Originally Posted by sprucemoose
Nah, didn't run my day, but did cause me to do more research. You are of course right about the tin plated vs. zinc plated sleeves......
I might be taking Snopercod up on the offer to sell some of his excess 250 tin sleeves.
Jeff and I discussed the zinc vs tin plating issue offline. I was curious, and I had made industry contacts while researching for Kitplanes, so I promised to make some phone calls. The questions were (1) when did the standard change from zinc to tin, and (2) why?
Turns out one of my contacts is the fellow who actually wrote and submitted MS-51844, with the then-new tin requirement, way back in 1968. The change was made (as one might expect) to reduce the possibility of galvanic corrosion. Zinc is an excellent sacrificial anode. Tests found that given an adverse environment (electrolyte exposure, notably salt water), tin plated sleeves on stainless cable were superior. As a bit of trivia, nickel plated sleeves also tested well, but cost more and never gained acceptance.
Ok, so what about Jeff's problem, a bunch of stainless cables already made for a Breezy, using zinc plated sleeves? Unofficially
, no difference in strength, and many, many in service, both on purpose and by accident. The issue is strictly corrosion. Given the application is a Breezy in Wisconsin, and thus unlikely to ever be flown in the rain or dunked in the ocean, a builder might make a reasonable decision to use the existing cables, rather than build a whole new set. The smart guy might squirt a little penetrating spooge on them from time to time to keep moisture out, and note the zinc sleeves in the build log, just in case it winds up on floats many years in the future. It would arguably be an unwise decision on an all-weather airplane, including an RV.
Remember, in the case of a certified airplane, you may use AC43 information only in the absence of manufacturer's guidance.
Instructions from both National Telephone (Nicopress brand) and Loos & Co (Locoloc brand) are specific; the current standard is tin
plated sleeves on stainless cable. The same is true for all the MIL specs. Bottom line, for certified
, it's tin plated sleeves on stainless cable, no exceptions.