LG Bulkhead Reinforcement Preparing Strut Attach Tab
Landing Gear Cover Axles, Brakes & Brake Lines Landing Brake
In this step, I will build up two attach tabs on the main gear strut and then install it in the fuselage between the landing gear bulkheads. However, a precise jig is needed to support the lay up. Per plan, I lined up the strut against a perfectly vertical backboard. Then I leveled the floor and had the strut legs centered to 67.5" (depending where I take the measurement. My 67.5" is at 1/4" from the front tip of strut). I marked and set the front tips of the strut at 9.25" from back wall and leaned the top of the strut against the backboard. I used a long straight edge to make sure both tips are in alignment. Most importantly, I double checked all the measurements 20 times such that they are correct.
Since I was out of pine boards, I cut out a 3/4" x 5 1/2" particle board for the back side of the jig such that it will fit on top of the strut and leveled at the same time. This took a lot of patience and as I looked back later on, its well worth the effort. As shown, the curvatures were carved out to fit against the back side of the main gear strut. Then I laid the backboard on a flat surface and glued down the cross members with weights as shown. I clamped a couple boards in between to keep the cross members flat and parallel.
Once cured, I mounted the partially built jig onto the strut, leveled and clamped in place with the big red clamp at the middle - holding it at 90o side by side AND front & back. This is temporary while I work on the 2 front faces.
Then I carved the two (2) front faces, clamped down for trial before glue down. Everything is squared, measurements are correct and looks good so far.... then Murphy showed up...
Note the base of the front faces - half of it is inside the strut while the other half and outside the strut. The glass tab is not going to sit smooth over the front face I must have screwed up in some dimensions some where...
I re-checked all the instructions, re-measured every dimension and angle - everything seemed correct. The 2 widest spots of the strut is slightly under 5.75" located at the center lines of the TAB positions (13" from the center, Ch 9 Fig.13). The box is squared and leveled and there is no room for the front face to go .
Come to think of it , if the box has to be 5.75" wide with straight edges per plan, while the edge of the strut is curved with its widest spot at 5.75" (remember we have to remove the bulge at Ch 9, p.2, para.3?). Then how could I prevent the front face from sticking out past the strut - other than at the widest location? Got questions and no answers ...
A late night e-mail to Wayne Hicks and a morning response followed. Basically, don't sweat it, mine was like this too - try modeling clay, smooth it out and here's a picture for your reference... what a great support! Made my day to boot... With that settled, I clamped the jig in place, making sure its level from the floor to the top of the jig, bondoed the jig onto the strut and let cure overnight.
[Hindsight: I filled all the gaps with bondo. The jig is secured to the strut alright - it took me 6 hours to break the jig loose later on. You may want to be a bit skimpy on the bondo stuff.]
The next day, I made sure the work table was level. Then I transferred all the dimensions onto the work table, removed the strut and jig off the back wall and placed the whole assembly (with the legs up) resting on the box at the pre-marked location. The jig lined up perfectly on the work table and the legs were leveled at 0.0o first try! No shimming was necessary .
I was extra careful in handling the strut because I heard all these horror stories from other builders about the strut tipping over - grabbing their fingers with it or whacking them in the mouth on its way down. Surprisingly, mine was quite stable and has no tipping tendency - lucky I guess.
My next task was to check the location of the leading edge relative to the 9.25" (or FS 108.25). The plumb line was right on with the right leading edge but the left was 3/32" aft. I was really puzzled by it and pouted about it over an hour before deciding to move forward. I have to compensate for it by moving the wheel axle position a bit forward later on.
My next step was to smooth out the transition edge between the jig and the strut such that the glass (tab) can lay down nicely. I went to the local crafts store and got some modeling clay that is supposed to harden in 24 hours - good enough. Laying down the clay was a bit of a challenge right from the start... its like used gum and it does not want to smooth out at all. I tried pressing them with fingers, putty knife and credit cards with no success. I just couldn't make a nice smooth curvature for the transition. Then ... Grandma's rolling pin !!!
Got myself a couple sizes of wood dowels and went at it. The modeling clay rolls over like a puppy ...and in no time the transitions were done, nice and smooth. After it cured (in 24 hours), I took a 220 grit sand paper and touched it up lightly - turned out great!
