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.
I don’t want to assemble and glue the fuselage before I’m absolutely 100% sure about the firewall and the attachment of the landing gear struts. To prepare for this step I did an alignment test, and it seems that I can get it nice and straight with only a couple of extra clamps:
Couldn’t resist putting the tail pieces on there as well. Looks very good, nice and straight. I will do another test including the wing tubes before final assembly, making sure they are perfectly parallel and horizontal. Thinking about using 24h epoxy so I have the time to clamp and align everything without having to rush while the glue sets. If I would use white glue, gluing part by part, I probably would build up quite a deviation over that long fuse, giving me no options to do some final fine-tuning and alignment.
Before I can assemble the fuselage, I also need to finish the servo tray. Easier now it’s not in yet. I want to place one rudder servo and two elevator servos in here. And I want to leave options open, so I can decide whether to run them on one channel with a split cable, or run them on a separate channel each. The latter is way nicer, but I’d need a new radio. Also, this way I can still decide to orientate them pointing either inward or outward, depending on what gives the nicest geometry for the push-rods. So, I drew a template in CAD:
And cut the holes in the tray nice and straight:
Another small job finished:
Then onto the landing gear blocks. The plans suggest using basswood, but the stock LG blocks are not big enough, so I decided to cut them myself from a larger block of basswood. One of the sides is angled, which can be cut with the scroll saw perfectly well, if you’re patient:
After finish sanding the cut blocks to the exact dimensions they came out very nice:
And the fit is just per-fect! Fits like a glove:
One more for the back and they’re ready, apart from the routed slots for the spring steel landing gear struts. I don’t want to route those slots before I’m sure about the wire thickness of the spring steel, so I’ll leave them like this and move on to the landing gear and its wing first:
I’m making good progress, but can’t finish up the fuselage before the exhaust and landing gear are done. In the meantime I might start working on the tail surfaces to keep things going.
The next step is to design and build the custom muffler. I’m going with a simple design, I hope it will be effective and that it doesn’t create too much back pressure. From what I got from experienced builders I think this could work. At first I planned filling the chamber around the perforated tube with steel wool but I’m told that will clog with oil residues over time, so I’ll leave that out. Let’s see how this plan works out!
The muffler will be made entirely of stainless steel. Thin-walled perforated tubing is hard to come by, so I ordered a thin-walled tube with a diameter of 15 mm and a thickness of 0.5 mm. I drew a template in CAD and taped it around the tube to drill the perforations myself. Easier said than done. I did expect the tube to deform, so I put a 14 mm thick spruce rod in it, but it got stuck by the burrs from drilling into the steel… also, a 4 mm drill bit turned out to be too thick and a 2.5 mm bit didn’t bite / slipped away. My solution was to mark all 230 holes lightly with the 4 mm drill bit and then puncture the steel with my 2.5 mm bit afterwards. Then, I removed the wooden core by drilling it out from the sides with a 12 mm wood drill, before cleaning up the inside of the tube with a file.
So, after drilling 460 holes with my column drill, some filing and sanding, I can say I’m rather proud of the result:
Next challenge: the exhaust pipe itself (outer wall). Buying a 40 mm stainless steel tube is easy, but they’re all 1.5 or 2 mm thick. We’ve tried to roll a 0.5 mm stainless steel sheet into a tube, which was doable, but TIG welding it turned out to be almost impossible (even with backing gas). Although a second attempt came out better, I’ve continued my search online for some ready made tubing. Hours into it, still no luck. Until I got the idea to search for a suitable thermos. And to my surprise I found a very small one that was just long enough. With an outer diameter of 45 mm it could very well be the case that the inner tube was about 40 mm wide. So I’ve ordered one and cut it open. Luck was on my side: the inner tube has a diameter of exactly 40 mm and the wall thickness is a beautiful 0.32 mm!!
After that, I cut two disk out of 0.5 mm stainless steel sheeting, bringing it to the exact right dimensions with a lot of sanding and patience:
Then I cut 15 mm holes in the center (drilled undersized and carefully brought to 15 mm with a milling bit and some sanding). It’s coming together nicely up until now:
My fellow club member helped me out with hard-soldering the parts together, as I do not have the equipment or the skills to do so myself. Very grateful to have such supportive and attentive guys in our hobby!
