developments in elastic memory composite materials for...
TRANSCRIPT
Developments in Elastic Memory Composite Materials forSpacecraft Deployable Structures1
1 0-7803-6599-2/01/$10.00 © 2001 IEEE
Michael Tupper,Naseem Munshi,
Fred BeaversComposite Technology Development, Inc.
1505 Coal Creek DriveLafayette, Colorado 80026
Troy MeinkAir Force Research Labs
Kirtland AFB, NM 87117505-846-9331
Ken GallDepartment of Mechanical Engineering
University of ColoradoCampus Box 427
Boulder, Colorado 80309303-735-2711
Martin Mikulas, Jr.Department of Aerospace Engineering
University of ColoradoCampus Box 429
Boulder, Colorado 80309303-492-6899
Abstract— Near-term and future spacecraft and satelliteswill require large ultra-lightweight structures andcomponents that must be efficiently packaged for launchand reliably deployed on orbit. A new materialtechnology called Elastic Memory Composite (EMC)materials, shows promise in meeting these needs. TheEMC polymer matrix materials enable a fully curedcomposite structure or component to be deformed orfolded for efficient packaging into a spacecraft or launchvehicle, then regain its original shape with no degradationor loss in mechanical or physical properties. Acomponent using EMC materials is fabricated in itsdeployed, on orbit shape using conventional compositemanufacturing processes. Then by heating the materialand applying force this fully cured composite material canbe folded or deformed for packaging. When cooled, itwill retain the packaged shape indefinitely. Whenreheated the structure will regain its original shape withlittle or no external force. This packaging/deploymentcycle is reversible. This paper reviews new developmentsin EMC materials technology including materialproperties, analytical and designs tools, testing andevaluation protocols, and new applications.
TABLE OF CONTENTS
1. INTRODUCTION2. BASIC DESCRIPTION OF EMC MATERIAL3. HIERARCHICAL MULTI-DISCIPLINARY APPROACH4. MICRO-STRUCTURAL MODELING5. EMC MINI-BEAM6. CONCLUSIONS7. ACKNOWLEDGEMENTS
1. INTRODUCTION
Designs for near-term and future spacecraft have beenconceived with very large apertures and structures forEarth and Space Science observatories, antennas, solar
sails, and sunshades. These spacecraft will require the use ofvery large (50 to 100 meter) ultra-lightweight apertures andstructures. A continuing challenge is the packaging anddeployment of these large space structures to enable them tobe stowed into existing launch vehicles.
Current deployment techniques include mechanical hingemechanisms, strain energy booms, and inflatable tubes. Strain energy booms offer excellent specific stiffness andsignificant flight heritage. Inflatable structures offer goodpackaging efficiency and deployment control. To increase theperformance and versatility of the inflatable structures, fiberreinforced composites with polymer resins have become thesystem of choice. Most of these systems require on orbitprocessing and face significant challenges before they areincorporated into operational systems.
A new material technology, Elastic Memory Composite(EMC) has been developed which may potentially eliminatenearly all the shortfalls of current spacecraft deployablestructures. EMC materials are traditional fiber reinforcedcomposites with a polymer resin that exhibits shape memoryproperties. These materials are processed in the same fashionas other thermoset fiber reinforced composite materials, butdiffer from traditional resins in that after cure they can beelevated above their glass transition temperature (Tg) anddeformed. If held in the deformed state and cooled they willremain deformed without constraint. When deployment isdesired the shape memory response can be activated byelevating the material above the Tg. Once above it’s Tg thematerial will self deploy to its original processed geometry.
Structures manufactured with these resins have the potential tomatch, or exceed, the performance of strain energy deploymentstructures in specific stiffness and the inflatable structures inpackaging and deployment control [1]. However, thesesystems are still in the early stages of development and requirefurther development before they are ready for space flight.
The Department of Defense and NASA have an interest instructural elements that can be compacted on earth, storedin a compacted fashion, and then deployed and rigidizedin space. Although space curable composites, strainenergy booms, and inflatable tubes are some exploredpossibilities, shape memory polymer composites are anemerging replacement for such structures. [1]
2. BASIC DESCRIPTION OF EMC MATERIAL
Materials with an ability to recover mechanically inducedstrains upon heating are classified as shape memorymaterials. Aside from large recoverable strains, shapememory polymers have advantages over other materials(metals and ceramics) exhibiting shape memorycharacteristics, including low density and low processingand material costs. [2]
Figure 1 shows the packaging and deployment cycle of anelastic memory composite tubular structure developed forspace applications. As shown in Figure 1, EMC tubesshow significant promise as deployable structuralelements since they can be highly compacted and fullyrecover their original shape.
