Stressed Skin Repair Question

On Sun, 13 Jul 2008 17:21:39 -0700, "RPM the A&P"
wrote:

Hi,



I'm looking for input on the best way to layout a repair of some "hangar
rash" on the tail boom of my Taylor Coot amphibian project.



The damaged area is on a 10in diameter .065in 6061 T6 tube that serves as
the tail boom on this aircraft. The part was dropped and sustained a crease
roughly perpendicular (but not quite) to the length of the tube.



If it were my money on the aircraftand if I owned it.
I'd throw out the tube and replace it.

2 reasons.
the rivet holes will reduce the strength of the tube no matter how you
lay out the repair.

aluminium and particularly 6061 is subject to fatigue.
you cant ever get away from this because it is an inherent
characteristic of aloominum.
these tubes are not the optimum shape structurally and have stresses
that arise from poor resolution of the loads on them.

I WOULD REPLACE THE TUBE.

ymmv
Stealth Pilot

Thank you for your recommendations.

Agreed. I would love to replace the boom and I have tried to do so for some
months now. Regrettably, they no longer appear to be in production. FWIW,
the original listed in the Coot bill of materials was a
Reynolds-manufactured irrigation pipe.

A number of aluminum distributers have informed me that there are no drawn
tubes in this diameter and wall thickness, or anything close to it,
currently available from any manufacturing source.

Additionally, the rolled and welded tubes that I have located are
unacceptable due fabrication quality, alloy, or both. In fact, I purchased
one tube sight unseen from a former Coot builder, but it turned up with such
extreme tooling (roller) and welding marks that I have reassigned it to
become a pair of reflecting telescope bodies and nothing more. Fortunately,
it only cost me $20. :-)

Finally, after contacting all the folks that I have been able to find in
North America who have been know to have spare Coot components, I've still
failed to turn up an acceptable replacement.

Fortunately, although this boom will be enclosed in a tail fairing, the
repaired area can be made highly inspectable.
For now, I am still planning to pursue a repair.

However, based on your recommendation, let me expand the scope of this
request...

If anyone on the group is aware of a source of drawn tubing that's 116 inch
long, 10in OD, ~.063in wall thickness, and that's made out of 6061-T6,
6063-T3, or 5051-T3, I'd love to hear about it.

Thanks!

Russ


"Stealth Pilot" wrote in message
...
On Sun, 13 Jul 2008 17:21:39 -0700, "RPM the A&P"
wrote:

Hi,



I'm looking for input on the best way to layout a repair of some "hangar
rash" on the tail boom of my Taylor Coot amphibian project.



The damaged area is on a 10in diameter .065in 6061 T6 tube that serves as
the tail boom on this aircraft. The part was dropped and sustained a
crease
roughly perpendicular (but not quite) to the length of the tube.



If it were my money on the aircraftand if I owned it.
I'd throw out the tube and replace it.

2 reasons.
the rivet holes will reduce the strength of the tube no matter how you
lay out the repair.

aluminium and particularly 6061 is subject to fatigue.
you cant ever get away from this because it is an inherent
characteristic of aloominum.
these tubes are not the optimum shape structurally and have stresses
that arise from poor resolution of the loads on them.

I WOULD REPLACE THE TUBE.

ymmv
Stealth Pilot

RPM the A&P wrote:

Thank you for your recommendations.

Agreed. I would love to replace the boom and I have tried to do so for some
months now. Regrettably, they no longer appear to be in production. FWIW,
the original listed in the Coot bill of materials was a
Reynolds-manufactured irrigation pipe.

A number of aluminum distributers have informed me that there are no drawn
tubes in this diameter and wall thickness, or anything close to it,
currently available from any manufacturing source.

Additionally, the rolled and welded tubes that I have located are
unacceptable due fabrication quality, alloy, or both. In fact, I purchased
one tube sight unseen from a former Coot builder, but it turned up with such
extreme tooling (roller) and welding marks that I have reassigned it to
become a pair of reflecting telescope bodies and nothing more. Fortunately,
it only cost me $20. :-)

Finally, after contacting all the folks that I have been able to find in
North America who have been know to have spare Coot components, I've still
failed to turn up an acceptable replacement.

Fortunately, although this boom will be enclosed in a tail fairing, the
repaired area can be made highly inspectable.
For now, I am still planning to pursue a repair.

However, based on your recommendation, let me expand the scope of this
request...

If anyone on the group is aware of a source of drawn tubing that's 116 inch
long, 10in OD, ~.063in wall thickness, and that's made out of 6061-T6,
6063-T3, or 5051-T3, I'd love to hear about it.

Thanks!

Russ



It might be more productive to ask the composite guys about how to make
a glass copy...

"cavelamb himself" wrote

It might be more productive to ask the composite guys about how to make a
glass copy...

Good point. It would be possible (if this suggestion would fit into the
design) to make the replacement tapered towards the end, which would
probably allow the weight of the glass replacement not exceed the original
tube's weight.
--
Jim in NC