Wednesday, December 30, 2009

Trimming Wing Rib Gussets

The gussets on the wing ribs are mostly triangles and rectangles. They are glued on with the corners of the gussets sticking out past the curved upper and lower sticks.

In the factory photos you can see that they trimmed the corners of the gusset with a belt sander to create a smooth contour on the edges of the ribs. That actually works very well with soft glues like they used in the mid 1920s. Resorcinol is very hard once it cures and is not as easy to trim with the belt sander.

What really works well is a straight sided router bit with a roller bearing for trimming Formica.

You need a sole plate for the router with a very large radius on the edges so the gussets and any stray nail heads do not hang up on the edge. I made this one with a scrap of plywood and rounded the edges on the belt sander. I've lost my little table/router stand so I just clamp it in a work mate.

Adjust the height of the roller so it is near the top of the stick. This assures you get any glue which may have dripped down a stick. Also you need to rout each side of the rib once the gussets on that side are dry. Otherwise the roller will follow the gusset or glue from the first side or be adjusted so low it won't clean up all the glue.

Remember to rout in the spar openings as well. You'll need to touch up the inside corners with a mill file.

Monday, December 28, 2009

Wing Rib Gusset Glueing & Nailing

Now that the Christmas rush is over in the embroidery shop I'm back to building wing ribs while working on other projects. I've realized there are some things which could use some more explanation.

When mixing the glue I've found that mixing by volume vs by weight is the easiest. I've also found that the amount of glue needed to put all the gussets on 2 sides of a rib is exactly the amount using 4 teaspoons of Liquid Resin with 3 teaspoons of Powdered Catalyst. I've found that clear plastic drink cups work great. Recently I got some shallow clear plastic pill dispensing cups, they're even better, harder to spill. I use a metal teaspoon since it's easy to level the catalyst with a popsicle stick. It's also easier to wash the metal spoon clean after measuring each ingedient to make sure the unused portion in the can is not contaminated. One of the nice things with Resorcinol is that it washes up with water until it cures and becomes waterproof.

I measure the catalyst into the drink cup and the resin into the pill cup. The drink cup is easier to poor from slowly while mixing in the pill cup. The 3rd cup in the picture is a gauge to double check whether I've put in the correct amount of resin.

I reuse the cup for the Catalyst so I've drawn a line on it as a double check in case I get interrupted while measuring.

That doesn't work as well with the Resin since I use that cup to mix the glue. Since the cups are clear I have a cup which I can set the Resin cup into to check that the correct amount of resin was measured. I also have a line on it for the volume after mixing which is less than the 7 teaspoon total.

I've made 2 little videos to help explain how to install gussets.

The first covers applying the glue, just to the areas needed.


The second covers using the nailer.


These methods seem simple and obvious but they reduced my time to build assemble and nail both sides of a rib from 2-1/2 hours to 1-1/2 hours. With so many ribs to build it's a big savings over holding the nails with pliers and using the tack hammer.

Sunday, December 6, 2009

Elevator Horn Material Thickness

I've been working on how to make new elevator and rudder control horns. They are not used on the Waco Ten so there aren't many people to ask. There is one on each elevator and the rudder. They are stamped as 2 metal shells and welded together along the edge to form a rigid streamlined shape. There is no drawing I've found for these and they are more complex than almost anything else on the plane so I believe they were simply purchased as new WWI surplus. We built our Fly Baby with a lot of WWII surplus parts from the A & N store before they discovered Levis and Nike.

The outside shape was easy and I'll cover that in another posting. The bigger problem was the metal thickness. I have one horn on the rudder which is in good shape and one on one elevator. This elevator has rust problems but the horn is usable so I didn't want to damage it to measure the metal thickness.
Also at each end there is a piece of steel welded in the tab end making the tab 3 layers thick all welded along the exposed edge. The three layer tab measured .110" thick which leave a couple possibilities for the 2 shells and the inserted tab. The most likely combination was all three being 20 gauge steel (.o359").

The idea was to make a go-no-go gauge from 2 pieces of welding rod with feeler gauges taped between them. with this the thickness of the tab insert could be measured and the thickness of the shell becomes half of what's left from the .110" total

We don't need an exact measurement just close enough to determine the gauge size of the steel. By adjusting the stack of feeler gauges between the wires in .oo2 increments it was easy to show that the steel is 20 gauge.

I've included a video which explains this better but even at the lowest resolution it's 62 mb. I have a higher resolution version but it's 229 mb. If you have a high speed connection check out the video.