Unmanned Systems Technology 009 | Ocean Aero Submaran S10 | Simulation and testing | Farnborough report | 3W-110xi b2 TS HFE FI | USVs | Data storage | Eurosatory/UGS 2016 report

49 Peter M Wintrich is head of development. Wintrich points out that when he set up the company, existing small displacement two-strokes were primarily for the likes of chainsaws, and exploited high rpm. High rpm is inappropriate for aviation use, in particular in terms of noise and vibration and of the speed of a directly driven propeller. “It is better to exploit higher torque with lower rpm,” he observes. Over time, cylinder fin dimensions have been altered and the number of transfer ports has increased from two to six (for certain engines), but otherwise the core technology has remained fundamentally the same. In the world of aviation, well proven technology tends to be the most highly valued. 3W’s core technology is the same throughout its current range of air-cooled two-strokes, in terms of aspects such as valving and porting. 3W does not make single-cylinder engines of greater than 85 cc displacement in view of the way in which vibration increases with cylinder displacement, hence its preference for a 110 cc engine to be a twin. With the rise of the UAV market, in 2010 3W decided to develop heavy fuel versions of some of its gasoline engines. The 3W-110xi b2 TS HFE FI (hereafter referred to as the 110xi) was one of the first, and at the outset was intended to run purely on Jet A1. It was developed in response to a customer requirement for a naturally aspirated twin-spark UAV engine that provided 10 bhp with a maximum cruising crankshaft speed of no more than 6800 rpm with port injection of heavy fuel. The customer needed this for a weight of no more than 5 kg including starter/generator, engine control unit (ECU) and fuel and ignition systems including the fuel pump, a target that was beaten by 0.5 kg. The 110xi was developed from a well- established 106 cc gasoline-fuelled twin, available in both carburettor and injected versions. That in turn was developed from 3W’s first twin, which had a 120 cc displacement and dates back to 1986. The main changes compared to the existing gasoline 106 cc twin were an adjustment of both bore and stroke plus development to allow the engine to run on heavy fuel in injected form. The initial test bench running of the 110xi was in 2010. A few months later the customer asked for the engine also to run on JP5, which proved not to be an issue. At the end of 2010, initial examples were delivered to an agent, who supplied them to an undisclosed military customer in North America. With a few hundred sold each year across a number of customers, the 110xi is now a well proven power plant. Schudt emphasises that the 110xi is a genuine multi-fuel engine, which exhibits no significant loss of performance across the range from regular gasoline through to JP8 jet fuel, with no recalibration of the ECU necessary. Indeed, no cleaning is required in the process of fuel type changeover. 3W has proved this by testing four fuels across that range side by side with the engine running continuously. “It just shook a little due to air in the line as one fuel supply canister was switched for another,” remarks Schudt. He adds that, typically, to avoid significant engine modification a UAV operator would need to buy separate engines for use with gasoline and heavy fuel. That is clearly not the case when using the 110xi. We asked Wintrich, what is the secret to this genuine multi-fuel capability? “We gained it almost by accident,” he replies. “We expected to have to make some significant changes, but to our surprise that wasn’t necessary. This 3W-110xi b2 TS HFE FI | Dossier Unmanned Systems Technology | August/September 2016 We gained this multi-fuel capability almost by accident. We expected to have to make some changes but that wasn’t necessary Rapid prototyping was used in development of the 110xib2 TS HFE FI