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
30 Vol.3 No.12 / December 2014 KL AUS SAVIER'S DETERMINATOR Although Klaus' plane appears perfectly built, with absolutely no ripple on the wing, his flow visualization re- vealed another surprise. He said, "On a recent laminar flow test, I noticed that the extent of the laminar flow varied slightly between the two winglets. One has more laminar flow on top (inboard) and less on the bottom (outboard) than the other. This clearly indicates that the installed inci- dent is slightly different." One of Klaus' remarkable traits is that he is completely honest: He reports his failures as well as his successes; he shows photos of his instruments to prove his performance claims; and he doesn't talk about anything he hasn't done yet. He has an extremely high reputation in the industry for his integrity. Perhaps the most innovative concept Klaus has come up with isn't even obvious to people looking at the Determina- tor. Other Long-EZs use a so-called NACA duct engine cool- ing air inlet on the bottom of the fuselage. The NACA duct was invented in 1945 by the National Advisory Committee for Aerodynamics (NACA), a precursor to NASA. It came up with a design for a standardized, low-drag submerged duct, as shown in Figure 12. The reason the duct starts out narrow and then widens is to increase the area slowly to avoid flow separation. The ver- tical sides of the duct produce two counter-rotating vortices that roll off the sides and into the duct. These vortices cause more air to move into the duct than normally would. Klaus looked at NACA ducts that had been in use for 70 years and wondered something: "How do the two vortices created by the duct shape fit into the rectangular opening?" So Klaus played with the shape of the edges of the inlet. Fig- ure 13 shows the duct he flies on the Determinator. The result? Klaus got a two-fer. "I saw an improvement; both a reduction in drag and an increase in cooling," he said. Aerodynamicists have been known to say that they would sell their grandmother for 15 counts of drag. If that is the case, then Klaus can measure his aerodynamic improvements in deca-grannies! WEIGHT Extra aircraft weight costs performance in a number of areas. For instance, the wing needs to develop more lift, which in- creases the drag. The need for more lift means that the heavier airplane will stall at higher speed than the lighter one. It takes more control authority to get the same angular rates with more weight, especially if that weight is toward the front/ back or left/right of the aircraft. Extra weight means more load on structural members, meaning they might have to be sturdier and heavier. More weight might mean a shift in the airplane's center of gravity. On the other hand, reducing weight arbitrarily could get you into trouble, too. Of course, cutting back on structural elements is a problem, but even cutting back on that wing skin thick- ness or heavy counterweight could increase the risk of fl utter. On the Facetmobile, the two counterweights on the elevons weighed 7 pounds, and they af ected the CG of its light, long airplane. It goes without saying (although some should have been told) that you need to know what you're doing if you plan to increase or decrease your airplane's weight. Klaus naturally applied his methodical, persistent approach to cutting weight on the Determinator. For example, when he was changing the injector location, he made an all-carbon-fi ber intake plenum. He also built a 9-quart oil sump that weighs 2.1 pounds. The sump alone saved 11 pounds. Klaus again warns that such engine parts require a specifi c process. "They should be vacuumed for reduced porosity and only use cured epoxy from an oven at least 300°F," he warned. Some of Klaus' other weight-saving changes include replacing the plywood and glass fi rewall with a high-temper- Figure 12: A standard NACA cooling air duct. Figure 13: The duct Klaus designed for the Determinator. Photography by Lynne Wainfan