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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Page 11 of 32

12 Vol.4 No.4 / April 2015 A BIG BORE RANS SUPER S-7S This was not Hal's first trip to Oshkosh or his first RANS S-7. He attended AirVenture ten years ago with a RANS S-7 (a short-tail version) but stayed in the homebuilt camping area. Before the RANS, he flew a Kolb FireStar. His new RANS S-7S was completed in 2010, but it was not initially Rotax powered. Hal is a diesel mechanic, and it made sense that he should have a diesel airplane; so he planned for a Gemini diesel. However, when the new Courier neared completion, Gemini engine deliveries were delayed, so he installed a Subaru engine instead. Soon after that he began working on a big bore conversion for Rotax 912 engines with Wayne Flemington of Southland Rotax in Winchester, California. Hal is a machinist and an engine builder who, in his day job, runs a field service truck for Joy Global, a company that builds and services mining equipment. His truck is a rolling repair and machine shop that can handle tasks most of us can't even imagine. He is not the first to offer oversize cylinders for the Rotax 912. At first he tried boring out the stock Rotax 79.8-millimeter cast aluminum cylinders and installing steel sleeves, a tried-and-true method already in use. It worked, but piston-to-cylinder tolerances had to be set higher to allow for different rates of thermal expansion between the steel sleeves and the aluminum piston. The result was more power but also more oil burning and poor heat transfer. It was then he decided to borrow from the well-estab- lished Porsche off-road racing technology. He designed 88-millimeter aluminum billet cylinders for oversizing the Rotax 912. They are cut out of a solid round of aluminum with a lathe, and most of the aluminum ends up on the floor. The cylinders are then Nikasil plated and fitted with forged aluminum JE pistons especially manufactured for the Zipper kit. The low-expansion pistons could be run much tighter in the billet cylinders, and they cool better with no oil burning. The prototype Vetterman dual exhaust system is visible with engine cowling removed. Hal on takeoff at AirVenture 2014 with a young passenger getting a free ride. Photography by Dan Grunloh

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