Making Ribs

Original rib partsThis is all of the original ribs received with the project.  It doesn’t look like much, but surprisingly there is a perfect sampling of every size and type needed to recreate the wing.  Lower left rib is used at the wing root adjacent to the gas tank.  You can see the hole to view the gas gauge.  The second from the bottom on the right hand side is a compression rib.  Short ribs at the top are used in the aileron area.  There is a small section of wing tip bow including the mounting pad for a navigation light.  In addition to these original pieces, the project included a complete set of Monocoupe factory drawings required to build the wing.  The Monocoupe 110 wing is 32 feet long with a 5 foot chord and is a solid piece.  There are 26 ribs.  18 ribs are “A” ribs, which are the largest.  There are two each of size “B”, “C”, “D” and “E”.  The B through E ribs are all different sizes, each sequentially smaller creating the unique shape of the wing tips.  Although the 18 A ribs are the same size, there are many different flavors depending on location on the wing: root, compression, plain, aileron area, etc.  In addition, there are 30 nose ribs and 8 tail ribs which are located between the 32 primary ribs.  The only way to produce all of these ribs with any degree of quality and consistency is to tool up.

Aluminum rib templatesUsing the original ribs and the Monocoupe drawings for reference, a template was cut out of 0.063” aluminum for each section of the A—E ribs.  The A rib template is shown here.  Notice two different tail pieces: one for the full width wing and one for the aileron bay.  The rib webs are made from 3/16” thick aircraft grade mahogany plywood.  Pieces were rough cut from stock, then clamped to the aluminum templates and cut to exact dimensions using a router and router table.

Cap strips after routingThe capstrips are made from 1/4” x 1/2” spruce and a router was used to cut the 3/16” wide groove to accept the rib web.  The forward 8 inches of each capstrip was soaked in hot water for 2 hours and clamped in a jig to take the shape of the forward part of the rib.

 

 

 

 

Rib in jig being gluedThe ribs were assembled one at a time in the jig shown.  A piece of aluminum angle is used across the bottom and false spar blanks are used to locate the pieces.  The forward part of the aluminum angle was notched every half inch so it would bend to the needed shape.  Also shown is the basswood doublers glued to reinforce the rib webs.

New ribsRib production went real fast once a system was organized.  This kind of progress is great in the beginning, but in reality, provides a naïve sense of progress that leads to stupid thinking like—hey this plane is going to fly next year!

 

 

 

 

Nose rib interpolationI didn’t have patterns or plans for the nose ribs between the B, C, D, and E ribs.  I made patterns out of poster board, tested fitted, adjust and repeat many times until the final shape was dialed in.  I used 1/4” by 1/4” strips of spruce to simulate the leading edge skins to make sure the nose ribs tapered down properly.  This was a lot of trial and error, but it worked out great.