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."