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17 working for the government and this was my first job in the private sector, when the time came to raise the money to commercialise the Greased Lightning I wanted to be able to say we already had a UAV in production.” The Hercules is an octocopter that is designed to fly only in helicopter mode. Being a simpler vehicle than the Greased Lightning, it won’t require as much money to get into production, and will serve as a test bed for a new hybrid power plant for both. However, the Hercules will have to work as a commercial product, so it will have to offer advantages over both fixed- wing UAVs and multi-rotor craft. “What operators really want is the ease of use of a multi-rotor and the endurance of a fixed wing,” Fredericks says. Battery-powered multi-rotors, he says, typically squeeze only three hours of use into an eight-hour day because of the time spent travelling to and from the work area for battery swaps. The target for Hercules is almost six hours of use, which he says will reduce an operator’s cost per unit area imaged, for example, by about 45%. The Hercules has an unusual configuration in that its eight rotors are in two rows of four, one row behind the other, and under each pair of rotors is a fairing that contributes to lift in forward flight while minimising drag in hover mode. Each pivots like a weather vane. When the Hercules takes off vertically the fairings point almost vertically down and swing back when it transitions into forward flight. Fredericks says, “I designed that reflex camber line to be statically stable, and it will pivot to whichever angle it needs to minimise drag and generate some lift.” The prototype stage Fredericks began building the first Hercules prototype in early 2016, and it made its maiden flight in the April. He also started recruiting, with former NASA intern and mechanical engineer Weston Lewis joining in the June. “Weston is doing the structural and mechanism design, running the wires and things like that,” he says. The prototype under test at the time of writing is the second. It flew for two hours and 16 minutes, unofficially beating the Guinness world record of two hours, six minutes, seven seconds set on October 30, 2015, by Spider Drone Security in Romania. The Hercules is built from off-the shelf carbon fibre components such as plates and rods. In the next prototype, the company plans to use high-modulus carbon fibre pre-preg to save weight. Fredericks says, “We are starting to iterate the design again to make our third prototype, and with that one we are going to focus on reducing empty weight. Our current flying prototype is a little overweight, but the next one will be able to fly for three-and-a-half hours.” He chose to build a sequence of prototypes to save time on analysis of different designs. “I wanted to make intuitive decisions on how to build it and then fly it,” he explains. “So we’ve been light on the analysis side and heavy on the testing side.” Further planned enhancements include an increase in Hercules’ gross weight from the current 36 lb, focusing on upgrading the propulsion system. Power comes from a DLE two-stroke petrol engine, which is to be replaced by a fuel- injected Desert Aircraft 35. As part of the reason for Hercules’ production is to develop the power plant for Greased Lightning, further engine options are planned, including a diesel, so the coupling through which it powers the generator is modular. Bill Fredericks | In conversation Unmanned Systems Technology | April/May 2017 The Hercules octocopter will spend most of its airborne time in forward flight, so the fairings below the rotors pivot freely to create lift with minimum drag