DaSH PA -- Dead Simple Human Powered Airplane: Glue barrier in Outer Main Wing Spar + Drivetrain Parts and Ribs

Prepping a lipstick camera to inspect the inside of an Outer Main Spar

We continued to biscuit the wing spars this past weekend. All went fine with the Outer Main Wing Spar #1. Then, when biscuiting the taper on Outer Spar #2, we ran into a blockage when trying to get the last few biscuits in the large end of the taper past the sleeve joint between the straight part of the spar and the tapered part of the spar (the last 2.4 m of the Outer Spar is tapered in order to fit inside the wing skins, and to save weight in this lightly loaded part of the wing).

It was hard to figure out exactly what was going on since the joint was about 4 m down the tube, but if we squinted hard and threw a bunch of light in there, we thought we could see a rim around the joint. Glue? We weren't sure.

So we bought a lipstick camera, mounted it on a pole, and sent it down the pole. It was clearly a large rim of glue that had squeezed out between the sleeve and the outer spar when the joint was glued, and which created a 5 to 10 mm rim around most of the inside of the part, preventing the biscuits from passing.

On the advice of the tube manufacturer, we tried to knock the glue ridge out with a second aluminum pole. This was somewhat successful, but we couldn't get all the excess glue out that way. We are now trying to develop a way to sand the ridge down far enough to allow passage of the biscuits into the taper.

We found glue ridges on at least two of the wing spars (one Outer Main Spar and one Longer Outer Main Spar). Several others were clean with no excess glue. We'll inspect the rest (three more tubes to look at) on Wednesday and clean them all out once we have the tool working well.

Our first attempt to inspect the glue joint used a vehicle inspection device, but it was not long enough to see the problem area, even with an extension attached.

Taping a lipstick camera onto an aluminum pole to inspect the joint

The glue ridge that was causing all the trouble. Here we are attempting to knock off the ridge with an aluminum pole.

Video of attempt at knocking off glue ridge

Another video of attempting to remove glue ridge

Some of the large chunks of glue that came out as a result.

We couldn't get all the excess glue out by just knocking it with a pole, so we started to develop a way to sand the rest off.

Sanding a connector (a phone modular jack connector) for the lipstick camera so it will fit inside the aluminum pole.

Rounding the edges down

Partially sanded down

Finish sanding the part

The finished part

Fitting the phone connector into the pole

Putting the lipstick camera into the end of the pole

Dremel attached to end of camera pole, with small light

Ready to Go!

We found the Dremel body blocks the view of the camera, and it isn't possible to see the area getting sanded. We're going to try a Dremel extension next, to see if we can get a clearer view of the work area while sanding the glue ridge.

An attempt to make a hook to pull back on the glue ridge to dislodge it (didn't work)

Connie and Craig biscuiting one of the Outer Main Wing Spars

Taping the syringe in the middle to reconnect the biscuiting tool with a biscuit that didn't get enough glue, so we can re-engage with the biscuit and add more glue

The view of the first biscuit at the end of an Outer Main Spar. The yellow foam ring in front was used by the manufacturer to glue in a short 50 mm straight stub of tube at the end of the taper.

Video of glue application through biscuit

Note how about 2/3 of the way through the glue application, glue shoots farther out than we want, and gets onto the foam piece. We found that in most of the biscuiting we can see at the ends of tube, there is a large lake of unused glue in front of the biscuit that doesn't do much. We try to tilt the spar up after we finish biscuiting so that that glue can at least settle back against the biscuit and do perhaps some good. Fortunately, we are not counting on these glue joints for strength, just to keep the biscuits in place so they can do their anti-buckling job through mechanical interference.

Improving the biscuit gluing process is definitely something to be worked on for the future. If we found a better way to glue the biscuits, we might save a couple hundred grams.

Clamping up the biscuits after gluing

We received the Longer Outer Main Spars in two parts, a 100 mm straight section tapering to 50 mm, and a 50 mm straight section. These were shipped unassembled in order to save space in the shipping container (all our other parts were max 6.7 meters, but once glued together, the Longer Outer Main Spar part is 8.5 m long). We had to glue them together, which makes the parts slightly over 8.5 m, then we will cut to exact length after the glue dries.

Prepping the 50 mm spars to glue into the rest of the Longer Outer Main Spars

The pieces don't fit exactly the same in each side, with less overlap in spar #1 (Right) than in #2 when they fit snug inside the taper (tubes moved to all the way through the tube to the left after gluing)

West System G-Flex used to join the tubes together

Applying glue to where the 50mm outer tube of Longer Main Spar will join into the inside of the tapered part

Glue ready at foam ring and at area where tubes will contact (no glue on bottom 1/3 of each, we'll spin tube around once it is through the larger tube, in order to spread the glue around)