I’ve got too many unfinished projects in my workshop (a pretty common “problem” among aeromodellers I think). As the monerai is now in a phase where it requires long waits for paint to dry I have time to tacke the other projects. One of the unfinished projects is a brand-new Chocofly DG800 that’s been sitting in my workshop since Autumn and that I’m keen to get ready in time for the start of the new flying season.
The Chocofly DG800 is the successor to the DG600 (still available from RCRCM). The DG600 was one of my favourite planes and also the glider that got me into slope soaring in Hahnenmoos. I sold mine a few years ago as I wasn’t flying it enough, I wasn’t entirely satisfied with the build quality from RCRCM and one of my club mates was keen to buy it from me. I did however miss my good old DG600. When Dani (Chocofly) raved about his new DG800 I ordered one, together with my flying buddy Georg.
Georg has started building his DG800 and kindly given me his notes (see also below, downloadable as a PDF file in the correct size). As a results my build can be pretty quick. I’ll be using the cool new Chocofly LDS system that I already used on my Ventus which is very precise and robust. I’ve glued the servo horns and servo frames into wings and fuselage and should have the wings and fuselage ready shortly. A bit of a hassle will be the canopy, as I’ll be installing a FES system that seems a challenging fit with the canopy. More on that later.
A few years ago I built my “AvantiHawk“, a combination of the “Duckhawk” glider from the United States with wings from the Chocofly Avanti (which are similar to the scale wings, albeit much deeper). I’ve always toyed with the idea of getting an Avanti fuselage so that I can fly the same wings with the thinner fuselage as well – ideal for handstarts.
One of my club colleagues crashed his Avanti on the slope last year (catching a tree). He destroyed the right wing and broke the nose of the fuselage. The right wing was not salvageable, but the fuselage was. He played with the idea of ordering a new set of wings, but eventually decided against it and kindly gave me the broken fuselage as well as tailplane and the left wing. Chocofly kindly provided me with the missing wing joiner and a new canopy, as well as the servos for the fuselage and motor. I’ve started fixing the fuselage, using multiple layers of 100gr glass. I’ve also inserted a new motor bulkhead and extended the fuselage somewhat, so that I can fit the new Chocofly/MIGflight outrunner for 6S and the matching 42mm Spinner (rather than the 45mm Spinner that was used before). The fuselage needs a final sanding and is then now ready for it’s final coat of paint. The components are ready to be built in once it’s painted.
The only problem is that my wings are white and the fuselage and tailplane are yellow. Respraying the entire fuselage white is usually not a good idea (you will always see that it was once yellow), but I can make the upper side of the tailplane white to match with the wings. The underside of wings and tailplane are the same blue. Also cool is that the new canopy as well as spinner and propeller are white, so I’ll probably go with a yellow-white (and blue underside) colour combination. I do however still have to find a spraycan with matching yellow.
The canopy came out well – except that the small pins that I put in to avoid the center part of the canopy standing out when it gets hot (from standing in the sun) broke off when releasing it from the fuselage. Not a big issue, I’ll just have to do it differently.
On Saturday I went to one of my Hahnenmoos flying buddies who has a CNC milling machine and had offered to cut the sides of the landing gear. I’d prepared a DXF file for the sides earlier using QCAD, so it was easy to convert and upload to his CNC computer and cut the sides. I use 2.5mm glass fiber plate. Unfortunately I couldn’t find a black or white plate, so it’s green-ish, but that’s not too bad either.
I now need to position the gear into the fuselage, cut the opening on the bottom of the fuselage to size and glue it in using thickened epoxy resin.
I’ve yet to decide if I’ll add a FES motor to the Monerai. The main issue is that the tail is very light and there is no space to put the batteries far behind the center of gravity. I’ll decide on adding FES before sending the glider off to the paint shop.
I do however want a tow hook. And of course I still needed to fit and install the canopy.
The towhook I built myself, using a servo I had lying around still, and our usual DIY setup. The same with the canopy lock. I like these to be “hidden” below the wing/fuselage.
Fitting the canopy is always a lot of work – usually saved for a day that I feel up to it and pull it through in one go. I roughly cut it to shape using my Tamiya canopy scissors. Then it’s a lot of sanding/trying/sanding/trying until it fits. Most of the sanding is done using my permagrit. After that I glued the canopy to the frame using thickened epoxy resin (aerosil and micro-balloons), this time also adding some grey colourant (after waxing the fuselage to make sure that the resin only sticks to the canopy). The whole thing took me more than 5 hours…..
