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Elfe S3: start building the wings

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This afternoon I put the first wing of the Elfe S3 into vacuum. We always build the wings “upside down”, starting with the upper side first.

Before being able to do so it does take a bit of preparation:

  • Of course you need the wing cores cut from foam (which we already did back in Autumn).
  • Make sure you clean the wing cores from any “angel hairs” resulting from the cutting (using a vacuum cleaner with brush).
  • Prepare the negative “covers” with packaging tape that doesn’t stick to epoxy resin (try out different brown tapes – we’ve found that the one sold at the Landi in Switzerland works very well – and is very cheap).
  • Prepare building board, so that you can tape the negative of the underside of the wing into the right position onto the building board.
  • Tape the negative of the underside of the wing into the right position on the building board and also prepare it with brown packaging tape.
  • Prepare the ebechi (abachi) wood (0.8mm) by lightly sanding it nice and smooth and paint it with nitro base primer (nitro hartgrund) to ensure that the ebechi doesn’t absorb too much of the epoxy resin.
  • Prepare the carbon fabric (we prefer to use biax ±45° 100g/m² from Suter – it’s got great torsional stiffness and is very easy to work with). For the upper side I use carbon for the entire wing area. Georg likes to only use it in the area of the D-box, the control surfaces, the wing joiner and where the servos are glued in). I’ve found that the weight penalty of doing the entire wing in carbon is minimal (20-30gr per wing) and it gives the upper side of the wing a much nicer shape, with less deformations.

Once all that is done prepare the epoxy resin (I used around 100gr in total of epoxy and hardener). Using a soft roller, first apply some to the ebechi. Then put the carbon fabric onto it and roll to “pull up” the epoxy. Add more epoxy resin as necessary. You can use a hard roller and some kitchen paper to remove excess epoxy (I “removed” around 6gr on the entire wing – very minimal).

Assemble all the bits of the wing into the negative, making sure the wing cores are in the right position, cover with the negative “covers”, making sure you fix key bits with a bit of painters tape.

Then put the whole building board into the vacuum bag. Start the vacuum pump and leave it running for 10-12 hours at -150mbar. I use a webcam and a timer so that I can check the pressure from time to time (although my vacuum pump has no trouble keeping this up).

Elfe S3: Fuselage nr. 4 (mine!)

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On Thursday Georg and I built Fuselage nr. 4 of our Elfe S3. Today we took it out of the mould.

Andi had again spray painted the mould very nicely. Building went a bit faster than last time (we usually need between 5 and 6 hrs with two persons).  The upper side of the fuselage looks great. The underside has more airpockets at the rear, we probably didn’t press it enough with the small rollers after closing the mould. It’s not a big problem to fix though, as the fuselage will be painted afterwards anyway. The weight is just over 1.5 kgs – also within the usual range.

Elfe S3: Wing Joiner sleeves and horizontal stabiliser

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I prepared the four wing joiners four our Elfe S3 last winter already. Now that we have the fuselage sizes I could do the sleeves around the joiner, that will go into the wings. These are made of woven kevlar, with a second string of kevlar wound lightly around it. I first made the wing joiner nice and greasy using bicycle grease (a really thick coat), followed by 1.5 rounds of clingfilm or thing plastic vegetable bag. The kevlar sleeve is epoxied around that. I then apply tear-off tape and hang a weight at the bottom of the sleeve and let it cure. Once cured, repeat that for the other side of the joiner.

I’ve started building the horizontal stabiliser. Although the stabiliser will be in two parts, we built is as one – including most joiners – separating it afterwards.

We cut the foam a few weeks ago and Georg made a great plan for building the stabiliser – as usual (all by hand – see the last picture below). I prepared the carbon and glass layup, to be placed between the foam and ebechi, applied the epoxy and put the first side in a vacuum bag for 11 hours. I then cut out the various openings for the 10×1 carbon tube with glass sleeve (main joiner for the two halves), balsa where the 4mm steel pin joining the two halves will come, as well as small brass tubes with the 2mm steel pin for the elevator control. I also cut out a foam strip, inserted it into a carbon sleeve, which will be where the elevator will separate from the tailplane. Also make sure you remove a bit of foam from the leading edge and add in some thickened epoxy, so that you can sand it into a nice leading edge afterwards. Plus I inserted small bits of plywood at the end of all three pins connecting the two halves to prevent that these pins are pushed through into the foam when building up the plane later on. Then I epoxied the carbon and glass inserts onto the ebechi, closed the stabiliser and again put it into vacuum for 11 hours.

Once fully cured, I carefully separated the two halves of the stabiliser and sanded back the ebechi and the leading edge into shape.

