concave area on forward RV-14 fuse.

While working on the RV14 fuselage I noted a concave area in the forward fuselage, aft of the firewall and forward of the main spar.
I am not sure if it is just my aircraft but I suspect not as the culprit is the F-01419 side skin stiffener. This is a formed .063 thou part that runs parallel, below the upper main fuselage longeron. It is fastened to the firewall and the main spar 1403 bulkhead. Note that the 1402 bulkhead is not installed in the picture. The 1402 bulkhead, clecoed in position did not get rid of the con-caved skin.



The picture below shows the gap in the skin at the location of this 01419 stiffener. The skin at the upper fuselage longeron and the stiffener lower then the one in question are straight and true. The curved nature of the missing 1402 bulkhead clearly shows that this area is not supposed to be concave, if anything it might even suppose to be convex, or push out, rather then in. The gap is not large but with paint applied it will most definitely show.



This particular part, as mentioned is made from .063, and as it comes out of the box it is curved in two directions. Clecoed in position gets rid of the curve in one direction but forces the part to dish inwards.
I am interested in what others have found in this area after riveting? A long straight edge extended from the firewall to the main spar bulkhead will tell the story.

Not really familiar with the -14 yet but if that is simply a formed angle, minor fluting could solve the problem.

Mel,
Prior to this, in previous builds, I had not had the occasion to flute .063 stock and although difficult, I was able to bring the left side into alignment. This got rid of the "dished" appearance of the skin in this area.

It looks like a friend with a shrinker would be helpful? We always like your input Tom. And of course yours too Mel

While many builders have not experienced the use of a shrinker, they are very nice to have. We have used one to shape the long curve on the longerons for a couple of RV12s and several tip up canopy frames.
Anyway I love tools and highly recommend trying one if available. You have to get a little aggressive or use a longer handle on 1/8 angle but it turns out perfect.
Larry

We had to flute the rather thick canopy rails on the early RV-6 tip-up.

I do have a shrinker/stretcher but I am concerned about the mode of action of the tool.
The "teeth" of the unit have to grab the metal and then the handle action pulls the metal together, at least in this application it would. I feel that the marks left by the teeth are potential stress points. The potential for subsequent damage is much less with shrinking then it is with stretching metal. When stretching metal not only do the teeth leave marks but the metal is pulled directly at those marks. With soft non-structural aluminium I do not believe this to be a major issue but with 2024 cracks can easily form.
I have limited the use of this machine to non structural parts, canopy faring adjustments, baffles, farings, etc. I used the tool on my engine baffles and after a few hundred hours numerous cracks have formed on the tooling marks left by the shrinker/stretcher. This is a worst case scenario with the associated engine vibrations but it does emphasize that caution should be considered depending on the application.
I can only speak to the issues I have seen with my shrinker/stretcher. Other units may use a different mode of action that does not leave stress marks.

They do make no mar heads units that do not leave teeth marks but they are NOT cheap.

Tom Martin said:

I do have a shrinker/stretcher but I am concerned about the mode of action of the tool.
The "teeth" of the unit have to grab the metal and then the handle action pulls the metal together, at least in this application it would. I feel that the marks left by the teeth are potential stress points. The potential for subsequent damage is much less with shrinking then it is with stretching metal. When stretching metal not only do the teeth leave marks but the metal is pulled directly at those marks. With soft non-structural aluminium I do not believe this to be a major issue but with 2024 cracks can easily form.
I have limited the use of this machine to non structural parts, canopy faring adjustments, baffles, farings, etc. I used the tool on my engine baffles and after a few hundred hours numerous cracks have formed on the tooling marks left by the shrinker/stretcher. This is a worst case scenario with the associated engine vibrations but it does emphasize that caution should be considered depending on the application.
I can only speak to the issues I have seen with my shrinker/stretcher. Other units may use a different mode of action that does not leave stress marks.

Click to expand...

I agree about the stretching part, kinda like outside loops versus inside loops? but shrinking within a common sense arena ? I do respect your input though as always. Larry