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Alterations to Z-12

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tx_jayhawk

Joined: 10 Jun 2006
Posts: 9

Posted: Thu Jun 28, 2007 9:48 am Post subject: Alterations to Z-12

I have essentially a Z-12 type setup with primary alternator, 20 A B&C standby alt, and  PC 680 battery.



Question is this...why would you not have the standby alternator powering the essential bus directly as opposed to the main bus?  I know the "juice"gets there eventually, but it seems like a couple of extra hops that you may not want.  If you lose the main alt and can't power everything on the main anyway, why not route the standby alt power direct to where you want it (essential bus)?  Alternatively, I suppose you could have some sort of switch/relay to change from main to essential (from the standby).



Any thoughts?



Thanks,

Scott

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nuckollsr(at)cox.net
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Posted: Thu Jun 28, 2007 11:37 am Post subject: Alterations to Z-12

At 10:48 AM 6/28/2007 -0700, you wrote:



 	  Quote: 	
		  



I have essentially a Z-12 type setup with primary alternator, 20 A B&C 

standby alt, and  PC 680 battery.



Question is this...why would you not have the standby alternator powering 

the essential bus directly as opposed to the main bus?  I know the 

"juice"gets there eventually, but it seems like a couple of extra hops 

that you may not want.  If you lose the main alt and can't power 

everything on the main anyway, why not route the standby alt power direct 

to where you want it (essential bus)?  Alternatively, I suppose you could 

have some sort of switch/relay to change from main to essential (from the 

standby).



Any thoughts?



Thanks,

Scott


	


    Check the notes for Figure Z-12 in both the text of Appendix

    Z and the chapter on system reliability. Z-12 is NOT INTENDED

    for NEW DESIGN. It's an example of how the SD-20 can be ADDED

    to an existing "spam can like" architecture.



    If you're airplane is already flying with an an a-la C-172 system

    installed and you're wanting to convert to an all electric

    configuration with a minimum of chop-and-hack to the existing

    system, then Z-12 should be considered. This is what's happening

    to hundreds of TC aircraft that are receiving the benefits

    of a vacuum pump driven, second alternator.



    What makes you think you NEED 20A worth of backup power?

    In what ways does Z-13/8 fall short of facilitating a comfortable

    termination of flight should you happen (unlikely) to loose the

    main alternator? Under what anticipated flight conditions would

    you find that 8+ amps of continuous engine driven power + battery

    reserves would not fill the bill for getting on the ground

    comfortably? Before you jump to an answer, let us suppose that

    there were NO practical solutions for a vacuum pump driven alternator.

    If that component were not in our bag of tricks, how would it

    alter the way you plan to use your airplane? The point of the

    thought problem is to deduce whether 20A vs. 8A of backup

    really drives safety issues  . . . or is it just a cool, $1000,

    8 pound solution to a problem that doesn't need to be solved

    when $400 worth of hardware weighing 4 pounds will do just fine.



    I'd judge that a VERY small fraction of the OBAM aircraft

    community can really justify so large a second alternator.

    Let's start with Z-13/8 and then figure out the lowest cost

    of ownership, minimum parts count approach to meeting your

    mission goals.



    Bob . . .



        ----------------------------------------

        ( "Physics is like sex: sure, it may   )

        ( give some practical results, but     )

        ( that's not why we do it."            )

        (                                      )

        (                 Richard P. Feynman   )

        ----------------------------------------

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