Experimenter

MAR 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/471466

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EAA Experimenter 33 design? "It's my design choice. Some people will like it; some will not." Four thousand man-hours went into the crank design and analysis. All that weight saving, improved cooling, and mod- ern design and materials mean little, however, if power doesn't go up, and power comes from the amount of air the engine can efficiently process. The high-performance camshaft's new profile design results in higher lift; the cam also has adjustable timing gears to allow setting the optimum timing. The aluminum "pressure recovery plenum" with integral tapered intake tubes and electronic injection fuel rail aids this mission while reducing weight. The inlet is in the standard position for ease in retrofitting and can be either vertical or forward facing. As the plenum has two options for servo location, the unused location mounts a pop-off valve to save the intake in the case of a backfire. It fits closely under the engine, designed to complement the new sump. Port, combustion chamber, and cam profile are an integrated system and cannot be designed in isolation. Higgs noted, "When I designed the components for the AX50 series engines, these were all considered as one, not as separate issues." High inlet charge density increases inlet charge vol- ume, increasing performance. Higgs explained, "With an increase in airflow tumble in the combustion chamber, we can improve the mixture stability. This improves the engine's knock resistance." Then power can be increased even more. Airflow depends primarily on two complementary fea- tures; port design and cam profile mated to ACE's compu- tational fluid dynamics capability rendered a design with high flow and low port losses, increasing valve flow area to complement high flow ports. The extent to which the intake system packs large volumes of high-density air into the combustion chamber determines what engine guys call "volumetric efficiency," or VE. Higgs added perspective: "For comparison, a stan- dard engine has about 85 percent VE; our racing engines produce over 114 percent VE." The new sump has two iterations by design, one being a simple replacement with fitting locations to allow con- nection of a Christen Eagle oil kit to the system. The sec- ond iteration is a full dry sump conversion with scavenge pumps to reduce "windage" losses and allow continuous inverted flight. New mechanical technology is enhanced by parallel new material technology. The ACE engines prefer unlead- ed fuel, but they can use 100LL avgas. Higgs cautioned, "If you use leaded aviation fuel, you are stuck with using traditional aviation oils and their limited service life. If you use unleaded fuel, you have several fully synthetic oil options." Detail of cylinder base, with lands for spherical hold-down fasteners. The 409's crank size is apparent when it's in the case. Micro-polishing on this piston pin makes the best use of modern lubricants.

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