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6 Mission-critical info for UST professionals Platform one April/May 2017 | Unmanned Systems Technology Hybrid UAVs are usually complicated because they combine mechanisms from at least two other types of craft. However, Electronflight’s Tilt Rotor/Separate Lift and Thrust (TR/SLT) hybrid – which is part octocopter, part tilt rotor – is being developed with simplicity in mind (writes Peter Donaldson). A tilt rotor is a helicopter/fixed-wing hybrid, while an SLT is a hybrid multi- rotor/aircraft, so the TR/SLT concept combines four aircraft types. The simplest variant will have six, twin- blade electrically driven rotors, two fixed to the fuselage on vertical axes to provide lift only, the other four in pairs mounted at opposite ends of struts that pass through each pivoting wing tip/nacelle at right angles to the wing’s chord and its span. Differential thrust between the rotors will provide the tilting force that moves the rotors from the vertical to the horizontal and back, eliminating the need for actuators. All the rotors will provide lift in vertical flight, while in forward flight the rotors on the fuselage will be feathered, leaving the wing to provide lift and the tip rotors the thrust. According to the company’s Joe Renteria, the TR/SLT is potentially more efficient than a typical SLT vehicle in both flight regimes. “During VTOL, the dedicated vertical lift rotors are augmented by the thrust from the nacelles, so the rotors can be made smaller and lighter to reduce dead weight and drag in forward flight,” he said. In its simplest version, Renteria said, the TR/SLT could have only two moving airframe components – the wing tips and nacelles. “The biggest challenge is in the software,” he said. “There is nothing similar to the TR/SLT hybrid on the market, and while any variety of flight controllers would be able to do the job, the software just does not exist.” The main body of the aircraft and each tilting nacelle will be individually stabilised around the pitch axis, but must also work together to provide roll and yaw control for the vehicle as a whole. “Everything required has been done before though, so it is really just a matter of putting old code elements into a new combination,” Renteria said. Target markets include surveillance, reconnaissance and cargo delivery. Renteria is building a simple prototype, which he plans to fly later this year. Airborne vehicles Is it a ’copter, is it a plane? The TR/SLT’s developer says it will be simpler and potentially more efficient than other hybrid craft