The military’s long tradition of composites usage continues in next-generation aircraft and boats.
Advanced composites manufacturers have historically had to overcome the key challenges of long qualification times and high costs associated with new technology or material use in military vehicles or equipment. Even though the market can be challenging to enter, when designs offer substantial cost, time and weight savings, opportunities exist in the military market.
Here’s a look at two recent developments that build upon a decades-long tradition of composites technology in the military.
The Latest Generation of Fighter Jets
The first widespread use of composites in military fixed-wing aircraft – as well as the first structural use of advanced composites – were on fourth generation fighter aircraft. According to Don Kinard, an F-35 engineer at Lockheed Martin, the F-16 from Lockheed Martin was one of the first advanced fighters to use composites on the empennage in the mid-1970s. During the next several decades, structural composites grew to comprise five to 12 percent of the weight of aircraft in fourth generation fighters. Today’s leading-edge fifth generation fighters take advantage of developments in advanced materials to comprise even more composites.
The F-35 Lightning II Program – also called the Joint Strike Fighter Program (JSF) – is the core of the Department of Defense’s (DOD) next-generation aircraft weapon system for the Air Force, Navy and Marines. Lockheed Martin won the contract to develop the F-35s, which feature three variants: the F-35A for conventional takeoff and landing, the F-35B for short takeoff and vertical landing (STOVL) and the F-35C carrier variant.
The F-35B is the first operational supersonic stealth fighter designed for short takeoff and vertical landing. It is 50.5 feet long and has a wing span of 35 feet. Kinard estimates that composites now account for as much as 25 to 30 percent of the aircraft’s weight. It uses a combination of graphite, glass epoxy and bismaleimide (BMI) composites mostly for exterior doors and skins.
Kinard explains that military customers for JSF aircraft are interested in performance and affordability improvements. Cost-and-weight trade studies drive composite usage, so the most affordable material is used for each particular application.
Carbon fiber and ceramic fiber composites also are finding their way into military jet engines. Ted Lynch, executive vice president of SAMPE, says the DOD is the largest single user of aircraft fuel, so it’s extremely interested in any technology that reduces fuel usage. Lynch says JSF engines now feature carbon fiber composites, replacing titanium in certain areas. Composite components such as fan blades and eventually turbine sections could help engines become more efficient.
New Designs for Small Combatant Craft
In 2009, Structural Composites Inc., West Melbourne, Fla., began developing an advanced lightweight hull and deck for small combatant craft using inexpensive composite materials. Scott Lewit, president of the company, says the non-inflatable boat it helped design is the first to use advanced combatant technologies and single-skin construction.
The 850B small combatant craft prototype is prepared for ship interface trials.
Rigid hull inflatables are one type of small combatant craft widely used throughout the Navy, with one or more on every ship. They patrol waters, protect forces and harbors, carry demolition teams to sites to dive for mines or other threats, and transport people and equipment. Special forces use them for search and seizure anti-terrorism operations.
According to Lewit, a much lighter non-inflatable design allows for combined uses and reduces the number of specialty boats a ship has to carry. “Being lighter and more capable means it can perform more missions and hold more people,” he says.
Lewit’s company partnered with Lockheed Martin, the Brunswick Corporation and Zodiac Marine to develop five new technologies under the U.S. government’s Small Business Innovation Research grants:
- Sandwich-free construction without a core or heavy stringers
- Low section single-skin framing
- Membrane thin laminate panels
- Suspended cockpit
- New resin coating technology called “shark skin” whose strain to failure changes, allowing the coating to change from brittle to elastomeric
