Sunday, February 28, 2010

First Short Half Compression Rib

The outboard compression rib on the upper wings is a short (ends at the rear spar) light rib with a compression stick glued on the inboard side. There are some blocks which get added to the nose rib after the gussets are all on so it fits the jig. I temporarily modified the rib jig to clamp the upper and lower sticks tightly to the solid nose rib. Some pieces of carpenter shims and scrap sticks made this easy enough for 2 ribs.

These more than the other ribs need to stay in the jig until the glue is set. I did use a few nails to help hold the nose sticks.

I also left the sticks long at the aft end until gussets are on both sides.

The gussets on the inboard side of each rib need to be trimmed before installing to fit the compression stick. I think it will be installed on the rib as the rib is installed on the wing to get the bolts in and make it all fit correctly.

Rib Leading Edge Fixture

I want the leading edge stick to form a nice straight line when it's installed. Therefore the ends of all the ribs need to be cut to match. To do this I made a simple fixture to use on the table saw to cut the angle on the leading edge of the ribs. The cut is tipped 16.5 degrees from the spar which is both easy to locate from and relevant to getting the leading edge straight.

The references to hold the rib are the front and bottom of the spar, and the top of the rib at the nose. I've since removed the stop below the nose. The other 2 in front of the spar and at the top of the spar are just there so I don't grossly misalign the rib and ruin it.

I hold the top of the fixture with my finger tips and the bottom of the rib with my thumb while cutting and it all works very well. The next time you come back to do another stack of ribs it's easy to align the blade with the front of the fixture, just don't cut into it and slowly make it shorter.

The guide stick is glued and screwed to the bottom of the board and everything laid out from it.

Friday, February 26, 2010

Heavy Compression Ribs Finished

All the sections for the Heavy Compression Ribs are finished. They'll be assembled on the wings to assure a tight fit to the spars once the regular ribs are installed. There are only 2 aft sections because the upper wings are cut out for ailerons. On those ribs there are only short sticks added over the spar. The ends of the sticks do not follow the top of the center section but, are bent down so the end of the stick does not touch the fabric on the top of the wing.

Tuesday, February 23, 2010

Building More Heavy Compression Ribs

Today I made the rest of the parts for the other 3 heavy compression ribs. Instead of the complicated cutting I'm gluing 1/4" webs to 7/16" x 1/2" sticks to make the "L" sections. In the factory photo it looks like glue is smeared in the corner like the factory made them of 2 pieces.

Monday, February 22, 2010

Heavy Compression Rib Finished

With the 2 heavy members made I cut the 3 vetical sticks and the gussets to hold them in place. A lot of time was spent getting all these right since each has a different angle on each end. I suspect the factory used square cut pieces for this as they did on the light ribs. For sure the stick in the middle and the gussets could all be done as rectangles.

I made a board with some guides to hold every thing in position, not really a jig, while assembling the 4 ribs, 2 lefts and 2 rights.

The nose and tail sections will get installed on the wing to allow the main load bearing part to be carefuly fit between the spars as the wings are assembled. The edge of the nose and tail sticks get glued to the 1/4" web for about 5" past the spars. I'll come back to this when I put a wing together

Friday, February 19, 2010

Wing Rib Nose Gussets

The wings need 104 gussets for the nose portion of the ribs. To make these quickly and uniformly I rough sawed them from the 1/16" 90 degree mahogany plywood with a very fine toothed band saw blade. Even my best efforts with the band saw will not yield uniform parts. Stacking them does not work because the blade wanders more the taller the stack. Instead I used my router to make parts quickly and all within a fine tolerance. I did this by making a steel pattern, attaching it to a holding block and routing the finished shape with the same formica cutter I use to trim finished ribs.

The template is made from 24 gauge galvanized sheet steel from Lowes. I find galvanized steel the best to make templates from. It's cheap (always a recommendation) and easy to work with both in cutting and filing carefully to a scribed line. Steel also holds up well in use as a template. The plywood on top of the template is needed to allow the roller to follow the template and postion the gusset so the blade can cut it.

The screw points peeking out from the plywood are there to hold the gusset in place while running the cutter around the template. for this I like the very pointed coarse thread screws like drywall screws. You only need about 1/32" of the sharp tip pointing out to hold the gusset from slipping. I clamped the block in a vise, set the gusset on it and, ran the router quickly around the edge.

If I were doing it again I would turn the process upside down by drilling a 1-1/4" hole for a vacuum cleaner hose with some air paths out to the screws like in the other block below. You put the block on the hose, set the gusset on and, with the router upside down in a stand run the template around the cutter. It really works slick and quick.

Heavy Compression Rib Members

The wings have several different ribs along with the light ribs. One such is the heavy compression rib at the strut attachment point. This rib uses the light contruction for the nose and tail portions with heavy members between the spars. The first step in making these ribs is the 2 heavy members cut from 3/4" wide spruce. The curve and spar cuts were laid out using a light rib as a pattern along with the drawing dimensions (D/N 3662).

With the cuts all drawn on the sticks, the first cut was made for the 1/4" wide web. The order of the cuts is important to be able to handle the sticks as each cut is made.


The next cut was the ends of the sticks to fit the spars. The miter was set by using a straight edge lined up with the saw blade and the cut line on each end of the sticks. Not only are the spars tipped from square but, each stick is at a different angle to the spars.


Next, the curves were cut on the band saw and sanded smooth.
The last cut was made to form the 7/16" thick foot of the "L".