Urupema: ready for the paint shop

The filler/primer on the wings was sanded down again, to get a really smooth surface. Last week we also got the canopies, which we had produced by a friend, using our mould. I spent quite a bit of time fitting it to the canopy frame, before fixing it with epoxy resin. It looks quite good. I also fitted the towhook and bungee hook, as well as an extra bulkhead to hold the seat inlay. Today I prepared all the parts for spray painting (canopy is always a lot of work to prepare), as well as the tools to hold the parts during spraying and letting the paint harden out. Tomorrow I’ll bring all of it to Andi, the master painter in our building team. I hope he can get a slot in the paintshop over the weekend. I am very curious to see how it will come out…spray painting tends to be quite merciless in showing where you made mistakes……


Urupema wings and elevator: sanding the glass and applying filler/primer

The 49gr glass covering wings and elevator hardened out nicely, and I couldn’t help putting the plane together to see how it looks, now also with the landing gear :-).

Today I sanded the wings and elevator and cleaned them. After that I applied the primer/filler. First with a roller and then pulling it deep into the (few) pinholes using a spatula. I hate this part, as the primer stinks like hell. While it needs around 20deg C to harden out I cannot apply it outside, so I spent the morning in the workshop using a face mask. Now the primer can harden out over the weekend. On Monday it’s sanding time again….

Urupema landing gear and wheel cover

Fitting the landing gear required fiddling a bit with the correct position of the two spants to ensure that the center of the wheel is 2cm behind leading edge of the wing. Then cutting the hole at the bottom of the fuselage to the right size so that the wheel fits through. The suspension is a couple of rings of inner bike tube, which we also use for our retract able gears. I always first provisionally fix the spants with a few dots of 5minute epoxy, and once everything is in the right place I fix it using 12hr epoxy.

Fitting the wheel casing is done with two 4mm screws. I first cut some plywood to size, fixed it in the right position on the fuselage with a few dots of 5min epoxy resin, then drilled the holes, removed the plywood from the fuselage and fixed it to the wheel casing. Using a syringe and some coloured 12hr epoxy resin I filled the small gap between the wheel casing and the fuselage to ensure a perfect fit.

Urupema: covering wings with glass and building canopy frame

After giving the wings a final fit, filling some minor uneven surfaces on the lower side of the wing with polyester putty, the next step is covering the wings and elevator with 49gr glass fiber (lower side of the wings first). Before doing so we apply a watery primer (to avoid too much resin being absorbed by the abachi wood), which is slightly sanded and then the wing is wiped clean of all dust. The 49gr glass is applied with a roller and resin that has white colorant added as well as around 15% methanol (50gr resin, then add hardener etc. per wing). The methanol makes the resin very watery and easy to apply using the roller (and an old teflon frying pan).

I also finished the canopy frame and started builing the “lock”. The canopy frame looks quite good already, but will need a layer of filler before I can spray paint it. It was built by applying tape around the canopy base and two coats of liquid wax on theĀ  areas where the canopy frame is lying on the fuselage. The frame is then built using first a bit of thickened epoxy (with micro-balloons and a bit of aerosil), then adding a bunch of carbon fibers. It is then further “filled out” with thickened epoxy. After giving it a rest of a few hours, allowing it to harden out a bit, I first rolled the upper side of the frame (after first applying cling film), to even out the top surface. I then filled any small uneven bits with thickened epoxy again and applied two layers of glass (280gr and then 160gr), and allowed it to harden out like that.

Urupema landing gear assembly

We wanted our Urupema to have a landing gear with suspension (as we often fly on pretty rough alpine slopes). Georg designed it, and Richie built the mould for the cover. We spent a lot of time sourcing the right size of the various bits and pieces. The sides are made of 5mm glass fiber. A friend was able to mill the glass fiber sides on the basis of our drawing, and another friend helped us thread and cut aluminium parts to size. Today I assembled my landing gear. Fits perfectly.

Urupema: motor bulkhead done and wings, rudder and elevator first fit

Last week we built my second wing, it came out of the bag very nicely. Georg also built the rudder of my Urupema (in the mould). I spent a few hours sanding the abachi wood of the elevator and wings, and had a first fit. I also cut off the nose and installed the bulkhead for the motor, which also worked well.

Pretty excited, this is going to be a beauty. A lot of work to be done still though, experience says that once the wings are fit it’s about a third of the work done. But I hope to have my Urupema airborne by early June.

How and why do we do it?

