Ouch, A Little Rib Repair

[ysifly2]

Well..Rats! Saw something I did not like today, and found a cracked rib. It is just under the fuel tank ....
Bah...Humbug!

Well, I will second that quote. As we were enjoying a great day of flying, I happened to notice looking out along left wing, that there was a spot along the bottom of the wing at the first rib out, that looked like it was “bowing” up quite a bit more than I recalled seeing before.

So, when got back as I was doing post flight cleaning and checks, I made sure to check on this spot... well... it would appear I have a broken false rib, under the left tank just behind the main spar. you can just barely see an upward indentation along the rib line


Will try and post a video that I took as well.


I still have more investigation to do, and not yet familiar with how the rib terminates at the main spare.
Does this appear to be something that will be accessible with tank removed? (Not that I’m looking forward to that :-/ )


Bryan


edit: added u-tube video link

[Steve Pierce]

I suspect the rib has broken at the front spar. The tank bay ribs have another cap strip riveted to the top but the weak spot is at the front and rear spars where there is just the bottom cap strip and no further support like the full ribs with the diagonal braces.
20191009_100306.jpg

Here is someone's repair at the rear spar. According to the document posted on the first post of this thread no repairs are allowed forward of the spar.
20191009_100314.jpg

[Vagabondblues]

Memo 10 may or may not really be intended for cracks right at the spar. In other words the repair would go beyond or forward of the spar. Would it be possible to use the Univair stamped ribs in the repair? (they look just like the second rib in Steve's first picture) Of course the fuel tank would have to come out but the Univair ribs (p/n U1226-00)are designed to be cut apart and riveted together after installation. I am thinking that this was by design to prevent pulling all the other ribs off. So...you could cut out the old rib. then you would cut the new univair rib into three parts, feed it into place, re-rivet the doublers and then re-attach the fabric with pop rivets and plastic washers. Apply tape over the pop rivets, which will cover the stitching holes.

Just an idea.

[ysifly2]

Thanks for the pictures Steve! worth a thousand words as they say.

... possible to use the Univair stamped ribs in the repair? ... Just an idea.

good thought... I will see about that as an option after getting the tank out and a better look at the actual condition.


understand the rib repair memo.. but is there some criteria that defines when a finding warrants an immediate 'go under the knife' action as it were, versus, noted and addressed at a later time? thinking something like, if ribs 1 thru 5, immediate action, if 6 thru x, then if more than 'y' damage then action.?
just seems like many wings when being recovered, require multiple ribs repaired or replaced... so, obviously they had been operating like that for some time?

less than 500 hours since complete recover on my airplane... so, just trying to build my knowledge base...
and with this forum, I keep on learning.. and adding things to be sure to inspect

Thanks!
Bryan

[Steve Pierce]

I found a cracked tank bay rib in my Clipper wings when I tore them down. I am anal about weight but went ahead and installed all new Dakota Cub tank bay ribs that are a tad heavier. The cap strip is an extrusion so much stronger in that area. It is strange because I have not seen these issues on long wing Pipers, only in the Short Wings. I repaired that area in a rib 20 plus years ago before I knew about Memo 10 and I never had an issue with it again.

[Vagabondblues]

I have not seen these issues on long wing Pipers,

Like low horsepower applications, smaller prop, smaller pulses of air drumming the fabric in the prop wash?

I like the Univair rib for the fact that you have approval to cut it and add a doubler in the cut area.

[Steve Pierce]

I think it is the longer span but am not sure. I maintain Super Cubs with 180 plus horsepower and long props. The difference might be the jury struts halfway between the wing attach and the strut attach.