Buffalo Brewster (HobbyKing)(920mm)

We’ve been looking to practise some formation flying with some of our colleagues in our club and have been looking for a suitable plane for a while now. Our two main criteria were; 1) must be scale foamy for less than CHF 200,-; and 2) it must be able to fly relatively slowly. When HobbyKing had its Buffalo Brewster (920mm) on sale, we didn’t wait long and ordered a few. Unfortunately we hadn’t seen the plane fly “live”, but the many videos and reviews on the net gave us the confidence that this couldn’t be too bad a little plane.

We’ve had quite a bit of flying time with these little fellas over the past few weeks. The opinions on this aircraft are very divided, with some hating it and others loving it. One thing is very clear though: out of the box, it doesn’t fly very well at all, but with a bit of work it can be made into a fun plane. After a lot of test flying and fine-tuning, we found that the following changes are essential to get this plane to fly:

  1. Center of Gravity: the internet fora are full of people adding lots of weight to the nose of the plane. Don’t. It flies best with a standard 3S battery (ours are in the 170gr range) pushed forward as much as possible. No extra weight needed.
  2. Elevator Servo: the Servo that comes with the plane has two problems: 1) it’s too imprecise and some have quite a bit of play; and 2) the servo arm is way too long. The Buffalo is very sensitive on the elevator and needs relatively little throw (around 8mm up and down). With the long servo arm and the imprecise servo it flies like a dolphin, impossible to trim it into a straight line. With the Servo Arm shortened and the connector as close as possible to the servo it’s a different plane. If the servo has too much play then I’d also recommend changing the servo (I replaced mine with a metal gear servo).
  3. The motor’s side and down thrust should be adjusted. It pulls too much down and too little to the right. We’ve found that moving one washer from the top left screw to the down right screw (viewed from the front of the plane – see picture below) corrects this. Note that there are differences between individual planes and some may need a bit more, or less, and it’s worth playing around with it a bit.

With these changes, the Buffalo flies surprisingly well and precise. Most of all, it has a huge speed envelope – from slow to superfast. Even then it remains a plane for more skilled pilots. Fortunately it’s incredibly robust though. We hope to start practising some formation flying in the months to come.

Diana 2 Flyday

Dani Aeberli from Chocofly.com organised the first Diana Flyday on 16 August 2020, in Eglisau, Switzerland. He brought together 27 Dianas, with pilots coming from as far as Geneva, including three scratch-built Diana 1 (4.28m), a whole bunch of Diana 2 (4.28m, both scratch-built and the Chocofly version), as well as the 5m version of the Diana 2 (scratch-built, and Baudis, and a combination of both), and the Chocofly 6m and 7.5m versions. Our building team was represented by Georg Staub (who came with 8 Dianas!), Andi Schwerzmann (4 Dianas) and myself (also 4 Dianas – lined up in the first two pictures below). Our team supplied all the scratch-built planes (the amazing 4.28m Chocofly Diana2 is the commercial version of the one built by members of our team). Georg and I flew our already 14 year old Diana 1, still a fantastic glider, and we also enjoyed some amazing flying of Dani and his 7.5m Diana2. A you’ll have concluded already by my ample use of superlatives: an awesome day, and a big thank you to Dani for organising it. See below for a few pictures. More pictures and videos can be found on the social media channels of chocofly.com.


In-between…Chocofly Kobuz 3

Over the past few months I’ve sold a few planes that I wasn’t flying enough (Snipe DLG, 2.5m Tomcat, 3.4m DG600 and my 5.14m Chocofly SB-14), so there was some space in my budget and hangar. During our club’s traditional flying week in Hahnenmoos in the third week of June Dani Aeberli from Chocofly sold me a spare Kobuz 3, one of his latest new models, a small one, with 2.18m wingspan. I was very impressed with its performance and since the colour was yellow/black I couldn’t resist – spotting a potential for cool decorations.

