Mission-adaptive rotor blade with circulation control

1. A rotorcraft comprising:

an airframe;

a rotor mounted to the airframe, the rotor including a plurality of blades each defining a blade duct and a plurality of vents along a longitudinal extent thereof;

a plurality of valves positioned to control airflow from the blade duct through the plurality of vents;

a compressed air source in fluid communication with the blade ducts; and

a control unit operably coupled to the plurality of valves and programmed to adjust the valves to control a velocity of air exiting the valves effective to achieve a first longitudinally varying flow velocity magnitude profile of airflows exiting the valves of the plurality of valves along each blade in a first operational mode and adjust the valves effective to achieve a second longitudinally varying flow velocity magnitude profile of air flows exiting the valves of the plurality of valves along each blade in a second operational mode, the control module further programmed to adjust the valves to achieve one of the first and second longitudinally varying flow velocity magnitude profiles responsive to a pilot input;

wherein the first operational mode includes at least one of taking off, hovering, and landing;

wherein the second operational mode is autorotative flight;

wherein the first longitudinally varying flow velocity magnitude profile is closer to a first figure of merit than a geometry of the blade, the first figure of merit being suitable for the first operational mode; and

wherein the second longitudinally varying flow velocity magnitude profile is closer to a second figure of merit than the geometry of the blade and the first longitudinally varying flow velocity magnitude profile, the second figure of merit being suitable for the second operational mode.

2. The rotorcraft of claim 1 , wherein the control system is further programmed to adjust the valves effective to achieve a third longitudinally varying flow velocity magnitude profile along each blade in a third operational mode;

wherein the third operational mode is unloaded flight.

3. The rotorcraft of claim 1 , wherein the valves are coupled to piezoelectric actuators, the piezoelectric actuators being operably coupled to the control unit.

4. The rotorcraft of claim 1 , wherein the control system is programmed to cyclically vary the first and second longitudinally varying flow velocity magnitude profiles with a period equal to an integer multiple of a period of rotation of the rotor.

5. The rotorcraft of claim 1 , wherein the valves are mounted to the blades proximate a leading edge thereof.

6. The rotorcraft of claim 1 , wherein the valves are mounted to the blades proximate a trailing edge thereof.

7. The rotorcraft of claim 1 , wherein valves are mounted to the blades proximate both the leading and trailing edges thereof.

8. A method for operating a rotorcraft comprising:

flying the rotorcraft in a first operational mode, the rotorcraft including an airframe and a rotor mounted to the airframe, the rotor including a plurality of blades each defining a blade duct, a plurality of vents distributed along a longitudinal extent thereof in selective fluid communication with the blade duct, a plurality of valves coupled to the blade, each valve of the plurality of valves controlling a velocity magnitude of airflow from the blade duct through a vent of the plurality of vents, the rotorcraft further comprising a compressed air source in fluid communication with the blade ducts of the plurality of blades;

while flying the rotorcraft in the first operational mode adjusting the plurality of valves effective to achieve a first longitudinally varying flow velocity magnitude profile of the airflows exiting the vents of the plurality of vents along each blade of the plurality of blades;

transitioning the rotorcraft to a second operational mode; and

while flying the rotorcraft in the second operational mode adjusting the plurality of valves responsive to a pilot input effective to achieve a second longitudinally varying flow velocity magnitude profile of the airflows exiting the vents of the plurality of vents along each blade of the plurality of blades, the second longitudinally varying flow velocity magnitude profile being different from the first lift profile;

wherein flying the rotorcraft in the first operational mode includes at least one of taking off, hovering, and landing;

wherein flying the rotorcraft in the second operational mode comprises flying the rotorcraft in autorotative flight;

wherein the first longitudinally varying flow velocity profile is closer to a first figure of merit than a geometry of the blade, the first figure of merit suitable for the first operational mode; and

wherein the second longitudinally varying flow velocity profile is closer to a second figure of merit than the geometry of the blade and the first lift profile, the second figure of merit suitable for the second operational mode.

9. The method of claim 8 , further comprising:

flying the rotorcraft in a third operational mode; and

while flying the rotorcraft in a third operational mode, adjusting the valves effective to achieve a third longitudinally varying flow velocity profile along each blade;

wherein the third operational mode is unloaded flight.

10. The method of claim 8 , wherein the valves comprise piezoelectric actuators.

11. The method of claim 8 , further comprising, while flying the rotorcraft in the second operational mode, cyclically adjusting the valves.

12. The method of claim 8 , wherein the valves are mounted to the blades proximate a leading edge thereof.

13. The method of claim 8 , wherein the valves are mounted to the blades proximate a trailing edge thereof.

14. The method of claim 8 , wherein the valves are mounted to the blades proximate both the leading and trailing edges thereof.