Integrated assemblies are the Holy Grail for design
engineers because they lighten structures, reduce assembly costs, and increase
In the new approach being used by Boeing with help from NASA, dry carbon fiber structures are stitched together and then placed in a heated tool. A vacuum is pulled and epoxy resin is infused into the structure.
"The composites technology used in the (787) Dreamliner is 25 to 30 years old," says Andy Harber, senior project manager, design engineering for Boeing. "In the new approach, there is no lay-up and no autoclaves."
The Dreamliner represented a dramatic increase in aircraft composites'
use, with about half of the structure made with carbon-reinforced plastic
(CFRP). As reported by Design
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required development of autoclaves larger than those ever previously used.
Otherwise, the technology was similar to composites technology long-used in making fiberglass composites. Hand lay-up is an open mold process in which successive plies of reinforcing material, usually fiberglass or resin-impregnated reinforcements are applied to a mandril. Curing is accelerated in an autoclave.
Deliveries of the Dreamliner are running more than three years late because of a variety of problems, including issues with fasteners and attachment points in the composite structure.
No decision has been made at Boeing about potential use of the new assembly technology for commercial aircraft. But Harber says Boeing expects to use the technology in a next-generation blended wing body aircraft designed for reduced noise and pollution.
The process received its first field test as
replacement landing gear doors in C-17s used as transport
aircraft in Afghanistan. "On Sept. 17, 2009, we delivered to NATO eight landing
gear doors featuring resin-infused, stitched composites," says Harber.
The original doors were made with traditional materials and had taken a beating in the rough landing environment in the battle zone. Tools for the C-17 doors were developed by Process Fab Inc.
The first licensee for the Boeing-developed technology is General Dynamics Armament and Technical Products, which was awarded a $17 million contract by Boeing for the production of composite components and spares for the C-17 Globemaster III aircraft. Production and program management is being done at General Dynamics' advanced materials facility in Marion, VA.
The latest version of the Boeing composites technology is called Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS).
"This is completely reinventing how a composite structure is designed and manufactured," says Harber. One of the keys is a vacuum infusion process in which a minimal amount of resin is pulled into a tool to cover the fibers.
Another key to the use of PRSEUS is use of a pultruded rod attached to the skin as a stiffener. This could eliminate the need for thousands of fasteners on an entire aircraft. Pultrusion is a process dating back to the 1950s in which composites are pulled through a heated die, creating a very strong linear shape. Many ladder rails are made via the pultrusion process.
The test bed
for this new materials technology is an experimental aircraft developed by
Boeing and NASA called the X-48. To date, the aircraft has been unmanned and built to small scale for testing purposes.
Boeing's Phantom Works has been developing the blended wing body aircraft concept in cooperation with the NASA Langley Research Center. Two models have been built under contract by Cranfield Aerospace in the UK. NASA and Boeing completed initial flight testing of the Boeing X-48B last year.
"This project is a huge success," says Fay Collier, manager of the project in NASA's Aeronautics Research Mission Directorate. "Bottom line: the team has proven the ability to fly tailless aircraft to the edge of the low-speed envelope safely."
The blended wing body is a dramatic departure from the "tube-and-wing" approach used in commercial planes. Many engineers feel that design has reached its potential. It's not clear though how comfortable passengers would feel in such a radical departure as the blended wing.
PRSEUS technology is also a leap of faith for commercial aircraft, where use of traditional composites was a radical departure.
"Boeing is studying a number of advanced materials including PRSEUS for use on future airplanes," says Boeing spokesman Bret R. Gardner. "However, we have not made any decisions about whether we will use this material or not."
But it will have life in the next phase of development for the blended wing body aircraft, which remains an experimental aircraft.
Next year NASA will test a mid-fuselage section of a hybrid wing body aircraft made with the PRSEUS technology to determine its potential flight worthiness.
If all goes well, Boeing will use its jointly developed blended wing body as an entry in the Environmentally Responsible Aviation Project sponsored by NASA. The project's primary goals are to develop unconventional aircraft designs with the potential to reduce noise, fuel burn and nitrogen oxides (NOx) emissions.
pinning its hopes on the integrated assembly made possible with advanced
composites technology as key to its work for NASA in developing an
environmentally responsible aircraft.
For this project, the Boeing team will define a concept for an aircraft that can achieve speeds up to 85 percent of the speed of sound, cover a range of nearly 7,000 miles, and carry between 50,000 and 100,000 lb of payload, either passengers or cargo.