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#1
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control failure
aluminum control tube failed causing helicopter crash. The helo had an
anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. .. |
#2
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control failure
Which helicopter type was it?
"Stuart & Kathryn Fields" wrote in message .. . aluminum control tube failed causing helicopter crash. The helo had an anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. . |
#3
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control failure
A 269A Hughes (and subsequent models) has some critical parts hard
anodized. I don't recall any parts with "normal" anodize. Do you have any cites on the cleaning issue? I would be interested in reading them. Gary Stuart & Kathryn Fields wrote: aluminum control tube failed causing helicopter crash. The helo had an anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. . |
#4
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control failure
Gary: Fatigue Design of Aluminum Components & Structures, Sharp, Nordmark
and Menzemer, a chart, page 110, shows decrease in fatigue life due to pre-cleaning as well as the affects of Alodine and a couple of different thicknesses of anodic coatings. Gary: The text that "Gary K" wrote in message ... A 269A Hughes (and subsequent models) has some critical parts hard anodized. I don't recall any parts with "normal" anodize. Do you have any cites on the cleaning issue? I would be interested in reading them. Gary Stuart & Kathryn Fields wrote: aluminum control tube failed causing helicopter crash. The helo had an anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. . |
#5
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control failure
Kirt: It was a Oshkosh Grand Champion Safari.
"kirt hood" wrote in message ... Which helicopter type was it? "Stuart & Kathryn Fields" wrote in message .. . aluminum control tube failed causing helicopter crash. The helo had an anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. . |
#6
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control failure
Stuart & Kathryn Fields wrote:
aluminum control tube failed causing helicopter crash. The helo had an anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. It seems unlikely to me that anodizing was the real culprit here, since the anodized layer is normally only .001" thick or so. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I'm not an expert on anodizing, but I am an engineer, and I've studied anodizing because I own two sailboats that have aluminum components exposed to a salt-water environment, and anodizing is a great way to passivate aluminum to prevent corrosion. The aluminum hydroxide layer formed by anodizing is around an 8 on the hardness scale--roughly the same hardness as rubys. Do you have any links to the research you are citing? If this is really a problem, I'd like to learn more about it. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. If there was an existing flaw in the aluminum tube _before_ it was anodized, the anodizing might very well make the flaw worse, as it would eat away at the edges. Just my thoughts... I could be wrong. Have been before, and will be again. Don W. |
#7
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control failure
Don: I've got numerous phone calls to anodizing firms who have confirmed
the decrease in fatigue life due to anodizing. I've got a photo of a fatigue failed anodized control tube, none of the non anodized control tubes in any of the other similar helicopters even those with more hours have failed. Further if you consult the excellent text: titled Fatigue Design of Aluminum Components & Structures, Sharp, Nordmark and Menzemer, a chart, page 110, shows decrease in fatigue life due to pre-cleaning as well as the affects of Alodine and a couple of different thicknesses of anodic coatings. Further: In a report authored by Thart, WGJ and Nederveen, the following was stated: "Constant amplitude fatigue tests on anodized unnotched specimens reveal that sulfuric acid and sealed chromic acid anodic layers cause the largest decrease in fatigue strength. Phosphoric and unsealed chromic acid anodic layers do not significantly affect fatigue life. Scanning electron microscopy of fracture surfaces confirms that fatigue cracks initiate at cracks in the anodic layer". Mo Shiozawa, Kazuaki; Kobayashi, Hirokazu; Terada, Masao; Matsui, Akira. Japan Society of Mechanical Engineers, Transactions A. Vol. 66, no. 652, pp. 74-79. Dec. 2000 "The anodized film is fractured at an early stage of the repeated tensile fatigue process, because it is too brittle to accommodate the substrate metal." Mo A P.E associated with the anodizing community said it even stronger. "Never anodize flight critical components" Van's of Van's RV aircraft and the subject was anodizing spars, said that anodizing has been known to reduce fatigue life as much as 50%. Boeing Aircraft has a special process whereby the ameliorate the effects of anodizing on