Yet another bus(s) concept

[foka4]

I'm in the process of deciding which components to put on which bus. I feel like I have a nice plan in the works, but it'll require a large relay, and I'm not sure which direction to take. (more on that at the end of the post)

I'm planning on a Z-13 style setup, with the following objectives:

1) E-bus with capability to get me back on the ground in night IFR with the Master switched off.
2) Steady-state emergency load on e-bus less than 8A (for sustained operation w/SD-8 backup alternator), though intermittent loads may be >>8A.
3) Intuitive operation for the average IFR pilot (no weird "switchology" to start and operate the aircraft, minimal complexity to switch to reversionary modes)
3) Isolation of avionics during engine start

Conceptually, I'm thinking of feeding the e-bus from the avionics bus. The rationale is that the Master will energize only the equipment necessary for startup. Next, the avionics bus is energized, which in turn brings power to the remaining systems (radios+e-bus stuff). Simple to operate, good isolation, with the expected e-bus behavior. Nice, eh?

Here's the breakdown of my planned system:

Main bus equipment
(nominal operating current=~6A)
*battery contactor
*EFIS w/ engine monitor
*Fuel boost
*Fuel primer

Avionics bus equipment
(nominal operating current=~5A)
*Panel lights
*AP servos
*SL-40
*Intercom

E-bus equipment
emergency steady state current=~5A
"everything on" steady state current=~35A (all lights, pitot heat)
Peak current (radios blazing, flaps in motion, ...) >45A
*Backup EFIS
*430W
*327 transponder
*Nav lights
*strobe lights
*landing lights
*flaps
*pitot heat

Here's the rub: The avionics+ebus can draw a peak load of 50A or so (lights, pitot heat, flaps, ...). Normal loads will be much less, especially when switching it on or off, but I want to size things appropriately. For the e-bus feed from the avionics bus, I can use a good SCR-type power diode, so it'll be up to the task with manageable heat and voltage drop.

For switching the avionics bus, the best solutions I can think of at the moment are:
1) put a huge relay between the master bus and the avionics bus
2) move the lights to the main bus. This would take the maximum Avionics+e-bus load down to about 15a, but would make nav and landing lights unavailable when running on the e-bus, greatly complicating emergency procedures in some cases.

Thoughts or suggestions would be appreciated.

Thanks,

Matthew

[N941WR]

I would suggest removing the strobe, position lights, pitot heat (BIG drain), and transponder from your EBuss.

If you are IFR and your transponder goes, there are ways to deal with that. The strobes and position lights aren't needed in an emergency to get you home. The landing lights may help but if you are low on power when you come in to land, all they will do is drain the rest of your power. Same goes for your flaps. You might find yourself doing a go around with partial flaps and now way to retract them.

When designing your EBuss, think about what the planes needs to fly and nothing more. Not much really; no radios, no nav, no flaps, no lights. Heck, no electrical system.

Now think about what you need to find your airport and land. The 430W will do all that, so keep that powered up. To keep the plane right side up, you will want your EFIS powered. Are you REALLY good on instruments that you can fly your RV IFR w/o an auto pilot? If you answer no to that question, put the AP on your Ebuss and you are good. What about your ANR power for just your headset? No, that's not really needed but I would rather have that than my position lights and strobes.

Just some thoughts for you from a guy who built a simple day/night VFR ship w/o an EBuss.

[Ironflight]

First, let me say that I believe there are a wide range of solutions for providing a reliable power architecture, so I won't give you a single answer that i feel best....but if you take a step back and look at your design, you might ask why bother to split the busses at all. You essentially have EVERYTHING on your E-bus....the stuff you don't is so trivial (load-wise) that you might as well put it on the same bus and make it super reliable. I'd postulate that lights really aren't essential to getting down under night IFR conditions - you'll be going to a well-lit runway if you still have power (probably), and I bet that you probably trained for no-landing light landings anyway....

Just a thought, since you asked.

