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..
.