The kobuz has been sitting in my workshop since my return from Hahnenmoos at the end of June. As I limit my work on planes to rainy or cold days (the other free days are for flying or cycling), I only managed to complete it last week. Much work went into the “smoked” canopy, an option that’s definitely much cooler than the standard intransparent black cover that comes with the plane (it always annoyed me on my DG600). Chocofly provided the smoked canopy glass, the seat pan, a 3D printed control stick and the printed instrument panel, as well as two 3D printed parts to attach the front and rear of the canopy. Putting the parts together and figuring out a canopy lock that works flawlessly required a bit of time. The canopy set also came with a plotted sticker for the canopy frame. Unfortunately this was in white, a no-go for this plane. Dani however kindly provided the plotting file, which I was able to convert to my Silhouette Cameo so that I could plot a perfect black canopy frame sticker. The result can be seen on the pictures below. Once I had fired up my plotter and unable to resist the great yellow “canvas” of the plane, I also fitted it out with some the symbols and brands of my Flemish/Belgian background. For those unfamiliar with Belgian beer, Rodenbach is a fantastic beer made in my birth town of Roeselare in Flanders, Belgium. The beer is unlike anything else you will have ever tasted, and definitely worth trying (I always keep a crate of it in our cellar).

The epoxy Resin of the battery board hardened out on Saturday morning. And I got lucky with the weather, with great slope conditions forecast for Saturday, so I maidened the Kobuz on Saturday afternoon, on our favourite slope. The first flight was tough. I had just spent almost three hours non-stop airborne with my JS3 (totally awesome), and had a hard time convincing myself to land and having a go at the Kobuz. I’d programmed the Kobuz based on the settings suggested by Dani, the owner of Chocofly. Since I know he loves flying with huge throws, I had already reduced them by a third. But they were still way too big for my taste. The plane also needed quite a bit of left trim. On top of that the lift suddenly stopped after 30mins of excellent conditions and I had to make a quick landing into the slope. That also gave me time to further reduce throws, increase expo and adjust trim. With those changes, the second flight went way better. Soon I was doing 230kmh flybys and having great fun. Unfortunately after 20 minutes the lift again suddenly stopped and another quick landing into the slope cut the flying fun short.

Before leaving to the slope my wonderful wife handed me a few bottles of Rodenbach beer to take along. They provided a very welcome toast with my flying buddies after a great day on the slope and a successful maiden flight.

After two relatively short flights my first impressions: this is a really really cool little plane. I’m amazed at how well it retains speed, even with “only” 2.55kg. It also thermals surprisingly well, although it’s hard to keep it in the air when conditions turn bad (but of course the JS3 is not really a comparison here…). As I had to give quite a bit of up trim with positive camber and down trim with negative camber, I’ll be moving the CG backwards on a next flight. I’ve also increased camber quite a lot over the suggested values (I always program three positive camber settings on the right slider of my transmitter, small, medium and huge), which the Kobuz seems to very comfortable with. This is a plane that I’ll be taking along as a 2nd “in-between” plane on excursions to the slope.

Note: when I bought my Kobuz and wrote this blog post, I wasn’t aware that the smoked canopy was actually a one-off production. Following the success of my Kobuz pictures on social media (and the fact that it really does look very cool), Chocofly has now included this canopy in the list of available options :-). Way to go Dani!


JS3 – and then there were three!

Today my JS3 had another 2.5 hours of flying in light lift on our local slope. It was also the first time that we had three out of our four JS3 (Georg’s, Richie’s and mine) airborne on our slope at the same time. So much fun. The more I fly my JS3, the more I like it. It’s by far the best plane in light thermals in my scale glider collection. Even in light thermals it picks up every bit of lift. It loves tight curves, adding meter after meter of altitude. Stalling behaviour is excellent, even with large camber and lots of up elevator. It just needs rudder for a nice tight curve, and reacts amazingly well to even the tiniest of outer aileron throws. It’s a dream to fly, so easy, it mostly flies itself, and amazingly responsive. As I’ve only flown the 5.14m (18m) version so far I’ve been taking it easy on the fast flyby’s (the wings are very flexible and I don’t want to risk a flutter), but it does seem to like them too. I’m hearing that the prototype of the commercial version, to be produced by Chocofly, is nearing completion – I’ll report on that one as soon as I get some postable material.

