https://fmh.club/2016/06/27/bespannen-eines-rumpfes/
27 June 2016 by Herbert
Covering of a fuselage
Here in the workshop blog, I would like to describe how we can handle all the work. As the fuselage of the DFS Kranich 2 is coming, here comes the description:
We have used the following materials:
CECONITE 102
IRSA Klebelack (adhesive varnish)
IRSA DD-Lack (DD-varnish)
IRSA DD-Härter (DD-hardener)
IRSA Spezialverdünnung (special dilution)
Preparatory work:
The fuselage was spatulated and sanded. Then, it is released with the compressed air, in order to remove all the dust. Now, the IRSA Klebelack (adhesive varnish) is diluted with 30% IRSA Spezialverdünnung (special dilution). Then, you can paint with brushes with black bristles, so that it is easier to find loosening brushes. After that, you should let the layer sufficiently dry. Therefore, we try to postpone covering actions always in the warm season. Applying of the varnish should always take place outside, as the evaporation steams are not really healthy. After approximately 2 hours in the heat, the second undiluted layer can be applied. Always apply quickly, as otherwise the previous varnish coat can scratch off again. After this, we let it dry for one day. Coat 3 and 4 now follows. After the fourth coat, the fuselage should now have a slightly shining surface. The parts which are still mat get a fifth coat.
Covering:
Normally, CECONITE 102 is used for gliders. It covers 92g/m2 and is sold with a width of 182cm. We now put the fuselage on one side. Then, we stroke with the hand palm over the fuselage. Once for the love to the glider, but especially to feel dust inclusions, tears and brush hair. No matter how small the imperfections are; they have to be equalised. After that, we roll the CECONITE 102 lengthwise onto the middle line. Now, the middle line is adhered to the CECONITE with IRSA Spezialverdünnung (special dilution). Until now, do not tighten it too strongly, but crease-free if possible. Then, you work from the middle to downwards. You always have to work in segments. This means we create squares which are adhered onto the edges. If the dilution is evaporated and the parts feel dry, the segment can be made crease-free. The best way is to carry it out with the hairdryer. But not too hot and not too close. Otherwise, you better use the iron. When the segment is smooth, apply the dilution with the black haired brushes again with IRSA Spezialverdünnung and press the CECONITE with gloved hands. Always work piece by piece, always consider the whole, otherwise, there is one place with great creases which have to be cut in. The CECONITE is shrunken with a hairdryer, in order to avoid this. In this process, hold the free end with one hand and pull through the trunk edge. Now, remove the crease with the hairdryer and when it is beautifully smooth, rub in with IRSA Spezialverdünnung. Firstly, let it get cold, otherwise the dilution evaporates too quickly. It can burn, if the application is badly carried out and the dilution is used during hairdrying. You can also carried it out with the iron, but this will last too long and creases can occur. If creases occur on the surface which is already finished, you can carefully get rid of it and avoid high temperatures and iron. This does not work for fillets! The challenge on the fuselage are area transition, fuselage tip, rudder transition, i.e. all parts which have kinks, fillets and narrow radii. There you must have a lot of patience and dry as described above, i.e. process piece by piece. If nothing helps, you have to cut. The occuring impacts are filled out by us, but only very thinnly along the line – do not fill out the whole area. We tilt the edges onto the other side. If the cover is applied onto the already covered side, the approximately 5 cm adhesive varnish must be applied again. Otherwise, the edge will not be supported. Finally, a layer of adhesive varnish is applied. The LBA required that CECONITE is embedded as artificial fibre. So, do not forget!
Varnishing:
If you have worked properly, you can varnish now. As described before, the fuselage can now be touched with a lot of love, so that you can feel imperfections and foreign objects. We use the IRSA DD Lack after discussions about the colour tones have been finished. Although the selection of colour tones is limited, we mostly mix the suitable tones from the available base colours. A mixing table for different quantities results through the resin scale. EXCEL made it possible. Recently, the colour tones are ready mixed at IRSA. IRSA also offers to create a special tone directly on request by the customer. Simply, ask IRSA: 004982828944-0. When varnish and hardener are mixed together, the viscosity is adjusted with IRSA Spezialverdünnung. We spray with a 1.4 mm jet. Applied too thinly runs but applied too thickly does not run and depends on the ambient temperature. After time, you have to develop a feeling for it. If decorations are required, sand the parts of the under varnish where the decorations are applied. We use the 320 wet abrasive paper. Then, mask and paint or spray the strip or pattern. Before the varnish has already dried, remove the adhesive tap. If you do this one week later, the edges will become frayed out. At least this happens at our house. We also use foil from the sign maker for some samples. It is easier.
Now, the most important thing:
Now, work through all Material Safety Data Sheets before starting work and only work in very well ventilated rooms. Use nitril gloves (the others dissolve) and, if available, also use an active carbon mouth protection. Do not get too close with the hairdryer which should have a temperature adjustment, because the adhesive varnish burns like tinder. And take your time.
The report is only a listing of the working steps how we do it and not a working instruction. In general, we do not guarantee any liability for possible damage.
Herbert Kersten
