As engineers design more structural components using composite materials, the resin transfer molding (RTM) process is seeing increased use in business jets. Bombardier’s Belfast facility is employing RTM to build Learjet 85 wings, and Gulfstream vendor North Coast Composites of Cleveland, Ohio, is using RTM to make G250 rudders. The rudder’s ribs and skins are made in a single RTM cycle, according to North Coast president Richard Petrovich, and the closeout spar is added later.
Resin transfer molding involves injecting resin into a complex steel mold of the rudder structure, into which dry fiber is placed before the mold is closed. Copper mesh for lightning protection is also part of the rudder and laid into the mold. The G250 rudder is unique in that North Coast Composites was able to incorporate the rudder closeout ribs in the mold instead of making the ribs separately and attaching them later with fasteners. The completed RTM-made rudders require minimal final machining. The complex steel rudder mold weighs 38,000 pounds, Petrovich said, and includes two-ton steel mandrels between the spars. The mold is good for making thousands of parts to a high degree of accuracy.
The big advantage of RTM is that it requires no oven or autoclave. The resin is injected into the mold in a carefully designed and documented process, including monitoring of temperature, pressure, flow rate, degassing of the resin and how the resin is heated before it is injected. RTM-made parts are much more consistent in shape and weight compared with vacuum-bagged composite parts made with single-sided tooling. North Coast also manufactures RTM parts for Boeing, Nordam and GE (engine vanes) and is bidding on many other composite components for aerospace manufacturers. “The highest application will be in areas where you need precision, repeatable parts,” Petrovich said.
The G250’s vertical stabilizer features a “bird splitter” structure. Israel Aircraft Industries (IAI), which manufactures the G250’s airframe, incorporated the splitter structure on the leading edge of the vertical fin. The sharp edge of the splitter helps protect the airplane’s structure and critical systems by splitting the bird’s carcass if it hits the vertical fin’s leading edge. According to Gulfstream, “It is not uncommon for some business jets to have a bird splitter to protect vital aircraft systems.”
The G250 is on track for joint FAA and EASA certification this year. Three flight-test G250s have logged more than 830 hours aloft as of mid-March. The first non-flight-test G250, S/N 2004, is nearly finished at IAI facilities in Israel, and Gulfstream’s Dallas facility has been producing the interior furnishings for this airplane. G250 interior and paint completions will be done in Dallas.
Work also continues at Gulfstream’s Integration Test Facility in Savannah, Ga., where the G250’s Rockwell Collins-based PlaneView 250 avionics suite is being put through its paces, including testing of the head-up display and enhanced vision system. Earlier this year, Gulfstream finished structural and limit load tests on the G250 fatigue test article. This airframe is undergoing further testing to evaluate structural integrity during more than 40,000 cycles, according to Gulfstream.