Attach Tabs

Step 3 ATTACH TABS & INSTALLATION

Here's the plywood set up for the first part of making a jig for the attach tabs. I have the 31" piece of plywood fastened to the work table and the main landing gear, MLG, strut set up in the right place. It's been centered and set at the right angle.

In order to get the MLG strut centered, I needed to cut some notches in the plywood. Plans say 31" wide, maybe this needs to be 30". No, the MLG strut isn't off center, I had to make notches on both sides.

I used my spline, the only thing I had that was long enough and straight enough to see if the floor it level. Turned out I needed about 6 credit cards worth of shims on the right side to get this puppy level. My Smart Tool sure makes quick work of this sort of jigging job.

I then built spacer A, beveled it 60 degrees, vice the 45 called for, and sanded it on the belt sanded until it sat on the MLG strut and was exactly level.

Once I built and installed spacer B, I realized I had mounted my spacer C too low. No worries, I just cut about 3/16" off of the center of it with my band saw and then put the assembly back together. Given that I had screwed, rather than nailed or glued this assembly together, this was no big deal.

I then finished making all of the spacer pieces and screwed them together. Using the band saw and belt sander to make sure all parts fit pretty good on top of the strut, I then removed the assembly, mixed up and applied the bondo, then placed the assembly on the MLG strut again. Once I check the whole thing level, I let the bondo cure.

It appears that the plywood I braced the strut against in previous steps flexed a bit, or, some other form of error was induced. I had a hard time getting the strut to come out level, with the right sweep on both sides. I tried clamping in various ways but this didn't appear to work very well as the wood I used kept breaking when I applied enough clamping pressure to get everything right. I thought about this for a while and then gave up - the strut was level and square and so forth but the plumb bob showed one leg of the strut about 3/32" forward of the line, and, the other about the same behind. It will have to stay this way and be adjusted when mounted in the fuselage.

I ended up needing about a 1/4" spacer in the front of the box to get the alignment mentioned in the previous step. A piece of aluminum scrap fit the bill just fine.

Once I had the spacing right I bondoed the jig box to the table per plans. I like to do this with a stir stick making a bit of a fillet with the bondo. I didn't put bondo "underneath" the jig box to make it a little easier to remove from the table once I was ready for that. You can clearly see the 1/4" gap, due to the spacer I needed to put under the "leading edge" of the box to get the sweep right.

I had to remove one of the screws I used to build the box. It was in the way of the 1/4" holes that would be drilled after the layup is done.

Once I had the box on the table level and so forth, I needed to re-draw the lines on the box at the right level height (since they are supposed to be an even distance all around from the table, and, I had to lean the box back). Given that the "trailing edge" was flat on the table, I measured those accurately and transferred that height to the front side. My height was 2 3/16", no where near the 4.25" that the plans mention. I don't think that measurement is right, for the record, it can't be. You use a 2x4 as a drilling jig later - and those are less than 4" in height... can't be 4.25!

Here I am re-marking the height line for the 1/4" holes. I used my 4' aluminum ruler, clamped in place, to make things a little easier.

I guess I used too much bond on the strut when I fixed it to the jib box with bondo. Some squeezed out onto the plywood and made a bit of a bump on the side of the strut. This would have to be removed to avoid having any bondo between the strut and the attach tab layups in the next couple of steps.

Here's the jig box and strut covered with plastic and tape ready for the layup. If you look closely you'll see the bondo places I mentioned in the step above. I have already used my Fein tool, a chisel, file and etc. (carefully) to remove the excess bondo.

Not only were my clamps too short for the next step, they did not have enough depth to reach the middle of the blocks I made. Time to visit my father-in-law's workshop - he has every tool known to man. I'm glad I discovered this now - before the epoxy started curing!

I never stop liking this method of cutting fiberglass. The rotary cutter makes this so easy, combine that with a nice straight edge and a table covered in plastic (I used a piece of tub surround) and this becomes a pleasant, accurate, quick to do task.

