air space

Nylon vs Solartex

some thoughts from GEOFF GRAHAM

I don't know whether very much research/comparison testing has been done on these materials but there has always been lots to say vis a vis the comparative strength imparted to a model structure. However, I doubt that much of it was based on science and more on experience and prejudice.

I have used many different techniques and, like many others, I have learned by making what at the time seemed like disastrous mistakes. When the covering stage is reached the builder has already invested so much in creating the airframe and it is natural to wish to avoid risking spoiling the lot. Iron on, heat shrink materials have made for a much easier and in that respect, safer life as they can usually be removed quite easily if it all goes wrong. Going for nylon or silk can be seen as a risky option and of course the model needs to be a pretty substantial one in any case. To add to that fear of falling at the last fence we can add other more serious factors. Application of nylon or silk requires dope at every stage and anyone who has used it will know about the fumes given off. As a youth in the fifties, we only had tissue and dope to use as we could not afford large aircraft or silk. I actually loved the smell of dope but even then it used to make me sneeze for hours and I am sure that I never ventilated my bedroom when using it on whatever I was building. Today, in my 60's I can't even smell the stuff!!!!! Symptoms of asthma are brought about either by dope, Clearcoat fuel proofer, balsa dust or perhaps a cocktail of all three, I don't know for sure. Consequently, I wear a 3M's ventilated hood when doing much balsa sanding. Protection against fumes is a very much more difficult and costly thing to install so I try to minimise use of dope and Clearcoat. When the weather allows it, I apply these compounds outside my workshop in the fresh air. Another option of course made possible by the development of water based, acrylic materials is the use of sanding sealers which are solvent free.

As to the competing strength of nylon and Solartex, I reckon that the greatest quality of nylon or silk is the sure knowledge that it is comprehensively attached to the airframe. Doped on, if properly done it has to be so. On the other hand, iron on materials are frequently less securely attached. For that matter, the adhesion will vary across a single airframe. I have also found that the adhesive on for example, silver Solartex, seems to have a much lower adhesion factor than conventional Solartex. For these reasons I always, always apply BalsaLoc. As belt and braces, when I have applied one piece of iron-on, I then do the edges of that with BalsaLoc before applying the overlapping piece. I have been told that this practice is quite unnecessary but I would rather be secure in the knowledge that the covering is well attached and thus contributing real strength to the structure. Furthermore, I have much less trouble with edges lifting these days.

There is another material that I have used and it is still (I think) available. American in origin, it was a "nylon type", iron on, heat shrunk covering. The Nymph shown on the attached photos, has its wings covered in that material I BELIEVE - I say this because the model is nearly 20 years old and I might have recovered the wings in that time. It doesn't change the facts though. It was certainly originally covered in the material described. It was applied as nylon - doped on - and then heat shrunk. Thus it gave the benefits of both. It was securely fixed to the airframe and could be shrunk to a real drum tight tension. Super stuff. I have just seen an advert on pages 12/13 of RC Model World for April. Galaxy models are advertising some stuff called SIG Koverall and it sounds extraordinarily similar to the material used by me 18 years or so back to cover Nymph wings. I will get some soon and try it and then I will be able to say yes or no. If my memory serves me correctly though, I bought my original stuff from Blackburn Models.

Geoff's comments re Sig Koverall are interesting - I was seriously considering using this material for my Citabria, although I'm still put off by the necessity to use dope.

It is distributed in the UK by JP Perkins, so should be obtainable from most model shops. SIG describe Koverall as "a cloth covering of the type used in full-size aircraft, but in a lighter weight (1¼ oz. per square yard) for models. Koverall can be used on almost all R/C models - large or small. Its superior strength and low price has made KoverAll a real favourite with builders of giant size models. KoverAll is an uncoated, heat shrinkable plain fabric available in white only. It has no glue on it. To adhere KoverAll to a model, either dope it on using the traditional silk-and-dope method, or better yet, use SIG Stix-It heat-activated covering adhesive. Once KoverAll is stuck down around the edges, it can be shrunk perfectly tight with an iron or heat gun. Seal the KoverAll with 1 to 2 coats of clear dope and apply finish of your choice."

SIG KoverAll is available in three sizes - 36" x 48" sheets, £3.95 each; 48" x 72" sheets, £6.95 each and 48" x 5 yard rolls at £13.99 each. Six-It adhesive is available in 8 oz (·237 ltr) cans at £4.49