Monnett Monerai: wings and tailplane design and building start

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.

 

 


Monnett Monerai: tailboom, small bits and styro cutting

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.



Diana4: closing the first 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.


Diana4: preparing to close the first wing

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.


Wing building technique: materials and tools

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.

Materials

Tools


Diana 4: upper sides of the wings

Today I bagged the 2nd upper side of the Diana4 wings, having done the first one earlier this week. Bagging the wing is not all that much work – less than an hour. It’s the preparations that take most time.

After preparing the foam cores (see previous post) comes the incredibly important work of drawing the layout of the wings onto the building board and positioning the foam shells. We build upside down (upper side first). Once all the measurements are done and double-checked I position the foam shells and glue them to the building board using painter’s tape. Then I apply thin brown packaging tape on the edges of the shell on the board as well as to the individual shells of the underside of the wing. It’s important to find a packaging tape that doesn’t stick to epoxy resin – the purpose is to avoid the shells sticking to the wing core or other shells.

Once the board and shells are prepared I prepare the ebechi (abachi) wood. We use 0.6mm ebechi, prepared by a carpenter friend or purchased through RIK Modellbau. This ebechi is cut to size using the plan of the wings – important is to make the ebechi for the upper side approximately 4mm longer (depending on wing profile). I then draw the layout of the carbon inserts onto each of the four ebechi sheets (so I know where to position the carbon when glueing it to the ebechi). We rarely do a full carbon layup – that’s not necessary and would only add weight to the wings. The carbon inserts are just big enough to cover the carbon D-box at the leading edge of the wing, the control surfaces at the back of the wing as well as the positions for the servos and the wing joiner. Once the layout of the carbon inserts is drawn onto all four sheets I carefully sand the inner side (where the epoxy is to be applied) of each sheet and clean off the dust. I then apply a transparent primer (“Hartgrund”), 50% diluted, to avoid the epoxy completely soaking the ebechi. Allow this to dry out and another quick sanding and the ebechi is ready to be used.

Once all that is done it’s time to prepare the resin. I used around 60 grams of resin for the upper side. It is possible to do it with 10-15 grams less for weight watchers. Using a small roller I apply the resin to the parts of the ebechi sheet where the carbon layup is coming. I then put the carbon layup onto the ebechi and push it on using the roller. Then I use the roller to apply most of the resin to the carbon layup. I leave a few grams of resin and add a few drops of foaming agent and let this rest a bit. I then use a hard rubber roller and kitchen paper to roll excess resin off the carbon layup. Then use the soft roller to apply the remaining resin with foaming agent to the parts of ebechi not covered with carbon.

Then put the ebechi with carbon layup onto the shells. I use six or so small bits of double sided tape on the shells to make sure that the ebechi doesn’t shift. Then put the wing cores onto the ebechi, fix the outer ends in the right position with a bit of wax tape and fix the cores together with a bit of the same tape. Then close the upper shells, lightly fixing them into place with painter’s tape. Then bag the entire building board, use a vacuum cleaner to remove most of the air of the vacuum bag and then start up the vacuum pump. Stabilise the vacuum pump at -1.5 bar and let it run for 12 hours. I use a cheap webcam to watch the pressure of the pump so that I can go do something else and occasionally check the webcam on my smartphone. The entire setup runs over a timer that automatically switches off after 12 hours.

When I was cleaning up after bagging the 2nd wing I noticed the appropriate newspaper article used to protect my workbench (see last picture :-)).



Start building season Winter 23-24: Wings of the Diana4

The summer weather is still not showing signs of coming to an end and I’m trying to squeeze out as many hours of flying as possible. Shorter daylight hours however provides an opportunity to use mornings and evenings to start preparing for the coming winter’s projects. l’m expecting a nice Chocofly surprise in the next few weeks/months that will have priority, but shouldn’t be too much work. The main project for coming winter will however be the Diana4, which I’m hoping to maiden in Spring 2024. Work on the Diana4 already started last year. The fuselage is as good as done (just need to fit the canopy): I also finished the elevator and rudder, built the wing joiner and prepared the sleeves.

The next step is building the wings. We cut the styrofoam cores for the wings at the end of last year. The original Diana4 will have a wingspan of 18m, that means that our scale 1:3.5 will have a wingspan of 5.14m. As my car is just large enough to accomodate 2.5m wings, I will build them in one piece.That makes the wings easier to build and, importantly, saves weight.

Today I started preparing the building board. I’m normally using an 18mm MDF board of 260x40cm to build the wings. For the Diana4 I have extended the board with another 30cm. I’ll also need to extend my working table to accomodate the longer building board (I’m using IKEA tabletops, which are light, incredibly stable and perfectly straigth). After preparing the board and table I started preparing the foam cores. Using a vacuumcleaner with a brush I removed the “angle hair” on the cores, resulting from the hot wire cutting. I also removed the last 4-5mm of the trailing edge of the wing cores to ensure that the trailing edge of the wings is nicely sticking together and can be sanded really thin.

Next step is to draw out the wing layout on the table and prepare the foam shells.

 


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 3000 grit diamond finish pad (also wet, by hand). Once that’s done the shine is already pretty nice. To finish it we use a machine to apply fast-cut compound and finish off with a machine polish. The products we use are shown on the pictures below (all 3M).


JS3 (Chocofly) Settings

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

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

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

Center of Gravity: 110m (or more)

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

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

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

Ailerons (values inner side wing):

  • Small: 5mm (up)
  • Big: 9mm (up)

Add (each separately over switch):

Flaps:

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

Airbrakes/inner flaps:

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

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

Elevator:

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

Butterfly/Airbrakes:

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

Camber settings:

Speed: 1mm up entire wing

Thermal S: 2.5mm down entire wing

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

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


Ventus 2c: back from the paintshop

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

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


EMB400 Urupema: Wolfpack on the Slope

On Monday we had a wonderful slope outing with three Urupemas.

The unanimous agreement among the three pilots was that we need to fly this glider more often. The “wafer thin” wing profile (7.3%) with full carbon layup makes for super speed retention and among the friendliest stall behaviour on planes I’ve flown. It also allows for lots of camber to squeeze every last bit out of those thermals. This is a glider of contradictions, super friendly to fly and yet also scary as it picks up speed so fast with a bit of down elevator (even with full camber) and retains speed so long when flying figures.

Some new pictures of our slope outing below. Some earlier videos can be found here:


 


ASW-20: Maiden flight

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

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

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

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