REFLECTOR: Reflector Digest, Vol 100, Issue 10

Lawrence Epstein ljepstein at hotmail.com
Thu Jul 4 12:51:57 CDT 2013


I strongly recommend the following reference for aircraft wiring/electrical
systems:

http://www.eaa.org/experimenter/articles/0903_aircraft_wiring.pdf

Granted, it is written by Greg Richter (BMA), but it goes through a logical
analysis of what sort of redundancy is necessary and where. He addresses
back up batteries (no need if you are 24 V) on page 5 and 2nd alternator
("overkill") on page 6.

Lots of good stuff here.


On Thu, Jul 4, 2013 at 11:15 AM, Patrick Sieders <pjsieders at comcast.net>wrote:

> Brooke and Dave,
>
> You all have a point in simplicity. On backup systems however, I disagree.
>
> Many production airplanes had backup systems : electrical and suction
> instruments.
>
> These days we are all leaning/using electrical EFIS screens etc. So to
> have another backup alternator in lieu of the old vacuumpump is just common
> sense.
>
> Take it from a guy flying an electric airliner, being told we always will
> have instruments(i.e. EFIS SCREENS) to look at.. I have met Murphy in IMC...
>
> Patrick sieders
>
>
>
> ------------------------------
> From: Dave T Nelson <dtnelson at us.ibm.com>
> Sent: July 04, 2013 10:09
> To: reflector at tvbf.org
> Subject: Re: REFLECTOR: Reflector Digest, Vol 100, Issue 10
>
> Brooke - well said, Sir!
>
> The comparison to other no redundancy systems (like your entire airframe)
> is spot on, and reinforces my philosophy - stay away from complexity, and
> build it really, really well - but just once.  Adding all the stuff I hear
> about is adding extra weight, complexity, and failure modes.
>
> How many Cessnas, Pipers, Beechcrafts, Mooneys, etc., are lost due to the
> lack of an extra alternator?  An extra battery?  Where you see a store
> bought airplane accident due to an electrical failure, it's pretty much
> always due to smoke or fire in the cockpit... How much extra risk are you
> adding for that kind of problem with all of your additional redundant
> systems?
>
> Take great care in building, but build it once and keep it simple.
>
> Dave
>
> Dave T. Nelson
> T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
> Program Director, ISC ECAT NPI & Test Engineering
>
> ----- Message from Brooke Wolf <bwolf1 at tds.net> on Wed, 3 Jul 2013
> 21:32:32 -0400 -----
> *To:*
>
>    reflector at tvbf.org
>
> *Subject:*
>
>    REFLECTOR: Electrical system
>
> Reiff
>
> As we go through the mental gymnastics of 2 alternators or 2 batteries or
> primary busses or essential busses or main busses or emergency busses or
> battery busses and redundancy galore, let us not forget we have only one
> engine.  Safety and associated redundancies should balance.  Just food of
> thought.
>
> Brooke
>
> On Jul 3, 2013, at 4:11 PM, *reflector-request at tvbf.org*<reflector-request at tvbf.org>
>  wrote:
>
>
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>    Today's Topics:
>
>     1. Re:  Electrical system (Jack Prock)
>
>    *From: *"Jack Prock" <jackprock at wavecable.com>
>    *Subject: Re: REFLECTOR: Electrical system*
>    *Date: *July 3, 2013 4:10:30 PM EDT
>    *To: *"Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>    *Reply-To: *Velocity Aircraft Owners and Builders list <
>    reflector at tvbf.org>
>
>
>    Reiff,
>
>    The only thing that I would add is that you start your engine using
>    the battery, but fly using your alternator(s).  If you were going
>    to decide between having a duplicate of one OR the other, I would go
>    with a duplicate alternator.
>
>    If the battery goes out, you can’t start... get jumper cables, start
>    the engine, you’re on your way... just like a car. (assuming 12 volt system
>    )
>
>    If your single alternator goes out, you run on your battery(s) until
>    it/they die (while you look for a place to land)...
>    at night... over mountains, not a good scenario!!  Other backups will
>    help... but the pucker factor goes way up when
>    (almost) everything goes dark!
>
>    The consequences of one, far outweigh the consequences of the other.
>
>    That is just my opinion... and just like assholes, everyone has one!!
>
>    Jack
>
>    *From:* *Reiff Lorenz* <Reiff at lorenz.com>
>    *Sent:* Wednesday, July 03, 2013 12:24 PM
>    *To:* *Velocity Aircraft Owners and Builders list* <reflector at tvbf.org>
>
>    *Subject:* Re: REFLECTOR: Electrical system
>
>
>    Terry,
>
>    Thank you for all the details. This is all very helpful. I like your
>    suggestion about the heat-shrink labeling, even though it's expensive. For
