Unmanned Systems Technology 021 | Robot Aviation FX450 l Imaging Sensors focus l UAVs Insight l Liquid-Piston X-Mini l Riptide l Eurosatory 2018 show report l Zipline l Electric Motors focus l ASTS show report

52 T he rotary-type internal combustion engine has a lot to commend it. Overshadowed by the piston engine in the automotive field, the burgeoning world of UAVs has given the rotary a new lease of life, thanks in particular to its power density, lack of vibration and reliability. Ongoing development of the technology, and improvements in materials, have overcome the rotary’s early reliability challenges. However, the fact remains that, as invented by Felix Wankel and demonstrated by him in working prototype form some 60 years ago, the established technology has various drawbacks, including an inefficient dynamic combustion chamber shape and sealing difficulties. Liquid- Piston has developed a new type of rotary engine that overcomes those and other disadvantages. Liquid-Piston’s rotary is not of the Wankel type; rather its innovative design in effect turns that established approach inside out. It offers the same benefits with a new type of combustion system that promises far greater efficiency. Its combustion chamber shape is far more effective, and its unique operation further enhances performance. To date, Liquid-Piston has developed two versions of its new-generation rotary ‘X’ engine, both of which prove that its concept is fully functional and well-suited to UAV use. Here we probe one of those – the small displacement, spark ignited X-Mini – to reveal the clever technology behind this innovative naturally aspirated, four-stroke power unit. The basics As with a Wankel, the Liquid-Piston rotary engine has a rotor spinning within a stationary housing, the combustion occurring between those two elements promoting its rotation. That force applied Ian Bamsey investigates this new take on the rotary that challenges Wankel designs on efficiency and performance Inside-out thinking August/September 2018 | Unmanned Systems Technology