EMB400 Urupema: Wolfpack on the Slope

On Monday we had a wonderful slope outing with three Urupemas.

The unanimous agreement among the three pilots was that we need to fly this glider more often. The “wafer thin” wing profile (7.3%) with full carbon layup makes for super speed retention and among the friendliest stall behaviour on planes I’ve flown. It also allows for lots of camber to squeeze every last bit out of those thermals. This is a glider of contradictions, super friendly to fly and yet also scary as it picks up speed so fast with a bit of down elevator (even with full camber) and retains speed so long when flying figures.

Some new pictures of our slope outing below. Some earlier videos can be found here:


Chocofly JS3: losing the winglets :-(

We’ve had some really good slope conditions over the past few weeks and I’ve been mostly flying my Chocofly JS3. I just love this glider. It’s my favourite choice if the winds are weaker or, as often happens in summer, when you can expect sudden gaps in lift. The JS3 will allow you to battle through low-lift episodes much better than most of my other gliders.

The many hours on the slope however also showed that the JS3 does have an upper limit in terms of speed. I own an early production version of the lighter GPS edition. I prefer this version as the lower weight and somewhat more flexible wings give it better thermalling properties. But it’s not made for vertical drops, tight loopings and ultra-high speed passes – I own other planes that are (including my other favourite, the Chocofly Diana2!).

The slope conditions were at times however just too good not to test the JS3’s limits. We’ve done multiple high-speed passes at well over 260kmh, but noticed that the winglets were starting to get a bit “noisy”. Ever since I lost the winglets of my scratch-built JS3 in Autumn last year I’ve been keen not to push my JS3s too far. But due to a stupid combination of unfortunate circumstances (of which I am to blame) I ended up in a steep dive with a brief loss of signal. The speed of the dive (260kmh) and the sharp recovery turn out of the dive were a bit too much for my JS3. Upon landing, I noticed that I lost my winglets. I always attach them with a strip of tape over the top and nose of the wing, but they were literally “torn out” of the outer wing, damaging a few cm of the underside of the outer wing. Fixing this is not a big issue and a new set of winglets has been ordered, but I promised myself and my JS3 that I will behave in the future….really!

Chocofly JS3: testing the short wing version (4.28m)

Although I built a short-wing (4.28m) version of my scratch-built JS3, somehow I never got around to flying it. The long version (5.14m) simply flies awesome so I’ve never seen the need to install the short outer wings. Plus the short version doesn’t quite look as good as the long-wing version.

Chocofly also offers its JS3 in the long and short outer wing version, but I only ordered the long outer wing version. A few weeks ago Dani (Chocofly) put his set of short outer wings in my hands and urged me to give them a try. We’ve had some awesome slope conditions in the past few weeks, so I did. My impressions confirmed what Dani told me: it’s a very different plane. The JS3 becomes very agile (rolls great 🙂 ) but at the same time doesn’t seem to lose much of it’s thermalling capabilities. It’s a nice addition to the JS3 that extends the range in which the glider can be used to conditions with stronger lift and wind and where the pilot wants a more agile plane.

For me, the JS3 already had the broadest range in which a glider is excellent to fly. I’ve never flown a scale glider that is so good to fly and so much fun in conditions with very little lift way up to good slope conditions. The short outer wings further extend this range upwards. Interestingly, I did notice that the JS3 accelerates faster, but I did not notice a large difference in the top flying speed (see my next post). Important to note however is that even in the short wing version it doesn’t match the Diana2, which is still my favourite plane for good to excellent lift conditions. This in partly because my JS3 is the lighter GPS edition (and thus not as robust and heavy as the Alpine or HG Editions – my Chocofly Diana2 is an early Alpine Edition), but also because of the winglets – which limit the top speed of the JS3 (the Chocofly Diana2 comes with a set of “tiplets” for when it really gets “hot”)(see my next post). That’s however no criticism of the JS3 – it’s an amazing plane for the slope, but not built as a slope racer. I very much enjoyed flying the short wing version and have ordered a set of short outer wings.

Below a few pictures of the short and long outer wing version side-by-side.

Out on the slope – Photo session EB-29R

We’ve been spoiled with quite a few fantastic slope days over the last few weeks. I’ve been mostly flying my Chocofly JS3 and this week also my EMB-400 Urupema. Both planes still require some fine tuning (elevator incidence, center of gravity).