Here I am part of the way through the outside attach tab layups. In this picture I'm laying on one of the pieces, with the plastic still on the "back" side, and, you can see the wax paper on the front side. Once the bottom of the piece is in the right place, I used the tweezers to pull of the wax paper then drape the whole piece across the strut and down the other side. Push it around a bit until it's in the right place, squeegee through the plastic, then remove the plastic. Keeps the mess down, keeps the bubbles out. Repeat this process about 20 more times and you're done!

I used my Dritz electric scissors to make these cuts. I put an extra piece of wax paper underneath the plastic, layup, and wax paper on top to protect the table from the epoxy that oozes out a bit after you make the cuts. You can also see the marks, which I made on the wax paper on top of the layup, used to cut the pieces to the right size.

Here's the strut with all of the BID and UNI layups on before peel plying and applying the blocks and clamps. This layup took me about 4 hours, by myself. I did the UNI pieces, then took a quick break for lunch, then did the BID. I used my heat gun when I started the BID layups to ensure I had plenty of liquid epoxy for the first BID layup to stick to once I started again.

I did the peel ply in several pieces - seems to lay down better that way. A couple layers I knew would help here also because a lot of epoxy was going to come out when you clamped and squeezed it.

I used some woodworking clamps borrowed from my father in law. I had to be careful that I made them parallel (the jig box helped since the surfaces of it are) but they worked great for this. Plenty of jaw opening, plenty of depth, lots of pressure. I did cover the jaws of them with box tape just in case, though, they're not my clamps!

Once the layup cured, and I got back from my week-long class, it was time to remove all the blocks, peel ply and jig box. The butt of my hammer worked great to pop off the blocks. I struck the top of the hammer with a rubber mallet.

Nice, flat, bubble-free, attach tabs. I did have a couple of spots on the insides of these where the wood was not flat (like from a knot) that the epoxy/glass perfectly molded to.

I used the HSS blade on my Fein to cut the extra glass, and epoxy (which ended up on the table) loose from the rest of the attach tab.

I then used the Fein to trim away some of the bondo. This allowed me to use a longer piece of 2x4 for the drill jig, and, not have to carve or cut out the back corner of that jig so it would fit flush to the attach tabs. I was careful not to remove so much bondo as to risk having the jig box come loose or wiggle some.

Using the most square 2x4 I had, I gently clamped it to the attach tabs (after marking the right height on it and drilling the 1/4" hole in the drill press, of course) and drilled the 1/4" pilot holes in the tabs. My cordless drill on slow speed had no troubles with the 50 layers of glass.

I needed to re-mark the attach tab outlines after doing the layups since it was hard to see the lines on the box through the 50 layers of epoxy and glass. Since I had already drilled the holes before doing this, I simply inserted a dowel into the 1/4" pilot holes, marked its center, then used a compass to re-draw the outlines.

Then it was time to remove the box from the table. I again used my Fein tool, with the HSS blade, to cut a slot in the bondo. This blade eats fiberglass, thus, bondo is no challenge. The box simply lifted off of the table once I had cut a slot in all the bondo. On the sides where there was no gap, I just cut the bondo until I saw wood chips and knew I was into the box behind the bondo.

Once most of the jig box has been removed from the strut, it was time to cut the tabs to shape. I used the sabre saw on it slowest speed. Worked fine. Took a while, completely dulled one blade, but if you went slow it worked fine.

Given the width of the final layup was way more than the 3" it needed to be, I decided to use my Fein to trim the layup. Working carefully from the side, then top, then side, then top, I cut small pieces away until I was very close to the strut and the 3" width line I made. I think I will sand the last couple of bumps off or file them so I don't cut into the strut or layup.

Rather than using a candle to drip wax into the attach tab holes in preparation for the next layup, I brought out some paraffin and a propane torch. I had the paraffin laying around because we use it to lubricate bicycle chains.

Given that I didn't have enough fiberglass to do the inside attach tab layups (and had to wait until my order for more came in) I started building the MG-1 and MG-2 pieces I'd need for later steps. This shot shows me cutting the 1/4" aluminum for MG-2s to width using the band saw, a metal-cutting blade and a stop that can be set to accurately cut the blank piece to width.

