68 Developing the J-1 The concept behind what eventually became the J-1 started in laboratory research at the University of Maryland; first theoretical work, then practical work, all aimed at better understanding how pulsejets operate, down to their most granular chemistry and physics. “Those were small testbed engines, maybe 1.5 ft in length or so, and propane-fuelled initially. We gradually stepped up to experimenting with bigger engines, maybe a few feet long, and still propane-fuelled, but still scientific study articles, rather than being platforms meant for optimising performance,” Maqbool recounts. “Those shed a lot of light on how pulsejets worked and how they might be engineered towards different ends. Then, somewhere around 2016-17, we decided to cross the valley into a full-scale pulsejet device to see if we could make something that would generate meaningful, real-world relevant quantities of thrust.” In 2015, Wave Engine had already formed and been incorporated, although its real activities (as a company spun out of the University of Maryland) started after some point in 2017. To form blueprints for prototyping such a system, the company at Maryland first canvassed virtually every prior pulsejet engine design and item of literature to review and extract what made the most sense. Rounds of continuous, iterative optimisation followed, with hefty reviews over points of geometry, dimensions and physics. In a major step forwards, using their basic understanding of the fluid dynamics, combustion, acoustics and other processes happening inside the engine (Maqbool having published two scientific papers on the matter), and the fundamental theory that all that entailed, Maqbool and his team were able to develop some computer numerical modelling software from the ground up. That software helped shed critical light on how the engine ought to be shaped, and how changing input or output factors would influence the design requirements. “But, as with all practical projects, you can get incredibly helpful theoretical answers out of simulation software, but it’s never going to be perfect, because you eventually have to turn your prototype device on and start seeing what the simulation didn’t account for,” Maqbool says. “The J-1 today has genuinely come from equal parts literature review, theory-based simulation work and experimenting with physical prototypes.” In addition to the shortcomings of the Argus As 014, which kept it from gaining popularity in crewed aircraft after the end of World War II (and other nations’ pulsejets of the era were held back for similar reasons), Maqbool and his colleagues identified two more critical engineering targets necessary for modernising pulsejets for the requirement of UAVs this year, which occupied much of the past seven to eight years of development. “One was optimising the engine design to start and operate on liquid fuel, because despite the inherent multi-fuel nature of pulsejets, most past designs were started or sometimes even operated entirely on propane,” Maqbool explains. “For a practical aerospace application, running entirely on liquid fuel was critical to producing a respectable amount of power. That was one of the first things we aimed for when we started making a full-scale engine after 2017.” As a result, the J-1’s combustion cycle has been engineered for running on October/November 2024 | Uncrewed Systems Technology Developing the J-1 involved considerable literature review, software simulation and testing of prototypes to overcome the dearth of modern data on pulsejets …a full-scale pulsejet device to see if we could make something that would generate meaningful, real-world relevant quantities of thrust
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