The JS3 is just a dream to fly, but I need to work a bit on the aileron throw and differentiation still.

The Urupema was a bit too nervous for my liking (very aggressive on the elevator, especially at higher speeds), but with increasing the elevator incidence and moving the center of gravity forwards it seems to have improved a lot. I’ll need to do a bit more experimenting still. The plane still amazes me – it combines the characteristics of a number of my favourite planes. It has totally friendly stall behaviour (with a very low stall speed) and thermals very well. But it also accelerates immediately as soon as the nose tips down even slightly (even in full camber!) and has an almost scary speed retention.

Last Thursday Richie joined us at the slope with his EB-29R (8m, 8kg). He built the plane entirely from scratch, including plug and fuselage moulds. With 8m the wings have lots of flex in them and the plane is definitely not built for high speed flying. But it thermals incredibly well and easily does very tight turns. Due to the low wing load, it’s also a breeze to start by hand – Richie didn’t need much more than a flick with his wrist to get it airborne – so cool to see!

I took my Canon camera to the slope to do a bunch of pictures of the EB-29R for an upcoming journal article. Here you can find the best pictures from the photo shoot, as well as some earlier pictures, videos and more information on the EB-29R.

Alpine slope season start

A spell of warm weather and a nice northerly means alpine slope season start! On Monday our shaper Richie and I spent the afternoon on our favourite slope. There’s still quite a bit of snow there, but the landing area was clear.

For me a chance to fly my Chocofly JS3 again. Richie was flying his wonderful 6m scratch-built JS1. We spent two hours non-stop in the air with endless lift – awesome conditions. I’m hoping for a next opportunity soon….


Richie Oberholzer is one of the key members in our building team. He’s built the fuselage plugs for all our recent projects, but also regularly has his own unique projects – all of them scratch-built. One of his latest ones is his 8m wingspan EB29-R, which he’s been working on along other projects in the last few years, and which he maidened on 1 April 2021. On his request I put together a couple of videos and pictures of this absolutely amazing project. They can be found on this separate page.

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.


A day at the races – EMB400 Urupema in awesome slope conditions

Finally, spring weather! And added to that a stiff northern breese (“Bise”), means time to head out to the slope. Yesterday’s conditions were almost scary – a stiff and gusty wind, and very turbulent conditions. We decided to take our Urupemas, which were built for precisely such conditions, although the turbulent conditions pushed them to their limits. The tall grass unfortunately meant that a catapult launch is difficult and a dangerous hand-start was necessary – fortunately this went ok, although two starts were close to going wrong (planes over 6kg on a slope without a drop and gusty winds is challenging). Below a short video of yesterday’s flying.


Slope season start!

As the snow starts to clear from nearby mountains and temperatures are slowly going up, we had a couple of days of great wind for our favourite slopes. Most nearby slopes are good to fly when we have a northern breeze (“Bise”). About a 10 minutes drive from where I live is the Pfannenstiel Hochwacht. It’s not the best of slopes, but a good place to head out to when the weather is too cold to make longer flights or when you just want to head out for an hour or so.

In mid-April we had three good consecutive days of Bise, but still very cold and cloudy weather, and most of my usual flying buddies didn’t feel like heading out in the freezing cold. I spent three lovely but freezing cold afternoons up on the Pfannenstiel with my Chocofly 2.8m Taranis and my Chocofly 2.2m Kobuz, accompanied by a few friends. The Kobuz is a lot of fun to fly, you notice it’s smaller size and the fact that it’s not a purpose designed aircraft – it’s “lively” and requires you to work the sticks :-). The Taranis is a completely different plane. It’s got a huge speed envelope, is pretty hard to stall and totally stable to fly even in the most turbulent and windy conditions. Lots of fun – including some high speed passes at over 310 kmh (without ballast in the lightest version of the plane!).

Last week the weather got a bit warmer and sunnier and with another few days of Bise we were able to head out to our favourite (private) slope in Toggenburg. We opened the slope season there with our Diana 2, the 4.28m version (both scratch-built and the Chocofly version of the same plane), and on the 2nd day we took out the 5m Diana2. My mate Richie also “slope-maidened” his brand-new EB29R – with an incredible 8.3m wingspan and only around 9kgs. I got some time on the sticks of the EB29R – an amazing thermaller. See the video I did on the first slope flight below.