One of the critical dimensions was the position of the 1/4" hole on the tabs - it has to be .75" above the highest point on the strut AT the 13" mark. I wanted to double check that dimension before glassing the tab. At this point, the hole location is somewhat difficult to reach with any form of measuring device.
I measured the height of the 1/4" hole above the floor of the cross member (white surface), in my case it is 1 1/4". Then I added .75" to that, making it exactly 2". I cut up a small triangle (as shown) with that total height (2"). Then I measured and marked a line at the 13" position. In this case, its the distance between the hole and the edge of the jig. I set the triangle right on the marked line. If the tip of the triangle touches the highest point of the strut with no gaps - you are right at .75" per plan. Mine was right on... In other words, the 1/4" hole locations are exactly to plan.
[After thought: Though my triangular measuring jig looked right on, somehow, it doesn't sit right in the back of my mind. I didn't quite trust my measurements for the 'highest point' across the top because its too wishy-washy, and it is hard to pin point exactly where those measurements should be taken. So after I finished with the first set of glass, I did the measurement differently (see below).]
I cut the glass strips and prepared them per plan. The only difference was that I cut them 3.5" wide instead of 3.8" wide because eventually I have to cut them back down to 3" wide from tip to tip anyway. It turned out that the glass tapes tend to slide around and by the time you got 45 layers on top of each other, their alignment may be less than 3" of useable stack. Once I realized that, I was real careful in lining them up including the squeezing step. I got my 3+" without too much to spare.
Note I put plastic sheets AND packing tape on the table before squeezing the tabs with clamps. [Lots of epoxy oozed out all over the place when you are not watching...].
I also peel plied the top for a smooth transition.
After glassing the tabs, I proceeded to drill the two 1/4" holes using the 2x4 alignment fixture per plan. As I mentioned above, I was not comfortable with the way the measurements were established per plan - though the two hole locations were pretty close to level. I decided to take the longer of the 2 dimensions from the reference point up for establishing both the 1/4" hole locations (in this case, upwards from the top of the table surface, with the gear legs resting on the jig up side down). The reason I took the longer dimension was because locations of the holes will fall inside the .7" - .75" envelop if it is off. Since my table was leveled to 0 degrees, the 1/4" holes were level as well.
At this point of the project, I have not worked a whole lot with bondo. Concerned about the stability of the jig and strut, I filled all the gaps with bondo. Well, the jig stuck with the strut very well (actually too well) throughout the task. When it came time to remove them - they would not budge at all. Eventually, I had to totally destroy the jig before I could get the strut loose - took me 6 hours. You can see the mess I made in those 6 hours, the tools I used to do the damage include hammer & chisel, hack saw, circular saw, jig saw, Fein tool, Dremel, palm sander, sanding pads, sanding sticks and lots of @#$%&*! My poor jig, looking as if it crossed paths with Chainsaw Leatherface, ended up in many many unrecognizable pieces. The good news was that the strut was freed un-harmed .
[Hindsight: Got an e-mail tip that if I heat up the bondo a bit first, the removal effort would have been much easier. Just don't heat it up too much that affects the glass underneath.]
The next step was to trim the tabs to 3" wide over the strut terminating to 1 1/2" radius ends. I first traced out the cut lines with dark marker on the tabs. The Fein cutter is perfect for the job because I can make a straight cut (along the cut lines) and through the 45 layers of glass without cutting into the strut. Since the glass tab is thick and tends to get hot while its being trimmed, I alternated the sides of a round cutter on two separate cuts at the same time. Once the glass was cut, I smoothed out the edges and radii with a palm sander (60 grit). Some hand sanding here and there was needed in the end. Here's the strut standing on its trimmed tabs. There's no rocking - meaning the tabs are accurately trimmed to the same dimensions.
I laid the strut on its side and filled the 1/4" holes with wax per plan. Then I repositioned the strut upright and filled the inside corners with relatively dry flox. Then I brushed them lightly with pure epoxy so that it smoothed out nicely. I then applied the 20 continuous plies of UND (#3) and then the 25 layers of BID (#4). The number of plies for UND and BID are reverse compared to (#1 & 2) - I almost missed it.