The technique can be reversible, provides for positivefiber alignment and gives desirable packagingcharacteristics while offering satisfactoryphysical/mechanical properties. Although this approachmay be considered high-risk/high payoff, these featuresprovide high reliability and ease of handleabilityunattainable by other approaches. Since a well-controlledheating rate is not as critical for the elastic memoryapproach as for one involving chemical cure, a simplesolar concentrator may offer adequate energy fordeployment. [3]
3. HIERARCHICAL MULTI-DISCIPLINARY
APPROACH
The evolution of understanding in any field of science ispredicated on the proper interaction between experimentand analysis/theory. While the sequence ofexperimental/theoretical activity is not necessarily alwaysclear a priori, the essence of the ‘scientific method’consists in observing physical facts and formulating ananalytical framework for them to produce a scheme oftheory by which other physical results can be predicted.
Important in the qualification of ‘theory’ is that ‘predicted’facts must arise under circumstances separate from those whichproduced the original data and parameters. Therefore, a modelfirst requires data to determine the physical parameters derivedfrom a sufficiently broadly construed experiment ormeasurements, but does not become a theory until itspredictive capability is tested on data which are not part of themeasurements that determined the original parameters of theproposed theory. [4]
Successful implementation of the EMC material technologyrequires the development of sufficient physical experimentaldata describing the EMC behavior; establishment of suitabletechniques for obtaining data describing this behavior; creationof analytical models and theories that can be employed topredict this behavior; and preparation of guidelines for thedesign of components exhibiting this behavior.
Development activities for EMC materials require concurrentinvestigation into different material aspects using a variety oftechniques and disciplines. Results from one investigationmay impact on another investigation. Furthermore, for EMCmaterial, it is important to consider both the elevatedtemperature low modulus state, and the lower temperaturerigid state.
The Hierarchical Multidisciplinary Approach (HMA) to EMCmaterial science development was created to identify thevarious activities, protocols, and developments and to trackthe results. The basic structure of the HMA, illustrated inFigure 2, uses physical size as the basis for categorization. The overall goal of the effort is to gain a fundamentalunderstanding of the EMC material behavior. With theincorporation of the HMA material science-basedmethodology, tests and evaluation methods will beinvestigated at these different material size scales to gatherbehavioral data for the development of analytical models andtheories. The HMA is a living process, and is continuallybeing modified to include new information, new test methods,material performance results, requirements, and models.
4. MICRO-STRUCTURAL MODELING
Based on initial studies and experiments, one key materialaspect was identified as critical confirm that the potentialbenefits of EMC could be realized and that further study wasjustified. This aspect was whether the EMC material could beefficiently packaged without inducing damage, or in otherwords, “Where do the fibers go?”
As-fabricated fullycured EMC tube
Apply heat andforce to compress
and fold
Cool to holddeformed shape
indefinitely
Apply heat only todeploy tube tooriginal shape
Tube re-deployedto original shape
as curedFigure 1 - Demonstration of Fully Cured Elastic Memory Composite Material
Figure 2 - Hierarchical Multidisciplinary Approach to EMC Material Science
The answer was to be found in the micro-mechanicalbehavior of the EMC material during packaging. Microscopic and analytical efforts were undertaken toelucidate the behavior. The goals were to gain anunderstanding of what is physically happening at the micro-structural level, determine material characteristics whichenhance the ability of the EMC material to be packagedefficiently, develop micro-structural models of the observedbehavior, and fabricate EMC material specimens that can beefficiently packaged without damage. The process andresults of these studies are described as follows.
A simple beam theory model was used to guide theexperimental studies and expectations. For the case of arigid matrix we considered the ‘Beam Stress’ equation (1)and the ‘Moment in a Beam’ equation (2). Substitutingequation (1) into (2) and simplifying, we arrived at anexpression comparing the ratio of the radius of curvature, R,and the beam thickness, t, to the strain in the beam (ε),equation (3). The minimum R/t value is achieved when thebeam is strained to its limit εl. The factor of 2 multiplyingthe strain results from the fact that tensile strain exists onthe outside of the beam and compressive strain on the insideof the beam. Both the tensile and compressive sides of thebeam can be taken to the strain limit, enabling the effectivestrain in the beam to be 2 εl.
