Circuit Breaker Switches

[Nev]

Another data point. I'm using the Dynon ACM (the equivalent of a VPX). It was simple to install, and I can view all the circuits on screen and select them on/off.

FWF I've used the VP PPS which is a small "black box" that handles the starter, alternator, battery etc. It's also a simple and clean installation.

Click here to view.

[zkelley2]

The only downside to the VPX is to my knowledge none of the Electronic ignition or injection companies recommends using it for their components and want more robust backup power. If you're not using those, then I don't think there is one other than cost.

[David Swartzendruber]

I think the other downside of the VPX or similar products is that if it doesn't work, you can't do anything but send it back to be fixed. A simple system with circuit breakers or fuses and discrete switches allows you to troubleshoot it and fix it yourself.

[Ejs014]

The VPX brings a lot of convenience and bells and whistles. I’m sure it’s the best thing out there as long as it’s working. The devil is in the details of the integration. You could end up with a single point failure (power supply?) that effects the entire electrical system. If I were using it I would want to integrate it so it wouldn’t leave me grounded. I can troubleshoot breakers/switches/wiring etc but as David mentioned if it craps out you are left with sending it back to the manufacturer for a repair (cost?). Also need to take into account what type of flying you do, VFR vs. IFR. It looks like the pro version may have dual power supplies but I’m not sure if that’s for redundancy or additional load capacity.

[Utah-Jay]

I am going with the Dynon/Advance Flight Systems version of the VPX, it is called an ACM or Advance Control Module
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[svyolo]

I don't have any experience with CB switches in GA aircraft, but I like that they reduce mechanical connections. I do have 30 years of experience using CB's in commercial/military, and would rate those CB's as one of the least reliable things on the aircraft. But GA uses an order of magnitude fewer CB's so probably much less of an issue. When you have several hundred it becomes more of an issue.

I really like the VPX and Dynon modules and sort of wanted to use them. I really like the VPX PPS and may end up using it down the road. My issue with the ECB stuff is how it interacts with other software controlled stuff. Different software, just like different hardware, can interact in a way that makes the whole thing unstable. I have EFI and chose to avoid the ECB stuff for now, even though I like it. Both B&C and SDS have a few disclaimers about VPX use, probably mostly as a, well, a disclaimer. They have not tested every corner of the envelope, and probably don't want to.

I wired up everything myself because I could. There is no individual thing I did, that I hadn't done before except one thing - designing and constructing an entire electrical system from scratch. I can't say I actually learned anything new other than figuring out how to make the wiring for a fold down instrument panel without excessive stress on the wiring. I spent several hundred hours on wiring. I would have rather just bought a VPX or Dynon, and if I can next time, I will.

I am happy with the end result, but wow, it was a lot of hours. So far, no smoke.

[svyolo]

I think in hindsight, if I had known about Dynon's ACM before I bought my avionics (I am not sure they were available then) it would have pushed me into their brand.

[Nev]

All the points mentioned above are possible, but whether they should be cause for concern is a different matter.

When I was planning my avionics install, I made an effort to move ahead to a modern way of doing things where it seemed to make sense, and where there was a solid track record already established in that area. I was trying to reap the gains in reliability and increased functionality. My aircraft will not be IFR capable so that greatly simplified things. (I'm not certain that being IFR in a private aircraft such as this would increase safety at all - and may well decrease it, (but it is fun to do) but that's another discussion. Same as adding a second engine doesn't usually increase safety, and often decreases it.

To my mind, my main concern is having a single fault in the electronics that requires a return to the vendor for fixing or replacement. Regarding the Primary Power System (replaces the FWF circuitry), a failure there could result in a major inconvenience, but it shouldn't cause an engine stoppage once running. Whether it's any more likely to fail remains to be seen, but I suspect it's probably less likely to fail than the traditional contactors.

I'll also be testing my Dynon ACM thoroughly during the test phase to ascertain that it runs as I'm expecting. That includes being able to isolate the ACM (turn the master switch off) and keep the engine running. My electronic ignition is not battery dependent, so if the battery (or a battery circuit fails), the engine should keep running. If it doesn't, I'll be changing things so that it does.

I've set my switches up with the Master on the left, then Alternator, then Avionics switch. During start The master goes on for engine start - this powers up the left EFIS. Once the engine is running, the Alternator switch goes on, then the Avionics switch, which powers up the right EFIS and all other avionics. If I get smoke, battery or alternator failure during flight, I switch off from right to left - Avionics switch first to reduce drain, then if necessary the Alternator switch. This leaves the left EFIS on. I can then power the Master off, and leave the left EFIS on standby battery. Or turn it off completely, and revert to the primary navigation display which is 42 inches wide and made of Acrylic. Landing without avionics is not the slightest concern. In any aircraft.

Other than that, it's a single engine aircraft and there are quite a number of other potential single failure points. I'm thinking of that little thread that connects the control stick to the cable bellcrank under the front seats......if that thread ever strips out, having a failure of the Primary Power System would seem like a very nice alternative. (I'm just illustrating a point). There are many parts that I could become focused on, but I deem them to be a small and acceptable risk and I'll try to minimize these risks in a sensible way.

[m.mooney]

Other than that, it's a single engine aircraft and there are quite a number of other potential single failure points. I'm thinking of that little thread that connects the control stick to the cable bellcrank under the front seats......if that thread ever strips out, having a failure of the Primary Power System would seem like a very nice alternative. (I'm just illustrating a point). There are many parts that I could become focused on, but I deem them to be a small and acceptable risk and I'll try to minimize these risks in a sensible way.

