Background on Morphing Systems
The desire for multi-mission capability in military and civil air vehicle systems has created a need for technologies that allow for drastic wing shape changes during flight. Since most current aircraft are fixed-geometry, they represent a design compromise between conflicting mission segment performance requirements, such as high-speed cruise, low-speed loiter, and low turn radius maneuver. If a hybrid aircraft is designed to combine several flight profiles, the wing design must maximize overall efficiency of the anticipated mission. Through morphing, the aerodynamics of the aircraft can be adapted to optimize performance in each segment by changing areas such as the camber of the airfoils and the twist distribution along the wing.
Adapting the shape of wings in flight allows an air vehicle to perform multiple, radically different tasks by dynamically varying its flight envelope. The wing can be adapted to different mission segments, such as cruise, loitering, and high-speed maneuvering by sweeping, twisting, and changing its span, area, and airfoil shape. Morphing wing technology is considered to be a key component in next-generation unmanned aeronautical vehicles (UAVs) for military and commercial applications.
CRG successfully demonstrated the self-deploying capabilities of its (Veriflex®-based composite) material in the fabrication and deployment of a sub-scale, carbon fiber reinforced wing. The sub-scale wing was heated, collapsed, and rolled up into a tight package. Once cooled, the structure maintained the rolled up configuration until it was heated and deployed to achieve the memorized wing shape, as shown in the center of the figure below.
Adaptive structures allowing drastic wing shape changes have been a long-term goal of the aerospace industry. CRG is developing two methods of allowing wings to change from a slow-flight loitering, high-efficiency configuration to one designed for high speed and maneuverability. This shape change can occur repeatedly with no loss of material integrity.
CRG’s shape memory polymer, Veriflex®, is being used to create a seamless wing skin that can be heated, reshaped by the internal wing structure, cooled, then reheated and moved back to the original shape. A real-time morphing wing shape increases versatility in the flight capabilities and function of an aircraft.
Veriflex is also being used to develop hinges that allow wings to bend at set points. This will allow planes to change from a loitering configuration to high-speed and high-maneuverability shapes.
CRG has worked with other development partners in developing morphing aircraft technology. The goal was to develop and demonstrate viable composite materials and process technology to support multiple Air Force morphing structural applications. We developed a prototype of a form-fit, improved-function wing ready for simple integration and operational testing. In the process, we applied a unique suite of smart materials technologies, such as CRG’s shape memory polymers (Veriflex®), dynamic composites (Veritex™), and dynamic syntactic foams (Verilyte™). We also employed smart materials, engineering design, process development, fabrication, and other supporting technologies to meet goals and requirements.
CRG's smart structures engineering team focuses on integrating multiple smart material technologies with conventional actuation mechanisms and on developing a variety of smart adaptive or morphing structures. We have demonstrated realistic morphing structure concepts for near-term applications. These and other program efforts will help CRG better understand TRL levels, define near-term morphing capabilities, help identify the next enabling materials technologies necessary to round out structural morphing composites capabilities, and predict mid- and far-term morphing capabilities.
Understanding how birds perform by making their wings morph, or change shape in flight is one step in CRG research efforts to dramatically increase the efficiency and maneuverability of aircraft. Flight capabilities in nature provide a demonstration of feasibility and proof-of-concept for man-made morphing architecture. In fact, the morphology of a pterodactyl’s wings and body shape provides an excellent model for morphing mechanisms and adaptable air vehicle systems.
Compared with the subtle capabilities of a common bird’s wings, mechanical flaps and slats and pivoting wings are heavy, complex and inefficient. Although these wings are the result of clever ingenuity and years of engineering design, they increase the radar cross-section of a plane and can’t operate at high flight speeds. The ability to substantially change a wing’s shape seamlessly in flight through the use of CRG’s SMP technology will produce aircraft that can fly both fast and slowly, with optimal efficiency at every speed. These vehicles will burn less fuel, run more quietly, fly longer, take off and land in shorter distances, and maneuver more quickly and with greater agility.
In programs with the Air Force Research Laboratories (AFRL), the Defense Advanced Research Projects Agency (DARPA), the Army, Lockheed Martin Skunkworks®, and other commercial companies as well as through internal R&D, CRG scientists are exploring technologies that could one day liberate aircraft from flaps, slats, and ailerons so that they more closely emulate the astonishing adaptability and control of bird flight.
Novel Design Principles
The ultimate goal of research in these morphing programs is to develop new design principles for fully adaptable systems. These design principles would consist of integrated systems using morphing mechanisms, propulsion systems, control systems, structures, and materials. CRG has demonstrated feasibility in all these areas. For example, the figure below demonstrates one of the company's completely new designs for the underlying structure of a morphing aircraft wing.
In the interest of developing entirely new systems to incorporate shape-changing technologies, CRG's engineering research for morphing wings consists of selection of actuators, designs for morphing mechanisms and skins, integration of these components into a wing structure, experimental verification of aerodynamic and structural performance of a wing segment, and incorporation of the adaptable wing into a complementary morphing air vehicle. CRG’s research in shape memory polymers and morphing structural design has contributed significantly to the development of adaptive wings.
The Veriflex Family of Materials and Morphing Technology – An Ideal Match
Shape memory polymer's list of applications continues to grow as researchers and customers experiment with it, and CRG helps integrate the new technology into existing systems. Continued demand for Veriflex as a resin system has prompted its sale to the general public through our spin-off company, CRG Industries.
Morphing applications in particular benefit from the capabilities of shape memory materials. CRG has demonstrated feasibility for adaptable systems in manufacturing, military applications, space systems, aerostructures, and propulsion. An overview of some of those applications is outlined below:
- complex-curved, filament-winding mandrels
- customizable and reusable molds
- rapid composite manufacturing
- adaptive wings
- morphing aerostructures
- portable, deployable, configurable habitats
- portable, deployable bridges
- deployable mirror mechanisms
- SMP membranes
- deployable space optics
- collapsible, deployable habitats for planetary exploration
- lightweight gel propellant components
- rolling diaphragms for propellant chambers
Morphing, adaptable systems increase the usefulness and capabilities of a wide range of applications, and CRG has taken a leadership role in research involving morphing technologies. Through the use of innovative smart materials, process engineering, and integration into real-world systems, the results of this research are already revolutionizing the way we design aircraft, build manufacturing systems, equip multipurpose vehicles, and deploy space mirrors.