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Performance and Rotor-Based Control of a Shrouded Rotor MAV in Edgewise Flow

Alfred Gessow Rotorcraft Center University of Maryland. Performance and Rotor-Based Control of a Shrouded Rotor MAV in Edgewise Flow. Vikram Hrishikeshavan Graduate Research Assistant. Inderjit Chopra Alfred Gessow Professor and Director.

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Performance and Rotor-Based Control of a Shrouded Rotor MAV in Edgewise Flow

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  1. Alfred Gessow Rotorcraft Center University of Maryland Performance and Rotor-Based Control of a Shrouded Rotor MAV in Edgewise Flow VikramHrishikeshavan Graduate Research Assistant Inderjit Chopra Alfred Gessow Professor and Director AHS International Specialists’ Meeting on Unmanned Rotorcraft and Network Centric Operations, Tempe, AZ, Jan 25-27, 2011

  2. Motivation Perimeter surveillance, building searches Rotor based MAVs - Hover capability - Maneuverability within confined spaces - Handle gust disturbances Need to study vehicle performance in adverse flow conditions and enable sufficient contrallability

  3. Rotor Plane Main Vortex VortexSheet Main Vortex Wake Obstruction Low Reynolds Number Effects Re = 10,000-100,000 Increased profile drag Strong tip vortex Increased tip losses Low Re aerodynamics limits rotor performance

  4. Performance Improvement : Shrouded Rotor • Reduces tip loss effects • Improves power loading • Protects rotor • Sturdy structure

  5. Shrouded Rotor Performance 25 122 mm unshrouded rotor (FM ~0.6) More thrust for same power 20 No shroud 15 Mechanical Power (W) Shroud 10 5 0 0 50 100 150 200 250 300 Thrust (g)

  6. 1.8 Kg 0.3 Kg 115 Kg Weight 2 Kg 0.25 m 2.2 m Rotor diameter Shrouded Rotor Vehicles GTSpy Cypher

  7. TiShrov – Shrouded Rotor MAV Weight 300 g Hingeless rotor (245 mm dia) Circular camber, sharp LE carbon/epoxy Driven by 75 W brushless outrunner motor Shroud (45 g) Carbon /epoxy Battery 3 cell 800mAH 20C LiPo IMU Complimentary filter gyro and acc input for pitch and roll attitude Vanes for anti-torque Two deflectable flaps for yaw control

  8. Flight in Hover Flybar Flybarless

  9. Response to Edgewise Flow Adverse pitch up tendency

  10. Outline • Performance in edgewise flow • Strategies to improve controllability of shrouded rotor in edgewise flow • Flight tests

  11. Shroud Design Circular inlet Elliptic inlet Elliptic inlet shroud – more hover efficient (Lakshminarayan,Baeder (2010)) - CFD

  12. Hover Performance Measurement • 2% thickness (t/c) • 8-13% circular camber • Sharpened leading edge • 2: 1 Taper @ 80%R

  13. Hover Performance Circular inlet shrouded rotor Elliptic inlet shrouded rotor 3%R tip clearance 10% improvement in power loading with elliptic inlet shroud

  14. Performance in Edgewise Flow

  15. Edgewise Flow: Asymmetric Pressure Distribution Hover, no gusts Hover, edgewise gust

  16. Edgewise Flow: Momentum Drag

  17. Forces in Edgewise Flow Thrust Pitching moment Drag

  18. Measurement of Forces in Wind tunnel Unshrouded (open) rotor Circular inlet shrouded rotor Elliptical inlet shrouded rotor

