Following a question from one of the readers of this site I’ve added a new “how to” section on how we cut out the wiring channels for the wing servos. I hope this is useful.
In all my recent builds I’ve used Chocomotion servos (supplied by www.leomotion.com) in combination with the IDS system supplied by Servorahmen.de. When deciding to install the IDS system, we’ve found that 1) you need good and strong servos; and 2) at ridiculously high speeds even the strongest servo may give up as the lever from the IDS system is simply too short. In our earlier builds we used Futaba 3174 and KST x08 (aileron) wing servos. Unfortunately I’ve had quite a few serious burn-outs and control surface flutter at speeds over 240kmh on my scratch-built Diana2, even resulting in one Futaba servo catching fire (fortunately the plane is still alive!).
The Chocomotion servos are much stronger than the Futabas (no breakage so far, and the newer versions now also have little or no play). For the Urupema’s flaps and flaperons we use the Chocomotion 10/10, as with our JS3. For the ailerons we’re for the first time using the Chocomotion 8/6 instead of the KST X08. The “normal” X08 is simply not strong enough for the ailerons using IDS in larger planes when you want to fly it fast (I’ve killed way too many of those…an they’re not cheap). The X08plus is much better (no breakage so far), but in view of our good experience with the Chocomotion brand, we decided to try out the Chocomotion 8.0/6.0 instead, as it should be a bit more powerful than the X08plus.
As we have quite large control surfaces on the Urupema, we also decided to replace the standard control horns on the control surfaces with our own, using a bigger lever to reduce stress on the servos. It was quite a bit of work to cut them out of glass board (by hand), but I hope that it will allow the servos to hold at higher speeds.
Learning how to make the seals for the wing control surfaces has been a bit of a process for me. We always use a silicon hinge (see two posts earlier), usually at the underside of the wing. This means that a nicely set seal really helps the plane look good, but of course also helps flight characteristics. In the past I’ve had to redo the seals quite a few times when they didn’t come out well, or I had to spend a lot of time sanding them. The Urupema, my third fully scratch-built plane, has the nicest seals I’ve made so far, and I’ve learned again for next time.
What I’ve learned so far: of course the tape is really important. We use a relatively hard PVC tape that is easily removed once the epoxy resin has cured. Also important is cleaning, especially when you have carbon in the wings. It just takes a bit of carbon dust to give you ugly black spots in the nice white seal. The first few seals I set I made the expoxy too thick, which meant that it didn’t distribute nicely the seals looked ugly. I still thicken the epoxy with micro-balloons and a bit of aerosil (and of course apply colorant), but it can stay quite liquid. Use a good syringe to apply it on the tape. Wait for it to cure to a point where it’s still elastic enough to bend, but no longer liquid. Then insert the tape under the wing (I use a ruler) putting the control surface at around a 20-30 degree downward angle. Fix into position and let the epoxy cure. If you apply colorant, you may want to give it some extra time to really harden out (depending on the temperature in your workshop). I usually leave it for two days, then remove the tape and sand the seals down to size (allowing enough upward movement).
For the Urupema I had a lot of work shortening the seals to get enough upward movement in the control surfaces, something to take into account for next time. They’re also quite thick, but then weight isn’t as much of an issue with this plane. I’m pleased with the result.
For the past few projects I always had one of my friends help with cutting out the control surfaces in the wings and elevator. It’s something that easily goes wrong and then ruins lots of hours of work on the wings. With the Corona lock-down rules, having seen it done a few times and actually having all the required tools in my own workshop I though it was time to do it myself. And it went surprisingly well, without any major hiccups, and was easier than I feared – although it does need a steady hand! I used an ancient Dremel with a 0.8mm bit for the underside of the wings (hinge) and a 1.5mm bit for the upper side of the wings. One of my colleagues in our club made a very clever add-on for the Dremel that allows you to guide it along an aluminium ruler. The rules is positioned and glued to the wing with bits of double sided tape. My mate Georg also very helpfully provided a template for cutting out the servo openings, which made it easy to do those.
