Rotorcraft system for command mode transitions

1 . A method comprising:

determining an angular rate of a rotorcraft based on a pilot input of the rotorcraft;

determining an attitude reference for the rotorcraft based on the angular rate, the determining comprising:

determining an attitude difference from a trim attitude of the rotorcraft;

determining a linear acceleration error for the rotorcraft;

determining a trim attitude of the rotorcraft, wherein the trim attitude is based on the linear acceleration error; and

summing the attitude difference and the trim attitude to generate the attitude reference;

determining a flight command for the rotorcraft based on the attitude reference; and

controlling flight control elements of the rotorcraft based on the flight command.

2 . The method of claim 1 , wherein the pilot input represents an angular rate command.

3 . The method of claim 1 further comprising applying a gain to the linear acceleration error to generate a linear acceleration feedback signal, wherein determining the trim attitude comprises integrating the linear acceleration feedback signal.

4 . The method of claim 3 , wherein determining the attitude difference comprises subtracting the linear acceleration feedback signal from an Euler rate of the rotorcraft and integrating the result.

5 . The method of claim 1 , wherein determining the linear acceleration error comprises applying a gain to the attitude difference to generate a linear acceleration reference and then subtracting a sensed linear acceleration of the rotorcraft from the linear acceleration reference.

6 . The method of claim 1 further comprising equating a linear speed reference to a sensed linear speed of the rotorcraft.

7 . The method of claim 1 , wherein the rotorcraft is in an angular-based command mode, and further comprising transitioning the rotorcraft to a linear-based command mode.

8 . A method of operating a rotorcraft, the method comprising:

receiving a pilot input signal at a flight controller of the rotorcraft, wherein the pilot input signal represents a command to change an angular rate of the rotorcraft when the rotorcraft is in a first command mode, wherein the pilot input signal represents a command to change a linear rate of the rotorcraft when the rotorcraft is in a second command mode;

generating, by the flight controller, an angular rate signal based on the pilot input signal;

generating, by the flight controller, a linear acceleration feedback signal based on the angular rate signal, wherein the linear acceleration feedback signal is subtracted from the angular rate signal when the rotorcraft is in the first command mode;

generating, by the flight controller, an attitude feedback signal based on the angular rate signal and the linear acceleration feedback signal;

generating, by the flight controller, an actuator command signal based on the attitude feedback signal, wherein the actuator command signal corresponds to the pilot input signal; and

transmitting the actuator command signal to an actuator of the rotorcraft to control the flight of the rotorcraft.

9 . The method of claim 8 further comprising:

when the rotorcraft is in the first command mode, generating, by the flight controller, a linear speed signal based on a sensed linear speed signal; and

when the rotorcraft is in the second command mode, generating, by the flight controller, a linear speed signal based on an integration of the linear acceleration feedback signal, wherein the attitude reference signal is based on the linear acceleration feedback signal.

10 . The method of claim 8 further comprising generating, by the flight controller, a trim attitude signal based on the linear acceleration feedback signal.

11 . The method of claim 8 , wherein the second command mode is a Translational Rate Command (TRC) mode.

12 . The method of claim 11 , wherein the linear rate of the rotorcraft is a translational rate, wherein the angular rate signal is based on a pitch acceleration command corresponding to the translational rate.

13 . The method of claim 8 , wherein the first command mode is a Rate Command/Attitude Hold (RCAH) mode.

14 . The method of claim 8 , further comprising transitioning the rotorcraft from the first command mode to the second command mode.

15 . The method of claim 8 , wherein generating the attitude feedback signal comprises integrating the linear acceleration feedback signal.

16 . A flight control system 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 to:

operate the rotorcraft in an angular-based command mode, comprising:

receiving a first pilot control signal representing an angular rate command for the rotorcraft;

generating a first linear acceleration feedback signal based on the first pilot control signal;

generating a first trim attitude signal based on the first linear acceleration feedback signal; and

generating a first flight command for the rotorcraft based on the first pilot control signal and the first trim attitude signal;

operate the rotorcraft in a linear-based command mode, comprising:

receiving a second pilot control signal representing a linear command for the rotorcraft;

generating a second linear acceleration feedback signal based on the second pilot control signal;

generating a second trim attitude signal based on the second linear acceleration feedback signal; and

generating a second flight command for the rotorcraft based on the second pilot control signal and the second trim attitude signal; and

transition the rotorcraft between the angular-based command mode and the linear-based command mode.

17 . The flight control system of claim 16 , wherein operating the rotorcraft in the angular-based command mode further comprises:

generating an angular rate signal based on the first pilot control signal;

subtracting the first linear acceleration feedback signal from the angular rate signal to generate an attitude signal; and

adding the attitude signal to the first trim attitude signal to generate a total attitude reference signal.

18 . The flight control system of claim 17 , wherein the subtraction of the first linear acceleration feedback signal is initiated at a transition from the linear-based command mode to the angular-based command mode.

19 . The flight control system of claim 17 , wherein the first trim attitude signal is generated continually while the rotorcraft is operated in the angular-based command mode.

20 . The flight control system of claim 16 , wherein the program further includes instructions to limit a magnitude of the first pilot control signal.