I thought it would be very challenging, but the main landing gear bolted to the fuselage without much of a fight. I’d spent days wondering how it could be done. As it turned out, I found I was able to do it single-handedly. Good preparation was a key factor.
Initial fitting revealed several things that needed to be addressed. First, there was space between the composite landing gear and the heavy steel brackets where it attaches to the fuselage with M10 Class 12.9 bolts – two on each side. I confirmed with the factory what I quickly suspected – too much gap. I found out that the gap, if any, must be 0.5mm or less. I was seeing just under 3mm. The factory offered to make custom laser-cut stainless steel shims. I measured and provided details about the LH and RH gap distances and received the shims in just a few weeks. Beautiful.
Next, the long M10 bolts needed to fit easily though concentric holes in the sheet metal channel and heavy steel brackets in the center fuselage. The brackets were perfect, but holes in the channel were a little bit tight. The slightest attention with a tapered reamer made it all just right. It was good to realize that this should be done before struggling to fit the bolts through the landing gear without sufficient clearance.
With a pair of tapered pins I’d made from spare 10mm bolts, inserted front to back, I was able to set and then hold the landing gear in position and slip in the actual mounting bolts. The bolts went in from the back, through the fuselage, shims and other mounting hardware and pushed the pins out the front. The elastic stop nuts were tightened to 25 NM, as specified in the Sling 2 LSA Maintenance Manual. (There’s treasure trove of important Sling 2 assembly procedures and details in that manual.)
All Sling Aircraft models are designed and manufactured in South Africa. Measurements are specified in millimeters and most of the fasteners are metric. There is, however, key structural hardware that is AN aircraft hardware – much more typical for aircraft designed, built, flown and maintained in USA. Detailed fastener documentation for my aircraft will be very important to anyone performing maintenance and they will need to be alerted about this beforehand. Spare fasteners may not readily at hand at a typical shop. I expect to keep some spare hardware in the aircraft for repairs.
Assembly of the adjustable seats has been straightforward. They’re made up of 2 hinged panels that have a simple channel structure, sandwiched with identical skins – top and bottom. Inside the seat base is spring-loaded lever and cable mechanism for the slide locking pins. I opted to adapt some clevis pins instead of using the kit-supplied (large) solid rivets to assemble the linkages. The rivets proved difficult to deal with. It took a few days of pondering, but I eventually realized that custom fabrication of clevis pins were the way for me to go.
The only metal preparation I did was deburring and scuffing with a Scotch-Brite pad. I may or may not paint the seats as they’ll be almost entirely covered by the upholstery. The structures and panels fit perfectly and went together quickly. Sling 2 seat design has apparently changed over the years. The recently manufactured parts I had didn’t exactly match the construction manual, but understanding and dealing the differences was not difficult.
There are now at least 2 ways that the piano hinge can be mounted between the seat base and back, so that it can folded forward to access the luggage compartment area. The deciding factor seems to be how far beyond perpendicular to the seat base the seat back will naturally recline. The construction manual shows the hinge on the surfaces, riveted across step transitions where the side channels overlap the skins. The hinge, mounted to the back and bottom edges of the seat panels just seems more appropriate and allows for about 21 degrees backward and no restriction (until the panels meet) in the forward folding direction. That’s perfect. Seat recline angle is set by side-straps anchored to brackets at the edges of the seat panels.
The seats slide on rails mounted to the center fuselage. Clearances are pretty close, but appear to be perfectly aligned. Finding that helps to confirm that the center fuselage is built straight and square. Oh let me tell you that’s good news!
I’ve finally gotten back to building after hours of rivet-by-rivet QB build construction review. Parts inventory reconciliation and almost daily communications with TAF was accomplished over a couple of weeks.
The preparation and priming of the rudder structure was done before QB delivery, as I anticipated having to furl the curtain walls of my paint booth to eventually accommodate the fuselage and wing panels in my shop. Having the prepared parts on hand, left me in position to do a quick test fit and then permanently rivet the structure. The assembly went well, in the same manner as the VS and HS components.
The horizontal stabilizer assembly started by fitting together 2 sections of rear spar channel with the center section sandwiched by doubler plates – front and back. The result is over 8ft long. Appropriately sized cleco fasteners temporarily hold the parts together. A laser level helps to confirm that the channel is true – straight and free of twist.
The rear channel components were permanently fastened with a combination of 4.0 x 10mm and 3.2 x 8mm pulled rivets. Assembly continued with ribs joining with the front spar channel and clecos hold the front components as they are fitted and fastened in a similar fashion as the rear.
I’ve found that when 2 or 3 parts are sandwiched together with many rivets, it can be a little tricky to get a relaxed fit. Many overlapping holes must align precisely, in order for the rivet shanks to fit through all of the layers easily. I try to take whatever time is necessary to get the best concentric alignment of as many holes as possible, so that little or no reaming is necessary. The kit parts are punched very precisely and overlapping holes will likely line up, given the chance.
My assembly process starts with just a few clecos, while test fitting rivet shanks in many or most of the holes. Then I loosen and reset those few clecos until there is good natural alignment of as many holes as can reasonably be achieved. Eventually, a majority of the holes will line up perfectly, leaving only a very few that may need a little reaming to easily accept a rivet. Straight-shank chucking reamers seem to do a great job. Use the exactly right sizes. #30 and #20 are common.
The HS structure, without skins, is somewhat delicate. I’ve used a couple of stiffeners, from a Vans Aircraft workshop (skills practice) kit, clamped to the innermost HS ribs to provide support while the entire structure is riveted.
The HS structure is symmetrical. At some point, a decision must be made as to which side will be the top and the other side, therefore, the bottom. For my HS, continuity of how the rib flanges relate to the spar channels has turned out to be somewhat better on one side than the other. The side with the best potential for smooth skin support was chosen to be the top. I used a black permanent marker to make indications inside the front spar channel, where they can be seen during the various assembly phases.
With the HS top chosen, left and right HS panels become apparent. 2 Heyco 0.375in snap-bushings have been placed in the rear forming holes of the 2 innermost left-side ribs and anchored with some dabs of gray RTV. The nylon snap bushings are intended to protect the pitch trim servo wire (cable) as it passes through the ribs. I’ve elected to use nylon snap bushings instead of the rubber grommets supplied with the kit.
I’ve had the empennage sub-kit since late July. Today – finally, in November – I’m very pleased to have pulled my first rivets.
It’s taken me this long to get my act together to the point of seeing my way clear to assemble a few parts. As is happens, the VS rear channel is a good starting point.
If things weren’t exciting enough for one day – I opened an email from Barry Jay (TAF) and was surprised to find first pictures of my factory quick-build. The fuselage is built up with evidence of many alodined parts and even some gray paint on interior spaces.