Ernest,
I understand your reasoning.
But just imagine yourself over some "no chance to walk away if the C hits the fan" area, and you start to think different.
The clamps in the certified helicopter I mentioned didn't do anything to increase my confidence in them or the helo (although it is one of the toughest I have ever seen demonstrated....).
At least I would expect a requirement for safety wire on both clamps.
But it seems experience showed no need for that, replaced by a daily inspection.
Never saw one getting loose either, and as it is "just" the low pressure cooling circuit, I doubt the hoses would come off even without any clamp on them. But .....
As a sample to what Lynn says below:
The new (well it has a few years now) Sikorsky S-92 was the first helo to be certified to a new set of rules. One of them is a "known flaw" - rule.
Meaning, there can be no part on the helo, that could jeopardize safety, even if manufacturing flaws are detected during the lifetime of a part.
Lets say you find a crack during an inspection, that developed due to an undetected air bubble during casting. Rule (and subsequent testing has/had to proof this) says " No matter. The part has to hold up it's intended lifetime anyway!". I doubt that any sane operator would keep a visibly cracked part on the aircraft, but on a complex machine like that, there are corners you only see during assembly and then during "resurrection" or "salvage".
Obviously, this Rule will be hard to implement on smaller craft, for sheer lack of space and cost.
Back to the clamps:
I am scrounger on weight. If I can find a good quality worm-clamp that even "looks" less heavy than a constant pressure clamp I go for it and safetywire it - I would safety wire the constant pressure too.
Even if your spring clamp is all that's needed - it defeats the purpose (for me), as it would make me uncomfortable just thinking about them - when I am over a place with nowhere to land....
In any case:
The very few, very cheap clamp cases I saw getting loose, where not related to heat expansion cycles, but to lack of self-locking ability on the worm thread ( ..can you imagine that!) or vibration loosening the worm. I don't see how a constant pressure would avoid this on a cheap CP-clamp.
SO it comes down to quality, CP or not...
Price is not the deciding factor - unless you go for mercury-free manufacturing super-worm clamps....
Enough rambled,
TJ
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
I doubt you are wrong!!
TJ
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