I've been asked several times about modifying a Fly Baby to not
need the external bracing wires. So, what about it?
Well, one way to answer is to look at the Warner
Spacewalker/Revolution/Sportster, or whatever name it has,
now. It's basically a Fly Baby with a cantilever wing.
Here's a photo of a Spacewalker wing under construction.
The aft spar looks like a 3/4" - 1" spruce plank, like the Fly
Baby, but the front spar is a thick, high, wooden block.
Looks to be about 6-7 inches tall, and ~3.5 inches wide. I
actually think this is a box spar, not solid, but obviously it
would need to be built up (and built straight!). That
wing is at least 8" deep, compared to ~6" for the Fly Baby.
The top of the Fly Baby spars are beveled to match the slope of
the nose ribs, center ribs, and trailing edge ribs. Be
hard to bevel/curve the top of that box spar, so you'd probably
end up using big one-piece ribs like the Spacewalker.
The other factor is, what does that been ol' beefy spar bolt
onto? Not a stock Fly Baby center section, of course,
since the two bulkheads are only ~3/4" wide to match the stock
spars. So you'd have to beef up Bulkheads 3 and 5 to make them
just as wide as the box wing spars, AND move the opening higher
to that the lower part of the bulkhead matches the height of the
wing. This opening is what your legs stick through when
you fly, so it'll make the cockpit a bit more awkward.
I've toyed with the idea of going to an aluminum
wing...C-section spars and metal ribs. But I'd still keep
the wire-braced design.