Building a 2m Duo Discus

[joe yap]

I've been fascinated by scale gliders since years ago. I own a few glass slippers by now but they are a little too expensive to do some experiments on. I longed to try aerotowing and also wanted to try to fly a scale glider at Sedili. I wish for a cheaper and smaller plane to start off with but with so many uncertainties, I decided to scratchbuild a 2 metre scale Duo Dicus.

Since the airframe is meant to be sacrificial if any mishap were to happen, I decided to go for blue foam construction for the fuselage. As for the wings, the most accurate method of building such narrow wings that I'm capable of, is of balsa sheeted white foam wings.

I have a piece of 2" blue foam, but the flatness and surface finishing is far from perfect. There will be a lot of preparations prior to hot wire cutting the basic fuselage profile. But before all these, the first thing to do is to cut the templates.

The plan is drawn with Autocad and printed in A4 sizes. I aligned the A4 sheets with a steel ruler, pinned them down and joined them. The patterns were rough cut, sprayed with 3M77 and pasted on hard cardboards before being cut into the individual templates.

[joe yap]

The basic side profile templates were cut and so are the ones for the plan profile. The fuselage will be made from 2 foam blocks on each side and later joined with epoxy. The 2 blocks of blue foam were rough cut out using a penknife.

[joe yap]

If you look into any piece of blue foam you bought at all angles, you'll realised that there are hardly any edge which is perfectly flat. Some even have very rough surfaces. You can't start off cutting the profile with foam blocks like these. You'll need at least 3 flat and square surfaces.

To achieve that, I use templates to cut the first straight edge with aid of an engineering square. After this, this surface is used as a datum to hotwire cut the other faces of the block.

Only after achieving a flat and square block, then it's possible to build a fuselage as straight as possible.

[joe yap]

Using the previously cut flat surface as the datum to align the templates, The plan profile is being hotwire cut on the 2 foam blocks. After removing the templates, the waste materials are coated with 3M77 and tacked back to the basic fuselage blocks. The 2 blocks are also joined with 3M77 after cutting. This is necessary as it'll provide a square and flat surface to mount the templates for the side profile.

[joe yap]

With the templates pinned in position, the side profile is hotwire cut. Note that the holes for the wing joiner tube and incidence pins are marked and cut from the templates. The hole for the wing joiner tube is hotwire cut out and the holes for the incidence pins are simply drilled into the foam block. This is to ensure the correct aligment and positions of the holes, before the fuselage is being shaped. Once the templates and the waste foam are removed, there'll be not datum surface to ensure the correct alignments.

[joe yap]

At this stage, you'll probably be very tempted to remove the waste foam from the basic fuselage block, but there's something else need to be done before doing so. Any cuts that require templates are to be done at this stage before the foam wastes are seperated, or else it'll be very difficult with no more flat surface as a datum.

[joe yap]

For this case, it's the canopy cut out. The template if arranged as such is the cut is made less than perfect, it'll only screw up the canopy block instead of the fuselage block itself. There are 2 choices of making the canopy. You can use back the foam block as the canopy itself, or you can later mould it from clear plastic. Either way, the canopy block is also coated with 3M77 and glued back in position. It'll help when carving the fuselage later.

[joe yap]

With all the basic cuttings done, now it's the time to seperate the fuselage block from the waste. Looks good, isn't it? It's also straight, square and warp free. This will create a good foundation for carving and shaping.

[alamin2]

another amazing built by the man himself ~ joe!!

joe, pass me some skills of yours will ya ?

haha .. im still practicing cutting 5mm compressed foam

[joe yap]

With the canopy block temporarily glued in place, the entire fuselage is carved with a sharp penknife and sanded to shape.

[joe yap]

Next comes the vertical fin. The templates are printed, pasted on cardboard ( mounting board) and cut to exact shapes.

[joe yap]

Due to my anxiety, I forgot to snap shots of the foam cutting for the vertical fin. Anyway, this is the result. Pretty straight forward though. The rudder is then seperated from the fin.

[joe yap]

With some masking tapes, the fin and rudder are mounted on the fuselage to check for fits.

[mathsinstrument]

Man, rc would definately be cheaper with those hands on mine....
I am interested in non powered flights, find them very graceful and relaxing....

Great work out there joe.... Never fail to fascinate us..... Maybe one day you might open ur doors for disciples like me?

[joe yap]

I have already passed on my skills and knowledge to some modellors who are keen enough to learn. I'll be glad to guide anyone who is interested as I always do. This is not kungfu and so, there's no such thing as disciples for such hobby. My posts are meant to share the techniques I have adopted for my constructions, which anyone can easily pick up.