Unmanned aerial vehicle drag augmentation by reverse propeller rotation
View Patent ↗An air vehicle configured to augment effective drag to change the rate of descent of the air vehicle in flight via propeller shaft rotation direction reversal, i.e., thrust reversal.
1. An air vehicle comprising:
at least one propeller, each propeller comprising at least one blade having a constant pitch angle;
at least one propeller motor configured to reverse propeller direction of rotation of the at least one propeller while the air vehicle is in flight; and
an autopilot configured to maintain airspeed of the air vehicle above stall conditions using the propeller motor while the air vehicle is in flight.
2. The air vehicle of claim 1 wherein the motor is configured to drive the propeller via a propeller shaft, and wherein the motor is an electrical motor configured to drive the propeller shaft in either of two angular directions.
3. The air vehicle of claim 1 wherein the at least one propeller is at least one forward-mounted tractor propeller.
4. The air vehicle of claim 1 wherein the at least one propeller is at least one aft-mounted pusher propeller.
5. A method of in-flight augmentation of an air vehicle descent rate comprising:
regulating, via an autopilot, an airspeed value of the air vehicle by regulating a motor; and
generating an input to effect a change in the in-flight descent rate of the air vehicle via direction of rotation reversal of at least one propeller of the air vehicle, each propeller comprising at least one blade having a constant pitch angle; and
rotating, via the motor and responsive to the input, the at least one propeller in a direction of rotation for generating forward air vehicle thrust.
6. The method of claim 5 wherein the motor driving the at least one propeller is an electrical motor configured to drive the at least one propeller in two angular directions.
7. The method of claim 5 wherein the at least one propeller is at least one forward-mounted tractor propeller.
8. The method of claim 5 wherein the at least one propeller is at least one aft-mounted pusher propeller.
9. The method of claim 5 wherein the at least one propeller comprises two blades.
10. The method of claim 5 wherein the at least one blade comprises a counterweight.
11. A method comprising:
reversing, via an autopilot, a direction of rotation of at least one motor of an in-flight air vehicle, the at least one motor connected to at least one propeller comprising at least one blade having a constant pitch angle;
detecting, via at least one sensor, an airspeed of the in-flight air vehicle dropping toward a stall speed; and
generating, via the autopilot, a downward bias to an acceleration command based on the detected airspeed of the in-flight air vehicle.
12. The method of claim 11 further comprising:
generating an input to set a rotation rate of the reversed propeller of the in-flight air vehicle to pin-wheel the at least one propeller.
13. The method of claim 11 further comprising:
generating an input to set a rotation rate of the reversed propeller of the in-flight air vehicle to free wheel the at least one propeller.
14. The method of claim 11 wherein reversing the direction of rotation of the least one the motor further comprises:
generating a voltage of opposite polarity of an original voltage, wherein the at least one motor of the in-flight air vehicle is a brushless direct current (DC) motor.
15. The method of claim 11 wherein reversing the direction of rotation of the least one the motor further comprises:
generating a reverse phase of an original phase, wherein the at least one motor of the in-flight air vehicle is an electrically commutated alternating current (AC) motor.
16. The method of claim 11 wherein generating the downward bias to the acceleration command further comprises:
maintaining, via the autopilot, one or more maneuver limits of the in-flight air vehicle.
17. The method of claim 11 wherein generating the downward bias to the acceleration command further comprises:
maintaining, via the autopilot, a limit below a threshold on at least one of: an acceleration command, a bias, and an error path of the in-flight air vehicle.
18. The method of claim 11 wherein generating the downward bias to the acceleration command further comprises:
maintaining, via the autopilot, a flight trim of the in-flight air vehicle proportional to a drag produced by reversing the direction of rotation of the at least one motor.
19. The method of claim 11 wherein reversing, via the autopilot, the direction of rotation of the at least one motor increases the drag of the in-flight air vehicle.
20. The method of claim 11 wherein the at least one propeller is at least one of: a forward-mounted tractor propeller and an aft-mounted pusher propeller.