Holes
Time involved:
Stuff We Used:
2 Gallons Bonderite C-IC 33 AERO – Aircraft Spruce and Specialty
2 Gallons Bonderite M-CR 1201 AERO – Aircraft Spruce and Specialty
AKZO NOBEL EPOXY PRIMER 2GAL – Aircraft Spruce and Specialty
Eck- Aircraft Spruce and Specialty
120 Grit Sand paper- Cash’s Hardware, (Behind Dunkin Dognuts) Mystic, Connecticut
Weird Tools
For most of the past 7.5 million years, (4,000 if you live in the Bible belt) people have lived in a bleak world devoid of human made holes. This sad state of affairs ended about 150,000 years ago, with an advancement that was as world changing as the development of fire and the creation of the Slim Jim Monster Meat Stick. In what is now known as Morroco, in Bizmoune Cave, early Aterian hole researchers and design engineers developed proprietary methods and tooling for installing holes into something you can hold in your hand. It was through this relentless dark drudgery that they found a way to make holes in a then underutilized natural resource, the shell of the Tritia gibbosula snail. This is one of the earliest times archeologists have seen holes in something that was both portable and in something calciferous BEFORE the advent of skull trepanation. The new hole equipped shells were openly traded for goods on the massive African marketplace, in other words, they were a new a value-added object that could be sold to make a buck.
To meet the raging need for holes in those early days, artisanal hole makers engaged in a relentless toil with the crudest of tools to feed humanity’s hunger for holes in things. Yet, the raging famine for more holes remained unmet, overtaxing the hole making capabilities of the period. By the time the crushing demand was noticed in South Africa, another innovation occurred that would change humanity forever and launch the great South African Hole making tradition.
Just 300 KM to the east of Capetown South Africa, in the cliffs where the Majestic Cape Fold Mountains gracefully brush the sea, rests a cave we now call Blombos cave. Being ensconced in the hard-to-reach cliffs along the coast but sequestered from the tourist encrusted beaches to the west, it was the perfect workshop. Brightened up with a few pieces of artwork, it provided a pleasant atmosphere for work. It was here, long, long ago, wizened hole engineers incorporated another cutting-edge innovation to lay the foundation of the great and storied 75,000 year old South African hole tradition.
Huddled in the protective environment of the cave, these clever hole researchers realized that the frenzied churning out of holes in everything from Wildebeest hooves to human noses by all the Do-It-Yourself hole makers was a good market for a mass-produced device to make holes with. For the first time ever, they would specialize in making the tool that makes the product, a concept still well understood by South Africans. The engineers eventually prototyped a new bone awl device that could be mass produced and sold to the tribe’s trading partners. Brilliant.
Oddly enough, the tribal management had sufficient brain power to understand what the engineers were on to. They immediately saw the business case for making and selling the things that made holes. Soon, a hole making device for the masses became available across the entire continent, and holes began to propagate across South Africa.
In short order, more sophisticated tools, Jewelry, musical instruments, and yes, clothing could be produced like crazy all over the country. In turn, these new things spurred on new industries in South Africa, including tourism. Vacationing Kalahari bushmen could warm themselves in hole equipped animal skin coats to see the penguins in what is now known as Simon’s town.
As we mentioned in our last episode, we related Evan Brunye’s sage teachings on how the fuselage skins fit together perfectly. Very little match drilling of the holes is needed, if any at all. The holes in the skins match the holes in the ribs and other overlapping skins, and rivets should fit easily in them. All of this is due to precision, the ability to repeatedly produce copies of an object which are very close to perfect to the original. This precision allows for a skin on Evan’s sling to fit in the same spot on our sling precisely, though it is doubtful he would want to try doing this. This could only work if the holes in the two pieces matched perfectly, if they don’t, something is wrong somewhere.
As we mentioned in the last entry, we had a real head scratcher of a problem with the holes along the front edge the ones (circled in the drawing below from the Legos assembly book v7.9). They were not matching up with the holes in Rib 3 when we tried to install the side skins (P/N RF-SKN-104-C-C-3 and RF-SKN-004-C-C-1). As we usually do when we beat back procrastination long enough to publish a new blog entry, we let the other builders know about our progress and findings on Facebook.
