X-48B Preliminary Flight Test Results

Fundamental Aeronautics Program Subsonic Fixed Wing Project National Aeronautics and Space Administration

X-48B Preliminary Flight Test Results

www.nasa.gov Brian R Taylor Aerospace Engineer Dryden Flight Research Center 2009 Annual Meeting Fundamental Aeronautics Program Subsonic Fixed Wing Project September 29-October 1, 2009

Background Hybrid Wing Body Unique Challenges Approach and Methods Preliminary Results Future Research and Improvements • • • • • Turbofan Development Intelligent Flight Control and Optimization Airdata Calibration Parameter Identification – – – – System Level Metrics X-48B Background Flight Research Program Approach Flight Status Research Future Efforts Fundamental Aeronautics Program Subsonic Fixed Wing Project

Outline • • • • • •

Program Project Wing Aeronautics Fixed

NASA Subsonic Transport System Level Metrics

…. technology for dramatically improving noise, emissions, & performance

Investigate Advanced Multi-Discipline Based Concepts and Technologies Reduce Uncertainty in Multi-Disciplinary Design and Analysis Tools and Processes Enable Major Changes in Engine Cycle/Airframe Configurations Fundamental Subsonic

SFW Approach - Conduct Discipline-based Foundational Research - - -

Wingspan: 20.4 ft Weight: 525 lbf Thrust: 54 lbf each (3 JetCat turbojets) 10 elevons 8 split ailerons (4 clamshell pairs) 2 winglet rudders • • • • • • Design and fabrication contracted to Cranfield Aerospace Evaluate low speed stability and control of hybrid wing body configuration in free-flight Evaluate flight control algorithms Evaluate prediction and test methods for hybrid wing body class vehicles Remotely piloted from ground control station 8.5% dynamically scaled (rigid body) 20 control surfaces – – – – – – – Research partnership of Boeing, NASA, and AFRL Purpose Airframe Fundamental Aeronautics Program Subsonic Fixed Wing Project

X-48B Background • • •

Flights XX-XX Slats Retracted Flights XX-XX Increasing Risk Block 6: Slats Extended Block 5: Assaults Limiter Departure Flights 35-XX Slats Retracted Flights 21-XX Block 4: Slats Extended Block 3: Flights 13-20 Maneuvering Engine Out Flights 1-12 Slats Retracted PID / Stalls / Block 2: Slats Extended Block 1: Expansion Envelope Fundamental Aeronautics Program Subsonic Fixed Wing Project

Flight Research Program Approach

Angle of attack up to 23 degrees Angle of sideslip up to 20 degrees Slats extended and retracted Forward and aft C.G.

– – – – 58 flights completed as of the end of August Initial envelope expansion complete PID and approaches to stall have been performed Stalls performed at forward C.G., slats extended and retracted Regression testing of software update in preparation for departure limiter assaults in work Fundamental Aeronautics Program Subsonic Fixed Wing Project

Flight Status • • • • •

Boeing Lead

Envelope Expansion Stall Characterization Turbofan Development (Parameter Estimation) Increments to Aero Model Dynamic Departure Limiters Included in presentation Optimization Development Development Adaptive Flight Control

NASA DFRC Lead

Airdata Calibration Method Intelligent Flight Control and Parameter Estimation Method Real-Time Stability Monitoring Fundamental Aeronautics Program Subsonic Fixed Wing Project

Research Leads

3-D multiblock Navier-Stokes turbomachinery analysis code – From 35 to 60 minutes Analyze fan performance using CFD (SWIFT) Results of testing and analysis used to develop improved fan • • • Gain engine development experience Increase flight time Initial development of 50 lb thrust direct replacement followed by 80 lb thrust to reduce number of engines from 3 to 2 Build turbofan around existing engine core and gear reduction set Initial fan geometry scaled existing open rotor helicopter fans Currently performing static and dynamic thrust testing at DFRC Planned installation on X-48C if flight tested – – – – – – – Objectives Approach Status Fundamental Aeronautics Program Subsonic Fixed Wing Project

Turbofan Development • • •

CFD analysis courtesy of Rod Chima, NASA GRC Fundamental Aeronautics Program Subsonic Fixed Wing Project

Turbofan Development

Control Effector 1 Peak Seeking Trajectories from Four Starting Points distribution Control Effector 2 Kalman filter Control surface positions as controls Does not accurately model induced drag effects Likely not representative of real world aerodynamics Provides adequate gradient for testing in simulation Evaluate sensor and computational requirements • • • • • • Demonstrate real-time drag minimization Operable over a wide range of flight conditions and weight variations HWB trailing edge control surfaces allow tailoring spanwise lift Approach Estimation of local performance index gradient Define optimal control surface trim positions X-48B aero database shows potential for ~5% drag reduction X-48B simulation – – – • – – – – Objective Benefits Status Fundamental Aeronautics Program Subsonic Fixed Wing Project

Intelligent Flight Control and Optimization • • •

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Va VwSin VwCos      maneuvers via autopilot heading change Constant airspeed and bank angle Time history of groundspeed, flight path angle, and heading Estimated true airspeed, wind speed, and wind direction • • • Reduce flight time required to evaluate air data calibration Fly “wind circle” Estimate vehicle states with linear regression True airspeed estimation converges well after 180° Reduced time to verify airdata calibration from 6 minutes to 1 minute – – – – –

