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98 PS | FusionFlight VTOL UAV A part from a few fighter aircraft that entered operational service, such as the Harrier family and of course the F-35B Lightning 2, VTOL aircraft that use vectored jet thrust to get off the ground, hover and transition to and from forward flight have been confined to the realm of r&d (writes Peter Donaldson). UAVs that use this technique are even rarer, but FusionFlight’s JetQuad AB5 is one of them. The designers of those fighters chose different power plant configurations to achieve the same result. The Harrier has one engine, two exhaust nozzles at the back and two nozzles that tap air from the compressor at the front. The F-35B meanwhile has a single engine, with a vectoring exhaust nozzle at the rear and one engine-driven lift fan, again only for take-off and landing. The JetQuad has a different layout again. It uses four microturbine engines, one on each corner and each with its own curved vectoring nozzle. Four jet engines in a vehicle with a take-off weight of just 130 lb might seem to be a recipe for a toy with neither a useful payload nor worthwhile endurance, but the company’s performance figures indicate that this is not so. FusionFlight claims a payload of 40 lb in a vehicle that weighs 50 lb dry, with endurance figures of 15 minutes in cruise flight and 30 minutes in loiter mode, along with a mission radius of 25 miles – numbers at the upper end of what most electric multi-copters offer these days. While those figures are not particularly remarkable in themselves, when combined with the JetQuad’s speed and altitude capabilities – the company claims a cruise speed of over 300 mph and a theoretical ceiling above 30,000 ft – it becomes clear that the vehicle offers something very different and possibly unique in a UAV that is small and light enough to be carried by one person. The JetQuad AB5 measures 4 ft long, 4 ft wide and 2 ft high. The centrally mounted fuel tank holds 5 US gallons (40 lb) of diesel, which is readily available almost everywhere, very quick to replenish and much more energy dense than any battery. These factors compensate to a useful extent for the jet engines’ thirstiness. The four engines together burn fuel at a maximum rate of 0.3 US gallons per hour, and produce a maximum total thrust of 160 lb for take-off, giving a thrust-to-weight ratio of 1.2, according to FusionFlight’s figures. Although still a developmental vehicle, the JetQuad has the look of a prototype. The company says the technology can be scaled up to use larger aviation- certified engines, while its boxy, carbon fibre fuselage could be replaced by a smoother lifting body with better aerodynamics that could improve its payload, range and endurance. Whether the JetQuad turns out to be little more than a curiosity or creates a whole new segment of the UAV market remains to be seen, but jet VTOL is an idea that will not die. Now, here’s a thing “ ” April/May 2020 | Unmanned Systems Technology FusionFlight claims a cruise speed of more than 300 mph and a theoretical ceiling above 30,000 ft for the JetQuad AB5 (Courtesy of FlightFusion)