Today we maidened the first of our three Diana4 – the one built by Georg. He finished it just last week (having started the build at the end of last year – very fast, as usual). His Diana4 came out at 6.4kg, 7.1kg with ballast.
As always with a brand new plane, it needed a bit of finetuning. Georg started off with the CG of our Diana2 (which has the same wing profile), but that turned out to be too far back. Also mixing in down elevator with the butterfly needed a few tries. Once he got the settings in the right range the plane just didn’t want to come down anymore. There is still some more fine-tuning to do, but it’s a wonderful glider that will surely see much “airtime”.
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 :-).
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….
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.
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.
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.
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).
Building the canopy frame is always a bit of a pain. Here’s the method we use. First applying loads of tape to protect the fuselage in the parts around the frame. Then apply three layers of wax (leaving each layer to dry and polishing it carefully with some soft cloth). Then apply some thickened and coloured epoxy resin (with a “fast” hardener) and wait for the epoxy to cure a bit. Then I applied a layer of 100gr glass fiber, followed by four carbon rovings (entire length). I again waited for the epoxy to cure a bit. And then the “construction work” begins. Using coloured epoxy, thickened with lots of microballoons (so it stays in shape when applied) I built up the canopy frame on top of the carbon rovings/glass base. The result usually looks quite messy, but that doesn’t matter. Just make sure you apply enough material, so that you can sand away enough to get the frame into shape. I usually wait a few days for the epoxy to fully cure before sanding the frame into shape. Before sanding, make sure you drill the holes for the front pin and the rear lock. I always sand the inner part of the frame before releasing it from the fuselage. I use 2mm steel wire for both the front pin and the lock.
In August 2022 I got a second fuselage for my Chocofly JS3 and built this as a “light” version, without retractable gear and towhook, but with a light outrunner FES (6S). As I lost the winglets for my JS3 just before that and I only got a new set of Winglets in the beginning of December, I did not yet get a chance to maiden the new fuselage before winter. Today’s great weather was the perfect opportunity to give it a go.
There are a number of reasons for me to get a second fuselage and set it up with a light FES. The first is that I really like Chocofly JS3 with the Jetec70, but the club airfield where I fly most doesn’t allow us to fly with impeller (it’s in a sensitive area). The second is that I wanted to have the possibility to fly a very light JS3 for conditions with very light thermals. The version with the JETEC70 weighs about 6.7kg. My scratch-built JS3 is about 6.6kg. The Chocofly version with the FES fuselage however only weighs 5.9kg. This weight difference makes quite a difference. It almost turns on its wingtips and is even harder to stall than the other version. But speed retention is of course much worse.
The maiden flight and subsequent flights to fine-tune the glider went well. It’s a dream to fly and a breeze to land. I like this version and look forward to flying it often.
With the fuselages and tail sections of both the Diana 4 and Ventus 2c well advanced, it’s time to start on the wings. I will do the wings of the Ventus 2c first. All previous wings I built with my mate Andi. These ones I will be doing by myself.
The first step is to mount the cut styrofoam parts to the building board (which takes a lot of measuring), clean them and glue together the upper part, prepare the obechi wood, draw out the layout of the carbon on the obechi (which takes even more measuring) and cut the carbon for all four surfaces.
We always build our wings “upside down”. I will first be doing the two upper parts, and then I will add the spars, in the same step as closing the lower part of the wing. All in all four “vacuum sessions”.
Each wing will be built in one piece. Once the wing is sanded and glassed, I will cut off the two outer segments and glue them back at the right angle.
A few details on how we build our wings:
We build the “traditional” way, around a foam core, cut with a hot wire. It allows for a light wing, perfect for the type of flying we do. The foam we use is from Schurg Modellbau in Germany. Our club purchased a truckload of the stuff decades ago, but it’s now running out, so we’ll be looking for a fresh supply – ideas for suppliers in Switzerland are more than welcome!
The foam cores are glued onto 0.6mm obechi (abachi) wood. A good supplier in Switzerland for this is RIK Modellbau in Mosnang.
We use carbon cloth to reinforce the wings at the front (carbon D-box) and rear (control surfaces), as well as around the wing joiner and underneath the servos. We’ve experimented with different types of carbon cloth over the years. Our favourite is 100gr Carbon Biax supplied by swiss-composite.ch. It’s good value, fibres are at a 45 degree angle, and it’s easy to cut and use.
Sometimes things don’t go quite as planned, even if you’ve done it plenty of times. Installing the motor bulkhead of the Diana4 was a pain. The carbon bulkhead was just a bit too big for the fuselage, and I was sloppy in making the first cut on the nose. I ended up having to remove the bulkhead (fortunately only fixed with a few dots of 5min epoxy) and sanding it down by mounting it on the drill and rotating it on a bit of 120 grain sandpaper. Even the second try wasn’t quite as good as I wanted it to be, but with a few corrections on the fuselage it will come out fine once the fuselage is painted.
In-between I produced two covers of the instrument panel. The first one in the mould that was spray painted, the second one using thickened epoxy as the “basis”. Making these small parts in the mould are good for using left over bits of glass. Two layers of 160gr, or a layer of 50gr, one of 100gr and one of 160gr are more than enough for a robust cover.
The full-size Diana 4 is not yet ready and we don’t have any pictures of what the instrument panel will look like. So I’ve had to make something up. Below is the result. It’s actually almost identical to that of our JS3. The only thing I changed is the logo at the top of the VNE chart. Click on the link below to get a printable PDF file – if that’s of use to anybody.
