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: http://experimenter.epubxp.com/i/434207
22 Vol.3 No.12 / December 2014 KEEPING UP A FAMILY TRADITION sheeted only forward of the main spar. This formed a torque box that carried all of the various loads the wing would experience. Behind that, it was fabric covered. When Randy did his wing, he went one step further and sheeted the entire wing, like the CAP 10. In fact, he copied a num- ber of changes that were made in the CAP 10 wing. He said, "I wanted the wing to be not only stiff but also smooth as well. So I continued 1/16-inch birch ply from the spar to the trailing edge. When I finished it, I used boat cloth over the ply, which is really thin fiberglass with resin. With very little filling and some sanding, you can get a nice, smooth surface. "I also changed the wing incidence from four degrees to two degrees and took the dihedral from five degrees to three degrees and used electric actuators for the trim and flaps." The tail is also wood and the structure mimics that of the wing but much smaller. Its trailing edge is laminated like a tip bow to provide the requisite curve. The one-piece skins are very gentle compound curves, which Randy ac- complished by forming them in place when wet. As with the CAP 10, he also balanced the elevators and inset the elevator trim in the left elevator. The basic structure had a few complexities, which Randy worked out with no problem, but as is often the case with airplanes, some of the lesser assemblies caused as much or more headaches. In this case, it was the canopy. Being a tandem airplane, the canopy is a visual focal point of the design and one of the areas that took a lot of work to get right. The tubing structure itself was complicated enough, but the Plexiglas covering was a story unto itself. Randy said, "I hadn't anticipated how tough doing the canopy and windshield was going to be. I would have actu- ally preferred to buy the canopy, but by the time I got that far, I was looking at each new part as a challenge to see if I could do it. And the Plexi work definitely fell into that category. I didn't want to go with some sort of one-piece, flat-wrap canopy. It would be too angular and would con- flict visually with the rest of the airplane's lines. I wanted something with just the right shape, and the only way I was going to do that was to do it myself. "The first thing I did was study a section in [Ladislao] Pazmany's building book that addressed forming Plexiglas. Then I made a big wooden form and covered it with flan- nel. To heat the plastic, I built an oven, and the Plexi sheet was suspended from a telescoping, overhead rail that could be extended. I could bring the whole sheet up to tempera- ture, then roll it out. I had five other guys over, each with gloves and welding vise grips. We grabbed the hot sheet and stretched it down over the mold. "I'd be lying if I said it worked the first time. I ruined a few sheets of Plexi [while] learning, but it was something I wanted to try to do. The entire process covered a couple of years, but I'm glad I went that route. I'm proud of having done it." We would be remiss if we didn't delve deeper into Randy's do-it-yourself oven; a lot of builders would benefit from his experience. He explained, "The oven is made from galvanized steel sheet and metal 2-by-4's, with fiberglass insulation. The heaters are eight electric resistance ele- ments with switches on the outside for each element. Once I got it hot, I shut two or four of them off. There is a fan to circulate the air, also. I had a thermocouple in the center of the bottom edge of the sheet, and when the temp hit 320 degrees, we got it on the mold as quickly as possible. When the Plexiglas gets too hot, it bubbles and is ruined. "The pieces of Plexiglas were different sizes, depending on which part of the canopy was being done; the canopies are 1/8 inch and the windshield is 3/16 inch. The back can- opy was the largest but was quite a bit smaller than 4-by-8. "I tried to get the room as warm as possible because, at the most, you might have a couple of minutes to work with the hot Plexiglas. When the first windshield worked out, it was a beautiful thing!" When it came time to cover the airplane, Randy went with Ceconite with nitrate, then butyrate with Randothane over it. "Painting was difficult," he said. "I had to do some parts twice because the yellow just didn't cover. Next time, if there is a next time, I'll know that, if I'm painting yellow AIRCRAFT SPECIFICATIONS Top speed (V NE ): 183 knots Cruise speed: 120 knots at 2,300 rpm Full throttle speed: 149 knots at 2,650 rpm Landing speed: 60 knots Takeoff roll: 1,000 feet Rate of climb at gross: 800 fpm at 95 knots Range at 65% estimated: 3.5 hours Range at 50% estimated: 4 hours Empty weight: 1,174 pounds Gross weight: 1,700 pounds Useful load: 526 pounds Fuel capacity: 26 gallons Wingspan: 26 feet, 6 inches Wing area: 117 square feet Length: 22 feet, 9 inches Cabin width: 24 inches Cabin length: 84 inches, rudder pedals to rear seat Engine: Lycoming O-320-E2D Prop: Sterba 70-by-68, wood