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control failure



 
 
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  #1  
Old April 8th 07, 04:15 PM posted to rec.aviation.rotorcraft
Stuart & Kathryn Fields
external usenet poster
 
Posts: 328
Default 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  
Old April 8th 07, 05:41 PM posted to rec.aviation.rotorcraft
kirt hood
external usenet poster
 
Posts: 2
Default 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  
Old April 8th 07, 08:33 PM posted to rec.aviation.rotorcraft
Gary K
external usenet poster
 
Posts: 5
Default 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  
Old April 9th 07, 02:15 AM posted to rec.aviation.rotorcraft
Stuart & Kathryn Fields
external usenet poster
 
Posts: 328
Default 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  
Old April 9th 07, 02:16 AM posted to rec.aviation.rotorcraft
Stuart & Kathryn Fields
external usenet poster
 
Posts: 328
Default 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  
Old April 10th 07, 05:53 PM posted to rec.aviation.rotorcraft
Don W
external usenet poster
 
Posts: 52
Default 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  
Old April 10th 07, 08:30 PM posted to rec.aviation.rotorcraft
Stuart & Kathryn Fields
external usenet poster
 
Posts: 328
Default 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  
Old April 10th 07, 09:23 PM posted to rec.aviation.rotorcraft
Don W
external usenet poster
 
Posts: 52
Default 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  
Old April 11th 07, 01:13 AM posted to rec.aviation.rotorcraft
Stuart & Kathryn Fields
external usenet poster
 
Posts: 328
Default 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  
Old April 11th 07, 01:30 AM posted to rec.aviation.rotorcraft
Gary K
external usenet poster
 
Posts: 5
Default 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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