The company also does not apply the process for the vertical and horizontal stabilizers, Harter says, because they do not have integral stringers.
Even so, Tomblin sees great potential from a quality standpoint for the process. “Resin systems are so advanced that they can approach autoclave quality with near-zero voids,” he says.
Bombardier's RTI process has been in test for several years. It took eight months to construct the Learjet 85 test article.
Like so many others, Bombardier is following in Boeing's footsteps with regard to introducing large-scale composite structures into commercial aviation manufacturing. Boeing began experimenting with prepreg composites in the late 1970s with 10 737-200 horizontal stabilizers that were put into commercial service for about 15 years. When those aircraft were retired, Boeing and NIAR did a post-op examination of the tails and could find no evidence of fatigue. “They don't age,” Tomblin says of the composite structures, which is exactly what Boeing says when it markets the 787.
From there, use of CFRP progressed through the 767 to the 777, where it first emerged in a large flight-critical structure on the rudder. Again, these showed excellent service-life qualities. The 777 was the warm-up for Boeing's real goal, shifting entirely away from aluminum alloy airframes on the 787. For that aircraft, complete fuselage barrels and wings are produced with prepreg carbon fiber tape cured in autoclaves.
The autoclaves needed to cure composite structures are expensive to buy and operate, given that cure times for large structures like a wingbox or fuselage barrel are measured in shifts, not minutes, and tie up the entire machine.
So the industry is looking for ways to avoid autoclaves. Many of the 787's smaller composite parts are not dependent on autoclaves, such as the vacuum-assisted resin-transfer molding process used by Hawker de Havilland, a Boeing subsidiary, for trailing edges. One assignment for the company's Fabrication Div. is to explore ways to eliminate autoclaves.
Much of NIAR's research help for its industrial clients is process-oriented, tackling “what-if” projects to discover how well they will work in manufacturing to produce a flyable product.
Although it is a practical, not academic, institution, NIAR's home is on the campus of Wichita State University. “We are geared around certification,” Tomblin, its founder and executive director, explains. “Getting a part onto a plane is what we do.”