aerodynamic design of the lockheed martin cooperative

Reference: AIAA 2008-0157 Analytical Methods, Inc. 1

Aerodynamic Design of the Lockheed Martin Cooperative Avionics Testbed

(Reference AIAA 2008-0157)

Robert LindAnalytical Methods Inc

James H. HogueLockheed Martin Aeronautics Company

Ian J. GilchristAnalytical Methods Inc

Analytical Methods, Inc.

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Text Box

http://www.am-inc.com/PDF/catb.pdf


Introduction

• Lockheed Martin Cooperative Avionics Testbed• (CATBird) • Heavily modified Boeing 737-300 airplane • Operated in the Experimental Category • Testbed for F-35 Joint Strike Fighter (JSF)

• Sensor operations• Data fusion • Operational environment

• External modifications to the basic airplane• Replacement of the nose radome • Sensor wings on the forward fuselage• Strake antennas on the aft fuselage• Spine and canoe antenna fairings

• Heavily modified internal fuselage• Simulated JSF cockpit and • Engineering and observer stations

SensorWing

Noseextension

Canoe

Spine

Aft Band 2

Aft Band3 - 4



Design and Analysis Approach

• Predict airplane behavior with AMI design and analysis methods and tools• MSES, VLAERO, VSAERO, MGAERO, FPI

• Wind tunnel testing• Verification and calibration of linear data• Non-linear data

• Baseline airplane flight testing• Baseline data for further validation• Reduces risk that an airframe-specific anomaly is mistaken for a CATBird problem

• Clear CATBird for full operational envelope where possible• Reduce risk for flight test expansion

• Primary areas of concern• Basic stability and control• Air data system effects• Stall speeds and handling qualities• High speed characteristics• Engine inlet flow• Design aerodynamic loads

• The airplane is operated in Experimental category• Full compliance with CFR14 Part 25 regulations not required• Lockheed Martin independent board used as airworthiness authority

SensorWing

Noseextension

Canoe

Spine

Aft Band 2

Aft Band3 - 4



Nose Extension and Sensor Wing Design

• Nose extension completely replaced existing radome• Minimization of air data system disturbance

• Portions of JSF leading edge mounted to CATBird on ‘sensor wing’• JSF relation between radome and LE must be maintained• Effect is definitely destabilizing• Possible engine inlet effects




• JSF lofts supplemented with chordwise and spanwise fairings• Conflicting design requirements:

• Stability impact required minimum area and therefore minimum chord • High speed characteristics required low t/c and therefore maximum chord

• Maximum feasible t/c and airfoil curvature used




• Final loft coordinated with manufacturer• Flow quality acceptable at design operating Mach numbers• Airplane stability decrement predicted to be 16% MAC

• Compensation to be provided by a change to the aft cg limit



Aft Band 2 Design

• Portions of JSF horizontal tail mounted on aft fuselage• Fairing design completed to avoid transonic flow• Wind tunnel showed no strong impact of planform area on airplane characteristics• Initial aerodynamic loft was complex and difficult to produce• A simpler loft was developed with an acceptably small performance penalty



Fuselage Spine and Canoe Fairing Design

• Forward section design to minimize suction peaks under AOA and sideslip• Double-elliptical planform with shoulder fullness control

• Constant section used maxim allowable curvature and smooth variation• Aft section design to minimize pressure recovery gradient



Low-Speed Characteristics

• Testing performed at University of Washington Aeronautical Laboratory’s (UWAL) Kirsten Wind Tunnel in Seattle, WA

• Closed loop double-return capable dynamic pressure 100 psf• 12x8 ft test section

• Wind tunnel model fabricated by Aeronautical Testing Service Inc of Arlington WA• Developed from a photogrammetric scan of the baseline airplane• 1/12 scale model with full component buildup, control surface and flap deflections • All CATBird and baseline 737-300 parts



Low-Speed Characteristics

• Two separate wind tunnel entries• 140 hours of testing • 780 data runs• 112 configurations• Component buildups• Control effectiveness• Flow studies• Flaps cruise and deployed• In and out of ground effect

• Wind tunnel results verified predicted stability decrement• Small increase in trimmed CLMAX• No significant change to control effectiveness or lateral-directional stability• Data used along with analytical and baseline flight test results to produce an aerodynamic database for further study and analysis



Low-Speed Characteristics• Basic sensor wing aerodynamic performance verified

• Stability increment• Flow quality over sensor wing• Limited study of sensor wing wake trajectories



