Airworthiness Evaluation of a Scaled Joined-Wing Aircraft

Airworthiness and Aeroelastic Performance Evaluation of a Novel Joined-Wing Aircraft

Jenner Richards, VP Operations, Quaternion AerospaceAfzal Suleman, Director, Center for Aerospace Research, University of Victoria

International Workshop on Energy Efficient Aircraft, Configurations, Technologies and Concepts of OperationSao Jose dos Campos, Brazil 2013

• Introduction/Background

• Methodology

• Initial Feasibility Studies

• Preliminary Design and Testing

• Configuration Evaluation using 5m test article

• Nonlinear Investigation of JW

• Concluding Remarks

• Questions

Introduction

Background

• USAF Sensorcraft Challenge

– Air Force Research Laboratory’s (AFRL) Next generation, HALE reconnaissance platform

– calls for advanced ISR capabilities and Long Endurance

– Candidates include Boeing, Northrop Grumman, Lockheed

• Joined Wing Sensorcraft

– Boeing's Candidate design

– Joined Wing

• unique benefits and challenges

Introduction

Introduction Background

POTENTIAL BENEFITS• Sensor integration in all 4 wings (360o field of view)

• Potential aerodynamic and weight advantages

PROBLEM• JW geometry and structural design leads to nonlinear

aeroelastic responses. (ex Potential aft wing buckling) •Computational studies have characterized these

effects but no flight test data exists to benchmark these tools

SOLUTION•Flight Testing – A reduced scale, aeroelastically

tuned RPV provides a low cost and effective way to investigate these nonlinear responses

Introduction Background Methodology

Feasibility Studies ScalingOptimization Framework

Results

Preliminary Design and TestingStability and

ControlAvionics

Reduced Complexity

Tests

Configuration Evaluation using 5m Aircraft Design Fabrication

Flight test planning

Ground testing

Flight testing

Non Linear Response Investigation SizingDetailed Design

Preliminary Testing

Upcoming Work

• Incremental Approach– Scale– Complexity– risk

• Project phases…

Introduction Background Methodology Collaboration

AFRL:Project Lead

Boeing:Conceptual Design of JWSC

Quaternion Aerospace:Analysis, Design, Fabrication, Testing

UVic CfAR:Student Support, Design Facilities

Virginia Tech:Flight Test Planning, Instrumentation, Testing

Project Support:Ned Lindsley,Max BlairPete Flick

Principal InvestigatorsAfzal SulemanRobert Canfield

Entity Role Team

Graduate Students:Jenner RichardsTyler AaronsJeff Garndand RoyoAnthony Ricciardi

Feasibility Studies Goals ScalingOptimization Framework

Results

Feasibility Studies Goals

• Goals

– Determine if full scale response can be reproduced at reduced scale

– Generate governing scaling laws

– Develop computational framework for optimizing aeroelastic response

Feasibility Studies Goals Scaling

Strategy– Define scaling parameters using simplifying

assumptions• Thin airfoil theory

• Inviscid flow

• Small disturbance, linear PDE

– Optimize stiffness and mass distributions of reduced scale model to achieve desired response

Feasibility Studies Goals Scaling

45 m

5 m 1.85 m

Full Scale 5m “GSRPV” 1.85m “Mini”

Full Scale GSRPV Mini JWSC

Span 45.6m 5m 1.85m

Test Point Speed 86.4 m/s 28.6 m/s 17.4 m/s

Test Point Weight 7.045e4 kg 92.7 kg 4.64 kg

Test Altitude 0 m 890 m 0 m

• Scaling parameters used to generate scaled article and test conditions


• Optimization framework matches structural response of reduced scale (5m) aircraft to that of scaled baseline aircraft (45 m)– Update stiffness to match static deflections then update mass in

second loop to match modal response

Mass matching

Stiffness matching


• Applied to variety of geometries

• Simple truss geometry in Feasibility study

• Simplified Test Case

• Low fidelity JWSC Beam Model

• Higher fidelity FE models


Results

• Findings

– Developed a robust scaling framework for linear aeroelasticity

– Feasible to investigate scaled response at 5m span

– 1.85 m scale may require non-conventional fabrication techniques (perhaps even 5m)

