Maiden Flight of the Ventus 2c

Maiden flights are nerve-wrecking. Always. We usually do them in aerotow, which is the safest option (during the tow it’s unlikely that something will happen and after release you have enough height (time) to correct something that’s wrong). As I did not put a towhook into the Ventus, the next-best option is to launch it using our bungee.

Before the maiden flight we always get a colleague to double check programming and settings – which more often than not finds a smaller or even bigger “issue”. The Ventus decided to “release” the propeller and spinner during the standard “full throttle test” – even though I checked and tightened it while preparing the plane in the morning. No other issues turned up during the check, so after reaffixing the prop and passing the “full throttle test” it was time to launch it.

The moment of truth is right after the plane releases from the bungee. This is when all the hours of work either turn into a success or – when you’re very unlucky – catastrophic failure. The Ventus was a great success. It flew off like it already had dozens of launches behind it. No trim needed, just perfect. Even better was that after a short burst of motor to get to 100m above ground (where usually the thermals on our airfield start) it flew straight into a thermal and started rapidly gaining altitude. My flying buddies, impressed with the launch, half-jokingly told me how cool it would be to have a one-hour first flight.

Their “prediction” was way off. After a full two-hour first flight, with a grand total of 25 seconds motor time, the pilot’s batteries were empty. I also wanted to make a number of minor changes in the programming (reduce elevator throw and add a bit of down elevator with the throttle) and check these in a second flight. The second flight also lasted a full hour and was ended only by my need to head back home.

The Ventus 2c is a really nice all-rounder. The handling very much feels like the JS3 – although of course not quite at the same level. The weight of 4.66kg is also just right. A floater, easy to hand-start and perfect for those light winter, spring and autums conditions.



Ventus 2c: ready to maiden!

The final bits (finishing wiring, determining the Center of Gravity, installing all the bits in the right place and programming the transmitter) are always a lot of work. But now it’s done and the Ventus is ready to maiden. I’m very happy with the final weight: 4.65kg, nicely under the 5kg target I set myself. With a 4.5m wingspan I expect it to be a real floater and easy to make hand starts.

I’ll be pretty busy with other things in the next week, but hope to maiden it as soon as possible. 🙂

Ventus 2c: installing the wing servos (2)

After glueing in the servo horns on the side of the control surfaces the next step was to prepare the 3mm threaded rods in the right length. Then I glued the Chocofly wood/carbon servo frames in place. To do this, I first installed the rods on the side of the control surfaces, allowing me to center the frames with servo in exactly the right place. I applied a few dots of 5 minute epoxy to fix the servo frames. Then I removed servos and rods and applied thickened 12hr epoxy around the servo frames. After allowing the epoxy to cure I could then do the final installation of the servos and rods.

The wiring I prepared earlier and was thus easy to install. I removed all the servo plugs and soldered the servos straight onto the wiring – for reasons of weight, space and reliability – I don’t intend to ever replace the servos :-). The servo openings I closed using the bits milled out earlier and white foil I plotted using my Cameo 3.

The new LDS system is amazingly robust and without any play whatsoever. Adding to that the much greater ease of installation compared to systems I used earlier, this is a great system to use. Even though more expensive than the earlier systems we’ve used, it’s definitely worth it’s money. I’ll also be using it on my next builds.

Ventus 2c: installing the wing servos (1)

For the Ventus2c I will for the first time be using the new Chocofly LDS PRO system. The wood/carbon servo frames, as well as the perfectly fitting aluminium servo horns I already used for the Orlik. The carbon control horns and the aluminium/steel/brass connectors are new. Although heavier than the system I previously used, it’s also much more robust. Most importantly, it’s easier to install as you can shorten the 3mm threaded rod to the right length and slightly adjust it to the perfect centering position once the servos are installed.

Another important change compared to previous builds is that I prepared all the openings in the wing and wing control surfaces before setting the hinges and seals. In the past I’ve ended up damaging the seals or even the wings when making those openings afterwards. Doing it before makes the process much less risky and results in a cleaner build.

