65 The J-1 engine is the first off the production line from Maryland-based Wave Engine, and it has been designed with UAVs in mind; specifically, UAVs with MTOWs of up to 200 lb (90.7 kg). In visual terms, the system presents exactly per the mechanical description above: two metal pipes, a combustion chamber, an ECU and some fuel-management parts (as well as a spark-ignition system). In terms of performance, it produces thrust up to 53 lb of force (24 kg of force; 236 N) and has a thrust-specific fuel consumption (TSFC) of 54 g of fuel per kilonewton-second (g/kN.s), with an operating throttle range of 55-100% of maximum thrust. It weighs 7.5 kg and measures 163 x 32 x 14 cm. Extra specifications are either in the works or being finalised through benchtesting. Jets, not detonations As part of understanding pulsejets, it is important to briefly distinguish them from pulse detonation engines. The latter have been discussed significantly across aerospace over the past decade, but operate based on a phenomenon termed ‘detonation’ in which the speed of the chemical reactions are equal to or faster than the speed of sound. By contrast, a pulsejet such as the J-1 operates using ‘deflagrations’, meaning that its combustion reactions are slower than sound. Therefore, pulsejets are a simpler type of engine, particularly from a combustion perspective. To understand the benefits of a pulsejet engine, it is best to compare it against a gas turbine, given that both produce thrust effectively using jets of hot air and are generally meant for high-speed flight, rather than the slower, longer-endurance flights of Ottocycle engines such as reciprocating or rotary engines. Gas turbines, whether for UAVs or crewed aircraft, are expensive devices composed of a small number of highly complex and costly metal parts; their expense coming not only at the point of purchase but also in running maintenance costs. These expenses rise when trying to develop gas turbines for smaller UAVs, as the components become more complex and expensive to manufacture the more they shrink, and the thermal efficiency (hence fuel efficiency) of gas turbines drops dramatically as the engine design gets smaller. However, pulsejets are mechanically simpler than piston and Wankel engines, using very few parts, all of which are geometrically uncomplicated to manufacture en masse. This makes them relatively inexpensive to own and operate (albeit with a SFC still higher than that of reciprocating and rotary engines, although as suggested the use case is notably different for such engines). “Historically, pulsejets achieved their greatest practical success during World War II, powering the German V1 flying bombs, because they were high-speed, cheap, and mass-producible power plants,” Maqbool recounts. “The reason it didn’t achieve much success afterwards, especially in commercial applications, was because it used a mechanical valve to seal the combustion chamber’s pressure during ignitions, which wore out after maybe 45 minutes, and that was the lifespan of the engine. That ruled it out of pretty much all passenger aircraft, and a lot of defence aircraft too.” Wave J-1 | Engine dossier Historically, pulsejets achieved their greatest practical success during World War II, powering the German V1 flying bombs Uncrewed Systems Technology | October/November 2024 Pulsejet engines such as the J-1 are among the most mechanically simple in existence, consisting of two pipes joined by a combustion chamber
RkJQdWJsaXNoZXIy MjI2Mzk4