37 degree fitting

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"?

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

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"?


Veedube...

No, the law of common sense. The fittings for hoses and tubing are 37 degrees,
whereas those made for air conditioning are another value and those for
plumbing are....and those for autos are....another.

If you want leak-free fittings, you have to use parts which mate with the
correct and matching angles.

Neal

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

Actually, the 37deg. ftg Does put a little more pressure on the mating
surfaces.---Envision a 10 or 15 deg fitting, like forcing a long tapered
pin into a long tapered hole--fits real tight.----And that's exactly what
the
newer line of MS hoses does---I haven't measured the angle but it looks
on the order of 2 to 5 deg. This gives a very tight fit and still uses
aluminum
mating parts. The downside, if any, is that the mating pieces must be
machined
to very close tolerances, or the "plug" will bottom out in the socket
before
the tapers come into contact. Jerry

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"?

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

The 37° is the angle of the taper seal in aircraft fittings. Automotive uses
45°. So when you work on an aircraft, that is what you expect. Mixing the
two could be a big problem. With that said, My Factory built Bellanca has
two different style fittings as it was built with war surplus Air Corp
fittings. Since they are no longer available, some of the later repairs and
alterations use the current style fittings. They are both 37° but the nut
threads are different. AC fittings were gray, Current are blue.


--
Cy Galley - Chair, Emergency Aircraft Repair
Safety Programs Editor - TC
EAA Sport Pilot


"Ernest Christley" wrote in message
. com...
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"?

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

As almost everyone else said, it's the AN standard at 37 degrees. If you have
to flare tubing and there's not much to do, a standard 45 flare kit can be modified.
We had to do that on our plane for an STC installation... needed ONE end flared.
Rather than spending $100 on a tool to use once, or potentially more than that for an
aircraft shop to do it, we bought a $10 Home Depot special. Chucked it up in the
lathe at 37 degrees and cut a new flare taper... worked fairly well (aside from being
a bit of a POS flare tool to begin with).

YMMV
-Cory

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"?

: --
: http://www.ernest.isa-geek.org/
: "Ignorance is mankinds normal state,
: alleviated by information and experience."
: Veeduber

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

Cy Galley wrote:
The 37° is the angle of the taper seal in aircraft fittings. Automotive uses
45°. So when you work on an aircraft, that is what you expect. Mixing the
two could be a big problem. With that said, My Factory built Bellanca has
two different style fittings as it was built with war surplus Air Corp
fittings. Since they are no longer available, some of the later repairs and
alterations use the current style fittings. They are both 37° but the nut
threads are different. AC fittings were gray, Current are blue.



So when you put automotive parts in an aircraft...

That is not a joke, BTW.

Very good answers from several people. Thank you Cy, Jerry and Kevin.
But your answers all beg the question, "If the 37 flare holds better and
is less likely to damage the hose...why would anyone standardize on 45?"

Is the 45 easier/cheaper to make?

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber