Chocofly JS3 – ready to fly again!

My Chocofly JS3 is ready to fly again. Chocofly kindly supplied me with two new outer wings and a new wing joiner. I also replaced one of the outer wing servos (gear was damaged) and fixed the small cracks in the fuselage, as well as the connector of the left winglet. I replaced the hinges of the landing gear doors with some more robust ones (the ones supplied by Chocofly unfortunately did not hold long, I’m back to our usual and proven method), and fixed the EDF bulkhead, which had a few small cracks and made a few other smaller repairs and improvements to my JS3. The wings have no scars from the accident, but the repairs on the fuselage are still visible. I hope to have the fuselage repainted in the coming winter to remedy that – but now it needs to fly! Unfortunately the weather has been pretty bad in the last few weeks, fingers crossed that will change soon….

When disaster strikes – Chocofly JS3 damaged :-(

It’s been a few years since I had major damage to one of my planes. Unfortunately disaster struck again on Thursday last week. After maidening Georg’s Chocofly JS3, I wanted to have a flight with mine as well. Upon the start in aerotow, the right wingtip of my JS3 touched the ground, I overcompensated and before I knew what was happening it flipped over to the left and crashed upside down just meters after the start.

Fortunately the damage is relatively minor for what was a pretty serious crash. Both outer wings can probably be made usable again with repairs (but will need replacing, also for optimal performance), and one of the small wing joiners of the outer wings needs replacing. There are a few minor cracks in the cockpit area of the fuselage and the EDF cleanly broke off. I was really lucky that there is no damage to the inner wings, elevator, rudder and tail of the fuselage. With a new wing joiner, some work on the outer wings, fixing the smaller cracks in the fuselage and re-attaching the EDF, I should be able to restore my JS3 to flying service again soon. I’ve already ordered new outer wings and will probably have the fuselage resprayed the coming winter to restore the plane to full glory.

The worst thing is that I was really very much looking forward to flying the Chocofly JS3 in Hahnenmoos starting Sunday. That will not be possible.

Another lesson learned. Flipping over after overcompensating at the start in aerotow is not uncommon. Most of my flying mates have had serious crashes (and much worse damage than my JS3 suffered) this way. But it’s something that can be avoided by asking somebody to hold up the wing of your glider upon the start. I was stupid. I definitely won’t forget this for next time.

Slope testing the Chocofly JS3

After Friday’s maiden flight in aerotow, I could test the new Chocofly JS3 Rapture on the slope today. The conditions were perfect for the JS3, very light lift, with great intermittent thermals. We had three JS3 on the slope, one scratch-built by Georg Staub, identical to my scratch-built, with around 6.3kg, one scratch-built by Richie Oberholzer, without FES, around 5.5 kg, and my Chocofly with JETEC E-70 with around 6.6kg. We were all flying the 18m/5.14m version (I only have this version for my Chocofly JS3, and always fly the longer wing version with my scratch-built).

The Chocofly version is virtually identical to our scratch-built JS3. The differences are of course that the wings are fully moulded, whereas our own are foam core with carbon/glass layup. The elevator of the Chocofly JS3 is approximately 1cm less deep, and the fuselage approximately 2cm thinner. In addition the wings have 3 rather than 4 control surfaces.

With the identical wing and elevator profile, the performance of both planes is however very similar. We did some formation flying in different camber settings. My JS3 and that of Georg performed equally well, with the Chocofly version giving the impression of being slightly more performant in thermals. With more robust wings, the upper end of the speed spectrum is of course also higher for the Chocofly version – I got to 230kmh in some of the low passes.

The JS3 (both my scratch-built and the Chocofly version) ist the best scale glider I have for flying in thermals. It picks up the least bit of lift and allows for slow, tight turns, very similar to a F5J glider. With the multiple dihedrals in the wings, it turns mostly on rudder and only needs minimal aileron. Even with massive camber settings it is hard to stall, and it announces a stall very nicely – nasty stalls are very rare. The nice things about the Chocofly version is that the 5.14m also allows for higher speed passes, and of course having a JETEC rather than FES makes the plane so much nicer to look at.

