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/118927
S c o t t Ehn i 's Tur b in e - Po w e r e d Z e n i t h C H 701 S P to "something I'd feel safe in," Scott said. So, the decision was made to scratch-build the 701. some of which sticks out into the breeze, allowing him to reduce drag and weight. Modifications The 701 normally has welded fuel tanks installed into the wing bay just aft of the spar. But this plane has "wet wings" (the structure of the wing is sealed and serves double duty as the fuel tank) to feed the thirsty little turbine (even though the skins are only 0.016-inch thick), holding about 21 gallons total with 9 of those gallons ahead of the spar. Zenith specifies the 10-gallon tanks be located behind the spar, with "long-range" tanks added to the next bay out, so as fuel is burned, the CG migrates. As Scott considered his options, he elected to add fuel to the leading edge (rather than the next bay), leading to minimal CG changes with fuel consumption. Numerous tweaks to the design were justified based on two factors: 1) Scott wanted to reduce as much drag as practical; and 2) if he could sacrifice a little material for the sake of reducing build time, he did. One mod that Scott is particularly proud of is the streamlined fairings they fabricated for the trailing edge of the round wing struts. While the round tubing is affordable and gives the best weight-to-strength ratio for this application, it's not very aerodynamic. Instead Scott devised an elegant method of using hose clamps to secure the fairing. Another interesting mod crafted by Scott and Kary is the single-piece flaperon. The plans specify a two-piece arrangement, affixed where they meet in the middle, but with the outboard section being offset to cause the inboard section to stall first at high angles of attack. That gives the pilot good aileron control at low airspeeds and before a full stall. And once again, because of the manufacturing facility he owns, Scott was able to make the flaperon in a single piece and include some lateral twist to maintain the designed stall characteristics. The one-piece flaperon also eliminates the inboard/outboard connection hardware, Every part of the basic airframe was built by hand in Scott's shop—except the wheels/tires and nuts and bolts. The propeller and the engine core were, of course, built by others, but virtually everything else was fabricated in Scott's shop, including the polycarbonate (Lexan) windows. Ironically, Scott will say that the hardest task of the entire build was the bubbles in the doors. After contacting experts in the field to hopefully farm out that process, he was told specifically that it couldn't be done—that it wasn't possible to form a bubble in a flat sheet of Lexan and still be able to see through it. Admittedly, Scott said they ended up scrapping about four sheets of Lexan in the process of making the Tis side-view of the engine shows how tidy and well thought-out everything is inside the engine compartment. To read an alternative view about the use of turbine engines in homebuilts, read this article. 18 Vol.2 No.4 / April 2013 Photography by Pat Panzera