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Unmanned Aerial Vehicles (UAVs), commonly referred to as drones, are becoming more popular for obvious reasons. With the planes effectively eliminating the risk to the pilot, the market for these airplanes is booming around the world. In an interview, Lockheed Martin’s research engineering senior manager for advanced development programs, Steve Ericson, tells us more.
(Published on May-June 2006 – JEC Magazine #25)
AN INTERVIEW WITH STEVE ERICSON, RESEARCH ENGINEERING SENIOR MANAGER, LOCKHEED MARTIN
JEC Composites Magazine: What specific composite applications are used on drones, and on which Lockheed models?
Steve Ericson: Lockheed Martin uses composites in both primary (wings, fuselage, control surfaces) and secondary structures (edges, inlet ducts, fuel tanks) for Unmanned Aerial Vehicles (UAVs). Composite materials such as those qualified in manned aircraft are used in some LM UAV work. Other vehicles use commercially available fibreglass and/or carbon fibre for structure.
Specific composite material selection depends on factors that include vehicle size, speed, temperature environment, fuel exposure and weight. A tailored approach is generally taken on Lockheed Martin specific programmes to reduce overburdening requirements, reduce cost and increase productivity where appropriate. LM uses considerable amounts of reduced-curing-temperature materials for prototype production along with proprietary Vacuum Assisted Resin Transfer Moulding (VaRTM) and Resin Transfer Moulding (RTM) resins and fabric systems, when allowed by the operating environment of the end product.
J.C.M.: What types of composites are used and why? What advantages do they offer?
S.E.: Fabric materials used include glass, quartz and carbon fibres. Fibre material forms include woven and non-woven fabrics, tows and braids. Matrix materials include BMI, a variety of epoxy and higher temperature resin systems.
The advantages of composites are numerous, but centre around the cost of producing complex shapes at low rates with high strength-to-weight ratios at an affordable cost for our customers.
We also build composite parts with specific electrical properties, including radomes, sensor covers, and vehicle edge structures. Composites are the only way to produce these types of components.
J.C.M.: Where do you purchase the composites for the drones, and how are these composites manufactured?
S.E.: Composite raw materials are generally purchased from usual commercial sources. We have development programmes to produce materials that meet specific programme requirements or are leveraging new technologies such as nanomaterials. Hand-laid (wet lay-up) and automated lay-up techniques using prepreg materials are employed. Lockheed Martin is equipped to produce composite parts including design, analysis, and tooling for prototype and production parts. Lockheed Martin also buys some composite components built to specifications from qualified suppliers.
J.C.M.: How long has Lockheed been using composites for drones, and what is the general trend? Are they being used more or less frequently in drones?
S.E.: Lockheed Martin has been using composites in manned airplanes since its very beginnings. Airplanes like the Lockheed Vega, Orion and Sirius used moulded plywood for the fuselages and wings. Large concrete moulds were constructed and each layer of the plywood was laminated to the air vehicles’ contours. Early UAVs such as the D-21 drone (1960s) used advanced high-temperature composites in the wing edges like the A-12 and SR-71 programmes. The first LM glass fibre/ epoxy UAV intended for production was the Aquila. This vehicle started the process within LM for programmetailored, low-cost composites even though it did not make it in to production. In the 90s, Lockheed Martin and Boeing jointly developed the RQ-3 Darkstar. The vehicle was constructed largely from low-temperature-curing composites using rapid-prototyping manufacturing and tooling techniques.
Lockheed Martin continues to develop novel high-performance and cost-effective composite solutions for UAV’s. 60 years of UAV experience has included vehicles operating at low speed and altitude, all the way out to Mach 3+ at high altitude. Recent work relies heavily on large-scale integrated structures to reduce cost and weight to make UAVs affordable and high performance.
An excellent example of integrated structure is the JASSM missile where the body of the missile is produced with a braided preform with VaRTM infusion to produce a shell with integral stiffeners in one step.
We see the use of composites continuing to increase in our UAV work. With proper design, tooling and fabrication techniques, composites offer the ability to produce UAV airframes more quickly and cheaply than conventional metal structures.