The "essential bus"

[Bruce Hughes]

Hi Group

I had a recommendation/requirement from my technical advisor to
do some rewiring of the Longeze project.   I am in the middle of that.

I will have most of PIDG terminals and ring terminals replaced
in the next day or 2.   Now I am wondering what should be on
the "Essential Bus".   It is not too late to make changes, on
your recommendations.

I have 7 circuits on appropriate sizes circuit breakers.   All of the larger
stuff, generally.   On circuit breakers: Strobes, Nav lights, landing
lights, electronic ignition, alternator field, alternator output, and
the "essential bus".

Everything else is on fuses.

The Essential bus presently is the following:

1. Radio
2. Transponder
3. Intercom
4. Altitude encoder
5. CHT/EGT (all 4 of each) gauge
6. Fuel pump

All 6 of those essential circuits are on individual fuses PLUS the circuit
breaker for the essential bus.

There are 11 other circuits which are on fuses, only.   EVERYTHING
operates off the Master solenoid, of course.

I am wondering if ANYTHING ELSE should be on the "essential bus".

I will appreciate all comments.

Thank you very much.

Bruce Hughes

[D]

Howdy Bruce -

Perhaps a Spare1 and Spare2 (and maybe even a Spare3) just to avoid any major surgery when you decide that something needs to be added to your "get me home" bus?

Other random thoughts that may/mayn't be applicable to your architecture:
-- Any nav to go with that comm?
-- Electric nose gear or electric landing brake?
-- Secondary ignition?
-- Voltmeter (to know how long you can prolong the agony)?

One final thing that caught my eye was that "EVERYTHING operates off the Master solenoid."  I'm guessing that this statement applies to everything except your E-Bus circuit breaker... which is fed directly from the battery (or the battery side of the Master solenoid) through a switch?  Perhaps your E-bus is also dioded to your Main bus (bus side of the Master solenoid) which makes the "EVERYTHING" true... as long as the Master solenoid is pulled in?  Just wondering how your buses are tied together.

Hope to see some pics of your handiwork once the rewire is complete!  

D

[Bruce Hughes]

D, power goes to everything when I switch the master.   I did not want
to have a Master but I was persuaded by a friend with the following
"If you suddenly have smoke in the cockpit, you WANT a single switch
that kills everything".

IN SERIES to the master, I have many circuit breakers as the previous
email said.

Yes, I have a digital voltmeter which is NOT from one of the usual
avionics companies and cost me about 1/10th of what they charge.
Clock/timer looks just like it, sitting by it.   Neat pair.   The company
has a quantity discount on 10.   Could run most of my sensors off
of those 10 with a little experimentation (there is a big sign in the
cockpit that says "EXPERIMENTAL"

No electronic nose gear.

I have one electronic ignition (Klaus's) and one magneto.   May go to
2 EI later.

I once had a nav/comm combo.   Radio died.   VOR then useless so
I took it out and got a modern ICOM.

I have a few ideas of additions but have not put in spare lines.
Thought of that but do not want to "spook" the DAR.    I just want to
get it in the air, soon.

Every day of my life I am doing "major surgery".   I don't worry about
having to change something.  Each change makes it a little safer.
 

Bruce Hughes

[Drew]

The interesting point that is being stated (which is what I will be doing soon also) is to include another wire and switch to bypass the solenoid.

What would be interesting to find out is---is there anyone with knowledge that knows whether that is a risk that needs to be mitigated-----are the odds of failure so low that mitigating that risk is not worth the effort.

[maprather]

Bruce,

I propose that you consider the inclusion of a battery buss for the electronic ignition and possibly the fuel pump.  The battery bus might be as simple as connecting a fusible link for the EI directly to to the battery terminal, and then to a switch/breaker on the panel.  Be sure to size the fusible link to protect the wire (only peripherally related to the peak current rating of the EI).  It would seem to be a shame to have to drop back to single ignition because of an electrical failure that forced you to open the master contactor, but which was unrelated to the ignition system.

I agree with the inclusion of a master contactor, btw.  Though, possibly not just for the reason you propose.