some parts. I had a 36' McGregor catamaran with an anodized mast that I sailed in the open ocean in the South Pacific. Even with the cracks in the anodized layer, the frequency of vibration in the mast was much lower than the 17hz associated with the helicopter. Looking back I would expect the mast on the sail boat to have a much longer life than helicopter parts. More data. The failed control tube was inspected by a laboratory in Canada and they proved that there was no existing flaw prior to the anodizing. The crack started after the anodizing and the control tube with a small load applied, but subject to the vibrations produced by a helicopter, failed in fatigue with very few hours. Experience can be misleading. I've been in the amateur helicopte game since 97 and I'm a retired engineer but I had never heard that the fatigue life of anodized parts could be reduced as much as 50%. "Don W" wrote in message t... Stuart & Kathryn Fields wrote: aluminum control tube failed causing helicopter crash. The helo had an anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. It seems unlikely to me that anodizing was the real culprit here, since the anodized layer is normally only .001" thick or so. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I'm not an expert on anodizing, but I am an engineer, and I've studied anodizing because I own two sailboats that have aluminum components exposed to a salt-water environment, and anodizing is a great way to passivate aluminum to prevent corrosion. The aluminum hydroxide layer formed by anodizing is around an 8 on the hardness scale--roughly the same hardness as rubys. Do you have any links to the research you are citing? If this is really a problem, I'd like to learn more about it. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. If there was an existing flaw in the aluminum tube _before_ it was anodized, the anodizing might very well make the flaw worse, as it would eat away at the edges. Just my thoughts... I could be wrong. Have been before, and will be again. Don W. |
#8
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control failure
Stuart Fields wrote:
Don: I've got numerous phone calls to anodizing firms who have confirmed the decrease in fatigue life due to anodizing. I've got a photo of a fatigue failed anodized control tube, none of the non anodized control tubes in any of the other similar helicopters even those with more hours have failed. Further if you consult the excellent text: titled Fatigue Design of Aluminum Components & Structures, Sharp, Nordmark and Menzemer, a chart, page 110, shows decrease in fatigue life due to pre-cleaning as well as the affects of Alodine and a couple of different thicknesses of anodic coatings. Further: In a report authored by Thart, WGJ and Nederveen, the following was stated: "Constant amplitude fatigue tests on anodized unnotched specimens reveal that sulfuric acid and sealed chromic acid anodic layers cause the largest decrease in fatigue strength. Phosphoric and unsealed chromic acid anodic layers do not significantly affect fatigue life. Scanning electron microscopy of fracture surfaces confirms that fatigue cracks initiate at cracks in the anodic layer". Mo Shiozawa, Kazuaki; Kobayashi, Hirokazu; Terada, Masao; Matsui, Akira. Japan Society of Mechanical Engineers, Transactions A. Vol. 66, no. 652, pp. 74-79. Dec. 2000 "The anodized film is fractured at an early stage of the repeated tensile fatigue process, because it is too brittle to accommodate the substrate metal." Mo A P.E associated with the anodizing community said it even stronger. "Never anodize flight critical components" Van's of Van's RV aircraft and the subject was anodizing spars, said that anodizing has been known to reduce fatigue life as much as 50%. Boeing Aircraft has a special process whereby the ameliorate the effects of anodizing on some parts. I had a 36' McGregor catamaran with an anodized mast that I sailed in the open ocean in the South Pacific. Even with the cracks in the anodized layer, the frequency of vibration in the mast was much lower than the 17hz associated with the helicopter. Looking back I would expect the mast on the sail boat to have a much longer life than helicopter parts. More data. The failed control tube was inspected by a laboratory in Canada and they proved that there was no existing flaw prior to the anodizing. The crack started after the anodizing and the control tube with a small load applied, but subject to the vibrations produced by a helicopter, failed in fatigue with very few hours. Experience can be misleading. I've been in the amateur helicopte game since 97 and I'm a retired engineer but I had never heard that the fatigue life of anodized parts could be reduced as much as 50%. Stuart, Very interesting! A lot of things that you run into in engineering are counter-intuitive, and this is apparently one of them. I had not heard of this phenomenon before now. I'll certainly look into this some more when I get some time. Don W. |
#9
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control failure
