3W-International exhibited the new 3W-180 SRE hybrid Wankel engine at Xponential in May 2017. Six months on, CEO Karsten Schudt reflects on the introduction of the new engine.
The 3W-180 SRE hybrid Wankel engine is unique in the drive technology for UAS. The engine features 180 ccm and a short-engine mass of 6.8 kg. Its high-power version achieves 38.5 hp at 7500 rpm (rated power is 28 hp at 6000 rpm). A 5.66 hp/kg power-to-mass ratio with a consumption of 340 g/kW at full load results from this. The hybrid system, which feeds in 15 kW for a time (e.g. 30 s to 60 s) independently of the storage systems capacity, is unique. This additional power can be drawn upon when, for example, starting a helicopter or during the acceleration of a fixed-wing aircraft.
Since the engine isn’t sold as an individual engine, but instead only as a complete drive unit, initial customer projects are now approaching completion. “The engine must be adapted exactly to the UAS in order to optimally extract the former’s power. This time we’re working closely with our customers”, explains Schudt.
The Wankel engine offers a number of benefits for many customers. Its construction is compact with few moving parts. The degree of mechanical effectiveness is therefore favourable since there are few friction losses. The compact construction enables greater power density with light weight and modest space requirements. Displacement is smaller compared to other internal combustion engines. Nonetheless, the Wankel engine offers high power and torque with very low-vibration engine operation. In contrast to the Otto engine, the Wankel engine consumes less fuel at high rotational velocity and can be driven with both gasoline and Heavy Fuel (HF).
A number unmanned helicopter manufacturers contacted 3W-International in the months following the initial launch; helicopters require high rotational speeds to climb and hover, making the engine an ideal option. “This hybrid system, as well as the very good power-to-mass ratio, opens up entirely new possibilities for us”, says Schudt. “It’s precisely the high power with low mass and consumption that render the engine especially interesting for helicopter applications. Specific requests are on the table and we assume that we’ll implement a few of them in 2018”, confirms Schudt.
The engine is in demand for military applications, where noise levels are an important consideration. “Customers complain that noise reduction for Wankel engines is too involved. Through our own development capabilities, we’re able to develop silencers, among other things, for each engine that comply completely with each customers’ specifications”, says Schudt, describing the development portfolio. Observing silencer volume for the engine is particularly important here. “Otherwise the muffler diminishes the engine’s power”, continues Schudt.
As such, the ideal engine-silencer combination is created for each engine, to optimise the silencer’s effectiveness without diminishing the engine’s power in the process. Rotational speed in operation is crucial in this connection. “This is one reason why we work closely together with our customers during the engine’s initial integration. Our customers very much appreciate the fact that they benefit from our experience and in part realize more rapid project implementation”, says Schudt.
3W-International has also received requests from outside of the UAS industry. For example, using the engine as a generator system for hovercraft, for construction machinery, use at large events, in civil protection, and on large construction sites. Using the Wankel engine as a flexible generator would ensure the power supply when the actual drive motor isn’t being used.
“We’re glad that the engine has a broad application spectrum and can be used in a multitude of vehicles. It doesn’t matter to us whether it finds application as a drive or as a power generator”.