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:

JS3 slope start

JS3 on our airfield


Georg’s Urupema

While I’m still working on the wings of my Urupema, and Andi is working on the fuselage of his, our “Master Builder” Georg has been making excellent progress on his. He’s finished the rudder (with Rotational Drive System – RDS) and elevator installation and his plane is just about ready to be spray painted. It looks awesome.

We also got most of the parts of the landing gear together, including some bits that were cnc milled by a colleague. I’ll need to do some work on the missing bits today.

Georg also checked the weight of his Urupema. He’s expecting a take-odd weight of around 6300 gr., which means 63 gr/dm2. With the ballast in the chambers it will be around 78 gr. /dm2. Another plane that will be great both for thermals and heavier slope work.


Urupema decals

In the meanwhile I’ve also been searching the web for Urupema pictures to help decide what we want our Urupemas to look like. As the plane was built in so many version, with so many different decals we’ve decided that we have a bit of liberty with this, but will allow ourselves to be inspired by the version that’s most photographed on the internet (see for instance here). We will go for a Brazilian design. I’ve identified the fonts of both the logo under the cockpit (Microgramma bold-extend) and the registration number (Bahnschrift Semibold Condensed) and done a first design of what our decals can look like. We now need to decide on the registration numbers we want to use. I’ve also ordered a couple of Brazilian flag stickers, which we may stick to the tail fin if they look nice enough. Note that the below file links through to the PDF version of the graphics, which are free for anybody to use.


Urupema build progress – wings

It’s been a while since the last update on our Urupema build, and a lot has happened. We finished building the four fuselages (Georg and Andi pushed out the last three while I was on vacation). Two sets of wings are done. Andi and I have been working on the third set of wings (mine) over the past week. Yesterday we bagged the first, which came out very well. We hope to bag the second wing of my Urupema sometime next week. We’ve been using 160gr carbon biax cloth for the full surface of the wing (top and bottom), in addition to progressive carbon rovings (37 at the top and bottom for the first 10cm, reduced to one at full length of the wing), and of course the usual carbon sock around the wing spar and control surface hinges. We’re also building ballast chambers on both sides of the wing joiner. The result is an incredibly stiff wing, with a nice flexibility at the tips, exactly how we wanted it.

In-between: another Diana2….

With the JS3 maiden flight still to go, my favourite plane by far remains the Diana2. So far I had three versions: my 1:3.5, 4.28m and 5.65kg scratch-built (my favourite!), the Chocofly derivative of our scratch-built (identical size and profile), with 6.3kg (Alpine version) as well as the Baudis/Chocofly 1:3, 5m version (8.2kgs). The great thing about the Diana2 is that it’s such a versatile plane and can be flow in weak thermals and in extreme slope conditions. It performs very well at low weight (a real “balloon”) but also carries ballast and higher weight extremely well, when it becomes a real racer. I’ve been wanting to built a “light” version for a while. Chocofly was able to supply me with an extra fuselage, which I’ve now built as a light glider. It’s ready to maiden, and I hope to do a first aerotow soon, and use it on the slope afterwards.

Swift S1 Maiden flight (OO-YES)

And finally the winter fog cleared! Yesterday afternoon I took the Fridayfly Swift S.1 (2.8m, 4.6kg) to our airfield for its maiden flight. Start was using our club’s catapult. The leomotion motor (L4031-2550, with 6.7:1 gearbox and RFM 16×13 Prop, running on 6S) has plenty power. It needed a bit of up elevator, and the throws are quite large. Unfortunately the conditions were far from perfect for flying, incredibly bad visibility and a low sun meant being very careful. And this time of year you can just about forget about any thermals, especially with a heavy plane like this of course (it’s meant for the slope, not our airfield). It flies incredibly well though, and I’m looking forward to taking this to one of our local slopes soon, and Hahnenmoos in June….

OO-YES ready for its maiden flight

My Fridayfly Swift S.1 (2.8m) is now ready to maiden. The plane was mostly built when I picked it up in Germany a few weeks ago. I was hesitating whether to fit a motor or leave it as a glider. The problem is that the winds on most of our slopes are not that reliable and I don’t want to have to land this baby way out. Also, I have enough light planes, and this one can do with half a kilo of extra weight for the motor. So Urs from Leomotion.com built me a nice and powerful little motor :-). Programming the plane was easy, now waiting for the fog to clear, so I can maiden it on our airfield….

First Urupema Fuselage

On Monday we built the first fuselage of our 4.28m EMB400 Urupema from our new mould, and took it out of the mould this morning. The first fuselage out of a new mould is always the most difficult one. While the fuselage looks great, we made a few small mistakes during production and it isn’t perfect. But since we will spray it anyway to hide the seam we can easily correct those mistakes. We’re pretty happy with the result, especially the last picture below where we fitted the plug for the rudder and the elevator. The next fuselage will be better still. Three more to go….

