Good point, George.

I certainly am guilty of over engineering things.  That is the major reason my aircraft empty weight was originally 1170 lbs which is about 120 lbs heavier than the average RV-6A.  My motto was (is?) if in doubt, make it stout!!  So an oz here and an oz there and soon it added up to 120 lbs more than I would have liked.

Fortunately 44 lbs of that was due to two batteries which I initially though absolute essential but after 6 years of flying and hauling around that extra 22 lbs and never using it except to help start on a cold morning, I now fly with one 14 lb battery.  But, it took six years of experience before I could give up that extra battery.  Now, If I could get one of Bill Dube's new 3.5 lbs batteries for less than my annual income (joke! Bill), I would put another battery back in.

But, as has been mentioned and inferred, if you don't feel comfortable with a certain approach then you will find some justification for using a different approach.  Like fuse vs circuit breaker - both certainly do the job they were intended to do, but I just can not bring myself to using a fuse for a flight critical system.  I do use them for secondary systems. Don't want to start that war again, but just using it as an example.

Ed
----- Original Message ----- From: "George Lendich" <lendich@optusnet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, October 08, 2007 6:26 PM
Subject: [FlyRotary] Re: Hose clamp myth busters

Time and time again, experienced people place themselves in situations where another second or two of engine power, is the difference between an interesting story, and a heart wrenching tragedy. Last fall two pilots, in a  borrowed Bonanza, hit the edge of a ditch off the end of a long runway. No  engine power left to manage. Another 12 inches of altitude. Another second  of power and they could have been explaining this story to the FAA or plane  owner, or others at the next meeting. 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.

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.

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.

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.

Ernest,
I agree with your statement we tend to overengineer everything, I believe through ignorance and I don't think that's too critical of myself and others, but before we challenge those more experienced, I think some experimentation should be involved.
It's your idea, so what about testing these spring clams to pressure (and over) and over extended time to see what the outcomes really are!?
George ( down under)

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