Rob, see below:

 

Shannon (who is spearheading a very informative discussion -- thanks!)

 

Thanks, glad you are finding it useful.

 

I'm curious as to why an EFIS, a Garmin 430, a backup attitude indicator, and

autopilot and a transponder would all be on an essential bus!  Second, why

wouldn't the landing gear be on there?

 

Let me try and explain.  First, my background:  I’m a EE, so my experience is with modern solid state factory controls.  I have found these modern electrical (solid state) controls to be more dependable by far than their mechanical moving part ancestors.  Therefore, I have a lot of confidence in modern electronics and very little in mechanical parts of old. 

 

With that said, the EFIS (chelton) is my primary means of attitude, heading, airspeed and altitude, as well as engine data and GPS.  Also important to me are a backup GPS (Garmin), a backup attitude indicator (JET 2”), and very importantly, an autopilot. 

 

I stress the autopilot as I strongly feel it can fly the plane better than I can, especially when I am in a stressful situation like a switch to an ESS bus would be.  Therefore, I feel the AP is a must.  I can flip it on and let it fly while I try and figure out what’s going on.

 

Now, as far as the transponder and the audio panel.  I feel it is necessary to have the audio panel so if I have a passenger I can communicate with them to help diagnose the problem.  Also, this allows me to communicate with ATC, so it’s basically needed.  Transponder is optional I guess.  However, I’ve designed my power system such that if this failure occurs, I have enough battery power for continued operation to outlast my fuel.  This design takes into account all the components above that I mentioned.  I feel these components are the most important to getting me to the ground safe (transponder included to allow ATC to clear the path).  Also, they are all clearly labeled in the AUX/ESS area on the CB panel, so further load shedding can easily be done if needed.  I’d rather have them on and be able to shed them than not to be able to get to them.

 

You also questioned why I didn’t have things like gear and flaps.  My response to that is that I can always flip the MAIN buss back on when I’m on final and pop the gear and flaps down.  Also, the gear is free falling, so it is of little concern.  The flaps are hardly needed to land safely I don’t think (though quite helpful).  Also note the gear indicators are on my ESS/AUX buss, so that info is available.

 

OK, it's clear that Shannon is using his essential bus as a simple (one

switch?) means of load shedding rather than a true "emergency" bus. 

 

Yes and no.  In its basic form, there are two busses, MAIN and ESS/AUX.  If the main alt fails, flip the MAIN ALT off and the crosstie on and carry on (shed load as you feel necessary).  If things get worse than that, its probably an emergency.

 

Now, to show how the emergency buss comes in.  Bob calls the Chelton “pampered”, because it needs to reside behind an AV MASTER, which he feels is ridiculous with the technology available today.  I tend to agree.  However, the fact remains it needs it (experimental version, certified is suppose to be DO-160, but not sure...I played it safe). 

 

So, what I did was create a hybrid buss off the ESS/AUX buss that I call ESS/AUX AV.  It is fed from the ESS/AUX buss, through a big diode and with a solid state relay that is operated by a standard lancair issue Eaton switch.  This is my true ESS or emergency buss.  If I have problems, the components on it are what I (feel I) need on. 

 

So, to make it a true emergency buss, it has to have a backup:  ie, in case the battery contactor fails, in case the switch or solid state relay fails.  This is accomplished in BobN form by having an ALT FEED switch.  I used a locking hyd pump switch from lancair.  This switch gets power through a 30A fuse directly from the battery (before contactor), and it feeds into the ESS/AUX AV buss.  If things get hairy, flip the AUX/ESS ALT FEED on and turn everything else (masters) off.  That gets me down to the basics, and there are a minimal number of parts count between it and the components.

 

In fact, I have two AV busses that are set up this way.  I originally had two ALT FEEDS, one to each AV buss.  However, I have recently switched the second ALT FEED to feed power to the part of the AUX/ESS buss that isn’t behind the AV MASTER.  This basically gives me the capability to feed the whole AUX/ESS buss directly from the batteries, so the AUX/ESS buss is truly backed up and can be considered an emergency buss.

 

Most people won’t need the AV MASTER and the solid state relay, as they won’t be fussing with something like the Chelton.  And, most won’t need the second ALT FEED.  By design and component count, my system is more complex than most.  However, I fully understand it, and I am really comfortable with it.  Since I’m the only insured pilot on the plane, I don’t have much to worry about in teaching it to anyone else, though it is really quite simple once you see it.