Low-Speed Characteristics• Stall maneuvers simulated with 3 DOF program• Focus on pitchup and pitchdown at stall• Program calibrated by reproducing baseline stall using full nonlinear wind tunnel data and flight test control input • Results showed good agreement with flight test results• Increased confidence in CATBird simulations

N35LX Stall Flight Test Time History Elevator Deflection, Load Factor, 1g CL

Weight 108,000lb CG 0.305MAC

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 5 10 15 20 25 30 35 40Time (sec)

n z C

L

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Elev

ator

Def

lect

ion

(deg

)

Flight Test CLSimulation CLFlight Test Load FactorSimulation Load FactorFlight Test Stick ShakerFlight Test ElevatorSimulation Elevator



Low-Speed Characteristics• CATBird simulations showed no appreciable decrement in behavior

Baseline 737-300 and CATB Stall Simulation108,000lb, Flaps 5, Aft CG

-20

-10

0

10

20

30

40

50

0 5 10 15 20 25 30 35 40

Time (secs)

δelev, α, θ

0

0.2

0.4

0.6

0.8

1

1.2

1.4nz, V/100Vs

b737 elevatorcatb elevatorb737 thetacatb thetab737 alphacatb alphab737 nzcatb nzb737 v/100vscatb v/100vs



Air Data

• Effect of chined radome on air data examined• China clay and minituft flow visualization to track vortex• Mini pitot probes to track blanking

• No CATBird effects foundF-35 Program Information

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High Speed Analysis

• High speed analysis used overall aerodynamic database• Efforts focused on dynamic stability, trim runaway, and upset recovery• No problems or significant CATBird effects found• Airplane cleared for flight testing

Comparison of B737/CATB Short Period ResponseLoad Factor From Trimmed Flight At 35,000 ft, 71,000 lbs., Aft CG, Stick Fixed

0.0

0.5

1.0

1.5

2.0

2.5

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

Time (s)n z

B737 CATB

B737-300 Upset ManeuverSpeed Increase From Mc/Vc At Continuous Power

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00

Time (s)

Spe

ed (K

CAS)

O FT 10,000 FT 20,000 FT 25,000 FT 25,960 FT 35,000 FT



High Speed AnalysisComparison of B737/CATB Short Period Response

Pitch Attitude From Trimmed Flight At 35,000 ft, 71,000 lbs., Aft CG, Stick Fixed

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

Time (s)

Thet

a (d

eg)

B737 CATB

Comparison of B737/CATB Short Period ResponseLoad Factor From Trimmed Flight At 35,000 ft, 71,000 lbs., Aft CG, Stick Fixed

0.0

0.5

1.0

1.5

2.0

2.5

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

Time (s)

n z

B737 CATB

Comparison of B737/CATB Phugoid ModeAltitude History From Trimmed Flight At 35,000 ft, 71,000 lbs., Aft CG

34000.0

34200.0

34400.0

34600.0

34800.0

35000.0

35200.0

35400.0

35600.0

35800.0

36000.0

0.00 50.00 100.00 150.00 200.00 250.00 300.00

Time (s)

Alti

tude

(ft)

B737 CATB

Comparison of B737/CATB Phugoid ModePitch Attitude From Trimmed Flight At 35,000 ft, 71,000 lbs., Aft CG

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

0.00 50.00 100.00 150.00 200.00 250.00 300.00

Time (s)

Thet

a (d

eg)

B737 CATB

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Releasable to Foreign Persons


Sensor Wing and Engine Inlet Interaction

• Areas of concern were engine ingestion of wake and/or vorticity• Sensor wing wake trajectory study performed using VSAERO

• Sensor wing wake streamlines traced aft• Engine highlight streamlines traced forward • Engine mass flow effects included

• Wake ingestion classified as ‘None’, ‘Possible’, and ‘Definite’




• Results tabulated as functions of airplane Mach number, AOA, and CL• No ingestion for positive airplane CL at cruise• Wake ingestion boundaries developed as a function of airplane normal load factor for various weights and altitudes• Information used in test planning and flight manual supplement development

Free Flight Wake Ingestion ThresholdsZero Sideslip, Flaps Up

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

00.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90

MACH

Ang

le o

f Atta

ck (d

eg)

Possible Wake IngestionThreshold

Definite Wake IngestionThreshold

Definite Wake Ingestion

Possible Wake Ingestion

No Wake Ingestion

Minimum Weight Wake Ingestion Thresholds at Sea LevelWeight = 95,000 lbf, Flaps Up

