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21 “I still believe the idea is good though, because a major problem with a tilt-rotor is that the downwash of the propellers hitting the wings of the machine when it tilts creates moments that are very difficult to control. But in this configuration, all the downwash is free- flowing and it doesn’t touch the wings.” Tourn regards Lariviere as a mentor, from whom he learned the value of always looking for new ideas in aeronautics. One of these turned out to be the E Yo Copter, which is now the focus of his efforts as inventor, financier and manager. “I have been involved in international marketing, negotiating hundreds of franchise or licence agreements, partnerships or acquisitions worldwide for more than 50 years,” he says. “All the skills and insights I have acquired have become useful in the development of my drones. “At the age of 78, I have a new challenge to address in bringing E Yo Copter to government as well as commercial attention.” The vehicle is Tourn’s concept, although he says several engineers did the detailed design calculations. Besides Tourn, there is currently one full-time engineer, Joan Goyeneche, who reports to him and who did the design work on the current configuration. Supplier support “Sometimes I feel lonely reporting to myself,” he jokes, acknowledging however the support of several outside engineers and organisations. These include Markus Zipperer and Roman Kulosse, president and production director respectively of JetCat jet engines; president of industrial machinery company AMECA Max Mandrioli; managing director of Volz Servos Phillipp Volz; Stefano Baiardi, co- owner of SAB Helidivision, which makes the rotor blades; and Embention Veronte, which supplies the autopilot. After the post-tsunami inspiration, he had the basic concept worked out by 2007. He filed the first patent in 2008, the second in 2015 and there are more to come. July 2014 saw the maiden flight of the proof-of-concept vehicle, then named Heli-Lift, at JetCat’s premises in Ballrechten-Dottingen, Germany. These days the vehicle, designated the E Yo 200-05 Experimental, embodies the current configuration. That includes a fuselage combining welded aluminium tubes and carbon fibre reinforced plastic (CFRP) box sections, a JetCat P200 engine that turns the rotor by ducting its exhaust gases through Inconel thrust pipes set below and at 90 º to the blades, and the two CFRP blades. This aircraft, Tourn says, has demonstrated excellent flight characteristics. The company is now fine-tuning the thrust pipes, also known as hot line ducts, to achieve maximum thrust and payload. Its successor now under construction is designated the E Yo 550-01. It includes improvements such as the more powerful 550 N thrust P550 Pro engine from JetCat, a new composite structure that uses high-modulus carbon fibre, ceramic exhaust ducts for better resistance to high temperatures, a new turbine-style electrically powered yaw control thruster and an improved autopilot. This is the version that Tourn plans to present to the European Aviation Safety Agency by the middle of this year. Between the first prototype and the latest design, much has changed, he says, adding that all the parts have been swapped or modified at least three times in pursuit of greater safety, redundancy, performance and payload. “Each day is a voyage of discovery,” Tourn says. “We started with an ugly aluminium frame, exposed wires and add-ons, went through various tail boom designs, suffered overheating exhausts, vibration, resonance and poor payload to achieve the current machine. It uses the most sophisticated materials, needs no tail boom and carries a higher payload.” The configuration presents several engineering challenges. These range from starting the jet engine in its vertical position, managing radiative, conductive and convective heat flows to finding the right balance between internal and external drag in the rotating thrust arms. For example, the thrust arms need to be long enough to keep their hot exhaust from impinging on any parts of the rotor system, controls or airframe that might be damaged, but without being so long that the internal drag robs them of too much thrust. A new NACA profile now shapes the rotating arms to minimise their external drag. Jean-Claude Tourn | In conversation Unmanned Systems Technology | February/March 2018 Artist’s impression of an E Yo Copter, named for its electronic yaw control system, with an underslung load