After cutting the pieces basically to size, I spray-glued a CAD drawing (after printing, of course) to the blank with the holes and dimensions thereof on it. I use this to center punch the holes and help me remember what size to make each hole, to countersink, etc.

Here's the finished MG-1 and MG-2 pieces after drilling, countersinking and etc. These didn't take too long but man, that's a lot of holes to drill. I did all the holes in steps, of course, starting small then moving up to the eventual drill size. Include the countersinking in MG-2 and I think I drilled over 100 holes!

I put some 2x4s on the jig table to support the strut while doing the inside attach tabs layup. I also added some plastic, some cardboard "dams" taped on with box tape and some other sticks to support the plastic and keep the mess under control.

Look very closely at this picture - don't the attach tabs look a little long? More on that later...

Here's a shot of me doing the flox corner before doing the inside attach tab layups. The end of the mixing stick makes a nice sized filled for this sort of work.

To make the layups, per the plans, you start with the right number of layers and wet out a large piece of fiberglass, then cut it to size to make the multiple layers you're going to need. I did this on a piece of plastic on the jig table to keep the mess down. Here's the first layer wet out and waiting for the second layer.

Laying on the second layer.

I used the heat gun on many of these layers to make it easier to get the bubbles out from between the layers as they went on.

Here's both attach tabs with half of their inside layers on. They turned out pretty nice altogether, lots of extra glass hanging over but that's better than not enough. They're ready for the second set of layers.

When I have a fairly large area like this to wet out with epoxy, I use the squeegee rather than a brush or something else. I pour a bunch of epoxy in a couple of strips, then, spread it quickly with the squeegee. Keeps me from having to put as much on, and, saves a bit of epoxy. I find if I use the brush, I tend to over-saturate the layer and end up taking most of that epoxy back off again anyway.

Here's the second set of layers, after being cut up. I put plastic over the jig table, then, wax paper over and under these layers. Mark the wax paper with a marker then cut on those lines. Pull off one layer of waxed paper, apply the layer, squeegee it bubble-free and into the right place, then remove the top layer of wax paper. Some folks use plastic film, same process.

Here are the attach tabs with all the inside layers installed. I added a piece of plastic film before I clamped them (see below.) You can also see the little dam I made from corrugated paper to keep the epoxy drips from running down the landing gear strut. You can also see the plastic under the center section. I try to keep the mess under control during layups like this, makes the job a little easier and more pleasurable to do because there's less clean up at the end.

With a piece of plastic over the last layer, I used a double squeegee technique to get the layers to stay in the corner while I removed the last of the bubbles from the spaces in between the "stacked on" layers.

I then added some blocks of wood and clamps to the whole assembly. I put some peel ply in between, also, put box tape on the wood to keep from having it all stuck together when it cured.

Trimming the attach tabs once they were cured was hard. We went through a couple of hack saw blades to get to this point, cutting the larger chunks away first with the hack saw.

Carefully cutting the attach tabs to width on the sides of the tabs.

The Fein Sander with the HSS blade works great for trimming some of these areas that the hack saw or the jig saw has trouble with.

Another shot of the Fein sander in action. I really like it for thick layups like this, you can take your time and saw a little at a time without worry of overheating the part or dulling a jig or hack saw blade.

Here are the attach tabs trimmed to size - well, at least to match the inside. I also use the Fein to trim the sides of the tabs on the top and bottom of the strut. I went ahead and left my edge square, with a small rounding of the corner to avoid a stress spot, but, didn't blend them into the strut.

Drilling the 1/4" holes in preparation for later steps where the inserts are installed.

1/4" holes all drilled, ready for the MKMGA installations.

My daughter Emily frequently helps me with installation steps that involve crawling underneath things. She gets the fun of doing it, I get a willing and able small person who fits in tight places and has very small hands as a helper. Works for me!

I had to finish trimming the ends of the landing gear cutout to get the strut to fit into place. I had left the previous layups long so I didn't accidentally cut them too short, now it's time to trim them to size.