  19. Pitching Moment Measurement Open jet Wind tunnel Pitching moment measurement Bearings Drag load cell

  20. Drag Measurement Edgewise flow Drag load cell Linear bearing

  21. Thrust: Open Rotor 24 deg collective No change in thrust

  22. Thrust: Circular Inlet Shrouded Rotor

  23. Thrust: Elliptical Inlet Shrouded Rotor Thrust for each rotor relatively unaffected by low edgewise flow

  24. Drag: Open Rotor Drag (g) 2 m/s 1 m/s

  25. 60 50 40 30 20 10 0 1500 2000 2500 3000 3500 4000 RPM Drag: Circular Inlet Shroud 2 m/s Drag (g) 1.7 m/s 1.3 m/s 1 m/s

  26. Drag: Elliptic Inlet Shroud 2 m/s 1.7 m/s Drag (g) 1.3 m/s 1 m/s

  27. Drag: Comparison Elliptic inlet shroud Circular inlet shroud 3300 RPM Drag (g) Open rotor Shrouded rotor drag-speed slope is much higher than open rotor

  28. Projected Surface Area Elliptic inlet has more projected surface area in direction of flow Leads to more drag

  29. Pitching Moment Circular inlet shroud Open rotor 2 m/s 1.7 m/s 2 m/s 1.3 m/s 1 m/s 1 m/s

  30. Pitching Moment Elliptic inlet shroud 2 m/s 1.7 m/s 1.3 m/s 1 m/s

  31. Pitching Moment: Comparison (3300 RPM) Elliptic inlet shroud Circular inlet shroud Open rotor 300-400% higher pitching moment than open rotor

  32. Alleviate Pitching Moment Flaps Vents - Increased weight (flap actuators) - Structural integrity of shroud reduced - Complex control in free flight Use rotor with swashplate control

  33. Rotor control authority in edgewise flow

  34. Rotor Control Hingeless, flybarless rotor Force response ~ 45 deg delay Rotor generates nose-down moment Swashplate transfers cyclic (10 deg max) Edgewise flow

  35. Control Authority: No Edgewise Flow Open Rotor Total control moment (g-cm) 180 Control authority drops at higher collectives 220 280

  36. Control Authority: No Edgewise Flow Total control moment (g-cm) Total control moment (g-cm) Elliptic inlet shroud Circular inlet shroud 180 240 240 180 300 300 Control authority increases quadratically with RPM Higher operating RPM -> Higher control authority

  37. Comparison: No Edgewise Flow Elliptic inlet shroud Circular inlet shroud 80-100 % Open rotor

  38. CFD study on MAV shrouded rotor (Lakshminarayan, Baeder 2010) Ratio of shroud thrust to total thrust Rotor blade location - Shroud thrust contribution increases as rotor collective increases - Most of shroud thrust at instant rotor passes a given azimuth

  39. Shrouded Rotor Control Authority Control Authority = Mrotor+ MShroud +ve cyclic -ve cyclic Shroud augments rotor control authority

  40. Control Authority in Edgewise Flow M2 (Nose-down moment) +ve cyclic -ve cyclic

  41. Control Authority in Edgewise Flow (2 m/s) Operate rotor at lower collective to minimize control authority reduction

  42. Elliptic inlet shrouded rotor: Increase in adverse pitching moment not equivalent to increase in control authority – more sensitive to edgewise flow Only circular inlet shroud considered in following sections What is the gust tolerance?

  43. Gust Disturbance Response Pitot tube Open-jet wind tunnel Gimbal PID attitude control IMU

  44. Gust Disturbance Response Pitch (rad) Gust ~ 2 m/s Can the tolerance be increased ?

  45. L1 Increase Control Authority L2 1) Increase cyclic pitch () 2) Increase differential lift for a given cyclic pitch ()

  46. Cyclic Pitch Magnitude old new 100 150

  47. Cyclic Pitch Magnitude Shrouded rotor New 150 Old 100

  48. Differential Lift L  c More control moment - Increase L for a given  Increase chord of the airfoil Does it depend on solidity and/or planform?

  49. Blade Planforms (a) Original planform (b) Rectangular (c) Taper 140% chord (d) Rectangular 140% chord Measure instead of Tested with circular inlet shroud

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