Monnett Monerai: further work on the wing control surfaces and finalising work on the tailplane and fuselage

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Work on my Monerai has been progressing steadily over the past few weeks and I hope to have it ready to maiden in the next few weeks.

The wing control surfaces have been cut out. I sanded bach the part where the control surfaces move under the wing when the surfaces are deflected upwards. After sanding I glassed it with 50gr glass, which was then again lightly sanded to keep it as thin as possible and allow the largest possible upward deflection. The control surfaces were then glued to the wing using silicon.

While waiting for the silicon to cure I finished work on the tailplane, wiring and fuselage. In the V-tail I installed two KST X08H Plus servos, which are light and relatively powerful. To avoid any play I splashed out on the expensive but really nice servo frame and LDS kit from Tomas Liu Studios. Rather than installing this as LDS I used a normal clevis and a carbon control horn in the control surface. It’s the first time I am using this set. Unfortunately the aluminium servo had a bit too much play on them, but I managed to reduce that to almost nothing using a drop of locktite. I’m pretty pleased with the final result, the installation is pretty tight, using the full throws of the servos, there is virtually no play and the setup looks good as well. The tips of the V-tail were painted dark red. I’ll do the same with the wings once these are done.

Power for the glider comes from 2x 2S LIPO batteries, reduced to 7.4v through a Hacker/Emcotec Dualbat DPSI (with magnetic switch). I’m using this system for all my gliders and am very happy with it. All the wiring has been prepared, I’m waiting until the wings are finalised to balance the glider and deterimine the final position of all the components.

I weighed the total setup, and I expect the glider to have a flying weight of around 3.6kg – including around 60gr of lead in the nose. Pretty good.

All that remains now is setting the seals for the control surfaces of the wings, installing the servos and then finalising the programming.

Monnett Monerai: decals

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There are quite a few Monerais still out there, including some for sale, but not too many good quality pictures or designs that caught my liking.

To my surprise I found that there are several Monerais that were built and registered in Belgium. Two of these can be found on the website of the Aviation Society of Antwerp – the OO-70 (with pylon motor) and the OO-72. Coincidentally, I’ve traditionally given all my gliders without FES a Belgian registration number. So the decision was very easy to go for the OO-70 registration number for my Monerai. Unfortunaly the picture on the website of the Aviation Society of Antwerp isn’t too clear on the rest of the decals and since the Monerais were often repainted and changed I decided to go for my own design.

As information on the Monerai is starting to disappear from the web (the website containing the plans and building information is no longer online), I post a cleaned up version of the logo of the monerai here.

 

 

Monnett Monerai: polishing

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Although the paintjob on my Monnett Monerai was really good, we like to polish our gliders after they are painted and the paint is fully set (usually takes a few weeks). Polishing the paint gives the glider that bit of extra gloss and smooth surfaces and gets rid of the slight “orange skin” structure in the paint. It’s a lot of work though. I divided it over three days, around 2-3 hours each day.

A short “how to”: First we get rid of the orange skin structure by wet sanding all painted surfaces with 800 grit sanding pads (Georg even starts with 600 grit sandpaper), followed by 1500 grit and then a 3000 grit sanding pad (all by hand). After that we machine polish all surfaces using a fast cut compound, followed by a machine polish compound. See the last picture below for the materials used. In Switzerland we purchase all materials through sury.ch – unfortunately only in larger quantities, but then they last a lifetime of building gliders.

 

 

How to: make a carbon wing joiner

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We use a standard carbon wing joiner for most of our projects. It’s slightly conical and has a 6 degree V-shape/Dihedral. See the picture below for the sizes of the joiner resulting from the mould. The mould for the wing joiner is close to 20 years old. It’s a pretty simple setup, made of wood and aluminium. It has been used countless times and is still going strong. For the Elfe S3 we reduced the dihedral of the mould to 1 degree (the mould allows for this).

Here’s a description of how we build wing joiners out of this mould. All references to materials are to the R&G Webshop.

Setup:

The setup consists of 1) a roll of CF-Roving Tenax-E HTS40 F13 24K 1600tex (Art. 205.0024), mounted on an easy-rolling dispenser; 2) a 70ml syringe with a short piece of tube (I use motorcycle fuel lines) mounted in a self-made holder (to drench the roving with resin)(the syringe is held by a standard broom holder); 3) a small turntable to help cut the carbon roving to the right size; and 4) the mould. See the pictures below for more detail. The syringe and turntable are screwed to my workbench to make sure they stay in place.

Waxing the mould:

We apply three coats of liquid wax. Allow each coat to dry and then lightly polish with a piece of soft cloth. Apply some bicycle grease to the screws to close the mould (to avoid them getting stuck due to a bit of wayward resin).

