The Elevators

6/9/04

I got a few hours here and there in the shop this past weekend and got the elevators done. That was a milestone on this project to get something done in only a few days. OK, they are small and uncomplicated but I'll take what I can get. I thought about building them using the "half ribs glued to a sheet of balsa" method but decided to stick to the plan and I'm very happy with the finished elevators. They look great and weigh only 20 grams each.

I have cutting ribs and stack sanding down now and feel completely happy with the results. The key to making a good stack of ribs is perfect 90° alignment on the band saw, sander and drill press tables. You could do it with just hand tools but I like power tools.

Because of the design of the liberators elevators, there are two different ribs for each elevator half, I thought. As it turns out, all the ribs are the same, but the inside ribs (closest to the fuselage) are turned upside down. I didn't figure this out until after I was done. The plans show two different ribs, E4-6 and E7-12. I figured only the leading edge was different so I wanted to stack sand the back half of all of them together. The spar notches would need to line up so I started by copying the ribs, cut them out, drew a center line and stacked one on top of the other, I marked the 1/16" hinge hole with a pin and put another 1/16" hole near the rear for an alignment pin and jig, then marked for the spar notches. That way the hinge holes and the spar notches will line up on all the ribs. I ready to cut some wood!

 

This time I cut the rib blanks as rectangles and it made it much easier. Cut from 1/16 plywood and stacked in two groups, E4-6 and E7-12, I put glue on the ends to hold them together. That works good, a line of CyA down the ends and hit with kicker and it is ready for working with in seconds. I glued a template to each stack and drilled the 1/16" holes. I pressed in two 1/16" alignment pins and then drilled three 1/4" lightening holes. I cut the ribs out on the band saw and moved to the disk sander to finish them up. Sanding to the template then put both stacks together, finish sanded the rear half and filed the spar notches. When I took them apart I found that all the ribs are identical which amazed me a bit. I could have cut them all the same and then just flipped E4-6 upside down. That's intrigued me about the B-24. The rudders and elevators are counter balanced a bit with the leading edge sloping in two directions. Someday I may even find out why the designers did it that way and if it helped.

The ribs were slid onto two 1/16" rods, laid over the plan and onto the lower spar and with 1/4" spacers under the rear rod, glued them in position to the spar. The rods worked OK except it's hard to move one rib without effecting the others because the rod would want to move too. I finally glued down one end of the rods to scrap balsa and that helped. I might not use the rear rod on the rudders. I glued the top spar, leading and trailing edges on and slid the rods out. Then finished off the angled outer trailing edge and added the small sub ribs. These were easy. I made them from 1/16" balsa and I cut them rough, drilled a large hole for hinge rod clearance, filed the front and back to fit between the spars and leading edge and glued them in. The sub-ribs next to the hinge point were made from 3/16 balsa so the covering material has something to grab. I then added the balsa filler pieces for the control yoke and also added some extra bracing at the corners. I sanded it all to shape and then did it all again for the right half.

 


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Updated July 14, 2009