ITT Corp. has handed over the first major structural subassembly for the U.S. Marine Corps CH-53K heavy lift helicopter to Sikorsky’s development flight center in West Palm Beach, Fla. The delivery of the initial sponson—a 25 x 4 x 5-foot structure that attaches to each side of the helicopter and houses landing gear, fuel and other components—comes after three years of design and development using various composite materials to meet weight and structural requirements set out by the military.
Mike Therson, general manger of composite structures, says that ITT used a paperless software application known as life cycle analysis (LCA) to design the sponson under a joint effort with Sikorsky. The two companies followed a “100 percent integrated process” to meet the military’s guidelines for structural performance and weight, among other requirements. “We spent a considerable amount of time at their facility and they spent considerable time at our facility, so it worked both ways,” he explains.
Sikorsky’s three-year test program for the CH-53K will involve a total of seven prototypes—a ground test vehicle, static test article and five flight test helicopters. ITT is also under contract for the tail rotor pylon for the CH-53K, which is the final subassembly that will be installed on the airframe. The company anticipates first deliveries of the tail rotor pylon in March 2011. Plans call for handover of the final sponson for the seventh flight test aircraft in mid-2012.
ITT had to work with certain composite materials based on military requirements, “but how that material was oriented, how you lay out the plies, that was all on our shoulders,” Therson says, adding that composites enable two methods of saving weight—the specific weight of the material is lighter and the ability to orient the fibers to specific performance or structural requirements.
“It’s very safe to say that utilizing that process, we saved more than 30 percent in weight versus what would have been a similar or like metallic structure,” Therson notes.
Composites are also “corrosion resistant, so they’re virtually impervious to the environment. So you don’t experience the same corrosive considerations over time,” he says, adding that low fatigue properties of composites “basically will minimize crack propagation, therefore it has better ballistic capabilities than the metal alternative.”
There are maintenance advantages as well. “Because composites are corrosion-resistant, you eliminate a great deal of the maintenance associated with corroding metals, such as continual painting and continual replacement. The other thing is because composites are fatigue-resistant, the design life is three times as long” compared to the existing CH-53D/E, Therson says, adding that composites increase “survivability under harsh conditions.”
Grant Hall, senior director of composite structures at ITT, points out that the current CH-53D and E airframes flying today are essentially all metal. “Virtually the entire fuselage, cabin, tail, everything other than the external fuel tanks and the rotor blades—it’s all metal,” he says. The CH-53K represents the first time “an all-composite airframe in a helicopter format for heavy lift is going into service. And so it’s a great leap of technology, and it mirrors what you’re seeing in other military programs for fixed-wing aircraft, as well as the commercial airline industry. So this takes that same technology that you’re seeing elsewhere, and applies it to the military heavy-lift environment.”
ITT anticipates low rate initial production (LRIP) for the sponsons at its facility in Salt Lake City starting in early 2013 at a rate of around two shipsets annually. Once the testing program is complete, “the target is to expand to 24 shipsets per year,” says Therson. He adds that the sponson is a “highly tight, tolerant, very sophisticated structure from both the lab through integration. For each sponson, there are probably 50 different composite parts, as well as hundreds of metallic fasteners. It requires a well-trained workforce to meet the overall program requirements.” ITT will provide sponsons for up to 200 CH-35Ks during the life of the program.