Made some more progress on both elevators. They are not finished yet, but the basic structure is done on both sides. I need to add some reinforcements and blocks for the hinges, but I want to first build up the stab in the same manner, so I can add the reinforcements on all parts in one go. But the most important work on the elevators is done and they came out nice and straight:
Also, the trailing edges need to be sanded to a round shape. I want to build a sanding jig for that, to get a uniform shape:
I also made some progress on the muffler, but I will share that next time, as I need to do some polishing first :-).
Meanwhile I’m already well underway with the elevators. This is the same construction principle as the rudder, so I will not document this into detail, but still share some pictures of the progress now and then. Built the outer edge from strips of balsa:
And finished the first basic rib frame of one of the elevators:
Now I need to repeat this three times and add the reinforcements and blocks for hinges and control horns.
Back to the custom muffler. The front elbow still has to be fit onto the muffler. I can’t build this as a single piece, as the elbows are attached to the cylinder heads with thread in different directions. My idea is to keep the front elbow as a separate piece and connect it to the muffler using teflon tubing. The front elbow was already bent in the right direction, now I also cut it to the right length, could be a little shorter still, but this at least gives me room enough to work on the connection:
I had to come up with a way to mark the exact shape of the hole to cut for the angled connection to make between the two pipes. Again, angled in all directions, so it will not be a circular hole. And it has to be in the exact right location, as there’s no room for play. Also, the muffler was quite a lot of work up until this point, so I didn’t want to make a mistake here. Only one chance to get it right. After a bit of thinkering I came up with a solution using toothpicks. I put tape with the sticky side outwards on the exhaust pipe and stuck toothpicks to it so they just touched the muffler:
Secured it with another tape on the outside when finished, took it off and got my template:
Transfered to paper, then to a piece of pipe, and cut it in the exact right angle. This is a temporary piece solely used to mark the hole to cut:
I used a piece of wood to connect the two pieces, so I could extend it to the right length and get it in a straight line with the exhaust pipe:
Then I used pieces of tape to tape off the contour of the exhaust pipe:
Removed the temporary piece and got the exact shape and location of the intersection of the two shapes in 3D:
Traced it with a marker, ready to start cutting:
Cut the marked hole and gradually grinded it bigger, adjusting the shape bit by bit, until it exactly fit the new pipe in the right angle. Went rather quick due to the experience I gained with the first hole on the other side:
And stuck things together, not soldered yet, no glue or tape, it just fits and holds like this. Quite happy again with the fit:
I expect this connection to be easier to solder. Last time we had to connect 1 mm copper to 0.32 stainless steel. This extra piece of pipe I will use now is a 0.5 mm stainless steel one, which matches the material of the muffler way better, so it will be easier to heat them evenly. The pipe used will be a little bit shorter in the end by the way, as I want some play between the two pipes underneath the teflon connection. Too bad it won’t stay all metal, because I think that’s prettier, but it is what it is, I need to make it out of two separate parts.
This morning I finished the last part of the rudder frame. I still had to add one small piece of rib, but wanted to wait with that until I had finished the transition on the edge, to be able to make them fit together nicely:
So now the rudder frame is finished. I only need to sand the leading and trailing edge. Here’s a daylight picture of the result:
Still working on the rudder. It’s not going very fast because this part has to be scratched completely, but also because I like to work in a steady pace while paying attention to detail. I have laminated the center block using 1/4″ balsa sheets and tapered it:
Then I cut it in pieces to fit them between the ribs and the control horn. As you can see I tapered them in a steeper angle than the ribs, to prevent them from showing through the covering while still adding a lot of strength to the construction. And I am happy with the fit too, it goes in place neatly:
All three parts finished, the control horn fits in nicely but isn’t glued yet, I will do that later when I will assemble everything:
Onto the transition to the edge, for which I again laminated some 1/4″ sheet. Simply sawed the curved shape out of the block:
And made it fit against the already existing construction:
Then tapered it, which created an interesting shape:
Times two, glued and sanded, I now have this (which still needs to be rounded to mimic a tubular frame):
Small break from building the rudder, back to building the custom muffler.
First, we’ve bent the front exhaust elbow in a sharper inward angle, so it will fit into the top chamber of the muffler. Being chromed copper, it was quite easy to bend by hand without deforming the original bend:
Next challenge was silver soldering the muffler to the rear exhaust elbow, that was already shaped to exactly fit the muffler housing. The muffler was inserted in the extended firewall containing the guide or template for the exhaust, the engine protected with some thick sheet metal, and we double checked the angles and position of the exhaust. Ready for soldering:
That turned out to be quite a challenge though… we didn’t want to heat up the whole assembly to let the solder flow all around the seam while it was still attached to the engine. So the idea was to only tack it in place, remove the piece from the test stand, and do the rest of the soldering on the bench. This didn’t work at first, as the tack desoldered and the geometry changed. The second attempt was successful because we clamped everything in place very firmly after moving it from the test stand and template to the workbench.
Another challenge was the fact that the materials were different. Mostly in regard to the thickness of both pieces: 1 mm thick copper and 0.32 mm thin stainless steel. It was very hard to heat up both pieces equally, which made it difficult for the solder to flow properly. It took a few more attempts before everything was water-tight, but we got there!
