Airplane manufacturers are responsible for
time-consuming and expensive FAA certification testing to qualify every composite
combination for use in each aircraft design. The high cost of testing tends to
limit composite use to large commercial aircraft, leaving non-FAA-certified
experimental kit planes on the cutting edge of design in the general aviation
arena. As a Boeing engineer pointed out, one widely used carbon/epoxy composite
sold by a single company has 34 different procurement specification databases
governing its sale.
The certification process will become considerably easier thanks to the AGATE
(Advanced General Aviation Transport Experiments) program. Begun in 1995, AGATE
is a wide-ranging public/private consortium effort aimed at making U.S. general
aviation more affordable and safer. AGATE involves more than 70 entities,
including the National Aeronautics and Space Administration (NASA), the FAA,
aircraft manufacturers, universities and composites suppliers. The endeavor
encompasses training, safe ways to utilize air space and improvements in ground
infrastructure systems, in addition to promoting wide use of composite
materials. According to John Turiello, director of marketing and sales at
FiberCote Industries Inc. (Waterbury, Conn.), AGATE includes a streamlined
material certification program with preapproved supplier databases that will
enable composite aircraft parts and assemblies to be designed and built in as
little as one-half the time currently required.
The physical properties of traditional materials like aluminum and steel have
long been acepted by the FAA in the design of airframes. These "allowables"
mean the designer does not have to test every part to failure - an expensive,
time - consuming process - but may substintiate the design using various forms
of analysis, according to John Tomblin of the National Institute for Aviation
Research (NIAR) laboratory at Wichita State Universitey and chairman of the
AGATE Materials Group.
In the case of composites, the allowables vary rom company to company, an
inevitable result of different manufacturers making composite products with the
same raw materials. Further, composite allowablesare often cosidered
proprietary and generally are not shared with other airframers, which causes a
repetition of qualification testing, often for identical products. Under AGATE,
the material suppliers will characterize their composite materials and produce
FAA-approved prodcut-specific databases, with design allowables defined.
Manufacturers, in turn, will be able to use the preapproved design allowables
after executing an abbreviated material - equivalence test plan.
According to FiberCote's Tauriello, after a reported investment of $1 million,
three FiberCote products are now approved: E-765, a 3K plain-weave carbon/epoxy
prepreg fabric; Uni-carbon, a carbon/epoxy unidirectional tape; and a 7781
fiberglass/epoxy prepreg fabric. A 6K five-harness satin weave epoxy/carbon
prepreg fabric is currently being tested for lamina properties, and approval is
expected soon. Tauriello reports that several FiberCote customers have already
demonstrated savings of pu to 80 percent on material qualification costs and
significant time savings. " A radome skirt fairing designed by Flight
Structures ( Arlington, Wash. ) and built by Nova Composites ( Mukilteo, Wash.
)is the first part to our knowledge approved by the FAA that uses suplier -
generated allowables", says Tauriello.
Toray Composites America Inc. ( TCA, Tacoma, Wash. ) is another supplier
involved in the AGATE material certification program. According to Leslie
Cooke, aircraft business development manager at TCA, AGATE is a good fit with
his company's philosophy. "We produce large volumes of consistent and
reproducible prepreg, which is in line with AGATE's goals of tested and
standardized airframe materials", says Cooke. " Our approved
materials will be able to be used across the board in the aviation
industry." TCA expects final certification by the end of May for three
products, including a Torayca T700G 12K unidirectoinal carbon tape, a 7781
glass-fiber eight-harness weave fabric prepreg and a T700S 12K carbon fiber plain
weave, non-crimp fabric. the non-crimp12K fabric is ideal for the kit plane
market, because it produces a superior surface finish with few
"pinholes" and reduces the time and labor to prepare aircraft parts
for painting.
"USED WITH PERMISSION FROM HIGH-PERFORMANCE COMPOSITES VOL 8, NO. 3
MAY/JUNE 2000."