Diana2 Flyday!

Save the DATE!

Diana 2 Fly-Day…… Sunday 16.August 2020 at
Modellfluggruppe Zürich, Eglisau (https://mgzh.ch/unser-flugplatz/).
Bring your personal Diana 1 or Diana 2 and Fly with us!
Lets see how many we can get together…..World record??

Saturday 15th will be also first time DONs Grill & FLY

Please sign in on the Doodle Link before the end of July 2020…to make sure you can be part of it!

Looking forward to see you all there
ChocoFly Team


Further slope testing of the Urupema

Georg has been busy fine-tuning the settings of his Urupema in Aerotow. The CG has been moved back quite a bit, and he has reduced the decalage back to around 0.8 degrees. The result is a much gentler plane, with excellent stalling behaviour, and an even wider speed envelope.

Last week Wednesday I got the first chance to fly my Urupema on one of our local slopes. Before heading out I applied the new settings to my plane. Wow, what a difference. Georg and I spent four hours non-stop airborne with our Urupemas. Even in light lift, the plane was a pleasure to fly. During the flight I swapped transmitters with my mate Richie, who was flying his JS3, just to see the difference between the planes and let him have a first taste of the Urupema (he’s about to finish his, nr. 4). They are definitely two very different planes, both much fun to fly. Of course the Urupema is not a thermalling junky like the JS3 (which just refuses to come down), but the Urupema still flies incredibly well even in light lift. After Richie landed his JS3 I handed him the controls to my Urupema again and asked him and Georg to do some formation flying, so I could do some filming (Richie is a much better pilot and I’m a much better cameraman :-). The result is below. Enjoy.

Maiden flight of my Urupema

Today I maidened my Urupema on our club’s airfield, using the club’s catapult. I usually prefer to maiden planes in aerotow, much lower risk, but as thanks to Corona this is currently not possible. It was either catapult or wait. Since I plan to spend a week in Soaring Dreamland Hahnenmoos in a bit over a week, waiting was not an option.

The start went well, but the conditions were terribly turbulent, with massive downwinds and rare but strong upwinds. The landing was adventureous, with a terrible down and tailwind, and too much downrudder mixed into the crow programming, causing the plane to come in very fast on our small airstrip. Fortunately all went well, and the second flight went much better already, and Georg and I even managed to do some formation flying.

We’re still finetuning the settings on this lady, but she’s special. The speed envelope is amazing. You can circle in thermals at close to 40kmh, but she very quickly picks up speed. Without pushing it, Georg already had well over 260kmh. She needs a lot of rudder when circling in thermals, and really likes leaning into the curve. And it’s very hard to stall her, when circling in thermals you can pull the elevator like crazy. I’m only just getting to know her, but this is one special amazing plane. Happy.

Slope testing Georg’s Urupema

This has been an amazing spring of contrasts. While Switzerland has been in a “soft” lock-down, we’ve been enjoying perfect weather and, most importantly, a highly unusual amount of so-called “Bise” days. Normally the prevailing wind is West. But the last few weeks we’ve mostly seen Northerly winds, the “Bise”. This means that it’s impossible to fly on our airfield (which was closed for a few weeks anyway), but also means time for slope soaring. I’ve spent many hours flying on our favourite slopes so far this spring. Pure bliss, although coming down from the mountain back into Corona reality was sometimes something of a shock. Below are some pictures, as well as a video that I did of the first slope testing of Georg’s Urupema. I’m still waiting for a normal westerly wind so I can maiden mine on our airfield – maybe the end of the coming week….


Maiden flight of Andi’s JS3 and Georg’s Urupema

A big congratulations to Andi and Georg! Today Andi had the maiden flight of his JS3, the fourth and last one of the four we built and Georg maidened his Embraer EMB400 Urupema. As the maiden flights were on a different airfield and due to Corona restrictions I was unable to attend (5 persons max and no guests). Andi took some pictures, which you find below. A video of the maiden flight and the slope testing is in the next post. We will maiden further Urupemas in the next few weeks and do some further flights with our JS3.

