Experimenter

APR 2015

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

Issue link: https://experimenter.epubxp.com/i/492505

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EAA Experimenter 31 Flygas of ers self-designed high-performance cylinder heads that Stefano developed for the UAV engine described above. Two spark plugs per cylinder and improved airfl ow allow better cylinder fi ll- ing so that the performance increases by 20 percent. About 12 years ago, Stefano began with the production of mechanically driven centrifugal compressors for the four-stroke Rotax 912 engines. Over time, this has become the main activity of the small company. Stefano fi rst tuned 80-hp Rotax 912 engines for about 10 years and only recently adapted that kit to the 100-hp engines. Flygas tuning kits enhance the performance of Rotax 912 engines by 25 to 45 hp; the power boost depends on the boost (over)pressure. This overboost is limited to a maximum of 7.25 pounds per square inch (0.5 bar) above the environment atmo- spheric pressure so that the manifold air pressure (MAP) increases to 40 to 43 inches Hg. After installation of the mechanical supercharging, the 80-hp engines deliver 115 to 125 hp; the 100-hp engines increase to 132 to 145 hp. A Flygas-tuned 912 ULS engine delivers the following per- formance on the dyno: • 4800 rpm, 38 MAP, 110 hp • 5000 rpm, 39 MAP, 115 hp • 5500 rpm, 41 MAP, 129 hp • 5800 rpm, 43 MAP, 141 hp Stefano is especially proud of his construction because of the "advanced safety margins" of his tuning system. If the connect- ing belt that connects the supercharger to the engine fails, the stock 100-hp Rotax engine will deliver 81 hp. This power loss occurs mainly because of the engine's lower compression; lower compression means less developed power plus greater intake air resistance. The fresh air cannot be sucked directly through the carburetor as with the stock engines, but rather must take the longer path through the non-spinning centrifugal wheel and longer intake manifolds. The Flygas mechanical supercharging unit basically consists of an axial compressor driven by a toothed belt. The mechanical energy of the engine is used to drive the compressor, not the energy of the exhaust gases as in a conventional turbocharger application. Imagine the normal turbocharger in which the "hot section," the turbo wheel, has been replaced by a pulley that spins the centrifugal compressor wheel—the "cold section" of a turbo assembly. According to Stefano, his system has some signifi cant advantages over the turbocharger. First, the exhaust gas temperature is around 400°F lower (1,300°F instead of 1,650°F) because the engine breathes more freely (no turbo wheel in the stream of exhaust gases). The lubrication of the compressor is independent from the engine oil because a separate oil circuit with an additional oil pump is installed. No electrical or elec- tronic control for proper system function is needed. Like all power augmentation systems, the Flygas system also has some disadvantages. The mechanical drive of the compres- sor absorbs 3 hp because the energy required is taken from the fl ywheel of the engine. The engine weight goes up because the kit weighs 15.4 pounds. And the tuned engine loses the manu- facturer warranty, if it still had one. This is the heart of the Flygas tuning kit—the belt-driven centrifugal supercharger. It is the same turbocharger used in most automotive applications but without the "hot section." Flygas also is selling a fuel-injection system called Fly-Safe for the Rotax 912 engines; this setup still retains the original carburetors. The choice between fuel- injection and the original carburetors is made by pulling a red knob. These are the parts you get with the purchase of the Flygas tuning system.

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