Quote Originally Posted by dothedr3w View Post
The plan is to run an Edge Performance EP912STi. Is neither alternator switch required? or just not the primary alternator?

There's not nearly as much info on these as Rotax engines, but from the pics I've seen online they don't use the same starting method. I could be totally out to lunch here though.
Ah, OK. I'm certainly no expert on that engine. As I understand it, that's a modified 912ULS. I don't know the specifics of the Edge Performance EFI, what ECU they use or how any of it is wired. Perhaps one of the guys here who flies that engine can chime in with details.

Heated pitot tube is more of a future proofing thing in the event I want to configure for IFR in the future; plus the cost differential is pretty negligible. I believe the EP912STi comes with a single alternator, with the option to bolt on a second. It has been recommended to run a 32A alternator, and bolt on an 18A as backup. I like the piece of mind a 2nd alternator adds as well. Open to suggestions!
Copy re the pitot tube. You may want to fly a Kitfox before you invest money in making one IFR capable. They're known for being very maneuverable, not for Bonanza-like stability...

If the EP912STi has a different electrical system then my comments may not be applicable. If you only get one alternator as standard on the engine then perhaps a second one makes sense. I'm using a 912iS, so I have the luxury of two DC generating systems from the factory. I'm installing a single battery that's sized to carry engine and minimal avionics loads for a reasonable length of time when the battery is near the end of its life. That said, you have to be comfortable with your plane, not me -- I'm just some random guy on an internet forum!

I just discovered DigiKey relatively recently and I love that place. Fair prices, good inventory, fast shipping. I should probably look for non-illuminated switches there as well!
You should have seen their inventory before COVID ruined the world. There's a lot more of their catalog out of stock now than there used to be.

So are you saying to have all this power-up with the master? Is 'load shedding' antiquated notion with the lower consumption of modern avionics? This is all very new to me.
Not necessarily; I'm just saying that the worry about depleting the battery by turning everything on while listening to ATIS and asking Ground a couple of questions about local departure procedures is overblown. There's definitely a case to be made for separately powering some of the avionics to permit load shedding. I'm doing it in my airplane. My Battery Bus will power a Main Bus and an Essential Bus, but the Essential Bus will have a second feed, via a relay tied to the battery side of the main contactor. On the 912iS, in the event of stator/regulator failure, the ECU/Fuse Box will run the engine from the remaining charging circuit and battery charging is lost. I'll flip one switch to load-shed the entire Main Bus, leaving me with the standby instrument (MGL ASV-2), comm radio, interior lights and landing/taxi lights -- just enough to get safely on the ground in this exceedingly unlikely scenario. The Essential Bus alternate feed path is there to bypass a failed main contactor, but it can also be used as a "radio only" switch for pre-flight activities.

Bob Nuckolls' book shows dual batteries paralleled for engine starting in designs with large engines or remote batteries (he even has a design for an Aux Battery Management Module), but his architectures do not run them in parallel for normal operation. Two Earth-X batteries would be massive overkill for starting a 1.2-liter four-banger.

The idea behind the vigilus was just to give engine instruments a dedicated display, plus it cooperates well with the Dynon, and can piggyback its sensors. I like the idea of an iPad becomes it's completely independent of the aircraft systems. [SNIP] ...you raise a very good point regarding the 7" HDX screen; that could replace the Vigilus and iris EFIS, and serve the function of both.
A separate engine display does allow more real estate on the EFIS for PFD and moving map, and there's nothing wrong with that if you want it that way. The iPad can also serve as an ersatz EFIS, minus the air-driven instruments and airframe-referenced ADAHRS. The 7" Dynon could definitely serve the functions of the Vigilus and Iris, but if it's part of the overall SkyView network, I'm not sure it could be powered from a separate bus for emergency backup. Perhaps that's a question for the Dynon forum.

All illuminated switches will be eradicated...I just got mesmerized by how cool they look. You're absolutely right that they're a distraction and serve no real purpose.
Again, I'm just some random guy on an internet forum with my own opinions and biases. I'm sure there are other guys on this forum who are perfectly happy with their illuminated switches and don't find them distracting. Techniques and standards that are used by certificated airframers aren't de facto applicable to Experimental builders. I guess what I'm saying is that you should weigh what you read in this forum, or any other, through a safety-vs-preference lens. There are definitely right and wrong ways to do some things, but for many others it's just a matter of choice.

M1/M2 are Master 1/Master 2. The internets told me that the BMS internal to the EarthX batteries can be rigged to a fault light. Idea with the dual batteries/master switches is I could just swap to the alternate and flip off the problem battery without any interruption to service. Again, I could be totally out to lunch here.
OK, got it. I had forgotten that the Earth-X battery's BMS has a fault output. That too could feed to a configurable input on the Dynon (either directly, or via an EMS input).

Take a look at Bob Nuckolls' Z-101B architecture and see how he handles what he calls the Endurance Bus and electrically-dependent engines. Single battery with dual feed paths for critical items. Incidentally, Bob has no beef with two alternators.

I wish you hadn't said this...this is going to result in many sleepless nights. You're absolutely right about all the above, but I'm going to have to do some serious soul-searching here, cause that VPX system is très nice. What are the Pros of the VPX system in your opinion? I just like how it integrates with the displays.
I suppose the pros of the VP-X are ease of installation, seamless integration with the EFIS, load monitoring and alerting, and so on. The VP-X website probably has a comprehensive list. I want to be very clear that I'm not suggesting there's anything wrong with the VP-X hardware or software; I'm sure that it's all designed by competent and conscientious engineers. My argument is a philosophical one: I don't believe in spending money on up-front convenience that results in an electrical system design that's run by a box whose internals are unknown to me, that I can't service myself, and that forms a single point of failure for the entire aircraft. Yes, you could make a similar all-eggs-in-one-basket argument about the Rotax 912iS ECU, but I'm pretty comfortable with the engine's service history and with the "Rockwell-Collins" sticker on the ECU. If any other item of avionics in my plane goes dark, oh well. I've thought about what I would do if each item failed and the answer in a VFR airplane is the same for almost everything: land when convenient. Other than both fuel pumps and the ECU/Fuse Box, there's nothing that represents an emergency.

As long as the VP-X can't stop the engine from running, and if you like the unit's benefits and have room in your budget, then by all means go forth and enjoy!