated with a respective wheel and having circuitry configured to generate a wheel on ground (WOG) signal indicating that the respective wheel is in contact with the landing surface; and
a flight control computer (FCC) in signal communication with the plurality of wheel sensors, the FCC operable to execute a first hold loop having a first integrator and providing first control augmentation of a flight system of the rotorcraft, the FCC further operable to freeze the first integrator according to a number of WOG signals received from the plurality of wheel sensors, the FCC further operable to generate a first control signal according to a first value provided by the first integrator while the first integrator is frozen.

### Claim 2 (depends on 1)

The rotorcraft of claim 1, wherein the FCC is further operable to monitor an active weight on wheels (WOW) state by setting the active WOW state to a state in a WOW state machine, wherein the WOW state machine has an in transit state, and wherein the FCC is further operable to freeze the first integrator when the active WOW state is the in transit state.

### Claim 3 (depends on 2)

The rotorcraft of claim 2, wherein the FCC is further operable to set the active WOW state to the in transit state in response to the FCC determining that the number of WOG signals is one or greater.

### Claim 4 (depends on 3)

The rotorcraft of claim 3, wherein the FCC is further operable to set the active WOW state to the in transit state in response to the FCC determining that the number of WOG signals is one and further in response to a speed of the rotorcraft being less than a landing speed threshold.

### Claim 5 (depends on 4)

The rotorcraft of claim 4, wherein the FCC is further operable to set the active WOW state to the in transit state in response to the FCC determining that the number of WOG signals is one, in response to a speed of the rotorcraft being greater than or equal to the landing speed threshold, in response to a previous WOW state of the rotorcraft being the in transit state, and further in response to the number of WOG signals being one for a period less than or equal to a one WOG timer threshold.

### Claim 6 (depends on 5)

The rotorcraft of claim 5, wherein the WOW state machine further includes a single gear state and an in flight state;
wherein the FCC is further operable to set the active WOW state to the single gear state in response to the FCC determining that the number of WOG signals is one, in response to the speed of the rotorcraft being greater than or equal to the landing speed threshold, and further in response to one of: a previous WOW state of the rotorcraft being the in flight state, or the previous WOW state of the rotorcraft being the in transit state and the number of WOG signals being one for a period greater than the one WOG timer threshold; and
wherein the FCC is further operable to execute a second hold loop having a second integrator and providing second control augmentation of the flight system, the FCC is further operable to unfreeze the first integrator and freeze the second integrator when the active WOW state is the single gear state, and the FCC is further operable to generate a second control signal according to a second value provided by the second integrator while the second integrator is frozen;
wherein the first hold loop is a different hold loop than the second hold loop; and
wherein the FCC is further operable to set the active WOW state to the in flight state in response to the FCC determining that the number of WOG signals is zero, and wherein the FCC is further operable to unfreeze the first integrator and the second integrator when the active WOW state is the in flight state.

### Claim 7 (depends on 6)

The rotorcraft of claim 6, wherein the WOW state machine further includes an on ground state;
wherein the FCC is further operable to set the active WOW state to the on ground state in response to the FCC determining that the number of WOG signals is two for a period greater than a two WOG timer threshold; and
wherein the FCC is further operable to turn off the first integrator and the second integrator when the active WOW state is the on ground state, and the FCC is further operable to generate the first and second control signals according to values other than values provided by the first and second integrators while the first and second integrators are turned off.

### Claim 8 (depends on 3)

The rotorcraft of claim 3, wherein the FCC is further operable to set the active WOW state to the in transit state in response to the FCC determining that the number of WOG signals is two for a period less than or equal to a two WOG timer threshold.