For whatever unknown reason, my lay-ups cured much sooner than the last, so when I was ready to clamp down and squeeze out excess epoxy - it was too late. I performed the ritual anyway, but hardly any epoxy oozed out this time. My inside layers turned out thicker than the outside layers - hope this is OK.
Again, I used my FEIN tool to do the tab trimming and palm sander to round them off (36 grit sand paper). As the seam line starting to get thinner, I changed the sand paper to 100 grit and continued with the sanding until the seam between the inner and outer layers disappeared - felt like an eternity before it came about.
I placed the fuselage (upside down) back on the saw horse for this strut mounting step. I made sure the fuselage was level front to back and side to side. Recognizing that I will be taking some measurements on the floor relative to the fuselage, I clamped the fuselage to the saw horse and bondoed the saw horse to the floor. I then transferred the fuselage center line onto the floor with a plumb line (as shown).
[Hindsight: I am glad I did this because it is important that the fuselage measurement system lines up with your floor measurement system].
With a cross hair laser, I marked the FS108.25 positions on the floor per plan.
I set the strut in place on the fuselage, and tried to insert a 12" drill bit through the forward bulkhead, strut tab and the aft bulkhead (on both sides). 3 out of the 4 holes were way off while the 4th one was slightly off. Can't imagine I could be that far off, I spent tremendous amount of time (days) to find the "right" position - I shimmed this and that, jigged here and there... never got anywhere . I finally gave up and moved on.
I re-established the fuselage center line with my lasers and re-drew the mounting holes accordingly. I had to slot 2 holes and re-drill a new one per the new measurements. I made sure the new holes were level horizontally and fore & aft (note the bubbles on the level). After lifting the strut off... filing the holes a bit... put strut back on...measure... repeat..., repeat... and repeat (about 30 times), I finally got the leading edge of both legs on target at FS108.25 except I was about 1/4" off center.
[For the un-informed, this main gear strut is ~35 lbs and is an odd shape object (as you can see). Picking it up to chest high location, carrying it over to an open space, and then lowering it down to the floor level many times is not what I consider 'a walk in the park'. After 20 some odd times, I started to wobble around like a drunk...]
Not convinced I could be that far off AGAIN, I decided to double check my measurement systems. Maybe the fuselage center is off relative to the floor measurement system (remember I bondoed the saw horses to the floor?) Besides, moving every 1/4" can be a lot of work. I need to re-check all the measurements first. I remember Marc Zeitlin's good words - measure, measure and measure!
I re-checked the center line of the strut using a combination of the plumb lines and the cross laser. I re-measured the distance between the strut center line to the leading edge of both legs - they are the same as expected. I also put the 12" drill bits through the tabs and made sure they were level when the measurements were made (notice the 2 yellow bubbles resting on top of the 12" drill bits at the tabs?)
Then I mounted the strut back onto the fuselage, using the 2 leveled 12" drill bits (32 times and counting...), I re-checked that the center line of the strut aligned with the fuselage centerline and they did...
I doubled checked the plumb line from the fuselage center line to the floor center line to make sure they were aligned, and they were...
Still suspecting a discrepancy between the fuselage and floor measurement system, I placed a straight edge across the fuselage centerline and measured its distance from the plumb lines. They were 1/4" off, just as the floor! It was puzzling... I concluded that it had to be my neighbors who came and switched my Stanley measuring tape with an elastic one !
I decided to post the question to the Cozy Forum and see how critical the 1/4" off center is. I got 3-4 responses the next morning. What a group! - you don't even get that kind of support for a paid service. The general consensus was 'don't sweat it... BUT' - I knew it, there's always that killer BUT... Imagine pedaling down the road in a tricycle with the center wheel not lined up with the center of the two back wheels... except this time, I'll be going down the runway at 75+mph with 1200+ lbs behind me. I don't think so Bernie, do it right...
Well, I spent the next 3 hours moving the 4 alignment holes 1/8" to correct for the 1/4" off center. The final out come includes:
- 0.0o level for the fuselage;
- 0.1o level for the struts (1/4" is acceptable per plan);
- struts are centered;
- left strut plumb target is right on FS108.25; and
- right strut plumb target is 3/32" ahead of FS108.25 (or ~FS108.15).