Prepare the core of the joiner:

Previously we used a rohacell core for our wing joiners. For more recent builds we’ve found that it’s much easier (and cheaper) to use a balsa wood core. We use either 4mm or 6mm balsa. This is put into a 3K carbon sleeve (35mmØ 3K, Art. 200.4008).

Epoxy Resin:

I use two small joghurt cups to prepare the resin. Amounts needed:

  • 4mm Balsa Core: Approx 120gr Epoxy (90gr Resin + 31.5gr Harder)
  • 6mm Balsa Core: Approx 110gr Epoxy (80gr Resin + 28gr Harder)

I use black colourant to get nice and black wing joiners.

Set aside and thicken some of the resin in the 2nd cup (Aerosil) to apply to the mould and cover of the mould.

Building the joiner:

Apply epoxy resin to the balsa core (in the sleeve) using a small brush.

Apply thickened epoxy resin to the mould (this is to ensure that the surface of the wing joiner is nice and even, without air bubbles)

Then roll carbon rovings onto the turntable. I roll them in sets of 8. Use scissors to cut them into separate rovings at the right length.

Evenly put the rovings into the mould, starting at the edges.

Regularly spread out the rovings in the mould using an old credit card or a piece of wood .

The amount of rovings to use is as follows:

Wing Joiner with 4mm Balsa Core:

50 Rovings above and + 50 rovings below the core. In addition, add on each side of the core 4x13mm und 3x 17mm rovings in the center

Wing Joiner with 6mm Balsa Core:

40 Rovings above and + 40 rovings below the core. In addition, add on each side of the core 4x13mm und 3x 17mm rovings in the center

Note that you may need up to three rovings more on each side, depending on how much resin the rovings absorb (this can be adjusted by squeezing the tube coming out of the syringe – see picture)

Once all rovings and the core are in the mould, close the mould and let the resin cure for a few days.

 

Elfe S3: progress on the plug and the first wing joiner

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Our plug builder Richi has been working hard over the holidays and made good progress on the plug for the Elfe S3. Earlier this week he dropped it off at our airfoil designer Georg so that he can prepare the connections for the elevator and the wings to the fuselage.

During the holidays Georg also modified our standard wing joiner mould, decreasing the dihedral to 1 degrees – which we will be building into the root of the wing in addition to the dihedral halfway through the wing. Today I used the mould to build the first wing joiner. See the separate “how to” post on how we build our wing joiners.

New Futaba T26SZ – first impressions

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My trusty Futaba T18SZ is getting older and has had many hours of flight time – without any issues. As I don’t want to change to another system (Futaba never failed me, I have loads of receivers and I’m too lazy to re-program all my gliders on a new system) I was keen to try out the newly released Futaba T26SZ. As soon as one popped up in the inventory of one of my local model shops yesterday afternoon I rushed out and got it.

This afternoon I had my first flights with the new transmitter. Here are my first impressions.

First the good things:

  • One of the reasons that I always liked my T18SZ is the low weight. The T26SZ is 5 grammes lighter (922gr), very easy to handle and much lighter than some of the other brands.
  • The sticks feel great, very similar to what I was used to on the T18SZ. “Potless” sticks have been the rage over the last few years and are now standard on the T26SZ (although I’ve yet to meet anybody who had issues with the sticks on the standard T18SZ).
  • The operating system of the T26SZ is essentially that of the T18SZ, with a few extra “gimmicks”. That makes it easy to dive straight into. I was particularly pleased that the T26SZ did not build upon that of the T32MZ, which, in my view, is over-engineered and a pain to use. The model picture on the display as well as the possibility to assign sounds to switches are a nice new addition. Many will also appreciate the elaborate sequencing options.
  • A great plus is the 2nd screen at the top of the transmitter. It’s very easy to read and “always on”, providing the option to show either telemetry data or the timers (I’ve chosen the latter, as my telemetrics come via headphone). Another benefit is the new antenna, which is much less vulnerable and exposed than that on the T18SZ (I’ve seen them broken off on multiple occasions).
  • Transferring the first few models from my T18SZ to the T26SZ was a breeze, using a micro-SD card with a converter to a standard SD card. When copying the models from the card onto the T26SZ it automatically and instantly converts them to the new transmitter. All that remains is binding the receiver(s) as well as installing telemetry. Easy. I’ve not found any conversion errors so far.

