Gear tabs

Alright boys and girls... I hope you are ready for this one. Here, I will show you how I made my main landing gear strut tabs. They are used to mount the strut onto the fuselage.

So here is where we left off - the 1/4" plywood jigs Bondo'd in place showing us exactly where the tabs need to be. Before we can begin prepregging the first layup, we have to prep the tabs by sanding the Bondo on the outside nice and smooth. Here is the before picture:

Before sanding the outside, a little voice inside my head asked, "If you are going sand off the Bondo, what then will hold the tabs in place?!" So I mixed up more Bondo and blobbed it onto the inside corner. This allowed me to remove as much of the Bondo on the outside without worrying about knocking the tab out.

 Once dried, I proceeded to sand the outside nice and smooth.

I then built a small jig out of 2x4s to hold the strut upside down on my table.

It looks complicated but is in fact quite simple - the two 2x4s on the outside are screwed onto the transverse 2x4 going across. The transverse 2x4 is then clamped onto the table on top of shims in order to allow the pink rope to clear. The pink rope is used to tie the strut down in place.

Here is a close up showing I have enough room between the tab and the jig to perform the layups.

The temporary plywood tabs get covered with tape to make it easier to remove from the cured glass later.

All systems are a 'go' for the first layup...

Here is Elle working on the first prepreg - 18 plies of UNI 4"x13" (plans say 3x12 but I've learned my lesson with Burt).

 I painted plain epoxy onto the strut to assure a nice bond between the strut and prepreg.

 

I then placed the prepreg layup in place and pressed it down to rid of any air bubbles...

 Never mind the annoying UNI strands on the sides of the prepreg... those get trimmed and sanded smooth after cure.

Next up is the 18 ply BID layup (4"x3" BID cut at 45 degree). This one gets placed on the OUTSIDE and wraps around onto the leading edge. A 1/4" plywood square (4"x4") then gets clamped together to help keep everything nice and snug. Notice the cling wrap around the square - this is to prevent the layup from curing onto the plywood. 

Another 18 plies of BID goes on the trailing edge side. I then peel plied all the edges for a nice smooth transition.

 The whole process is repeated for the other side.

 I let them cure overnight and the next day it was ready to be trimmed.

I started out by making as many cuts as I could with my multi-tool.

I then sanded everything flush up to the 1/4" plywood jig. 

I used a metal file to round the armpits of the tabs. Having square armpits is a big no-no as this creates stress risers and could eventually lead to cracks.

Perfect!

It was now time to transfer the LMGA 5/8" hole from the 1/4" plywood jig to the glass tab. The plans say to use a 5/8" spot face tool - and that's what one should use. However, I committed a huge crime by using my router to perform this job instead. Although everything worked out great, this was extremely foolish as I took a huge risk - any mishap would have required me to cut the 18 (x3) plies off and start over from scratch. Luckily, I got away with it.

First I adjusted the height of the router bit such that the roller road along the edge of the plywood..

I then drilled out a pilot hole in the center of the tab..

I then carefully milled out the 5/8" hole... and presto, LMGA tube went in...

I repeated to mill the other 3 holes, and before I knew it, I was test fitting the strut onto the fuselage.

I re-checked all the measurements again and made sure everything was aligned as it was when I had Bondo'd the 1/4" plywood jigs onto the strut.

Now that everything checked out - I felt comfortable with proceeding to the next step - the inside tab layups.

Before prepregging could begin, the strut had to be prepped. First task was to remove the 1/4" plywood tabs - remember, these were only temporary to get us to this stage. To remove them, I used a hand-held grinder and removed as much Bondo as possible, being extremely careful not to come in contact with the strut or any fiberglass whatsoever.

I then popped it off with a flat head...

I then performed a Michelangelo and chiseled away as much Bondo as possible... 

Well... this is going to require more work than I thought!

Fearing I would be damaging the layup underneath, I put the chisel down and started to sand with 60 grit...

That was great, but it was too big to get down inside of the leading/trailing edges... so I went smaller...

That was great, but it was too big to get down inside of the groove... so I went smaller...

Finally, I had removed ALL the Bondo and the strut/tabs were ready for the final layup!

Notice how I sanded the strut dull... along with the inside wall of the tab...

As Elle was prepregging the 18 plies of UNI (4"x12"), I commenced to prep the strut.. here I am painting on plain epoxy..

To assure no air pockets are left inside the tabs, a thick fillet of flox went on to fill the voids...

And 18 plies of UNI go on...

I used a mixing stick to tuck the 18 ply layup into the corners...

Just as I was finishing up... Elle was ready with the 18 ply BID pad that goes on the inside of the tab.

A strip of peel ply and the tab gets clamped! Again, notice I'm using the same plywood 4"x4" square to hold everything in place. I covered the mating surface of the square with tape to act as a release.

This was repeated for the remaining tabs..

If you've been keeping count - that's a total of 216 plies for these tabs!!!

Time to trim... again.

Just as I did before, I used the vibrating multi-tool to trim as much as possible.

To drill out the 5/8" hole, I purchased a proper drill bit this time (rather than using the router - even if I wanted to use the router, I couldn't since it would have required me to place the router on the inside of the tab - which would not give me enough room). I started out by drilling a pilot hole...

And then the 5/8" bit... using the outside tab as a guide to coincide the holes...

And presto! LMGA tube inserted...

Now that I had the LMGA tubes in place, it was time to fine trim and smooth everything out...

I used the router to get both the inner and outer tabs to be flush... I then sanded everything smooth. I also sanded the tabs' armpits.

There we go! Much smoother and neat!

I purposely skipped the part about epoxying an alignment pointer (to align the LMGA tube forward or aft). My plan is to remount the strut onto the fuselage and flox the tubes in place - then remove the strut from the fuselage and apply the last layup which permanently holds the LMGA tubes in place.

Here I am remounting the strut, checking for a good fit...

Looks perfect! Next up will be to permanently flox the LMGA in place and apply the last layup over the tubes and onto the strut!