(1)
(2)
(3)
For a graphite/epoxy composite beam with a rigid matrix, areasonable allowable strain is 0.01. Substituting this intoequation (3) this yields an achievable R/t value of 50. Thisis indeed the limit of the R/t value used for the design ofstrain energy booms that are flown today.
However, an EMC beam at a temperature above the matrixTg has a soft matrix and the fibers do not strain. Thisresults in a strain distribution in the bent beam with thetensile strain equal to zero and the maximum strain in thebeam is equal to the compressive strain. For this type ofbeam, the neutral axis, region of zero strain, is at the tensileor outer side, of the bent beam, as shown in Figure 3.
tRo
Ri
+εεεε=0-εεεε
Figure 3 - Strain in a Beam with a Soft MatrixAssuming a linear distribution of compressive strains, theradius of curvature of the beam, R, can be related to themaximum local compressive strain by the followingexpression, equation (4):
(4)
σ = Eε =M
t2
I
Rt
12ε
=
nm’s µµµµm’s mm’s cm’s m’s
Fiber ArchitectureVolume Fraction
Packing Factor & Stiffness
Uni
Weave
Polymer ChemistryCarbon Nanotubes
Structural Component
StructuralLevel
Nano-Level
Fiber/MatrixInterfaces
Matrix
Fiber Interface
PolymerChains
Chemical Structure of the Chains
Open Grid
Laminate
Laminate DesignBend Radii
M = EIy" = EIR R
t1ε
=
where t is the beam thickness and ε is the maximumcompressive strain in the beam. [5] This expressionindicates that, for a beam with a soft matrix, obtaining agiven R/t value would require a compressive strain limittwice that of a conventional beam with a rigid matrix. TheR/t value appears to be a reasonable figure of merit to use todetermine efficiency of packaging of composite laminatesand structural components. These R/t values must beobtained without damaging the composite or degrading itsstructural properties. Equations (3) and (4) are plotted inFigure 4, illustrating the added strain limit needed forbeams with soft matrices as compared to those with rigidmatrices. Since conventional composites can be bent to R/tvalues of 50, R/t values significantly less than 50 arerequired in order to realize a significant packaging advantagewith an EMC structure.
Range for Conventional Gr/Ep
R
R/t
t12ε
=
Strain [[[[εεεε]]]]0.01 0.02 0.1 0.5
1
2
10
20
50
100
Rt
1ε
=
Figure 4 - R/t Curves for Rigid and Soft Matrix Materials
Further investigation of a beam with a soft matrix wasneeded to determine how best to bend an EMC material tosmaller R/t values, which requires obtaining highercompressive strain limits without inducing damage in thecomposite. Considering an ideal inextensional beam inbending, the lengths of the inner and outer surfaces are equaland must remain equal at all times. If one end is held fixedand displacement between the inner and the outer portionsof the beam is allowed, the magnitude of the resultantdisplacement is δδδδ = ππππt for all beams, regardless of radius ofcurvature. This effect is illustrated in Figure 5.
t
δδδδ = ππππt
Ro
Ri
72.3o
Figure 5 - Beam Bending Model
For an actual beam, the accumulated displacement, δ, mustbe zero. In fiber reinforced composites the primarycompressive deformation mode is associated with fibermicro-buckling. The stiff embedded fibers cannotexperience the necessary large compressive strains withoutmicro-buckling. The simple end-constrained paper tabletmodel shown in Figure 6 demonstrates geometrically themagnitude of the buckling amplitude that must occur toaccommodate a 180° bend. As the fibers micro-buckle,large interlaminar matrix shear strains occur as shown inFigure 6.
Figure 6 – Compression-Side Buckling of Folded Tablet
A heated EMC matrix has a very low shear modulus, andmicro-buckling occurs at large bend ratios. The matrix doesnot have the stiffness to support the fibers in compression. The fiber micro-buckling enables a large effective fibercompressive strain because the length of a buckled fiber issignificantly shorter than that of an unbuckled fiber. Effective strains well above traditional material strain failurelimits are achievable through fiber micro-buckling. However, the geometry dictates that the amplitude of amicro-buckle needs to be large to accommodate a smallchange in the length, ∆ , on the inner compressive side ofthe beam, this is illustrated in Figure 7.