The first of our three Diana 4, the one that Georg Staub is building, is nearing completion. It came back from the paint shop almost two weeks ago and Georg is now in the process of finishing the wings. It should be in the air in another month or so. So time for me to finish the decals. The decals I’ll be cutting are inspired by the Diana 2 logo, as well as the layout of the Diana 3 and the plans of the Diana 4 available on the internet. As there is no full scale Diana 4 as of yet, that’s all we have to work with for now. Linked through below is a full scale PDF of the decals, made by me, in case anybody else is interested and wishes to use them.
With my previous projects I built the wings and stabilisers together with Andi, using his workshop and pump, or borrowed a vacuum pump. As I hope to build quite a few more planes in the future and wanted to have a go at building a glider all by myself, I though it was time to purchase my own vacuum pump. For building the horizontal stabilisers I used a small KNF vacuum pump that I purchased second hand a while ago. It worked well with the smaller vacuum bags, but it will be at it’s limit with the larger bags that building the wings of the Ventus and the Diana 4 will require. Last month I thus ordered a larger pump through Lindinger – it’s also a KNF pump, made in Germany, and distributed through R&G. It took almost a month to be delivered, and seeing the production date on the pump it looks like it was made to order. Am looking forward to trying it out on the wings of the Ventus.
Earlier this week I picked up the rudder for the Diana 4. Fellow builder Georg built three of these for us, using the mould he made for the JS3 rudder. As usual it’s very nicely done and extremely light.
The tail sections of both the Diana 4 and the Ventus 2c are now as good as ready (of course the horizontal stabilisers and the Ventus rudder still need covering and painting):
45 degree angle reinforcement to avoid torsion in the vertical stabiliser (3mm balsa, covered with 49gr glass on both sides);
vertical reinforcement to close the vertical stabiliser before the rudder
rudders fitted and brass tubes (pull-pull system with kevlar wire) fitted
elevator servo installed, including wiring
The pictures of the (transparent) tail section of the Ventus show best what’s where. We always prepare a sheet of 3mm balsa wood with 49gr glass on one side (glass applied in a 45 degree angle). The balsa wood reinforcements are then glued in with thickened epoxy resin and 49gr glass (also in a 45 degree angle). With the Ventus I also applied two thin carbon rovings – that’s because I felt like it and had it lying around, but it isn’t really needed ;-). Together, the two reinforcements give enough stability/torsional stiffness to the vertical stabiliser.
The Ventus 2c will get a powerful inrunner motor. This allows for a lighter motor with lots of power to enable easy handstarts on the slope. Urs Leodolter at Leomotion.com as usual helped me pick a really nice setup. With 6kg pull it should allow the Ventus to go near-vertical.
After building the two sides of the stabilisers in vacuum I used a balsa/carbon sandwich to build the tips and curves into the stabilisers. A lot of sanding to get it into shape, but the results look good. Both the Diana 4 and Ventus 2c stabilisers are not ready to cover (with 49gr glass).
It’s often the small things that take up a lot of time. I spent quite a few hours building the frames/setup for the servos in the fuselages of the Ventus 2c and the Diana 4, as well as the bulkheads for the landing gear and the towhook of the Diana 4.
The picture below shows:
The two units for the rudders. I will use the usual kevlar wire pull-pull system, using a small pulley that was designed and built within our club ages ago.
The servo frames for the elevator servos. These are built into the vertical stabiliser and then connected to elevator using a carbon rod with 2.5mm (Ventus) or 3mm (Diana 4) threaded metal rods glued into the ends.
The bulkhead for the towhook servo and the towhook entrance.
The Diana 4 will get a retractable landing gear. We’re running low on the stock of landing gear made by our club ages ago and only have a smaller version left. It requires an 89mm wheel rather than the 103mm wheel we used for the JS3 (which uses the same fuselage as the Diana 4). It still looks nice enough though, and the difference will be hardly noticeable. To install the gear I cut out the doors from the fuselage using my dremel with a 0.8mm milling bit. To give the doors a bit of extra stiffness I covered them with a layer of carbon fibre (before cutting them out of the fuselage). The doors are then attached to the hinges, made of steel wires through a brass tube. The landing gear is attached to 4m plywood.
Today I “closed” the horizontal stabiliser of the Diana4 (underside), having built the other side earlier this week. It’s now sitting in vacuum until late tonight. Below the plan and some pictures of the bits that went into it.
Yesterday we got most of the electronics for our Diana4, as well as parts for my Ventus 2c and two other gliders that members of our building team are currently working on (a scale 1:3.5 SB-14 and another Moswey III). The parts were supplied by Leomotion, as usual.
For the Diana and my Ventus 2C we will be using:
Chocomotion 10/10 on the brake and camber flaps
Chocomotion 8/6 on the ailerons
For all wing servos we are using the Chocomotion servo frames and aluminium levers (10/7/5mm).
MKS HV6130H on elevator
Chocomotion 12/9.5 on Rudder
In addition, we will use for the Diana4:
Chocomotion 12/9.5 for towhook
Chocomotion 180/30 for retractable landing gear
All Diana4 will get a FES motor: a Dualsky XM5060EA3-14, with a Freudenthaler Scale Spinner (43/6/0degr – mit Versatz) and a GM 18×10 Scale Prop and a Castle 100 Light ESC.
I’ll also put a FES onto my Ventus 2c, but will still need to determine which motor setup.
We’ve used all components before and have flown hundreds of hours with them – this is our preferred setup.
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