ORIGINAL: Montague
But I didn't see anything in there that contridicted what I said
. (my comment about the vortex being related to the lift could be taken out of context. I was assuming a fixed wing, already designed and built. Certainly, differnet wings, differnet chord, planform, etc blah blah blah will have differnet vortexes. But for a given wing shape in the real world, messing with the tip can do a lot, but, as I understand it, you aren't getting rid of, or even reducing, the vortex, you're "just" moving it around).
Anyway, Strykaas asked how to reduce the vortex, and my question in reply is "why?" If Strykaas is trying to reduce drag, I haven't a clue for suggestions, I don't spend much time worrying about drag. (just look at the picture I posted, uncowled engine, two servos and control rods hanging out in the breeze, a veratable drag farm). Heck, the mounting of the winglets on my plane creates a 90degree corner, and that's gotta be increasing drag right there.
However, if Strykaas wants better stall handling, that's something I've spent a LOT of time messing with, as getting even a small improvement in turning radius gives me a competitive edge in competition. Though I've been dealing mostly with "high" speed, high-G turns, not low speed flight. I don't know if that makes much difference.
Well... at low speed, induced drag dominates. Parasite drag is small. So, your best option for reducing total drag at low speeds is to decrease C_L (which is a factor in induced drag).
You can reduce C_L by either increasing your wing area (which will result in a smaller C_L to stay aloft), or by increasing your speed. This will of course alter the flight performance of your craft drastically.
Adding an engineered tip will reduce induced drag by effectively increasing the span of the wing. But, you are adding parasite drag by adding the tip. It is nonsensical to use a winglet (in the true sense of the term) on an RC craft unless you are going for distance/endurance. Winglets are designed for a single flight condition, and are not as effective at others and can actually detract from performance. You can use a modified tip (such as a Hoerner, drooped tip, or other variation) to reduce induced drag. A simple cutoff tip is a better bet than a smooth tip for reducing induced drag. Your best bet is to go with a Hoerner tip... it's simple and proven. I'll let whoever is interested to go find the old NACA memos on Hoerner tips et al.
The whole point of an engineered tip is to make spanwise flow more difficult... spanwise flow results from lift on a real wing.
Why would you want to reduce drag on an RC aircraft? Good question... i dont have a clear cut answer for that.