Lighter Than Air: Inflatable UAV Structures
Inflatable structure technologies offer advantages in military and commercial unmanned aerial vehicle applications.
The use of unmanned aerial vehicles (UAVs) is growing, both in military and commercial
intelligence, surveillance and reconnaissance (ISR) applications and in munitions with greater
mission adaptability. Many Department of Defense (DoD) roadmaps for implementation of UAVs and
unmanned aerial systems (UAS) have been released and indicate the need for improvements in
capabilities and equipment. Frederica, Del.-based ILC Dover LP has developed an enabling technology
that can significantly expand the mission envelope for numerous UAV/UAS applications.
New LTA vehicles for military applications that leverage inflatable wing technology include Global Near Space Services' Star Tower, a flying wing aerostat.
Inflatable aerostructures including wings, tails and fuselage components have been present in aircraft applications since the 1950s. These components were derived from the lighter than air (LTA) airships and fabric-covered aircraft that preceded them by decades. Recent advances in materials have brought this technology to a new level of performance, enabling its application to modern unmanned aerial systems. The single greatest benefit of this technology is that it allows compact packaging of large vehicles. It makes possible the easy transport of a robust package that rapidly expands into a vehicle of greater size and performance than any mechanical competitor. Examples include systems such as small UAVs delivered via a 155-millimeter shell from a ground asset or airborne C-130; release of a medium-sized UAV from an aerial platform such as an unmanned drone; or the rapid delivery of a large aircraft to distant locations from a transport missile.
Since 1947, ILC has been developing and manufacturing innovative aerospace structures using engineered softgoods solutions. Some of its more notable work includes the Apollo spacesuits worn by astronauts who walked on the lunar surface, the airbags that landed the Pathfinder and MER Rovers on the surface of Mars, and the M40 gas mask. For more than 40 years, the company has been designing and manufacturing LTA vehicles, including tethered aerostats, airships, balloons, and zeppelins, for civilian and military use. Over the last decade, it has been leveraging materials and structures technologies from all of its products to create high-performance inflatable UAV components.
An inflatable wing structure is shown in its packed state (top) and its deployed state (bottom).
The Need For Enhanced Capabilities
There are many diverse technologies employed in UAV systems today. Current operational needs are being met, but advancement is required to keep pace with expanding military and civilian needs. Knowledge of inflatable systems allows the system designer to realize greater possibilities outside the constraints of current technologies, thus enabling improved persistence, mobility, and capability. For many of the UAVs being delivered or fielded today, larger and more capable vehicles can be deployed if inflatable structures are used.
Growing military and/or civilian needs include: ISR; communications; munitions; persistence; system mobility; and greater footprint with fewer assets to improve effectiveness.
ILC Dover designed the Mars Pathfinder airbags to be highly reliable in the harsh Martian environment. The airbags are made from a silicone-coated Vectran® fabric.
Numerous examples exist for how inflatable structures can be applied to improve performance of current and planned mission scenarios. Two examples follow:
- Studies are currently being conducted on carriage-mounted fixed-wing UAVs for unmanned drones. Post release, the rigid UAV wing rotates and the UAV performs its mission. The size of the UAV, and thus its performance, are limited by aerodynamic impacts on the mother craft and structural performance of the UAV. The use of inflatable structures in the daughter vehicle provides a larger, more capable UAV in a smaller, more aerodynamic package for undercarriage delivery.
- Mobile military units can easily transport inflatable UAVs by backpack or small vehicle because they are highly packable compared to rigid systems. Larger aircraft per the transport weight and volume can be realized versus traditional rigid assemblies. The highly survivable nature of inflatable structures means that less experienced personnel can serve as operators and vehicle lifespan is extended. This advantage also expands the weather envelope because less care is required to operate the vehicles. The cost of logistics and training is therefore reduced.
ILC specializes in expandable flexible composite structures that demand high reliability and operate in harsh environments. Some examples include:
- LTA vehicles such as military surveillance aerostats, piloted airships and high-altitude vehicles;
- high-reliability products such as Mars Pathfinder airbags, munitions decelerators and habitats; and
- life-critical products such as spacesuits, and chemical-biological protective suits and masks.
In the 1970s, ILC developed and flew numerous inflatable UAVs. These included delta wing vehicles that had spans ranging from 4 to 15 feet and which leveraged aerostat and spacesuit technologies in their design and construction. The vehicles packed into small volumes for transport and were easy to pilot. However, the concept was ahead of its time, and development was halted.
