The plugs for the fuselage and the rudder are ready. Our shaper Richi has done an amazing job, as usual. The part where the wings join the fuselage was particularly challenging, as we will be using a pretty thin airfoil – unlike the original Elfe S3. With the wings sitting at the top of the fuselage Richi had to be creative in shaping that part of the fuselage.
Next step is building the moulds. We will probably only do the fuselage mould in Autumn – unless we are faced with a few weeks of non-stop rain. Georg has however started preparations for the mould of the rudder, which he will build. He will also be making four rudders for the four Elfes that we are planning to build. The wings will be in our usual styro-ebechi with carbon and glass layup building method.
Over the weekend I’ve been doing some background research into the Neukom Elfe S3 – in particular to find more information for the decals and cockpit for our Elfe. This post summarises the main points that I’ve found, as an effort to bring together key bits of information for further use as we work on our models. Note that Neukom was known for continuously improving/tinkering with his gliders, there are various versions of the S3, the below list also includes the S2/3, bot the x-tail and v-tail versions.
As far as I could find, in total 12 ELFE S3 (including a few S2/3) were registered in Switzerland over the years. Only two of these seems to be registered/flying in Switzerland still. Two were exported to the US and are still registered there. One is in the Transport museum in Lucerne:
HB-902, ELFE S 3 P, Baujahr 1968 Werknummer 18: still registered, stationed in Schmerlat
HB-903, ELFE S 3 P, Baujahr 1968 Werknummer 17: removed from the aircraft registry on 16 August 2012 following serious damage after outlanding on 4 August 2012. Official incident report (p. 41-42)
I’m still looking for good pictures from the cockpit. Below are two screen grabs that I took from the 1968 TV documentary.
Addition 3/3/2025: our club colleague Willy W. obtained a further picture of the “old” cockpit of the HB-902. Apparently it’s been modernised now, and we hope to get a picture of the newer version as well. I’ll be adding pictures below as we receive them.
Addition 12/3/2025: our club colleague Willy W. now also obtained a further picture of the current cockpit of the HB-977. I’ve added the picture below.
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:
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.
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.
We’ve started a new project with our building team: the Neukom Elfe S3. The Elfe S3 is a 15m glider, designed in Switzerland by Albert Neukom. It was first flown in 1966 and entered production that same year.
We are not aware of any recent scale models of the Elfe S3 in this size and, as usual, we don’t have much in terms of original plans to work from. Thankfully the glider compendium of Martin Simons (1965-2000) contains a good A4 drawing. I’ve had this drawing enlarged to full scale, so that our building team member and plug builder Richi can start work on the plug for the fuselage. Georg has started designing the wings. We are likely to build the moulds for the fuselage in Autumn 2025 and the first models in the winter of 2025-26, in the hope that we can maiden our first Elfe S3 in spring 2026.
We will be building a 1:3.5 scale version, so a wingspan of 4.28m. The airfoil will be our trusted MH-32, at 9% (1.7% curvature). We’ve been using this airfoil for our past few builds. It provides an optimal mix of excellent thermalling, speed and agility. We will also use six wing control surfaces and no air brakes. The tailplane will not be all-moving but we will use an elevator. We will also use a retractable gear, like the original.
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