Developments in Elastic Memory Composite Materials for
Spacecraft Deployable Structures
1
Michael Tupper,
Ken Gall
Naseem Munshi,
Department of Mechanical Engineering
Fred Beavers
University of Colorado
Composite Technology Development, Inc.
Campus Box 427
1505 Coal Creek Drive
Boulder, Colorado 80309
Lafayette, Colorado 80026
303-735-2711
303-664-0394
[email protected]
[email protected]
Martin Mikulas, Jr.
Department of Aerospace Engineering
University of Colorado
Campus Box 429
Boulder, Colorado 80309
303-492-6899
[email protected]
Troy Meink
Air Force Research Labs
Kirtland AFB, NM 87117
505-846-9331
[email protected]
Abstract— Near-term and future spacecraft and satellites
will require large ultra-lightweight structures and
components that must be efficiently packaged for launch
and reliably deployed on orbit.
A new material
technology called Elastic Memory Composite (EMC)
materials, shows promise in meeting these needs. The
EMC polymer matrix materials enable a fully cured
composite structure or component to be deformed or
folded for efficient packaging into a spacecraft or launch
vehicle, then regain its original shape with no degradation
or loss in mechanical or physical properties.
A
component using EMC materials is fabricated in its
deployed, on orbit shape using conventional composite
manufacturing processes. Then by heating the material
and applying force this fully cured composite material can
be folded or deformed for packaging. When cooled, it
will retain the packaged shape indefinitely.
When
reheated the structure will regain its original shape with
little or no external force. This packaging/deployment
cycle is reversible. This paper reviews new developments
in EMC materials technology including material
properties, analytical and designs tools, testing and
evaluation protocols, and new applications.
TABLE OF CONTENTS
1.
2.
3.
4.
5.
6.
7.
INTRODUCTION
BASIC DESCRIPTION OF EMC MATERIAL
HIERARCHICAL MULTI-DISCIPLINARY APPROACH
MICRO-STRUCTURAL MODELING
EMC MINI-BEAM
CONCLUSIONS
ACKNOWLEDGEMENTS
1. INTRODUCTION
Designs for near-term and future spacecraft have been
conceived with very large apertures and structures for
Earth and Space Science observatories, antennas, solar
1
0-7803-6599-2/01/$10.00 © 2001 IEEE
sails, and sunshades. These spacecraft will require the use of
very large (50 to 100 meter) ultra-lightweight apertures and
structures. A continuing challenge is the packaging and
deployment of these large space structures to enable them to
be stowed into existing launch vehicles.
Current deployment techniques include mechanical hinge
mechanisms, strain energy booms, and inflatable tubes.
Strain energy booms offer excellent specific stiffness and
significant flight heritage. Inflatable structures offer good
packaging efficiency and deployment control. To increase the
performance and versatility of the inflatable structures, fiber
reinforced composites with polymer resins have become the
system of choice. Most of these systems require on orbit
processing and face significant challenges before they are
incorporated into operational systems.
A new material technology, Elastic Memory Composite
(EMC) has been developed which may potentially eliminate
nearly all the shortfalls of current spacecraft deployable
structures. EMC materials are traditional fiber reinforced
composites with a polymer resin that exhibits shape memory
properties. These materials are processed in the same fashion
as other thermoset fiber reinforced composite materials, but
differ from traditional resins in that after cure they can be
elevated above their glass transition temperature (Tg) and
deformed. If held in the deformed state and cooled they will
remain deformed without constraint. When deployment is
desired the shape memory response can be activated by
elevating the material above the Tg. Once above it’s Tg the
material will self deploy to its original processed geometry.
Structures manufactured with these resins have the potential to
match, or exceed, the performance of strain energy deployment
structures in specific stiffness and the inflatable structures in
packaging and deployment control [1].
However, these
systems are still in the early stages of development and require
further development before they are ready for space flight.
