Building tips
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In this section I would like to share interesting building techniques that I have picked up along the way. One piece paper covered wing building instructions: (Sept 2005)Recently while attending the F3A world championships in France I had a chance to see one of those much talked about French design innovations. This new model I saw was constructed using unique building methods. The wing was constructed of foam, balsa false ribs, carbon fibre rod inserts, and finally covered with brown packing paper. This same paper is also used to wrap packages for post or shipping. So, I asked and was granted the instructions of how to construct a wing in this fashion. This was good fortune and I thank my friend in France (who knows who he is) for getting permission to send these instructions to me and also to translate them for me. This technique of building very light wings was perfected by non other than CPLR. These instructions I have just recently obtained are directly translated from French to English. I took the liberty of reformatting them just a bit. The weight savings is in using paper and white glue (which is water based) instead of balsa and epoxy.
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Above we see the internal structure of the one-piece wing in a drawing, and below we see an example of how it is supposed to look like when it is to the point just before paint. We can see that the wing constructed of foam core re-enforced with balsa ribs and carbon fibre inserts. Notice the color of the packing paper in use. This wing also has a very light custom made "pull-pull" system for the ailerons. I held it in my hands and found the weight remarkable. Also, it would appear that the wing is hollow which it is not. One is able to see in internal structure in sunlight. Wing Specs: Ready to paint, the wing weight is 615 grams with 2 servos included (Graupner DS3328 digital, 25 grams each) and pull/pull system installed. Wingspan is 1.80 meters, which may be a bit shorter than the norm but the weight of the plane ready to fly is around 3800 grams . The builder of this wing always tries to achieve something around 65 grams per square Decimeter (1 tenth of a meter) as wing load. For him, it is a good compromise for a plane to fly properly in any weather condition. So, he always determines the wingspan at the end after building and weighting all other parts ...and as he always builds very light, the wingspan can become shorter and shorter |
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Below we have a cook book style of step by step directions on how to build a wing such as seen above: To cover a wing with brown wrapping paper :- Coat the wooden parts with some white glue to have the gluing surfaces prepped for next steps. Let the parts dry . - Cut 2 sheets (back and front) of packing paper with paper fiber grain in length direction. Make sure to have excess so that a little bit would hang over the sides. We use the access paper to hang the wing in the drying phase. Be sure to hang the wing by the trailing edge with clothes pegs or office clamps ( at the end of the process) - Soak the 2 sheets of packing paper in a tub of water for ¼ hour (in the bathtub) Kick the wife out. - Apply a generous amount of diluted glue over all the paper. The paste, or glue is composed of a mixture of 50% white glue and 50% wall paper glue. The consistency of this mixture should be close to orange juice or rather liquid. - Make sure that all sheets of paper are wet and that the amount of glue remains consistent. - Lay the paper over the foam (shiny part of wrapping paper on the visible side )on both sides without pulling or stretching it too much . Just get rid of creases or wrinkles . Take care of getting paper stripes parallel on both sides .It prevents from warping…If necessary , apply some white glue on paper when some parts cover each other .. - At this stage , lay diluted white glue coat all over the wing. It will serve as a kind of primer you will be able to paint directly on to. Note that once this is dried take care that you do not use chemicals on the wing surface because it is only paper over foam . Chemicals such as Nitro would go right through the paper and melt the foam…. -Let dry slowly in the cellar without heating , climate control, lighting , air from window , etc …by hanging the wing from the trailing edge with office clips . The purpose of this is to have the thinner part (TE) of the wing drying first and so helping not to get a warp in the wing and having it look like a propeller….anyway ,even with a lot of attention , difficult to have a perfect straight wing at the end . But it is reported that CPLR flew with this default … Best to have humid conditions in construction phase like a cellar so that the wing dries slowly. - Wait for 48 hours . - Once dried , sand with 1000 grit dry paper to get rid of tiny parts of rubbish paper… -Ready to paint …
It is best not to add any harsh chemical tot he wing surface at this point to maintain good surface …In doing so, the outcome would certainly be worse than better. Fact is that it is quite impossible to have this method for making wings turn out as nice as with wooden surfaces however the goal is different in this exercise. The advantages of this method of building are: Cheaper and lighter than any other way of building. Material choice guide : Foam density : 15 to 20 kg/m3 (20 kilos per cubic meter) Important notes: To avoid possible structural failure: Tie carbon rod ends to each other with carbon string. Do this by first tying the two main carbon rods at the center of the wing and then finally the carbon rod behind the main spar should be tied to the main carbon rods. Do this to both sides of the wing panel. Also construct an I beam with the two long carbon rods and 5mm balsa plank. This will increase the strength of the wing. I'd like to thank Alain, Jerôme and the CPLR family who have supplied this description. I am told that CPLR's father is the pioneer of this method of building. Below is a shot of the wing in foam stage ready for the covering process
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