Unmanned Systems Technology 038 l Skyeton Raybird-3 l Data storage l Sea-Kit X-Class USV l USVs insight l Spectronik PEM fuel cells l Blue White Robotics UVIO l Antennas l AUVSI Xponential Virtual 2021 report

26 VTOL. Since the Raybird-3 can fly for tens of hours, the company typically has a wide range of choices over where it can launch and recover the vehicle, requiring only that conditions are viable for landing with a parachute. “We’d also lose reliability with VTOL, because we’d probably be relying on four electric motors that could fail owing to overvoltage, a loose magnet or bad weather, and then our ability to land safely would be compromised. By comparison, our catapult and parachute mechanisms are very simple and reliable,” Toptun adds. The company estimates that around 80% of the Raybird-3’s subsystems have been engineered in-house, although components have been selected from a wide range of suppliers. For example, the autopilot has largely been designed and produced by Skyeton engineers, as has the overall comms architecture (in terms of simulating and integrating antennas, coax cables and RF components). “And because customers’ data and survey requirements change from one mission to the next, we’ve already integrated and used 12 different payload sensors, as well as a variety of subsystems. For example, if a customer is a civil organisation, it doesn’t need a military-grade inertial sensor,” Knyazhenko observes. “It makes a big difference in operating costs, and allows us to price more reasonably for each user. Or, if you’re just doing photogrammetry for mapping, you don’t need an HD video encoder, let alone a gimbal.” These subsystems are laid out with the propeller and powerplant at the front, with the payload compartment and mechanism behind, followed by the fuel tank compartment and the major part of the wings attached either side of this section. Behind that is a compartment for avionics, including the core RF systems; the parachute storage and mechanical systems are fitted in the rear of the fuselage. With this architecture as a basis, Skyeton has successfully flown the Raybird-3 in temperatures ranging from -25 to +45 C, and launched from altitudes of 3.5 km above sea level – unusual for small UAVs, given the low air densities at such heights – without any fundamental changes or repairs being needed. Hull design Extensive software simulations were key to optimising the shape and thickness of the hull material to endure repeated catapult launching and parachute recovery, and to optimise hull aerodynamics. More than a year of research was performed to ensure the right layering, stitching and angles of composite materials in the hull. A mixture of carbon composite, fibreglass composite and aramid composites have been used throughout the structure, as well as some metal in the catapult connection points on the undercarriage and some Kevlar in the tail. Although Skyeton won’t disclose exact details, Toptun notes that some sections of the aircraft have eight layers of different materials to strike the right balance between strength and weight. “We launch with around 10 g of force, sometimes more, so we have to get the hull material right, as well as the connection and fit between the hull’s parts,” Stepura says. “We connect the two wings to the body by sliding them onto spar-like joints protruding from the fuselage, and then the tail booms’ carbon rods insert into the wings. With a half-turn locking mechanism on each wing securing the booms and joints together, swapping out wings and tails takes around 6 minutes.” Powertrain The Raybird-3’s powerplant is a GF40 engine from OS Engines (the GF40U-FI version of which was discussed in UST 23, December 2018/January 2019). It is a 40 cc system running on unleaded gasoline, which produces a peak power of 3.8 bhp (2.8 kW). “Based on our research, we found the GF40 was the best for our purposes,” Toptun says. “It was very important for us to have a single-cylinder, four-stroke engine to get a low vibration frequency, because that lends itself really well to keeping a stable payload and hence a stable output of high-resolution imagery. “We’ve often heard from our customers, after they’ve used UAVs from across the market, that they’ve had problems with the picture quality, so in addition to making sure we got the engine June/July 2021 | Unmanned Systems Technology The powerplant is a GF40 from OS Engines; using a four-stroke, single-cylinder spark- ignited engine was key to minimising vibrations that could affect payload image quality