Ventus 2c: seals for the wing control surfaces

I’m finally starting to get the hang of doing the seals for the wing control surfaces. In the past I tended to make the epoxy resin mix too thick, which resulted in uneven seals. The trick is to leave the epoxy resin mix relatively liquid – it should be thin enough to spread out evenly, but no so thin that it flows over the tape. Here’s how I do it:

  • make sure you clean the gap between the wing control surfaces and the wing – any dirt, especially carbon dust, risks leaving black dots in your seals;
  • apply a thick PET Tape (see for instance here – with thanks to Martin E.) to the control surface, leaving just enough space so that when the control surface is at around 20-30 degrees down deflection the seal is nicely underneath the overlap on the side of the wing;
  • position the wing in a position that you can apply the epoxy resin to the tape so that it flows a bit more towards the side of the control surface;
  • prepare epoxy resin, thickened with a bit of aerosil and lots of micro-balloons as well as a bit of colourant (I use white) – the resin should be thin enough to spread out evenly, but no so thin that it will run off the tape;
  • apply the resin to the tape using a syringe – I also use a thin pin or metal stick to make sure it spreads out evenly;
  • wait until the resin is cured enough so that it no longer runs off, but still soft enough so that you can mould it;
  • move each control surface upwards and carefully slide the PVC tape under the overlap on the side of the wing – I use a long ruler for this. The control surfaces should be in a down deflection of around 20-30 degrees, the tape will round itself and ensure a nice and even round seal;
  • allow the resin to fully cure;
  • once the resin is fully cured, sand it back to the correct depth so that you have the deflection that you require on each rudder, leaving enough so that there is no gap between the seal and the wing for normal downward deflection (of course this doesn’t apply to the downward deflection of the brake flaps in butterfly mode)

Below are some pictures that hopefully clarify the above.

Ventus 2c: wiring, fuselage, cockpit and decals

While waiting for the silicon hinges to cure I started preparing the wiring for the wings. I also finished most of the work on the fuselage, installing the rudder and elevator as well as the bungee hook. Using my trusty Silhouette Cameo3 I cut the decals, pushing the Cameo at it’s limit on the tiny letters that will come under the canopy. In a burst of inspiration I also finished the seat pan for the cockpit.

Ventus 2c: wing control surfaces

Cutting the wing control surfaces out of perfectly finished wings takes some convincing, but especially a clear mind and a steady hand. It’s a job I only do when I feel that the time is right and I’m ready for it. But even with all the precautions I usually do make one or more small mistakes, but fortunately so far never bad enough to ruin the wings.

After carefully measuring out the location of the cuts and checking the small holes in the wings that I made during building (to help locate the right place for cutting out the control surfaces) I finally felt that it was time to have a go at cutting. To cut the wings I use an old Dremel that has a brass add-on to help guide it and ensure a straight cut. I cut it along an aluminium profile that I attach to the wing in the right place using double sided tape. On the top of the wing I use a 2mm milling bit, on the bottom (where the hinge comes) a 1mm milling bit.

Once the control surfaces are cut out and cleaned from excess foam I sand back and then glass the upper protruding bit on the side of the wing (50gr glass cloth with epoxy resin). This is to ensure that the seal (which I will make later) will slide nicely and tightly under the wing. I also cut out all the openings for the servos and servo levers. Then I attach the control surfaces to the wing using good quality wax tape (not TESA, but one bought at a professional paint supply shop) and set the hinge using silicon, applied with a syringe. It’s then reinforced with bits of ebechi on double sided tape to ensure that all the control surfaces are in the right place while the silicon is curing. The silicon hinges take approximately three to four days to fully cure.

Ventus 2c: polishing

My mate Andi did a great job spray painting the Ventus, with an excellent finish. I could have left it at that (as we did with the Orlik), but a polish makes it just that bit nicer. Polishing the paintwork is a lot of work. It basically took me almost two half-days and a day of sore muscles in-between. But the result is pretty neat – a wonderful glossy finish.

To polish the plane we first sand it (wet, by hand) with either 800 grit paper or pads (some of us first use 600 grit) to remove the “orange skin” surface and make the paint perfectly even. Then another go at it using a 1500 grit pad and then a 300 grit diamond finish pad (also wet, by hand). Once that’s done the shine is already pretty nice. To finish it we use a machine to apply fast-cut compound and finish off with a machine polish. The products we use are shown on the pictures below (all 3M).

JS3 (Chocofly) Settings

I’ve had several requests for the settings that I’m using for my Chocofly JS3, so I’ve measured them and set them out below.

Note that all these settings are very much a matter of taste/preference and reflect how you fly. I like to have my center of gravity as much as possible to the rear and love it when the glider comes down straight as an arrow with a bit of negative camber. I also only fly with minimal throw on the wing control surfaces when I can, but have larger throws available over a switch. On top of that I always define a “speed” (negative camber) as well as three “Thermal” (camber) settings (“small”, “medium” and “large”), where “large” tends to be a lot, but reduced towards the outer control surfaces of the wing.

