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Sliced Ribs


Actual wing construction detail for the classic Pietenpol Air Camper (above). This rib design is a good example of one that can easily be replicated with the sliced-rib technique. The Gere Sport wing rib (at right) is very similar to the Pientenpol and is the basis for this article.


for structural strength as well. Nearly any airfoil can potentially be adapted to this technique although wings employing flat-bottomed airfoils and con- stant chord will be easiest to start with. The airfoil I have chosen shows a slight under- camber which is formed into the bottom rib stringer by wetting the balsa and clamping it over a bamboo “former” until dry. Step 1: Obtain an accurate sectional view


of the airfoil to be used. I have chosen a full scale airfoil whose construction can be close- ly duplicated with our technique. Step 2: Lay out the bottom sheet of the


airfoil “slab”. Note the grain runs chord-wise from leading edge to trailing edge. Mark the location of all vertical pieces of the airfoil section. For reference purposes, these pieces have been marked A, B, C, E, F, G in the pic- ture (note that there is also a vertical piece to support the leading edge of the wing which is not labeled in the picture. Also, the first two uprights have been pinned to the bottom slab piece). Step 3: Measure all vertical dimensions


The bottom sheet is pinned to the building board (above). Note the bamboo support which provides the necessary undercamber. Vertical pieces A-G are cut to match the airfoil section (below).


and mark them on a piece of balsa sheet. Please note grain direction! These are then cut out and glued perpendicular to the bot- tom sheet at the locations specified. Step 4: Glue in diagonal supports per


plan. Take time to get the joints tight which will increase the strength of the finished rib and make the rib less prone to break during slicing. Step 5: Glue on the top cover piece. This


sheet forms a fairly drastic curve over the front portion of the airfoil and thus, the wood should be soaked in hot water before gluing. The piece should be glued in place with water-based glue such as Titebond and clamped in place to dry. Alternately, the wetted top piece could be clamped over the airfoil and left to dry overnight. When suffi- ciently dry and formed, the top piece could be glued with CyA glue. Step 6: Carefully slice off the ribs. I have


had my greatest success using my razor saw on ribs of this dimension. For larger dimen- sions, cutting ribs off on a bandsaw or table saw with a thin blade might better serve this purpose. For smaller dimensional balsa, careful slicing with an X-acto knife or razor blade would do the trick. I have attempted to construct a slicing jig


by gluing a double-edged razor horizontally onto two balsa support blocks, which had


46 FEBRUARY 2012


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