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

2.000

2.500

3.000

0 50 100 150 200 250 300 350 400

KCAS

n

Flight Envelope

Possible Wake IngestionThreshold

Definite Wake IngestionThreshold

+1g Stall Limit

-1g Stall Limit

Definite Possible

No Ingestion




• Large engine streamline during takeoff roll engulfs sensor wing• Ingestion was predicted to cease before rotation speeds• Flight test group advised that any adverse engine effects would be noticed before rotation and the takeoff could be aborted if needed



Design Loads and Flight Loads Clearance

• Design aerodynamic loads calculated for new external parts• CFR14 Part 25 load cases formulated as a linear matrix of quasi-steady state conditions• Airplane flight condition and resulting sensor wing and aft band air loads calculated• Results surveyed to find critical cases for design• Aerodynamic model used to produce distributed airloads

• Design airloads for critical cases• Loads for flight test structural monitoring during envelope expansion



Flight Test

• Flight testing performed by AeroTEC of Seattle, WA• Detailed test planning with inputs and reviews from all team members• Daily pre- and post-flight briefings• Rapid data release to engineers

• Baseline flight tests before modification• Confirmed basic performance and handling of this airframe• Produced data for validation and calibration of analytical models• Reduced risk of an airframe-specific anomaly mistaken for CATBird problem• Airplane was flown to dive speed and Mach number

• Modified airplane flight tests • All external shape and structural modifications completed • Substantiated compliance with CFR14 Part 25 airworthiness criteria• Validated the effect of the external modifications

• Airplane aerodynamics• Air data• Handling qualities

• Validated flutter and other structural margins• Provided performance and flying qualities information for the CATBird Aircraft Flight Manual Supplement.



Air Data Boom

• JSF air data boom used on JSF radome for convenience• Boom not long enough for CATBirdinstallation• Significant effect on error at static source

CATBird Static Source DataHigh Speed Taxi Test

2440

2450

2460

2470

2480

2490

2500

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Time (sec)

Pres

sure

Alti

tude

- Fe

et

Pilot Static

Copilot Static

UNCORRECTED Nose Boom Hpi ft

Boom CFD Corrected Pressure Altitude Ft

GPS Altitude

• VSAERO used to provide local CP and data correction• Results verified by flight test



Stability and Control Flight Test Results

• Stabilizer to trim measured for a range of speeds at several weights and cg locations• Measured during hands-free trim and steady maneuvers

• Elevator position measured and effect accounted for• Resulting corrected stabilizer angle is a roughly linear function of trimmed CL.

• Slope proportional to airplane static margin• Intercept proportional to zero lift pitching moment

• Results validated stability increment predictionEquivalent Tail Angle to Trim

B737-300 and CATB - All Mach Numbers

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

CLT

Equi

vele

nt T

ail A

ngle

(deg

)

Flight Test CG: 7.00Flight Test CG: 28.00Flight Test CG: 20.00CATB Flight Test CG: 7

CG 7.0

CG 07.0

CG 16.0

CG 20.0

CG 24.0

CG 28.0

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Buffet Flight Test Results

• Flight test did not produce any unacceptable low or high speed buffet or vibrations• Sensor wing buffeting was observed

• High angle of attack conditions – wind up turns• Mach numbers above CATBird VMO/MMO during the flutter clearance flights• Neither produced any discernable airframe response

• Buffet characteristics of the CATBird were determined to be satisfactory• Flight test results showed good correlation with predicted buffet boundary

CATB Sensor Wing Buffet Boundary

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Mach Number

Sen

sor

Win

g C

L

FT No Buffet

FT Buffet

Est SW Buffet Boundary

Est WUT Conditions

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Summary

• Successful development and test program • In depth analyses

• Multiple reviews by experienced engineers• Realistic assessments of tool capabilities

• Recognition of tool limitations• Mitigations and conservatism applied where uncertainty existed• Open interchange and participation of engineers

• Customer • Contractor engineering• Airworthiness authority• Flight test teams

• Robust design and well-planned test process • Risks eliminated or reduced

• Design and analysis• Planned envelope expansion flight tests• Concurrent data review and analysis.

• Testbed was successfully demonstrated • Mission performance• Compliance with the appropriate CFR14 Part 25 airworthiness requirements


aerodynamic design of the lockheed martin cooperative

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