Horizontal Spar Bubble Repair

I had previously circled some bubbles between the core and glass on the spar that needed repair. Today I sanded them clean to get ready to micro and glass them. This will allow me to move on with hard point installation.

Using 60 grit, I sanded away the bubble being very careful to cause minimal damage to the core material. I deglossed the surface about 1″ around each bubble to prep for glass.

A closeup of some sanded bubbles. I’ll vacuum these out, clean the area with acetone, fill the bubble with micro and glass with one layer of BID.

Horizontal Spar Hardpoints

I did this last Monday 8/20/17, but didn’t get to post until today.

I did this exactly to instructions, but after I wished I had deviated a little and used my laser cutter.

From 1/4″ aircraft grade poplar plywood, I cut 20 1″ circles using a hole saw. I trimmed the flashing with a knife and sanded the loose bits off the sides and face. I did not sand them smooth.

2×4′ was the smallest I could order from Aircraft Spruce. Looks like I could have fit them all the way across and saved material if I’d thought of it sooner.

20 rough cut circles.

After trimming and sanding. Rough edges will help epoxy grip. All the loose material or over-sized bits are removed and they should fit nicely in the spar holes.

Before and after trimming and sanding. It took a long time to do them all. Next time I’ll just laser cut them a little larger and sand off the heat affected zone. Less mess and I’ll have a nicer finished product.

A Little Bit…

After I pulled my last set of ribs out of the flange molds, I haven’t had a lot of time to work on them. So I started trimming the flanges a little bit here and there as I had time. I found a hack saw blade works really well for this.

On Aug 7th I put the flanges on last 4 ribs and trimmed them the next morning. A hack saw blade with handle on one end really works well for this. It’s long enough to trim the whole flange, but gentle.

Untrimmed ribs just out of the mold.

Closeup of the trimmed flange done previously and the untrimmed side just demolded.

All finished horizontal ribs together.

HRIBs Continued

I flanges 4 more ribs tonight. 2x HRIB1, HRIB2, HRIB3

Both HRIB1 had bubbles under the glass on one side. I sanded and repaired these like on the Spar. 

I had done a bubble repair on HRIB3 previously, but I didnt fill the bubble with micro. I sanded out the bubble, cleaned the surface and glassed over the divot. This left an indentation about the size of a nikle. I wasn’t happy with the indenation on the rib and I wasn’t sure of the reduction in strength. Since this repair was already dry, I filled the divot with micro and glasses over the top so the rib, once again had a flat surface. 

HStab Spar 2

I put two layers of BID on each side of the Spar joint and repaired a bubble.

I sanded through the layer of BID on top of the bubble with 60 grit being careful on to disturb the foam and roughed up the area 1″ around. I filled the void on top of the foam with micro and cleaned any excess from the surrounding glass.

As usual I laid up the glass between plastic. I put one layer of BID over the micro and stippled it smooth.

I put the two BID stacks, one on each side and covered the up side with plastic to set.

After it was gelled this morning, I trimmed the excess with a knife. I also marked any of their bubble with a pencil so they could be repaired later. Before repairing them, I will lay out and cut the hard point for the elevator. There’s no point in repairing them if they just get removed for a hard point. The pencil makes them obvious so I won’t miss them later.

Horizontal Stabilizer Spar

I got the horizontal spar started today. The two sides were sanded on the edges to be the correct size and be symmetrical. The face of each side on the joining edges was scuffed with 60 grit and 1/4″ of foam was dug out from the ends. 

I made a 20gram mix of 5 min epoxy and thickened it with flox to be like thick cream cheese. I then packed the ends of each half where I had dug out the foam leaving a lot sticking out.

I made center marks at 3 places on each half and put plastic wrap over the location of the joint. I put the two halves together and lined up all the dots along the laser. I scraped off any excess flox.

The two halves aligned. Noted the pencil alignment marks.

I sanded off any excess 5min flox and took off the shine with 60 grit and trimmed the edges with a utility knife. 

Last thing I managed to cut 2 layers of BID for both sides of he joint. I cut the top piece to size and then added 1/2″ on both sides to add a slight taper in thickness to avoid stress risers.

Horizontal Stabilizer

Tonight marks the start of the KR-Super2 build. I completed glassing the first side of a 2’x4′ 1/4″ Last-a-foam panel and one side of two 3/8″ panels for h-stab skins. Work was done according to Chapter 2 as per instructions. 

I was initially going to use Ecopoxy for this build because it was described as odorless and non-toxic and ok for structural parts. I purchased a gallon kit. Later I became worried that is may not be a good substitute. Aircraft Spruce was not able to provide a mechanical properties of the Ecopoxy resin system and I also read that the Aeropoxy does not contain the cancer causing substance MDA and is tested by Rutan for all structural use. I switched back to the Aeropoxy. Ordered a gallon kit from Spruce 3pm Thursday and it showed up 5pm Friday with UPS ground. Not bad. That allowed me to get started tonight.

All-in, tonight’s work used about 1/4-1/3 of a 1 gallon kit. About $30-40 worth of resin.

I laid out a sheet of 1/2″ ply to provide a flatter surface than my garage floor. The plastic is to protect the wood.

I cut the BID for the first two sheets as per instructions. The final piece I straight cut. When following the instructions I only had the small triangles as waste. Straight cut definitely has more waste, but the large leftover rectangle can be used elsewhere in the future. The bias cut method proved very hard to keep the cloth weave aligned as I was rolling out the cut sheets on the micro’ed foam. It took forever to get the weave aligned again. The overlap of the two pieces of cloth is also heavier. For future glassing, I think I’ll stick to straight cut and accept the waste to make a better, light part in less time.

Above, 45 degree cut cloth laid out and trimmed to size.
Overlap of 1.5-2″

Straight cut cloth trimmed to size.

Cut BID rolled up and ready to go.

Mixing station set up. I would pour out the amount of resin needed, weigh it. Divide that by 100 and multiply by 27. That gave the exact weight of hardener to weigh out. Tonight’s project used about 1/4-1/3 of the Aeropoxy that came today.

I printed and bound the. Hold manual for easy reference.


My first attempt at mixing micro. It was a bit hard to spread. I mixed subsequent batches thicker and it spread on much easier.

Edit – the next time I mixed the micro 1:1 by volume with catalyze resin and this consistency was much easier to work with.

1/4″ foam nearly done with micro. I used an extra large scraper to speed things along. Just had to be careful to keep it flat and not let the edges dig into the foam.

Edit – the next time I used my yellow plastic squeegee to spread micro. Though it’s smaller, it seemed to work much better and faster.

Rolling the glass on to the foam was so easy with one big single sheet. Smooth by hand to eliminate air gaps between glas and foam.

Completed side 1 of the 1/4″ panel that will become various structural parts for the horizontal stabilizer.

I did the 3/8 panels with two glass pieces cut at a 45 degree angle. This was much less wasteful on the glass, but hard to align the two pieces of cloth to get the right overlap while keeping the weave pattern intact. 

Closeup of a finished panel.

Three panels with glass on one side. The 1×2 strips will give the wing skin panels a small curve that helps them conform easier to the airfoil shape of the h stab. 

Total time start to finish, about 4 hours.