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Old 20th Jun 2002, 10:54
  #73 (permalink)  
CRAN
 
Join Date: Mar 2002
Location: UK
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bcp,

This is my view...

The thing about helicopters is that there are lots of hidden phenomena at work that are not immediately obvious to a none-technical person.

There is a big difference between building a plane and building a helicopter. Just because you can do one doesn't mean you can do the other.

Lets take the example of fatigue, the huge oscillating loads that the helicopter is subjected to in its everyday operation place enormous demands of the structural integrity of the airframe. By virtue of the complicated mechanical arrangements required in helicopters load paths in the structure are often concentrated such as the steel tube frame of the 162F. Let's say you inadvertently scratch/score one of the member steel tubes of the frame - this scratch could develop into a crack and cause a structural failure 200, 500, 1000hrs later. Of course you would hope that you would spot such a flaw or notice you had scratched the frame before every flying and seek advise from the factory who would of course be in a position to give you the correct technical advise. In a concentrated load path such as a steel tube the size of a critcal crack would be very small indeed and very hard to see in many cases. So what if it goes un-noticed...........

In essence the people the fabricate and assemble certificated light helicopters, Robinson, Schweizer, Enstrom are companies with many technical experts with a great deal of experience in the field. The hands-on guys that work on the factory floor are extremely well trained and do a very limited scope task many, many times. Hence, the quality of there work is predictable and very high indeed. They have been trained in all of the supporting technical knowledge pertinent to there job and can spot things that may develop into problems during the aircraft's life.

None of this experience is available to a first time kit builder. It is 'assumed' that joe-public can learn how to assemble a helicopter for a limited manual 'monkey-see-monkey-do' and assemble it without serious error or oversight correctly first time. What happened to learning by your mistakes?


Let me just add - Of course you have the telephone help line and PFA rep, but in the case of the help line - how do you know what to ask about? The PFA Rep can't inspect everything.....hidden behind an inaccessible panels etc?

The earlier comment...So you think you can build a helicopter, would you trust your life on it? Is so so very true.

What we have to ask is....what about the guys that don't know any better....where's the safey net.

So that’s my 2p on kit building helicopters by amateurs. Now for a few words on 'unproven' light helicopters.

Lets have a think about the development of the (Proven) R22 over the past thirty'ish years. The R22 has become an extremely well used and proven machine. Used in many high demanding roles. Even today with all of the experience and expertise available at Robinson they are still modifying the design to improve it's reliability. The sheet metal work around the engine (just an example I know of) still cracks and has to drilled. In earlier versions frames and bits of structure cracked and had to be modified (this is normal for a new design and is not particular to Robinson) That’s after however-many-million flight hours and 3000 in service. By virtue of the small numbers [600] of Exec's in service and the low time on the fleet the design simply hasn't got that level of evolutionary-pedigree to be in the same league in terms of reliability and integrity. The problem is that the feedback loop to the manufacturer with regards design problems doesn't exist in the same way that it did/does at Robinson, the ships don't go back after 2000/2200 hour for a strip down and rebuild were the engineers in the 'know' can crawl all over the machine with all sorts of clever gadgets to find the little monsters hiding in the design. Therefore, it is reasonable to assume that it may take many more accidents and failures before design fixes filter through than were required for the rapid development of the R22.

I'm aware that i'm ranting a bit.....

so i won't mention: Construction quality variability or the effects of shifting the cause of failure from design flaw to a construction flaw in the eyes of the legal people. Maybe flying lawyer has some thoughts.

Hope this helps
CRAN
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