What equipment do you consider "essential?"

I'm getting hip-deep into electrical planning, which in turn has me thinking through various failure states and what equipment does and does not need to survive said failures. This of course gets fun quickly because it's easy to go way down the rabbit hole of uber-redundancy (a topic already being discussed in other threads here).

So that leads to the core question I'm having, which is deciding that "stuff" I really need. I plan on equipping the aircraft for IFR flight but not flying in actual IMC on any kind of regular basis. Avionics will be Dynon (likely two displays, plus Skyview radio/intercom/transponder) and probably a GPS-175 for the TSO GPS role. I don't plan on installing a second com radio, and instead keeping a handheld on board for backup purposes.

The first and most obvious thing to me is maintaining an attitude reference. I'll be equipping one or both displays with backup batteries, so even in case of a total electrical failure I'll retain the attitude reference.

After that, though, honestly I'm starting to feel like everything else is OK to do without. Primary com fails? I've go the handheld. Transponder is dead? I don't really care. ADS-B receiver? Totally nonessential. The GPS-175, at least, is debatable - I'll still be able to navigate via Skyview but have no capability to shoot an approach. The only other things I can think of are the boost pump and pitot heat, which both seem nice-to-have-but-not-essential to me.

Basically, this all boils down to whether it's worth it to have any sort of e-bus (pick your preferred "e" word here) at all. I plan on using a VP-X for circuit protection, and wiring up backup paths for these devices, while not horrible, does pretty quickly add some complexity inflation to the system. And I'm honestly not convinced that it's worth it, but I'm here to allow people to change my mind if necessary.

So with that in mind, what's "essential" in your plane? What's faulty in my reasoning above? Tear my rationales apart, that's what I'm here for.

I've considered the same issues.

I resolve it down to attitude reference and autopilot/nav. If everything else goes to pot, I think I can find an airport with that equipment and come pretty close to putting the airplane on the runway centerline in virtually any circumstance - even very low ceilings/viz.

I'm keeping my setup pretty simple but I do have both a main and essential bus. I'm using the EFII bus manager which really simplified things for me. I won't go into the pros and cons here about the bus manager because it's been discussed before and it's not focusing on your primary question. All I'll say about the bus manager is that it makes it very easy to divide your electrical system up into a main and essential bus.

So, with that being said, I have my PFD, MFD, AHRS, EMS, and autopilot servos along with my electronic ignition and fuel injection components connected to the essential bus side and these components are protected via standard old school breakers. Everything else is on the main bus side and is protected via standard automotive fuses.

Since I'm running an electronic ignition and fuel injection system I'm 100 percent reliant on my electrical system, I wanted to be able to easily shed power consumption and conserve power for the ignition and injection system but at the same time be able to maintain essential navigation and engine management information.

So basically, at a flip of a switch, I can shed all power going to the main bus and all available power is routed to the essential bus in the event of an alternator failure. So, even in a doomsday scenario and I have to ditch my IFR navigator, coms, transponder, audio panel, etc. I'll still have my vital equipment essential for navigating and engine management along with my fuel injection and ignition equipment, to get me home.... or at least to the nearest airport.

One thing I'll comment on regarding your equipment choices is your decision to have only one com installed and to have a handheld as your backup. Even though having a handheld available is always a good idea, I can't tell you how nice it is to have that second com available to you for daily use. I've had it both ways and I really like having that second com at my disposal.

Mark

I too will have EFI (and thus an engine dependent on the electrons). I'm planning on a diode-fed "engine bus" right off the batteries, such that I can kill everything else and still run the engine. The only other thing I have planned for that engine bus besides the "keep the engine running" stuff (ECUs, coils, fuel pumps, injectors) is a standby attitude display.

I figure my main EFIS has its own backup battery and "communicate" falls below "navigate" on the priority list. There's enough redundancy in the power system that I'm not worrying about having more essential or secondary buses; if things get bad enough (e.g. dual alternator failure) that I have to kill the buses or otherwise get really drastic and there's nowhere I can go that's VMC, I can either turn the buses back on long enough to shoot an approach, or I can fake it with EFIS/tablet navigation and synthetic vision.


I'm considering a second com radio, but only for operational convenience--assuming I can rig it up properly such that I can have both of them "active" and can transmit on either one by pressing the respective PTT switch.

and...

"...I'm planning on a diode-fed "engine bus" right off the batteries..."

Which is pretty much a function of the above mentioned Bus Manager...

My "standby" electric system powers the Garmin 420 and transponder. The Dynon FD180 automatically switches if main power is lost. I have to manually switch the others to the standby system.

I fly a lot of IFR and don't consider a #2 comm as a backup. I use it to get ASOS/ATIS and to monitor CTAF while still on center/approach freq to get an idea of the local traffic.

YMMV

I see a trend in the replies, which is to reduce the number of devices considered "essential". It's a good trend. The original intent behind the essential bus concept was quick load shedding under pressure, but there was a period where it seemed like every wiring plan we saw included a few more must-haves hung on the essential.

rocketman1988 said:

"...I'm planning on a diode-fed "engine bus" right off the batteries..."

Which is pretty much a function of the above mentioned Bus Manager...

Click to expand...

There is no good reason to diode-feed an engine power bus. All it does is reduce the available battery-only run time.

Mark33 said:

One thing I'll comment on regarding your equipment choices is your decision to have only one com installed and to have a handheld as your backup. Even though having a handheld available is always a good idea, I can't tell you how nice it is to have that second com available to you for daily use. I've had it both ways and I really like having that second com at my disposal.

Mark

Click to expand...

The only thing I find myself using a second radio for on a semi-regular basis is briefly monitoring a second frequency (eg getting ATIS at arrival airport while remaining with ATC), but the Skyview radio covers this use case by allowing you to monitor both the active and standby frequencies.

That capability was what really convinced me that I could do without a second radio in terms of workflow, which left me with just the backup consideration.

And...

Ok, Dan, we get it. You don?t like the EFII system. You are entitled to your opinion.

If you read my comment, all I said was the diode feed was a FUNCTION of the Bus Manager. I did not say it was good, bad, or necessary, just a function.

Enough said.

Happy Easter, everyone...

DanH said:

I see a trend in the replies, which is to reduce the number of devices considered "essential". It's a good trend. The original intent behind the essential bus concept was quick load shedding under pressure, but there was a period where it seemed like every wiring plan we saw included a few more must-haves hung on the essential.

Click to expand...

My thinking on this hasn't really been to facilitate load-shedding - I think if I need to do that I can turn things off manually, especially given that my system will be relatively simple. Instead, I've been thinking of in terms of an alternate feed to the system, where the e-bus feeds directly off the battery, bypassing the master contactor and VP-X. That, in turn, allows the failure of either of those two components to not be equivalent to a total electrical failure.

But, back to your point about having lots of "essential" hardware, I keep ending up thinking that the complexity of the alternate feed isn't worth it. I'd be adding a whole new circuit path to power...what? The boost pump? Maybe the GPS-175? Unless I start getting really liberal with the "essential" designation, it's not really doing much of anything.

N546RV said:

But, back to your point about having lots of "essential" hardware, I keep ending up thinking that the complexity of the alternate feed isn't worth it. I'd be adding a whole new circuit path to power...what? The boost pump? Maybe the GPS-175? Unless I start getting really liberal with the "essential" designation, it's not really doing much of anything.

Click to expand...

E-buss installation isn't terribly complex, but your bigger point is correct. You can do all of it with manual switching. It just takes longer and may lead to worse decisions.

The e-buss was designed to pare the electronics down to the essential items quickly and with the flip of two switches - the e-buss switch and the master. Then, you'd have power to the items you'd identified as essential when you were in a rational frame of mind, sitting on the ground, without the pressure of thinking through the problem as it occurred.

Sorry, but I?ll tilt at the windmill one more time.

For a modern, dual EFIS IFR RV the concept of ?Main and Essential? buss no longer make sense. There are better options. The design objective of load shed is way down the list. Providing power to maintain IFR flight is the prize. Design around this objective. Any setup with a single power path (all elements including connections, relays, grounds and switches) to a needed panel component is not acceptable (again for IFR designs).

For that matter anyone flying an RV with an electrically dependent engine must have an independent battery and power feed to the engine electrical components. I don?t care if you have four alternators - any single battery setup is a risk.