I’ve been putting off fitting the tailboom of the Monerai – too many variables and things that can go wrong. In the end I asked my mate Georg to help me. He’s the one who usually does the wing positioning of the plugs of our new models and also has the right gear and space. I had already mounted the tailplane at a 0 degree angle to the tail boom. That left deciding on the length of the tailboom, the right incidence of the tailplane in comparison with the wings and the exact positioning of the tailboom and V-tail.
We first positioned and fixed the fuselage pod and wings at an incidence of exactly 1.3 degrees, so that the tail boom could be fixed horizontally. We then prepared a support for the tail boom and roughly aimed it in the right position. Then we removed the tail boom, prepared epoxy resin and glued the tail boom into the correct position. Using our laser we double-checked everything and allowed the epoxy to cure. The next day I prepared and added some thickened epoxy on the inside of the fuselage as well as plywood bulkhead. I also used 10cm of leftover tailboom to reinforce the inside of the tail boom where it is glued into the fuselage (cutting it open on one side to reduce the diameter so that it fits).
The Monnett Monerai has a fixed suspended landing wheel. My mate Richi’s gave his Monerai a wheel without suspension. I’m not a big fan of unsuspended wheels – especially when you have bumpy landings on grass or slopes the forces on the wheel and risks of damage are too big. Most importantly, I thought it would just be nicer to build a suspended landing wheel – also to put the crash-course in CAD drawing that I had in August last year from a flying buddy on a rainy day in Hahnenmoos into practice.
The design of the landing gear is very much based on the well-tested design of our Urupema and Orlik – just smaller, with a 70mm foam wheel. The front and rear bulkhead are 4mm plywood and designed “by hand”. The sides of the gear were designed on QCAD and will be milled from 2.5mm glass fiber. To check if all the bits fit together and are sufficiently stable I first cut them out of 2mm plywood. A flying buddy will mill them out of glass fiber for me next week. The front and rear bulkhead are held together using wooden sticks that are just there for correct positioning and will be removed once the gear is glued into position in the fuselage. The suspension will be bicycle inner tubes.
The small things always take up a lot of time – especially if it involved waiting for epoxy resin to cure between the different steps. After sanding and fitting the wings I glassed the corners of the wing root (protection from transport damage), finalised fitting the V-tail to the tail boom (0 degree dihedral compared to the tail boom) and filled up the space between the two parts of the V-tail and the tail boom with thickened resin.
The next big step is glassing the wings. I used 48gr glass cloth, cut at a 45 degree angle (this means a 2cm overlap around 30cm from the wing root). I first put the glass on the wings (and tailplane). Then I prepare a mixture of epoxy resin, with a bit of white colourant and 30% methanol to make it really “watery”. The white colourant helps ensure that we will need less paint afterwards when painting the wings. Using a paint roller and an old non-stick frying pan I roll the resin mixture onto the glass, making sure that it’s nice and straight, without any folds.
I first do the underside, making sure that the glass is about the middle of the leading edge. After applying the glass I hang the wings leading edge up on the wing joiner and a piece of wood to let the resin fully cure (without warping the wings). After the resin is cured I will use a razorblade to cut away the excess glass and gently sand the edges.
Tomorrow I will do the upper side of the wings and tailplane in the same manner, with the only difference that I’ll wrap the glass over the entire leading edge. In total I need around 2x25gr of thinned down resin per side of each wing.
After fitting the wings I applied lots of wax to the fuselage and then used thickened epoxy to fill out the remaining gaps between the wings and the fuselage. The fit is now perfect.
Using a template I also glued the carbon tubes for both sides of the v-tail into the tailboom. Like the original, both sides of the v-tail are slightly off-center.
In-between I sanded back the canopy frame and applied an extra two layers of 100gr glass on top. I also did some work on the instrument panel and the seat pan.
Most importantly: time for a first fitting together of all the bits! it’s starting to look like a Monerai now. Still lots of work to do though. Next steps are to glass the wings and tailpane, finish fitting the tailplane to the tailboom and fitting the tailboom to the fuselage at the correct incidence. I’ll also need to start working on the fixed landing gear. More on all that later.
The main advantage of using ebechi to cover the wing cores is that it makes it easier to get rid of any uneven parts. These usually occur on the underside of the wing where the main spar or the two spars on either side of the hinges of the control surfaces are epoxied into the foam. The 0.6mm thick abachi usually gives enough “margin” to sand the uneven bits out.
