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Sopwith Camel – Spanning the Frames

Continued from: Sopwith Camel – Building the Frames

I recalled from my model airplane building years ago that covering the frames with silkspan (essentially tissue paper) was another fun step.  I remembered gluing the tissue to the frames, spraying the tissue with a water atomizer to shrink the tissue tight, and then applying multiple layers of airplane dope to give it a hard as “canvas” finish.

When I read the instructions, I saw that there were actually two different techniques available:  the dry method I was familiar with and a wet method I had not heard of where the tissue is dampened under a faucet and then glued down wet.  When I read the details of the latter, it seemed much more complicated and given that the wet tissue would be much more susceptible to tears when smoothing out the wrinkles, I decided to go with the tried-and-true dry method.  But a pretreatment step I did not recall for either technique was pre-doping the balsa wood to prevent the dope being used to adhere the tissue to the frame from just being absorbed into the wood.

The instructions indicated that the clear dope should be diluted 50:50 with thinner to make it dry faster and then three coats should be applied.  I mixed some dope with the thinner I had (which interestingly looked like milk, a type I had not seen before), but as I stirred to mix, the dope clumped together in a gelatinous mass.  I figured the paint thinner I used must have had some immiscible ingredient in it and so I quickly ran up to the hardware store where I found traditional water clear thinner.  But, when I mixed this new thinner with the dope, I got the same clumpy result.

I assumed the dope formula must have changed over the years and the model instructions had not been updated.  So, I decided to apply it undiluted but since I did not have enough dope left to treat the whole plane, I next had to run to the hobby store to buy more.  When I arrived, I discovered they had none, but they did have a dope sander finisher.  Only its instructions called for five coats followed by three more on top of the tissue.  This seemed to me to be quite excessive.

Figuring that the different instructions were aimed at ensuring the finished model would be fuel-proof (something critical for the kerosene-like fuel used in flying models), I decided I would scale back this approach since I was simply building a static model.  Opening this new material, I discovered it smelled just as bad as regular dope and so I had to paint it onto the frame outside.

Suffering through a July heat wave, I found that I could only apply a single coat over the entire frames early in the morning before the heat and stench overcame me.  Lightly sanding the frames after the dope dried, I applied two more coats to be sure the balsa wood was sealed enough before trying to glue on the tissue.

With the heat wave continuing over the summer, it was not until the second week of September before it was cool enough for me to venture back outdoors for the next step.  Since it had been many years since I had done this step, I decided to start with what should be the easiest frames to cover, the tail sections of the plane.  Also, due to their small size, I figured if I messed these up on my first attempt, that it would not use very much more of the tissue on a second attempt.

I was a bit timid in this first attempt and had to occasionally add additional dope to get the tissue to adhere to the outer surfaces of the frames.  Following the instructions, I then tried to stretch out any wrinkles.  I then left them to dry outdoors.

Before attaching tissue to any other frames, I decided to atomize the dried tissue with water to make sure that it shrank enough to give a tight finish.

All but one tail section dried very taut so having to redo just one didn’t seem too bad given the many years since I had done this.

I next started on covering the fuselage.

It was to be covered in individual sections, no doubt since it was tapered from front to back which would leave numerous wrinkles as less and less tissue was needed.  I did a few sections and began to feel more confident.  I did learn that once the dope dried, you had to be very careful when trimming the excess tissue not to cut into the overlapped tissue sections already finished (which I did more than once).

As I was adding tissue pieces to the frame, I decided to try one of the lower wings (since it was shorter than the single piece upper wing).  The instructions indicated that a single piece of tissue was to be used for top and bottom from the inner most rib to the outer most rib.  This was to be my biggest challenge getting all the wrinkles out of such a large piece.  Once attached, trimmed, sprayed, and dried, it came out fairly good, but part of the top still wrinkled.

I decided to try to first respray the wing to see if the tissue would shrink up anymore but that didn’t work so then I thought of patching the wrinkled part to avoid having to redo the whole wing.  I began to wonder what kind of “fun” I recalled in doing this step.  In the end, I decided to redo the whole wing since I had more than enough extra tissue and I really didn’t want a “patch job.”  I guess you get plenty of tissue in the kit just for such occurrences and this of course, extended my “fun.”

Meanwhile, for the second lower wing, I decided I would try a different approach.  I figured if I first attached the single piece of tissue to the leading edge and let that dry, then I would have better leverage to pull the tissue taut over first the bottom and then the top of the wing.  I did this but then did not trim the excess tissue until after I had sprayed just in case, I needed to re-stretch any part.  This approach worked much better.

I used this alternative approach for the top wing also and it worked just as well.  In fact, once I had the wings covered and trimmed, I recalled the reason I liked this step so much from my earlier days of building balsa wood model airplanes—it reflected a realistically finished wing.  Just like the real thing, the interior of the wing was made of wood and the tight tissue covering was akin to the tight canvas on a full-size airplane.

With all the frames now covered with taut tissue, …

…the last step was to apply several coats of clear dope to get that tough canvas feel and then move onto the next assembly step.  But then the unexpected happened.

      To be continued…

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