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Stressed Skin Repair Question
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. I have removed the displaced material and now have an opening 4.1in long and 1.1in wide. Since I'll be joining two sheets of .065, I've selected -6 rivets. I also realize that I'll need to slip roll the patch. I'm now trying to apply the guidance for stressed skin repairs found in AC 4313-1B around paragraph 4-58 figure 4-16 and tables 4-9 through 4-11 (note that there is apparently no table for 6061 T6). Here is a link to an image showing the current state to the repair: http://rilinterface.com/Cootnest/Ima...e/DSCN0997.jpg I'd love to get folks' input on how best to lay out the repair for this. Thanks! Russ http://rilinterface.com/cootnest |
#2
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Stressed Skin Repair Question
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. I have removed the displaced material and now have an opening 4.1in long and 1.1in wide. Since I'll be joining two sheets of .065, I've selected -6 rivets. I also realize that I'll need to slip roll the patch. I'm now trying to apply the guidance for stressed skin repairs found in AC 4313-1B around paragraph 4-58 figure 4-16 and tables 4-9 through 4-11 (note that there is apparently no table for 6061 T6). Here is a link to an image showing the current state to the repair: http://rilinterface.com/Cootnest/Ima...e/DSCN0997.jpg I'd love to get folks' input on how best to lay out the repair for this. Thanks! Russ http://rilinterface.com/cootnest I recommend using 2024-T3 for the repair doubler, putting it inside, and putting a filler on the outside. This is not because the 2024 is stronger, but because it will be much easier to buck large, hard rivets against a harder material than 6061. The heads go against the 6061 outer skin, you'll need a 5x rivet gun and a really heavy bucking bar. You can also use fresh icebox rivets (-D, -DD) or heat treat AD rivets, (if you're daring enough). The most important thing is to thoroughly prime and seal the skin and repair doublers before riveting them together. Rivet spacing in 43-13 seems really close to me, compared with actual rivet spacing in aircraft or in aircraft structural manuals. I'm too lazy myself, but MIL-HDBK-5 will give you FAA acceptable numbers for calculating the number and size of rivets needed for the repair. Your photo really sucks, by the way. Without knowing the location of the damage on the aircraft, there's no way to determine the load path. With digital cameras and unlimited web space, there's no reason not to upload a couple hundred photos of the aircraft to a Google photo album. -- John Kimmel I think it will be quiet around here now. So long. |
#3
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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 |
#4
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Stressed Skin Repair Question
Thanks for the tips, John!
I'll certainly take a look at that mil-spec I'd like to offer one point of feedback. The tone of your comment, "Your photo really sucks, by the way," is outside of what I would consider productive. The photo was offered merely to show the relationship of the damaged area relative to axis of the part. To clarify, I'm looking for help interpreting the AC 4313 guidelines for patch size, rivet count, and rivet spacing. That said, if a qualified aerospace engineer steps forward to offer assistance with a deep analysis of this tailboom component and its repair options, and he or she would find it helpful, I can certainly provide numerous high resolution images from my self-hosted IIS box. - Russ "John Kimmel" wrote in message ... 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. I have removed the displaced material and now have an opening 4.1in long and 1.1in wide. Since I'll be joining two sheets of .065, I've selected -6 rivets. I also realize that I'll need to slip roll the patch. I'm now trying to apply the guidance for stressed skin repairs found in AC 4313-1B around paragraph 4-58 figure 4-16 and tables 4-9 through 4-11 (note that there is apparently no table for 6061 T6). Here is a link to an image showing the current state of the repair: http://rilinterface.com/Cootnest/Ima...e/DSCN0997.jpg I'd love to get folks' input on how best to lay out the repair for this. Thanks! Russ http://rilinterface.com/cootnest I recommend using 2024-T3 for the repair doubler, putting it inside, and putting a filler on the outside. This is not because the 2024 is stronger, but because it will be much easier to buck large, hard rivets against a harder material than 6061. The heads go against the 6061 outer skin, you'll need a 5x rivet gun and a really heavy bucking bar. You can also use fresh icebox rivets (-D, -DD) or heat treat AD rivets, (if you're daring enough). The most important thing is to thoroughly prime and seal the skin and repair doublers before riveting them together. Rivet spacing in 43-13 seems really close to me, compared with actual rivet spacing in aircraft or in aircraft structural manuals. I'm too lazy myself, but MIL-HDBK-5 will give you FAA acceptable numbers for calculating the number and size of rivets needed for the repair. Your photo really sucks, by the way. Without knowing the location of the damage on the aircraft, there's no way to determine the load path. With digital cameras and unlimited web space, there's no reason not to upload a couple hundred photos of the aircraft to a Google photo album. -- John Kimmel I think it will be quiet around here now. So long. |
#5
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Stressed Skin Repair Question
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 |
#6
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Stressed Skin Repair Question
RPM the A&P wrote:
Thanks for the tips, John! I'll certainly take a look at that mil-spec I'd like to offer one point of feedback. The tone of your comment, "Your photo really sucks, by the way," is outside of what I would consider productive. The photo was offered merely to show the relationship of the damaged area relative to axis of the part. To clarify, I'm looking for help interpreting the AC 4313 guidelines for patch size, rivet count, and rivet spacing. That said, if a qualified aerospace engineer steps forward to offer assistance with a deep analysis of this tailboom component and its repair options, and he or she would find it helpful, I can certainly provide numerous high resolution images from my self-hosted IIS box. - Russ He's just like that most of the time, Russ. But while crass, the comment was correct. The thing I'd worry about on a Coot tailboom is WHERE that cutout was located. Not knowing where the damage is, it's hard to make a valid sugestion. Way aft is probably not too bad, but up front? I'd probably agree about replacing it. FWIW Richard |
#7
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Stressed Skin Repair Question
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... |
#8
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Stressed Skin Repair Question
"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 |
#9
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Stressed Skin Repair Question
On Jul 13, 5:21*pm, "RPM the A&P" wrote:
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. I have removed the displaced material and now have an opening 4.1in long and 1.1in wide. -------------------------------------------------------------------------------- I'd go with the patch. But I'd like to know more about that portion of the structure, especially with regard to the condition of the surrounding area. Depending on what's already there and the condition of the tube, I'd probably try to distribute the load a little better -- might come out looking more like a sleeve. -R.S.Hoover PS - John got it right. Seems kinda casual to risk your life on a snap-shot... for all we know there could be a bullet hole on the other side :-) |
#10
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Stressed Skin Repair Question
This is a 10-inch diameter tube. How far from an open and accessible end of
the tube is the damage located? It may not be possible to reach the patch on the inside of the tube to properly buck the rivets... The photo and description indicate the damage is across the tube. 4.1-inches is a quite a chunk of the total circumference (13%) to removed and then attempt to bridge with a riveted patch. The cited sections of AC43.13 may not be appropriate repair guidelines for this particular tube structure. If the builder's handbook does not provide repair guidelines for this tube, you should probably hire a qualified aircraft structural engineer to develop a suitable repair technique that the experimental/homebuilt inspector (FAA) will accept. wrote in message ... On Jul 13, 5:21 pm, "RPM the A&P" wrote: 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. I have removed the displaced material and now have an opening 4.1in long and 1.1in wide. -------------------------------------------------------------------------------- I'd go with the patch. But I'd like to know more about that portion of the structure, especially with regard to the condition of the surrounding area. Depending on what's already there and the condition of the tube, I'd probably try to distribute the load a little better -- might come out looking more like a sleeve. -R.S.Hoover PS - John got it right. Seems kinda casual to risk your life on a snap-shot... for all we know there could be a bullet hole on the other side :-) |
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