The Department of Defense and NASA have an interest in
structural elements that can be compacted on earth, stored
in a compacted fashion, and then deployed and rigidized
in space. Although space curable composites, strain
energy booms, and inflatable tubes are some explored
possibilities, shape memory polymer composites are an
emerging replacement for such structures. [1]
2. BASIC DESCRIPTION OF EMC MATERIAL
Important in the qualification of ‘theory’ is that ‘predicted’
facts must arise under circumstances separate from those which
produced the original data and parameters. Therefore, a model
first requires data to determine the physical parameters derived
from a sufficiently broadly construed experiment or
measurements, but does not become a theory until its
predictive capability is tested on data which are not part of the
measurements that determined the original parameters of the
proposed theory. [4]
Materials with an ability to recover mechanically induced
strains upon heating are classified as shape memory
materials. Aside from large recoverable strains, shape
memory polymers have advantages over other materials
(metals and ceramics) exhibiting shape memory
characteristics, including low density and low processing
and material costs. [2]
Successful implementation of the EMC material technology
requires the development of sufficient physical experimental
data describing the EMC behavior; establishment of suitable
techniques for obtaining data describing this behavior; creation
of analytical models and theories that can be employed to
predict this behavior; and preparation of guidelines for the
design of components exhibiting this behavior.
Figure 1 shows the packaging and deployment cycle of an
elastic memory composite tubular structure developed for
space applications. As shown in Figure 1, EMC tubes
show significant promise as deployable structural
elements since they can be highly compacted and fully
recover their original shape.
Development activities for EMC materials require concurrent
investigation into different material aspects using a variety of
techniques and disciplines. Results from one investigation
may impact on another investigation. Furthermore, for EMC
material, it is important to consider both the elevated
temperature low modulus state, and the lower temperature
rigid state.
As-fabricated fully
cured EMC tube
Apply heat and
Cool to hold
Apply heat only to
Tube re-deployed
force to compress
deformed shape
deploy tube to
to original shape
and fold
indefinitely
original shape
as cured
Figure 1 - Demonstration of Fully Cured Elastic Memory Composite Material
The technique can be reversible, provides for positive
The Hierarchical Multidisciplinary Approach (HMA) to EMC
fiber alignment and gives desirable packaging
material science development was created to identify the
characteristics
while
offering
satisfactory
various activities, protocols, and developments and to track
physical/mechanical properties. Although this approach
the results. The basic structure of the HMA, illustrated in
may be considered high-risk/high payoff, these features
Figure 2, uses physical size as the basis for categorization.
provide high reliability and ease of handleability
The overall goal of the effort is to gain a fundamental
unattainable by other approaches. Since a well-controlled
understanding of the EMC material behavior. With the
heating rate is not as critical for the elastic memory
incorporation of the HMA material science-based
approach as for one involving chemical cure, a simple
methodology, tests and evaluation methods will be
solar concentrator may offer adequate energy for
investigated at these different material size scales to gather
deployment. [3]
behavioral data for the development of analytical models and
theories. The HMA is a living process, and is continually
being modified to include new information, new test methods,
3. HIERARCHICAL MULTI-DISCIPLINARY
material performance results, requirements, and models.
APPROACH
The evolution of understanding in any field of science is
predicated on the proper interaction between experiment
and analysis/theory.
While the sequence of
experimental/theoretical activity is not necessarily always
clear a priori, the essence of the ‘scientific method’
consists in observing physical facts and formulating an
analytical framework for them to produce a scheme of
theory by which other physical results can be predicted.
4. MICRO-STRUCTURAL MODELING
Based on initial studies and experiments, one key material
aspect was identified as critical confirm that the potential
benefits of EMC could be realized and that further study was
justified. This aspect was whether the EMC material could be
efficiently packaged without inducing damage, or in other
words, “Where do the fibers go?”
Chemical Structure
of the Chains
Polymer
Chains
Weave
Uni
Structural Component
Polymer Chemistry
Carbon Nanotubes
NanoLevel
Fiber Architecture
Volume Fraction
µm’s
nm’s
mm’s
Packing Factor & Stiffness
cm’s
Structural
Level
m’s
Laminate Design
Bend Radii
Fiber/Matrix
Interfaces
Open Grid
Matrix
Fiber
Laminate
Interface
Figure 2 - Hierarchical Multidisciplinary Approach to EMC Material Science
The answer was to be found in the micro-mechanical
behavior of the EMC material during packaging.
Microscopic and analytical efforts were undertaken to
elucidate the behavior.
