Spar Inspection

[rotaxflyer]

I'm finally getting to my annual and inspecting the spars. A couple small black lines concern me. I'm thinking it is nothing to worry about, but a second opinion or two would be welcome. The first photo is just for orientation.

Thanks in advance.

Andy Sinnamon

[mulwyk]

Re: Spar Inspection

pencil marks?

[1938BF50]

Re: Spar Inspection

Or a spinder web full of dust.....

From the stamped rib I am assuming you have a BC-12D? What are those wood "filler strips" between the ribs (top and bottom)? Was this the norm on later ships?

[Howard Wilson]

Re: Spar Inspection

The large obvious one looks like it might just be a scratch in the finish. The wood doesn't look damaged. Have to look closer.
The one that gets my attention comes out from behind the rib at about the 2 o'clock level of the medium size hole in the rib, heading off to the right a little under the rectangular flash reflection. Maybe nothing. Hard to tell even with the good pic.

[Pearson]

Re: Spar Inspection

The dark lines on your spar look like where the sap has cooked out of the wood and then become covered with mold, or mildew. I suspect that if you look around, you will find more.

I, like Mike, am wondering what the wood is at the top and bottom of the spar. It looks as if the spar was not tall enough so someone put cap strips on it to make it the correct height. My plane had these under the tabs at the front and rear of the wing fuel tanks. But that was only to raise the tank up so the filler neck would stick out more. It looks like someone did it on your plane to correct for an incorrectly sized spar.

Are these strips of wood between all of your ribs? Or is it just one bay?

[VictorBravo]

Re: Spar Inspection

Could be strips of wood glued onto the spar for the metal leading edges to screw into. That in itself would not be bad news.

However, if someone drilled and screwed those strips onto the top and bottom edges of the spars, they were weakening the spars and it is possibly very dangerous IMHO.

I think you need to look VERY carefully and see HOW those wooden strips are attached to the spars. If you cannot see any glue, that might be very bad news IMHO... Hank?

[rotaxflyer]

Re: Spar Inspection

Ok, well I'll be measuring the spar and looking very closely for any sign of screws or nails in the top and bottom edge. Thanks everyone. I'll keep you posted.

Andy

[mike lutz]

Re: Spar Inspection

paint brush brissell?

[Robert Lees]

Re: Spar Inspection

The one that gets my attention comes out from behind the rib at about the 2 o'clock level of the medium size hole in the rib, heading off to the right a little under the rectangular flash reflection. Maybe nothing. Hard to tell even with the good pic.

Looks like a lamination line to me. My main spars were made up of vertical & horizontal laminations, very nicely done. My guess, based upon looking at the grain changes, is that Andy's spar at this point is made up of 5 horizontal laminations

The darker, shorter line (Andy's original question) looks like either sap or possibly glue squeezed out of another lamination & not tidied up after manufacture.

A view from the front would confirm. Make a small hole in the fabric ahead of the front spar, underneath the wing (the metal leading edge doesn't go all the way back to the spar underneath) and use that now-under-utilised borescope that we borrowed for the strut fitting inspection.

[N96337]

Re: Spar Inspection

Mine were laminated from a bunch of pieces too....and the old glue lines can look like a crack in the right light. The biggest line in your second picture looks like a scratch to me, albeit an old one. It would be wise to look those seams over very closely, as the ones on my spars were starting to weaken... seems that old glue doesn't stand up to spending most of it's life outside in the deserts too well. My new spars are one piece each.
I've seen wood fillers like that on other planes, so maybe Bill's right about what they were up to there.
The one thing I was waiting to hear was a bunch of wailing and gnashing of teeth about it being rib stitched!
John

[Ray36048]

Re: Spar Inspection

OK, I will bite. How did this plane with stamped ribs get rib stitching approved?

[Hank Jarrett]

Re: Spar Inspection

Making holes in the extreme fiber (the very top or bottom) of a spar is a really bad idea. Not as bad as a saw cut, but pretty bad. Kind of like the difference between something that makes your hair stand on end and making it burst into flames.
If you DO have a line of screws or nails driven into the edges of the spars a full analysis might show the spar is still strong enough for use, but it won't matter much. I doubt you will find an IA anywhere who will allow it (even WITH a full analysis) to be used.
I hope it is glued to the top and bottom and the fasteners aren't driven into the spar. If it is perforated it may well be good for a pattern for new spars and nothing else.
Hank

OK, the wood would still be really good for secondary structure like stringers.

[rotaxflyer]

Re: Spar Inspection

Ok folks,

I measured the spar - it is the correct size. The blocking seems to be attached mainly to the leading edge aluminum and not really to the spar at all. I got it to move in a few places by pushing on it.

The plane was repaired and recovered in '87 by a TC licensed AME. At that time the rt wing spars were replaced. I assume the rib stitching was accepted on the basis of AC 43-13 - that is what it says in the logs. Anyway, there is no sign of the stitching cord chafing on the edge of the stamped ribs, which I assume is the potential issue.

Finally, one of the dark lines was removed with my fingernail, so it was indeed the remains of a paint brush.

Thanks everyone.

Andy

[N96337]

Re: Spar Inspection

Sounds like you're good to go Andy.... personally, I like rib stitching better than the wire. It uses the whole rib web for strength, not just the flange. According to our FSDO here, it's totally legal through the basis of AC43.13 unless it's specifically forbidden by the mfg.
John

[astjp2]

Re: Spar Inspection

I think rib stitching is an alternate method, simple 337 during the recover. I perfer it.