Lastly, I cut the open end of the scale exhaust at the right angle, and although I still have some sanding and shaping to do, it is already looking great:
And this is what it looks like from underneath. The inner assembly still has to be soldered to the outside wall, but at least the fit is perfect already:
Here you can see the end of the pipe from an angle, shows nicely that the functional exhaust pipe is hidden in the outer tube. From the side, you wouldn’t tell it’s there and it sure has the appearance of the original scale exhaust:
And this is what it’ll look like when it is fully finished and installed:
I also bought an extra cylinder exhaust tube from Roto, as it originally came with two different ones, sitting in different angles due to the different orientation of both cylinders. For me though, I want to bring them together in the center of the engine, so this seems easier to work with for my setup.
Now the challenge will be to create the transition from the original exhaust pipes to my custom muffler. Part of the challenge also is that the exhaust pipes attach to the cylinder heads using threads instead of being bolted on, which makes the geometry change while attaching it (the exhaust pipes point in the opposite direction) so I need to incorporate some flex tubing into my design. I hope it’s going to work out, because it would be totally awesome to have a working scale exhaust!
After trial fitting the engine in different positions, I landed on the following position, down and side thrust for the engine:
As mentioned before, I didn’t quite like the commercially available mufflers and didn’t know where to fit them inside the fuselage. Then, I got some valuable help from a fellow club member. We took up the challenge together and decided to try our luck at building a custom muffler in the shape and position of the original scale exhaust! Of course, it’s still not a sure thing we will succeed, but if we’d do that would be fantastic! This would be much more practical to install, it would be outside of the fuselage which is better for cooling, and above all, it would look awesome!
I took the only two photos that exist showing the original exhaust and measured the dimensions and angles, as well as the position where it would protrude the fuselage side. Then I’ve calculated the required volume. As far as I can see right now, position, angle and length would all be exactly scale, only the diameter would be slightly over-sized. Scale diameter would be 28 mm, I’m aiming at 40 mm right now.
Time to continue working on the firewall. This is the second version with better dimensions for the engine mount. I also drew the firewall from the kit on it for reference and cut a hole for the exhaust:
Here you can see the one degree side thrust and one degree down thrust:
The engine nicely fits onto the new firewall, fixed with 5 mm Allen bolts into T-nuts attached from the back:
Then I’ve built a test stand for running in the engine later on:
But it also serves another purpose: building the muffler! I’ve cut holes in such a way that if I fix the custom muffler into it, I have exactly the right angles both backwards and sideways. Also, I’ve added a piece that resembles the fuse side so I can test and fine-tune how the exhaust should pass through the fuse side:
But for running in the engine it wouldn’t be practical, and I also want to be able to work on the engine easily, so I’ve made it detachable using magnets:
The idea is to first build the custom exhaust, and when that’s finished and firmly attached, I will cut away the sides so the muffler can move freely when I’m running in the engine.
Working on the test firewall at the moment. I am building a test stand that doubles as a firewall construction test bed as well. The new firewall will be made of 9 mm birch ply and attached to the original firewall with bolts and washers, to get the right down and right thrust angles:
This new firewall will be glued to the sides as well.
After mounting the engine, I’ve tested the alignment of the prop shaft and checked the clearance of all engine parts with the fuse sides. I think this position works very well (which is one degree down, one right, and 10 degrees tilted to create more space for the exhausts):
Also, the carb fits well within the available space and doesn’t touch the fuse side:
I couldn’t resist checking what it looks like wit the prop on…:
Now, I’m going to redo the new firewall, to fix some small alignment issues, and reshape the cutout of the original firewall to accommodate the rear exhaust pipe. It takes a while but we’re getting there!
Tonight I spent some time adjusting the wing tube holes, to get them to the right size while aligning them on both fuselage sides. In this picture already halfway, enlarging the front hole from 41 to 42 mm:
And the other smaller hole will go from 25 to 27 mm.. not much of a change, but precise work, since this determines the alignment of the wing tubes. If the sides don’t match up exactly, the wings will not sit straight and that would look horrific. First, I’ve marked the new whole size and position:
And then I just sanded them to the right size, went well:
Checking if angles are perpendicular:
And checking the distance between the holes with the root rib:
After transferring the holes to the other side of the fuselage, I did another mock-up, this time including the wing tubes. Impressive sight, and surprisingly sturdy without any glue yet:
Alignment looks great. Did not spent any time on checking and final alignment, but by the looks of this, I think perfect alignment will be achievable quite easily. From the front:
And from the back, everything is looking sharp:
This is one of my favorite pics up until now, I’m really satisfied with how everything fits and the airplane really starts to come alive: