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Old Oct 07, 2010, 02:32 AM
if you see my flying, run
The Land of Unlimited Bureaucracy and Sauerkraut
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Serrated leading edge for a flat plate profile wing

This is about simple light acro foamies with flat plate wings made of 3mm Depron.
It is my understanding that the flat plate works reasonably good at those very low Re numbers due the turbulator-like effect of the edged leading edge. Would it be possible to increase Clmax or even improve overall L/D even more by serrating the leading edge to induce some sort of vortex generator effect?
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Old Oct 07, 2010, 06:04 AM
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Do you know specifically what Re range you're in?

At very low Re (less than 20000) laminar flow seems to prevail over the whole wing anyway. Because of the air particles relatively low energy/high viscosity the boundary layer just doesn't reach transition.

I would guess (!) turbulators might hinder performance at these Re's. As you get into higher Re then turbulators will help for sure.

But as with all things 'Low Re' - it's difficult to predict!

What aspect of performance are you trying to improve specifically?

Try it and post as to how you get on!
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Old Oct 07, 2010, 06:59 AM
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Not that low; Re would probably be around 150.000. I'm aiming at stable airflow for precise maneuvering and good control authority. Drag is not a big issue.
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Old Oct 07, 2010, 07:06 AM
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If you mean control authority at low speed/high alpha then have you considered LERXs (Leading edge root extensions) or 'stall strakes' ahead of the tail surfaces?
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Old Oct 07, 2010, 07:15 AM
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One of my designs had longitudinal axis stability issues at high alpha, dutch roll probably. Adding a strake to the vertical fin actually improved the stability. Either due to the larger vertical stab area (damping side slips), the strake vortex (causing the airflow to attach better), or both.
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Old Oct 07, 2010, 02:48 PM
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Modifying a wing to incorporate sawteeth is certainly easy enough to try. Go cut a wing up and see how it works out. If you don't like it or want to play with another style just slice off the first inch to remove the sawteeth section and glue or just tape on a new piece and cut a new pattern.

The issue with 3D is that the "best" isn't always what you want. The reason flat plates work so nicely for 3D models is the fact that they do stall on command and so deeply that they simply stop in mid air. Adding turbulation that encourages a later stall may well prove to be counter productive in that the model may turn further around the corner when full up is pulled before stalling and coming to a nose up hover with no residual upward travel.

Much like the fellow in the Pietenpol thread found we don't always want the most efficient and lowest drag lift producer.
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Old Oct 08, 2010, 03:03 AM
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I'll try it out next week. Problem is to find a scientific approach to judge the difference rather 'feeling' what I expect. I'll add a serrated edge to one side of a flat profile biplane and see if it yaws, drops wings or whatever which it already does anyway because my foam constructions twist and bend even in the lightest airflow and I'm such a lousy pilot.
For these planes, I prefer rather high lift coefficients and airflow attached at high AOA to make slow speed stunts possible. Drag is not an issue since there's more than enough power. I love anything that involves stalls, especially snap rolls, but these light foam models seem pretty bad at it in so far as any stalled maneuver rather reminds me of a leaf tumbling down, I think they simply lack intertia to make it look convincing. I'll leave that to the big models.
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Old Oct 15, 2010, 11:45 AM
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Concerning the topic, you might enjoy this:



http://www.rcgroups.com/forums/showt...st+development
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