The goals were to gain an
understanding of what is physically happening at the microstructural level, determine material characteristics which
enhance the ability of the EMC material to be packaged
efficiently, develop micro-structural models of the observed
behavior, and fabricate EMC material specimens that can be
efficiently packaged without damage. The process and
results of these studies are described as follows.
A simple beam theory model was used to guide the
experimental studies and expectations. For the case of a
rigid matrix we considered the ‘Beam Stress’ equation (1)
and the ‘Moment in a Beam’ equation (2). Substituting
equation (1) into (2) and simplifying, we arrived at an
expression 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 the
beam is strained to its limit εl. The factor of 2 multiplying
the strain results from the fact that tensile strain exists on
the outside of the beam and compressive strain on the inside
of the beam. Both the tensile and compressive sides of the
beam can be taken to the strain limit, enabling the effective
strain in the beam to be 2 εl.
t
M 2
σ = Eε = I
(1)
M = EIy" = EI
R
(2)
R = 1
t
2ε
(3)
For a graphite/epoxy composite beam with a rigid matrix, a
reasonable allowable strain is 0.01. Substituting this into
equation (3) this yields an achievable R/t value of 50. This
is indeed the limit of the R/t value used for the design of
strain energy booms that are flown today.
However, an EMC beam at a temperature above the matrix
Tg has a soft matrix and the fibers do not strain. This
results in a strain distribution in the bent beam with the
tensile strain equal to zero and the maximum strain in the
beam is equal to the compressive strain. For this type of
beam, the neutral axis, region of zero strain, is at the tensile
or outer side, of the bent beam, as shown in Figure 3.
t
Ro
-ε
+ ε=0
Ri
Figure 3 - Strain in a Beam with a Soft Matrix
Assuming a linear distribution of compressive strains, the
radius of curvature of the beam, R, can be related to the
maximum local compressive strain by the following
expression, equation (4):
R = 1
t
ε
(4)
where t is the beam thickness and ε is the maximum
compressive strain in the beam. [5] This expression
indicates that, for a beam with a soft matrix, obtaining a
given R/t value would require a compressive strain limit
twice that of a conventional beam with a rigid matrix. The
R/t value appears to be a reasonable figure of merit to use to
determine efficiency of packaging of composite laminates
and structural components. These R/t values must be
obtained without damaging the composite or degrading its
structural properties. Equations (3) and (4) are plotted in
Figure 4, illustrating the added strain limit needed for
beams with soft matrices as compared to those with rigid
matrices. Since conventional composites can be bent to R/t
values of 50, R/t values significantly less than 50 are
required in order to realize a significant packaging advantage
with an EMC structure.
For an actual beam, the accumulated displacement, δ, must
be zero. In fiber reinforced composites the primary
compressive deformation mode is associated with fiber
micro-buckling.
The stiff embedded fibers cannot
experience the necessary large compressive strains without
micro-buckling. The simple end-constrained paper tablet
model shown in Figure 6 demonstrates geometrically the
magnitude of the buckling amplitude that must occur to
accommodate a 180° bend. As the fibers micro-buckle,
large interlaminar matrix shear strains occur as shown in
Figure 6.
Range for Conventional Gr/Ep
100
R/t
R =1
t ε
50
Figure 6 – Compression-Side Buckling of Folded Tablet
20
R 1
=
t 2ε
10
2
1
0.01
0.02
0.1
0.5
Strain [ε]
Figure 4 - R/t Curves for Rigid and Soft Matrix Materials
Further investigation of a beam with a soft matrix was
needed to determine how best to bend an EMC material to
smaller R/t values, which requires obtaining higher
compressive strain limits without inducing damage in the
composite. Considering an ideal inextensional beam in
bending, the lengths of the inner and outer surfaces are equal
and must remain equal at all times. If one end is held fixed
and displacement between the inner and the outer portions
of the beam is allowed, the magnitude of the resultant
displacement is δ = π t for all beams, regardless of radius of
curvature. This effect is illustrated in Figure 5.
δ = πt
72.3o
Ri
Ro
t
Figure 5 - Beam Bending Model
A heated EMC matrix has a very low shear modulus, and
micro-buckling occurs at large bend ratios. The matrix does
not have the stiffness to support the fibers in compression.
