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From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-891047@logan.com>
Subject: Re: [FlyRotary] Re: Fuel filter selection
Date: Wed, 21 Dec 2005 09:19:44 -0500
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>>>
>>> So, the parts from Summit Racing will be here tomorrow, and I have a 
>>> beautiful 45* flare tool, lots of fittings and lots of aluminum tube.
>>
>
> AAARGH! What was I saying!!  It's bad enough to have a slip of the 
> tongue...but a slip of typing!?  I'm going to go home and measure the 
> thing anyway before I go any further.
>
Yes, smart thing to do.  The 45deg automobile flare tools are cheap, the 37 
degree aircraft AN flare tools are a bit more expensive.
I've heard two stories about how the AN (Army Navy) specification came 
about.  One was that during WWII a lot of cheap, poorly made fittings were 
resulting in accidents/malfunctions - so the Army/Navy decided to change the 
fitting from 45 to 37 deg so that only those firms with valid production 
contracts (for fittings) would go to the expense of retooling.

The second (perhaps more plausible) reason was that the 37deg flare puts 
less stress on the metal than the 45 deg flare resulting in fewer failures. 
But, in any case if you use AN then you must use the 37 deg tool.  Double 
flare 37 deg tools are even better for small tubing - but  very expensive.

Ed A