I think that's good enough and time to move forward! I have spent way too much time on this 1/4" mystery (and... Susann agreed ).
There are the 8 metal anchor plates for supporting the struts onto the fuselage, namely the MG-1 and MG-2. I cut them out with my band saw, put in the center holes and counter sinks with my drill press. I used hot glue instead of bondo to hold the plates in place before removing the 1/4" pilot rod and the strut. I think bondo is a bit overkill and they are much more difficult to remove compared to hot glue and you really don't need much to hold the plates in place at this point.
The bottom edge of the 2 fwd MG-2s sat right on the bend of the forward bulkhead. Instead of cutting them shorter, I just used the grinder and removed the lower obstructing edge as shown. I pretty much followed the plan when installing the MG-1 and MG-2. A couple of the S60 screws were a bit short, most likely I will have to replace them later.
Accordingly to the plan, I am supposed to open up the MG-2 holes to 5/16". I could not figure out the purpose for this step, because in a couple steps later, I will have to open it up to 5/8", but I followed the plan and did it anyway. [Hindsight: I wish I hadn't done so because I see no benefit to the step and secondly, it eliminated an important 1/4" pilot (alignment) hole when drilling the landing gear attach holes in the fuselage.]
I did not flox the MG-1 & 2 at this time because I wanted to be able to check the final position of the landing gear and be able to make minor adjustments, if needed. Besides, I wanted to alodine the parts before making them a permanent structure to the fuselage.
I bought the spot facing tool from Aircraft Spruce for the next step - $38! Before I started drilling on the real parts (i.e. the MG-1 & 2), I tried it on a left over piece of 1/4" aluminum. This tool did not remove material as well as any common counter bores. All it did was to generate heat and melt the plastic caps on my C-clamps - worthless! Since I do not want to heat up the fuselage fiberglass, I ended up blasting the MG-1 and MG-2 with compressed air every 30 - 45 seconds throughout the entire drilling step - just to keep the brackets and fiberglass layers from overheating. The tool got pretty dull by the time I was done - costly tool for a single step operation. I think you may be better off getting a counter bore w/ a 1/4" pilot for it.
I did not follow the plan drilling sequence per Fig. 27 because once you have completed the forward bulkhead holes, you are left with the 1/4" pilot holes in the aft bulkhead and MG-1 only (remember, I opened up the MG-2 to 5/16" earlier per plan?).
Since I opened up the MG-2 to 5/16" per plan, I cannot use them as a pilot hole for this step. That means I must maintain both the 1/4" pilot holes in MG-1s as long as I can. My drilling sequence was as follows:
- drill aft MG-2 and aft bulkhead first, but stop short of going through aft MG-1;
- drill fwd MG-1, fwd bulkhead and fwd MG-2;
- complete drilling aft MG-1.
[Hind sight: Though it took an extra step, as I realized later, the installation for the MG-4 bushing, the landing gear struts and MG-3 tubes were painless.]
I misread the M9 drawing when installing the MG-4 bushings. On the right end of the shaft, I thought it consisted of the flange of the MG-4 bushing and a washer (though the left showed only a washer). I interpreted it to mean that the bushing goes from the outside towards the inside. With that arrangement, my MG-3 tube will be too short with a 3/16" gap between the end (of the MG-3 tube) and the MG-2. Though the shaft will go through all of them, what is going to keep the landing gear from sliding back and forth?
Puzzled by this, I posted the question in the Cozy Forum. I received 3 - 4 responses within a day ranging from a graphical illustration to a phone call. What a support group! I owe a big thank you to Wayne Hicks, Dale Rogers and Kent Ashton - who clarified the MG-4 bushing orientation for me. They are supposed to go from the inside toward the outside!!! Since the diameter of the MG-4 bushing has the same diameter as the MG-3 tube, the drawing (as drawn correctly) will not have a larger flange at the inside face of the MG-2s.
I repositioned the bushings and to my surprise, the flanges of the bushings took out the gap between the MG-3 tube and the MG-2s and I got a snug fit!