Sanding the ebechi is a messy job. I usually do this outside and was lucky that today was relatively warm and windy. To sand the ebechi I use my favourite Permagrit (the really rough side), my trusted old bosch sanding machine (80 grit sandpaper) as well as a block with 100 grit sandpaper. Most important is to sand the leading edge of the wings into shape. During the building I put a few mm of resin thickened with microballoons at the leading edge, which makes it much easier to sand. I also use a small template to check the profile of the leading edge at different places of the wing. The template I used for the Monerai is the same as the one I will use for the Diana4 – the wing profiles are not identical, but close enough. A good trick to make sure that you sand the wings evenly is to mark the entire wing with a pencil. Once the pencil stripes are sanded away you have sanded enough and any uneven parts are most likely to have been sanded out.
Sanding reduced the weight of each wing by almost 40gr. Both of them now weigh exactly 482gr each (I weighed the wings during sanding to make sure that they weigh the same).
After sanding the wings I fitted them to the fuselage. The wings are attached to the fuselage using 6mm aluminium pins that are glued into small bits of plywood that I inserted into the base of each wing during the build. On the side of the fuselage they fit into short aluminium tubes that I glued into the fuselage earlier. To ensure that these pins are in the right place I first make the two holes in the fuselage for the wing joiner and make sure that the openings in the fuselage are just big enough to keep the wings in the right place. I check the position of the wings using my laser, as well as by measuring the distance to the table and to the nose of the fuselage. I then fix the first wing using tape, remove the other side, and use a long 5.5mm drill (thanks Aliexpress) to mark where the hole for the aluminium pin needs to come. I do the same for the other wing. I then drill open the holes for the four pins, making sure that there is enough play to enable the pins to set themselves in the exact right position. After waxing the fuselage around the area where the pins go in I then glue the pins into the wings using thickened epoxy resin (with cotton flakes), put both wings onto the fuselage and wait for the epoxy to cure.
Last week Friday I closed the 2nd wing, with help from EP. We’ve built up a nice routine and division of labour, so that closing it now takes us less than two hours. On Saturday I took the wing out of the vacuum bag. After sanding off the rough edges the scales showed a weight of 518.5 grammes. That’s a weight difference of 1.1gr compared to the first wing we built earlier last week (519.4gr.) – the closest I’ve ever come with building wings and well within the margins. Wing flex and torsional stiffness of both wings seems excellent.
All the main bits and pieces of the Monerai are now ready in their “crude” form. Now comes the long process of putting it all together. Just to see where I am weight-wise I weighed all the bits – it adds up to around 2.4kg. My mate Richi, whose monerai is ready for its maiden flight, has a take-off weight of 3.6kg. I hope I can keep mine in that same range, but under 4kg.
Today I worked on the tail end, skid and canopy frame. I also installed all the wing plugs in the fuselage. Next step is to sand the abachi on the wings, before fitting them to the fuselage and then glassing them.
Today I spent a few hours preparing the 2nd wing of the Monerai for closing. Measuring, cutting out the foam and especially preparing the Rohacell core of the main wing spar always takes quite a bit of time. All is now set for closing the 2nd wing, which we will do tomorrow.
I got a question via the comments form on the buildup of the main spar, especiall how I connect the sleeve of the wing joiner with the rohacell core of the main spar. I always glue the different core bits of the main spar together using 5 minute epoxy, fixed with a small piece of painters tape (picture below). This is really only to make sure that the core of the main spar stays together while handling. It doesn’t add to the stiffness of the wing. The stiffness of the wing is provided by the carbon sleeve around the entire core (from wing root to wing tip), by the carbon rovings below and on top of the main spar (for the Monerai 2×19 at the root and 2×2 at the tip) and of course the carbon layup underneath the ebechi (note that the carbon layup continues under the main spar for the entire length of the wing, in the first 75% of the wing covering the entire width of the wing, in the last 25% only the carbon D-Box as well as the area of the control surfaces).
So to be clear, the buildup from inside to outside is as follows:
– in the area of the wing joiner: carbon wing joiner (stays in the joiner sleeve during the building of the wing); kevlar sleeve wing joiner; 3k carbon sleeve; 19 carbon rovings; carbon layup (100gr biaxial); ebechi.
– in the area after the wing joiner (from inside to outside): rohacell core; 3k carbon sleeve (reducing to 1k towards the tip); 19 carbon rovings (reducing to 2 at the wing tip); carbon layup (100gr biaxial); ebechi.
– Important: once the Ebechi is sanded into shape I’ll also add a layer of 50gr glass (diagonally), before applying primer and then paint.
