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).

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.

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: 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.


Ventus 2c: wingtip dihedrals

The Ventus wing has multiple dihedrals. The first two were built into the wing as part of cutting the wing’s foam core. The last two (6 and 15 degrees) were too much for the thickness of the foam and must be added after the wing is completed. As it only concerns the outer two wing segments, there is no need for complicated spars or internal reinforcements. I simply separated the last two segments with a saw, sanded them back to get the right angle, removed some of the foam on both sides of the cut and re-attached the two segments using epoxy resin thickened with cotton flakes and aerosil. I did this in two steps, to make sure that I got the right and identical dihedrals on both wings. After letting the epoxy cure I will put a thin strip of 49gr glass fiber (45 degree fibers) over the seams, both on top and underneath the wings. That should be strong enough for this glider.

Ventus 2c: fitting the wings and covering them with glass

Having completed the basic build of the wings I first spent a morning sanding down the ebechi and getting the leading edge into the right shape. A lot of very dusty work, best done outside on a sunny day. After that it was time to fit them to the fuselage. Lots of measuring and trying, before glueing the 6mm aluminium pins into place. To ensure a perfect fit with the fuselage I then first closed the end of the wings with a bit of carbon and with a bit of epoxy with lots of microballoons filled any remaining gaps between the wings and the fuselage. Following that I completed the wingtips, in two steps, using small bits of balsa wood, glued on using thickened epoxy resin. Following all that was another coat of transparent primer to ensure that the ebechi doesn’t absorb too much epoxy.

Then it was time to cover the wings in glass. We use 49gr glass, applied at a 45 degree angle to improve the torsional stiffness of the wings. We apply it using a paint roller and an old anti-stick frying pan. The epoxy is mixed with 30% methanol, so it gets really watery. First the underside, then let the epoxy cure (with the wings hanging leading edge up, to avoid deformation). Then the upper side, again letting the epoxy cure with the leading edge up.

Ventus 2c: closing the wings

It’s always satisfying to see the wings of a new build for the first time “in full”. I spent two mornings with help of my flying buddy EP to close both wings – the first time I am doing this in my own workshop. I was a bit nervous about how accurate my calculations for the thickness of the main spar were (if you get it wrong then the carbon roving “overflow” from the cutouts, which is a pain to correct afterwards) – but they proved about right. I’m also not unhappy with the weight of the wings: 588 and 594gr. I’ll be able to reduce the slight difference in weight when sanding down the ebechi. The wings are around 40gr heavier than the ones built in my club twenty years ago (they came out at around 450gr). The reason for that is that all inserts in the wing are carbon rather than a combination of kevlar, glass and carbon in the earlier builds. The biggest difference is that I significantly beefed up the amount of carbon rovings in the main spar – the wing is nice and stiff – perfect for the slope  :-).

Ventus 2c: Instrument panel

While searching the net for good pictures or examples of Ventus 2c instrument panels I was surprised by how little I found. Fortunately there was a nice drawing of an instrument panel among the papers from the first builds of the Ventus in our club 20 years ago. As this may be useful for others as well I’m posting it below. I’ve also found a good enough picture of an panel “in action” and used that to pick the instruments. I know the compass isn’t really in the right place….


Ventus 2c: preparing to “close” the wings

We build our wings “upside down”, i.e. the top side first. That’s the easy bit. The underside is much more work. First comes all the measuring and drawing out the position of the main spar, wiring channel and the spars at both sides of the hinge of the control surfaces. I mark the right position of each on packing tape, doing both wings at the same time and regularly cross-checking to make sure that all is in the correct place.

Then comes cutting out the foam for the three spars. Foam is a killer for blades. As we re-use the foam cut out of the two rear spars (carefully “dug out” using a sharpened screwdriver), it’s important that these cuts are clean. The same goes for the cutout of the main spar – too big or too messy and the calculations for the amount of carbon rovings no longer work, or the main spar may end up positioned slightly skewed. To make sure all is cut straight we use a thick board that is placed horizontally using a small inclinometer and cut along the edges of the thick board. I also cut out a bit of foam at the leading edge, so that I can fill it with micro-balloons in resin (easier to sand the leading edge into shape). Make sure that all surfaces that were glued before are carefully sanded and cleaned of dust so that the next layer of epoxy resin sticks. Using thick plywood I also prepared to bits that will be glued into the root of the wing and into which the two 6mm aluminium pins will be glued to attach the wing to the fuselage.

