Method of reducing a nose-up pitching moment on a ducted unmanned aerial vehicle

• US 6,170,778 B1
• Filed: 04/22/1999
• Issued: 01/09/2001
• Est. Priority Date: 04/22/1999
• Status: Expired due to Fees

• Current Assignee: Sikorsky Aircraft Corporation (Martin Marietta Corporation)
• Original Assignee: Sikorsky Aircraft Corporation (Martin Marietta Corporation)
• Inventors: Cycon, James P., DeWitt, Christopher W., Scott, Mark Winfield
• Primary Examiner(s): Barefoot, Galen L.
• Application Number:
  US09/296,716
• Time in Patent Office: 628 Days
• Field of Search: 244/17.11, 244/23.B, 244/12.3, 244/6, 244/7.R, 244/7.A, 244/7.B
• US Class Current: 244/6
• CPC Class Codes: B64U 10/13 Flying platforms
• CPC Class Codes: B64U 20/65 Composite materials
• CPC Class Codes: B64U 2101/00 UAVs specially adapted for particular uses or applications
• CPC Class Codes: B64U 2101/30 for imaging, photography or videography
• CPC Class Codes: B64U 30/10 Wings
• CPC Class Codes: B64U 30/14 detachable
• CPC Class Codes: B64U 30/20 Rotors; Rotor supports
• CPC Class Codes: B64U 50/13 using external fans or propellers
• CPC Class Codes: B64U 50/14 ducted or shrouded

Abstract

A method for reducing a nose-up pitching moment in an unmanned aerial vehicle during forward flight. The unmanned aerial vehicle includes counter-rotating rotor assemblies that are mounted within a duct. Each rotor assembly includes a plurality of rotor blades. The method involves adjusting the rotor blades to have substantially zero pitch. Then rotating the rotor assemblies to produce a virtual plane across the duct. The virtual plane is operative for substantially deflecting air passing over the fuselage away from the duct. In one embodiment of the invention, the method involves the further step of obstructing at least a portion of the bottom of the duct to inhibit air that is flowing across the bottom of the duct from passing into the duct.

Claims

1. A method for reducing a nose-up pitching moment in an unmanned aerial vehicle during forward flight, the unmanned aerial vehicle including counter-rotating rotor assemblies mounted within a duct, the duct extending downwardly through a fuselage in the unmanned aerial vehicle, each rotor assembly including a plurality of rotor blades, the method comprising the steps of:

adjusting the rotor blades to have substantially zero pitch;

rotating the rotor assemblies to produce a virtual plane across the duct, the virtual plane operative for substantially deflecting air passing over the fuselage away from the duct.

2. The method of claim 1 further comprising the step of providing a plurality of passively pivotable deflectors on the bottom of the fuselage, the deflectors extending across the duct, the air flow across the bottom of the fuselage causing the deflectors to pivot and substantially close off the bottom of the duct.

3. The method of claim 1 further comprising the step of obstructing at least a portion of the bottom of the duct to inhibit air that is flowing across the bottom of the duct from passing into the duct.

4. The method of claim 1 wherein the unmanned aerial vehicle includes a pusher propeller, the method further comprising the step of generating a negative pressure aft of the duct by increasing the amount of air flowing past the duct by rotating the pusher prop, the negative pressure creating a suction force on the air passing over the top of the duct thereby drawing the air past the upper surface of the duct.

5. The method of claim 1 further comprising the step of increasing the speed of the rotors.

6. The method of claim 1 wherein the unmanned aerial vehicle includes a fuselage extending aftward from the duct and a pusher prop assembly mounted aft of the fuselage, the pusher prop assembly further including a shroud disposed about a pusher prop and vertically spaced apart directional vanes attached to the shroud aft of the pusher prop, the method further comprising the step of controlling the orientation of the directional vanes for controlling the direction of air flow out of the pusher prop assembly to create a lift component on the vehicle aft of the duct for counteracting nose-up pitching moment.

7. The method of claim 1 wherein the unmanned aerial vehicle includes a pair of wings attached to the fuselage, the wings having a pivotable trailing edge and tip portion, the method further comprising the step of pivoting the trailing edge and tip portion to create a lift component on the vehicle aft of the duct.

8. The method of claim 1 further comprising the step of at least partially closing off the bottom of the duct to increase the amount of air flowing past the lower surface of the duct and aft of the aircraft, the increased air flow generating a suction on the upper surface for drawing air past the top of the duct.

9. The method of claim 1 further comprising the step controlling the air flowing past the upper and lower openings of the duct by generating a higher air flow past the lower opening of the duct and aft of the aircraft, the higher air flow on the lower surface of the aircraft generating a negative pressure on the upper surface of the aircraft aft of the duct opening, the negative pressure suctioning the air across the upper opening of the duct and thereby reducing the nose up pitching moment on the aircraft.

10. A method for restricting air flow into a duct of an unmanned aerial vehicle during forward flight, the unmanned aerial vehicle including counter-rotating rotor assemblies mounted within the duct, the duct extending downwardly through a fuselage in the unmanned aerial vehicle, each rotor assembly including a plurality of rotor blades, the method comprising the steps of:

adjusting the rotor blades to have substantially zero pitch;

rotating the rotor assemblies to produce a virtual plane across the duct, the virtual plane operative for substantially deflecting air passing over the fuselage away from the duct; and

providing a plurality of pivotable deflectors on the bottom of the fuselage, the deflectors extending across the duct, the air flow across the bottom of the fuselage causing the deflectors to pivot and close off at least a portion of the bottom of the duct, thereby increasing the amount of air that passes under the fuselage, the increased air flow across the bottom of the fuselage generating a negative pressure aft of the duct on the top of the fuselage that creates a suction on the air passing over the duct.

11. The method of claim 10 wherein the unmanned aerial vehicle includes a pusher prop assembly mounted aft of the duct, the pusher prop assembly further comprising a shroud disposed about a pusher prop and vertically spaced apart directional vanes attached to the shroud aft of the pusher prop, the method further comprising the step of controlling the orientation of the directional vanes for controlling the direction of air flow out of the pusher prop assembly to create a lift component on the vehicle aft of the duct for counteracting nose-up pitching moment.

12. The method of claim 10 further comprising the step of increasing the speed of the rotors.