>    planning/drawing software I'm leaning toward Visio. (Turbo-CAD does have
>    some good features, too.)
>
>    I'm still working on the right tradeoff between redundancy and
>    complexity. Lots of suggestions from other builders to do 2 batteries.
>    Others say 1 battery and 2 alternators. Andy Millin sent me his diagram and
>    he's got 3 batteries! The Vertical power system simplifies some of this.
>    They have multiple configurations for dual batteries and/or dual
>    alternators and/or ground power plugs, but it's still not as easy as
>    connecting everything to one box.
>
>    Builder Bill Stockman lives near me. He's retro-fitting his long-wing
>    SE with a Vertical Power system and a Garmin G3X. I'm hoping to be able to
>    help him and learn about wiring a VP system in the process.
>
>    I may have similar W&B issues to what you describe. I'm a skinny guy
>    and don't want to have trim issues, but I also want to take some of my
>    larger friends in the front seat (6'3 & 260 lbs.)  Maybe there's some
>    middle ground between the two extremes?
>
>    Looking forward to talking to you at Oshkosh!
>
>    Reiff
>
>
>    *From:* reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org<reflector-bounces at tvbf.org>]
>    *On Behalf Of *Terry Miles*
>    Sent:* Tuesday, July 2, 2013 11:46 PM*
>    To:* Velocity Aircraft Owners and Builders list*
>    Subject:* Re: REFLECTOR: Electrical system
>
>    Wow.  Dave, that is a very nice summary.  I did all of my
>    wiring...every inch, every connector, every everything.  I would repeat a
>    lot of what you offered, if asked, and that is:  keep track of wire size to
>    fit the current load, secure stuff properly so it cannot rub against
>    anything,  (I used that black wax lace stuff.  Yank on every connector
>    after you make it to test it.   Check every BNC you make for continuity and
>    twist it around a little before you declare it sound.   If you make 25 pin
>    connectors becareful with pin crimps, and especially the outboard most pins
>    when you go to secure the entire bundle.  (You can google how to tied the
>    knots.)  I read all the Nuckols stuff faithfully as I educated myself and
>    choose against the double alternators, but I do have a pair of Odessey 925
>    batteries located forward of the carnard bulkhead in the RG and have not
>    had water issues so far.   The main distribution is after of the carnard
>    bulkhead.   I did the 2 batts in part for wgt and bal since I am 150 pounds
>    and heard stories of trim issues.  While it is another discussion,  the
>    decision for one or two batts was and always will be debatable.  It might
>    have been better for me to use removable ballast since I cannot take
>    anybody much over 200 lbs and put them in the front seat.  My inflight draw
>    is about 4 amps, much much different from days gone by.  I will run out of
>    gas before I every run out of batt power.  I replace one batt every 18
>    months to two years.
>
>    Making wire streams (I like that term) would have been some good
>    advice for me.  I didn't do that and actually installed the wiring a little
>    at a time and added a lot of after the fact stuff....and I do have a lot of
>    loose single wires going hither and yon (sp?) back and forth from port to
>    starboard behind the instrument panel.  I used auto fusing mostly but do
>    have about a dozen in view aircraft grade CB's for stuff I want to know
>    about...ignition, transponder, hydro pump and gear control gizmo...stuff
>    like that.  There are also decisions about putting more than one component
>    into a single fuse/breaker.
>
>    I bought a $300 plus wire labeling system that uses heat shrink.  The
>    dam heat shrink refills were about 35 cents an inch, but I thought that was
>    money well spent, as well as being able to work at a base level with
>    turbo-cad to do the drawings since I experienced endless edits in that
>    department from my first paper drawings.
>
>    If you do your own wiring, I would call Dave first since he offered.
>     I am only a Saturday afternoon electrician-avionics tech, but I can
>    certainly add my name if you want an opinion about doing your own harness
>    and/or tacking the job of installing all of the avionics and doing those 2
>    gazillion settings on your own.  Being able to buy both an AHRS and an
>    autopilot from the same vendor is a big plus not available to me.  I have
>    GRT stuff and I like it.  Besides buying mil spec wire, buying high grade
>    teflon tape is a good idea too.
>
>    Terry
>    ------------------------------
