37 degree fitting

Ernest Christley wrote:

The most recent Sport Aviation has an article on make up hoses. The
author states that 'you must use 37 degree fittings' and as is typical,
gives no reason why. Is there a reason for this that involves the laws
of nature, vs the "laws of the FAA"?

There is no FAA rule specifying the type of flared fittings you must
use in your homebuilt aircraft. However, the flared fittings used in
most modern aircraft are 37 degree AN/MS fittings. Also, the flared
fittings used in professional race cars are typically 37 degree AN/MS
fittings. There is no "magic" in the 37 degrees. It is simply an
aircraft standard that has become a de facto performance standard for
several non-aviation applications as well. The flared fittings under
the hood of your family car are likely SAE 45 degree fittings. The
flares used in your home plumbing are also 45 degrees. Someone
mentioned Tony Bingelis' books. Tony specified AN/MS 37 degree flares
in his books. AC 43.13-1b specifies AN/MS 37 degree flares as well.

David O -- http://www.AirplaneZone.com

On Wed, 16 Jun 2004 05:11:24 -0400, David O wrote:

Ernest Christley wrote:

The most recent Sport Aviation has an article on make up hoses. The
author states that 'you must use 37 degree fittings' and as is typical,
gives no reason why. Is there a reason for this that involves the laws
of nature, vs the "laws of the FAA"?

There is no FAA rule specifying the type of flared fittings you must use
in your homebuilt aircraft. However, the flared fittings used in most
modern aircraft are 37 degree AN/MS fittings. Also, the flared fittings
used in professional race cars are typically 37 degree AN/MS fittings.
There is no "magic" in the 37 degrees. It is simply an aircraft standard
that has become a de facto performance standard for several non-aviation
applications as well. The flared fittings under the hood of your family
car are likely SAE 45 degree fittings. The flares used in your home
plumbing are also 45 degrees. Someone mentioned Tony Bingelis' books.
Tony specified AN/MS 37 degree flares in his books. AC 43.13-1b specifies
AN/MS 37 degree flares as well.

David O -- http://www.AirplaneZone.com

45 deg flared fittings seem to work OK in non-aviation applications, if
used with the fittings and tubing material that are appropriate. But the
higher flare angle forces the end of the tube to stretch further when the
flare is formed, putting more stress on it. So even if you could find 45
deg flared fittings, there is no guarantee that aviation tubing could take
a 45 deg flare without later cracking. You would be
conducting a big experiment. Yes, this is experimental aviation, but
tubing is usually used in critical systems (fuel, oil, hydraulics), and
this is not the place to be conducting experiments.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

37-degree is the most common angle used for industrial fluid power apps.
(hydraulics, high-pressure lube, etc.). However, 45, 90, and a few other
oddball/metric/Japanese standards do exist... just to ruin someone's day when
something breaks.

Harry