Unmanned Systems Technology 011 | C-Astral Bramor ppX | IMUs | Autonomous farming | UAV Turbines UTP50R | London Show report | Advanced materials | Las Vegas Expo report

21 overall because the sweep of the wings extends them behind the body. With a 4.7 kg take-off weight, the ppX airframe has an optimum cruise speed of 16 m/s (58 kph), a Vne (velocity to never exceed) of 30 m/s (108 kph) and an endurance of up to 3.5 hours with a service ceiling of up to 5000 m above sea level. The propulsion system includes a lithium- polymer battery, a brushless electric motor and a 13 in folding propeller. Structurally the ppX is based on its rTK predecessor, but features new command and control and mission planning software, as well as improvements in data processing and flight stability. Engineering challenges According to C-Astral’s co-founder, chief design officer and head of strategic r&d Nejc Trost, the principal engineering challenges in developing a UAV able to deliver such a high level of accuracy involved maximising endurance and stability for the lowest practical weight. In turn, that meant a pursuit of low drag through the BWB configuration, a combination of aerodynamic refinement and active control for stability, an all- composite construction for subtle shaping, strength, stiffness and durability, and tailored RF transparency. Further challenges included developing and testing precision electronics and maximising user-friendliness given the system’s electronics complexity. Trost emphasises that the aircraft is naturally very stable, a characteristic he describes as the first prerequisite for precise mapping, the second being an extremely precise GNSS receiver and antenna assembly. The ppX is a little larger than its nearest competitors, he says, so it can also carry more sophisticated equipment, in particular the GNSS receiver – a professional-grade device from Septentrio of the same accuracy as those installed in ground survey equipment. Achieving great precision in such a small platform also made RF shielding a big challenge. When the company was formed in late 2007, there was still much to learn about BWB aerodynamics at this scale, with studies indicating increases in endurance of 25% or more compared with conventionally configured aircraft with a mainplane, fuselage and tailplane. Trost says C-Astral was one of the first manufacturers to demonstrate such a benefit in an operational commercial small UAV. The choice of a BWB configuration also makes for an airframe that is mechanically simpler than conventional fixed-wing designs, which he regards as too complex. In 2005, before the legal formation of the company, the engineers began exploring the possibilities of the first of a new generation of autopilots on the market by designing airframes to make use of them. “The first design was a conventional aeroplane that had everything – ailerons, elevator, rudder, flaps and throttle C-Astral Bramor ppX | Dossier Unmanned Systems Technology | December/January 2017 A team prepares to launch a ppX from the standard bungee catapult. Note the remove-before-flight tags securing the cover for the pitot tube, the recovery parachute hatch and the propeller blades folded back before the motor starts