Very well said. I completely agree with your logic and like your electrical architecture. At the end of the day, this whole flying thing is about sensible risk management.
Mike

[BravoGolf]

Yesterday I had my EFIS reboot twice, once after take off and once again as I was headed back. Nothing like a black screen to get your attention. Of course I’ve already sent information to the manufacturer and it will get fixed. But it has made me less confident in modern electronics. If an attitude indicator rolled over or the battery relay failed oh well. I can probably walk into any FBO and get a relay.

[rodsmith]

What brand EFIS?

[Nev]

I am going with the Dynon/Advance Flight Systems version of the VPX, it is called an ACM or Advance Control Module
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If you purchase it from Advanced Flight Systems, nearly all of the cables are of fthe shelf. And they really are "plug and play".

Incidentally, I read something that I think Jared might have written a while ago about placing the ADYHRS in the wing root. Having just installed the magnetometer, I like his idea and it would simplify things a lot. If I was doing it again, I would probably place the ADYHRS, magnetometer, air temp prob, and Pitot, all in the same wing.

As it was I took more of a scatter gun approach

[PaulSA]

Certainly for Dynon, the ADAHRS has to be close to centreline - I'm not sure the wing root suffices. As for the electronic breakers, it is interesting that the UK starting approving night/IFR on homebuilds a few years ago. They specifically excluded VPS equipped aircraft on the grounds that the design was not robust enough in the event of a major fault ie, a single-point failure issue.

[jaredyates]

The space between the fuselage and the fuel tank works great. They provide a diagram with the range of acceptable locations in the documentation, and it's +/- 6 feet left-right of the centerline, and +/- 12 feet forward and aft of the centerline.

[rv8bldr]

Lots of good stuff deleted....

...revert to the primary navigation display which is 42 inches wide and made of Acrylic....

Love this :-)

[BravoGolf]

Hate to sound like a dinosaur but what is the MTBF of the electronics we are installing? There are a lot of good products out there but I can’t find data about failure rates. Which forces us to design, purchase and install lots of redundancies. I installed one CB switch because I was worried about failure rates but I have a CRJ’s worth of electronics. Seems backwards in retrospect. Sorry about the thread drift.

[svyolo]

If I planned on IFR (I am notI would have two EFIS, but I also will have a tablet and a phone. The navigation and EFIS apps work well enough to get me home. I have turned those apps on at 370 and they worked beautiful. That is a lot of backups, at least for me.

[jaredyates]

Hate to sound like a dinosaur but what is the MTBF of the electronics we are installing? There are a lot of good products out there but I can’t find data about failure rates. Which forces us to design, purchase and install lots of redundancies. I installed one CB switch because I was worried about failure rates but I have a CRJ’s worth of electronics. Seems backwards in retrospect. Sorry about the thread drift.

I think there is definitely something to this. In our blue plane I had the Skyview system operational for almost 6 years and around 300 hours. In that time I had three different screen failures, in each case rendering one screen unusable. I never had any trouble at all out of the D100 series but didn't have quite as much time in service to compare. I'm finding myself in a new situation of deciding how to equip a panel and it's not an easy choice. I will say that the technology can bring very good utility, but that utility is going to vary from one operator to the next. Our Dynon brought ADS-b in and out, being able to display our position on a map, along with layers like rain, traffic, terrain, and predicted glide range. If that system is operational on a plane with a turn radius like ours, I don't know how it would be possible to have a CFIT situation. Similarly, if a pilot respects weather and wind minimums and only flies in the daytime, I think it is equally near-impossible to have a CFIT situation. If a pilot is always looking outside, then automated traffic systems are much less necessary, unless the hazard is coming from one of our blind spots, which are probably half of our 360 degree sphere. Having a GPS that feeds my location to a 406 ELT would expedite SAR by perhaps hours, compared to a 406 ELT that isn't GPS-informed, and perhaps days when compared to no ELT or a 121.5 ELT. But as to whether it is worth it or not, it depends very much on the mission.

I also think far too many builders underestimate how important electrical architecture is, especially if we are going to build such technically-advanced planes. There are situations in our projects where we can express artistic preference with the details and there are situations where compliance with the smallest details is crucial. Designing how switches, busses, alternators, and batteries interact is absolutely in the latter category for me. Personally, I wouldn't consider any of the commercial power distribution products at this point. The no-go factors are the required effort to understand its internal workings and failure modes, not being able to repair it in the field, and above all, not seeing the need for it. Our plane had a very robust electrical system, with dual alternators, load shedding by bus selection, and backup batteries. And we did it all without any of the products. It would be no problem to do it again, also without any of the products. What is the problem that these expensive boxes is going to solve? Being able to reset tripped breakers on the go? I never had a blade fuse blow and didn't plan to troubleshoot it in flight if it had.

[Ejs014]

I will add there are ways to design a robust system using newer electronics but the opposite is also true. ADS-B In is a game changer. Most people don’t realize what else is flying around them until they are really close not to mention weather.

Scott hit the nail on the head. I deal with reliability and safety on a daily basis in my profession. Manufacturers don’t have the real world data to calculate real MTBF numbers. Their numbers are theoretical not accounting for integration or environment. It’s typical to see MTBF numbers in the thousands of hours for electronic boxes. There’s a system safety process adopted by most of aviation that takes the architectural design and the reliability numbers to create fault trees and hazard analysis. It’s all about risk management. Newer designs have more redundant systems for this reason. The FAA dictates what the reliability has to be for given functions based on the hazard created by the failure of the component.

If you are staying day VFR there’s less risk period. Look outside and fly the aircraft. Electrical capability VFR should make the aircraft safer relatively speaking. More situational awareness, navigation and communication.

It gets really complicated when you add in night flying and IFR.