When we mentioned we had a problem with our holes, we got a few suggestions about how to align the holes, match drilling and reclecoing in a different order, and using a reenforcing strip. These are great ideas, and worth remembering. We also got a rather irritated response from Brother Michael “Maximum Mike” Berardo who shared his insights and wisdom with us. “Let’s get to the point.”, he wrote. “I don’t have enough time in the day to read every word someone writes about their build. Not being mean, just being factual.” He is correct. Not everyone has all day, let alone enough soothing eye drops to read through our screeds, so, might we suggest reading it over a couple days to ease the pain.
In the end, after trying reclecoing, using our different aligning tricks, such as clecoing starting from the top, and clecoing from the bottom, we finally decided to tell the guys at Torrance and Tedder field of our predicament. We got a response back and had a nice email conversation concerning the revision of the Legos assembly book with Heinrich Broodryk, a draughtsman at Tedder field. He suggested swapping out the two 302 Ribs with new ones, and Tammy Surmon shipped a pair out to us with the greatest expediency.
It would be a while before we got them, and unless we tossed out our plan of doing the fuselage in the same sequence as it shows in the Legos book, we wouldn’t make any progress. So we started in on the centre fuselage (We’ll call it the “CF”, this is aviation, let’s use our acronyms boys and girls!), which was the part we will sit and enjoy our sling flights in. We will prattle on about that in a little bit, but for now, we will skip ahead to when we got the new ribs in.
The ribs arrived shortly before Airventure, which we sadly skipped this year. We had a bit of compensatory joy when we checked them out against the originals, and as we had hoped, the holes were differently spaced, and matched the skin holes perfectly, and we had the new ribs riveted in place in short order, no match drilling required, Evan was correct.
And Now, How We Amused Ourselves While Waiting For The New Ribs
We won’t bore you, dear reader, with the monotonous blather about us going through our stores of parts, fishing out all the CF pieces for their time in the parts spa with all its scraping and filing, the allodining and priming mess, we will leave all that said and done. Instead, we will get right into the assembly, starting with the floor framing.
Arranging all the ribs into the complex framework appeared a bit daunting at first. The multicolored drawings in the Sling Legos book made the whole affair look like a giant avocado slicer had gotten itself terribly inebriated, had carnal relations with a set of football goal posts and progenerated what was depicted on page 61 of the legos book v7.9. A hideous medieval device that Fouquet would have lounged on while awaiting trial i n the dungeon de Chateau d’Angers. Which is definitely NOT something one would want to sit in for a flight across the Atlantic, lest it make one’s butt look like it got grilled over a commensurately sized hibachi. Nevertheless, that is what it was, and we had to sort out what rib went where so we wouldn’t have problems putting the Sling Flight Appreciation Seats in. Our butts would love us.
After pouring over the lovely technicolor pictures depicting the framework assembly, we drew a few helpful conclusions. The first is that there are two sets of components, the goal post like spar carry throughs and the Main Gear Channel made up the first set, and the ribs the second set. The Rear Spar Carry Through and the Main Gear channel needed assembly, and the whole lot needed to be accessorized with various mounting brackets, some seat belt mounts and autopilot servo mounts. The second is the mind grating and tedious variation in way the ribs faced. Some face inwards, some outwards. Finally, there was a whole passel of rivnuts to install. At the build centre in Torrance, they installed these after the ribs were installed so we decided to do it that way with all the ribs held firmly in place.
We started with accessorizing the primed floor ribs. It didn’t take long to get the elevator servo and seatbelt brackets mounted, and there wasn’t a lot of fuss with them either. This was the exact opposite of the snarling prickly irritating time we had with putting the nuts on the screws that held the aileron servo bracket to the main spar carry through.
Positioning and holding the tediously cute little M4 Nyloc nuts in place had its own special spot on the Worlds list of irritating things to do, right below standing in the express checkout line behind 12 barely literate people who want to pay by check.
