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

24 Dossier | Skyeton Raybird-3 Stepura points to its wing profile for example, which was originally based on the widely used Clark Y airfoil designed by Virginius Clark in 1922. It has a thickness of 11.7% and is flat for 30% of chord, but it has been optimised over time to better suit the small size of the Raybird-3, given that such small aircraft and their aerodynamics were not so closely researched in the early 1920s. “We also wanted great resilience and durability throughout both the hull and powertrain, to ensure the aircraft can survive back-to-back missions of considerable duration but still keeping within that 25 kg weight limit for flexible and certifiable flight operations,” he adds. “The Raybird-3 has carried out individual mission flights of 25-30 hours’ duration for some customers without problems, and can fly for longer still if we’re asked to really push it – weather and payload-induced drag permitting.” To push the endurance further, the Raybird-3 has a tractor propeller, which Skyeton’s engineers found in tests to improve overall flight efficiency by 15%, despite the widespread popularity of pusher propellers. Also, the payload gimbal is retracted when not in use to eliminate its drag profile, and many permutations of wing, fuselage and tailplane combinations were simulated and tested before arriving at the UAV’s current shape, with its downward- facing winglets and twin tail (the latter being mounted on twin booms). Skyeton’s CCO Roman Knyazhenko adds, “In pursuit of endurance and durability, we’ve also tested and iterated the system to maximise how much we can take off and land over its lifetime.” Knyazhenko explains further that he and his team studied the range of existing 25 kg catapult-launched UAVs, and found the average competing craft to be capable of between 15 and 30 recoveries before some kind of failure (such as a fault or crash) would occur. “Our Raybird-3s on the other hand consistently exceed 250 recoveries between faults,” he says. “That is a testament to the durability our engineers under our CTO Mykola Toptun have aimed for, as well as the system’s cost-efficiency in terms of minimising maintenance requirements and hence the bill to our customers. “But we know we’re also competing with helicopters for long-endurance aerial surveillance. Even so, we’ve consciously chosen not to incorporate a VTOL or hover configuration into the Raybird-3, keeping it as a catapult-launched, parachute-landing system, and we’re ready to prove this engineering decision was the right one.” Skyeton has two main reasons for forgoing VTOL transition. The first is that it estimates aerial survey helicopters, and the few VTOL UAVs capable of endurances of longer than 10 hours, hover for only 10% of their total flight time over their lifespans. The other 90% of that long-endurance survey requirement can be filled far more cost-effectively by their 25 kg UAV, and to a degree of safety that is unreachable by manned helicopters. The second is that in its own studies of flight efficiency – both aerodynamic and fuel-related – Skyeton’s engineers have found it impossible to maximise the efficiency of fixed-wing operations while including some mechanical components for enabling VTOL. According to its research, VTOL transitioning is viable only in wind speeds of less than 5 m/s. Even if these conditions can consistently be found – which is by no means guaranteed – incorporating VTOL creates heavier and bulkier airframes, to the detriment of aerodynamics and endurance. This, the company says, is the critical reason why it does not incorporate June/July 2021 | Unmanned Systems Technology The Raybird-3 has a tractor propeller and engine at the front, a payload compartment behind for retracting the gimbal, and a precisely designed composite hull We know we are competing with helicopters for surveillance but we have chosen not to incorporate VTOL or hover, and kept it catapult-launched