dieFluggeister

In Nov 2005 Quiet Flyer Mag there was a good article on winglets pertaining mostly to full scale sailplanes and its application to RC soaring but only briefly mentioned racing/pylon. Too bad. (but then I guess it is "Quiet Flyer") Most of the pylon wing tip design today seems to be a swept tip with a pointed TE which seems to be more for aesthetics. I think that given the higher Reynolds Numbers and vortex generating hard turns of model racers, winglets would be especially worth consideration for racers. Reducing tip loss and induced drag, allowing shorter spans and reducing profile drag might be the result. Better tip flow, less separation, better aileron function were also mentioned in the article.

I know winglet design is critical to performance and that low Re's of models are a problem. What has been done in the RC racing area? It seems that even a 2% gain would be a real advantage to these guys, yet I can't find any info on the subject.

Tall Paul

At which point in the course is this 2% gain to be achieved? Winglets works best at one airspeed. Racing speeds vary a lot in a race.

js3

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This topic is of interest to me. I'll be interested to see what the experts say here. Just getting my forum subscription entered.

dieFluggeister

Thats a good point Tall Pall, I dont know exactly how much airspeed varies but the winglet would be optimized for a particular airspeed - say projected speed through the turns. Should it work at varying degrees within an airspeed range?

rgunder

Winglets are very sensitive to design. There have been many engineers that have worked long hours "optimizing" a winglet, only to find that that drag in the wind tunnel was either the same or worse than the wing without the winglet. The winglets that you see on full scale aircraft, such as the Airbus A-320 and the newer 737's are the result of tens of thousands of hours of CFD and wind tunnel testing. The winglets that you see on full scale sailplanes comes primarily from cut and try testing, and the fact that some of the designers seem to have an ability to see air molecules and know how to use them. If you hit on a winning design on your first attempt, pat yourself on the back - you are among the few If you do add them, make them as light as possible, and please by all means share some photos. Good luck.

Tall Paul

The angle of attack of the wing varies a LOT between the straight flight to the turn, and in the turn. The g-loading can vary past 30 in the turn, which requires a large change in alpha. The winglet would have a problem handling both situations.