Here's the landing gear install inspection crew. From the left, Emily, my daughter, Sean, my son's best friend, James, my oldest, and Matthew, our youngest. They told me the landing gear at this point looked like horns on a bull!

I used a straight 2x4 to drill the 1/4" holes in the strut. The tabs are still too long here, more on that later. Don't they look a little long?

Marking and drilling the landing gear hardpoints for the 1/4" rods was next. I used a piece of steel as a straight edge, my rulers were either too long or too short to reach.

Well, the attach tabs being too long is quite evident here. The center portion of the strut won't fit down into the NACA scoop, when I got to this point I realized I had measured wrong somewhere. I'm not sure if you can tell but the ruler won't touch the bottom of the NACA scoop when laid over the top of the strut.

I used a block of wood as a spacer to draw a cut line on the landing gear cutout while the gear was in the fuselage, on the 1/4" rods, centered between the landing gear bulkheads.

Given that I didn't want the attach tab holes to be off-center in the attach tabs, I had to re-drill the landing gear hard points to line up with the holes in the attach tabs once they were shortened. I don't think this will cause too much of a problem, they only moved in about 3/8", and, there is plenty of solid fiberglass bulkhead reinforcements all around the new holes.

Trimming the attach tabs to the CORRECT length once the holes were located in the CORRECT place.

Now, the strut fits into the fuselage and the NACA scoop will not be obstructed by the landing gear strut...

My dad helped me with many parts of the attach tabs at this point. He and my mom were in from Florida.

He knows how to clean up, too! Good job, Dad!

I used the belt sander, after trimming the attach tabs with the hack saw, Fein and jig saw. The belt sander worked well to get the tabs sanded right down to the circle we drew on the tab.

Here's the tabs with the new holes drilled and trimmed to the CORRECT length. The old holes are still visible, I filled them with flox. Given they are way outside where even the washers will install, I don't think them being there will cause a problem.

My rotisserie needed to be disassembled and changed around a bit to mount the landing gear. I needed to be sure the fuselage was level, and plumb, it was difficult to do that with both ends free to rotate. I took the fuselage off of the rotisserie and added some 2x4 lumber, across the short way, for the fuselage to sit on. My dad being here sure helped, the fuselage is not heavy at this point but it is a bit awkward.

here's the attach tabs and strut installed with 3/16" rod I had laying around from my model rocketry days. There was enough misalignment in the tabs and holes that I could not get the 1/4" rods in at this point.

Here's the marks I made in earlier steps on the sides of the landing gear cutout between the landing gear bulkheads. I need to trim this a bit more before the strut will fit properly.

Tape on the floor was the start of my measuring system.

I used a jig saw to trim the cutouts after marking them.

My son James helping with some drilling operations. Note the safety glasses - safety first is a good lesson to teach him!

Drilling the landing gear bulkheads with the long 1/4" drill bit.

I used some large fishing weights with hooks on them as plumb bobs for these steps. The tape cross on the floor is where the center of the aft of the fuselage is supposed to be.

Same weights used on the ends of the landing gear to check sweep and square.

A close up of the weights. There were cheap, and, I had a bunch so I could hook them all on, let them settle down from swinging and check the square and sweep and level all at the same time.

Once the fuselage was jigged onto the modified rotisserie, I had to shim it until it was level and plumb. The floor is so far off of level that my screw-on feet on the rotisserie didn't have enough adjustment to compensate. I ended up with 1/4" pieces of plywood under some of the feet.

Measuring from the center of the front of the fuse to the point where the plumb bob on the front of the landing gear strut reaches the floor to check square.

Lines on the tape on the floor were used for marking where things were supposed to go.

I also put some small pieces of wood, on both sides, between the attach tabs and aft landing gear bulkhead, to make sure the gear is centered between the bulkheads. Drilling a hole, then cutting a slot to the hole, allowed me to insert and remove these easily without them falling out as the gear got jostled around.

Don't move - don't breathe! Fuse is level, square, plumb, the landing gear is centered, square, level and has the right sweep. Quick! Mark and drill holes for the MG-1 and MG-2 pieces!