My settings reflect the fact that I mostly fly my gliders in light thermals and on the slope. Others will have different settings and preferences. Also important to note that I’m still not 100% satisfied with these settings and, as with all my gliders, will continue to fine-tune them – the only way to get these right for you is to fly and adjust (not copy values from some vague internet blog ;-).

Center of Gravity: 110m (or more)

Longitudinal dihedral (Elevator Incidence): slightly increased with two layers of 3m vinyl tape at the back (imprecise, yes I know :-))

Differential of ailerons (more aileron throw up than down):

  • Speed: 100-80
  • Normal: 100-60
  • Thermal S: 100-50
  • Thermal M: 100-50
  • Thermal L: 100-45

Ailerons (values inner side wing):

  • Small: 5mm (up)
  • Big: 9mm (up)

Add (each separately over switch):


    • Small: 3.5mm (up)
    • Big: 5.5mm (up)

Airbrakes/inner flaps:

      • Small: 1mm (up)
      • Big: 2mm (up)

Rudder: 25mm (or maximum mechanically available)(measured @ lower end)


  • Small: 3mm (up&down)
  • Big: 4.5mm (up&down)


  • Flaps: 8mm up
  • Airbrakes/inner flaps: 47mm down
  • Elevator: 25mm down

Camber settings:

Speed: 1mm up entire wing

Thermal S: 2.5mm down entire wing

Thermal M: 4mm down Airbrakes/inner flaps, 3mm flaps, 2.5mm ailerons

Thermal L: 6mm down airbrakes/inner flaps, 4mm flaps, 2.5mm ailerons

Ventus 2c: back from the paintshop

This morning Andi delivered my Ventus 2c back from the paintshop, where he painted it yesterday. It looks awesome, once again an excellent job.

From experience I know that still 30-40% of the work needs to be done – mostly “small” and less visible jobs: polishing, cutting out control surfaces, setting hinges and seals and installing all servos and electronics. Hope to maiden it this year still.

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:


ASW-20: Maiden flight

We’re currently going through an unusually long period with northerly winds (“Bise”). This is great for slope soaring (all our favourite slopes are north-facing), but flying at our club’s airfield is not recommended. Our airfield is on the leeside of the mountain along lake ZĂĽrich. In the morning the flying is ok(-ish), but around noon usually the Bise starts pushing its way over the mountain, causing very turbulent conditions with evil downwinds. Flying is really hard then, no fun, and the risk of seriously damaging the plane is significant. Before the bise pushes through, conditions are also challenging, with often gusty and changing winds, often also from the South or South-West, which means landing with tailwinds. Sometimes we also have amazing thermals for a short while just before the Bise pushes through and makes flying impossible.

Nonetheless I decided to take the ASW-20 out to our club’s airfield for its maiden flight. At our airfield I can safely start the glider using the bungee and landing is way easier than on the slope – especially without having any recommended butterfly settings. I was hoping that going out early enough would allow me to get enough flights in to get the basic settings of the glider in order, so that I can then safely take it to the slope and to our club’s annual outing to Hahnenmoos starting on 17 June. After a thorough double-checking of all functions the first start went very well. No trimming was needed, the ASW-20 flies like on rails. Over five flights and landings I fine-tuned the down-elevator mix for the butterfly function, reduced the throw on the ailerons and mixed in a bit of down elevator for the motor function so that it goes up nice and straight with medium positive camber. Landings were tricky – the first landing went into the tall grass, due to a stiff tailwind and too much down-elevator mixed into the butterfly braking. After that was corrected landings were better, but challenging with increasing and very gusty tailwinds.

The plane is what I expected it to be. It is incredibly responsive to rudder and ailerons, needing very little thrown on both. It has a wide speed spectrum, from very slow with lots of camber, to nice and fast with negative camber – even with its low weight. All characteristics which are great for a plane to use on the slope.

I now hope to be fly it on the slope in the next few days.


