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Many builders wind up fitting an auxiliary shelf in the tail cone, for light weight avionics. I’m a fairly large guy and am not looking forward to crawling into the tail cone after it is fitted to the fuselage. As such, I’m trying to prepare as many items as I can now, so that if/when I need them, they’ll be easy to fit.
It takes some messing around to build a bracket for the J stiffener that keeps the shelf straight, but apart from that the shelf itself is simple. I made it out of 0.0625 inch Alclad, with a 1/4 inch flange folded on the front and rear edge. I have no idea what avionics might be fitted to this shelf, but down the road it’ll be a simple matter to lay out items on the shelf, drill lightening holes etc., fit everything and bolt the shelf in place.
Yes, I have a fuse kit. In order to minimize freight costs, it is common in Australia to combine crates into one consolidated shipment. I combined the wing and fuse kits, but due to unforeseen circumstances at the time, I was not able to perform the fuselage inventory within 30 days. Given the quality of the other shipments, I didn’t lose any sleep over this, so apart from a peek inside, I left the crate be. I did order some extra Alclad along with the fuse kit, for building future brackets etc. I finally needed some of that Alclad in order to build an Auxiliary avionics shelf for the tail cone. This Alclad was on the bottom of the fuse kit, so it was finally time to open up the crate and inventory the kit.
Everything was accounted for and I’ve now got the fuse parts all stacked away and the crate out of the garage. The inventory went quickly because I already had almost all of the necessary rivet containers, parts drawers etc. set up.
I completed fabricating the brackets required to finish the aft section of the tailcone. Before disassembling the tailcone, I decided to work ahead a bit and prepare/fabricate various parts for the empennage attach section, including the trim system. There are a lot of parts to prime for the tail cone, and a few more won’t make any difference. I also added a bracket that Van’s sell, nominally for a Whelan strobe kit, but it can be re-purposed for many different uses. I don’t have specific plans for it at this stage, but it’s easy to fit now so why not.
I’ve continued to assemble the tail-cone over the past few days. Got to the point where the top skins and stiffeners are fitted and match drilled, so the tail-cone is now “torsionally stable”. Still some more brackets to make and various miscellaneous parts to fit before the tail-cone will be ready for disassembly.
Time to start the tailcone! Many hours of de-burring, but the bulk-head parts are “large” so the storage shelves get rapidly emptied, which is a good thing. I used the drop saw to cut the 45 degree angles on the F-1047 J stiffeners. It does a great job but leaves a sharp edge on the “flat” part, which needs to be filed flat again prior to de-burring.
After several days of preparation, I finally started assembly and now have the bottom and right skins cleco’d in place and match drilled to their respective stiffeners. More to come…
Time to take the rudder halves off the shelf and rivet them together. By far the hardest part of this process is riveting the rudder trailing edge without turning it into something resembling the roof of the Sydney Opera House. After researching this topic some months back, I decided to try and do this without hitting the trailing edge with a rivet gun. The method I used has been described elsewhere (and I’ve lost the link), but the description was scant so I’ll go into some detail here.
Back when I prepared the rudder components, I match drilled the trailing edge to a section of Aluminium angle, 2 metres of 50×50 angle, 5 mm thick. This is thick enough to be a sturdy reference straight edge, but still thin enough to be able to get cleco’s through the trailing edge and through the angle. Match drill this before dimpling the skins, so that the #40 holes will be as accurate as possible. Note that the holes are not perpendicular to the surface of the angle section – they are perpendicular to the chord line of the rudder, so about 5 degrees off the perpendicular.
I clamped the Aluminium angle to one edge of the workbench, flush with the surface, and placed one layer of masking tape across the bench edge and the base, just to prevent any marking of the rudder skin surface. I used the 3M F9460PC double sided construction tape (available from Van’s) but the method would work just as well with Pro-seal. With a helper to hold the other skin up off the trailing edge wedge, as each set of ribs were riveted together, I removed the remaining paper from the double sided tape up to the next set of ribs, and also cleco’d every hole in the trailing edge up to a few short of the “next” ribs to be done, working from bottom to top of the rudder. Once all ribs were riveted together, I had a continuous line of cleco’s all the way along the trailing edge, which was held down firmly against the perfectly straight Aluminium angle base. Since the rudder was held securely on the workbench at this point, I also put the front spar in place, installed all of the LP4-3 rivets from the front spar into the shear clips, and riveted the left skin (the one on top in my arrangement) to the front spar, since this was easy to do with the pneumatic squeezer. I left it this way for two days.
