Experimenter

DEC 2014

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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28 Vol.3 No.12 / December 2014 KL AUS SAVIER'S DETERMINATOR He also made several changes to the Long-EZ's canard. He modified the canard's airfoil, sharpening the leading- edge radius from the standard Roncz airfoil. Klaus decided on the Dornier-style upswept tapered tips instead of the typical Hoerner tip he has on his VariEze, and he modi- fied the elevator's deployment angle. The stock configura- tion deploys to 25 degrees; Klaus found that after some slot changes, flow stays attached to the elevator all the way to a surprising 45 degrees. "Obviously, making any changes on your airfoils can easily be disastrous," Klaus cautioned. "In- creasing the lift capability of the canard—or your tail—can drive the main wing into a stall, and we all know how that plays out!" He also changed the direction of the gap between the wing and the ailerons. The plans call for the gap to be lined up perpendicular to the wing 's swept trailing edge. Instead, Klaus lined this gap up with the direction of flight. This reduced the small drag caused by the edge of the elevator being angled into the wind. He also added a foam insert to the gap to further reduce drag. These changes can be seen in Figure 7. Note also the accidental flow visualization—some oil re- mained in the hinges and flowed out during flight. The lines that don't line up with the direction of flight show that there is some spanwise flow. More on that later. To seal other gaps, Klaus uses a special blue flash breaker tape, as seen in Figure 8. What's so special about this tape? First, it doesn't leave a residue. Second, it doesn't fly off when Klaus races. Third, rain doesn't chisel under the edges, causing the tape to come off. Finally, it's available commer- cially at some airplane equipment supply shops. Swept-wing aircraft typically experience fl ow from the wing root to the tip, especially at high angles of attack. Unless miti- gated, this spanwise fl ow can cause poor stall characteristics: tip-stall; increased landing and takeof speeds; and pitch-up at stall. Spanwise fl ow also can reduce control-surface ef ective- ness and can even blank the areas behind the wing. To deal with this problem, fences are sometimes used. Fences are typically fl at plates that stick out perpendicular to the wing, extending from the leading edge to the trailing edge. They dam up the spanwise fl ow and shed a vortex at high angles of attack. This can cause the boundary layer to stay attached longer, which can delay stall and improve control system ef ectiveness. Vortilons are another tool to battle high angle-of-attack fl ight qualities. Like fences, vortilons are typically fl at plates that stick out perpendicular to the wing. But vortilons extend from the lower surface past the leading edge. Compared to fences, vortilons have less drag in normal fl ight because of their smaller wetted area. Here's where Klaus' innovative thinking paid off for him and hundreds of EZ pilots who have used his idea. He looked at fences that cover the entire chord of the wing and thought of a better way. Spanwise flow doesn't just travel along the wing; it flows behind the wing, too. So Klaus shrank the size of the fences and designed them to extend past the trailing Figure 7: Aerodynamic improvements to the ailerons. Figure 8: Klaus uses this special blue "fl ash breaker" tape because it doesn't leave a residue and doesn't come off in fl ight. Photography by Lynne Wainfan

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