ASW-20: Ready for maiden flight

The ASW-20 is ready for its maiden flight. As I got the plane with all servos and IDS installed, the work wasn’t that much, but still took me a day and a half. Especially installing the FES was a bit more work than planned. I took the recommended setup, which, unusual for me, requires the bulkhead to be placed all the way at the front of the fuselage (usually I have a few mm at the front to also insert a carbon roving there). Positioning the bulkhead also wasn’t easy, as the nose of the ASW is all but round and I didn’t manage to get the fuselage as perfectly round as usual. Also the 3-4 degrees downward angle of the motor actually looks very much up and the 40mm Spinner isn’t quite as nice as the 42mm Spinner I usually get. But it still looks more than fine.

There were also a few mishaps with the wiring. The pre-installed wiring for the elevator and rudder servos had a shortcut between the signal wire of both the elevator and the rudder, so that they couldn’t be operated independently. I redid all the wiring for the elevator and rudder. Also one of the wing servos wasn’t working, but fortunately just turned out to be plugged in wrongly in the wing – which was easy to resolve.

I did some decals based on a Swiss ASW-20 I found on the web – I may do something different if I find something nicer.

The plane is now 4.76kg, well below the planned weight of 5-5-5kg. Together with the powerful 6S leomotion outrunner setup that should make for very easy handstarts.

Here are the specs of the ASW-20:

– Wing Servos KST x10 and X08plus (ailerons)
– Elevator and Rudder Futaba 3174
– LeoFES L4632-340
– Freudenthaler Scale-CFK-Spinner 40/6.0mm/+0® mit Versatz
– LeoFES L46xx Spant 38mm aus CFK (probably a 40mm would have been better)
– Leomotion Carbon Propeller 18.0 x 13.0 Scale (8m m) – weiss
– ESC Castle Light 100

I’ll fly it with 2x 3S 3300mAh LiPos and a 2S 450mAh backup LiPo running over a Scorpion Powerguard. I also use two Futaba R7008SB receivers in an S.BUS Setup over a Dualsky S.Hub Duo. I’ve set the center of gravity at 85mm as recommended, but with space to move it further back.

New Project: ASW-20 (Mächler)

My new ASW-20 ist there!

One of the other pilots we frequently encounter on our favourite slope is Christoph Mächler. Many of the building techniques we use for our self-built planes originate from him. For the past year he’s been flying a really cool (and fast!) ASW-20 that impressed me very much. The plane is built for him in the Ukraine, using old fuselage moulds he bought a while ago, using new wing profiles and layout that he designed himself. The building techniques are still very similar to ours – the wings are foam core, but with plenty of carbon, glassed and spray painted. Unlike our builds, the rudder is a very light balsa ribs with oracover. The wing joiner is full carbon.

I’ve always like the design of the ASW-20 and am also always on the lookout for good slope planes that are performant but also light enough to hand-start on the slope. Last summer he offered to have one built for me. The plane arrived last week. The build quality is excellent – better than my self-built planes. It’s a bit heavier than how we would build it on account of having way more carbon in the wings, but that’s a good think as I want to use this plane as a slope racer.

Wingspan is 3.8-4.1m (different wingtips). Flying weight should be around 5-5.5kg. The plane came with KST servos and IDS (RDS for the rudder) fully installed. All I need to do is install the FES and bungee hook, finish the electronics, program my transmitter and it should be good to go. I hope to maiden this before we head off to our annual club flying week in Hahnenmoos on 17 June.

Diana 4 and Monerai: canopy frame and seat insert

While waiting for the Ventus 2c to come back from the paint shop I’ve been working on the Diana 4 and the Monerai. For the Diana 4 I started work on the canopy frame. First I applied good quality painters tape to protect the fuselage from resin spillage. Then I applied two coats of liquid wax on the area where the canopy frame is built. Then came a coat of thickened epoxy with grey colourant. Allow some time for this to cure until it’s less liquid but still sticky. Then came a layer of 49gr glass, followed by a five carbon rovings going around the entire canopy (staggered so that they end/start in different spots). Then I built up the rest of the frame using epoxy with grey colourant and very much thickened using micro-balloons. It’s not sitting in the workshop to fully cure (needs a few days) before I can sand it into shape.

While waiting for the canopy frame to fully cure I also built the seat insert for the Monerai, using an old mould for the SB-14. The procedure here is very similar to making the canopy frame. The mould is waxed. Then apply slighly thickened epoxy with grey colourant. Allow to cure a while, but it still must be sticky. Then apply two layers of 160gr glass, also with epoxy with grey colourant.

As you can see in the pictures below I didn’t wait long enough to apply the glass and had a few nasty air pockets in the folds of the seat pan. These can be easily corrected with surplus epoxy thickened with micro-balloons. Allow it to cure, sand to shape and it’s good to go.

