112 propulsion-system behaviour and responses to control inputs. Dynamic inversion is a technique that approximates such nonlinear dynamics with a set of linearised equations to make control easier. The resulting control laws generate commands based on the desired trajectory and the aircraft’s current state. They are designed to provide robustness against uncertainties in the system and disturbances encountered in flight, relying on feedback control that involves continuous measurement of the aircraft’s state, comparing it to the desired state and adjusting the control inputs to minimise the difference. CycloTech is using a model-based controller design to develop its flight control algorithm. “Model-based controller development allows detailed tests and verification in simulation; namely, software-in-the-loop testing and hardware in the loop testing on different levels. Furthermore, the pilots can fly the aircraft directly in a flight simulator,” says Kinast. The company has been working on flight dynamics for about four years with the University of the Federal Armed Forces in Munich, which Kinast describes as very fruitful for both sides. “Through that we are able to combine modern flight-control theories with the CycloRotor technology in the FCS [flight control system] – right from the start in the initial design and during its improvement over time.” Materials and structure The primary structure of the airframe consists of a layup of prepreg carbon fibre-reinforced polymer. The loads from the four CycloRotors are transferred to the structure through a suspension system with integrated damping capabilities. The landing gear is a conventional, skid-type design, similar to a helicopter’s landing gear. The only metals in the airframe are aluminium and titanium, used for inserts, brackets and fasteners. With a maximum take-off weight of 85 kg, Bumblebee 2.0 is designed as a flying testbed for the company’s CycloRotor technology and is operated with a visual line of sight. Testing times Hofreither reports that Bumblebee 2.0 is making good progress in its test programme, having successfully completed a series of dynamic bench tests, along with free flights indoors and outdoors. In the flight tests it has demonstrated its ability to take off, achieve a stable hover, manoeuvre effectively, and land smoothly and precisely. He adds that the team has optimised the vehicle’s performance via an iterative, incremental approach to testing, logging more than 750 flights. Rigorous data collection during the flight tests has provided valuable insights April/May 2024 | Uncrewed Systems Technology CycloRotors are built from carbon fibrereinforced polymer and supported at both ends. The blades themselves, along with the pitchchange mechanism, are the most highly loaded components (Image courtesy of CycloTech) Bumblebee 2.0’s role is to expand the flight envelope, demonstrate decoupling of the pitch axis from the flight direction, and show off its capabilities to the public and industry (Image courtesy of CycloTech)
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