Paul

[Kevin Horton]

Originally Posted by foka4

I'm in the process of deciding which components to put on which bus. I feel like I have a nice plan in the works, but it'll require a large relay, and I'm not sure which direction to take. (more on that at the end of the post)

I'm planning on a Z-13 style setup, with the following objectives:

1) E-bus with capability to get me back on the ground in night IFR with the Master switched off.
2) Steady-state emergency load on e-bus less than 8A (for sustained operation w/SD-8 backup alternator), though intermittent loads may be >>8A.
3) Intuitive operation for the average IFR pilot (no weird "switchology" to start and operate the aircraft, minimal complexity to switch to reversionary modes)
3) Isolation of avionics during engine start

With your current plan, if the main alternator fails, what are all the actions you must take to end up in the endurance configuration? If I understand the design, you would need to manually select a bunch of stuff OFF (pitot heat, lights, etc). If you forget to turn some of this stuff OFF, the load will be more than 8a, and the battery will be discharging. That could end very badly, when the battery finally is exhausted. Don't count on you noticing that the battery is discharging. You will be busy, and under a lot of stress. You won't be working at 100% efficiency.

I think a better plan is to strictly limit stuff on the ebus so that the load is no more than 8a. If you need the landing lights at the end of the trip you can select the master switch ON for a couple of minutes just before landing.

Set the system up to make the alternator failure procedure fool proof.

If you move the high load items off the ebus, and only put avionics on the avionics bus, then the need for high current relays probably disappears.

[foka4]

Great input, guys. Thanks!

I guess you have a good point with respect to the complexity of load shedding the e-bus during an emergency. I've had a hard time deciding the best balance between options and simplicity. Putting everything on the e-bus leaves options, but also the responsibility of managing them. As you indicated, what's the point of an e-bus with everything on it? (Aside from the load of the master relay coil, I guess.)

Strobes and nav lights can obviously go on the master bus. Recognizing that landing lights aren't essential for IFR ops, I can take those off as well. (I routinely land at night without my landing light. It's mostly for spotting deer on the runway, as far as I'm concerned.) Pitot heat still seems like a good idea, but probably not essential with gps-based EFIS systems. With all that stuff moved to the main bus, the loads balance out a lot better. Hey, I'm back to a conventional e-bus/Master bus system. The pendulum swings back to center...

Still, it's hard to have a conventional e-bus and still provide isolation for all the radios during startup. Which leads to the Matt-o-matic Bus, Rev 2:

Try this on for size:

Master bus:
*Equipment: lights, flaps, pitot, boost pump, primer, master contactor
*Offline during e-bus only operation.

Avionics bus:
*Equipment: Com2, audio panel, transponder, EFIS 2, 496
*Avionics Master switch isolates from Master bus for startup isolation.
*Offline during e-bus only operation.
*Audio panel automatically reverts to Com1 during e-bus operation.
*EFIS 2 internal battery keeps it alive during e-bus only operation.
*Handheld GPS internal battery keeps it alive during e-bus only operation.

Master E-bus:
*Equipment: EFIS1/EMS and AP
*Fed from master bus through diode.
*Diode feed provides engine diagnostic info during startup.
*Emergency feed through E-bus alternate feed switch, as usual.

Avionics E-bus:
*Equipment: GNS430W (Com1)
*Fed from Avionics bus through diode.
*Isolated from Master bus during startup by Avionics Master switch.
*Emergency feed through Avionics E-bus alternate feed switch (may be one pole of DPDT E-bus alternate feed).

A little more complicated than some systems, but compared to a Z-13, there are no additional single points of failure, as far as I can determine. Operation in E-bus only mode looks just like a Z-13.

Comments apprecated...

Thanks,

Matthew

[apkp777]

I used the Nuckols Z-13 schematic. Additionally I decided to use the AVMaster relay (from Spruce). Supposed to provide isolation for the Avionics during start up and protect from voltage spikes, so it doesn't really matter how it powered up. I have an Essential Buss with just the important stuff, radio, nav, EFIS, Trnspdr. Everything else on the main buss. I went with breakers, only because in a real life power failure, I can isolate the load much better. I opted for simplicity. Yours looks good, not too complicated.