Ventus 2c: Ready for the paint shop

I’ve not had the chance to keep updating the blog, so here’s an effort to catch up. Three weeks ago I finished the preparations to enable the Ventus 2c to be sent off to the paint shop. It’s been painted with filler and sanded again. Also the fuselage got a thin coat of filler on the seam (not visible on the pictures below). Unfortunately the paint shop has been very busy and I’m still waiting for a slot. I’m hoping to have it back in the next few weeks.

Ventus 2c: painting the canopy

Canopies are nicest with a white band around them. Painting this is always a bit tricky. Some of my mates paint it by hand. I like to spray paint it. This is a bit more work, but in my view gives a slightly better result. I first sand the edge of the canopy that I intend to paint. Then comes the most important part: covering the bits that should not get paint on them. I first apply good wax/painters masking tape around the edge. This must be good quality tape – cheaper tapes (including the commonly available TESA) often result in the paint getting under (or through) the tape and ruining the canopy. Make sure this is well pressed onto the canopy. Then comes the job of covering all the rest. One small hole anywhere in the covering and the canopy is ruined – spray painting will always find this hole. So don’t save on tape and make sure all is carefully covered. After that I first apply a few coats of primer to make sure that any remaining small gaps on the edge are filled. Allow this to harden out and, if necessary, slightly sand to remove any uneven parts. I then use a standard car paint to spray paint the edge. Important is not to wait too long with removing the tape – I usually wait until the paint is ok to touch but hasn’t fully hardened out. Waiting longer may result in chipped edges (one of the reasons I paint the canopy myself at home, and not with the rest of the plane in the paintshop).

Ventus 2c: filler

Before having the wings and tailplane spray painted, they first need a coat of primer to ensure an even surface and fill the structure of the glass covering and any pinholes in the glass covering. This is a terribly messy and smelly job, best done in a well-ventilated area on a not too cold/not too warm day. Not one of my favourite bits. I apply the primer using a metal “Japan Spachtel” (Japan or Surface spatula) and a paint brush. Note that this primer is extremely agressive and will dissolve plastic containers as well as normal paint rollers. I also use a good mask while applying it.

Ventus 2c: assembly to check if all is ok

With canopy and wingtips all done, it’s time to assemble my Ventus 2c to check if all is ok – and of course to admire the result of my work so far. I also weighed the glider. As in the picture it’s now at 2.71kg – this is without filler, paint and most of the electronics (except for elevator servo and cable, which are already in the fuselage). This means that it should be possible to get a final flying weight of less than 5kg – as planned. Fingers crossed.

Next step is to apply filler to the wings and control surfaces and give them a final sanding. Then I’ll need to prepare the plane for the paintshop.

Ventus 2c: canopy

Cutting the canopy to size and glueing it onto the frame is one of those jobs that’s tricky and easy to get wrong. Worst of all is that any mistakes are very visible afterwards – a badly fitted canopy can really ruin a glider. No wonder I’ve never met anybody who actually likes doing this. Same here. I always wait for a day that “feels right”. I first check that the canopy frame is sanded to size (approx 1mm back from the outside of the fuselage – depending on the thickness of the canopy). Then I make the first rough cut of the canopy, place it over the frame (mounted onto the glider) and mark where I should cut it. Important is to make sure you mark the center at the front and rear of the canopy, to make sure that it’s always in the same place. The first “rough” cut I do using my Tamiya canopy scissors. Then it’s time for the (very rough) permagrit and 80grain sanding paper. Fit, sand, repeat (very often). I usually takes me 2-3 hours to get it right. Just be extremely careful with the sanding – one slip over the canopy and it’s ruined….

Once I have a fit that I’m satisfied with it’s time to glue the canopy to the frame. I do this using epoxy resin thickened with aerosil and micro-balloons. First I make sure that the fuselage is nicely waxed and protected with tape. Then I use a syringe to add glue all over the frame. Then comes the tricky part: carefully place the canopy over the frame and center the front and rear markings. Then I use wax tape to glue the frame in place. In areas where the frame is standing out I use leftover ebechi wood (vertical grain) with double-sided tape to make sure that the canopy is level with the fuselage. Now it’s time to let the resin cure and see how well I did this time.There will always be places where there was too much or too little epoxy, and I’ll need to make some small corrections after the first epoxy is cured.