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.

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Page 13 of 36

14 Vol.4 No.3 / March 2015 BILL AND K YOUNG CL APP'S CORVAIR-TAILWIND as a project. It was far enough along that on the first day I was able to hang the wings, finish the struts to align the wings, cut off the O-200 mount, and build my Spyder Corvair engine bed mount. So we were able to jump right on it. The only serious change was cutting the vertical fin loose and offsetting it the other direction because the Corvair is spin- ning the other way." This particular Tailwind was something of a hybrid as it had the more sophisticated W10 wings with the extend- ed trapezoidal tips mounted on an older W8 fuselage that's slightly narrower, with less headroom than the W10. It also has the older squared-off tail. One of the aspects of the Tailwind that worked well as a test bed for Bill's Corvair conversion was the fuel system. "The Tailwind has a simple 25-gallon aluminum header tank right behind the firewall," he said. "All my Spyder conversion engines work best with a simple gravity feed fuel system. Even on low-wing aircraft, I suggest installing a header tank and transferring fuel from the wings to the header. When you're not dependent on engine-driven or electric fuel pumps, you increase your safety margin considerably. The biggest safety concern, if you look at accident records, is fuel management. I choose to increase mechanical reliabil- ity by eliminating the mechanical stuff. (If you don't have it, it won't break.)" The wings came to him in what might be considered "quick-build" condition, with the primary structure in place but needing all control systems installed and the skins applied. As Bill described it, "The wings are quite simple: basically nothing but wooden ribs, spars, and skins. Because the spars and ribs were already done, all I had to do was inspect ev- erything, install the control system, and skin the wings. They have a 1/16-inch mahogany skin root to tip, top and bottom that laps over a rough-shaped leading edge block. Then once the leading edge is sanded to shape, it's all covered in a layer of 3.5-ounce fiberglass cloth and West epoxy system. Once cured, the wing is lightly sanded, minor filler and epoxy primer applied, and it's ready for paint. It makes for a very stiff wing." Hundreds of Tailwinds have been built over the years with a wide variety of engines, including V-8s, but to Bill's knowledge, this is the first Corvair installation. He said, "Part of why I wanted to do it was because of the challenge. It had never been done before, and the Corvair seemed like a natural. However, the challenge of building the Corvair engine into an airplane engine is also one of the things that brought me to it in the first place. To many, the attraction of the Corvair is its lower costs for both initial buy-in and maintenance. It costs me more in some regards, but the gains aren't necessarily seen in dollars. "However, because it is such an easy engine to build, for many people the attraction is not only building your own plane but your own engine as well. It really is an engine that anyone who can build an airplane can easily build the engine, and we have helped many people do just that. In general, if you build the engine yourself, you'll typically have around $5,000 invested. If you have one built by a known Corvair rebuilding company like Azalea using first-quality parts, including an aftermarket billet crank, you can expect to spend $9,000 to $12,000. "I am using a 52-inch three-blade Warp Drive with modi- fied tips. It works well as a climb prop and for testing." THE CORVAIR ENGINE According to Bill Clapp of Azalea Aviation, "My focus is to develop a mar- ketable, low-cost option that an A&P would not be scared to touch. That requires bringing the engine into an appearance and functionality similar to that of an O-200. "We fi rst tear down the core motor. We have collected many cores (we keep about 30 on hand at any time) so typically will tear down fi ve at a time. We will normally only keep the case, crankshaft, heads, distributor, cylinders, rear housing, and assorted small parts. The rest gets shipped out for core value to Corvair car shops or is recycled. As we process and clean the parts, we will inspect them for suitability in an aircraft engine or car. (I still drive Corvairs and build car engines when needed.) We inspect/clean the cases and have our integral front bearing (IFB) hous- ing installed. The crankshafts (if they are good standard cranks) have the gear/fl ange removed and our IFB prop hub installed. It is then sent off for magnafl uxing, grinding, nitriding, and polishing. We also have the option of new crankshafts. The heads are rebuilt with some modifi cations done to the intakes. All new springs and valves are installed. New forged pistons, remanufactured or new cylinders, camshaft, new connecting rods, and bearings, and it starts to go together. Also available is the inte- gral rear alternator/starter (IRAS). It is a 32-amp alternator driven off the crankshaft (no extra moving parts or brackets/belts/brushes) and a simple starter (off the shelf from NAPA). "We include a heavy-duty oil pan with an extra quart of oil capacity. The distributor is rebuilt (now with ball bearing option) and recurved with a dual ignition (points and electronic) setup. It has proven to be reliable and simple to set up. We do keep a single plug in the heads because we have shown that failure of a plug does not induce too much vibration and still have partial power (75 percent); this is an obvious advantage of a six-cyl- inder motor. I've never had a plug failure, but I did fl y a pattern (takeoff to landing) on fi ve cylinders (plug removed) to test its capability. "We have a dedicated section of our shop for engine assembly (clean room). Once the engines are assembled, we run them on a dynamometer that I designed where we can check for performance and condition. Once we have about three hours of run time on them and are confi dent in the engine, it is packaged and shipped out. "We do have customers who build their own engines, and we help pro- vide parts, expertise, and information that they may require. Many choose to assemble their engines here at our shop under our supervision and run them on the dyno before going home. We take each customer where they are at and take their goals into consideration before accepting or advising them on a path to take. From what I've seen, I believe that the full potential of what this engine could mean to experimental aviation is just starting to be seen."

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