Some of the responses are discussing the technique of tubing that was formed to make the edges of flying surfaces on certain airframes. Lots of designs did this., but I understand the quesiton to ask about the scalloped look along the trailing edges of surfaces. It looks that way because there was no underlying structure except a length of wire, around which was bonded and sewn the covering material. You can do the same thing in miniature.

I read John Cole's reply. Sounds right to me at that size and those materials. I don't generally use iron-on covering, and 30# line seems large to me. If he's using 30# metal trace line, one needs to be careful with using any kind of wire or metal framework at right angles to one's radio: it's a giant antenna!

So here's my solution, which also ain't pretty, but works. I use some stuff called Spiderwire, which is a non-stretch fishing line. I dunno what it is--some kind of kevlar, graphite, or other unobtanium. It has a waxy feel and doesn't take any kind of adhesive particularly well. It comes in different weights, but you can't break any of it no matter how hard you try, so there's no reason to get the heavy duty stuff. I use it also for rigging biplanes and pull-pull cables (the "smoke" color is a fair approximation for dirty flying wires!). As John did, lay it across the tips of the trailing edge ends of the ribs. BUT, you need to have the tip of each rib hardened to prevent the line from acting like a knife and simply cutting into the rib end grain. The full size practice was to cap the end of the rib with a metal clip (like a shoe) that also held the wire in place. I use very fine whisker wire to do the same thing. Once the entire trailing edge is draped along the ribs, the ends of the spiderline have to be secured at the root and the tip to keep it from pulling loose under the strain of the shrinking covering. I sew it into the wood, using a piece of a toothpick for a hard point in the root and tip ribs. Then a tiny drop of CyA at each rib t.e., just to tack the wire there. Whew! Covering with silk means laying the excess over on itself to surround the wire. I do the bottom surface first, and overlap only enough to let it grab. The top piece of covering can overlap further, as it won't show as much from the bottom. Take care to make sure the overlap lies as flat as possible flat, as it will bunch up some as the dope cures. Practice on a scrap piece, as this takes some deftness and I ended up ruining my first effort at it! The scalloped effect will occur naturally as the covering shrinks, as John notes. The line will pull in between ribs, but only up to a point. (I tried monofilament fishline, and it was so stretchy that it just continued to pull in, leaving the covering saggy; it didn't work well for me.)

You will think it looks untidy when you first get it done, but, oddly enough, it will have just the right amount of "crudity" to it when the final finish goes on so that it looks like the same thing done on the full-size some 90 years ago. There's a reason for that: they did it this way back then, too! Have fun, especially with fabricating billions of the little wire clips, most of which you will lose in the clutter on your workbench before you can ever grab them with the tweezers to get them in place.

Jim