– Flight worthiness considerations pose large constraints on scaling process

• Openings in OML such as access panels

• System weight and volume reservations

• Sizing based on critical non flight loads

Preliminary Design and Testing

GoalsStability and

ControlAvionics

Reduced Complexity

Tests

Ground testing

Flight testing


Goals

• Gain better understanding of unique configuration and develop tools for future work, Specifically…

– Determine Stability and control characteristics• WT data not cleared by AFRL

• Wind tunnel model did not include free-free conditions

– Investigate control schemes

– Develop flight simulation for SW and HWIL

– Evaluate and program autopilots

– Develop best practices and train crew

– Test findings with reduced complexity test models


GoalsStability and

Control

• Detailed analyses performed using vortex lattice codes (AVL,HASC)– Verified with Fluent®CFD and wind tunnel results– Used to calculate load distributions for various flight

maneuvers (used for subsequent FE load cases)– Alpha/beta sweeps and control surfaces perturbed to

calculate coefficients and stability derivatives– Scaled moments of inertia for test point and predicted

inertias for empty aircraft used to calculate dynamic stability


GoalsStability and

Control

• Areas of concern:– Results show good flying qualities (MIL-F-8785C) with exception of

marginal dutch mode stability

– Yaw authority insufficient using conventional rudder

• Various solutions investigated– Scheduling of existing surfaces (14+)

– Addition of vertical surface with rudder

– Addition of conventional tail


GoalsStability and

Control

• Over 15 control surfaces leads to non-unique solution to control problem

• Many permutations investigated to determine control scheme based on – Sufficient, uncoupled response (pitch roll yaw)– Redundancy of control– Minimum controller effort– Simplicity– *load alleviation

• Example, yaw control while maintain trim

A

A


GoalsStability and

Control

• 6 DoF Flight Simulation• Built using Simulink (including table lookup for non-linear

aerodynamics)

• Includes simulation of APM and Micropilot control laws

• Graphical output to Flightgear and Xplane

• Main tool being used for simulation of aircraft to

• investigate and validate control scheduling schemes

• simulate flight maneuvers required throughout flight test planning

• optimize flight tests for maximum time on station


GoalsStability and

ControlAvionics

• Three sets of autopilots evaluated

– Micropilot

– APM 2.x

– Piccolo SL+ and Pic II

• Autopilots integrated and tested in 6 configurations


GoalsStability and

ControlAvionics

• Mobile Sprinter Command– Built in Diesel generator, and battery bank– 45’ pneumatic mast with antenna tracking– Two workstations (ground control operator, payload

operator)– Pilot station with boosted RC link– 5 telemetry links, 3 discreet video links, Wi-Fi– Scene lighting– APM, DJI, CloudCap, Kestrel and Micropilot GCS

Name (First Flight) QtyMTOW

WingspanObjective

FP Foamie (03/2010)

11 kg

1.68m (3.67%)• First flying model• Investigate predicted yaw instability

TC Foamie (06/2010)

32.1 kg1.85 m

• Correct shortcomings of Foamie• TO and LDG strategies• Control Surface Scheduling

Mini SC (10/2010)

8+4.6 kg1.85 m

• Control development• Test manufacturing techniques• Test Plan optimization

QT1.1 UAV (09/2009)

423 kg

3.06 m• Instrumentation testing• Flight test procedure development


GoalsStability and

ControlAvionics

Reduced Complexity

Tests


GoalsStability and

ControlAvionics

Reduced Complexity

Tests


GoalsStability and

ControlAvionics

Reduced Complexity

Tests

Configuration Evaluation using 5m Aircraft

Goals Design FabricationFlight test planning

Ground testing

Flight testing


Goals

• Determine flightworthiness of configuration and investigate flying qualities

– Design flight worthy aircraft and systems

– Develop tooling and construction capabilities

– Build aircraft and integrate instrumentation

– Ground testing to ensure risk reduction

– Evaluate configuration for follow on flexible investigation



Ground testing

Flight testing

• FE Model

– 2d layered shell elements (>100k)