Objective Approach Results

Fundamental Aeronautics Program Subsonic Fixed Wing Project

Airdata Calibration • • •

Response 20061212 Database 20090218 Database PID Results (mod24) Slat Extended Input Wind tunnel Analytic Dynamic analysis Validation of advanced techniques • • • • Risk reduction during envelope expansion Comparison to predictive results Control law refinement – – – mathematical model of a system based on observation of the system inputs and response Value of in-flight parameter estimation Focus on rigid body dynamics with an emphasis on control surface effectiveness Fundamental Aeronautics Program Subsonic Fixed Wing Project

Parameter Identification Background Determination of the parameters of a • •

Tools and methods developed to perform parameter estimation applicable to future vehicles Better flight testing techniques to improve parameter estimation – – X-48B provides unique opportunity to validate test methods to address identification issues associated with HWB configurations Validation of parameter identification techniques and methods Fundamental Aeronautics Program Subsonic Fixed Wing Project

X-48B Parameter Estimation Benefits • •

control of multiple Adjacent control surfaces have similar response (nearly coplanar) Adjacent control surfaces influence each other Allocation of control effectiveness utilizes common surfaces for dynamic modes Closed-loop flight control responds to excitations as disturbances Low wing loading (~5 psf) Low Reynold’s number • • • • • • Control surfaces Unstable in large regions of the flight envelope Susceptible to turbulence Airdata system in significant local flow Control surface positions inferred from actuator position – – – – – HWB X-48B Fundamental Aeronautics Program Subsonic Fixed Wing Project

HWB Unique Challenges • •

Surfaces 1, 2-5, 6, 7, and rudders

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Virtual elevator, aileron, and rudder

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Boeing gangs control surfaces

Pitch is symmetric movement Roll is differential movement Yaw is winglet rudder movement or asymmetric clamshell deployment

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Multiple elevators, ailerons, and rudders Defined control surface movement correlates to control allocation architecture

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Constrained control effectiveness

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Pitch Roll Yaw Fundamental Aeronautics Program Subsonic Fixed Wing Project

Constraints Used in Parameter Estimation

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Combines individual surface excitations Enables identification of coplanar control derivatives

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Super Maneuver

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Fundamental Aeronautics Program Subsonic Fixed Wing Project

Treating Identifiability – Super Maneuvers •

Excitation of surfaces simultaneously at different frequencies Combinations for symmetric, anti-symmetric, clamshell, and fully independent – – Multisines Fundamental Aeronautics Program Subsonic Fixed Wing Project

Treating Identifiability – Multisines •

80 knots Low wing loading at low Reynold’s number Airdata in significant local flow Open-loop response Traditional control surfaces Hand flown doublets Airspeed: 60 – Analytic: 0.1097 Estimated: 0.1025 α – – – – – – – – TG-14A parameter estimation Flight data CL Verified output error technique for low Reynolds number, low wing loading aircraft • • • • Fundamental Aeronautics Program Subsonic Fixed Wing Project

Method Validation with TG-14A

Airdata and turbulence models • Known environment Closed-loop response 20 control surfaces – – – X-48B simulation Fundamental Aeronautics Program Subsonic Fixed Wing Project

Method Validation with Simulation •

10 degrees angle of attack Slats extended, aft CG

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Same initial conditions as longitudinal flight data

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Surface pair symmetric doublets

Fundamental Aeronautics Program Subsonic Fixed Wing Project

Method Validation with Simulation Results •

Data collected during 1 flight 10 degrees angle of attack Slats extended, aft CG 5 repeats of each doublet

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Surface pair symmetric doublets

Fundamental Aeronautics Program Subsonic Fixed Wing Project

Preliminary Flight Results •

Data collected during 3 flights 10 degrees angle of attack Slats extended, forward & aft CG 5 repeats of each doublet

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Surface pair anti-symmetric doublets

Fundamental Aeronautics Program Subsonic Fixed Wing Project

Preliminary Flight Results •

errors Trade between kinematics and aerodynamics – Roll/yaw coupling could have higher error • Evaluation with X-48B simulation has started Validate against aero model An upgraded flight computer will provide the capability for performing multisine maneuvers in flight Currently deduced from actuator position Linkage slop and bending could introduce significant and unknown Aircraft inertia directly correlated to moment parameters Parameter estimation only as accurate as the aircraft inertia – – – – – – – Flight conditions of interest and doublet sequences defined for super maneuvers Multisine control surface excitations Measure control surface position Inertia swings Fundamental Aeronautics Program Subsonic Fixed Wing Project

Future PID Research and Improvements • • • •

Super maneuvers, multisines Effect of surface deflection and influence of adjacent surfaces Large potential for reduction in aircraft weight – – – Continue method development Investigate non-linear control surface effectiveness Definition of necessary hardware upgrades for flight testing Reduced actuator requirements • • • • Increments to aero table Parameter estimation Intelligent control Tufting to investigate boundary layer Improved control allocation – – – – – X-48C wind tunnel testing X-48B limiter assaults NASA DFRC research flights Research Opportunities Fundamental Aeronautics Program Subsonic Fixed Wing Project

Future Efforts • • • •

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