I prepared the logo and decals for my mate Richi’s Monerai a while ago (his is ready for the maiden flight). Finding a usable version of the logo wasn’t easy. Until around a year ago there was a full website with documentation on the Monett Monerai – including building instructions and plans. Fortunately I saved the logo from that website already last year – just before the website went offline. Here’s the logo, I also have a digitised version if anybody needs it – just send me a message over the contact form.
Last week I put both the upper sides of the wings in vacuum. On Monday I prepared the layout and spars for the first wing. Today I “closed” the first wing, with help from my flying buddy EP.
Preparing the spars was a bit more work than usual as I had to do the calculations for the amount of carbon rovings on the main spar and decide on depth of the control surfaces. I used in total 2×19 rovings at the root and 2×2 rovings at the tip, distributed using Christian Baron’s helpful excel sheet. The width of the main spar is 25mm at the root and 6mm at the tip. I used three different types of carbon sleeves around the main spar, a 3k for the first third and 1k sleeves for the middle and outer third. The amount of rovings at the root was determined on the basis of the space available after deducting the space required by the wing joiner and sleeve. I’m curious to see how heavy the first wing will be.
The upper and lower side of the tailplane (V-tail) are now done. The Ebechi and leading edge are sanded into shape and the tips are glued on. For the tips I used two pieces of 5mm Balsa with a layer of carbon glued in the middle. The tailplane is now ready to be glassed.
The upper side of both wings is also done. I’ve decided to use the full length of the carbon cloth and at the end of the wing just use carbon for the D-Box and the control surfaces. The weight penalty of this shouldn’t be too big.
Today I also started building the canopy frame of the Monerai. I first taped off the area around the canopy and coated the part where the frame is built up with three layers of wax. Then I painted a layer of thickened and coloured expoxy resin onto the fuselage and let this cure for an hour and a half – so that it’s still nice and sticky but also nicely stays put when adding material to it. I then added a layer of 80gr glass, using coloured epoxy. After that I added 10 carbon rovings, each just more than half the size of the canopy, to provide the rigid basis of the canopy frame. After waiting again for an hour and a half I then used epoxy resin, again coloured but also thickened with lots of micro-balloons, to build up the basis of the frame. It looks nothing like the nice frame it should become, but that’s normal. Once the resin is fully cured it should have enough material on it to allow me to sand the frame nicely into shape.
I also finished the bits from the small moulds (instrument panel, skid and tailboom end). The tailboom end was a bit of a pain. On the first try I didn’t manage to release it from the mould and ended up breaking it. For the second try I cut open half the mould and closed the cut with a piece of tape, before waxing it and building up the tailboom end out of 160gr glass. No problems releasing the 2nd attempt this morning.
The plans I got for the Monerai are very rudimentary – basically just the size and outline of the wings and tailplane. My mate Richi, who’s already finished his Monerai, also told me that he wasn’t too happy with some of the design choices he made. So I went through it again with Georg, our usual wing designer, last week. Based on his input I did a more detailed drawing of the wings and tailplane, in particular in relation to the main spars and size of the control surfaces. The plans are still very rudimentary, but as the wing design is very simple (straight wings and tailplane) and I’m the only one building the plane like this for now, that more than suffices.
Earlier this week I ordered the 0.6mm ebechi wood for the wings and tailplane of the Monerai at RIK Modellbau (balsa.ch), and got a confirmation just a few hours later that it was ready for pickup. I went to get it yesterday and it’s the usual excellent quality – a great shop.
After preparing the sleeve for the other side of the wing joiner today and the sleeve for the wing joiner of the tailplane I decided to start preparing for building the tailplane (cutting the ebechi to size, drawing out where the carbon inserts come, cutting the carbon, painting the ebechi with primer and briefly sanding the ebechi). That went much faster than expected so I also went ahead and put the first side of the tailplane into vacuum.
I’m giving the building of the Diana4 a short pause to allow the resin to fully cure. No rest for the wicked though: time to do more work on the Monnett Monerai! Many of the “small” things take up a lot of time. I prepared the bulkheads for the fuselage and did a first “dry fit” of the tail boom. I’ve also started preparing the moulds for the instrument panel and tail. Today I also spent a few hours with my mate Georg to cut the styro cores for the wings and v-tail, as well as to complete details of the wing design. I’ll start building the wings and v-tail of the Monerai next.
Both wings are now ready in their “rough” form. They came of the vacuum bag well, nice and straight and not too much sanding needed to level out the unevenness of the spars on the lower side. I’ll now let them rest a few days and then wait for a day with nice weather to sand down the ebechi and sand the leading edge into shape. 5.14m is a lot of wing!!!