### Claim 9

A flight control computer (FCC) for a rotorcraft, comprising:
a processor; and
a non-transitory computer-readable storage medium storing a program to be executed by the processor, the program including instructions for:
receiving one or more signals indicating a weight on wheels (WOW) count associated with a number wheels of the rotorcraft that bear weight of the rotorcraft;
providing a first set of integrators in a first set of hold loops that generate first control augmentation signals for a flight system of the rotorcraft;
providing a second set of integrators in a second set of hold loops that generate second control augmentation signals for the flight system;
maintaining a WOW state machine having at least a single gear state and an in transit state;
determining an active WOW state of the WOW state machine according to at least the WOW count;
freezing the first set of integrators in response to determining that the single gear state is the active WOW state, wherein the first set of hold loops generate the first control augmentation signals according to first values provided by the first set of integrators when the first set of integrators are frozen; and
freezing the second set of integrators in response to determining that the in transit state is the active WOW state, wherein the second set of hold loops generate the second control augmentation signals according to second values provided by the second set of integrators when the second set of integrators are frozen.

### Claim 10 (depends on 9)

The FCC of claim 9, wherein the program further include instructions for:
setting the active WOW state to the in transit state in response to the FCC determining that the WOW count is one and further in response to the FCC determining that a speed of the rotorcraft is less than a landing speed threshold;
setting the active WOW state to the in transit state in response to the FCC determining that the WOW count has been one for a period less than or equal to a one WOG timer threshold, in response to the FCC determining that the speed of the rotorcraft is greater than or equal to the landing speed threshold, and further in response to a previous WOW state of the rotorcraft is the in transit state; and
setting the active WOW state to the in transit state in response to the FCC determining that the WOW count has been two for a period less than or equal to a two WOG timer threshold.

### Claim 11 (depends on 10)

The FCC of claim 10, wherein the WOW state machine further has an in flight state and an on ground state; and
wherein the program further including instructions for:
setting the active WOW state to the single gear state in response to the FCC determining that the WOW count is one and that the speed of the rotorcraft is greater than or equal to the landing speed threshold, and further in response to one of a previous WOW state of the rotorcraft being the in flight state, or the previous WOW state of the rotorcraft being the in transit state and the WOW count having been one for a period greater than the one WOG timer threshold;
setting the active WOW state to the in flight state in response to the FCC determining that the WOW count is zero, and wherein the FCC is further operable to unfreeze the first set of integrators and the second set of integrators when the active WOW state is the in flight state;
setting the active WOW state to the on ground state in response to the FCC determining that the WOW count is two for a period greater than the two WOG timer threshold;
operating the first set of hold loops and the second set of hold loops in a turned on mode and operating the first set of integrator and the second set of integrators in an unfrozen mode when the active WOW state is the in flight state; and
turning off the first set of hold loops and the second set of hold loops when the active WOW state is the on ground state.

### Claim 12 (depends on 9)

The FCC of claim 9, wherein the second set of hold loops includes at least one hold loop that is absent from the first set of hold loops, and wherein the second set of hold loops includes at least one hold loop that is in the first set of hold loops.

### Claim 13 (depends on 12)

The FCC of claim 12, wherein the first set of hold loops includes at least a position hold loop, a speed hold loop, and a heading hold loop, and wherein the second set of hold loops includes at least the position hold loop, the speed hold loop, the heading hold loop, and an attitude hold loop.

### Claim 14 (depends on 9)

The FCC of claim 9, wherein the instructions for providing the first set of integrators include instructions for:
providing the first set of hold loops, each first hold loop of the first set of hold loops having a first integrator of the first set of integrators in a first integral signal path and having a first proportional signal path; and
generating, in each first hold loop, one of the first control augmentation signals according to a first proportional signal from the first proportional signal path and a first integral signal from the first integral signal path; and
wherein the instructions for providing the first set of integrators include instructions for:
providing the second set of hold loops, each second hold loop of the second set of hold loops having a second integrator of the second set of integrators in a second integral signal path and having a second proportional signal path; and
generating, in each second hold loop, one of the second control augmentation signals according to a second first proportional signal from the second proportional signal path and a second integral signal from the second integral signal path.