So, again putting on the Nomex suit for the predictable pushback. If you must, please provide some logic to go with your protest beyond ?this is what I do?.

Carl

rocketman1988 said:

If you read my comment, all I said was the diode feed was a FUNCTION of the Bus Manager. I did not say it was good, bad, or necessary, just a function.

Click to expand...

Yep, that was my understanding. I said there was no good reason for that function, specifically a diode between a supply battery and an engine bus. It's an unnecessary voltage drop, wasting power to heat. I don't care who incorporated it.

Carl Froehlich said:

.....I don?t care if you have four alternators - any single battery setup is a risk.
Carl

Click to expand...

Agreed!.... and this brings me back to simplicity, ease of installation, and redundancy of the bus manager. I know this is drifting away from the O.P.'s original question(s) but hopefully he'll still find some relevance here.

I understand that there's some folks who don't like the bus manager and have dissected the way it's designed and have pointed out/criticized its redundancies...and I'm sure with all good intentions and legitimate concerns regarding safety, but for a dumb shade-tree mechanic like myself, the B.M. was the way to go.

The B.M. allows me to: 1. Have a separate main and essential bus with easy load shedding at the flip of one switch. 2. Allows me to have continuous/autonomous monitoring of my fuel pressure with automatic switching to the backup fuel pump in the event of the primary pump failure, and 3. It allows me to run a two battery setup with one of those batteries being lithium iron. I know you're not suppose to mix and match lead acid and lithium batteries for reasons of both charging and discharging, but the B.M. allows me to do this.

My setup consists of two batteries/one alternator and as mentioned above, one battery is lead acid and one is lithium iron (which is strictly my backup battery). The lead acid one is my primary battery and carries all of the heavy load, including starting duties. Once the engine is running and the alternator is charging, the B.M. "manages" both the charge and discharge of both the lead-acid and the lithium iron batteries. In the event of an alternator failure the B.M. "manages" the discharge of both batteries in a way that optimizes the available battery power without having to worry about one of the batteries back-feeding into the other one or having to worry about flipping switches back and forth and managing battery power on my own.

Once again, I know there's many ways to skin a cat, but the B.M. has allowed me to have a fairly sophisticated electrical system with redundancies but done in a very simple manner that even a dumb shade-tree mechanic like myself can install.

Mark

Carl Froehlich said:

...

For that matter anyone flying an RV with an electrically dependent engine must have an independent battery and power feed to the engine electrical components. I don?t care if you have four alternators - any single battery setup is a risk.

...
Carl

Click to expand...

I think the key here is "electrically dependent engine"....

Keep one magneto and then a single battery is OK when your EFIS/PFD has it's own battery back-ups.

Who has had a battery actually fail in flight?

az_gila said:

I think the key here is "electrically dependent engine"....

Keep one magneto and then a single battery is OK when your EFIS/PFD has it's own battery back-ups.

Who has had a battery actually fail in flight?

Click to expand...

So the EFIS backup battery will keep the EFIS going - and you loose autopilot, comm radio, your TSO GPS navigator, VOR/LOC/ILS receiver and transponder. Not my definition of continued IFR flight.

Properly maintained batteries are very reliable. The stuff between the battery and where you need the power tends not to be so reliable - especially if something else hooked to the single battery decides to go up in smoke.

Carl

"....and you loose autopilot, comm radio, your TSO GPS navigator, VOR/LOC/ILS receiver and transponder..."

Still have a GPS on the EFIS/PFD/MAP and a hand-held radio.

Fuses/CBs protect the rest...

Handheld radios generally have very limited range unless you have an external antenna.

flyinga said:

Handheld radios generally have very limited range unless you have an external antenna.

Click to expand...

Yes, but in an emergency...

Who has had a battery actually fail in flight?

Click to expand...

My 6-year-old PC680 failed while flying. I did not notice anything amiss until closing the throttle for landing. Then the Dynon D-180 rebooted. Another symptom was unstable voltage: plus and minus 1 volt. The D-180 did not have an internal backup battery at the time, but does now. The Rotax alternator does not supply much current at low RPM. The battery failure was intermittent at first. Sometimes it worked fine. Other times it was open circuited. I sent the PC680 to Bob Nuckolls who opened it up and found a broken weld.
Even though my battery failed suddenly without warning, it is a very rare event.

