Fuel tank wear on bottom and front caused by rivets &...

My plane has approx. 370 hrs. and I'm currently doing my condition inspection and found wear pits on the bottom and front of the fuel tank:

1. There are two wear pits on the bottom of the fuel tank caused by contact with the two aft most rivet heads of the right most set of rivets on the baggage floor.
2. There is a wear line on the bottom of the tank caused by the front edge of the center rear baggage floor cover F-1206E (now F-00081 if an owner has the two piece version for leaving the fuel tank in place).
3. There are two wear pits on the front right portion of the fuel tank caused by two rivet heads from F-1204F-R that is attached to the center section.

My plans are to glue down strips of silicone rubber baffle material over all of the offending rivets and baggage cover edge. I may also try adding washer(s) between the center section ?C? channel and the front of the tank (F-1205 forward tank bracket) on one or both of the bolts (BOLT-00002) that secure the front of the tank to see if this will push the fuel tank away from the offending rivets in front of the fuel tank. Any ideas on how to better remedy this problem?

I suggest that all owners consider inspecting these areas of the fuel tank because although the pits are not deep, I'm sure that these will not take long to become deep. As much work as we all have put into these tanks, we don't want to lose the integrity of these and have to repair them. Also, no one wants to see anyone have a safety issue due to a suddenly leaking fuel tank. Note that not much wear can be detected on the rivet heads.

Could you take a few photos and edit/circle the areas of concern on the baggage floor and center section?

MartySantic said:

Could you take a few photos and edit/circle the areas of concern on the baggage floor and center section?

Click to expand...

I second that request.

I have done inspections on RV-12's with much higher time than 350 hrs and have seen none of the issue mentioned.

Tank wear and causes: description and pictures

I need to correct my earlier post. The two wear pits to the bottom of the tank are the worst pits and are pointed to with the sharpie pens in the first pic. There are actually six wear pits caused by the aft most baggage floor rivets (5) shown in the second pic. with the worst offenders shown by the pens. The third pic shows the wear line encircled in blue ink caused by the front edge of the rear baggage floor cover pointed to in the fourth pic. The fifth pic. has the pens pointing to the wear pits on the front of the tank caused by the rivet heads pointed to in the sixth pic.

A possible explanation for the two rivets in the last photo (that mount the ELT) is that I am pretty sure the plans call for flush rivets at that location (flush head aft side).

The rest I am not sure about other than if there is maybe something particular about your specific fuel tank. Besides contact with rivets, there is evidence of fretting from contact with the edge of the baggage floor cover. By design, the tank bottom should not be close enough for that to happen.

It would be helpful if you would cut and paste (BTW, thank you for taking the time to provide photos) everything you put in this post, and submit it as an official service difficulty report to Van's engineering (process described in the back of the RV-12 Maint. Manual).

Good job finding those issues. Thank you for taking the time to report and photo them so that we all can be safer. I appreciate your efforts.

Perhaps the popular obsession with not removing the fuel tank for annual inspection is not such a great idea
Just a thought
DaveH
120485

Maybe a thin sheet of cork underneath? Cork is often used to isolate fuel tanks from vibration / chaffing.

The last photo has my attention, those rivets on mine are squeezed rivets, those in the photo look like something other than that, nut sure just what they are.

Flush rivets not called for on ELT bracket

Scott-

Just riveted the ELT bracket on a few weeks ago and I do not remember seeing a call-out for flush rivets in the ELT bracket ... so looked at the plans. Page 31B-12 rev 1 calls for an AN470AD4-4 with manufactured head on the aft side towards the fuel tank.

Is this something we should be changing?

Thanks to all responders.

Don, the rivets aft of the ELT are dome head rivets (AN470AD3-4 or AN470AD4-4 by rev.: 1) per page 31-15 of the KAI.

John, I note that you are not the original builder. This of course adds a few unknowns into the equation. Random thoughts:

Those rivet heads do not look to me like I would expect. Maybe something not as called out in the plans?

Your tank seems to be sitting lower than it should. Maybe it was deformed during construction, like maybe overinflated during leak testing?

Possibly something non-standard about the rear support bracket?

I finally have had a chance to do some follow-up on this.... See comments below

jrich said:

I need to correct my earlier post. The two wear pits to the bottom of the tank are the worst pits and are pointed to with the sharpie pens in the first pic. There are actually six wear pits caused by the aft most baggage floor rivets (5) shown in the second pic. with the worst offenders shown by the pens. The third pic shows the wear line encircled in blue ink caused by the front edge of the rear baggage floor cover pointed to in the fourth pic. The fifth pic. has the pens pointing to the wear pits on the front of the tank caused by the rivet heads pointed to in the sixth pic.

Click to expand...

I have no explanation for the tank contact with these rivets. I am wondering the same thing that has already been asked.... whether it was possible that the tank was over pressurized during leak testing, causing some permanent bulging. This is not a problem that has been reported previously.





It appears that the dimples in the cover for the flush screws are not fully formed. I can tell this by the distorted reflection visible around the perimeter of the screw dimples. This will cause the panel to pucker between the screws. Combine that with what ever problem is causing the contact with the baggage floor rivets and you have contact with the edge of the cover plate also.





I was incorrect about the flush rivets.
The plans do specify on DWG 31B-13 to use AN470AD4-4 with the manufactured head located aft as is shown in the above photo, but it looks like the wrong (3/32" instead of 1/8") sized cupped rivet set was used which caused the manufactured head to bulge.

I think Scott has come up with the reason those rivet heads look strange. I never thought about it before, but I suppose setting with the wrong die set could concievably squeeze material upward, making the rivet head proud. Suggest you measure the height of those rivets and compare to correctly set rivets.

As to where the bottom of the tank contacts the floor, if that turns out to be caused by a deformed tank, it might be permissable to pad the gap with some rubber material so you dont have to replace the tank. Suggest you consult with Van's on that one. It will put some minimal pressure on the baggage floor.

How about some follow-up information?

Inquiring minds want to know. Did you ever determine the cause(s) of your issues, and what did you do to resolve them?

I discovered very light chafing on my riveted tank when pulling it for inspection, but the wear was very slight only occurring at the removable access covers as shown in the photo with the sharpie. I placed a 1/16 sheet of plastic between the tank and floor after smoothing the edges of the access cover on offending side. No further problems as again the wear was barely visible.
When I did changeover to a welded tank of same dimensions and shape however I raised the rear of tank by 1/16" as a precaution.
dick seiders