I assume that your airplane is VFR only?  Based on that, I see that the items required on the E-bus are very minimal.  My understanding of the idea of the E-bus/main bus split is to allow you to shed unnecessary loads (and also to quench fires) with the flip of one switch (the master), and yet still maintain comfortable control of the airplane.  This implies an alternate feed path for powering the E-bus (a switch and a wire).  This would be good because it would allow you to power up essential equipment without having to suffer the power hit of keeping a contactor closed (several watts).

It seems that only one of the items that you currently list on the E-bus could be construed as required for comfortable controlled flight - the comm.  That's pretty normal on a VFR airplane.  

For a night VFR (and light IFR) airplane, I'd propose that the only things required on the E-bus are cockpit lights, any electrically powered flight instruments (turn and bank/turn coordinator, EFIS, electric AI), plus at least one navigator (power jack for the GPS?).

Assumptions on my part:

Controlled flight doesn't require much.  You've just got to be able to keep the wings rightside up, and be able to navigate to your destination (or a safe airport).  It would be convenient to be able to talk with the outside world.  Once your airplane is debugged and healthy, you don't really need to know precisely what your EGT's/CHT's are.  You don't have to transpond.  If you have an electrical failure, see and avoid (you were already doing that), and call up ATC and tell them where you are and where you want to go.  No biggie.

It could even be argued that your e-bus doesn't need a comm.  That's why you bring a handheld comm radio, right?  

The aeroelectric connection is a great resource for airplane electrical system design.  Starting point:

http://www.aeroelectric.com/

List of model system architectures (not to be confused with precise schematics).

http://www.aeroelectric.com/articles/Rev11/AppZ_R11F.pdf

Good luck!


Regards,

Matt-

[JonC]

Out of the things you mentioned, I'd only go with...

1 - Comm
2 - Option to turn on Fuel Pump
3 - Option to turn on Electronic Ignition
4 - Artificial Horizon (if electric)... can save your butt if you have to punch a cloud or there is no horizon reference.

You don't need to squak if you have a power failure... as long as you can talk to them then you are fine, plus transponders draw a good deal of power. You need to talk to your passenger and keep them informed, but the intercom is unneccisary load.... you can yell over your shoulder.

Why optional on the fuel pump and EI? Most planes will fly fine without them on, but if you have to go-around you want all the power you can get.. would suck to make it down through clouds and all just to crash on a go-around cause the engine died of fuel starvation or you couldnt produce enough power.

CHT/EGT is not important. If it is of concern to you then pull your power back a little and richen the mixture... to quote one of my instructors... "Engine gauges and redlines mean nothing in an emergency, if overboosting, overtemping, overreving or just blowing the thing to hell is going to get you home, then let the damn thing melt... but don't say that on your checkride."

Only last thing I might add to that is a GPS... but only if you do night-ops or IFR.

[NWade]

Just a little follow-up on Jon's comment - since my CFI just made a similar statement during simulated-engine-out practice the other day:

"As soon as something happens to the airplane, the insurance company owns it.  The plane and everything in it is worth precisely $0 to you - all you care about is how it can get you safely on the ground."

T'was an interesting way to state the obvious (or at least, in retrospect it seems obvious); but is so seldom considered...

--Noel
(Solo or bust this week!)

[Bruce Hughes]

Yes, I read Nichols' Aeroelectric Connection before I started and
much of the system is based on his ideas.

I will be VFR daytime only;  have only a few instruments that require
any electrical power.   And a few have internal lighting which is not really
necessary.

I plan to NEVER fly when I need inside lighting.

My GPS is portable and has batteries (will take spares).

The noise cancelling headsets need a little power but work
without power, just noiser.

Most of the heavy load is on circuit breakers instead of fuses;
the nonessential bus is 12 lines which carry very low current.

I may need some weight in the nose so I will add a 2nd, smaller
battery for the electronic ignition, fuel pump, and radio (I don't want
to be messing around with a handheld radio in an emergency).   I
WILL carry the handheld as a backup.  

Bruce Hughes