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Old Jan 15, 2011, 01:31 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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A better way is to just use turbulator strips ahead of the region where you think the air will separate. The tubulence along the skin behind the strip acts like a glue to hold the upper laminar flow onto the surface for longer.

Consider too that 10 km is a jogging/slow running pace. The time tested method for flying this slowly and even slower is a low wing loading. Free flight models have been flying at this sort of speed range for literally 100 years now. You could do a lot worse than to adopt that pattern of design and building so that you achieve the same results.

Since the key to this at such reynolds numbers is light weight I'd suggest that the stuff needed to blow or suck air through the wing will increase the wing loading more than it may help. If you want to experiment with it then great. But if your goal is to just fly super slowly then make your models like the free flight guys make their models.

In full size circles blowing is generally used for encouraging extra lift from flaps during takeoff and landing. So the vents are in the wing where they can blow higher velocity air over the upper leading edge of the flaps.

For separation control I think you'll find that the more normal method involves sucking away the boundry layer. And where you suck it away matters. At low reynolds numbers and high Cl's separation can occur much earlier than the high point of the wing. It can even be just barely behind the leading edge. Free flight modelers found this out and it was common to glue on turbulator trip cords from coarse thread to the upper side of the leading edge strip on many competition towline gliders back in the 50's through to the late 70's at least. They may well still be doing this in some events.

So the odds that your blowing or sucking system would be located at the right chordwise position for best effect would be highly risky unless you can do some wind tunnel or wind tunnel like testing to determine where the separation occurs at the expected Cl and Reynolds number and then experiment with position, hole size and spacing and how much to blow or suck to control any separation bubbles.

In the end I guess it would come down to how much extra lift can you get out of the wing from such a system. Would it even provide enough of a difference to make up for the extra weight of the pumping system components? Factor this against a proven methodology demonstrated by free flight model design coupled with lighter weight.
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Last edited by BMatthews; Jan 15, 2011 at 01:41 PM.
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