[Hindsight] Due to the snug fit of the strut, bushing and the main landing gear, some builders had a tough time removing the main gear later on. I took Wayne Hicks advice and added some anti-seize (from any auto parts store) to the strut. In addition, I ground off a slight face to one end of the strut, such that I can turn it with a wrench if needed.
With the experience of the spot face tool from Aircraft Spruce, I did not want to spend another $38 to drill the 3/4" holes on the strut tabs. I decided to go with a hole drill (with a 1/4" pilot) from Lowe's instead (~$9). I did a trial run with the newly acquired hole saw on a scrap piece of lumber and found that there is excessive play between the hole and the MG-3 tube. With the critical alignment requirement, I preferred to have a tighter fit and not introduce additional play at this point in the game. I decided to call it quits for the day and slept on it - I was not happy .
Most hole saws have raker style teeth - i.e. some teeth point inward while others point outward to produce a better cut. The outward teeth are the ones that establish the overall hole diameter. I used a caliper and located the outer most tooth - it was about .774" instead of .75", thus giving me that unwanted clearance. With my Dremel and sanding bit, I made a few light brushes down the side of the protruding teeth and tested the hole diameter on a scrap piece of wood. Notice the nice fit between the 5/8" dowel and the hole in the background? That also equates to perfect fit holes for the MG-3 tubes.
I did not follow the drill sequence of the plan (again). I drilled from the outside towards the inside of the strut tabs, but stop short before cutting all the way through with the first hole - thus retaining the 1/4" alignment holes for the first end. Using both 1/4" alignment holes, I drilled through the second tab - single shot. Then I came back to the first tab and completed the drilling from the outside towards the inside. I ended up with a set of snug fit holes for the MG-3s.
I had to grind down the glass surfaces (between the tabs on top of the strut) a bit such that the MG-3 tubes could go straight through (from hole to hole) without obstruction. Eventually, they get covered up by foam and glass - no one will ever know...
With the MG-3 tubes fitted in the strut tabs, and the MG-4 bushings oriented correctly in the MG-2s, I picked up the strut and placed it in position on the fuselage. Hoping I do not have to pound the shaft through the tube with a hammer, I thought to myself...
Shaft #1 (left) slide in easily, with minor wiggling - that is good...
Shaft #2 (right) slide in with little persuasion but stops at far end of tube at MG-2. Oh..Oh. Little pushing, lifting and shuffling, no go. Harder pushing, lifting and shuffling - still no go. Hmmm... Back off shaft #1 out of its far MG-2 hole. Now go back to shaft #2 and push... IT WENT THROUGH all the way! That's more like it. Back to shaft #1, it went through all the way as well. OK - so far so good.
Checked fuselage centerline relative to floor centerline with plumb - they stayed aligned, good...
Checked fuselage level and it is at 0.0o - getting better...
Checked strut level and it is at 0.0o ... YES!
Dropped plumb lines from forward edge of struts and with little pushing (back and forth), right plumb target right on FS108.25 - aaaalright!
Left plumb target at 3/32" forward of FS108.25 - well, that's good enough...
Both struts are centered - Maaaaarvelous...!!!
The strut alignment is hereby declared good-to-go .
After putting dimples onto the MG-3 tube and adding foam to the bottom of the tube, I re-mounted the strut back onto the fuselage and double checked its positions. While mounted, I floxed the MG-3 tube to the strut tabs and allowed to cure. Once cured, I removed the strut (again) and added 2 layers of BID over the MG-3 tube per plan. There is not a whole lot of instructions for glassing the washer onto the outside surfaces of the tabs. Here's what I did:
I first cut up 8 squares of BID (3.5" x 3.5") and made 4 2-layer squares of BID tapes. Come to think of it, I should have made a 2-layer 7" x 7" and cut it up to 4 squares... really alert today!
Once made, I cut a 5/8" hole in the middle of the BID tape squares. Then I applied dry flox around the outside edges of the 4 washers and brushed them down with pure epoxy. Next I brushed pure epoxy on the glass mating surfaces.
I removed one of the plastic plies from the BID tape and slipped the glass through the MG-3 tube onto the washer (with the second plastic ply still on the glass). The remaining plastic ply keeps the glass from distorting, especially at the hole location. Once I pressed down the glass onto the tab, I pulled off the second plastic ply. With a brush, I carefully smoothed the BID over the washer and removed all the bubbles. I then peel plied the bottom edge of the glass.
