Back to flight, the tale of a wrecked Isaacs Fury

[Anyun]

This peanut was built many years ago by Lars T. While it flew well it had a short active life, as the laminated wing tips and tail outlines were not sturdy enough. A few years ago he gave the wreckage to our model flying club in the hope that someone might bring it back to life.

As can be seen from the photo the model was quite thoroughly wrecked, and over the years parts had gone missing, but it still seemed possible to resurrect the model. So let's begin the tale of the Fury that lost it's tail (together with quite a few other parts)

/Andrea

[Anyun]

After the covering had been removed, it was evident that the wings were past rescue, the structure having been broken or warped in too many places. The fuselage however seemed in a better condition. Here the damaged parts have been removed and the broken upper longerons spliced with new strips

[Anyun]

..and here the structure has been fully mended. Lars had used paper (or very thin cardboard) to make the curved parts of the fuselage. The rear part was undamaged so i kept it, and decided to use the same technique to recreate those parts that were damaged and had to be removed.
I used thin paper (about 40-50 g/dm2, thinner than normal copying paper). It was sort of okay-ish, but the paper was a bit too thin and sensitive and I couldn't avoid getting some wrinkles and creases.

[Anyun]

In an effort to fix things, I covered the paper with tissue. It was patently unsuccessful. In addition to increasing the weight, it also increased the wrinkles. The incredulous pilot inspects the work and gives his opinion - Do you really expect me to fly in this ... thing!? I mean, shouldn't aircraft makers take some pride in their work?
Quite right mr Pilot, this won't do.

[Anyun]

So, off with the paper and tissue and start all over again. I had the idea to try using drafting vellum. As an idea it was not bad, the material was easy to work with and the resulting sheeting looked very good. Now, what will happen when you cover the rest of the fuselage with tissue? Well, as paper tolerates acetone and this paper is covered with some plastic looking material that looks impervious to water, surely there can't be any problems?

Turned out that reality was quite the opposite. Where water droplets had fallen (from the water shrinking) there were small pockmarks, and where the material had been subjected to acetone (I use the dope/acetone method to fix the tissue) there were larger pockmarks.

So, off with the paper and tissue and - pick yourself up, dust the table off and start all over again

[Anyun]

Well, third time's a charm. Now I had the idea to dope tissue over the thin 40 g/m2 paper, and use this laminate to form the sheet parts. This idea actually worked.
I used a grey tissue and the resulting look would be quite fine for imitating sheet metal without painting (however, this model will be painted silver all over).

[Anyun]

I the mean time, the tail surfaces and the lower wings had been made. The stabilizer unfortunately warped a bit after shrinking and doping. I made a new one, and took the opportunity to increase it's size to about 110%. The first one had scale size and looked a bit tiny, and Lars told me that the one he used had been enlarged.

[Anyun]

And here's the upper wing. I had got some small wrinkles at the rear end of some ribs on the lower wings, and to prevent this I added triangular braces at all the ribs on the upper wing. This might or might not be worth the effort.

[Anyun]

After everything had been painted (it's silver all over, so no problems here), it was time to put all the pieces together. First the central wing struts were made. They consist of 1 mm carbon fibre rods that fits into holes made in the fuselage and wing structures. The carbon rod was clad with balsa and the struts then covered with tissue.

[Anyun]

Time to mate fuselage and wing, and now things are beginning to look a bit more aeroplaneishly. The part of the rigging that can be done without the lower wings in place was also done now. The rigging wire is some flexible thread sold for model building purposes. It is easy to work with and most importantly, its flexibility prevents the whole thing being ripped apart if the model lands in high grass.

The rigging is threaded through small eyelets made of thin copper wire that has been anchored to the structure. To thread the wire, a simple "needle" made of thin copper wire was used, as shown in the last photo. It's just a length of wire folded over, the rigging wire can be fixed in the fold and the needle can then be used with fingers (if there is space) or tweezers (if not).

[Anyun]

And finally, the upper wing in place and (partially) rigged

//Andrea

[g_kandylakis]

Hi Andrea, welcome!

Yes, it has been a few years... great to have you here.

Quite n undertaging putting this back together, looks like a very good job, I hope Lars does not ask it back in the end.

George

[OZPAF]

Thanks for your interesting account Andrea. I was wondering if a tissue over 20g/m2 glass cloth - bonded with minimal epoxy would work as a replacement for the paper that you used.

I laid up a section as an experiment and apart from being light - it is quite flexible, but I didn't know what to use it for at the time. A rough estimate would be around 46G/m2(including the epoxy on the glass) - similar to the 40g/m2 paper that you used.

John

[gravitywell]

MAN.....talk about perseverance!

[Anyun]

Thanks for the comments!

John, that was an interesting idea with the tissue/glass cloth combination, it might actually work well for this kind of application. What kind of surface finish did you get, was it flat or did the glass cloth texture show through?