Corrosion Evaluation Help

In trying to restore an uncompleted, decades old project, some corrosion is
evident in the wing spars and as an old non-aero engineer, I would like to
know the basis or the process for evaluating it before proceeding.

The spar has stacked, rectangular-bar caps
riveted to a "C" shape web (as in the Midget Mustang designed by Long) with
the quantity and vertical size of the cap strips being reduced as
progressing outboard. IE: at root,(6)-1/8" thick x 1.5" high straps ending
with (1)-1/8" x 3/8" high near wingtip.

After becoming lost in several engineering design articles because some
critcal number or statement was either omitted brevity or not understood
(most likely), I gave up trying to mentally reconcile the tapered leading &
trailing edge wing-loading with the reduced caps of the spar.

Once again the lookers at my field G are divided over the necessary
actions to take with most saying "just clean up, paint to prevent again and
derate plane slightly from the designed +/-9 G's.

My problem is in trying to determine a "go-no go" approach. Although the
stacked (6) caps at the root have no corrosion, my gut tells me that a few
thousands of surface corrosion, not involving an edge or rivet, would be
repairable easily and not even require the proposed "G" derating.

It is out where the stacked caps are reduced in both quantity and height
where I exceed my "gut" G.

Any help would be appreciated. Thanks, Dick

Dick wrote:
In trying to restore an uncompleted, decades old project, some corrosion is
evident in the wing spars and as an old non-aero engineer, I would like to
know the basis or the process for evaluating it before proceeding.


Max limits we use is: 10% of the material thickness lost to corrosion
and you replace it. ie. if your part is .125", then if the material is
..1125" or less in any area, it gets replaced.

Craig C.

In article .com,
wrote:

Dick wrote:
In trying to restore an uncompleted, decades old project, some corrosion is
evident in the wing spars and as an old non-aero engineer, I would like to
know the basis or the process for evaluating it before proceeding.


Max limits we use is: 10% of the material thickness lost to corrosion
and you replace it. ie. if your part is .125", then if the material is
.1125" or less in any area, it gets replaced.

Craig C.


Usually, there is no corrosion under the lap joints of the spar. A
little phosphoric acid (Aluminum Jelly) applied, then washed off and
thoroughly dried should do the trick. I take it that the corrosion is
just surface corrosion, not intergrannular or filiform corrosion.

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If you are restoring it, why not take it apart and restore it? That way you
have piece of mind and know if there is any corrosion throughout or not.

Patrick
student SPL
aircraft structural mech