Tag Archives: fabricate

LH Landing Light – Lens Retainer Strips

Several months ago, I’d taken a look at the landing/taxi light lenses and what it might take to mount them nicely. The LH wing panel was sitting horizontally on a workbench at the time.

About the first thing I noticed was that the mounting holes around the perimeter of the lens did not all correspond to the holes in the wing where the lights and the lens go. The holes lined up (pretty well) with the lens on the outside of the skin, but not when I put the lens in the opening, behind the skin – where it really belongs.

The other thing wasn’t really so much something I noticed, but rather, I realized that I needed to find a better solution for mounting the lens than the factory provided for – sheet metal screws through the skin and into the plexiglass lens. That’s just not going to cut it.

Now I had another classic opportunity for inspirational procrastination. I put the time to good use. It took weeks, but once again – procrastination paid off! The idea of retainer strips with anchor nuts came early. I also found that I’d likely use #4-40 hardware, because metric MK-1000 nut plates are absurdly expensive and challenging to source in the US. I hate mixing hardware standards on this bird, but that’s just how it goes. The blind anchor nuts on retainer strips behind the lens stuck in my head as an obvious solution.

What was not obvious to me at the time, was how to hold the retainers in place so that the lens could be fitted and fastened with the little screws. I made a prototype with a hand-cut strip of 0.020 aluminum and held the anchor nuts with AN426AD-3-3 solid flush rivets. The strip was flimsy and I attempted to hold it against the backside of the lens with – if you can believe it – sewing thread. Once I got the screws started, I’d pull the thread out. I was too unwieldy.

Weeks went by. Then it hit me – the same basic idea, but with 0.5 x 0.025 stainless steel strips, held to the plexiglass lens with little #4 CSK screws and ny-lock locknuts. I had to make new holes in the bottom half of the lens to match the wing, made six retainer strips and mounted them to the lens. Now I have a lens that is easily installable and removable. I’ve come to believe that this is what the factory does for the Sling TSi and I might have seen it if I’d looked at the TSi construction manual. Oh well. I got there. I’ll repeat the fitting and fabrication process for the RH lens assembly.

Ailerons – Fab, Rework and Pre-Assembly

Aileron assembly has been delayed by ignorance and procrastination. It’s amazing how long it took me to decide to lever $20 out of my pocket for a tool. There’s an anchor nut that gets attached to a rib with a couple of stainless steel rivets that have a 120 degree countersink. I was reluctant to spring for a 120 degree, #40 pilot cutter. This left me pondering various alternative ways I might proceed to attach the anchor nuts. The door was left open because the construction manual doesn’t say anything about it. But, I did have reference examples – other builder’s and identical anchor nuts mounted in my quick-build fuselage. I finally ended up getting the stupid pilot cutter and then mounted the anchor nuts as I knew they should be from the very beginning.

Another self-inflicted setback has been in play. Sometime earlier, I’d riveted one of the aileron hinge bracket and rib sub-assemblies together. Unfortunately, something I’d noticed, but dismissed during initial fitting, had to be corrected. The bolt holes on the inner and outer aileron hinge brackets were not in alignment. To compound the problem, I reasoned that it would probably be ok to ream the bolt holes a little – make them oblong – and somehow that work out ok. Wrong! The result was better alignment, but at the cost of precision (proper) fit.

Sloppy fit for the outer aileron hinge just isn’t going to cut it. What could I do? Eventually, I did what I I should have done in the first place – ask the factory for guidance. I sent an email and got an overnight response directly from Mike Blyth – designer of all Sling Aircraft models. The outer bracket just needs to be bent a bit more. So simple! That absolutely did not occur to me. Sadly, I’d ruined (by reaming) the inner and outer brackets for one aileron and needed new ones. TAF USA rushed me replacements. Fantastic service!

With new brackets in hand, I slightly increased the bends on the outer brackets for both ailerons, removed the old brackets from one of the ribs and riveted all of the sub-assemblies together. Beautiful! I can sleep again. No more worries thinking about how I would try to rationalize wobbly ailerons to myself, the DAR, my technical counselors and everyone else.

Seat Assembly

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!

Rudder – Composite Tip and Beacon

Never underestimate the amount of procrastination required to get something done.

As usual, parts preparation takes most of the time. The fiberglass tip, as supplied in the kit, was a bit rough. There were quite a few voids and other imperfections in the layup. The trailing edge was too fat to fit nicely with the skin. Cutting and re-gluing with a bit of glass cloth and West 105 epoxy resolved that. The contour of the tip leading edge needed building up and shaping – requiring several passes. Epoxy takes hours to cure, so each step takes a day. Epoxy filler and wet-sandable primer attends similar time-sinking characteristics. Along the way, test fitting and match drilling of the mounting (rivet) holes was accomplished.

I didn’t really like the way the construction manual prescribed M4 rivnuts for the aluminum doubler that serves as the mounting base for the strobe. My concern is that rivnut installation might crush the fiberglass. I opted instead to make a new part that uses MK1000-06 anchor nuts and is riveted in place with AN426-3 solid flush rivets. Having the patience to eventually arrive at the decision to do this and then actually fabricating the mounting plate demanded all of the procrastination I could muster.

Copious foot-dragging precipitated the decisions about wiring and method of tip attachment. For some reason, I just didn’t want to shorten the (rather stiff) wire bundle of the Aveo Mini Max LED beacon. At the same time, I didn’t want the splice to be at or near the point where the wire exits through the bushing in the rib. A loop seemed the answer. And so it was. Final fitting of the tip to the rudder and pulling of the 3,2 x 8 mm rivets went well. I’d long struggled with the temptation of making the tip removable, à la Pascal Latten, by installing dozens of anchor plates, flush rivets and #4-40 screws, but my steadfast procrastination eventually paid off and the scales tipped in favor of just pulling rivets and being done with it.

EL – Pitch Trim Servo Retainer

Building an experimental aircraft from a kit is more than just a paint by numbers affair. And, with so much information available online – finding several ways to accomplish a task is not unusual, especially if you look. As it happens, I spend hours and hours searching for and looking at how others are doing things to build the same model, as well as similar types – or just general whys and hows of related skills or techniques.

Sometimes I come across an idea that just seems better than what I see in the kit construction manual. (20 years of aircraft ownership and maintenance have shown me that [most] aircraft designers and manufacturers do not actually walk on water.) My kit instructions describe a process that may possibly go beyond what the servo manufacturer – Ray Allen Company – anticipated as an acceptable way to mount their T2-7A servo.

My kit instructions call for enlarging 4 holes on the servo mounting rails (of the composite housing) from their original 0.125 (1/8) inch size to 0.2340 (#A) inch, and then setting an M4 steel rivnut into each hole. The documentation for the servo indicates that the holes may be enlarged to approximately 0.1440 (#27) inch, just enough to clear a #6-32 screw. The M4 rivnut approach seems like it risks the servo. Apparently other builders have had similar concerns and pursued alternatives.

For the Sling 2, the pitch trim servo sits flat on a tray that is riveted to the structure, inside the elevator. 4 screws pass through holes in the bottom elevator skin, the tray and the servo rails – and then must thread into something. I expect that #6 washers and elastic stop-nuts would be just fine. But, they may be just a bit fiddly to work with under the circumstances. Space inside the elevator is tight.

A fellow Sling 2 builder came up with what I thought was a great way to go – fabricate a pair of 0.0625 (1/16) inch thick aluminum straps with 6-32 (K2000-06) nut-plates attached with solid flush (AN426) rivets. The straps not only accept the screws, they also capture the entire length of the mounting rails on either side of the servo. When I first saw it, the solution immediately struck me as simple and solid.