Today I closed the first wing, with the kind help of my mate EP. While EP inserted the carbon rovings into the opening for the main spar (using the tool with the syringe on the picture to apply the correct amount of epoxy resin to the rovings) I applied epoxy to all the spars and in all the cutouts of the wing. Once he finished inserting the first set of 26 rovings we inserted all the spars as well as the ballast tube and plywood. While he then inserted the remaining 26 rovings on top of the main spar I prepared the ebechi with biaxial carbon. We used three batches of 80 grammes of epoxy in total, around 40 grammes of which was thickened with micro-balloons to fill out the leading edge, cutouts between the control surfaces and levelling out the space between the main spar and the top of the wing (where needed). We then closed the wing and inserted into the vacuum bag. Here it will remain for the next 12 hours, under close watch of my webcam. Tomorrow I can unbag the first wing and then start preparing the 2nd wing for closing – hopefully sometime next week.
The preparations for closing a wing require quite a bit of very precise work. First I roughly mark the areas where spars, ballast tube, wiring and other bits need to come. Then I cover these areas with brown packing tape. Using waterproof pen I mark out the areas where I need to cut out foam. Cutting out the foam is done with a very sharp carpet knife (using multiple blades – they go fast). Cutting out the main spar is done along a level wooden board to make sure that the cut is perfectly straight and level.
Once the styrofoam is cut I carefully remove the bits that are no longer needed using a sharpened screwdriver. The foam of the two small spars on either side of the hinge of the control surfaces is used again to fill the carbon carbon sleeve and goes back into the wing. Also make sure you cut out a bit of the foam where the cuts between the three control surfaces are coming (so the edges of these control surfaces are epoxy with micro-balloons rather than foam). I then sand and clean out the areas where the foam is removed.
Next is the preparation of all the inserts. The two spars nearest the trailing edge of the wings consist of the R&G 200.5211 carbon sleeve, filled with foam that was cut out there. The main spar consists of three different carbon sleeves (R&G 200.4008 for the inner third of the main spar, EMC VEGA SC1062 for the middle third and R&G 200.5211 for the outer third). At the inner side of the wing the carbon sleeve starts around the wing joiner and its kevlar sleeve. From the end of the wing joiner onwards I prepare a core consisting of Rohacell. The right thickness of this core can be calculated based on the number of carbon rovings and the thickness of the sleeve. Our wing designer Georg usually prepares balsa inserts of the right thickness that you can put into the cutout of the main spar and simply sand the rohacell level with the wing foam core. At the inside of the wing I also insert two bits of plywood where the two aluminium plugs that will connect the wing with the fuselage will come. For the ballast tube I prepared two bits of balsa, one on top and one below, to make sure that it’s snugly in the middle of the wing next to the main spar. I also cut out the wiring channel using a small soldering rod and the two silver bits that Richi, another building team member, prepared. To ensure that I find the right place to cut out the control surfaces once the wings have been painted I drill four small holes 2mm from the trailing edge between the two rear wing spars at either edge of the control surfaces. Finally, I take out 2mm of foam at the leading edge of the wing, which is later filled with epoxy resin with micro-balloons to allow the leading edge to be sanded into perfect shape.
Once all bits are prepared I apply a bit of masking tape next to the main spar and mark out the number of carbon rovings that are to be pulled into the wing before closing it (the Diana 4 has 26 rovings at the first 4cm, decreasing to 1 roving for the last 10cm or so, on both sides of the main spar). Then I prepare all the tools for closing the wing.
I’ve had requests on tools and materials we use to build our wings, as well as a more detailed description on how we build them. I’ll be doing a detailed description on how to build the wings for my “how to” section on this website in the next few months. Here’s already the overview of tools and materials.
Foam cores: we’re using foam boards from Schurg (https://schurg.de/), approximate size: 100x50x6cm
UHU Por to glue together the foam shells (upper side)
5 minute epoxy (I like UHU Schnellfest) to glue together bits of the wing spars
A good thin brown packing tape to apply to the edges of the foam moulds to prevent the ebechi being glued to these by excess epoxy resin. Note that not all brown packing tapes are equally good. We use the cheap one from our local “Landi”
Vacuum Pump. I use two different pumps, a small and a bigger one. The smaller pump is very good, but when you build the wings the extra power of the larger version gives you a lot of extra security in case of minor leaks.
Vacuum bag, tube, connector and seal: all these bits can be found through R&G. I close the vacuum bag using a U-profile with a fitting tube. Press the bag into the u-profile and then press the tube into the U-profile to close it.