There are a few things that I’m not so satisfied with. Some of them I hope will be addressed in future software updates or as I explore the transmitter’s possibilities:

  • My main issue is with the sliders at the lower right and left of the T26SZ. As a glider pilot I use the lower left slider for the motor and the lower right glider to switch between different positive camber positions (I usually have three). The new sliders are much smaller, do not have much resistance (move too easily) and do not feel very precise. Whereas that’s simply annoying with the camber positions, it can be dangerous with the motor. Even though I use a safety switch for the motor on the transmitter, it’s (too) easy to touch the slider and engage (or disengage) the motor. Probably much of this just takes getting used to. I do however want to check if there’s a way to give the sliders a bit more resistance. I’ve yet to make up my mind if I like the fact that there are now two sliders on each side rather than the single slider on the T18SZ. On the left side I will probably tape over the outer slider.
  • A real pain is that the number of models that can be stored on the transmitter itself remains limited to 30 and you cannot operate a model from the SD Card. I had hoped that this number would have been increased. I’m about to hit the 30 limit on my T18SZ and dislike having to copy models from/to the SD Card (yes, I fly all my models, I’ve sold the ones I don’t fly).
  • Much less important, but still annoying, is the positioning of the micro-SD card. Getting the card it in and out is finnicky. Especially in the beginning I had to move the card it back and forth very often to get the hang of transferring the models and the model pictures onto the T26SZ. Once all my models are converted it should however be fine.
  • The model pictures option is fun, but requires some work as all pictures need to be exactly 160×80 pixels, in a 24bit BMP file and with maximum 8 characters in the file name. Do one thing wrong and it’s not recognized by the system. No mercy.
  • Even though there is a whole range of pre-defined sounds, there are some that I would have liked that are missing (camber settings) and all of them are in English only. I’ve not found a possibility to add new or custom sounds.
  • Can I please rename my telemetry sensors? I mostly use my SM Modellbau GPS Logger 3 and find the “borrowing” of wrong sensor names simply annoying.
  • The two functions that I missed most when I transferred from my T14SG to my T18SZ have not been brought back: autolock of the screen/menus (after x seconds) and the ability to adjust the telemetry volume through one of the dials on top of the transmitter. While that’s not a disadvantage compared to the T18SZ, it is a missed opportunity for the T26SZ. I spend much of my time on the slope and would like to be able to turn up the volume in strong winds/gusts. The manual is also very explicit about the need to lock the touch-screen, so an autolock really would make sense.

One final point to raise is that I’ve not yet been able to get my SM Modellbau GPS Logger 3 to work on the new transmitter. For some reason it gives weird values for the GPS sensor (multiplied by 256 and a minimum speed of 64kmh). There’s probably an easy fix for this, but I’ve yet to find it. [EDIT 30.9.2024: the new software update v.1.2 for the T26SZ remedies this problem – with many thanks to Arwico and Futaba for correcting this bug so quickly]

All in all my first impression is moderately positive, but I really need to use it more to form a definite opinion. So far, I find the transmitter an interesting evolution compared to the T18SZ, certainly not a revolution, that provides a number of improvements over the T18SZ, but also misses a few obvious chances. I was certainly not looking for a revolution in the new T26SZ, and am happy that it builds so much on the T18SZ. I do hope that the list of issues that I’m not too happy with will be reduced as I get to know the transmitter better and as Futaba comes with the inevitable software updates in the next few months.

Chocofly DG800: installation servos and motor (FES)

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As mentioned in my earlier post, this is a pretty quick build. The servos in the fuselage and wings are installed. I used the Chocomotion 10 and 8mm Servos with the new Chocomotion LDS system, all of which I’m familiar with from previous builds and which work perfectly. There is no play on the wing control surfaces whatsoever and I’m able to use the full range of all servos, with sufficient throw.

I also installed the motor bulkhead. I was a bit nervous about this one, as Chocofly now uses MIGflight motors with a new type of bulkhead that’s glued in from the front. This no longer allows me to use my usual method for installing the motor. It turned out to be easier than feared. I first did a rough cut and then sanded back the nose, repeatedly fitting the motor and bulkhead to see if the fit was right. In the end I fixed the bulkhead (with motor) in the right position using a few dots of 5 minute epoxy. I then removed the motor, covered the front of the bulkhead and the nose of the DG with wax tape and fixed the plane with the nose down. Using a small pencil I first added some white coloured resin on the sides of the bulkhead (from the inside), wrapped in a thin carbon roving and then filled up the rest with somewhat thickened epoxy resin. Curious to see how it comes out tomorrow. I do hope that I got the downward angle of the motor (usually somewhere between 3 and 4 degrees) in the right range.

 

Monnett Monerai: more canopy and landing gear

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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.

Monnett Monerai: fitting the tail boom

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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).

Monnett Monerai: Landing gear

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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.

Monnett Monerai: small steps and glassing the wings

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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.

Monnett Monerai: wing cores both ready

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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.

Monnett Monerai: wings and tailplane design and building start

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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.

 

 

Diana4: closing the first wing

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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.

Diana4: preparing to close the first wing

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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.