| After a considerable break from model building, and somewhat impoverished, I was horrified to find that the price of covering material appeared to be prohibitive. Various plastic coverings seemed to start at $30 a roll, and that neither wide nor long! As a student of the Reverend F. Callon’s book, “ABC of Aeromodelling” (or was it “Aeromodelling for Beginners”?), I have always been a stick and tissue man. Tissue was easy to apply. Just paste it on with boiled flour or “Clag”, water-shrink it and then apply Dope, being sure to pin the wing down at each operation to avoid warps. Many colours and different weights of tissue were readily obtained and of reasonable cost. “Modelspan” was my favourite, which I believe was an English brand: American tissue was also there to be had, but it didn’t shrink the uniform way the “Modelspan” did. Up until recently, I had quite a library of tissues, but these disappeared or were used up rather too quickly. So it was off to find some tissue from the Hobby Shop. Shock Horror, it was $4.50 for a single sheet! It was going to cost me the best part of $50 just for the tissue on a large F/F wing! Outrage! Considering I often fly over wheat stubble, this was as expensive as yachting! The new plastics resist puncture, but I did not like their properties at all. My structures required a taught covering for their strength, and the plastics did not have it. At the 1971 Nats in Northam, WA, final round of A/2, Mike Pettigrew only needed 120 seconds to beat me out of first place. At 110 seconds, he was still 50’ up and I was a gone goose. But then his plastic covered wingtips suddenly fluttered, and his model dived into the ground to give me the win! So much for plastic (and divine intervention!). After the 2005 Australian F/F Champs, I found myself in Canberra, visiting my sister Isobel. For some reason, we visited a textile/fabric shop and there to my joy and amazement I found what appeared to be a roll of heavyweight black tissue! It looked the same, random weave, and ripped just the same as tissue. It was in fact Vilene, a plastic concoction used by dressmakers. It was never going to water shrink, but the open weave suggested that it would certainly shrink when doped. However, its big selling point was the price: $5 per square meter, just a fraction of the price of tissue and plastic. I bought 5 metres each of black and white and put them to one side, in my pile of useful-in-the-future items. Recently, I visited another fabric shop, this time Textile Traders in Perth, and found lightweight Vilene at $3 for 5 metres (!) on special. Now I was ready to cover my proof-of-concept new F2B design, and I wanted it to be black. Perhaps this was the time to drag out the heavyweight Vilene from Canberra. The new design had carbon-capped ribs for rigidity, the carbon glued on with balsa cement rubbed through a single 12K roving. Not a very neat arrangement, but it meant I could glue the Vilene direct to the cap strips, again with balsa cement (Aeroflyte C23). This also meant I could dispense with spars, as the glued-on covering held the long, slender ribs in place very nicely. 
Now this is where the trouble started. I has no idea how much the doped and painted covering was going to weigh. However, as this design had no fuselage, flaps or tailplane, I figured I had some room for manoeuvre with respect to weight. In fact, the completed airframe with engine was only 32oz, less than half that of my poor old test-ship Firecracker. This is how the weight story emerged. The bare airframe weighed 556g. After gluing on the Vilene, and using the best part of 2 tubes of C23 in the process, the weight was up to 605g. One coat of Dope disappeared into the Vilene like a camel into quicksand, bringing the weight up to 635g. A second coat likewise disappeared, for a weight of 650g. This was getting out of hand, so I figured to finish the job with a thick coat of Feast-Watson polyurethane. This brought the weight up to 682g: but this too disappeared into the quicksand, so that another coat was needed and the fat old camel was up to 712g! Now this was a worry, as most of this was going behind the C/G, so I quit, leaving the surface finish with as much gloss as a shagpile carpet. It looked OK from about 3 metres away, so at least if I hid it from the stunt judges prior to the contest they wouldn’t know any better. 
Certainly the covering was drum tight. In fact, as soon as I started the motor the whole shebang sounded like a drum being pounded at 7000 belts per minute! Never mind, perhaps it would sound OK in the air. Well, its gale force winds and rain as I write this, so the reader will have to wait to see how the model flew. And of course, if it flies badly, you won’t hear another peep from me! 
Now here is the rub. That model has a 700 square-inch wing. The covering weighed 156g and would have been more if I had of persisted in getting a nice finish. But the Vilene cost less than $3, the dope was about $10, the C23 about $10, and the polyurethane about $4. The weight would have been a lot less if I had used the lightweight Vilene. My micrometer gave the thickness of the heavyweight Vilene as .0055”, while the lightweight was .0035” (the purchase docket showed “Vilene Tracing 1200”). I should have used the latter, but it was white. I should mention that the material also could be heat shrunk. I used my Ozito heat gun to shrink it, then doped more-or-less straight away. Rip-stop nylon kite and sailcloth, also heat-shrink, but quickly go slack again when they cool (also they cannot be doped). So what the heck is Vilene used for? Well some time back my Rosie made a silk wedding dress for her daughter: some 6 months later, after the baby was born, we were still picking bits of silk out of the carpet. The stuff just falls to bits when you cut it out. The idea with Vilene is that you don’t cut the silk out at all: you just back it with the Vilene and sew right thru the lot, with the pattern marked on the Vilene. Then the Vilene can just be pulled out from under the stitches, as it falls to bits, just like ripping tissue paper. Next time, I shall use the lightweight material. The Haberdasher tells me it comes in a number of grades, so it might be worth trying to find something lighter again. Well worth a try. |
