In a message dated 10/8/2007 2:09:41 P.M. Eastern Daylight Time,
echristley@nc.rr.com writes:
They
lived for weeks with terrible injuries, and
> both died leaving
behind astounding medical bills and shattered families.
>
> Spring clamps are acceptable on vacuum hoses to power some back
up gages.
>
I love the depth of information and
experience you bring to this list,
Lynn; but, unless you can point
to a spring clamp being the cause of
the mentioned accident, I'd say that
it is completely irrelevant to this
discussion. Mechanical failures
happen, and often they could be delayed
or avoided altogether if one part
was just slightly stronger. But
there's a long row to hoe to move
from that statement to spring clamps
only being acceptable for backup
vacuum gauges.
First of all, you probably won't get an airworthy sticker from your
inspector if a cooling system hose has a spring clamp on it anywhere. You may
have noticed that many of the boys are using full size upper hoses on their
installations when a one inch, or one and a quarter inch hose is more than
enough. The larger hose has significantly more area facing the coolant pressure
than the smaller hose. My wife's Renault popped the head gasket and the wire
formed hose clamps with a nut and bolt tensioner held up fine. The end tank
of the radiator came uncrimped and blew off. But it wasn't a spring clamp. So
there are situations where a spring clamp blowing off would have saved some
money. But the Renault didn't have spring clamps. I am suggesting that the boys
run a 22 or 24 pound cap instead of the more typical 12 or 16 pound cap.
I am inviting others to believe me when I say this and this and
that works. If somebody chooses to use the setup I suggest, then they leave off
three of six major elements of that set up, what can I say?
There is no positive locking feature on a spring clamp. You must
trust that the heat treat was damn near perfect, on a piece that has less than 4
cents in its manufacture. There is no place for this device on any aircraft,
even home built. It is not a reliability related decision. It is philosophical
problem. Devices that do not display a positive locking feature are seldom seen
on aircraft.
We don't have solid data, so we fall back to what feels good, but there
is some unintended hypocrisy going on here. If the spring clamps
aren't
up to the job, why would they be acceptable on back-up gauges?
Those
gauges are going to be the primary gauges after the primaries fail,
and
if the clamp failed it will kill ALL of them anyway. Why does it
feel
acceptable to use the clamps on the backups, but not the
primaries?
And why are the spring clamps found all over the cooling system of
some of
the most reliable passenger vehicles ever mass produced? I
doubt
Toyota, Honda, Ford, Dodge, or BMW use the feel good metric when
specifying their clamps. Mostly wire frame clamps with bolt and nut
plate, and not spring clamps,
but mostly because they are cheap.
There was no suggestion that spring clamps don't work, or are not
reliable. I have never seen any AN drawings for a spring clamp. The spring clamp
would work fine as a clamp for the back up vacuum gages,
because the barbed fittings would work without the clamps anyway,
and the suction on the lines will tend
to keep them in place without the barbed fitting and
without the clamp. The primary gages would be electric.
I'm not really ranting about hose clamps as much as the feel good
mentality . . . the dismissal of a solution without a quantification of
what it's supposed to do. I'm using little velcro straps to contain my
wire bundles. These things are amazing for a tube frame
airplane.
They're cheap, convenient, quick to install or move, allow
some play in
the wire while holding it securely and provide for non-abrasive
separation from the structural tubes. "But it's just velcro," a friend
complained. So I strapped a wire to a shelving support tube, and let
him hang from it. He gave up when the wire was cutting into his hands
instead of coming loose.
The aviation industry is rife with
over-engineering because someone
needed an extra ten feet to make the
runway. It's my belief that it
does nothing but drive the price
up. I say 'belief' because I have no
actual data to back up the
belief. Until there's some data showing how
spring clamps will fail in
a typical cooling system, I'm going to have
to reject that notion.
There's just way to much evidence showing that
they do work...reliably...for
years on end.
There are many cases of under-design showing up each year, as
once modern planes build up the hours.
If you get a close look at the hinge joint on the 175 elevator,
you probably would never fly one again. But they hold up just fine. On other
designs not so well. Cracking bulkheads and skins and so-on.
That being said, I'll actually use worm clamps. There's less
worry
about having the exact right size for every hose, simplifying my
inventory management.
The object of having extensive specifications for hose clamps and
all of those dodads and nicknacks for aircraft, is not a result of lesser hose
clamps having failed left and right at great loss of life and equipment. It is
to reduce the possibility of failure from one in a million to one in a trillion,
or an even lesser number. For any intent to below zero. There are many
aircraft parts where this kind of thinking cannot be used, due to cost. But
where it is possible, aircraft parts are failure proof, and must be defeated by
bone headed mechanics and, or, fate, but not for lack of design or
quality. Let the plane crash because of some pilot screwup, but please God
not because we saved 76 cents on the hose clamps. 99.999 percent of the time,
fasteners that are safety wired would not come undone should the wire be left
off, done poorly or wired backwards so as to be pulling in the loosening
direction. I have been working on airplanes since I was 14 years old. I am now
64. The house I just sold, has a Lear jet Fuselage in the game room. It isn't
the one you did right that gets you. But if you forget just one of those guys.
The one that has been in the trunion casting since 1949 will back out and hang
up on the gear door and that gear will not extend.
Maybe not today, maybe not this month, but it will. That nasty
FAA man will show it to you.
There are many things we could do and there would be no deadly
outcome, this time. But then you end up with a big number of items that will not
be accepted by the AI, so there is no monetary advantage. Stay on the side of
the best pieces, the best practices, and read the stupid check list every time.
Let somebody else test automobile fasteners in his airplane, or hose clamps, or
whatever. If you need to sell it, it is better if it looks just like an F-16
inside.
it's just my opinion.........I could be wrong.
Lynn E. Hanover