Maiden flight of my JS3

Almost three years after we kicked off our JS3 project, today my JS3, the third of four that we built, had it’s maiden flight. See some pictures and a short video below.

The first flight went very well, lasting 1.5hrs, and ending up racing GPS triangles together with Georg and his virtually identical JS3 (the first one built, which maidened almost two years ago). Pure bliss. It needs a bit of fine-tuning still, and will take a few more flights to get it perfect. It’s amazing how fast this plane picks up thermals – the best in my scale collection. And it almost flies itself. You park it into a thermal with a bit of rudder and it does all the flying for you. It’s incredibly stable. I’ve only flown the 5.12m (18m) version today, and am very happy with the amount of flex in the wings, which gives it a great “scale” look, “hanging” in the sky.

A small mishap had a good ending: At the end of the 2nd flight I lost my canopy when I was far out at around 100m elevation (note to self: check lock and secure with tape). We saw something drop down from the plane, but couldn’t see what it was. Fortunately my friends watched closely where it landed and we managed to recover it quickly – amazingly without a scratch! Landing without canopy was no problem, which also says a lot about how stable this plane is.

Andi is planning to have the maiden flight of his JS3 in the coming week. I’ll post some further pictures and movies on the JS3 in the future, hopefully also of our four JS3 together.

I do hope however that my next post will be about the maiden flight of our latest project, the Embraer EMB-400 Urupema, with a bit of luck in the next week or two.


Maiden flight of Richie’s JS3

Yesterday Richie’s JS3 had its maiden flight. As he builds all his planes without FES and super light, he went for a hand start on our favourite slope. Today his JS3 was joined by that of Georg. Here are some pictures and a short video that I cobbled together from the last two wonderful days. While the boys were playing with their JS3 I put my Diana2 (yesterday) and my AvantiHawk (today) through their paces. Tomorrow I hope to have the maiden flight of my JS3, more on that later.


Urupema ready to maiden!

The final “small” things always take much more time than planned, but the Urupema is ready for its maiden flight! I still intend to add some red stripes and more decals. For that we will need access to the paint shop though, which is not easy due to the COVID-19 semi-Lockdown here in Switzerland. They will need to wait.

The plane weights around 7.2 kg (4.28m wingspan, scale 1:3.5). I can add quite a bit of ballast (up to a 800gr brass) in the ballast chambers built into the wings. Am curious to see how this one will fly. Unfortunately the maiden flight will have to wait a bit. I first intend to maiden my JS3, which has been sitting ready to maiden in the workshop since November last year. Then I want to wait for our building team colleague Georg to maiden his Urupema. Not only is he a master in getting the plane’s settings right, he also has access to an airfield where he can maiden his Urupema in aerotow (the safer option for a fully new own design plane), whereas I don’t (due to attendance restrictions for guests on most nearby airfields as a result from COVID-19).

Installing wing servos and IDS

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.

Elevator and Cockpit

I’m not very good in making nice cockpits. Although I admire colleagues that do perfect scale cockpits, I just can’t be bothered to take the time to do it myself and usually do a very rudimentary job. I’m too keen to get onto the next project or go flying :-). The Urupema cockpit was a bit of an issue, since we had no pictures whatsoever of what the original looks like. While Richie made a all of us very nice seat pans, we re-used the instrument panel from our Diana2, which looks to fit quite nicely. I also lack the skills to make a nice seat, so I usually just cut a piece of felt to size.

As our Urupema is built for higher speeds than usual, having a robust elevator is important. Usually we attach our elevators with plastic screws (allowing them to break with rough landings on the slope), but this time we attach it with a metal screw, but the front of the elevator is attached with a carbon rod (allowing it to break there if the elevator gets caught in a rough landing). The control horn is glass fiber. As the elevator hinge is on the topside of the elevator, the lower side doesn’t need an epoxy seal, I just use tape.

