AV8TOR,

You can't count on much benefit from any particular wing tip, at any speed. For building simplicity, you can leave that last rib alone. If you'd like to save a little drag, and look better, carve yourself some nicely rounded tips from soft balsa. This will be almost as good as any other tip treatment you can do. The wingtip shape often gets a lot more discussion than it deserves. It's good to remember that the wingtip is a very small part of the wing, and it's not likely to have a big effect on performance.

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