Over the past 10 years, the company has engaged in the development of numerous inflatable UAVs, both large and small. The technology has matured to the point at which it is field-ready and can be engineered into practical systems without the need for scientific advancement. With the emergence of many highly capable lightweight sensor and weapons technologies, and a new emphasis on mobility and capability in a wide range of environments, inflatable aerostructures are poised to expand mission capabilities and experience significant growth.
The unique features of inflatable aerostructure technology allow the mission designer to expand beyond traditional approaches, thus broadening capabilities as compared to conventional technologies. Some of the features and attributes of the technology are identified below:
Compact Package Delivery: Large wings or vehicles can be fitted into small delivery systems including: gun or mortar launch and in-flight deployment; human launch by hand or mechanical device, such as a backpack system; launch from larger UAVs such as Global Hawk or an unmanned drone; small aerodynamic packages that can be released from aircraft undercarriage mounts; missile delivery systems; and tip extensions for high-aspect-ratio wings to increase delivery survivability.
Simple Rapid Inflation: Deployment times can range from 30 milliseconds for missile fins, to approximately 1 second for a 6-foot-span UAV wing, to 1.8 seconds for large inflatable structures such as the Pathfinder airbags, which measure approximately 600 ft3. Inflation can be accomplished in flight using gas generators or compressed gas. Foam inflation can be used to increase bending stiffness and longevity. Ground inflation can be accomplished using hand pumps or compressed gas.
ILC Dover designed and manufactured the envelope and ballonet of the 170,000-cubic-foot DIRECTV airship for airship advertising company The Lightship Group. Other components of the airship were manufactured by American Blimp Corp. Photographed by Allan Judd
Crashworthy technology: Test data show no damage to the inflatable structure after hundreds of flight crashes. The structures can fly in all weather conditions and with less concern for impact damage compared to rigid structures. They also can be flown by less skilled operators, which reduces training costs. Because the structures deflect and spring back to shape, no field replacement components are required. An inflatable structure can be compartmentalized to survive ballistic impacts. Also, compared to rigid aerial structures, inflatable aerial structures may have an easier transition to use in civilian airspace.
High-G launch survivability: Inflatable structures are easily packed for high-gravity (G) events such as a gun launch. The flexible nature of the technology makes them survivable.
Ability to configure the packed system to fit complex shaped volumes: The flexible components bend and fold to fit in the volume available.
Low cost for disposable or multi-use structures: Low-cost manufacturing can be employed to make disposable units. The structures can also be hardened for long-duration reuse.
Embedded technologies for multi-functionality: Electronic materials such as conductive circuits for antennas can be printed, etched or sewn on the wings. Because they can be used as flexible heat pipes, wings can act as radiators. Adaptive technologies can be added for shape morphing and wing morphing.
Low-mass technology: Inflatable structures can be designed for lower factors of safety than rigid structures because inflatables recover their shape after they exceed load limit. Therefore, lower G limits can be set. The structures can be built using lightweight high-strength textile materials such as Kevlar®, Spectra® or Vectran®.
Camouflage — low detectability: Inflatable structures can be made from radar-transparent materials, and the components can be made transparent or any color desired.
Easily configurable and scalable technology: Airfoil shape, camber, taper, thickness, aspect ratio and other parameters can be modified as required. The structures can range from gossamer structures produced from thin films to ultra-stiff bladder or restraint structures that are highly stiffened when pressurized. For highly loaded structures, it is possible to use hybrid inflatable/rigid element systems for increased structural capability.
Rigidization technology: Through the addition of specialized resins, inflatable aerostructures can become solid composite aerostructures, eliminating reliance on internal pressurization to continue load support. As they are not easily reversible, these technologies should be considered for one-time use applications.
Much of the technology employed in conventional UAV structures is similar to that used in the aerostat UAVs and airships ILC produces, in conjunction with prime contractor partners, for military and civilian use. The company’s UAV wings use the same configurations, patterning techniques, and materials as the fins that have flown on its aerostats for decades. This flight-proven technology reduces risk to inflatable UAV aerostructures. In addition, many of ILC’s LTA structures have been human-rated by the Federal Aviation Administration and are qualified to stringent requirements.
Editor's note: Dave Cadogan is director, Research & Technology, ILC Dover LP.