Alfred Gessow Rotorcraft Center University of Maryland Understanding High Advance Ratio Flight Graham Bowen-Davies Graduate Research Assistant Adviser: Inderjit Chopra Alfred Gessow Professor and Director
Alfred Gessow Rotorcraft Center University of Maryland Name: Graham Bowen-Davies Born in: Bulawayo, Zimbabwe (1984) Population: 11 Million Temperate: 50 F-90 F Never snows We had one Winter Olympian I was born here
Alfred Gessow Rotorcraft Center University of Maryland Name: Graham Bowen-Davies Born in: Zimbabwe (1984) High school: St. Georges College Jesuit college Oldest all boys school (115) Harare (Capitol City)
Alfred Gessow Rotorcraft Center University of Maryland Name: Graham Bowen-Davies Born in: Zimbabwe (1984) High school: St. Georges College Under Graduate: Mechanical Engineering Degree University of Cape Town 2003-2007
Alfred Gessow Rotorcraft Center University of Maryland Name: Graham Bowen-Davies Born in: Zimbabwe (1984 ) High school: St. Georges College Under Graduate: Mechanical Engineering Degree University of Cape Town 2003-2007 Currently working on: Ph.D. in Aerospace Engineering University of Maryland 2008 2014?) Proud team leader of the Gamera Human Powered Helicopter Team
Alfred Gessow Rotorcraft Center University of Maryland Name: Graham Bowen-Davies Born in: Zimbabwe (1984 ) High school: St. Georges College Under Graduate: Mechanical Engineering Degree University of Cape Town 2003-2007 Currently working on: Ph.D. in Aerospace Engineering University of Maryland 2008 2014?) Proud team leader of the Gamera Human Powered Helicopter Team My research topic is: Investigating the Aeromechanics of Variable Rotor Speed (With some morphing rotor studies)
Motivation
Helicopters are very good (at what they do) Insertion and extraction News and reporting Resupply and support Search and rescue
What about high speed? Helicopter: Westland Lynx G-LYNX Max Speed: 216 knots Year 1986 G-LYNX Fixed wing: Curtis R2C - 1 Max Speed: 224 knots Year 1923 Fixed wing: Lockheed SR-71 Blackbird Max Speed: 1905 knots Year 1976
Helicopter Aerodynamics 101: μ = 0.0 V ret = ΩR Hover V adv = ΩR μ = 0
Helicopter Aerodynamics 101: μ = 0.2 V ret = ΩR(1 μ) Cruise Hover V adv = ΩR(1 + μ) μ = 0.2 (100 kts)
Helicopter Aerodynamics 101: μ ~ 0.4 V ret = ΩR(1 μ) Cruise Hover V adv = ΩR(1 + μ) μ = 0.40 (170 kts)
Helicopter Aerodynamics 101: Roadblocks at High Advance Ratio Retreating blade stall - Vibrations and power Lift limited on retreating side - No longer able to trim Increasing parasitic drag - Limited installed power Compressibility - Power requirements rise - Vibrations increase dramatically
Helicopter Aerodynamics 101: Slowed rotor solution 100 % RPM 50 % RPM V ret = 0 Lift V V ret = ΩR - μ V adv = ΩR(1 + μ) V adv = ΩR(1 + μ) μ = 0.5 (220 kts) μ = 1.0 (220 kts)
Slowed Rotor Helicopters XH-51A (1965) 260 knots Slowed the rotor by 5% Stability issues 250+ knots Slowed the rotor by 20% Limited payload Goals of this research are: 1) Understand the performance and loads at high V-22 advance (1989) ratios X2TD(2010) 2) Validate predictive capability with test data
Description of Rotor Articulated 4 Blades Radius: 2.78 ft ( 1 / 9 th of UH-60) Rotor speed: 2300 RPM Mach No: 0.6 Tests Run Rotor speed: 30% Advance Ratio: 1.4
Analysis Description Comprehensive analysis Based on the analysis code UMARC Lift Distribution Capability Structural Model: Elastic Flap, Lag and Torsion Aerodynamics: Table look up Inflow model: Freewake (Bagai-Leishman) Solution type: Periodic, steady state trim Additional Capability Trailing edge flap and leading edge slats Variable radius and RPM modeling Coaxial (in progress) Stability analysis, bearingless rotor
Results: High advance ratio
Thrust C T /σ 0 Shaft Tilt, 0 Collective Wind tunnel tests UMARC analysis Why is the model generating thrust at zero collective? What is the analysis missing?
Does the fuselage matter? Maryland UH-60 No fuselage model No fuselage model Both the Maryland and UH-60A thrusts are underpredicted
Fuselage Representation Results on HART rotor by Amiraux et al. (2013) Uniform upwash over fuselage nose Assume linear increase with advance ratio Calibrated to HART rotor result Upwash in rotor plane: μ = 0.15 α s = 4
Does the fuselage matter? Maryland UH-60 With fuselage model No fuselage model Fuselage model improves thrust correlation A higher fidelity model of the fuselage is important for low thrusts.
Thrust, C T /σ Thrust vs. Advance Ratio Experiment Analysis 0 Collective Advance Ratio = 0 1.4 Shaft angle = 4 Shaft angle Shaft angle = 2 0 knots 170 knots Analysis does very well for aft shaft tilt. Fuselage is less important for high thrusts and aft shaft tilt.
Results: Thrust Reversal
Thrust Reversal Prediction α s = 0, μ = 0.25 μ = 0.25 Stall map V Analysis UM2013 Angle of attack below stall Angle of attack above stall V Normal force map
Thrust Reversal Prediction α s = 0, μ = 0.41 Stall map μ = 0.41 V Analysis UM2013 Airfoil unstalled in reverse flow V Angle of attack above stall V Lift
Thrust Reversal Prediction α s = 0, μ = 0.58 Stall map Analysis μ = 0.58 V UM2013 Airfoil unstalled in reverse flow V
Thrust Reversal Prediction α s = 0, μ = 0.82 Stall map Analysis μ = 0.82 V UM2013 Airfoil unstalled in reverse flow V
Thrust Reversal Prediction α s = 0, μ = 1.02 UM2013 Stall map μ = 1.02 V Analysis Airfoil unstalled in reverse flow V
Summary
Summary The University of Maryland Advanced Rotorcraft Code (UMARC) has been developed to understand high advance ratio aerodynamics Fuselage modeling can be important At low thrusts and for small shaft angles Thrust is well predicted up to an advance ratio of 1.4 Thrust reversal at high advance ratio is predicted well Reverse flow airfoil characteristics are important
Future Work Continue to evaluate the Maryland wind tunnel data Pressure gauge readings Blade bending moments New wind tunnel test Compare UH-60 and Maryland rotors at high advance ratio Incorporate a higher fidelity fuselage model
Acknowledgements Ben Berry for performing the wind tunnel tests and making the data available. Dr. Tom Norman for making the UH-60A data available.