6 years ago, Thierry Martinet, a friend of mine who is graphist/designer decided to investigate with Gerard Prat, an experimented modeller, the possible use, for foam/veneer wing covering, of a material he was using everyday for his job: colored vinyl (adhesive film). This material is usually used for vehicle lettering, light-box advertising, decoration of flexible-face material or windowpanes, and those for both indoor and outdoor use.
The main advantages of the vinyl are the following: Brilliant shades and a large color selection, excellent life-spans and stability (between 5 to 7 years which is much more than the average life expectancy of our gliders).In addition they have good plotting and application characteristics. The thickness is between 0.07 and 0.09 mm and includes the glue.
The main drawback is its weight, which is around 90 gr/m2 where classical covering films are from 50 gr/m2 to 70 gr/m2 (Solarfilm, Ultracote, etc…). So we can tell that the extra weight is about 20 to 40 gr/m2. But now consider the absolute extra weight for a 3 meters glider for example:
The covering area for such glider will be: 60 dm2 x 2 (under and upper side) = 1.2 m2 The extra weight will be around: 30 gr/m2 x 1.2 m2 = 36 grams And finally, these 36 grams corresponds only to 1.5 % of the final weight of the glider (2.4 kg).
In conclusion, I would say that the excess load is minor compared to all the advantages of this covering material. But, I agree that at the beginning, it’s not really obvious to imagine that this material can cover entirely a wing, especially the wing tips. So, my objective with this article is to share with you the expertise of Thierry and Gérard (and they encouraged me doing so!). I just hope that septic people will be convinced at the end of this paper!
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There is lot of different brands and references of adhesive films, but they are not all well adapted to our application. The main vinyl brands we use are JAC and ORACAL. The best ratio price/quality for our use if the Oracal plotterfolie serie 651. Lot of different colors are available in this range. You can also have a look on the JAC Serilux product range. The standard packaging is a roll of 25 m x 0.5 m if you order directly to the manufacturer. I recognize that it can be a little bit expensive if you just want to cover a rudder or a tailplane! For 5 years now, french kit manufacturers sell this vinyl retail at a reasonable price (~ 2.4 £ for 1m x 0.5m). In the operating mode, we can distinguish 3 main steps, which are:
PREPARATION Like classical covering materials (i.e Solarfilm, Oracover....), the surface quality obtained will depend of your skills, of the wood type and the vinyl quality. A very good surface quality will be difficult to obtain with balsa (which is too soft), but will be obtained easily with wood veneer. The best result is obtained with the Aningre (Latin name: Aningeria ) which has the particularity to have a very strong surface and thin grain (its color is dark brown). Between these two extremes, the Obechi give also really good result, with a little preparation. Do not bypass this stage because the final result is directly linked to the care taken during the preparation. For the preparation of the wing surface, we usually use abrasive paper (commonly use with water but that we use dry, of course). It is very resistant and can be vacuum-cleaned some times before being thrown. But before sanding, it can be necessary to apply some filler cement, either to eliminate a large defect, or to make the wood fibers almost invisible. The ideal filler cement exists: Its aspect is comparable to the toothpaste. In all cases, the objective will consist in depositing what it is just necessary to fill in spaces between wood fibers. You will thus avoid a tiresome sandpapering. Unfortunately, I won’t give you any references because they are certainly different in each country. Small detail, which helps for the finishing: We intercalate between the hold and the abrasive paper, a piece of foam, very flexible, of approximately 10 mm thick. Thus we obtain perfect curves (even visible to the eye under oblique light) and an impeccable surface quality by using a grain from 320 to 350 for balsa, 250 for samba and 220 with Aningre. A sanding with thinner sandpaper does not bring anything better to the finish after the covering. If you have installed elastic flaps (using nylon ribbon), cut out and articulate the control surfaces (ailerons, flaps), installation of the A.F, etc. During its handling, the vinyl attracts any kind of dust (static electricity). The only solution is to transform yourself into a beautiful cleaning lady: Pass the vacuum cleaner everywhere in the room where you plan to operate. I personally use an ironing board as worktable because the cotton sheet, which covers the table, is less sensible to the dust. Outdoor or in another room, clean conscientiously your wings (and wing blanks) with an air compressor or a vacuum cleaner and finally with a clean rag by “whipping” the wings (and not by “rubbing”) in order to avoid new static electricity. Never use a wet rag to fix the dust, because the wood fibers will react immediately by inflating, and you will certainly have to redo the previous sanding operation. For the very final cleaning of the surface of the wings, simply use your hands: This is, for the moment, the best tool that we found, and moreover which is equipped with very efficient sensors! Actually, you will feel under your hand the least dust or roughness, which, if you insist, will disappear. The hand’s skin acts like a thin sandpaper (grain: 400 or 600). Of course, all these advises are also applicable with any type of covering materials, not only adhesive films. |
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Thanks to Thierry Martinet and Gérard Prat who made an exceptional job by doing all these pictures, I propose to you to see how to operate, step by step, as if you were there! Prior to the beginning of the operations, cut your 4 vinyl panels with the correct planform of your wings plus a few extra centimeters of margin (width and length). The longer your wing is (or if it is you very first covering using vinyl) the larger the margin will be. For example, 6 cm on each side (leading edge + trailing edge = 12 cm) for a half wing of 2 m is a good value. Begin with the covering of the under-surface. You can use the wing core blanks to avoid your wing to slip on your worktable, but this is not mandatory. Vacuum-clean
also the two faces of the vinyl panels before spreading it over the
under-surface of the wing.
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