Unmanned aerial vehicles (UAVs) are increasingly in the spotlight in trouble spots throughout the world, but they are also finding increased use in civilian applications. In parallel, suppliers of advanced thermoplastics such as Sabic are addressing demands for aerospace grade materials that meet a number of stringent operational requirements.
The Silver Fox UAV weighs 36 lb, boasts a mission endurance of greater than eight hours, a payload of 5 lb, and is launched by a gas spring catapult.
|Ultem XP060 foam is employed in external payload fairings for the Silver Fox UAV.|
The U.S. military UAV market is similarly expect to expand in the coming years: a report conducted by Market Research Media states that the U.S. military UAV market is projected to grow at a 12% compound annual growth rate, reaching $18.7 billion in 2018. The report finds that the U.S. military UAV market will generate $86.5 billion revenues over the period 2013-2018.
With this market growth, there is an increasing need for advanced materials that will allow the range of UAVs to be extended and their air time to be raised despite the size of their payloads. The explosive growth of UAVs-together with the growing workloads expected of these aircraft-reportedly represents an opportunity for manufacturers to advance from materials commonly used in the radio-controlled (RC) aircraft hobby world and utilize more sophisticated solutions for these demanding applications.
Sabic claims it has met this challenge with its Ultem amorphous thermoplastic polyetherimide XP060 foam. During a recent project for BAE Systems, which developed the Silver Fox UAV for the military, the University of Dayton Research Institute (UDRI) used Sabic's Ultem foam to create an aftermarket fairing assembly for external payloads that reduced drag and restored system performance.
"Sabic's collaboration with UDRI demonstrates our commitment to continually innovate new material solutions that enable our customer's success. Our Ultem foam allows for maximum range and endurance by providing a solution that is strong and lightweight while meeting all of BAE Systems' critical performance requirements for the external payload fairing on the Silver Fox," said Kim Choate, Transportation marketing director, for Sabic's Innovative Plastics business.
"As the UAV market continues to grow and innovate, Sabic's Ultem foam offers customers a material that is superior to older, inadequate alternatives, such as RC hobby-grade styrene foams or vacuum-formed hard-shell plastic fairings," he added.
Due to the minimal remaining volume internal to the Silver Fox UAV, the military customer elected to mount an oversized payload module and an inertial sensor on the exterior fuselage of the aircraft. This presented a challenge considering that the payload shapes were non-aerodynamic and created significant drag, having a negative impact on the aircraft's range and endurance.
BAE Systems requested UDRI to create aftermarket fairing assemblies for the external payloads to solve these challenges. By using Sabic's Ultem XP060 foam—which added a mere 3 oz of weight to the UAV-UDRI—BAE Systems were able to reduce 92% of the profile drag of the un-faired payload and sensor module, and aircraft endurance was restored.
"Ultem foam was the ideal fit, meeting or exceeding all of the operational requirements for the Silver Fox UAV application. It is the only material able to deliver on the stringent requirements for UAVs, including light weight, strength, chemical resistance, transparency to radio frequency and processability," said Rick Scudder, Director of the UDRI Center for UAV Exploitation (CUE). "Ultem XP060 foam was the only material found that met the full list of performance properties for this challenge, and enabled the UAV to accommodate an additional customer payload without sacrificing performance."
The foam also fulfills many operational requirements, including being lightweight and stiff, but more importantly, remaining machinable by computer numerical control (CNC) milling and maintaining radio frequency transparency. Additionally, it must neither melt nor deform in high heat environments, nor shrink in cold environments. Ultem foam is highly processable and it is compatible with CNC milling to precise tolerances, thus obviating the need for molds, forms or tooling to achieve complex shapes and contours, ultimately translating into reduced total system costs. Additionally, because of its amorphous nature, it tolerates most of the adhesives used in the market today. It is also compatible with lamination and composite skins, including thermosets and thermoplastics, as well as metal.
Ultem XP060 foam is reportedly also an excellent candidate material for a broad spectrum of UAV applications such as wing cores, nose cones, cowlings, control surfaces, insulating panels, radomes and fairings. Additionally, it has potential applications in the rail, marine, and automotive industries—anywhere that honeycomb structures are used in strong, lightweight core applications.