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Hi all;

I have been asked to find a Stainless Steel to AN-QQ-S-757. The spec is obsolete (we are restoring a P-47 Thunderbolt WW2 fighter aircraft) and we have not been able to find anything via SAE. We think that 321 may be an acceptable substitute but we need some way of qualifying this. Any gurus out there on old specs?

Thanks in advance!


RE: AN-QQ-S-757

You will find it in Google.

RE: AN-QQ-S-757

Well, that was the first port of call, obviously. However, we need qualification of what the web says - just saying "I found it on Google" will not satisfy our regulatory authority. If anyone has any QUALIFIED evidence of alternates, then I would be pleased to hear from them.


RE: AN-QQ-S-757

Are you sure of the number?  Reason I ask is because QQ-S-757 is not coming up in historic specs or cancelled specs on the dodssp site.

RE: AN-QQ-S-757

It is not clear waht part are looking for but in the following sites they sell AN-QQ-S-757 fasteners, seal and aircraft structural parts. You can check with them.

According to those sites the material is CRES 321 per AN-QQ-S-757 part. However it may be that more stainless steels types are included in this spec.


RE: AN-QQ-S-757


I have a suspician... but I need-to-know...

Is the part made from sheet, plate, bar, etc?

Also... what is the title and function of the part?


Regards, Wil Taylor

RE: AN-QQ-S-757

We work with the old specifications, but I haven't been able to find a copy of AN-QQ-S-757.  I have one reference showing supercession from AN-S-757 (same as AN-QQ-S-757?) to MIL-S-6721.  The way to confirm this would be to find a base version MIL-S-6721 and look at the cover page for supercession information (haven't found this either).  And of course, MIL-S-6721 has been superceded by AMS 5510 and AMS 5512(ref www.ihs.com)

Does this help?  

RE: AN-QQ-S-757

QQ-S-775 is galvanized steel.

My dad built a small all metal homebuilt [T-18] when I was a kid (1967--1972). The designer had (2) options for the firewall and attaching structure [brackets, clips, etc]:

301/304 CRES Sheet 1/8-Hard
galvanized steel sheet, next gage thicker than CRES Sheet.

My dad chose to make the firewall and some stiffeners/brackets from Galvanized steel.

I thought this was very odd... and asked the designer [John Thorp] Why: he said the firewall and connecting parts had to survive the 15-minute fire just once... long-enough to get the bird safely on the ground.

Apparently use of galvanized steel sheet was VERY common in older aircraft for reasonable toughness/durability/fire resistance... and co$t $aving$.  

Regards, Wil Taylor

RE: AN-QQ-S-757

Hi Wil, I think this is AN-QQ-S-757, not -775?

RE: AN-QQ-S-757

I have seen numbers transposed on drawings and specs... after-alll... this is for a "throw-away" P-47 circa 1943.

Regards, Wil Taylor

RE: AN-QQ-S-757

Galvanized steel would probably need to be 40 thou thick to be good for 15 min fire these days, vs. 16 thou for stainless (and is it 18 for titanium?). On the other hand if the part's structural duty needs greater thickness...

RE: AN-QQ-S-757


For WW-II throw-away fighter acft**, a gage-thicker Galv Stl would work "OK" relative to more-precious CRES.

** many never reached 500-hrs TT... and high time fighter-trainers would have ~1500-hrs TT... when scrapped.

Today's design standards are vastly different from +50-yrs-ago design standards.

Regards, Wil Taylor

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