Method and apparatus for flight control of tiltrotor aircraft

1. A method for automatically controlling the flight of a tiltrotor aircraft while the aircraft is in flight that is at least partially rotor-borne, the tiltrotor aircraft being capable of flying in a helicopter mode and in an airplane mode, the aircraft having a fuselage and at least two tiltable nacelles, each nacelle having a rotor with adjustable-pitch blades controlled by cyclic swashplate controls and collective swashplate controls, the method comprising the steps of:

providing a flight control system;

providing longitudinal swashplate controls in each nacelle;

providing lateral swashplate controls in each nacelle;

operating the tiltrotor aircraft in the helicopter flight mode while the fuselage is positioned at a level pitch attitude;

generating a longitudinal-velocity control signal based on a pilot control input for generating a longitudinal velocity while maintaining the aircraft in the helicopter flight mode;

automatically tilting the nacelles with the flight control system in response to the longitudinal-velocity control signal so as to produce a longitudinal thrust-vector component for controlling longitudinal velocity of the aircraft;

automatically actuating the longitudinal cyclic swashplate controls for each rotor with the flight control system so as to maintain the fuselage in the level pitch attitude; and

maintaining the fuselage in the level pitch attitude;

wherein each nacelle is independently tiltable;

wherein the automatically actuating the longitudinal cyclic swashplate controls for each rotor counteracts a changing in pitch attitude that would otherwise result from tilting the nacelles; and

wherein the counteracting the changing in pitch attitude occurs simultaneously with the automatically tilting the nacelles.

2. The method according to claim 1 , further comprising the steps of:

providing collective swashplate controls in each nacelle;

generating a lateral-velocity control signal;

automatically actuating the lateral cyclic swashplate controls for each rotor with the flight control system in response to the lateral-velocity control signal so as to produce a lateral thrust-vector component for controlling lateral velocity of the aircraft; and

automatically actuating the collective swashplate controls for each rotor with the flight control system so as to maintain the fuselage in a level roll attitude;

wherein the collective swashplate controls for each rotor are actuated independently from each other.

3. A method for automatically controlling the flight of a tiltrotor aircraft while the aircraft is in flight that is at least partially rotor-borne, the tiltrotor aircraft being capable of flying in a helicopter mode and in an airplane mode, the aircraft having a fuselage and at least two tiltable nacelles, each nacelle having a rotor with adjustable-pitch blades controlled by cyclic swashplate controls and collective swashplate controls, the method comprising the steps of:

providing a flight control system;

providing longitudinal swashplate controls in each nacelle;

providing lateral swashplate controls in each nacelle;

operating the tiltrotor aircraft in the helicopter flight mode while the fuselage is positioned at a level roll attitude;

generating a lateral-velocity control signal based on a pilot control input for generating a lateral velocity while maintaining the aircraft in the helicopter flight mode;

automatically actuating the lateral cyclic swashplate controls for each rotor with the flight control system in response to the lateral-velocity control signal so as to produce a lateral thrust-vector component for controlling lateral velocity of the aircraft, thereby resulting in a changing in roll attitude of the fuselage from the level roll attitude; and

automatically differentially actuating the collective swashplate controls for each rotor with the flight control system in response to the lateral-velocity control signal so as to maintain the fuselage in the level roll attitude;

wherein the collective swashplate controls for each rotor are actuated independently from each other;

wherein each nacelle is independently tiltable from each other;

wherein the automatically differentially actuating the collective swashplate controls for each rotor prevents the changing in roll attitude of the fuselage; and

wherein the preventing the changing in roll attitude occurs simultaneously with the automatically actuating the lateral cyclic swashplate.

4. The method according to claim 3 , further comprising the steps of:

generating a longitudinal-velocity control signal;

automatically tilting the nacelles with the flight control system in response to the longitudinal-velocity control signal so as to produce a longitudinal thrust-vector component for controlling longitudinal velocity of the aircraft; and

automatically actuating the longitudinal cyclic swashplate controls for each rotor with the flight control system so as to maintain the fuselage in a level pitch attitude.

5. A method for controlling a response of a tiltrotor aircraft to a wind gust while the aircraft is in flight that is at least partially rotor-borne, the tiltrotor aircraft being capable of flying in a helicopter mode and in an airplane mode, the aircraft having at least two tiltable nacelles, each nacelle having a rotor with adjustable-pitch blades controlled by cyclic swashplate controls and collective swashplate controls, the method comprising:

providing a flight control system;

providing longitudinal swashplate controls in each nacelle;

providing lateral swashplate controls in each nacelle;

operating the tiltrotor aircraft in the helicopter flight mode while the fuselage is positioned at a level pitch attitude and a level roll attitude;

automatically tilting the nacelles with the flight control system so as to produce a longitudinal thrust-vector component that opposes a longitudinal component of the wind gust while maintaining the aircraft in the helicopter flight mode;

automatically actuating the lateral cyclic swashplate controls for each rotor with the flight control system so as to produce a lateral thrust-vector component that opposes a lateral component of the wind gust and to maintain the fuselage in the level pitch attitude, thereby preventing a changing in pitch attitude of the fuselage that would otherwise result from the tilting the nacelles to produce the longitudinal thrust-vector component; and

automatically actuating the collective swashplate controls for each rotor with the flight control system so as to maintain the fuselage in the level roll attitude, thereby preventing a changing in roll attitude of the fuselage that would otherwise result from the actuating of the cyclic swashplate controls so as to produce the lateral thrust-vector component;

wherein each nacelle is independently tiltable;

wherein the wind gust is sufficient to positionally displace the tiltrotor aircraft;

wherein automatically tilting the nacelles reduces position displacement by the wind gust;

wherein automatically actuating the lateral cyclic swashplate controls reduces position displacement by the wind gust; and

wherein automatically actuating the collective swashplate controls reduces position displacement by the wind gust by differential collective control.

6. A method for automatically controlling the flight of a tiltrotor aircraft while the aircraft is in flight that is at least partially rotor-borne, the tiltrotor aircraft being capable of flying in a helicopter mode and in an airplane mode, the aircraft having only a first tiltable nacelle and a second tiltable nacelle both nacelles located on outer ends of a fixed wing, each nacelle having a rotor, the method comprising the steps of:

providing a flight control system having cyclic authority limits;

generating a yaw-control signal based upon on a pilot control input for generating a yaw moment while maintaining the aircraft in the helicopter flight mode;

automatically tilting the first tiltable nacelle and the second tiltable nacelle with the flight control system in response to the yaw-control signal so as to produce a longitudinal thrust differential between the rotors for controlling yaw velocity of the aircraft, the longitudinal thrust differential between the rotors being a result of the first tiltable nacelle being rotated toward a front of the aircraft with the second tiltable nacelle being rotated toward a rear of the aircraft; and

wherein each nacelle is independently tiltable;

wherein the first nacelle and the second nacelle are on opposite sides of a longitudinal centerline of the fuselage; and

wherein the yaw-control signal is not limited by the cyclic authority limits.