Suter Industries | Dossier engine inputs, as well as empowering real-time calibration work. “The fourth screen isn’t always activated, but it typically shows our combustion analyser. Mainly during development, we’ll instrument an engine with some special pressure sensors in the combustion chamber to gauge pressure at every 0.1° of crank rotation, giving 3600 points of pressure per cylinder per rotation,” Giussani says. “All this data helps generate performance indexes of each engine – particularly at the start of combustion, mid-combustion, end of combustion, on combustion pressure and fluctuations thereof, knock behaviour – to understand how best to minimise losses and unwanted behaviour.” Additional monitors can be used for various tools such as fuel ancillary analysers, battery testing software and electric motor analysers for hybrid powertrains, with Suter’s test equipment portfolio including two battery simulators, one capable of outputting up to 100 kW at 1000 V, and the other capable of 250 kW. Since it began operating, Suter has consistently partnered with Kristl, Seibt & Co Gesellschaft (K&S) in Graz, Austria for all of its testing machinery and tools, including the design, manufacturing and configuration of all its dynamometers. “When it comes to something like testing equipment where precision in everything is absolutely vital, then it’s equally important to work with a partner who has a similar size, agility and culture to yours,” Giussani says. “We don’t make the kinds of engines that have existed for 100 years; we work in motorsport and uncrewed aviation, where you have to push the envelope to keep your customers. That means we’re often testing our engines to lengths or parameters that are beyond what has been done or at least documented before, which triggers unpredictable outcomes. So we need testing cells and equipment able to handle and measure that sort of thing, K&S’s dynos and sensors have always done so well.” From air to water Development of the water-cooled TOW 288 was pursued to fulfil integration cases in which the engine load runs independently of air-cooling performance (when coming directly from airspeed and propeller speed). Specifically, Suter had been asked for a version of the TOA 288 suitable for powering a helicopter. Traditionally, various factors prevent helicopter prop-blade downwash from sufficiently cooling the engine. For instance, helicopter engines tend to either have a shroud or fairing that blocks direct air flow from the rotor above (and in many UAV helicopter applications, the engine is installed where the cockpit of a crewed helicopter would be located, making propeller-derived cooling impossible). Additionally, the use of a variablepitch propeller to hover puts the engine at full load when there is zero forward movement through air, unlike in fixedwing aircraft, which would typically move fast through air and thus be exposed to heavy cooling while at full load. “To resolve that, one can either make a forced-air cooling system or make the full swap to a water-cooled version of one’s engine,” Kehe says. “The former option is less complex in terms of the design and engineering steps needed, but we went with the latter, because in principle you can get significantly more power out of a watercooled engine than an air-cooled one, and cooling with water-glycol makes your engine more thermally stable. “Additionally, we’d studied many cases, including some six-cylinder helicopter engines where they used forced-air cooling, and we saw that the blowers necessary for sufficiently blasting the cylinder heads with air actually took quite a bit of power to function, compared with how those same engines were configured and run on fixed-wing aircraft. So, contrary to what you might expect, the forced-air approach is not always more power-efficient than liquid cooling.” As indicated, the TOW 288 has the same combustion-chamber geometry and displacement as the TOA 288. Suter’s r&d for the liquid-cooled engine consisted largely of designing a water jacket around the cylinders, which took the place of the TOA’s aluminium fins. The jacket design and flow paths are conventional, and uncomplicated by Kehe’s description. While a liquid-cooled four-stroke can be prone to hotspots 73 Uncrewed Systems Technology | February/March 2025 The testing engineers watch multiple monitors, which display engine operating parameters, the test profile under way, the ECU software and, potentially, further useful tools
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