I used hot melt glue, rather than anything else, to fix the MG-1 and -2 pieces to the landing gear bulkheads while all this marking and adjusting went on. It's easier to "install" than bondo, and, easier to remove. It doesn't have as much strength, but, if you're careful jigging parts like this you really don't need much strength.

All my MG-1 and -2 parts were marked so I would not mix them up once all the holes were lined up and drilled. I used 1/4" rod for this step, you might try 1/4" all thread also, you could use nuts on it to hold things in place more easily.

Drilling the holes for MG-1 and -2 using a 90 degree drill I borrowed from my father in law. My electric drill had gone out before I did these, I ended up having to use my cordless, let's just say it worked fine but it needed a couple of charges to get through all of these holes.

Here's an MG-1 with the holes drilled and the AN hardware installed. 1/4" all thread was used here, with some washers (to hold the piece in place while all 4 holes were drilled) to ensure it didn't move around.

I used a hole saw with the long 1/4" drill I own as a pilot drill for the attach tabs. If you went slow, this drill bit could cut a very nice clean hole. I think you were supposed to use a counter bore for this step, these bits were a bit less expensive.

MKMGA pieces installed into the attach tabs after drilling holes.

All the metal parts installed into the attach tabs, test fitting to make sure I have it all set up right before floxing and final layups.

A shot of the MG-2 piece, with the AN hardware installed, and a short 1/4" bolt that was used to hold things in place while drilling took place. I was not able to drill the 4 holes around the periphery with the long rods or long 1/4" all thread in place, this was a quite acceptable substitute.

Test fitting the MKMGA parts, over the steel studs, through the MG-1 and -2 pieces. I did not flox any parts permanently to the fuselage yet, I plan on doing that after painting and after alodining the parts.

Here's a shot of inside the fuselage with the steel studs installed through the MG-1s.

Checking all the specs again, last chance, before installing the MKMGA pieces and washers into the attach tabs permanently. I am going to wait until later in the construction of the plane to flox the MG-1 and MG-2 pieces permanently into the fuselage. I'd like to alodine them, for starters, and I don't have any alodine on hand right now. Further, I'm thinking I might want to paint or do something and having them removable will give me options I don't have if they are permanently installed.

I used hot melt glue to hold the MG-1 and MG-2 pieces in place for these steps. In this shot the large holes for the 4130 steel bolts have been drilled as have the 4 holes for mounting of the MG-1s and -2s. The hot melt scrapes off pretty easily and a quick touch up with sandpaper makes the surface ready for whatever comes next. It smells better than bondo, too!

Here's an MG-1 still hot melt glued in place after drilling all the necessary holes. It was a lot of work to get the large holes drilled. My cordless drill batteries finally died (they don't hold a charge anymore) and my corded drill has a warped armature.

Here's a shot of the attach tabs curing after install the carved foam pieces, MKMGA (after dimpling) and the washers on the outsides with flox.

Another shot of this assembly after floxing together. I didn't make the foam pieces go all the way to the edge of the attach tabs so I would have a glass to glass bond for the BID wrap that goes over MKMGA and the foam pieces. I may have to round off the square edges on the attach tabs to avoid a stress concentration point later.

I used clamps, peel ply, sponge rubber, spit, cursing, etc. to get this BID layup to stay in place. It goes over the top of the MKMGA, foam pieces, has to overlay the inside of the attach tabs on the sides and bottom so getting it to stay in place was quite a challenge.

I used clamps and peel ply and sponge rubber, etc. to do the layups on the outside of the tabs as well. It was hard to get the BID to lay flat over the washers, down the side of the washer and onto the face of the attach tabs too.

The layups turned out OK, though. You can see the floxed in hole from a previous step wherein I made them too long. Better tool long that too short, I guess. I don't think this is a strength problem, either, at least I hope it isn't.

After trimming and sanding those last BID layups, the attach tabs are complete. I'm now ready to move on to the landing brake cover.

Click here for the next step, the gear cover.