I glued together the foam cutouts of the two rear spars using 5 minute epoxy and pulled over a carbon sleeve. The core of the main spar is made out of Rohacell – a dreadfully expensive material, but very easy to sand into the right size. The size for the Rohacell core of the main spar can easily be calculated using the really cool excel sheet by Christian Baron (link to the 2013 version, example filled out for an ASK18). In this case I used the layout that was used for the Ventus 2c built by Georg over 20 years ago – with a few minor modifications. The spar will be much more robust than needed, but since I plan to mostly use this plane on the slope, the extra stiffness is welcome. I’ll have 2×20 1600k carbon rovings at the root, reducing by one roving every 10cm, finishing with 2×2 rovings at the start of the penultimate wingsegment. The bits of the main spar are also glued together using 5 minute epoxy and then covered with a carbon sleeve.

The channel for the wiring was cut out using a small soldering iron with an attachment made by our building team mate Richi.

Once all the bits for closing the underside were prepared it was time to prepare the workshop, including setting up the tool for adding resin to the carbon rovings. All is now set, I hope to close the first underside in the next few days.

Ventus 2c: cockpit frame and instrument panel

After leaving the “raw” cockpit frame to cure for a few days it was ready to be sanded into shape (our epoxy cures in 12 hours, but it’s easier to sand if you leave it a few days). With a lot of material needing to be removed, this is a messy job, but the result is ok.

I also used a glass fiber plate that I made with two layers of 100gr glass to shape the cover of the instrument panel. The plywood panel is based on a drawing of the original cockpit panel. After potisioning this with 5 minute epoxy, I cut the individual glass segments. These I also glued in place with a few dots of 5minute epoxy and then added two layers of glass with epoxy resin on the inside.

My mate Georg gave me a really old seatpan from his stock that fits well with the fuselage.

The result isn’t totally “scale”, but good enough for me.

Ventus 2c: Building the Wings (upper side)

The upper sides of both Ventus wings are now done. This is the “easy” bit of the wing building. Before starting with the epoxy I first prepared the foam shells and cores. Using a brush on the vacuum cleaner I cleared the “angel hair” remains of cutting the foam. The parts of the upper shell are taped to the building board (which has carefully measured markings for the right position of all parts) and glued together with UHU POR. The leading and rear edge of the shells, as well as the area underneath the main spar, are covered with packing tape (make sure you find a version that doesn’t stick to epoxy). I also applied a few bits of double-sided tape to ensure that the ebechi stays into place.

The ebechi is painted with a primer to avoid it from absorbing too much epoxy. After the primer has cured, the side where the carbon and foam are applied to is sanded and cleaned.

I then prepared 45gr of epoxy resin (make sure you measure and note this down for the other wing shells – 35-40gr would have been ok as well). Using a small soft roller I applied the epoxy to the parts of the ebechi to be covered with carbon. Then I put the carbon in place and again applied epoxy to the carbon using the roller. After letting it rest for a bit I then used kitchen paper and a hard roller to remove excess epoxy resin from the carbon. I then added a bit of foaming agent to the remaining epoxy and applied that epoxy to the remaining areas of the ebechi wood (and also parts of the carbon).

I then put the ebechi with carbon into the foam shell (sticking it to the shell using the bits of double sided tape), after which I added the wing cores (make sure you position them carefully) and the top of the shell. I added some foam bits to the corners of the wing (to avoid them being pressed down too hard in the vacuum) and insert the whole board with wing into the vacuum bag. Using the vacuum cleaner I created a vacuum, and then attached my new vacuum pump. I stayed with the pump for a while to make sure it stabilises the pressure at -0.15bar and then I left it to run for around 12hrs (making sure that the room temperature is around 21 degrees). I use a timer to turn off the pump after 12 hours (usually late in the evening), leaving the wing in the bag until the next day.

After removing the board and wing from the vacuum bag I used a sanding block to remove any bits of ebechi or carbon sticking out (the carbon pins can be really nasty).