[Pat Stewart]

I agree with Paul, not sure why its needed. I have had two of Vans alternators fail. You just power down everything not needed on get it on the ground. More important is the alternator you buy which is why on the RV10 I am currently building I went with the Plane Power 60Amp not Vans elcheapo.

Pat

[David-aviator]

It is interesting to cross read the threads on this forum. Here we have an enthusiastic young aviator planning an electric system for night IFR in an experimental single engine airplane.

And across the way, we read about accidents that keep happening over and over. What can be done to prevent them from reoccurring? All kinds of ideas are presented, some very good, some very detailed and from the FAA we have an alphabet soup list of checklists covering every aspect of decision making and flying. It's all there, how to fly and not kill yourself or anyone else who might be along for the ride.

For some builders, there is this desire to create something just for me and make it perfect. The effort can be personally challenging and rewarding. But it won't change the inherent danger of flying a single engine airplane at night IFR.

One series of airplanes that keeps showing up in the NTSB reports are the SR20 and 22's. That airplane has some serious design work behind it and yet it keeps coming to grief, many times IFR.

OK, is there a message here? Yes.

I could offer my 2 cents on how to build an electric system but to what end? So a you can blithely file a flight plan from here to there and a half hour later, when things come unglued, ask "What am I doing here?!" Nope, I won't contribute to your building enthusiasm by endorsing in any way what the end goal is. It just is not a responsible thing to do.

We are all going to die someday, but in a single engine airplane at night IFR?. RIP the marker will say, where was my good judgement? Sorry to burst the bubble, but that's reality. Weather is chaos be it at night or day. These small machines can not be made safe to take it on.

[apkp777]

Originally Posted by David-aviator

It is interesting to cross read the threads on this forum. Here we have an enthusiastic young aviator planning an electric system for night IFR in an experimental single engine airplane.

And across the way, we read about accidents that keep happening over and over. What can be done to prevent them from reoccurring? All kinds of ideas are presented, some very good, some very detailed and from the FAA we have an alphabet soup list of checklists covering every aspect of decision making and flying. It's all there, how to fly and not kill yourself or anyone else who might be along for the ride.

For some builders, there is this desire to create something just for me and make it perfect. The effort can be personally challenging and rewarding. But it won't change the inherent danger of flying a single engine airplane at night IFR.

One series of airplanes that keeps showing up in the NTSB reports are the SR20 and 22's. That airplane has some serious design work behind it and yet it keeps coming to grief, many times IFR.

OK, is there a message here? Yes.

I could offer my 2 cents on how to build an electric system but to what end? So a you can blithely file a flight plan from here to there and a half hour later, when things come unglued, ask "What am I doing here?!" Nope, I won't contribute to your building enthusiasm by endorsing in any way what the end goal is. It just is not a responsible thing to do.

We are all going to die someday, but in a single engine airplane at night IFR?. RIP the marker will say, where was my good judgement? Sorry to burst the bubble, but that's reality. Weather is chaos be it at night or day. These small machines can not be made safe to take it on.

There are plenty of threads dealing with the safety issues surrounding single engine IFR. Here the fellow is simply asking how to design his electrical system so that he has IFR redundancy and night capabilities.

IFR does not mean IMC nor does it mean night-time. Having a well-designed electrical system if valuable for all flights and conditions. That being said, I too question a pilot's decision to fly in IMC at night in a airplane designed and built purely for recreation. Most RV's have more IFR capabilities than some 747s I have worked on. Still, you have to admit a well equipped and designed avionics suite looks really cool and provides a greater margin of safety when used appropriately.

[David-aviator]

Originally Posted by apkp777

.....Most RV's have more IFR capabilities than some 747s I have worked on. ....

That's quite a stretch, Tony. I hope no here really believes it.