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From: "Thomas y Reina Jakits" <rijakits@cwpanama.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-1873771@logan.com>
Subject: Re: [FlyRotary] Re: engine mount 4130 vs 304 SS
Date: Wed, 28 Feb 2007 10:09:17 -0500
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Ernest,

I am not so sure. If this would be the case, OEM's would use it....
Not being a specialist, I am guessing:

stainless is less flexible, more brittle, harder to weld than 4130
There may not be any stainless with similar properties as 4130....
For the relative ease to preserve a 4130 inside I would never bother with 
stainless.
If you are inot makeing your own frame, it is little extra work to 
drill/chamfer holes into all interconnecting positions. Use plug 
screws/bolts to rinse the interior with linseed-oil or SP-400 or whatever 
strikes your fancy for rust-protection. You also can install a valve and 
pressurize with Nitrogen or Helium - that way you control wether you have 
holes.
No holes, no more oxygene than the tubes held before closing - no ox, no 
rust :))

A relative crude example:
For some "tests" to mount a A/C compressor on a Lyc.-540, we bent up a 
bracket from stainless (quality unknown), like the one used for the 
alternator, but taller.
It broke within 5 hrs "operating time". Same bracket made from some 
non-stainless highstrength steel never expired.....

Thomas


----- Original Message ----- 
From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, February 28, 2007 9:38 AM
Subject: [FlyRotary] Re: engine mount 4130 vs 304 SS


> Russell Duffy wrote:
>
>> Greetings,
>>  As I ponder my choices for mounting the single rotor engine, I noticed 
>> something that surprised me.  304 stainless is cheaper than 4130 steel. 
>> One thing that's always bothered me about steel tube type construction is 
>> the concern for rusting inside the tubes, so stainless is appealing. 
>> There must be a catch here. Is there a good reason I should use 4130 
>> instead of 304?  Either will likely be sized much larger than needed, 
>> since I don't have the means to do any proper analysis of the strength. 
>> Thanks,
>> Rusty (Autoflight drive supposed to be shipping next week)
>
> Something Richard Sohn told me, and I soon after found to be VERY true. 
> The HAZ of stainless weldment will rust almost as easily as mild steel if 
> not properly treated.  It must either be buffed to the original shine, 
> passivated/pickled, or painted.  Since you won't have access to the inside 
> of the tube, going stainless may not get you much.
>
> I've often thought of a tube and fabric fuselage made of stainless would 
> make a lot of sense.  Most tube airframes are heavily overbuilt just from 
> a materials availability point of view.  That is, one size tube is just 
> barely under the stress limit, so there is no choice but to choose the 
> next larger size which give you an extra 50% margin.  Any increase in 
> weight from needing to use larger tubes would be offset by the work and 
> weight saved from not needing to paint it.  If there was a way around 
> treating the HAZ zone, it could be a winner of an idea.
>
> -- 
>         ,|"|"|,              Ernest Christley       |
> ----===<{{(oQo)}}>===----    Dyke Delta Builder      |
>        o|  d  |o        http://ernest.isa-geek.org  |
>
> --
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