Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

50 problem. “Our aim was to prevent the transfer of heat from the combustion chamber into the shaft and main bearing,” reports Cardozo. “However, neither exotic materials nor state-of- the-art surface treatments or lubricants would solve the problem. We therefore decided to address the core problem by developing an additional liquid cooling system integrated right into the heart of the engine. In so doing we removed the need for specialist surface treatments and lubricants, and created a cooling system that maintains acceptable operating temperatures throughout the engine’s power range.” With the latest water cooling system there is an impeller fitted to the non- drive end of the eccentric shaft, which is hollow. Rotron has not disclosed the precise details of the shaft’s internal design and coolant flow arrangement at this time. After the impeller has drawn coolant back out of the shaft, it is fed into the adjacent side plate, where it is introduced into a gallery that is interconnected with galleries in the other plates and the two rotor housings. Thus coolant is fed around the combustion side of the engine through galleries incorporated into all five plates/housings before exiting on the far side to the radiator. The O-ring seals between the plates and rotor housings act as water seals. The side plates carry fins that extend into the water gallery, increasing the surface area over which the coolant acts. The water gallery in each rotor housing surrounds the exhaust port exit. The concept of a liquid-cooled eccentric shaft brought an initial concern: if the eccentric shaft and the bearing are running much cooler than the rotor, will this cause a loss of tolerances between those components? In fact, it was found that the temperature of the rotor itself was also reduced, so that wasn’t an issue. The location of the rotor bearings made it impractical to measure running surface temperatures, but with the in- shaft coolant system in operation it was noted that there was a 20 C reduction in the temperature of air exiting the through-rotor cooling flow. Subsequent durability testing proved the concept beyond doubt. The liquid-cooled eccentric shaft was a breakthrough for durability, notes Cardozo. “We could get continuous high power from the engine without any detrimental effect to the main bearings. They come out silver every time – gone are the days of blued-up bearings!” This water cooling system was devised a few years ago and is now patented. It is worth noting that the small impeller on the non-drive side does all the work in terms of water circulation. Since it is firmly attached to the eccentric shaft it is always working while the engine is running. Autumn 2015 | Unmanned Systems Technology Performance of the RT600 LCR and XE engines The liquid-cooled shaft was a breakthrough for durability – the bearings come out silver every time, no more blued-up ones!