### Claim 15 (depends on 14)

The FCC of claim 14, wherein the program further include instructions for:
receiving feedback data at an input to an integral signal path of one of the first set of hold loops and receiving control data, at an input of a proportional signal path of one of the first set of hold loops, indicating a pilot control position.

### Claim 16

A method for controlling a rotorcraft, comprising:
maintaining a weight on wheels (WOW) state machine having at least a single gear state, an in transit state, and an on ground state;
determining an active WOW state of the WOW state machine according to one or more signals indicating a WOW count associated with a number wheels of the rotorcraft that bear weight of the rotorcraft, wherein the determining the active WOW state comprises using the in transit state as a buffer for a transition between the single gear state and the on ground state;
freezing a first set of integrators in a first set of hold loops operated by a flight control computer (FCC) in response to determining that the active WOW state is the single gear state;
freezing a second set of integrators in a second set of hold loops operated by the FCC in response to determining that the active WOW state is the in transit state;
unfreezing the first set of integrators and the second set of integrators when the active WOW state is an in flight state; and
generating control signals according to values provided by the first set of integrators and the second set of integrators when the active WOW state is one of the single gear state, the in transit state, and the in flight state.

### Claim 17 (depends on 16)

The method of claim 16, wherein the determining the active WOW state comprises:
setting the active WOW state to the in transit state in response to the WOW count being one and further in response to a speed of the rotorcraft being less than a landing speed threshold;
setting the active WOW state to the in transit state in response to the WOW count being one for a period less than or equal to a one WOG timer threshold, in response to the speed of the rotorcraft being greater than or equal to the landing speed threshold, and further in response to a previous WOW state of the rotorcraft being the in transit state; and
setting the active WOW state to the in transit state in response to the WOW count being two for a period less than or equal to a two WOG timer threshold.

### Claim 18 (depends on 17)

The method of claim 17, wherein the WOW state machine further has an in flight state; and
wherein the determining the active WOW state further comprises:
setting the active WOW state to the single gear state in response to the WOW count being one and the speed of the rotorcraft being greater than or equal to the landing speed threshold, and further in response to one of a previous WOW state of the rotorcraft being the in flight state, or the previous WOW state of the rotorcraft being the in transit state and the WOW count being one for a period greater than the one WOG timer threshold;
setting the active WOW state to the in flight state in response to the WOW count being zero;
setting the active WOW state to the on ground state in response to the FCC determining that the WOW count is two for a period greater than the two WOG timer threshold;
turning off the first set of hold loops and the second set of hold loops when the active WOW state is the on ground state; and
operating the first set of hold loops and the second set of hold loops in a turned on mode and operating the first set of integrator and the second set of integrators in an unfrozen mode when the active WOW state is the in flight state.

### Claim 19 (depends on 16)

The method of claim 16, wherein the first set of hold loops includes at least a position hold loop, a speed hold loop, and a heading hold loop, and wherein the second set of hold loops includes at least the position hold loop, the speed hold loop, the heading hold loop, and an attitude hold loop.

### Claim 20 (depends on 16)

The method of claim 16, wherein the generating the control signals comprises:
receiving feedback data at inputs of a first integral signal path and a second integral signal path and receiving control data, at inputs of a first proportional signal path and a second proportional signal path, indicating a pilot control position;
generating, in a first hold loop of the first set of hold loops, a first control signal according to a first proportional signal, generated according to the control data, from a first proportional signal path of a first hold loop of the first set of hold loops, wherein the first control signal is further generated according to a first integral signal, generated according to the feedback data, from a first integral signal path in which a first integrator of the first set of integrators is disposed and generated according to the feedback data; and
generating, in a second hold loop of the second set of hold loops, a second control signal according to a second proportional signal, generated according to the control data, from a second proportional signal path of a second hold loop of the second set of hold loops, wherein the second control signal is further generated according to a second integral signal, generated according to the feedback data, from a second integral signal path in which a second integrator of the second set of integrators is disposed and generated according to the feedback data.