Experimenter

NOV 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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Why wait? You've dreamed about owning an aircraft for years. Now is the time. EAA Finance Solutions will help you make those dreams a reality. It's easy, with no hassles and no waiting period–submit your documents securely online and get your answer within 24 hours. EAA members get access to member-exclusive discounts on already industry-low rates and loan fees on the types of aircraft they fl y. Making your dream a reality starts here. Visit EAA.org/fi nance today. Finance Solutions Administered by National Aircraft Finance Company EAA Experimenter 23 now you should know that since the air touching the wing is at zero velocity, the fl ange for the VG is not very draggy at all. The VGs themselves are angled relative to the oncoming wind, which is even more draggy. The extra drag of VGs during cruise fl ight is the price we pay for their ef ect near stall. The small vortices they produce create more drag than the bare wing would have. But at high angles of attack, VGs can keep the fl ow attached longer. At- tached fl ow, with its smaller wake, is much lower drag than separated fl ow. Whether VGs are net positive or negative, dragwise, depends on many factors including the airfoil, the amount of time the airplane spends in cruise condition, the VG configu- ration, etc. VG placement af ects their drag and their usefulness. If VGs are placed too far forward, they will trip the fl ow from laminar to turbulent too early, increasing drag, compared to the no-VG confi guration. On the other hand, if they are placed too far aft, they won't be very ef ective. The best place to put the VGs is in or slightly upstream of the boundary layer's transition zone illustrated in Figure 7. VGs have other problems as well. VGs are yet another sur- face protruding from the aircraft that may break of . In addi- tion, they may be problematic during icing conditions. If they are taller than the boundary layer, they could pick up ice. This is especially worrisome if you are fl ying through supercooled drizzle drops or freezing rain. On the other hand, if you are fl ying through those conditions, you may have bigger problems with icing on other parts of the airplane. Another problem with VGs is that they can be costly. The manufacturer has to design, fl ight-test, manufacture, insure, and distribute VGs. For certifi cated aircraft, the VG certifi cation process is quite expensive: The FAA requires that most, if not all, of the airplane's original fl ight testing be repeated. This cer- tifi cation can cost upwards of $500,000 for a lightplane. Since the market for VGs is somewhat small for each type of aircraft, the certifi cation cost must be spread over a small group of customers. Even for noncertifi cated aircraft. Extensive analysis and testing of VGs are required to determine the VGs' confi gu- ration: where on the surface they go, how tall they should be, their shape, how far apart they should be, how many VGs to put on a surface, how they will be mounted, etc. After the fi nal con- fi guration is determined, fl ight testing is necessary to evaluate their ef ectiveness—and more importantly—to ensure that the VGs do not adversely af ect the airplane. This is why it is impor- tant to let a professional design and test vortex generators.

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