The fiber micro-buckling enables a large effective fiber
compressive strain because the length of a buckled fiber is
significantly shorter than that of an unbuckled fiber.
Effective strains well above traditional material strain failure
limits are achievable through fiber micro-buckling.
However, the geometry dictates that the amplitude of a
micro-buckle needs to be large to accommodate a small
change in the length, ∆ , on the inner compressive side of
the beam, this is illustrated in Figure 7.
aa
Ll
∆∆
Figure 7 – A Large Buckling Amplitude is Required for a
Small Length Reduction
As previously mentioned, a key factor in determining the
feasibility of EMC materials is demonstrating that EMC
materials can be bent to relatively small R/t values without
damage to the material. In order to accomplish this, the
fibers must be allowed to micro-buckle on the compressive
side, to sufficient amplitudes to accommodate the length
differences between the outer and inner sides of the beam.
Furthermore, the most stable mode of fiber micro-buckling
is out of plane. Out of plane micro-buckling subjects the
matrix to very localized strains, which often result in
delamination. However, if the fibers can be forced to microbuckle in plane, a secondary stable state for the microbuckled 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 plane
rather than out-of-plane by a combination of tailoring the
EMC composite to provide a high strain capability matrix,
and the development of special bending techniques and
tooling.
Figure 8 shows a photomicrograph of a
unidirectional carbon fiber reinforced EMC laminate that
exhibits the desired in-plane fiber micro-buckling, enabling
this beam to be bent to an R/t < 10 without damage.
The inherent differences between the bending of a beam and
plate were considered. A beam is defined as a structural
member with a relatively small width-to-thickness ratio,
while a plate has a large width-to-thickness ratio. A plate
can be conceptualized as a series of parallel beams, attached
and constrained along their entire length. Thus the strains
resulting from the Poisson effect must be accommodated as
internal stresses in the plate, rather than through
deformations as is possible with a single beam.
5. EMC MINI-BEAM
Figure 8 - Photomicrograph of In-Plane Fiber MicroBuckles in an EMC Laminate Bent to an R/t < 10
Further consideration of beam theory and the bending of a
composite beam with a low modulus matrix shows that the
thickness may effectively decrease at the expense of
expansion along the width of the narrow beams (Poisson
effect). The latter mechanism will occur if a bundle of
fibers is bent in absence of a constraining matrix.
Expansion along the width of the beam will effectively
reduce the required strain by lowering t, and will allow
bending to tighter radii [5].
In the ideal case the Poisson effect results in contraction of
the beam on the tension side and expansion of the beam on
the compression side, and a reduction in the overall beam
thickness as illustrated in Figure 9. This figure illustrates a
cross section of a beam that is being bent downward, out of
the plane of the paper. The light gray rectangle is the
original (undeformed) beam cross-section.
Undeformed
Cross-Section
(+)
The concept of an EMC “mini-beam” was developed to take
advantage of the enhanced bending that can be realized with
fiber reinforced EMC materials, due to the soft matrix
enabling the fibers to micro-buckle and the Poisson effect
that reduces the effective beam thickness. An EMC minibeam is a fully cured EMC laminate with unidirectional
reinforcement that can be used as a unit element, or basic
building block of a structure. The mini-beam can be
evaluated using simple beam theory, which can then be
extrapolated to the design of larger structures incorporating
“trusses” utilizing EMC mini-beams as the basic structural
element. One such type of structure is an isogrid, or an
open-grid, type structure. An schematic example of an
EMC mini-beam is shown in Figure 10; this mini-beam
uses 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 undergone
bending. The matrix strains and the beam deforms,
allowing the fibers to displace rather than break. Thus the
mini-beam demonstrates a very high strain capability when
heated above its Tg, and can be very efficiently folded to a
tight radius, then deployed back to the flat, straight
condition with no apparent degradation of material
properties. In initial experiments, EMC mini-beams have
been bent to an R/T of 5 without apparent damage.
Poisson
Contraction
A
Thickness
Reduction
View A
Poisson
Expansion
(-)
Figure 9 - Poisson Effect in a Bent Beam with a
Low Modulus Matrix
In either situation (local elastic buckling or thickness
contraction) the matrix must allow enough fiber mobility to
avoid extreme local stresses/strains and permanent damage.