To note is that there is also a 4.28m version of the JS3. I have shorter outer wings for my scratch-built JS3, but, to my shame, have never flown it with these. I may however be tempted to order the shorter outer wings for the Chocofly version. With the shorter outer wings it should be quite the slope racer – although in the GPS version not as much as my Apline Edition Diana2 (with which I can do just anything). To be decided.

I’m still not done with determining center of gravity and longitudinal dihedral. I did move the CG somewhat backwards but have found that I still need quite a bit of uptrim on the elevator. I hope to get some test flights on one of our local airfields soon to sort this out. I also still need to sort out the battery issue. I’ve using 2 older 3S 3700 LiPos as a 6S setup, with 4mm plugs, which I’m not happy with. I’ll be measuring Ampere/Watt of the JETEC shortly to see what power flows, and will probably adjust plugs and battery. I’ll also replace my 2S LiPo that I use as a backup power source (next to the BEC). More on all that later.

Even with all this, the plane flies great already, it will only get better. I’m a big JS3 fan, together with the 1:3.5 Diana2 it’s my favourite plane.


Chocofly JS3 Rapture Maiden Flight

An unexpected opportunity to go maiden my Chocofly JS3 Rapture came up today at the Eglisau airfield of the Zurich model aircraft club. A windy and bumpy northern breeze, but some nice thermals and especially some great towplanes and towplane pilots and assistance from Dani Aeberli from Chocofly. The maiden flight went well, but the plane was a bit nose-heavy and had too little down-elevator in crow. Moving the battery to the rear fixed the CG issue, and it’s now flying just as nice as my scratch-built one. It’ll still need some fine-tuning though – but the turbulent weather wasn’t conducive for that today. Dani insisted on trying a self-start, something I hadn’t counted on being possible, but it went amazingly well – even uphill on a grass piste.

Here is a “quick and dirty” video and some pictures. More to follow.


Chocofly JS3 – ready for the maiden flight

With the JETEC E70 and retractable gear fully installed, and having prepared the rest of the components for the fuselage a few weeks ago, all that remained was finalising the installation of the components into the fuselage and programming the transmitter. It still took me more than two rainy days of work, but the JS3 is now ready for its maiden flight. The take-off weight is 6.67kg (this time weighed with my professional Mettler scales – having obtained different values from my cheapo scales earlier). That includes two 3S 3700mAh LiPos for the EDF, and a 2S 2200 Lipo as backup power (main power comes off the BEC from the ESC). I put the Center of Gravity at 103mm, identical to our scratch-built JS3 (which has the same wing layout and profile, but a larger elevator and thicker fuselage), this is also what Dani from Chocofly is flying his prototype with. Georg is also close to finishing his JS3 – once the weather is ok again we can maiden both our JS3 and my Moswey III.

That concludes my builds for this flying season. I’m pretty proud of a productive winter – having (finally!) finished my Moswey III, built a great towplane (Eco-Boomster) and completed the Chocofly JS3 Rapture. Now it’s time to go flying, do some maintenance, but also start on the next projects for the coming winter – more on that soon. And of course I’ll post some pictures and videos of the maiden and other flights :-).


Chocofly JS3 Rapture – installing the JETEC E70

The weather over the last few weeks has been dreadful. On the few days that were ok-ish I had other things on, so have been unable to go maiden my Moswey III. On the positive side, the many rainy days also meant that I had time to get back to my Chocofly JS3. Together with Georg Staub, our team’s designer, we fitted the JETEC E70 retractable EDF, as well as the retractable gear into the fuselages of both our JS3 (he’s also building one, identical to mine). It’s the first time we’ve done this, and was not without it’s challenges.

We were fortunate though that Dani from Chocofly was so kind to provide us with a perfectly fitting CNC cut mount for the JETEC. He also kindly supplied a perfectly moulded “spare” of the top of the fuselage, from which we could cut out the cover of the JETEC and allowed us to study and measure the installation of the JETEC on his JS3. I also made a drawing of Dani’s cutout in the top of the fuselage, which I digitised to allow me to cut both the positive and the negative template of the opening at the top of the fuselage on my Silhouette vinyl cutter (a PDF version can be found through the link, contact me if you want the version for the Silhouette vinyl cutter).