After that time, I removed the cleco’s holding the TE to the Aluminium base, drilled every second hole in the base out (in stages) to 13mm, and then used a step drill to go just a bit larger and effectively de-burr the holes. I further deburred the holes with a scotchbrite wheel in the die grinder, then scuffed by hand and cleaned the base to ensure that no sharp edges remained. I then re-installed the rudder back onto the base, with a cleco in every second hole. The large holes enabled me to get the rivet squeezer onto the bottom side of every second hole.
I (very carefully) used flush die to start the rivets, just enough to set the rivets in place but not enough to touch the bottom skin (which would have been a disaster). An inspection mirror is essential here, to check each rivet as it is done. To finish the rivets, I used a modified die on the fixed side of the squeezer (see picture). I ground a die down, so that it was 10 degrees off from flush, to match the angle of the rudder skins. The modified die is then held in place on the fixed part of the squeezer using a bit of gorilla tape (see pictures). Doing the initial partial set of the rivet with flush die is what allows using a single modified die to finish the rivet – it is easier to work with a single 10 degree ground die, than two die each ground at 5 degrees. Holding the squeezer upside down, with the flush die on the top skin, I was able to fully set each rivet in the trailing edge.
I backed the air pressure from the usual 90 psi down to around 60 psi for this operation. I also very carefully adjusted the squeezer gap as I did the first few rivets, checking for any witness marks around the manufactured head (from the modified die), doing some fine adjustments to the die with a file to take down any high spots. After a few adjustments, I was able to confidently squeeze the rivets to completely finish each one. The large holes in the Aluminium angle base actually helped with guidance!
At this stage, every second hole in the trailing edge was riveted. Removing all of the cleco’s, the rudder can be slid off the base. This worked so well, I decided to continue the process, and drill out every second un-drilled hole, again cleaning the base up to ensure no sharp edges remained. I then re-installed the rudder onto the base, with fewer cleco’s, and riveted the positions corresponding to the newly drilled holes.
I repeated this a third time, leaving only three cleco’s holding the rudder down. After that, I riveted the three remaining holes with the trailing edge simply hanging over the edge of the base, with no guidance.
The end result of all this is, the Aluminium angle has a large number of ugly holes in it, but that’s OK because it can now be discarded. On the other hand, the rudder trailing edge is perfectly straight. I held straight edges against the rudder trailing edge, and could not even find an air gap to try and measure how straight it is. I attribute this to the fact that the method completely avoids back riveting, and all rivets are set with the squeezer while the entire trailing edge is held completely flat.
Some of this work took place a few weeks ago, but I didn’t finish both trim tabs until yesterday, so here are the details.
I had to go back and fold the outside edges of the elevator trim tabs – which I held off doing until after they were primed. I cleaned up the saw marks from one of the inner sections removed when I made the supports, and glued on a piece of masonite to build up the thickness of the wedge so that it could be used as a folding jig per the instructions. Since it was from the same cutout, it was a perfect fit. Since I had already dimpled the skins, I also had to drill some indentations in the wedge to avoid damaging any dimples.
I made the folds and match drilled each end, and riveted on the horn and front spar to to the bottom skin.
Finished riveting the elevators, except for the leading and trailing edges.
It turns out to be better if you deviate from Van’s instructions. The manual has you rivet the front spar to the top and bottom skins, and then insert the tip rib assembly. In so doing, you have to buck the four AN470 rivets that join the front spar with the tip rib assembly, by lifting the corner of the elevator skin. I did this with the left elevator.
For the right elevator, I made a change. It’s easier to attach the tip rib assembly to the front spar before inserting the assembly into place. That way, you can use a rivet squeezer to set the AN470 rivets. You need to use a longeron yoke.
One other issue is the two AN426AD3-3 rivets that attach the top and bottom skins with their respective tip rib skin. The instructions have you buck rivets in the top with the bottom skin lifted, and use pulled rivets for the bottom (page 9-14). It’s actually possible to pass a tungsten bucking bar through one of the front lightening holes in the front spar. With a bit of manipulation, it is easy enough to insert the tungsten bar, buck these rivets, then extract the bar back out the front. I drove solid rivets into both the top and bottom skins using this method.
I attended the APS course held in Brisbane last weekend, mainly as a first step to learning more about aircraft engines. I went there in complete ignorance – hadn’t had time to review the online materials – but it didn’t matter. The course was well organized, thought provoking, and gave me a lot of insight into combustion events and the effects of mixture. There was a heavy focus on engine monitors and interpreting what the monitors are telling you, and a lot of data and video material from flight tests and engine dyno runs.
Apart from the course itself – which I highly recommend – there were several RV-10 owners/builders there, so a never ending conversation was always available on that front.