– Orthotropic materials based on constituent fiber/matrix

– Fillets modeled at shear web and spar cap interface

– All control surfaces modelled

– Parametric materials and Joint stiffness



Ground testing

Flight testing

• Structural Sizing

– Envelope solution from load cases

– Optimized layup sequence and orientations

Loads Analysis

A

APly BuildupOptimization

• Flutter Clearance Checks

– Flutter envelope

– Body freedom

– Control surface



Ground testing

Flight testing


Goals Design

• FE Model Tuning

– Material properties updated from experimental results

Load Test Strain Measurement Model Update

Tensile Testing


Goals Design

• Systems design

– Propulsion/exhaust

– Power distribution

– Landing gear

– Fuel tanks and management

– Avionics

• Full set of 5-axis tools for OML (12 in total)

• Carbon/Epoxy Vacuum bagged skins

• Carbon/Foam/Carbon laminate bulkheads

• Custom components

– Exhaust nozzles, landing gear, hinges etc


Goals Design Fabrication


Goals Design Fabrication

1.) Laminating Mold Blanks2.) Loading CNC Machine3.) 5-axis Milling4.) Finished Molds

5.

6.

7.

8.

5.) Laying up skins in molds6.) CNC Waterjet internal structure assembly7.) Final assembly of skin/internals 8.) Complete assembly in custom jig


Goals Design FabricationGround testing

• Ground testing to characterize aircraft and clear for operations

Static and installed thrust tests




Bifilar Pendulum Tests

PitchYaw




Static Loading Tests




Landing gear drop tests




Range and EMI testing




Ground handling and taxi tests




Pilot and ground crew training

• Flight test campaign (Foremost Alberta, October 2011)

– Very good flight characteristics(good agreement with predictions)

– Largest challenge was RF communications/RF interferences

– Aircraft wheel blew out on roll out



Flight testing



Flight testing



Flight testing

• Conclusions and outcomes

– Good agreement between predicted/measured response

– Control system and surface schedule validate

– Post processed data used to further tune analytic models• aircraft drag polars compared to CFD and WT models

• Determined in flight loading

• Experimental set of stability and control surface derivatives

Nonlinear Investigation

Goals SizingDetailed

Design/BuildGround Testing

Flight Testing Future Work

• Goals of this phase

1. Investigate geometric nonlinearities of JW configuration

2. Provide experimental validation of Analytical models

3. Develop and investigate compliant & airworthy structures

4. Investigate control of highly flexible aircraft


Goals

• Analysis of Boeing supplied configuration showed inadequate NL response– Configuration not“weight optimization”

– Small “boom up/boom down” reaction

– Too small to reliably measure in flight due to noise

• Decision to release “AE Scaled” constraint in favor of “AE tailored” design– Allows further softening of structure to investigate NL

response of interest• “Boom up/Boom Down”

• Aft wing buckling


Goals Sizing

• Investigation into main NL effects– Variables

• Forward wing, Aft wing and Boom running stiffness’

• Joint stiffness’ at wing/boom/fuselage interface

• Mass distribution

Joint Stiffness’Running Stiffness’


Goals Sizing

Mass Distribution

• Investigation into main NL effects– Responses

• boom deflection

• Boom reversal

• Aft wing buckling

Non Linearity Factor (Boom)

2.

1.

3.