After cure overnight, I trimmed the excess glass around the tab and along the sides. Glassing of the MG-3 tube onto the strut tab is complete!
I waited until I was satisfied with the strut position before floxing in the aluminum brackets. Since the alignment of the strut has been completed, I decided to disassemble the MG-1 and MG-2, alodine and then flox them in place permanently. Since I did not want to disturb the preset alignment (above) I first removed the strut and hot glued all the MG-2s in place. Then I carefully removed the 4 bolts that held the plates together and removed all the MG-1s for alodine.
I was supposed to alodine all the aluminum parts to protect them from corrosion. I picked up both metal prep #79 and alodine #1201 form Aircraft Spruce. I removed the metal brackets from the fuselage (one at a time) and made my first attempt.
Since this process required some dipping, rinsing, painting and rinsing again. I set up a small process line and tested it out with a left over piece of aluminum. To contain the solutions, I dropped a sandwich bag over the mixing cups for each process step. That way the solutions are contained at all times and eventually I can discard the used solutions in an environmentally safe way.
As shown, (from left to right) - metal prep/clean, rinse #1, alodine paint station, and rinse#2. I also made a few small hooks out of heavy duty paper clips for handling the parts. If you look close, you can see the MG-1s in cup #1 being cleaned.
I found that I have to leave the parts in the metal prep station longer (about 4-5 minutes) than the instructions for better results. Probably my parts were dirtier that normal. In addition, I only need very little alodine to cover up the parts (and I got a gallon of it). Just hope it keeps.
All in all, the parts turned out OK. I just wish the color shading/coverage is more even, maybe experience will get me there someday.
Once the MG-1s were alodined, I painted the part with flox and bolt them back in place, one at a time. I used the strut shafts to guide the MG-1 positions and being careful not to disturb their pre-set positions, I also slipped the MG-4 bushings back in place and allowed to cure.
Once the MG-1s were cured, I decided to re-check the strut alignment before alodining and floxing MG-2. The strut shaft at the pilot side slipped in as before. The passenger side, however, would go in through the forward bulkhead, but would butt right against the edge of the bushing at the rear bulkhead. All efforts (other than pounding it with a hammer) failed to get the shaft passed the bushing. With flashlight and mirror, I could see that the flat end of the shaft cleared the bushing, however, a small fraction of the thread (at the top) would not clear the bushing. Evidently, the Flox Gremlin came by during the night and moved my rear MG-1 a little - just for entertainment...
As always, troublesome parts are located at the most difficult to reach places and this was no exception. The rear MG-1 (that needs to be re-positioned) has limited access room. The only way to remove it is to pound it loose. However, the plate is floxed in place with the bushing through it. I tried to pound it loose with a hammer and screw driver at the edge & corner of the plate, hoping to 'spin' it loose but with no avail. I pounded it hard enough to knock the fuselage/sawhorse off its bondoed footing. Hoping to soften the flox, I heated up the plate with a soldering iron (Susann's iron wouldn't fit) and additional pounding - no success. I eventually ground down a screw driver tip and wedged it in between the plate and fuselage - being careful not to scratch up the glass surface. With patience working it up and down the edge of the plate... I finally popped the plate off! The bushing, on the other hand, was still in tact.
Removing the bushing was a whole different challenge. It has ~1/8" of lip at the MG-1 side and flush against MG-2. There was hardly any access room to get a hammer in there to pound it out. Of course I tried to pull it out with pliers (at the flange). All I ended up doing was chewing up the edge of the flange... the bushing was staying put. I was frustrated over this for a few hours and finally, got an idea...I used a Knock Out Punch (reversing the punch) to pop the bushing out of the hole. Took a bit of work, but much easier that a set of pliers!
After the MG-1 and MG-2 (at the passenger side) were removed, I repositioned & refloxed them correctly - this time. The leading edge of the strut is right on 108.25" for the pilot side and 3/16" (108.4375") forward. I can correct the 3/16" forward when installing the axle. The strut is also centered. With the above results, I decided that its time to move on...
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