We frabbled and priddled around with handling the consternating nuts with tape as suggested on Page 54 until the lackeys in our Clever Solutions Development Bureau (CSDB) recommended using a pair of thin wire crimpers to hold them in place in the narrow gap between the bottom and top pieces of the framing. The crimpers can be seen in the photo below, they are the yellow handled implement being wielded by a junior assembly intern. The Crimpers made the installation quick work, holding the nuts in place with accurate firmness. With the main components assembled, we were ready to move on to assembling the Center Fuselage itself.
We started the assembly with studying the images on pages 57 and 59. page 57 shows where the ribs go on the main gear box and the Main Spar Carry Through, and page 59 shows which direction they face when mounted onto the Rear Spar Carry Through. We would just love to write all about which one faces which way, but we are not so sadistic as that, just look at the pictures.
After our lengthy study time, we had the ribs clecoed and riveted in place in short order, with minimum redo. One bit of trouble we found was the tight fit we had between the gear box and the Centre Fuse Connecting Rib (P/N CF-RIB-001-X-C-2). The cut out in the Centre Fuse Connecting rib for the gear box was a bit tight, and made the rib buckle a bit when it was installed. It took a bit of adjusting to get the rivets into the rib and gearbox because of the buckling, but it eventually went together. The seat console brackets (CF-BKT-023-X-C-1) which we see listed on page 86 for the seat rail assembly, had to be nudged and worked into position on the Centre Fuse Connecting Rib as shown on 87. We also installed the rear bottom skin, which spans from the gear box to the ends of the rear seat ribs, making sure to leave the last couple of rivets undone for the bottom tail skin to slip between the ribs and the bottom skin. This may seem a bit impatient, but it helped keep the ribs from flopping about while fitting the torque tubes.
With the CF coming together and looking like a tasteful and elegant edition to Angersian dungeon décor, We moved on to the front part which has the moniker of “Bottom Floor Connection”. We have no clue as to why they call it that. It is about as descriptive and pertinent as ”chocolate Hay Bedposts” or “Crimson Compact microtomes”, but “Bottom Floor Connection” it is. We will shorten it to “BFC”, in keeping with the Industry obsession with acronyms.
This BFC is simple in concept. A pair of skins sandwiching a bunch of channels, essentially short versions of the longerons making up the horizontal framing members of the tail and sides of the CF. We had a wonderful and satisfying time clecoing and riveting the lot together, and short order we were gloating over the nice aluminum sandwich, with it’s reinforcing plates and carry through stiffener accents. Being on the roll we jumped ahead into the rudder pedals.
The pedals mount directly on to the BFC via the pedal mounting channel and pedal mount brackets. These were easy enough to cleco and rivet in place, but deceptively belied the tedious sanding that we needed to do next with the plastic bushings. This was the first encounter with the plastic bushings, which were cut in half to fit around the pedals shaft. We’ve seen a few Slingers substituting actual ball bearing systems to replace the plastic bushings in the torque tubes for the ailerons flaps and elevator. We found a good example in Brady Groth’s system he told us about on the Facebook Sling Builders page. which he claims works a bit too well, making the friction so low it “falls over in whatever over center position it is in”. We loved it.
We don’t have nice toys to fabricate anything like actual bearings so we are sadly consigned to using the original bushings. The challenging part is that the bushings needed to be fitted to the pedal shafts, and the shafts must move smoothly, able to allow the pedals to flop down onto the floor, all the while not having any wobble in the works.
To achieve this effect, the inner bore of the bushings is supposed to be sanded down making the hole wider. But then, if it isn’t sanded just right, it can be uneven, making the hole either crooked or not exactly circular. The CSDB issued an ingenious solution, at least for them. To deal with this we drilled a couple ¾ inch holes on either side of our Sling Assembly Bench and inserted a dowel into the holes to form an axel. We fashioned a crank handle on one end, and wrapped some 120-grit sandpaper around the dowel near the crank and our Bushing Sander was born. Somebody give us a patent. We simply had to hold the two halves of the bushing against the sandpaper and turn the crank.