∆L
aa
l∆
Figure 7 – A Large Buckling Amplitude is Required for a Small Length Reduction
As previously mentioned, a key factor in determining thefeasibility of EMC materials is demonstrating that EMCmaterials can be bent to relatively small R/t values withoutdamage to the material. In order to accomplish this, thefibers must be allowed to micro-buckle on the compressiveside, to sufficient amplitudes to accommodate the lengthdifferences between the outer and inner sides of the beam. Furthermore, the most stable mode of fiber micro-bucklingis out of plane. Out of plane micro-buckling subjects thematrix to very localized strains, which often result indelamination. However, if the fibers can be forced to micro-buckle in plane, a secondary stable state for the micro-buckled fibers, the localized strains in the matrix are lower,and higher fiber buckling amplitudes can be achieved,resulting in lower R/t values. [5]
The reinforcing fibers can be forced to micro-buckle in planerather than out-of-plane by a combination of tailoring theEMC composite to provide a high strain capability matrix,and the development of special bending techniques andtooling. Figure 8 shows a photomicrograph of aunidirectional carbon fiber reinforced EMC laminate thatexhibits the desired in-plane fiber micro-buckling, enablingthis beam to be bent to an R/t < 10 without damage.
Figure 8 - Photomicrograph of In-Plane Fiber Micro-Buckles in an EMC Laminate Bent to an R/t < 10
Further consideration of beam theory and the bending of acomposite beam with a low modulus matrix shows that thethickness may effectively decrease at the expense ofexpansion along the width of the narrow beams (Poissoneffect). The latter mechanism will occur if a bundle offibers is bent in absence of a constraining matrix. Expansion along the width of the beam will effectivelyreduce the required strain by lowering t, and will allowbending to tighter radii [5].
In the ideal case the Poisson effect results in contraction ofthe beam on the tension side and expansion of the beam onthe compression side, and a reduction in the overall beamthickness as illustrated in Figure 9. This figure illustrates across section of a beam that is being bent downward, out ofthe plane of the paper. The light gray rectangle is theoriginal (undeformed) beam cross-section.
ThicknessReduction
UndeformedCross-Section
( + )
( - )
PoissonExpansion
Poisson Contraction
Figure 9 - Poisson Effect in a Bent Beam with a Low Modulus Matrix
In either situation (local elastic buckling or thicknesscontraction) the matrix must allow enough fiber mobility toavoid extreme local stresses/strains and permanent damage.
The inherent differences between the bending of a beam andplate were considered. A beam is defined as a structuralmember with a relatively small width-to-thickness ratio,while a plate has a large width-to-thickness ratio. A platecan be conceptualized as a series of parallel beams, attachedand constrained along their entire length. Thus the strainsresulting from the Poisson effect must be accommodated asinternal stresses in the plate, rather than throughdeformations as is possible with a single beam.
5. EMC MINI-BEAM
The concept of an EMC “mini-beam” was developed to takeadvantage of the enhanced bending that can be realized withfiber reinforced EMC materials, due to the soft matrixenabling the fibers to micro-buckle and the Poisson effectthat reduces the effective beam thickness. An EMC mini-beam is a fully cured EMC laminate with unidirectionalreinforcement that can be used as a unit element, or basicbuilding block of a structure. The mini-beam can beevaluated using simple beam theory, which can then beextrapolated to the design of larger structures incorporating“trusses” utilizing EMC mini-beams as the basic structuralelement. One such type of structure is an isogrid, or anopen-grid, type structure. An schematic example of anEMC mini-beam is shown in Figure 10; this mini-beamuses unidirectional graphite fibers with an EMC matrix.
Figure 10 - EMC Mini-Beam with Unidirectional Graphite Fiber Reinforcement
Figure 11 illustrates an EMC mini-beam that has undergonebending. The matrix strains and the beam deforms,allowing the fibers to displace rather than break. Thus themini-beam demonstrates a very high strain capability whenheated above its Tg, and can be very efficiently folded to atight radius, then deployed back to the flat, straightcondition with no apparent degradation of materialproperties. In initial experiments, EMC mini-beams havebeen bent to an R/T of 5 without apparent damage.