>    To: *reflector at tvbf.org* <reflector at tvbf.org>
>    From: *dtnelson at us.ibm.com* <dtnelson at us.ibm.com>
>    Date: Sun, 30 Jun 2013 10:36:59 -0500
>    Subject: Re: REFLECTOR: Electrical system
>
>    Hi Reiff,
>
>    The power and ground bus bars I'm talking about is behind the canard
>    bulkhead in the area behind the panel - not forward of the bulkhead and
>    exposed.
>
>    In general, for exposed connections, the worry wouldn't be failure due
>    to shorting from the water, it'd be corrosion.  In general, galvanic
>    corrosion should be considered, but can be easily controlled with HW store
>    electrician's grease.  The relays and connections that I do have on the
>    forward (exposed) side of my bulkhead all have a dab of that stuff (main
>    contactor, hydraulic pump relays, battery connections, etc.).
>
>    I've never seen galvanic corrosion on my homemade brass bus bars & the
>    bimetal ring connectors I've used.
>
>    I've seen the other comments re. use of two alternators, etc. I agree
>    with the guidance from Richard Gentil - if you've got an electrical problem
>    you're going to want to land and fix it anyway.  Keeping your system as
>    simple as possible and building your simple system with reliability in mind
>    makes much more sense to me than trying to add all kinds of redundancy...
>    which just gives Murphy more opportunities to ruin your day.  I'd think
>    really hard before installing a system with two alternators, two batteries,
>    all kinds of switching relays, lots of extra wiring... failure points...
>    and things to go wrong.
>
>    My two cents.
>
>    Dave
>
>    Dave T. Nelson
>    T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
>    Program Director, ISC ECAT NPI & Test Engineering
>
>    Dave,
>
>    Terrific advice! Thanks for all the help.
>
>    Did you cover the power buss with anything? Is there any concern of
>    having a "naked" power buss in the nose? I have an RG, so I'm imagining the
>    entire inside of the nose will get wet if I take off or land in the rain.
>
>    I really appreciate all the info!
>
>    Reiff
>
>    *
>    From:* *reflector-bounces at tvbf.org* <reflector-bounces at tvbf.org> [*
>    mailto:reflector-bounces at tvbf.org* <reflector-bounces at tvbf.org>] *On
>    Behalf Of *Dave T Nelson*
>    Sent:* Saturday, June 29, 2013 1:12 PM*
>    To:* *reflector at tvbf.org* <reflector at tvbf.org>*
>    Subject:* Re: REFLECTOR: Electrical system
>
>    This is an excellent area for KISS.... Keep It SIMPLE!
>
>    In my installation, I used two connection blocks in the area behind
>    the instrument panel for both 12V and ground (4 total), one of each flavor
>    on the left and on the right.  I made them myself by soldering brass screws
>    into a brass plate.  I then used ring terminals on the wire ends.  The
>    terminals are then held tight with MS21042 nuts.  The idea is to avoid
>    having to have wires seeking 12V or ground from having to cross the whole
>    panel from the left side to the right (or vise-versa).  The ground system
>    should be simple - everything has only one grounding point (to avoid ground
>    loops).  On both power and ground, the buss bars are powered (or grounded)
>    via two wires for redundancy.
>
>    I used switch circuit breakers instead of switches with separate
>    circuit breakers (or fuses).  I wouldn't recommend that... I've had a
>    couple of them fail.
>
>    I used circuit breakers instead of fuses.  My reasoning was that I
>    want to be able to see at a glance if one had popped (hard to do with a
>    fuse).  I wish I'd used the type that allow you to pull the end of the
>    circuit breaker to switch a circuit off.
>
>    Don't buy used circuit breakers!
>
>    Use real aviation grade wire, not Radioshack junk.
>
>    I used, carefully and religiously, a wire size chart.  I've seen many,
>    many installations where folks use wire of way to low of a gauge (too thick
>    and heavy).  You'll be surprised how often you can use 20 or even 22 gauge
>    based on the current requirements.  Make sure the wiring chart you use is
>    for bundled wire, not single strand.  Make sure you use the right size
>    terminal for each wire.
>
>    I sized the circuit breakers for the load, not for the wire carrying
>    capacity.  There has been some debate on this, as Nuckolls would size the
>    fuse/circuit breaker for the wire, not the load.  IMHO I'm trying to
>    protect the expensive load (radio), and the wire will always
>
>
>
> [The entire original message is not included]
>
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