 

http://shannon.v8eaters.com/images/lancair/Knoepflein-l2k-121302.pdf

 

And that's

fine.  The architecture he suggests gives as much power supply reliability in

this backup mode as an average spam can has in it's primary mode.  (In fact,

that's the whole point he's trying to make.) 

 

Glad somebody got it J

 

The only remaining issues are

whether or not anything else is also broken and this is why Jeff and Hamid are

throwing darts  -- with Hamid's being a little less sharp and pointy. 

 

I totally agree with them that if you don’t know exactly what’s wrong, get to the ground.  However, if you can figure out what failed with the parameters you have available and its not a risk to continue, then by all means do.  Well, that is dependant upon you having designed your system to give you enough reserve to do so, which was most of my point to this whole discussion. 

 

I personally know that I can flip both ALT FEEDS on, turn everything else off (including both alternators), and have enough battery to go 3 hours with that stuff on.  I think everyone with an OBAM aircraft should have this ability.  Whether or not you use it is your choice decided upon by your own personal limits and the circumstances and parameters around a failure.  However, you should have the option, and your system should be able to do it.  It only provides a margin of safety and reliability to have this option, and it takes so little to get it.

 

However, if this were truly an "emergency" bus I would submit that you don't

need an autopilot, an EFIS or even a transponder.  Hell, I'd rather have the

landing gear than a transponder -- the transponder may keep ATC's blood

pressure down but I'd be more worried about my own.

 

I disagree.  See above.  Like I said, I trust the EFIS more than any of the other mechanical instruments (yet I do have the JET 2” AI online too, as well as a pitot static airspeed and altimeter).  I feel the AP is very important when stress it high, and I trust it to keep me rightside up better than my own hand.  I think the big thing to realize here is that you can easily have all the components you personally feel you need on your “emergency” buss, as long as you design it properly.  I personally chose the ones mentioned, as they are what *I* feel *I* need, YMMV.  Likewise, I designed my power system so I could keep them powered longer than my fuel tanks would last.  Pretty easy to do actually.

 

At work (Aviation Technology Group -- we're working on the Javelin jet which

will be FAR Part 23 certified) we're arguing about these very issues this

month.  We have to live by FAR requirements which basically require a 30 minute

"aviate, navigate, communicate" capability in the event of a generator failure. 

However, we are also interested in an above-and-beyond requirement which

allows us to shut down all of the electrons in the aircraft in the event of an

electrical system fire.  We would then operate on a separate mini-battery

powering a standby attitude indicator ONLY. 

 

 

This sounds like a good step in the right direction.  However, I would hold that you could accomplish the same thing with an alternate feed and a small ESS buss that has whatever you feel is needed on it (this would be the AI from what you’ve said so far).  I would strongly consider this way as you can eliminate the weight and complexity of the extra battery, and you can insure the battery the ESS buss is feeding from is charged and current (as it will likely be starting the engine and charged by the generator).  I don’t see what the extra battery gains you besides more complexity and weight.

 

My only other suggestion would be to put one of the simple wing leveler auto pilots on this emergency buss, a simple one that resides in a turn coordinator should suffice.  It would have its own servos too.  I would highly recommend this, maybe even more important than the AI.  The TC should be sufficient if the AP for some reason crapped in place of the AI.

 

So, I envision an emergency buss with an AI and a TC style wing leveler autopilot on it, feed through a diode with an EMERGENCY ALT FEED switch.  Things get nasty, flip the EAF switch on and turn everything else off.  Flip on the AP and try and figure out what’s going on, as you describe below.

 

This allows up to keep the "canopy side

up" if this happens in IFR.  (The FAR's only require that you be able to

operate VFR after an electrical fire.)  Each of our two PFD's would operate on

separate battery busses and we'd hope to be able to revive one of the busses

without the fire restarting.  With one PFD operating we get "navigate, communicate"

function restored.  We haven't come to any final decisions yet but you can

imagine why I find this entire thread so interesting.  (Actually the Dynon EFIS

would be perfect for this appliaction if it were certified....)

 

This troubleshooting phase is all the better reason to add the wing leveler.

 

Good luck, and thanks for the thought provoking questions.

 

Shannon

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