A
View A
Figure 11 - Schematic of an EMC Mini-Beam in Bending
Photomicrographs of the outside and inside of such a mini-beam are shown in Figure 12. In image 12a, the outersurface of the bent beam, flaring of the beam can be easilyobserved, resulting in an effective reduction of the laminatethickness during bending. In image 12b, showing the innersurface of the bent beam, the in plane micro-buckles can beobserved.
Figure 12 - EMC Mini-beam Bent to R/t of 5 Without Apparent Fiber Damage
(a) (b)
A simple open grid structure has been fabricated using mini-beams, as shown in Figure 13. This open-grid structure hasbeen successfully bent to a R/t of approximately 5 severaltimes and deployed back to the flat state with no apparentdamage to the mini-beam members.
Figure 13 - Simple Open-Grid Structure Fabricated from EMC Mini-Beams
These mini-beam structures can be extrapolated to thefabrication of large structural members, which exhibit highstiffness to weight ratios and very efficient packaging. Figure 14 shows an open-grid structural tube fabricated frommini-beam sub-structural elements. Fabrication of Open-Grid EMC tubular structures has been demonstrated. Thefabrication process is automated, the tooling is relativelysimple, and the structural design can be substantiallytailored. Open-grid EMC designs hold substantial promiseas low cost, ultra-lightweight, structurally efficientstructures that are easily and effectively packaged for launch.
Figure 14 - EMC Open-Grid tube with Mini-Beam Structural Members
6. CONCLUSIONS
A polymer matrix Elastic Memory Composite material hasbeen developed which shows promise for use in spacecraftdeployable structures. This new material shows thepotential to eliminate shortfalls of current compositedeployable spacecraft structures. A HierarchicalMultidisciplinary Approach to the materials sciencedevelopment of the Elastic Memory Composite materials isbeing pursued. Micro-structural models have beendeveloped and used to guide the understanding and furtherdevelopment of this new material technology. Experimentalresults have corroborated the premises made in the modelingeffort. Several components and structures have beenfabricated using EMC materials and have shown thepotential for significant packaging improvement relative tocurrent materials. Further work is required to betterunderstand the capabilities of the EMC materials and tofully realize their potential benefits. Work is continuing intheoretical modeling, micro-structural performanceevaluation, and application of this material technology to awide range of spacecraft structures and components.
7. ACKNOWLEDGEMENTS
Funding for this work has been provided by the U.S. AirForce Research Laboratory under a Cooperative Researchand Development Agreement, NASA SBIR Phase IContract NAS1-00031, National Reconnaissance OfficeContract No. NRO000-00-C-0058, and CompositeTechnology Development, Inc. (CTD). We thank PaulFabian, Craig Hazelton, and Rob Denis at CTD forassistance with material processing and testing.
REFERENCES
[1] T. Meink, K. Qassim, T. Murphey, M. Mikulas and M.Tupper, “Elastic Memory Composite Material: TheirPerformance and Possible Structural Applications,”submitted for publication in the International Conference onComposite Materials 13 Proceedings, June 2001.
[2] C. Liang, C. Rogers and E. Malafeew, “Investigation ofShape Memory Polymers and Their Hybrid Composites,” J.Int. Mat. Sys. Struct., Vol. 8, 380-386, 1997.
[3] C. May and A. Wereta, Jr., “Process Identification Studyfor Space Cured Composite Structures,” NASA ContractorReport 158942, September 1978.
[4] W. G. Knauss, “Perspective in Experimental SolidMechanics,” International Journal of Solids and Structures,Vol. 37, 251-266, Elsevier Science Ltd., 2000.
[5] T. Murphey, T. Meink and M. Mikulas, “SomeMicromechanics Considerations of the Folding ofRigidizable Composite Materials,” to be presented at theAIAA Gossamer Spacecraft Forum, April 2001.
BIOGRAPHY
Michael Tupper earned a B.S. inMechanical Engineering from ColumbiaUniversity, is a registered professionalengineer, and a co-inventor of CTD’sElastic Memory Composite materials. Among his responsibilities is thecontinued technical development ofCTD’s EMC materials, the developmentof commercial products utilizing thesematerials, and the formation of strategicbusiness relationships for the development andcommercialization of these materials. Mr. Tupper hasworked extensively developing specialized polymer andceramic-based materials including composites, insulation,adhesives, and coatings for use at cryogenic temperaturesand in other harsh environments. His responsibilities havefocused on the processing and handling of these materials. Additional responsibilities at CTD include marketing,production, customer liaison, and business development. Previously, Mr. Tupper worked at General Atomics in SanDiego, CA.
