question on rust pits on outside of tubing.

[tim bandy]

one of my pacers (the better one) has some rust pits on the outside of the lower longerons.
I have all ready replaced the last 3 feet at the back by grafting new tubing.
up forward between the pilots and rear seats---- near the piper splice--- there is some fairly deep pitting.
However-- the pitting looks old- and it appears that it in on the tubing that has the inner liner tube of the piper splice inside it. So the tubing is "double walled" there. There is also a cluster pretty close there too.

4313 says something about a limit of 10% of the tube wall for pitting. 10% of .035 is just .0035.
Thats not much of a pit. I often hear about the recommendation of doing the "punch test". That does not seem consistent with seeing .0035 pits and failing the area. This area looks like it could be bitch of an area to cut out because it is so close to the cluster there. I suppose I could weld on a fitted diamond shaped
scab patch--- it just wouldn't look that good under the fabric.

does the fact that the tubing is doubled up there at the piper splice mitigate the depth of the pitts any
as far as how an IA would look at it ? They look like they could be half the depth of the tube wall.
Looking for some real world advice here. I think its been flying that way for a long time. Of coarse that doesnt make it right -- OR-- safe---- and since Im stripping and sandblasting-- now is the time for remedies if there ever was one ! (also doing the SB 819 - and removing the sheet metal- so i'm down to the bone... ) Been trying to get a local AI to come give me an opinion---- but cant seem to hook up with one---
Thanks--- Tim

(the "normal" virtex's at the corners further back aern't so bad to cut out because there are only 2 cross tubes to deal with. But that cluster i aint looking forward to cutting that bad boy out---)

[Steve Pierce]

I blast the frame and then use an awl in the pit and use a plastic hammer to tap the pit and see if it penetrates.

[tim bandy]

thanks Steve--
I might as well test that--- I have nothing to loose at this point.
I have at least one more section of the lower longerons to replace-- in the baggage area. appears it was in some kind of accident and the tubes were bent down (or in) there and then straighten out. Right at the bend point - that left a very small flat-ish dent -- even though they got the tubes back out straight pretty well. There are a few more of then within a foot of there that may have happened at the same time. I'd like the AI to look at those too. Slightly out of round with some flat spots that look like about pea sized- also looking like a remnant of old bends that were straightened out.
does that sound like something that would fail the tube there ? (require at least one of the approved repair methods)

Tim
Will try the punch test on those pitts. On the other plane I see punch marks with some through. but I can see its longerons are toast all the way stem to stern.

[Steve Pierce]

Calibrate your elbow on a new piece of .035" tubing. I go by AC43.13 on the dents. If a tube was bent and then straightened I would replace. I have patched very small dents but a bent tube has compromised the structural integrity of that tube.

[tim bandy]

Yes--- on those "straightened out tube" caused dents----- My intuition tells me that that section would have much less
strength in compression now-----like flicking the side of the soda can that someone is standing on.
it looks like it was the longerons in the baggage floor. Those shouldn't be too hard to splice in. No huge clusters there.
I can practice on some of the tube I previously cut out that still has good wall.

I will have my local IA look at the cluster with pits. have to get him anyway to give me an estimate on the paperwork mountain. (he may laugh me out of the room )

FYI----- about 2 years ago Univair said they would charge 475$ to re-issue the gear conversion STC paperwork that has the N-Number on it. Just after that- the owner- 2 owners ago sent me the receipt where it was ordered from Univair. So at least I can prove Univair sold it to the plane now. I saw on their web page --- NOW---- that same paperwork is only 140$.
What do you suppose happened ? (before all I had were pictures of my gear--- and they said it looked like their product---- but Now i have the receipt...)

That doesn't seem like them to lower the price of anything...... do you reckon too many people complained?

tim