Setting the seals for the wing control surfaces

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.

Maiden flight of the Chocofly Diana2 – Glider version

When there is a stable high pressure area north of us, over Germany or eastern Europe, we usually have a stiff northern breeze, called “Bise”. Most of my favourite slope soaring spots are on north-facing slopes, i.e. time to head out. Unfortunately, being a northern wind, it’s also a freezing cold wind, which means that this early in the year you can add a significant wind-chill factor to temperatures already barely above zero degrees Celsius. In cycling we always say that there is no such thing as bad weather, just bad gear. Following that wisdom I went out on Tuesday to my favourite slope, with chilly but perfect wind conditions. The slope is perfect Diana territory – I usually fly one of my Dianas (Diana 1 or 2) there. With the whole Covid-19 lock-down I drove up alone and had to hand launch the plane myself. This is one of the reasons that last year I ordered an extra fuselage for my Chocofly Diana2 (1;3.5), and built it as a light glider without the usual FES (5.5 kilos). Normally I maiden my planes on a nearby airfield, using a towplane. But extraordinary circumstances require extraordinary actions. And as I know the Diana2 pretty well by now, having clocked many hours on the various version I have, I hand-launched it myself on the slope for the maiden flight. It flew off without any bother and I spent a wonderful 75 minutes in the freezing cold. The nice thing about the Diana2 is that it’s such an amazingly versatile plane. It thermals amazingly well and loves low as well as high speeds. At 5.5 kilos it’s not as fast my heaviest version, which weighs almost a kilo more, but still very fast and a lot of fun to fly. I’ll be taking this one to the slope more regularly.

On the slope I met up with my mate Richie, who was also flying his Diana2 (the Chocofly Diana2 is the commercial version of the design from Richie and Georg). Hence the photo below of the two sisters together. His Diana2 is even lighter, well below 5 kg, and on the slower side, but goes up like a little balloon in the least bit of upwind.

Urupema: cutting the wing control surfaces and setting the hinges

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.

Urupema back from the paintshop and fully polished

Earlier this week I also got the Urupema fuselage back from the paint shop. I spent quite a few hours sanding and polishing it to a shine. I first used 600 grain sanding paper, then 800, then 1500 and then a 3000 diamond polishing pad. After that I treated it with machine polish and shiner, using the polishing machine.

The paint shop and especially the polishing afterwards is always very unforgiving when it comes to small mistakes in the building. There are the inevitable spots where it’s not quite perfect, it’s obviously made by hand, but I’m satisfied. I’m particularly happy with the spray filler that I’ve used for the first time on the seam on the top of the fuselage and part of the wings. I was a bit nervous trying this out, hoping that it wouldn’t react with the final coat of paint. It came out well though. I couldn’t resist sticking a few of the decals on and putting the plane together for a photo session.

Now the hard work on finishing the wings starts. Next step is cutting out the control surfaces. No mistakes allowed there…


Watching Paint dry

Watching paint dry is not really my thing. Andi managed to secure a slot in the paintshop on Saturday and spray painted the wings and all small parts. The fuselage should be done in the next few days. I’m now waiting for the paint to harden out, after which the hard work of polishing starts.

I’ve been using the time to build a small glider, based on the mini-Uhu, but remote-controlled. Originally this was for our upcoming indoor glider-tow competition, which has now been cancelled due to the Corona crisis. I’ve also built a new Clik21 indoor plane, which had been lying around in my workshop for a while. I love that small indoor plane. I’ve built (and sold) multiple versions of it already, always trying to make it lighter improve it further. My current one weighs 93gr (no battery), but with a pull-pull rudder and elevator it wasn’t very precise to fly. Hence my wish to build another one. The new version looks again much improved compared to the previous one, with more stable ailerons and rudders, and a total weight of 95.6 grammes (without battery, i.e. flying weight 110gr).

I also finalised the Urupema decals and spent much time making the rudder control horns. Georg helpfully documented how he made his control horns, which I’ve copied. I’ll post a picture of the painted Urupema as soon as the fuselage comes back from the paintshop.