After correctly positioning the vinyl template, we used a dremel to cut out the opening for the JETEC. The correct positioning of the motor mount in the fuselage proved to be quite challenging. Georg constructed a tool that allowed us to fix the motor mount to the wing joiner to allow us to adust it to the correct position. We then fixed it on a couple of places with 5minute Epoxy Resin, before fully fixing it with 24hr Epoxy and a few strands of carbon roving. Cutting out the landing gear doors wasn’t too hard once we determined the position of the retractable gear (which was determined by the position of the JETEC). Once the whole thing was installed I cut the EDF cover to shape, again using the vinyl template, and fixed it to the top of the JETEC. A lot of work, but I’m pleased with the result.

Starting work on the Chocofly JS3

Finally found the time to start working on the Chocofly JS3. The build quality of the Chocofly JS3 is excellent, and the amount of work to be done not too bad, it’s a real joy to work on this.

I’ve glued in the elevator servo and prepared the pushrod. The landing gear (own production from our club), rudder servo and the towhook, are also ready to be installed, but I’ll wait with doing so until the Impeller is in place.

Today I started work on the wings and cut out/glued in the IDS rudder horns for all six control surfaces. Dani from Chocofly kindly provided fitting rudder parts and perfectly fitting aluminium IDS servo arms. Tomorrow I hope to finish installing the wing servos, and then will start soldering the wiring harness. The difficult part will be installing the impeller – which I’ve never done before…

The JS3 has a new sister

Corona-delayed, and a long wait, but she’s there. The Chocofly JS3, fully moulded, 5.14m wingspan, empty weight around 4.2kg. On Monday we picked up three JS for me and two friends in our building team. Ours are the first production builds of the lighter version (production nr. 3, 4 and 5), but wings are still very stiff and their torsional strength is better than our own scratch-built versions.

The Chocofly version is closely based on our scratch-built JS3. Chocofly has used the same wing and control surface profile and layout (all by Georg Staub, who also designed the “small” Diana2 and SB-14). The only difference is that the 5.14m version has “only” three control surfaces, rather than the four in our JS3. The fuselage is stunning, and based on original CAD data. Chocofly has a record number of orders for this plane, and the waiting list is huge. But it’s a beauty and I know it will fly very well – my scratch-built JS3 was my most-flown plane in 2020 and already has clocked up a couple of hours of airtime in 2021.

I’m deeply impressed by the quality of the build. I’ll be building mine with a small retractable JETEC E70, running on 6S. Unfortunately this means that I cannot fly it on our local club airfield (no turbines allowed), but I can fly it at the other club that I’m a member of in Gossau and of course on the slope. I’ve been dreaming of getting a glider with JETEC, and the fuselage is so beautiful that I just cannot bring myself to hack the nose off this one. Haven’t decided yet if I’ll add a landing gear – this will depend on whether there is enough space in the fuselage once the JETEC is installed, and the weight of the plane. Aim is to keep the take-off weight at around 6 kilos at most (my scratch-built one is 6.3kgs, which flies great).

First flights with the prototype of the commercial version of “our” JS-3!

Chocofly will be producing “our” JS-3 in a fully moulded version. Wing profile and layout are identical. The fuselage is newly made on the basis of the original CAD data. On Friday Chocofly’s Daniel Aeberli maidened the prototype. This afternoon he did some further tests at our club’s airfield. The prototype has a stiff middle wing that’s based on the “alpine version” specs. The outer wings of the 5.14m version of the prototype are in the GPS light version. The full plane, with JETEC 70 and 5S 5200 battery weighs only 6.3kg.

This plane is simply awesome, even better than our scratch-built versions. The first few production versions will be going to members of our building team, including a very lucky yours truly. I’ll be taking mine in the GPS light version, most probably also with a JETEC70 impeller.

The waiting list for this plane is unfortunately already extremely long, but it’s worth the wait. In the meanwhile, enjoy this “quick and dirty” video of this afternoon’s flights.

Chocofly JS3 – Prototype Test Flights from J├╝rgen L. on Vimeo.