Now, this picture spells trouble.
This is an image showing the rear control column assembly with airelon tubes. The bad news is that the back wall of the image is actually the rear spar of the center section. What is evident is discoulouring of wood and rust on attach bolts. That means that there is significant trouble there. So, not only that the system was stripped, the whole center section went down. More about the center section in a later post.
You can see the fuselage above in our rotary jig. Handy little thing. We have some improvments planned to make it even more versatile. Anyway. When the center section was off, another thing started our thinking process. Can you see that there was a repair made on the frame where the front spar of the center section attaches to the fuselage?
Here is another image of it. It is a patch repair. Not really up to AC-43B standards, but it means that the original plywood cracked and somebody scarfed in a patch to repair it. Now, what really got my attention is the fact that both sides had these patches and moreover, this patch again cracked. On both sides. Something was definitly happening there.
So out went the panel to see what was really happening under there. The fuselage is of course now upside-down. This photo shows Janez Cestnik - Cec - master aviation wood worker. He is one of three founding partners of aereform ltd. His cabinet making company has been running non-stop since 1902. Before Wrights, and way before Rusjan brothers. Enough said.
And here is the root cause of cracking skin. The longeron was actually delaminated from the frame. This frame is the most stressed frame of the whole aircraft. It caries both flight and ground loads from the main spar. The corner blocks were just not adequate for the task. On the image below you can see the longeron could be pulled from position by hand pressure. Therefore any patch that was made on the skin was just fixing the consequence, but not really the root cause.
On the other side the process was repeated.
And the same thing was discovered for the lower longeron. Look at it go!
The remedy was to install new corner block, consiledatining the joint and off course scarfing in new skin.
With this lesson in hand, we took a hard look at all the corner blocks in the fuselage. Some were already showing an extent of what was happening on this extremly stressed interconnection above. So the decision was made to replace all of the corner blocks. A bit of work again.
On the above image you can see the fuselage is already sanded. Spent a few cosy hours in there (somewhere around 30). More on the sanding of the inside of the fuselage later.
And when we were at it, we removed and installed new bottom skins. The old ones were oily from the residue oil flowing off the firewall.
First, since the fuselage was opened up and acess was easy, some wooden details were taken care of.
Like this flange that I made for the external power socket
Or this sequence of images showing the tidying up of rudder pedal attachment points
After these details, the skins were installed. In my opinion some of the best work so far done by Janez on any given aircraft
When the old skins went off, so did the engine mount bracket support. The locations are penciled out in the photo above. New ones had to be made. Janez came up with this absolutly genious way of making them. Try to figure it out from the series of images below:
More later.
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