technical details of 51%

Discussion in 'Rules and Regulations / Flight Safety / Better Pil' started by JMillar, Apr 11, 2011.

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  1. Apr 11, 2011 #1

    JMillar

    JMillar

    JMillar

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    Here's something that's been bothering me. The "major portion" / 51% rule has certainly been discussed a great deal in aviation circles, but I still don't know, how far can you push the rules. Tools are what I'm thinking of now.

    Say you need a custom tool to build an aircraft. I think Zenith wants you to use a special nose for a rivet puller, so let's use that example. If the company lent you the tool, there would be no question, obviously, that any work you do with it is still yours.

    If you need a jig for welding tubes, or if it's a composite aircraft that needs molds, I assume that you can rent, borrow, or buy the tooling from someone - since it's not part of the aircraft itself, you can't argue it's detracting from your contribution. Similarly, I assume that nothing prevents the kit manufacturer from renting out (or simply letting you use) their space. So you could layup their kit into their molds in their building, and you haven't changed the amount of work you do.

    Now, imagine you're really rich, and you want to build your airplane by buying a CNC tape layer. No problem there, you still do it all, right? Ok, one step further. Can you build your airplane in someone's factory, by pushing the button to lay tape over their molds, using their winder? Sounds like it should be "no!" -- why? What's the line?

    *I realize that even if all the parts are laid up by machine, etc., there's still a tremendous amount of work involved in putting together the aircraft. But, would those parts count as things you built, when you are tallying up the division of the construction?
     
  2. Apr 11, 2011 #2

    Tom Nalevanko

    Tom Nalevanko

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    I was present when the FAA did the 51% accounting of the Stallion. They view the situation very simplistically. It is not that hard to reach 51%. I would not waste the effort worrying about it.
     
  3. Apr 11, 2011 #3

    orion

    orion

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    This has been discussed quite a bit in various aviation circles and kit producing companies. The FAA has also been trying to figure out a "fair" approach to this but so far has only a simple checklist that divides up the airframe into pieces and then simply has two check columns. One is "built by builder" and the other is "built by company".

    The problem is that things take much longer to build if you consider all the factors involved in the building. For instance, the checklist does not account for things like special tools or fixtures so that's just a part of building a particular part and you don't get any extra credit, so to speak. The checklist also does not allow you to count something like the finishing steps of a composite airframe. Another area of composites that does not get full credit is the fact that molded composite parts are viewed by the checklist the same as raw materials in a metal kit (this part is being considered for change).

    But basically Tom is correct - right now the methodology is very simplistic. A few companies have invested time and resources into assembling a time study of part fabrication and kit assembly but for the most part, the simple checklist is it.
     
  4. Apr 11, 2011 #4

    autoreply

    autoreply

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    Would that prevent composite aircraft from joining fuselages and wings together before they go to the builder?
    Sailplanes (and other composite craft too I presume) take about 15 hours for the two skins and 2 spars to build and join, so that's 30 hrs for the wings and another 30 for the fuselage. The other 90% of the work is in steering (both in the wing and fuselage), internal structure and the like and in finishing, thus from a time-oriented point of view the builder would do 90%.
    Are you guys referring to the checklist in this document?
    http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgOrders.nsf/0/1ba6ee60e8779bd7862572c90063c0ac/$FILE/Order%208130.2f%20incorp%20with%20chg%203.pdf
    Order 8130.2F, page 223 and further?

    Van's has an interesting document about the new (or current?) regulations:
    http://www.vansaircraft.com/pdf/whats_new/percentrule.pdf

    What's the nature of fabrication? Does that exclude molded parts or preformed/predrilled metal parts?
     
  5. Apr 11, 2011 #5

    Topaz

    Topaz

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    IIRC, the FAA doesn't use a simple metric like "build hours" for this. They use "51% of the work" or "51% of the effort". It's deliberately vague. They are trying to discourage individuals and companies from pushing a kit right up to the limit. It's not in the spirit of the rule.

    The E-AB rule came about because some guys were putting, say, Aeronca wings, tail feathers, landing gear, and firewall-forward on their own fuselage and calling it "experimental". Which, strictly speaking, it was, but the FAA realized that the true intent in most cases is to amateur-build an airplane, not research some new aspect of aerodynamics or aerostructures. The FAA (rightfully) saw this as an attempt to circumvent the Part 23 certification process and formulated the E-AB rule to stop this practice. Kits such as we have now were not even on the horizon, and the rule has been applied to the kit situation as best as could be done. There has been talk of refining the E-AB rule many times to make it more explicit, but what comes out of that discussion is always, "We have it pretty good, and any major overhaul in today's environment will probably be a lot worse than what we've got now."

    Take the vagueness with gratitude guys. We could've ended up with something like in the UK, where each builder has to essentially do a full certification on their design, not much less onerous than the "regular" certification.
     
  6. Apr 11, 2011 #6

    RJW

    RJW

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    Agree with Topaz. Vague and simplistic is good. Clearly defined is bad. In the clearly defined case one would spend more time assembling the required truckload of paperwork that nobody would ever read than assembling an airplane. This is one of those rules that are better left alone. Kit suppliers are the ones that want this well defined. The mountain of paper wouldn’t be a problem for them. But if a new clearly defined rule trickled down to actual builders, which regulations of this kind often do, that would be the end of homebuilts.

    Rob
     

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