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

42 Dossier | Rotron RT600 UAV rotary engine Cardozo recalls. “That led us to establish Rotron as a dedicated rotary engine company in 2010.” The current Rotron engines have a similar geometry to the Norton rotary engines that were based on an original Fichtel Sachs engine design from Germany, notes Cardozo. “Aside from having a similar geometry, the rest is all a development,” he adds. “Our engines were inspired by Norton’s renowned rotary racing successes in the late 1980s but they are now lighter and smaller, with an even higher power-to-weight ratio, and they’re also more reliable.” Rotron makes a number of variations all based on core proven geometry and timing gear profiles but varies the width of the rotor. It offers single and twin versions, gasoline and heavy- fuel engines. Each application of the specific variant is individually designed for the given UAV platform. Here we will consider both the LCR (Liquid Cooled Rotor) and the XE (Exhaust Extractor) versions of the Rotron RT600 twin-rotor gasoline engine. Rotors and housing In the Rotron gasoline engines the rotor has an internal bush that forms both the outer race of the main needle roller bearing on which it runs and the gear that meshes with the stationary gear. The bush is pressed into an outer component which is then CNC machined in-house into the rotor shape. The final operation is to cut the timing teeth in the bush to form the rotor gear. To avoid the danger of cracking, this gear doesn’t want to be as hard as the bearing surface formed by the bush, so tricky heat treatment is involved. The manufacturing process involves induction hardening of the bearing race only. Cardozo notes that the tolerance between the rotor gear and the stationary gear with which it meshes is absolutely critical in terms of durability. For this reason Rotron keeps a selection of stationary gears so that it can individually match each pair. The combustion surfaces of the rotor are left uncoated. The combustion chamber is formed as dual pockets. Aside from the main combustion chamber recess pocket – and overlapping its leading edge – there is a small, shallower pocket that acts as a pressure relief area. The rear of the main pocket is carefully shaped to avoid charge getting trapped there and causing detonation. The gasoline-fuelled rotary isn’t otherwise prone to detonation. Rotron wire-erodes the surface finish of the trochoid surface, to which Poeton applies a nickel silicon carbide coating. Running against that, the rotor apex seals are investment cast from an alloy that is predominantly iron but has many other critical elements, including copper and titanium, the precise recipe undisclosed. The upshot is a very hard alloy that is now well proven in this application. Each apex groove contains a seal that is in two pieces, with an angled gap Our engines were inspired by the Norton successes in the late 1980s, but they now have a higher power-to-weight ratio and are also more reliable Autumn 2015 | Unmanned Systems Technology Exploded view of the RT600