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

72 – there’s almost no discernible wear,” Bogdanov asserts. “Of course, it takes a lot more tricks than just sealing to get Wankels right in 2024. We do some things with our lubrication and our cooling, for instance, that we’ll get into later. But realising we could do our sealing by leveraging what we’d learned in twostrokes was what motivated us to start cutting metal for the RW1-300, and then the RW1-79 afterwards for smaller UAVs.” The side walls, or mid-housing plates, are also made from cast iron to ensure all surfaces exposed to combustion and exhaust have the same mechanical and thermal properties. In the RW1-300, a liquid cooling jacket in the housing protects the cast iron against the engine’s higher power combustion temperatures. Forced induction A key concern of UAVHE’s regarding Wankels was the stability of their performance across varying conditions, particularly at different altitudes and air pressures, as well as various ambient temperatures. The RW1-79 and RW1-300 are hence electrically supercharged (with no throttle plate or servo), and governed by the ECU, such that a target manifold air pressure (MAP) is maintained across the power curves of the engines. “To maintain stable MAP from idle to 9000 rpm in a road vehicle amid clutch and gearbox changes is an engineering nightmare, but in an aircraft engine with a constant load and rpm for most flight hours, where you’re really just optimising for reliability and SFC [specific fuel consumption], the eSupercharger works well enough,” Bogdanov says. “Another reason for electrically supercharging the engines is that our fuel-injection technology requires highspeed airflow to maintain the number and size of our fuel droplets. We’re trying to keep the droplet diameters below 5 microns and our intake port is relatively small, so blowing air and fuel droplets through that very quickly helps prevent condensation.” Although the benefits of mechanical supercharging have been touted in a few previous issues – such as with DeltaHawk’s DHK180 (Issue 54, February/ March 2024) or Flygas Engineering’s GAS418S (Issue 42, February/March 2022) – controlling the supercharger electrically allows the RW1s to be precisely managed for these exact air-speed requirements. “In the RW1-300, we essentially use a modified Garrett turbocharger, split in half and combined with a BLDC [brushless DC] motor, along with 10 lines of code to April/May 2024 | Uncrewed Systems Technology While the RW1-300 is liquid-cooled, the RW1-79 is air-cooled via its supercharger pulling intake air through its motor... The seals are held in DLC-treated channels, ensuring the rotor is strong and hard enough to avoid wear from the tungsten carbide against the forged aluminium We’ve taken several units of our rotary engines apart after 600 hours and inspected them under microscopes – there’s almost no discernible wear