The rudder controls stops are a weirdly shaped pair of aluminum whatnot bent at the ends. They are mounted vertically on the pedals with two bolts, the bent tabs facing each other, one bent end at the top, one at the bottom. When one pedal is pushed as far as it will go, the top tab of one will hit the bottom tab of the other which stops it from moving any further. Of course, since they are facing one another, when one moves, it must be able to move freely past the bolts that hold its contorted twin in place as it swings back and forth, with 3mm clearance, (1/8” in American). This requires some shortening of the bent tab so it doesn’t snag the bolt heads as it swings, just how much shortening is cryptically discussed using pictures and a few terse sentences on page 73. Basically, there had to be at least 3mm between the tip of the tab and the bolt as it swings past, but it also must overlap the bottom tab of the other stop but at least 10mm. So, we marked a line 1cm from the tip of the tab, ground the tab down to the line deburred it nicely and had just enough overlap to make them contact each other.
Since we had the bushings for the pedals fresh in mind, we thought we would do to the other bushings for the flap and elevator torque tubes. These bushings are different. They were not cut in half and were larger to fit on the torque tubes for the other flight surfaces. The bushing for the Elevator Short Torque Tube Assembly (P/N CT-AEL-002-C-C-005) would not slip ont the ribs, the groove was not deep enough, we use a hand saw to cut it a little deeper on a couple of sides, and it fit nicely, without any buckling in the rib.
Of course, just like the rudder pedal bushings, they also needed some sanding. However, the crank idea wouldn’t work, the ¾” diameter was too small, and there wasn’t any way to easily put the bushing onto the shaft the repeated times we would need to do it. So, we chose another way, using the duct tape that we didn’t use on those tedious nuts on the spar carry through.
We wrapped another piece of 120 grit sand paper around the dowel at the end without the crank on it, and clamped the dowel so it wouldn’t spin. Instead of spinning the dowel, we would spin the bushing. Using duct tape. We slipped the bushing over the sand paper wrapped dowel, and then wrapped a rather long length of duct tape around the bushing, just a portion of the bushing, like a belt around a pulley. We could then spin the bushing by pulling the ends of the tape back and forth, spinning the bushing over the dowel, evenly sanding away the excess plastic from the inside of the bushing. After enough sanding, we had the results we wanted, the flap and elevator torque tubes spun freely in their bushings.
It was about this time when we realized the insulation that is supposed to be in the BFC wasn’t there. Drat. We wish on page 65 of the Legos book there was a nice note to emphasize the insulation part and direct us to look at page 25 for where to put the insulation. We had been wondering about the insulation, the stuff that came with the kit seemed a bit thin, and the fire test done by brother Adam Dickson on it was a bit frightening. Before we turned to the fire proof mineral wool we had left over from sound proofing the walls of our house bedrooms, we did some internetting and found the material at Wicks mentioned by brother .
we started off with installing rivnuts in the center console strengthening channels, which entailed drilling out the prestamped holes to a ¼ inch. not sure why they didn’t do this in the first place, but it gave us an excuse to play with the power tools some more. Rather than make a capital investment in another drill, We figured out pretty fast that mass productivity encouraged drilling all the holes out first before swapping the rivnut tool for the drill bit, making the affair a little less tedious.
One of the annoying parts in the assembly directions for the Bottom Floor Connection was that the stuff about insulating under the floor. it was shown on page 25, way back in the part about the tail. Easy enough to remember, particularly when you have the whole Bottom Floor Connection all riveted together nice and tight. Dag Nabbit. We spent the time stewing over that one scrolling through the Sling Builders page on Face book. That was when we found brother Paul Borror (sadly He is selling his project) description of a better insulating material on Wicks. We salved our disappointment of another redo by buying some the nice foamy insulation material. It’s a little thicker, but didn’t have the adhesive backing. We elected not to use any adhesive to hold the insulation in place since it would be filling the voids so tightly that it wan’t going anywhere. It was a simple job measuring the spaces and using those to cut the pieces, but It would be nice if we had patterns to work with, or perhaps a sheet of dimensions of the pieces. That said, we had the pieces cut and installed within a couple of hours, and with another half hour more riveting monotony and this embarrassment was over.