N546RV said:

So that leads to the core question I'm having, which is deciding that "stuff" I really need. I plan on equipping the aircraft for IFR flight but not flying in actual IMC on any kind of regular basis. Avionics will be Dynon (likely two displays, plus Skyview radio/intercom/transponder) and probably a GPS-175 for the TSO GPS role. I don't plan on installing a second com radio, and instead keeping a handheld on board for backup purposes.

The first and most obvious thing to me is maintaining an attitude reference. I'll be equipping one or both displays with backup batteries, so even in case of a total electrical failure I'll retain the attitude reference.

After that, though, honestly I'm starting to feel like everything else is OK to do without. Primary com fails? I've go the handheld. Transponder is dead? I don't really care. ADS-B receiver? Totally nonessential. The GPS-175, at least, is debatable - I'll still be able to navigate via Skyview but have no capability to shoot an approach. The only other things I can think of are the boost pump and pitot heat, which both seem nice-to-have-but-not-essential to me.

Basically, this all boils down to whether it's worth it to have any sort of e-bus (pick your preferred "e" word here) at all. I plan on using a VP-X for circuit protection, and wiring up backup paths for these devices, while not horrible, does pretty quickly add some complexity inflation to the system. And I'm honestly not convinced that it's worth it, but I'm here to allow people to change my mind if necessary.

So with that in mind, what's "essential" in your plane? What's faulty in my reasoning above? Tear my rationales apart, that's what I'm here for.

Click to expand...

Back to the original question and probably adding a new line of differing opinions than the never ending backup battery discussion. I am a firm believer that backup instruments need to be basic and different from the primary. It does not take a lot of panel space or extra plumbing to put in a steam gage airspeed indicator, altimeter, and tach. Probably lighter than the backup battery. Backup battery for EFIS still has single point failure since battery only addresses power failure.

I consider the following essential, in priority order.
Trim (mine is all electric)
EFIS
GPS Navigation (of some sort, preferably the IFR navigator)
Com
Autopilot

Next tier (probably not essential)
Transponder
Flaps
Boost Pump
Landing Light

It would be nice to get others to list what they consider essential, and not focus on their strategy to power the essential components

Here is my plan and simple architecture

I tend to agree with the outdated e-buss architecture for the modern day EFIS systems: For a dual screen G3X System with CB's to pull and shut down components and Isolate any loads.

I have a single Main Battery and Alternator,

If alternator goes TU, I have Main Battery (probably Earth X) for approximately an hour or more with GTN 625 still op.......

When that goes below 11 volts.....The TCW IBBS kicks on and will power for another hour or more the following essentials:

G3X Screen
GSU 25 ADAHRS
GEA 24 Engine Mon
Maybe GTN 625
Maybe GAD 29 ARINC

Will have Handheld Comm and the G5 with it's own seperate and isolated backup battery.

If after all that (approx 2+ hours of backup juice) my bladder will have exploded or I'm just really having a bad day.

I have to continually remind myself that I'm building a simple but yet capable IFR at times 9 machine and at the end of the day the big fan out front could always be the single point of failure...

IFR panel for RV

Here is your succinct answer to what equipment is needed:
Dynon SkyView (HDX) - Just one screen. Primary EFIS, Engine and Map 10"
Dynon D6 - Independent backup with separate magnetometer
Garmin GPS (430) or better depending on budget. - IFR approaches and Comm 1.
Dynon Radio for Comm 2.
PS Engineering Audio Panel.
Dynon Autopilot.

http://www.mykitlog.com/users/displ...n&project=607&category=4646&log=251845&row=49

The HDX and D6 give you redundant and independent EFIS which I think meets the IFR requirement for multiple gyros.

sglynn said:

...which I think meets the IFR requirement for multiple gyros.

Click to expand...

Here is EAA's answer to "Equipping a homebuild for IFR Operations": https://www.eaa.org/eaa/aircraft-building/intro-to-aircraft-building/frequently-asked-questions/equipping-a-homebuilt-for-ifr-operations.