Urupema Parts (electronics and servo mounts)

On Monday we had a team discussion on which electronics and servo mounts to use for our Urupema and ordered the parts on Monday afternoon.

Our electronics we always get at leomotion.com. We’re fortunate that their shop is a short drive from where we live, and Urs and his team offer excellent advise and service. Richie will, as always, build his Urupema without motor. The rest of us have opted for the newer version (Dualsky XM5060EA-14 KV340) of the same outrunner that we’ve been using for the JS3 (and in my SZD54, AvantiHawk and Taranis). It’s very powerful, extremely silent and good value. The only change is that we’ll be using the new “scale” propeller from GM (18×10 Scale), which should fit even better with the fuselage than the version we used on our JS3 (where we used an 18×13). For the servos we use the powerful Chocomotion/Fox 8 and 10mm (wing) and the 12mm (tow release). Elevator will be expensive but virtually indestructible MKS 6130. For our rudder we will use the trusted old Futaba 3174 with the Leomotion RDS adapter (rudder will be operated through RDS, more on that later). ESC will again be using the Castle Phoenix Edge 100 Light, which always works and is a breeze to program. We’re waiting for the new 43mm spinner from RFM with a slightly wider prop mount which should look better with the new GM props.

For our servo mounts and wing surface control we again went for the IDS system from servorahmen.de, which we ordered directly with them. We’ve been using Florian’s system for our past few builds and really like it. While a bit fiddlier to install than the “classical” system with clevises, the ability to build it almost entirely within the wing is aesthetically pleasing. It’s also very rigid, without any play on the system itself. The only “disadvantages” are that it needs quite strong servos (but the Chocomotion servos have plenty power) and when the wings are very thin it’s better to make your own control horn at the side of the wing control surface to ensure that the servo has enough leverage.

Oh, and the Urupema moulds have been polished to a shine, with six coats of wax and are waiting to be painted so we can build our first fuselage hopefully in the coming week.

Urupema fuselage mould

This morning we separated the Urupema fuselage mould, removing the plug. The two halves separated well, the mould is perfect. This afternoon we’ll polish the mould halves. After that Georg will add a few layers of wax, so that Andi can spray paint the coating and Georg and I can build the first fuselage next week.


Quite a few projects have been coming together recently. In July 2017 I ordered a Fridayfly (Uwe Freitag) 2.8m Swift, which I went to pick up at Uwe’s place in Germany last week. It’s fully built, including all servos, so not much work before I can get this one airborne. Today I installed the SBUS hub, receiver and programmed the plane. I also had some fun doing the decals. It doesn’t always have to be a Swiss flag on a plane and I’m proud to fly one with the flag of my other nationality ;-). And the registration number is quite obvious if the country code is OO……

JS3 – ready for its maiden flight!

The last bits of getting a model ready always take longer than planned, but my JS3 is ready for its maiden flight! I’m pretty excited about the final weight, around 6.6kgs with the long wings, so it should thermal very well. I still want to add some stripes to the underside of the wings and do some more work on the cockpit interior, but will wait with doing that until after the maiden flight.

We started the project in June 2017 (beginning of this blog) when we first laid out the enlarged plans on the floor of Georg’s workshop, fell in love with the plane and decided to build it, sharing out the work according to availability and skills in our team of four (Georg, Richie, Andi and myself). Georg, our lead designer, maidened his JS3 in spring 2018 (I think it was the first JS3 scale model to fly). Andi’s JS3 was finished a few weeks ago, and Richie is about to finish his. I’m so looking forward to the maiden flight of my JS3, and seeing all four of them in the air together.

This is only my second fully scratch-built plane (not counting the AvantiHawk), and the first one where I’ve been involved in every step of the process. But it was by far the most difficult build so far. The complexity of the wings, two sets of winglets and the exchangeable outer wings were a lot of extra work. My JS3 is far from perfect, there are many mistakes in it that I wouldn’t make again, but I’m still very happy with the final result. Having seen how Georg’s JS3 flies, I know all the work will be worth it.

JS3 – seals and installing servos in the wings

In between the work on our Urupema project I’ve been putting the finishing touches to the wings of my JS3. The seals on the control surfaces came out well in the 2nd try (messed up the first try and had to start again). All servos have now been installed, using the IDS system from Servorahmen.de. I still need to do some soldering and then prepare the covers. The JS3 should be ready to maiden soon…..