Due to the tape residue, burnt tape remnants and the excess flux the shine is gone, but the result is very rigid, water-tight and the geometry is perfect:
And after cleaning the piece and treating it nicely with some 320 and 600 grit sandpaper, a wire brush and a polishing disk it looks the part again:
And I am very pleased with the result, I think it looks awesome already:
As you can see, I’ve cut away the exhaust template from the firewall, because since the assembly is attached, I needed more space to assemble the piece. And it already served its purpose, since the geometry now is stable. When the exhaust is finished completely, I will cut away the rest of the firewall extension too, so the exhaust can move freely with the engine while breaking it in:
And the angle is perfect as well! Time to move on to the next phase of the muffler build, attaching the front exhaust elbow as well:
I now have finished all the ribs and the trailing edge of the rudder on both sides. I only have to add the balsa block behind the leading edge / main spar:
I slightly altered the construction proposed by the plans. The balsa doubler of the main spar is designed to be of the same size as the main spar itself, but it already felt quite stiff without the doubler, so I decided this was a bit too much. The doubler now goes from 3 to 6 mm instead of all the way up to 1/2″, so it still has a slope to it and adds a lot of strength, but you will not see it anymore once the covering is on:
I will apply the same concept to the balsa block on the lower half of the rudder.
It’s hard to get a good picture of it, but here you can see it is now symmetrical, being finished on both sides. The trailing edge still has to be sanded to a round shape to mimic the original tube frame:
I think I started thinking about the control horns a little late in the process, as I’ve found a few small glitches. Following the plans the control horn should go like this:
… and that’s also how the ply core is cut, but that’s not correct. The control horn should be placed behind the leading edge or main spar, and not through it:
To fix this I will have to cut through the leading edge. Also, I cut a small noth in the control horn so I can slide it over the ply core:
I could also make the notch in the ply core bigger… but still, this wouldn’t allow me to slide in the control horn from the side, so this solution seemed to be the better one of the two. By the way, the control horn exists of two parts and still has to be laminated (using epoxy).
To take a break from the (for me) challenging metalwork I decided to start working on the tail-feathers of this bird to keep some progress in the woodwork as well. A fun and relatively easy job without any dependencies on other parts of the build that would complicate things (like fuselage vs. landing gear or fuselage vs. engine/exhaust). Construction is straight-forward: balsa ribs over a ply core. Only the ply is pre-cut, you have to scratch-build the ribs. There’s two widths: 1/4″ and 3/16″. All ribs are 1/2″ high. That’s why I used the balsa cutter to cut 1/2″ wide strips out of balsa sheets with a thickness corresponding to the two widths:
The edges of the rudder should be bent out of 4 layers of 1.5 mm thick and 3 mm wide balsa strips, on both sides of the ply core. So this bent edge lies on top of the core, not around it. The advantage of this is that the rudder will be less vulnerable for hangar rash with its strong core, but bending such small strips of balsa and gluing them sideways nice and flat will be challenging. Also, it doesn’t add much to the strength of the construction, as it would do when using the more conventional bent ply edge around a full balsa rudder. This reversed approach is however quite easy to build while still being strong and light. So, I decided to drop the idea of layered bent edges and went with gluing strokes of balsa around the nautilus shaped curve of the rudder to keep the grain in the right direction:
Then I’ve made a template from an old set of drawings and cut the inside of the edge:
And after carefully aligning the piece on the core, I’ve glued it using some scrap plywood that is thick and straight so to keep the rudder absolutely straight while the glue sets:
And one for for the rudder, enjoying the process:
After cutting away the excess wood and sanding the edges I’m quite pleased with the result (and strength already). By the way, in the end this edge will be rounded to mimic the original tubes the rudder was built with:
Onto the ribs! The all are 1/2″ high in the center and slope towards the edge. Easy job, cutting them with the saw upfront and gluing them after sanding to a perfect fit:
And one more, the rudder already is incredibly strong and still very light weight:
Now just finish all the other ribs, the other side of the rudder, and of course the enormous stabilizer and elevators. To be continued!
The next step in building the custom exhaust is creating the connection between the cylinder exhaust pipes and the muffler. The pipe of the rear cylinder should fit right in, the front cylinder pipe requires bending. And I want to fix the rear cylinder exhaust pipe to the muffler permanently but the front one should be detachable for easy assembly. So it’s best to start at the back. I didn’t really know how to go with this task, as the exhaust pipe doesn’t sit perpendicular to the muffler (in both directions) and it doesn’t enter in the center of the pipe, so the hole will be an oval and not a cirkel. Also, the exact location is difficult to find.
After a few attempts and trials to find the location and shape of the hole, I got the idea to make a paper sleeve for the muffler and pack it with tape. This way I could cut a large hole for the exhaust pipe to enter, and then fill the hole with more tape to make it fit around the exhaust pipe nicely. Also, I needed to shorten this exhaust pipe. It needs to be even shorter in the final setup, but I’m taking baby steps here to not mess up. Turns out to work pretty good:
After the pipe fitted properly, I placed the paper sleeve back over the muffler:
And marked the hole to cut:
Then, I grinded the hole bigger gradually, test fitting it after every small adjustment, so I wouldn’t cut the hole too big. It did take quite a while, but I’m very happy with the result!
From the top, it looks the part as well!
Stepping back, the result up until now looks promosing:
I will probably first hard-solder this joint before continuing with the other exhaust pipe, so I have a stable geometry to work with.
By the way, turned out the exhaust pipes from Roto are made out of (chromed) copper, not steel or stainless steel… it should work but it’s less ideal, would’ve preferred steel or stainless steel. Bending will probably be easier, but the joint will not be as strong as with two identical materials.