Don: Be sure to share what you find. I think that I'm only scratching the
surface of some stuff. One thing I found and had never seen before was an equation relating the increase in stress due to a crack. It scares the hell out of me. I'm afraid to use a metal fork in my salad. The equation basically says that the max stress is 2 times the load divided by the area times the square root of the crack length divided by the radius of curvature of the end of the crack!!! If the radius of curvature was equal to the crack length, the max stress is already twice what you would calculate using the applied load and the element cross section. Now put a reasonably sharp crack and see what happens....as the radius approaches 0.001 times the length of the crack......???? "Don W" wrote in message et... Stuart Fields wrote: Don: I've got numerous phone calls to anodizing firms who have confirmed the decrease in fatigue life due to anodizing. I've got a photo of a fatigue failed anodized control tube, none of the non anodized control tubes in any of the other similar helicopters even those with more hours have failed. Further if you consult the excellent text: titled Fatigue Design of Aluminum Components & Structures, Sharp, Nordmark and Menzemer, a chart, page 110, shows decrease in fatigue life due to pre-cleaning as well as the affects of Alodine and a couple of different thicknesses of anodic coatings. Further: In a report authored by Thart, WGJ and Nederveen, the following was stated: "Constant amplitude fatigue tests on anodized unnotched specimens reveal that sulfuric acid and sealed chromic acid anodic layers cause the largest decrease in fatigue strength. Phosphoric and unsealed chromic acid anodic layers do not significantly affect fatigue life. Scanning electron microscopy of fracture surfaces confirms that fatigue cracks initiate at cracks in the anodic layer". Mo Shiozawa, Kazuaki; Kobayashi, Hirokazu; Terada, Masao; Matsui, Akira. Japan Society of Mechanical Engineers, Transactions A. Vol. 66, no. 652, pp. 74-79. Dec. 2000 "The anodized film is fractured at an early stage of the repeated tensile fatigue process, because it is too brittle to accommodate the substrate metal." Mo A P.E associated with the anodizing community said it even stronger. "Never anodize flight critical components" Van's of Van's RV aircraft and the subject was anodizing spars, said that anodizing has been known to reduce fatigue life as much as 50%. Boeing Aircraft has a special process whereby the ameliorate the effects of anodizing on some parts. I had a 36' McGregor catamaran with an anodized mast that I sailed in the open ocean in the South Pacific. Even with the cracks in the anodized layer, the frequency of vibration in the mast was much lower than the 17hz associated with the helicopter. Looking back I would expect the mast on the sail boat to have a much longer life than helicopter parts. More data. The failed control tube was inspected by a laboratory in Canada and they proved that there was no existing flaw prior to the anodizing. The crack started after the anodizing and the control tube with a small load applied, but subject to the vibrations produced by a helicopter, failed in fatigue with very few hours. Experience can be misleading. I've been in the amateur helicopte game since 97 and I'm a retired engineer but I had never heard that the fatigue life of anodized parts could be reduced as much as 50%. Stuart, Very interesting! A lot of things that you run into in engineering are counter-intuitive, and this is apparently one of them. I had not heard of this phenomenon before now. I'll certainly look into this some more when I get some time. Don W. |
#10
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control failure
Stuart,
Thanks for the lead. I have ordered the book. Stuart & Kathryn Fields wrote: Gary: Fatigue Design of Aluminum Components & Structures, Sharp, Nordmark and Menzemer, a chart, page 110, shows decrease in fatigue life due to pre-cleaning as well as the affects of Alodine and a couple of different thicknesses of anodic coatings. Gary: The text that "Gary K" wrote in message ... A 269A Hughes (and subsequent models) has some critical parts hard anodized. I don't recall any parts with "normal" anodize. Do you have any cites on the cleaning issue? I would be interested in reading them. Gary Stuart & Kathryn Fields wrote: aluminum control tube failed causing helicopter crash. The helo had an anodized aluminum control tube that failed in fatigue with less than 400hrs. The loading was low producing stresses in the area of 460psi. Discussions with anodizing folks say "Never anodize flight critical components" Some research has provided data indicating that some cleaners can also shorten the fatigue life of aluminum significantly. I've seen gyrocopters with long anodized aluminum control tubes shaking like your English teacher's No-No finger. The May 07 issue of Experimental Helo has a more indepth article on this with pictures of the helo before and after.. . |
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