Morphing: The Shape of Wings to Come

One of the really intriguing factors about the composites industry is that it is always on the cusp of the future. As technology progresses, our ability to manipulate the physical world around us evolves. Over the past several years the National Aeronautics and Space Administration (NASA), the Defense Advanced Research Projects Agency (DARPA), a number of high-level aerospace contractors and many universities have been researching a new field of "morphing aerostructures." While this technology has originally been targeted towards aircraft and unmanned aerial vehicle design, the concept has the potential for creating a new revolution in design for a number of applications outside of defense. Advanced composite materials will play a key role in this technology.

When talking about morphing images, some of James Bond 007's famous spy cars and gadgets or maybe lycanthropy may come to mind. In the context of what this technology could do for future military platforms, perhaps the latter analogy is not that far off the mark. Some of the concepts developed under the second phase of the Morphing Aircraft Structures (MAS) program, funded by DARPA, show how morphing wing designs can enable radical changes in an aircraft's ability to fly fast or economically, at high- or low-altitudes, enhance maneuverability or a number of other characteristics. The main focus on morphing has been in wing design.

Lockheed Martin Skunk Works' demonstrator, which debuted at the 2005 Paris Air Show, employs a folding wing that can be set in a number of configurations to achieve radical changes in the aircraft's wing area, angle of attack, drag, etc. Raytheon is using a Navy Tomahawk cruise missile fuselage for its work. NextGen's approach uses a Firebee drone as its design platform. By changing a number of parameters on the modified drone's wings (see illustration above), a wide range of flight profiles can be affectively achieved. Through the use of telescoping wings, "Raytheon's Morphing program intends to demonstrate revolutionary capability to allow a single missile to be able to perform multiple missions or the same mission more effectively," said Donald Uhlir, Raytheon's Morphing program manager. Morphing wings is the first in a series of steps to permit a cruise missile to travel at high speeds to a target area, loiter and then move to another target area, with speed changes from 0.3 Mach to 3.0 Mach. While DARPA plans to fly all three demonstrators, none of the programs is intended to field a weapons system. Rather, these technologies will be combined with other DARPA technologies, such as the aeroelastic wing shaping, on future efforts.

In each of these cases, and in a host of other development concepts, it has been the combination of the advances in computer design and control, light-weight composites structures and actuator systems that have enabled science fiction to become closer to scientific fact. Weight is a key driving factor in aircraft design, and more so with morphing designs. The weight of actuators and servo mechanisms for the Raytheon, NextGen and Lockheed morphing designs add considerably to the weight and complexity of the aircraft. Another company, CRG Industries LLC, has been developing a material technology, which has shown an interesting potential to simplify this reality.

CRG Industries LLC, based in Dayton, Ohio was spun off from its parent company, Cornerstone Research Group (CRG), in June of 2004 to commercialize its proprietary, shape changing, fiber reinforced composite technology. Since its inception in 1997, CRG has developed and licensed a number of materials and related technologies with potential applications for smart composites applicable to both military/aerospace and commercial needs. Some of these materials include conductive liquid crystal polymers, Verilyte™ syntactic shape memory foams, Veriflex™ shape memory polymers, Veritex™ smart composites.

The Veriflex and Veritex materials have recently received a number of Small Business Innovation Research program awards, Small Business Technology Transfer program awards, as well as development contracts from Lockheed Martin for "morphing" UAV development. Much of the work relates to morphing or smart composite structures and atypical aerospace composites — like the airfoil pictured here. Since most current aircraft are fixed-geometry, they represent a design compromise between conflicting performance requirements in mission segments, such as high-speed cruise, low-speed loiter and low turn radius maneuvering. In addition to providing interesting possibilities for packaging structural composites, a "morphing" composite could potentially alter and optimize discrete segments of a wing's airfoil by changing the camber or twist along the wing.

In demonstrating how a unique material or technology can seed ideas in a number of different applications, another use for CRG's shape-changing composites is in the field of reusable composite tooling. The Veriflex shape memory polymers also hold some very interesting possibilities for reusable composite tooling. The thermoset is used to create filament winding mandrels by placing a Veriflex polymer tube into a clamshell mold, heating the material to its elastic state and applying pressure to force the Veriflex materials to conform to the mold shape. After the composites over the Veriflex mandrel are wound and cured, the mandrel is said to be easily removable from the part and can be reformed in the clamshell mold for reuse.

The Veriflex polymers have also been used by the CRG to develop an alternative to metal injection molding tools. CRG claims that the Veriflex polymers offer the following advantages over traditional metal tools:

• Relatively inexpensive;
• Versatile, producing a range of geometrically different parts from one sheet;
• Increased production rates;
• Capability of fabricating many molds;
• Prototype production possible; and
• "Gentle" demolding process.

CRG's Veriflex material is designed to withstand elevated curing temperatures for most performance composites without deformation and offers a "gentle, simple" demolding process. After the composite part has cured, the mold is raised above the transition temperature, which allows it to retract to its memorized shape. CRG's tooling processes provide the opportunity to neutralize some of the disadvantages of traditional fabrication techniques for advanced composite parts. This tooling system also possesses versatility in size variations, including being capable of micro (nanometers) to macro (meters) replication.

Will the future embrace morphing structures? The ability to create subtle or dramatic changes in the shape of a structure could find interesting applications. Imagine large skyscrapers that can deploy "spoilers" or other otherwise morph to high attenuate wind loads. What about boats that could modify their hull's configuration to serve in littoral environments, heavy seas, or even deploy a hydrofoil? Imagine wind turbine blades that can "sense" the local wind conditions and tailor its airfoil to optimize energy output, or to shed aerodynamic loads along the blade's length to prevent occurrences of tower strike. A high-performance "rigid" or "wing" sail that could constantly optimize its 3-D shape could provide the winning edge in America's Cup racing. The possibilities are certainly intriguing, limited perhaps only by imagination and funding. If and when morphing technologies are applied, advanced composite materials will be there to make it happen.

Chris Red is the editor for Composite Market Reports (CMR). CMR publishes two aerospace newsletters, Advanced Composites Monthly and GraFiber News, in addition to Composites Industry Monthly, which is CMR's non-aerospace newsletter focusing on industrial, recreational, and other non-aerospace applications. Red is a regular contributor to CM and a frequent lecturer around the industry: 480.507.6882; cred@compositemarketreports.com.