Naseem. Munshi earned a B.S. in Chemical and PolymerTechnology from the Polytechnic of the South Bank,London, UK, and a Ph.D. in Polymer Science from thePolytechnic of the South Bank, London, UK. She is thePresident and founder of CTD, and the primary inventor ofthe Elastic Memory Composite material. Dr. Munshi hasformulated all CTD resin products and has been thePrincipal Investigator on numerous grants and contracts fordevelopment of polymer-based materials, including severalSBIR contracts. Dr. Munshi is internationally recognizedas an expert in the performance of epoxy resins andcomposites at cryogenic temperatures and under radiationexposure. CTD’s polymer-based electrical insulatingproducts, formulated by Dr. Munshi, are the standard ofcomparison for insulation of large superconducting magnetsaround the world, and are also widely used for insulation ofresearch and commercial superconducting magnet coils.
Fred Beavers earned a B.S. in Mining Engineering and aM.S. in Mechanical Engineering from the University ofArizona. He is the Director of Research and Development atCTD, and leads CTD’s commercial and government researchand development efforts, utilizing polymer and ceramiccomposite materials to develop new technologies andproducts such as the EMC materials. He has been integrallyinvolved in all previous EMC development anddemonstration programs, and was the Principal Investigatoron the Phase I SBIR program investigating EMC hinges fordeployable components. Previously, Mr. Beavers wasinvolved in the development of advanced compositecomponents for aerospace structural and thermalmanagement applications. Earlier he served as a US Navynuclear submarine officer.
Ken Gall earned B.S., M.S. and Ph.D. degrees inMechanical Engineering from the University of Illinois atChampagne-Urbana, and is an Assistant Professor in theDepartment of Mechanical Engineering, University ofColorado at Boulder. His research interests are centeredaround the behavior of materials, with emphasis on tailoringmicrostructures for the required properties and performancein applications. He has extensive experience in electronmicroscopy, mechanical testing, and the development ofmicro-mechanical models with industrial application. Hehas investigated microstructure property performancerelationships in numerous material systems, ranging fromNiTi and CuZnAl shape memory alloys to cast Al-Sialloys.
Martin Mikulas, Jr. earned B.S., M.S., Ph.D. degrees inEngineering Mechanics from the Virginia PolytechnicInstitute. He is a Professor Emeritus in AerospaceEngineering Sciences at the University of Colorado atBoulder, and is active in the development of new structuralconcepts for inflatable, deployable, adaptive, and compositestructures. Dr. Mikulas worked at NASA/LaRC from 1961to 1991 in advanced lightweight aerospace structures, andpioneered the application of composite materials inaerospace applications during the 1970s. In 1976, he spenta year at the California Institute of Technology conductingresearch on advanced concepts for deployable spacestructures. As head of the NASA/LaRC StructuralConcepts Branch, he focused on constructing largestructures in space. He developed and demonstratedstructural concepts through ground demonstrations andSpace Shuttle flight experiments. Dr. Mikulas is the authorof over 60 technical publications on advanced structures,and holds nine patents. He is an AIAA Fellow, receivedNASA medals in 1983 and 1988 for his contributions inthis field, and was elected to the National Academy ofEngineering in 1999.
Troy Meink earned a B.S. in Mechanical Engineering fromSouth Dakota State University, and M.S. and Ph.D. degreesin Aeronautical and Astronautical Engineering from theOhio State University. He is the Technical Lead for theIntegrated Structural Systems Group at the Air ForceResearch Laboratory/Space Vehicles Directorate. He alsoacts as a research engineer and technical program manager,specializing in launch vehicle and spacecraft structures. Previously, he was a ballistic missile flight test engineer atthe US Air Force National Air Intelligence Center. As a USAir Force navigator, he flew over 100 sorties in support ofOperations Desert Shield, Desert Storm, and ProvideComfort. As the Program Manager and chief test pilot forSORD aircraft development program, he managed thedesign and manufacturing team, and acted as chief structuraldesign. As chief test pilot he made the initial flights in theSORD 1A aircraft, and flew all flights through thepreliminary phase of flight testing. He also taught coursesin aircraft design and construction, and led a team thatdesigned, built, and successfully tested two experimentalaircraft.