Figure 11 - Schematic of an EMC Mini-Beam in Bending
Photomicrographs of the outside and inside of such a minibeam are shown in Figure 12. In image 12a, the outer
surface of the bent beam, flaring of the beam can be easily
observed, resulting in an effective reduction of the laminate
thickness during bending. In image 12b, showing the inner
surface of the bent beam, the in plane micro-buckles can be
observed.
(a)
(b)
Figure 12 - EMC Mini-beam Bent to R/t of 5
Without Apparent Fiber Damage
A simple open grid structure has been fabricated using minibeams, as shown in Figure 13. This open-grid structure has
been successfully bent to a R/t of approximately 5 several
times and deployed back to the flat state with no apparent
damage to the mini-beam members.
6. CONCLUSIONS
A polymer matrix Elastic Memory Composite material has
been developed which shows promise for use in spacecraft
deployable structures.
This new material shows the
potential to eliminate shortfalls of current composite
deployable spacecraft structures.
A Hierarchical
Multidisciplinary Approach to the materials science
development of the Elastic Memory Composite materials is
being pursued.
Micro-structural models have been
developed and used to guide the understanding and further
development of this new material technology. Experimental
results have corroborated the premises made in the modeling
effort. Several components and structures have been
fabricated using EMC materials and have shown the
potential for significant packaging improvement relative to
current materials. Further work is required to better
understand the capabilities of the EMC materials and to
fully realize their potential benefits. Work is continuing in
theoretical
modeling,
micro-structural
performance
evaluation, and application of this material technology to a
wide range of spacecraft structures and components.
7. ACKNOWLEDGEMENTS
Funding for this work has been provided by the U.S. Air
Force Research Laboratory under a Cooperative Research
and Development Agreement, NASA SBIR Phase I
Contract NAS1-00031, National Reconnaissance Office
Contract No. NRO000-00-C-0058, and Composite
Technology Development, Inc. (CTD). We thank Paul
Fabian, Craig Hazelton, and Rob Denis at CTD for
assistance with material processing and testing.
REFERENCES
Figure 13 - Simple Open-Grid Structure
Fabricated from EMC Mini-Beams
These mini-beam structures can be extrapolated to the
fabrication of large structural members, which exhibit high
stiffness to weight ratios and very efficient packaging.
Figure 14 shows an open-grid structural tube fabricated from
mini-beam sub-structural elements. Fabrication of OpenGrid EMC tubular structures has been demonstrated. The
fabrication process is automated, the tooling is relatively
simple, and the structural design can be substantially
tailored. Open-grid EMC designs hold substantial promise
as low cost, ultra-lightweight, structurally efficient
structures that are easily and effectively packaged for launch.
[1] T. Meink, K. Qassim, T. Murphey, M. Mikulas and M.
Tupper, “Elastic Memory Composite Material: Their
Performance and Possible Structural Applications,”
submitted for publication in the International Conference on
Composite Materials 13 Proceedings, June 2001.
[2] C. Liang, C. Rogers and E. Malafeew, “Investigation of
Shape 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 Study
for Space Cured Composite Structures,” NASA Contractor
Report 158942, September 1978.
[4] W. G. Knauss, “Perspective in Experimental Solid
Mechanics,” International Journal of Solids and Structures,
Vol. 37, 251-266, Elsevier Science Ltd., 2000.
Figure 14 - EMC Open-Grid tube with Mini-Beam
Structural Members
[5] T. Murphey, T. Meink and M. Mikulas, “Some
Micromechanics Considerations of the Folding of
Rigidizable Composite Materials,” to be presented at the
AIAA Gossamer Spacecraft Forum, April 2001.
BIOGRAPHY
Michael Tupper earned a B.S. in
Mechanical Engineering from Columbia
University, is a registered professional
engineer, and a co-inventor of CTD’s
Elastic Memory Composite materials.
Among his responsibilities is the
continued technical development of
CTD’s EMC materials, the development
of commercial products utilizing these
materials, and the formation of strategic
business relationships for the development and
commercialization of these materials. Mr. Tupper has
worked extensively developing specialized polymer and
ceramic-based materials including composites, insulation,
adhesives, and coatings for use at cryogenic temperatures
and in other harsh environments. His responsibilities have
focused 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 San
Diego, CA.
