Issue 55 Uncrewed Systems Technology Apr/May 2024 Sellafield’s UAV equipment l Applied EV Blanc Robot l Battery tech l Robotican’s Goshawk l UGVs l UAVHE RW1 rotary l Roboat UVD l Autopilots l Arkeocean UVD l UMEX 2024 l CycloTech UVD

UAVHE RW1 rotary | Dossier create a supercharger that self-balances for MAP,” Bogdanov explains. “On the RW1-79, we needed to further minimise the delay between accelerations or decelerations in the impeller rpm, and corresponding changes in MAP, so we engineered our own system there.” The supercharger’s impeller is CNCmachined from a lightweight, forged aluminium alloy, which Bogdanov says is specified for turbine wheels. The RW1-300’s impeller is roughly 5-6 cm in diameter, while the RW1-79’s is 2-3 cm. “In both engines, we consume up to half a kilowatt of power to run the supercharger, but we’re able to generate an easy surplus of electric power from the 11 kW generator anyway, and because we maintain a positive pressure from the intake port to the combustion chamber, we get benefits in fuel atomisation, SFC, thermal stability and reliability that more than pay for that power usage,” he notes. Rotor cooling The intake is the key contributor to the RW1 engines’ rotor cooling function. This is a perennial and arguably underappreciated aspect of successful Wankel design, as insufficient rotor cooling can rapidly lead to engine failure (as the combustion chambers and their rotors’ needle bearings are typically only millimetres apart). To date, the challenge has been resolved quite differently by each Wankel engine manufacturer featured in this publication. In the RW1-79 and RW1-300, the intake port is a rectangular opening on one of the sides of the housing’s end plates, but the ensuing air channel does not go directly into the Wankel intake chamber. Instead, air is routed through a lemonshaped aperture in the middle of the plate and passes into the apexes of the rotor. Before doing so, injectors for the first stage of fuel spray, as well as oil injectors, both sitting in the intake channel, dispense their fluid droplets into the air flow. Hence, the rotor is charge-cooled in a method that bears a small resemblance to Rotron’s approach to rotor cooling in its naturally aspirated RT600-LCR (Issue 49, April/May 2023), although it now leans towards its RT600-HC for its use of a Venturi-style exhaust ejector to increase the speed with which charge moves through and cools the rotor. As for the RW1 engines, once the supercharged air-fuel-oil mixture enters the rotor apex, it makes a rotation loop, lubricating and cooling the inner wall of the rotor, as well as the main bearing, and the internal and stationary gears. “Inside the ‘pocket’ of the rotor’s inner chamber, centrifugal force presses and accelerates the oil and charge, pushing into an array of very small channels, CNCcut about the apex seals and treated with diamond-like coating [DLC], so those are cooled and lubricated too. Then the mixture exits the rotor through a bypass channel and goes into the combustion chamber. We heavily CFD-optimised the mixture path loop so combustion occurs at an optimal front,” Bogdanov says. “DLC isn’t cheap, but it ensures the rotor is strong and hard enough at the points where it holds our apex seals. Those channels exhibit no measurable wear after hundreds of hours of operation, despite tungsten carbide being one of the hardest substances manufactured today.” Given that another perennial issue of Wankel engines is internal oil 73 Uncrewed Systems Technology | April/May 2024 ...with that air then being distributed into the ribs about the mid-housing