With all that done, we were getting ecstatic about joining the BSC to the part we would sit in (the carry throughs and assemblage of ribs). Of course, our excitement deflated like a set of tires running over a spike strip as yet again we found some trouble with holes. It almost goes without saying that for us something just had to go wrong with holes. It was a straightforward process to align the 2 rows of holes on the main spar carry through with the holes in the skin and rivet with stainless steel rivets. Nevertheless we wanted to test fit the two assemblies before we slathered on the Eck corrosion protection muck. It was a good thing we did, otherwise we would have burned through a whole tube of Eck in failure.
We started with resting the seating assembly (not a bad name for it) on it side so that we could go about the clecoeing. There are 3 rows of holes that attach the BSC to the bottom of the seating assembly, 2 on the main spar, and one on the gear box. We are supposed to rivet just the rows on the main spar carry through to the BSC, and not the holes that hold the BSC to the main gear box, that would be done after the main gear closing skin (P/N CF-SKN-C-C-01) is installed. So far so good.
We next positioned the BSC into position, aligning the holes of the BSC with the holes in the Spare carry though and the Main Gear Box. Everything lined up nicely, we were making progress. We clecoed away happily down the forward row of rivets, feeling pretty good about our progress. And then came the second row.
We saw right away that some the clecoes were a bit tight and had to be wriggled a bit to slip in, and others not going all the way through in a few places. We tried a inserting rivets in several other holes and got the same results, some rivets would fit through part way, no problem, but would not go through the second layer. Those that would go all the way through were clearly not centered in the top layer which would mean that the rivet bulb would not form properly. We are not sure what the boys at Tedder field call this top layer so we will call it the Rear Brace Angle (RBA), a conceptually better term than Bottom Floor Connection.
Like the main spar in the wings the 2 layers of the carry through have different sized holes, the bottom layer has smaller ones which hold the rivets, while the RBA’s have larger holes which allow space for the rivet bulbs to form. The holes in the two layers must be aligned for this thing to work. So we tried all the holes with rivets, shook our heads, took photos of the holes, and sent a few photos off to Tedder Field, and Carbon Copied Jean d’Assonville. we also got a response from sling technical suggesting we grind the holes bigger with a Dremel. Nice idea, until we tried angling the Dremel into position to grind out the holes. The Dremel was to big to fit in the space, there would be no real way we could effectively make the hole big enough. That’s just as well, our ham-fisted level of skill and grace would have make a hack of it. We could just see the DAR rolling his eyes at the complete mess holding the wings on. Not a happy prospect. We proposed using portable holes, a well-documented concept which was quashed by the anti-hole conspirators and never made it out of the prototype stage. But it was not taken seriously by the Folks at Sling anyway.
Jean fully understood the terrifying implications this would have. It would be cringe worthy to ponder what sort of technicolor conniption the DAR inspector would throw once he saw the gouging hack job with a Dremel tool we would have done to the poor thing. We also don’t want to forget the impact this was having on the storied South African Hole making tradition. Of course, there is also what Mr. Blyth would think. After briefly pondering those horrifying prospects, Jean informed us he would personally select a new Spar Carry through and send it forthwith.
We waited and watched some videos of Oshkosh on the youtube. Oh yeah, some how we found the time to derivet the original Spar carry through from the ribs.
The new unit arrived lovingly secured in bubble wrap to the bottom of a nice new plywood box. Naturally we wasted no time ripping it free and testing all the holes, making sure the rivets fit right, and after a day at the spa where it got a coat of puke green epoxy primer, it was ready.
It was quick work to get it installed in the CF, with all the ribs and brackets installed. With a nice coating of Eck on the holes in the BSC, the new Spar Carry through was riveted into place, joining the BSC and the CF part that you sit in together in happy non matrimonial bliss.
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