Naseem. Munshi earned a B.S. in Chemical and Polymer
Technology from the Polytechnic of the South Bank,
London, UK, and a Ph.D. in Polymer Science from the
Polytechnic of the South Bank, London, UK. She is the
President and founder of CTD, and the primary inventor of
the Elastic Memory Composite material. Dr. Munshi has
formulated all CTD resin products and has been the
Principal Investigator on numerous grants and contracts for
development of polymer-based materials, including several
SBIR contracts. Dr. Munshi is internationally recognized
as an expert in the performance of epoxy resins and
composites at cryogenic temperatures and under radiation
exposure.
CTD’s polymer-based electrical insulating
products, formulated by Dr. Munshi, are the standard of
comparison for insulation of large superconducting magnets
around the world, and are also widely used for insulation of
research and commercial superconducting magnet coils.
Fred Beavers earned a B.S. in Mining Engineering and a
M.S. in Mechanical Engineering from the University of
Arizona. He is the Director of Research and Development at
CTD, and leads CTD’s commercial and government research
and development efforts, utilizing polymer and ceramic
composite materials to develop new technologies and
products such as the EMC materials. He has been integrally
involved in all previous EMC development and
demonstration programs, and was the Principal Investigator
on the Phase I SBIR program investigating EMC hinges for
deployable components. Previously, Mr. Beavers was
involved in the development of advanced composite
components for aerospace structural and thermal
management applications. Earlier he served as a US Navy
nuclear submarine officer.
Ken Gall earned B.S., M.S. and Ph.D. degrees in
Mechanical Engineering from the University of Illinois at
Champagne-Urbana, and is an Assistant Professor in the
Department of Mechanical Engineering, University of
Colorado at Boulder. His research interests are centered
around the behavior of materials, with emphasis on tailoring
microstructures for the required properties and performance
in applications. He has extensive experience in electron
microscopy, mechanical testing, and the development of
micro-mechanical models with industrial application. He
has investigated microstructure property performance
relationships in numerous material systems, ranging from
NiTi and CuZnAl shape memory alloys to cast Al-Si
alloys.
Martin Mikulas, Jr. earned B.S., M.S., Ph.D. degrees in
Engineering Mechanics from the Virginia Polytechnic
Institute.
He is a Professor Emeritus in Aerospace
Engineering Sciences at the University of Colorado at
Boulder, and is active in the development of new structural
concepts for inflatable, deployable, adaptive, and composite
structures. Dr. Mikulas worked at NASA/LaRC from 1961
to 1991 in advanced lightweight aerospace structures, and
pioneered the application of composite materials in
aerospace applications during the 1970s. In 1976, he spent
a year at the California Institute of Technology conducting
research on advanced concepts for deployable space
structures.
As head of the NASA/LaRC Structural
Concepts Branch, he focused on constructing large
structures in space.
He developed and demonstrated
structural concepts through ground demonstrations and
Space Shuttle flight experiments. Dr. Mikulas is the author
of over 60 technical publications on advanced structures,
and holds nine patents. He is an AIAA Fellow, received
NASA medals in 1983 and 1988 for his contributions in
this field, and was elected to the National Academy of
Engineering in 1999.
Troy Meink earned a B.S. in Mechanical Engineering from
South Dakota State University, and M.S. and Ph.D. degrees
in Aeronautical and Astronautical Engineering from the
Ohio State University. He is the Technical Lead for the
Integrated Structural Systems Group at the Air Force
Research Laboratory/Space Vehicles Directorate. He also
acts as a research engineer and technical program manager,
specializing in launch vehicle and spacecraft structures.
Previously, he was a ballistic missile flight test engineer at
the US Air Force National Air Intelligence Center. As a US
Air Force navigator, he flew over 100 sorties in support of
Operations Desert Shield, Desert Storm, and Provide
Comfort. As the Program Manager and chief test pilot for
SORD aircraft development program, he managed the
design and manufacturing team, and acted as chief structural
design. As chief test pilot he made the initial flights in the
SORD 1A aircraft, and flew all flights through the
preliminary phase of flight testing. He also taught courses
in aircraft design and construction, and led a team that
designed, built, and successfully tested two experimental
aircraft.