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.
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