Dr. Carl P. TilmannAir Force Research LaboratoryAir Vehicles DirectorateAeronautical Sciences DivisionAerodynamic Configuration Branch

Workshop on Aerodynamic Issues of Unmanned Air Vehicles

Emerging Aerodynamic Technologies for High-

Altitude Long-Endurance ‘SensorCraft’ UAVs

4 November 2002

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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

Detection, tracking, and targeting of concealed or hidden targets

Eyes and Ears of WarfighterWorldwide 24/7 Coverage

Enabling AFRL Technologies

Aerodynamic Optimization

Conformal LoadBearing Antenna

Engine Fuel Efficiency

The Airbreather Component of the “Fully Integrated” ISR EnterpriseThe Airbreather Component of the “Fully Integrated” ISR EnterpriThe Airbreather Component of the “Fully Integrated” ISR Enterprisese

Sensor Craft InitiativeTransforming Vision to Reality

AFRL Technical ChallengesSensorCraft Technologies

Air Vehicle Structurally integrated radar aperturesHigh efficiency aerodynamics Lightweight aircraft structures

SensorsBeam forming across complex surfacesAffordability and advanced sensorsFully flexible waveforms

InformationOff-Board BM/C2, TCPED, FUSION-ATR

PropulsionMagnetic bearings / Integral Starter GeneratorHigh altitude, long endurance fuel burn reductionFull life hot section and maintenance free engine core

MaterialsWide Bandgap RF Semiconductors and PolymersHigher Temperature Turbine Engine MaterialsAffordable, Lightweight Structural Materials

Sized GeometryWing Area (Gross): 2300 Sq Ft Span: 214 FtLength: 118.6 FtSweep: 35 DegAspect Ratio (Gross): 17.4Wetted AR: 5.5

Statistical Weights (Lbs)Structure: 17500Propulsion: 3700Avionics: 1000Subsystems: 3000Other : 1400

Empty Weight: 26600Payload Weight: 4000Fuel Weight: 39400Gross Weight: 70000

Engines (2)14000 lb St Thrust (CF - 34B Class)SFC: 0.38

Vehicle Characteristics WE/WTO: 0.38L/D: 32

Statistical SizingStatistical Sizing“40 Hr Statistical Air Vehicle”“40 Hr Statistical Air Vehicle”

VA SensorCraft Tech AssessmentTrade Space Analysis

50,000 ft

60,000 ft

Climb≤200 nm

Cruise-ClimbIngress

3000 nm

Egress

3000 nm50,000 ft

65,000 ft

Descent≤200 nm

Loiter / LandLoiter / LandIdle / TakeoffIdle / Takeoff

40-60 hourLoiter-Climb

Multipoint Efficiency Challenge

WEIGHT 75,000 30,000

In-House Statistical Joined Wing SensorCraft

Mach 0.25 0.2Q (psf)

0.6 0.6

CL 0.220.35

70,000 ft

1 hour Loiter@ SL

93 61

V (fps) 280 224581

71,677

61

581

59

Numbers Based On Notional SensorCraft Mission Profile ; S=2300 ft2 ; W/S|TO=30 c=6.5ft

9.311.7 4.615-2.86Rec(millions)1.431.8 0.71 – 0.44Re(Millions/ft) 0.27 – 0.71

1.755-4.615

0.51

34,000

0.24

qSW

SpM

L

SV

LCL/

21

21 22

===γρSingle-point Design Is Not Sufficient for Sensorcraft MissionSingleSingle--point Design Is Not Sufficient for Sensorcraft Missionpoint Design Is Not Sufficient for Sensorcraft Mission

62,150

0.6

0.711

38

0.44

583

0.6

35,200

24

581

0.637

0.27

2.86 1.755

LETE

Technology Applicationsfor Sensorcraft

Airfoil Shape Changefor Multipoint Optimization

Active Control of StructureStrain & Deformation

Active Aeroelastic WingDeformation Management

•Aero Efficiency•Manage Structural Loads

Virtual Surface Creation•Performance•Flight Control

Turbulent Skin FrictionDrag Reduction

Laminar Flow on Swept Wings Using DREs

Control of Shock-Induced Boundary Layer Separation

Active Separation Control•Improved Maximum Lift•Gust Load Alleviation

LoiterDash

Multiple SensorCraft Concepts / Features

Multiple SensorCraft Concepts / Multiple SensorCraft Concepts / FeaturesFeatures

SensorCraft Concepts

LockheedLockheed

BoeingBoeing

NorthropNorthrop--GrummanGrumman

InIn--HouseHouse

IconIcon

UniversitiesUniversities

Primary Aerodynamic Challenges

• Operates over a large range in CL & Re• Limited coverage (side lobes)• Low survivability (very detectable)• Large aeroelastic deflections

• Operates over a large range in CL & Re• Crossflow instabilities destroy laminar boundary• Joined-wing juncture flow• Joined-wing structural modes not completely understood• Propulsion integration (?)

