[ihc] Flare fittings: more than you wanted to know

[Colin M Rush <salmineo@xxxxxxxx>]

        AN fittings are what people call "Army/Navy", but which actually
refers to "Air Force-Navy Aeronautical Standard".  This is a group of
fittings that include the 45-degree red and blue flare fittings that
folks usually call AN fittings, but also include 37-degree flare
fittings, banjo fittings, flareless fittings, and other pipe and hose
connections which are made to fit the military specifications for US
aircraft.  There is a similar spec called AND, which means "Air
Force-Navy Aeronautical Design Standard".  These are both military
conformance specs.  The military is now moving away from the AN spec, and
is using one it developed called the AS fitting, or "Aerospace Standard".
 Then there is a type of 37-degree fitting called JIC, which means "Joint
Industrial Conference", which refers to a group of specifications for
industrial fittings that was developed after the war in an effort to
reduce confusion among the different manufacturers.  This is an
industrial conformance spec.  The JIC fitting is also called an SAE
fitting, having the same spec, and the ISO fitting is the same too.      
   
        Lay people typically call the 45-degree fittings AN, and the
37-degree fittings JIC, but actually a 37-degree fitting could be an AN
fitting.  The differences between AN 37-degree fittings and JIC 37-degree
flare fittings has to do with the threads used.  I am guessing the JIC
standard fittings also are heavier-walled units, due to the high
pressures.  I would also guess that the AN spec means they have to be
light for use on aircraft, so they would be made of high-strength
aluminum or some other lightweight alloy.  Most of the JIC stuff I have
seen is steel, whereas most AN fittings I have seen are aluminum or
alloy.          
        Quick way to see which type of flare fitting you have:  hold two
fittings together at the bevel at right angles to each other.  If they
are both 45-degree fittings, then they will both form a true right angle
(90-degrees) whereas they will not if they are both 37-degree or are
mixed types.  If they are mixed, then the margins will be different
widths.  The AN system was invented before and during World War II along
with the current bolt classification system we use (Imperial
measurements, not metric), to allow better interchangeability among their
machines.  This would have been in the days of the Army Air Corp, as the
Air Force was not yet its own separate branch yet.  
You can learn a little more about the AN system at this link:
http://www.parker.com/tfd/fittingsolutions/ANFITTINGS.pdf
-Colin Rush

On Thu, 26 Feb 2004 14:27:04 -0600 Ryan Moore <baradium@domain.elided>
wrote:
> > Also, just FYI, aircraft use a different pitch to the flare than
automotive
> > applications do.  An automotive flare is 45* while a flare for an
aviation
> > application is 30*.
>
> AN flares are 37 degrees, as i recall.
>
> >  The idea is to prevent automotive fittings from being
> > usable on aircraft (if you use the aviation flare equipement it won't
fit).
>
> i'm not sure if this was the original intent. the aircraft flaring
system
> dates from the late 30s or early 40s, when the US military standardized
> what had previously been a very confusing situation.
>
 
Just relaying what they are teaching, we covered the flares, fittings etc
this week... the course I'm in at the moment is mainly for A&P students
with
the rest of us just thrown in there for some requirements.
 
<shrug>
 
- -Ryan

________________________________________________________________
The best thing to hit the Internet in years - Juno SpeedBand!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!