After cleaning out the foam, I sanded down the upper leading edge of the wing, so it’s razor sharp, and applied a strip of 60gr glass to protect the exposed abachi wood and give the edge a bit more rigidity. Once that was hardened out I set the hinges using silicon glue. This will now need to rest for approximately 5 days, after which I can start doing the seal on the upper side of the wings.
The “how to” section was expanded with information on how we build the fuselage moulds and the fuselages.I’ll keep on expanding the “how to” section with other issues, in response to question/requests for information. I hope it’s useful.
We’re regularly getting questions not just on how but also why we build our own gliders, and if it’s really worth the hundreds of hours of work that go into them. On 14 December 2019 we were invited at the 35th international aeromodelling symposium in Winterthur (CH) to give a presentation on our work. Unfortunately I was unable to attend, but the other three members of our building team, Georg, Andi and Richie, explained how and especially also why we do this. I put together the slides for the presentation, which are now uploaded here. It’s mostly pictures, with some text in German. The two videos were included at the end of the slide-show are available on my Vimeo channel:
Getting the decals for our planes made has always been a very tedious job. We either spent a lot of money having them produced commercially or had to beg friends with access to vinyl cutters to make them for us. As the newcomer in the team, and somebody who loves to play with computers, I decided to bite the bullet and bought a vinyl cutter myself. It’s a Silhouette Cameo 3. Not only is it good value for money, but it has excellent and very easy to use software.
I’ve started preparations for the decals for the JS3, which are going to be challenging. As a trial run, I redid the decals on a 14-year old Diana 1 (1:3.4, 4.28m) glider that I took over from Richie. Even though the Diana1 is 14 years old, it was one of the first planes built using the same techniques that we are now using for the JS3. With only 5.3kg it’s a light weight, excellent for more difficult conditions. I maidened it last week, after giving it a full refit of its electronics (and new decals!). Below some pictures of the old decals, done 14 years ago, and the new ones done on the Silhouette Cameo 3. I’m very pleased with the result. I’m even more pleased with my refurbished Diana1, which now looks like new and flies like a dream!
Oh, and I couldn’t resist adding two pictures of my new Diana1 and myself on the slope last week….
I wrote earlier about our servos, but not in detail: we will be using KST X08plus for the ailerons on the outer wing of the 5.14/18m version, ChocoMotion 8/5.0 for the ailerons, and Chocomotion 10/9.2 (in size identical to the KST DS225MG, but more powerful) for the rest of the control surfaces (6 Servos in the 4.28/15m wing and 8 Servos in the 5.14/18m wing).
Today I received a large package from Servorahmen.de in the mail. Servorahmen.de provides servo frames with Integrated Drive System (IDS) for all the servo types we will be using. We have used their IDS system on most of our gliders in the past few years, including last year’s scratch-built Diana2 (1:3.5). The frames fit well, are robust and good value. The IDS system can be fully integrated into the wing, so no ugly protruding levers or large holes in the wing surfaces. Most importantly, they provide a wing surface control that is extremely direct and completely without play. Fitting the IDS frames requires more effort than standard systems, but the result is definitely worth it. Below are two pictures of the system built into my 1:3.5 (4.28m) Chocofly Diana2 that I hope to maiden soon. The Chocofly Diana2 is identical to my scratch-built Diana2 (which was designed by members in our team), except that the wings were built in a mould.
We build our own wing joiners, from carbon rovings. The main wing joiner was built last year (I did a whole bunch in series over a couple of months). As we will have exchangeable outer wing sections we also needed smaller wing joiners for that part of the wing. The 15m (4.28m) version will have one with a 5 degree angle, the 18m (5.14m) version with a 2 degree angle. The moulds for the wing joiners were made by hand, and are precise enough for our purposes.
We form a kevlar sleeve around the main wing joiner. This sleeve will be built into the main wing.