• Operates over a large range in CL & Re• Crossflow instabilities destroy laminar boundary• Joined wing juncture flow• Stability & control considerations• Highly loaded airfoil at break• Large aeroelastic deflections

Sensor / Aero Interactions

•Placing sensors & antennae on a flexible wing requires attention to:–deflections which may impact sensor performance– impact of sensor on wing performance

• Aeroelastic• Aerodynamic• Control surface placement

•Recurring challenge: Allocating vehicle real estate between antennas and control surfaces–Stem from the desire for the antennas to have 360-

degree views– types of antennas can exacerbate problem

Wing Loading Distribution

X/C

CP

1

0

-1

-.5

.5

-1.5

0 1

Design Point CP Distributions

Orbital Research Inc.

Novel Active Flow Control DevicesAdvances Through Processes, Materials, MEMS

Displacement Amplification CompliantStructure Producing Amplified

Motion of 5mm @240Hz

•Objective–Create vortex pulses for active

separation control with very low energy requirements on the system

•Approach–Dynamic micro-VGs to convert the

freestream energy into BL–Test in Wind Tunnel

•Examples–Compliant structure with 20:1

displacement amplification–Arrays Co-Located Actuator and

Sensor pairs enabled by MEMS technology

AerodynamicSurface

Micro Actuator

Silicon Wafer

Micro-Sensor

FlowEffector

(Co-Located Actuator and Sensor)

Micro-VG Deployed Pneumaticallyby Opening MEMS Air Valve

High Frequency Compliant StructuresHigh Frequency Compliant Structures

Low Frequency Deployable VGsLow Frequency Deployable VGs

Active Wing Technologies

AFC – Laminar Flow Control Using DRE (Static)

AFC – Pulsed Vortex Generator Jets (Dynamic)

AAW

AS – Hingeless, Spanwise Variable LE and TE CS

AFC + AAW + AS

1h0021-014

Cdo Cdi WtCLmaxCLop

Benefits of HiLDA Active Wing Tech

• Individual and Synergistic Benefits of Active Wing Technologies are Being Evaluated

Technology Cross Influences

• AS Control Surfaces for AAW Applications• Study Influence on Laminar Flow of PVGJ, AAW, and AS

1H0021-028

AFC-DRE

AFC-PVGJ

AAW

AS

AS-CDi min

AFC-PVGJ AAWAFC-DRE AS AS-CDi min

Legend: Interaction Needs to Be StudiedNo Interaction ForeseenCumulative Effectiveness Reinforce Each Other

Laminar Flow on Swept WingsDistributed Roughness Elements

Total Streamwise Velocity ContoursRec = 2.4 x 106 x/c = 0.40

48 µm Roughness at x/c = 0.023, 12 mm Spacing Computations Include Curvature

Experiment

y (mm)

Nonlinear Parabolized Stability Equations

y (mm)

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

0 5 10 15 20 25 30

Advanced Engines

Laminar Flow Coverage

45% Chord Top75% Chord Bottom

100% Laminar Top & BottomAlways Turbulent

All Turbulent

Take

off G

ross

Wei

ght -

lb

25% Reduction in TOGW

PROBLEM: Crossflow Induced TransitionFavorable pressure gradient stabilizes traveling (TS) waves in boundary layer, but does not affect stationary (crossflow) waves. In the past, suction has been required for crossflow stabilization.

Benefit to Sensorcraft: Laminar Flow Results in Large TOGW ReductionsBenefit to Sensorcraft: Laminar Flow Results in Large TOGW ReducBenefit to Sensorcraft: Laminar Flow Results in Large TOGW Reductionstions

SOLUTION: Distributed RoughnessElements (DREs) of the proper spacing (wavelength) and size can create “favorable” disturbances that overwhelm the amplified-wavelength disturbances that otherwise lead to transition.

PAYOFF:

Many DRE Questions Remain

•How to design distribution. • Is it robust?

