Bends, Kinks and Splices

[mhorowit]

Apparently the bible for determining if a longeron (or other member) can be straightened or needs to be spliced is a Structural Repair Manual. What's the closest thing to a SRM for a '46 Tcraft?

Also - Are there any cases on a fuselage where metal can be heated, bent, then treated to regain it's strength (sorry, I don't know the terms, though I think 'temper' and 'anneal' fit in there somewhere) ?- Mike

[Mark Julicher]

Re: Bends, Kinks and Splices

Mike,
You need to get a copy of Advisory Circular 43-13B. It contains accepted practices for repair and will tell you exactly what you want to know about wood repairs. If you have lots of printer ink you can get it online and make a copy Otherwise, it should be available at your favorite pilot supply shoppe.

On another note, I guess some folks are just born lucky, but a pilot at my local aerodrome picked up a '46 BC-12 65 hp from a disolving partnership in our area for a whopping $10,500. This plane is in good shape with only a few fix-before-flying-again issues. It even has a fish bowl compass in good working condition. Maybe I can get the new owner to join the 'tribe'.

[mhorowit]

Re: Bends, Kinks and Splices

Mike,
You need to get a copy of Advisory Circular 43-13B.

I have it; doesn't say anything about the bend/no-bend limits (at least I didn't see it; I'll recheck though. Point me to a page ????) - Mike

[Mark Julicher]

Re: Bends, Kinks and Splices

Mike,
Sorry, I completely misunderstood your first post on this subject.

If you can't straighten a longeron by simple bending or perhaps heating and bending, you should probably cut out the bad spot and splice it. I base that on engineering classes, not from FAA documents. The yield strength of the material is probably not a big issue here, but even a slight residual bend reduces the buckling resistance of the tubing.

[mhorowit]

Re: Bends, Kinks and Splices

Mark - Those are the questions I'm trying to answer. If an A&P can bend a member back into place with nothing showing is that acceptable? How dramatic a bend is too much? Certainly if you see any buckling it's time for a splice.
How about heating/softening? What's the the reference that discusses the limits.? [I'm not asking you to answer these question, just trying to indicate which direction my mind is going; maybe I need to buy an A&P a beer and sit down with him - Mike

[jCandlish]

Re: Bends, Kinks and Splices

Hi Mike

I've previosly posted a link to the old Civil Aeronautics Manual 18 that discusses these kind of repairs,

was: http://vb.taylorcraft.org/showthread.php?t=1630
remains: http://www.candlish.net/taylorcraft/caa-18.pdf

Cheers

[mhorowit]

Re: Bends, Kinks and Splices

Hi Mike

I've previosly posted a link to the old Civil Aeronautics Manual 18 that discusses these kind of repairs,

was: http://vb.taylorcraft.org/showthread.php?t=1630
remains: http://www.candlish.net/taylorcraft/caa-18.pdf

Cheers

Is there a problem with that url? I'm not getting through - MIke

[Guest]

Re: Bends, Kinks and Splices

Mark - Those are the questions I'm trying to answer. If an A&P can bend a member back into place with nothing showing is that acceptable? How dramatic a bend is too much? Certainly if you see any buckling it's time for a splice.
How about heating/softening? What's the the reference that discusses the limits.? [I'm not asking you to answer these question, just trying to indicate which direction my mind is going; maybe I need to buy an A&P a beer and sit down with him - Mike

Hi Mike,
this may be more than you asked but look at Ac43.13-1B, 4-94(3) and accompanying figure 4-35 "dented or bent" this was 4-83 in the old version of the ac

also 4-91(d) in older version of ac this was section 4-80

Other than very very gradual bends (I don't believe your a thinking about those kinds) a normal bend results in damage (the straightening can add to that damage) and the ac (advisory circular) indicates tubing damage is repaired by sleeves, gussets or splices. figure 4-35

Straightening alone without adding a sleeve or splice isn't sufficient unless thru some miracle the tube had no damaged and you had straightened a tube without damaging it's shape (cross section or moment of inertia).

I have never seen that miracle on a bent tube but I suppose it is possible with the right skill, tools, mandrels...

It's probably easier to just add the patch, sleeve or splice rather than trying to force the miracle to occur.

Everytime I have straightened a tube I have sleeved it afterwars or I cut out the old tube and spliced in a new straight piece.

Perhaps a .25" or .3125" trailing edge tube on a rudder or elevator has been an exception and I have straightened and reused some pieces of it with patching the straightened part.

Basically you will be doing a lot of straightening and welding. The limits you are looking for don't exist. I would not pursue that .

Be careful heating. You need to heat but the stresses in surrounding parts can deform the part you are heating if you get it too soft. Clusters is where this can hurt you most. Afterwards just let it air cool (normalizing). Sometimes heating and straightening at a joint or cluster takes a little analysis, ie thinking thru how it bent and the sequence of heat and forces you want to apply to make it go back to shape (or as close as it can get). Got some very good results on upper cabin sections by carefull planning and analysis.

Sometimes carefull heating can help straigthen and reveal cracks (crack is high impedence to the heat flow and there is a color change along crack).

Hope this helps. like all free advice it's worth twice what you paid.

Dave A/P IA, no beer needed!

[mhorowit]

Re: Bends, Kinks and Splices

Thanks Dave - you've outlined the difference between knowing the theory and then knowing what's practical.Must be fascinating learning all this stuff _AFTER_ you feel comfortable that you can run a bead! i.e. how to avoid setting the fabric on fire, etc - Mike

[mhorowit]

Re: Bends, Kinks and Splices

Is there a problem with that url? I'm not getting through - MIke

Got it - MIke