Construction Details - Boxed Wing Tips




The boxed wing tips kit consists of some extra ribs and several lengths of sheet stock 6" wide. There is an instruction sheetwhich illustrates the installation in a general way. As it turns out, opinions vary even among experienced builders and the factory about just how to build this option. The first step is to install two flat bottom ribs and two curved top ribs at the end of the wing spars and cover them with sheet metal just as was done at the wing roots. These form the top and bottom of the 'box'. Next one or more sides of this box are covered. The factory says that only the outboard side of the box needs to be covered. Don Zank says "if all four sides aren't covered, it aint a box." Because I'll be installing nav lights on the wing tip bows I opted to only cover the outsides in order to keep weight down. This photo shows the sheet metal drilled for the spar tubes (2" hole saw tangent with one of the edges of the stock) and notched (at 'A') to allow the side to fit around the rear tip bow brace. The shape of the wing is traced only in the curved sections. Using a straightedge to draw the rest ensures that any slight bowing in the ribs will be straightened out by the side.







Here's the finished side in place prior to fastening. You can see that the 6" stock is not quite wide enough at 'A' leaving about a 5/8" wide gap. The instruction sheet shows this as much wider and says to fill this gap with a small piece rivited to the side sheet and the rib. This gap looked insignificant structurally to me so I left it open. This also made installing an additional brace to the tip bows very easy.

A note on the use of sawhorses: Although the manual suggests and most builders appear to use some sort of table to support the wings I found the use of sawhorses to be satsfactory and somewhat advantageous. I put top rails of straight clear stock on them. I carefully shimed them to ensure that the top rails were level and parallel; and at each use, I checked to make sure that the wing spars were in level contact at all four corners. There has never been any evidence of twist or droop in the structure. I'd never consider building the wing frame on horses, but since it comes from the factory structurally complete, horses seem to work fine. They make working around the wing easy, they allow clamping under structure, and they make turning the wings over a snap. Additionally, when inverted, the horses fit between ribs so the wing stays level with no weight on the ribs.







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