–M, CL, Re–Bending, twist, environments

•Must it be active or adaptive?–Spacing, placement, bump height, dimple depth… – If so, how do we change the distribution?

•How do we demonstrate it?–Tunnel, flight test, flight experiment, combination?–Under what conditions?

•Will it work at high CL?

MAW Multi-Component MechanicalStructure Trailing Edge Flap Design

Equivalent Compliant StructureTrailing Edge Flap Design

LoiterDash

Adaptive Structures Applications for Sensorcraft

For Sensorcraft, Adaptive Structures Are being Applied to:

• Control Wing Shape for Optimal Aerodynamic Performance Throughout the Mission

• Manage & Alleviate Structural Loads

For Sensorcraft, Adaptive Structures For Sensorcraft, Adaptive Structures Are being Applied to:Are being Applied to:

•• Control Wing Shape for Optimal Control Wing Shape for Optimal Aerodynamic Performance Aerodynamic Performance Throughout the MissionThroughout the Mission

•• Manage & Alleviate Structural LoadsManage & Alleviate Structural Loads

Trailing EdgeTrailing Edge

Wing Camber Wing Camber

Leading Edge ShapeLeading Edge Shape

Wing Warp/TwistWing Warp/Twist

Cd

Cl

0 0.004 0.008 0.012 0.016-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

BaselineFlap ±2.5°Flap ±5.0°Flap ±7.5°Flap ±10.0°Flap ±12.5°Flap ±15.0°

+ Flap Defl.

- Flap Defl.

≈ 52% Increase in UpperDrag Bucket Extent

≈ 45% Increase in LowerDrag Bucket Extent

XFOIL Predicted Results: NLF(1)-0414Re=1.0x106, 12.5% Flap, Trip Strip: Upper x/c=0.70, Lower x/c=0.65

Increased PerformanceUsing Stagnation Point

Control

Adaptive Trailing Edge Alone

Maintains “Low-Drag Bucket” Over Wide Range of CL

Adaptive Trailing Adaptive Trailing Edge Alone Edge Alone

Maintains “LowMaintains “Low--Drag Bucket” Over Drag Bucket” Over Wide Range of CWide Range of CLL

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-2.50

-2.25

-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

Baseline

XFOIL Predicted Results: NLF(1)-0414, CL=0.9, Re=1.0x106

Large Suction Peak andAdverse Gradient

Adverse Gradient ProducesT hick Low Energy B.L.⇒ T.E. Separation

x/c

CP

NLF(1)-0414

Adaptive Compliant Trailing EdgeTailoring Airfoil Performance

• Variable geometry compliant trailing edge• Adaptive TE expands low drag bucket via stagnation point/pressure gradient control

• Allows entire loiter to be performed at exceptionally high airfoil L/D (≈125-165)

+7.5° Flap

Reduced Peak and Favorable GradientDelay Transition and Produce a HealthierBoundary Layer ⇒54% Drag Reduction

Reduced Suction PeakFavorable Gradient

Min TOGWaspect ratio = 3.0

t/c = 0.040

• Basic AAW uses conventional control surfaces to aeroelastically shape the wing throughout the mission

• In fighter applications, AAW exploits wing aeroelasticity for:

– structural load reduction– control authority increase– induced drag reduction

• Fighter design studies have shown the impact of AAW on structural weight and TOGW

LETE

Aeroelastic twisting moment

Min TOGWaspect ratio = 5.0

t/c = 0.035

For Sensorcraft AAW Could:•Reduce Structural Design Loads•Improve L/D •Improve Antenna Performance

For Sensorcraft AAW Could:For Sensorcraft AAW Could:••Reduce Structural Design LoadsReduce Structural Design Loads••Improve L/D Improve L/D ••Improve Antenna PerformanceImprove Antenna Performance

AAW and Application to Sensorcraft

NGC Task 2Wind Tunnel Model Installation

• Model to be Mounted Off Side Wall– Model Pitch and Plunge

Restrained• Shape Control Achieved

with Combination SLA Trailing Edge and Hydraulic Actuated Control Surface

• Gust Load Alleviation (GLA) Test Using Hydraulic Actuated Control Surface

• Different Test Mediums for Each Test Goal– Shape Control – Air– GLA – R134a

Section A-A

Tunnel Width192 in(16 ft)

