Fabric finishing

...is actually not only about fabric. In this blog post I will try to illustrate why.

First let's start with a very nice picture. It shows the fabric samples taken from the old fabric. The Aero, as you might recall was painted in olive drab/dull gull gray scheme, when it came to our shop. But then when removing, various pieces some original fabric started to reveal itself. This is nice, since now we prepared samples of the original colour, best of all, which had never been exposed to daylight.

Next stop, paint store. Expensive stop actually!

But the colours are nice, aren't they?

On the raw fabric several coats of varnish or dope must be applied. Some of them by brush and some of them with a spray gun. It is quite easy to get white blush on the parts when applying the varnish with the spray gun. It looks like this:

This is white blush. The fabric is a bit whiteish instead of being transparent. It occures when the varnish is evaporating so fast that it traps the moisture from the air. It must be corrected by a special procedure. (Yeah, it was!)

The last varnish crosscoat is applied using a mixture of varnish and aluminium powder. This gives the parts an UV protection. At least it did so in the past, but now it is used for authenticity.

Aluminum powder gives the parts a silvery finish.

Now, again, this moves at a fairly rapid pace. What eats away hours is the detailed fitting. I will try to illustrate this on example of the elevator control attachment.

The elavator is on the left.

During intial fitting of the elevator control horn, you can see that the fit was not all that hot. But acceptable?

So what is wrong above? If you zoom in, you will notice there is a gap between the flange and the fabric surface. This gap is actually unairworthy. Why? Below you can see the picture of the original horn that was removed from the aircraft. If you zoom in again on the flange, you will notice that there are several cracks around the flange. These cracks are circular and are the result of the fit that was simmillar to above. However when you tighten the bolts it tries to pull the flange upward and the flange cracks. If not immediatily, then eventually.

So having to rebuild the horn during the restoration, we didn't want to do it again, so we produced a plywood shim that enabled us to tighten the bolts, press the flange down to the fabric, but not do any damage  at the same time.

The plywood shim is installed between the horn and the fabric.

Of course this is not just a thick piece of plywood, since it must conform to the elevator radius.

You can judge the shape by the sanded off layer of the plywood.

And here you can see the elevator horn and the shim, correctly installed. It took about two hours to get this right. Longer then five minutes to install it improperly, but beats having the part fail!

Installed, view of the bottom.

...of the top.

Overview

And everything tucked away avaiting the very near painting. Strech foil is used to keep the finish layer somewhat checmically active to asist in bonding to the paint.

See you next time!