Goals Sizing

• Structure optimized to achieve desired nonlinear response

• Conventional design fails (max stress)

• Unconventional build required (“Mini”)

Infeasible

Max Allowable (skins fail)


Goals Sizing

• “MINI JWSC” Redesign– Integrate Piccolo SL autopilot– Maximize internal space for instrumentation– Minimize weight– Move cg as far forward as possible– Maximize flight time



Design/Build

• Tailored Aluminum spars– 2024-T3 cold rolled– CNC Machined

• Rapid Prototyped internal structure– One point of contact no loads

transferred to skin

• Aerodynamic Shells– Composite construction– Removable for easy access to strain gauges

etc– Sealed with flexible tape (compression side)

and overlap (tension side)

• Control Surfaces– Special hinges to prevent load transfer



Design/Build



Design/Build



Design/Build



Design/Build

• Ground Based Instrumentation

– 20 linear strain gauges (10 ½ bridges)

– 4 accelerometers

– Visual deflections via cameras



Design/Build

• In flight Instrumentation

– 20 linear strain gauges (10 ½ bridges)

– Visual deflections via rear facing camera

– IMU data

• Ground testing

– Static loading rig

• Confirm air worthiness (load limit, control surfaces)

• Validate models

• Measure nonlinearity

– Ground vibration tests

• Determine mode shapes and frequencies




• Ground Testing Rig– Rigid machined aluminum frame bolted to optical table– 7 hard points to apply loads up and down using

turnbuckles– Aluminum frame can be mounted to shaker system




• Photogrammetric measurements– ~10 pictures take from various angles at each load step

using calibrated camera– Pictures processed using “PhotoModeller” software– Deflection data generated for each target




Flight Testing

• Force Measurement

– Up to 12 load cells with data ADC via hardware interface

– Custom Interface to calibrate, measure and record data




Flight Testing

• Strain Measurement

– Lab setup

• Strain logged fed in real time to data acquisition unit

• Strip charts, real-time FFT, HDD Recording (up to 1000 Hz)




• Strain Measurement– In flight setup

• Strain logged to on-board SD card (50 Hz)

• 5 Hz feed injected into autopilot telemetry stream for real time monitoring in ground station

• Custom LabView interface for real time visualization by pilot/ground crew




Flight Testing

• Initial “Rigid” flight tests to evaluate flight worthiness

– new pilot and crew training

– tune Piccolo autopilot for aggressive maneuvers

– investigate Auto Takeoff and flight




Flight Testing

• Test Points Evaluation (Primary Pilot, L.O.S.)– Push over pull up in FBW mode

• Pilot had great difficulty controlling g-loading while being read gs over headset

• Inner loop gains and g limit tuned to allow “burying of sticks” by pilot to hit g limit

• This method achieved a maximum of 2.2g’s

– Windup Turn• Maximum of ~1.5 g’s using 42 degree bank limit

• 2.5 gs will require very large bank angle (~66 deg)

260 265 270 275 280 285

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

Time (s)

Z A

ccel (g

s)

Z Acceleration During Pitch Down/Up Maneuver in FBW




Flight Testing

• Test Points Evaluation (FPV* Pilot, L.O.S.)– Push over pull up in FBW mode from pilot station in GCS

– Pilot able to watch strip chart and numeric data in real time

– Will take practice to comfortably operate while watching strip chart

*subject to SFOC approval

Strip Charts Numeric Disp Video FeedFlight Display




Flight Testing

• Test Points Evaluation (Autopilot)– Doublet Commands

• This mode requires the autopilot to be in command

• This method achieved a maximum of 3.2g’s (quite violent)

0 1 2 3 4 5-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

Time (s)

Z A

ccel (g

s)

Z Acceleration During Elevator Doublet Maneuver

1.2 sec




Flight Testing

• Upcoming Work

– Ground testing of flexible aircraft

• Static Loading

• GVT

– Complete integration

– Flight testing

– Post Processing/Documentation

Future WorkNonlinear

InvestigationGoals Sizing

Detailed Design/Build

Ground Testing

Flight Testing

Questions?

Documents

Airworthiness Evaluation of a Scaled Joined-Wing Aircraft