T.S. 72.0

ConceptualSLA Spanwise Trailing

Control Surface

ConceptualHydraulic-Actuated Control Surfaces

A

A

NASA/Langley TDTNASA/Langley TDT

HiLDA

StructurallyIntegratedSensors

Technology Interactions

AS

SurfacePressure

Modification

Increased CLReduced CDi

AAW

Laminar FlowReduced CDo

AFC

Control SurfaceLocation & WingSurface Shape

Control SurfaceLocation

ModifiedPressure Distribution

Shape Control

Separation ControlIncreased CLReduced CDi

Reduced CDi

ReducedWing Weight

GLA ReducedWing Weight

Objectives:–Aerodynamic Efficiency–Structural Efficiency–Reduced Weight

•Interaction of Technologies Key to Integration•Must be Compatible with Sensors (Materials, Location, etc.)

••Interaction of Technologies Key to IntegrationInteraction of Technologies Key to Integration••Must be Compatible with Sensors (Materials, Location, etc.)Must be Compatible with Sensors (Materials, Location, etc.)

Flow Control is in Competition with Other Technologies

0

10

20

30

40

50

60

70

80

90

0.40

0.45

0.50

0.55

0.60

Empty Weight Fraction

On-

Stat

ion

Tim

e (h

rs)

40

35

30

25

L/D = 20

2001 Technology Laminar Flow

Antenna IRAD,S-CLAS

AAW

AS

2015 Sensorcraft

Other Technologies

Notional Path to Performance Requirement

SensorCraft concept with advanced enginesSFC = 0.52

2000 nm mission radius

• Active Wing Technologies Have the Potential to Significantly Impact SensorCraft Design & Performance

• The HiLDA Program Will Provide Needed Quantitative Information

•• Active Wing Technologies Have the Potential to Significantly ImpActive Wing Technologies Have the Potential to Significantly Impact act SensorCraft Design & PerformanceSensorCraft Design & Performance

•• The HiLDA Program Will Provide Needed Quantitative InformationThe HiLDA Program Will Provide Needed Quantitative Information

ADAPTIVE STRUCTURESADAPTIVE STRUCTURES

ACTIVE FLOW CONTROLACTIVE FLOW CONTROL

ACTIVE AEROELASTIC WINGACTIVE AEROELASTIC WING

OBJECTIVES:• Apply AFC, AAW, and Adaptive Structures, to a Sensorcraft

wing design for load reduction and improved L/D• Demonstrate critical technologies in wind tunnel• Prepare for demonstration of high aerodynamic efficiency

in upcoming 6.3 programPAYOFFS:• Reduced structural loads and improved L/D for Sensorcraft

vehicle weight reductionAPPROACH:• Apply AAW to Sensorcraft wing configuration & evaluate

structural weight savings and L/D improvement• Determine optimum airfoil shape throughout mission profile• Evaluate active flow control methods to alleviate off-design

requirements • Apply active flow control and adaptive structure design to

maximize aerodynamic efficiency• Demonstrate integrated design in wind tunnel

High L/D Active (HiLDA) Wing

Deployable Vortex Generators

Shock-induced Separation Control

Control Surface Augmentation or Replacement

Pulsed Jets

Adaptive Wing Shape for Drag Minimization and Gust Load Alleviation

• Prepare for demonstration of ultra-efficient wing in upcoming 6.3 program

Technical ChallengesTechnical Challenges• Determine individual and combined technology

impacts on Sensorcraft• AAW/AFC/AS specific issues• Integrated design of active wing to max. efficiency

ObjectiveObjective

• NASA, UAV, Sensorcraft, ASC/RA, ACC-ISR

High L/D Active (HiLDA) Wing

PlayersPlayersPartners

•NASAPerformers

•Task 1 - Lockheed, Northrop•Task 2 - Lockheed, Northrop, Boeing

AAW

AS

AFCProblemProblem

CustomersCustomers

• Need significant increases in structural and aerodynamic efficiency to meet range/loiter requirements Sensorcraft concept.

• Reduced structural loads and improved L/D for Sensorcraft vehicle weight and cost reduction

Active Aeroelastic Wing

Active Flow Control

Adaptive Structures

NGC

Boeing

TASK 1 (LMAC, NGC)Technology AssessmentsIntegrated Benefit AnalysisActive Wing DesignAAW (Boeing)

TASK 2Develop Tunnel Testing PlanDesign, Fab, & Test (NGC)DRE Quick Look (LMAC)DRE Robust

Schedule / MilestonesSchedule / MilestonesFY01 FY02 FY03 FY04

LMAC