RV-10 Electrical System

[tspear]

Originally Posted by Bill Boyd

I've always felt a second alternator/dynamo is of more value than a second battery for the exact line of reasoning above. How long do you need backup electrics to last in what has become a glider?

Alternators fail a lot more than the piston engines...

Tim

[Carl Froehlich]

Originally Posted by az_gila

SNIP

If you must fly IFR to get to VMC conditions then it implies your engine is running... and a second alternator would do the job of keeping the avionics going.
SNIP

With a focus on IFR flight, I respectfully disagree with this statement. Twin engine aircraft (two alternators, one battery) have suffered total loss of power even though both engines (and both alternator) were still working. The problem with single battery designs is that no matter what you do, you will end up where a single fault will leave your panel dark.

This boils down to two batteries are better than one, but two alternators and one battery is not better than two batteries (again - this assumes you put some thought toward not building in single point failure risks). The reason is the second alternator protects only from a loss of the primary alternator, nothing else.

Carl

[AviatorJ]

Originally Posted by leok

No separate switches. I'm not sure why I would want them.

I have power to the Autopilot servos group powered through the VPX with an "Avionics Switch". I can still access the individual output for each individual servo through the VPX page to override the Avionics switch on single outputs.

It was suggested to me by a corporate pilot. The idea behind it was if you have some servo run away or some other craziness that you could offline them with a single switch and keep the rest of your avionics up. I've not flown enough with autopilot to have experienced an issue, plus I thought you could override the servos with sheer force. So I think between having a power switch on the 307, the VPX menus and ultimately the Avionics Switch.. I should be fine.

On the subject on electrical endurance. Given I'm running traditional mags my goal is to have enough power to run the GTN and EFIS long enough to get me out of IMC. Given the type of flying I typically do anything north of an hour is fine. If there's a multi-state area of coverage and IMC, then there's a high probability I'm not going flying.

[leok]

Originally Posted by AviatorJ

It was suggested to me by a corporate pilot. The idea behind it was if you have some servo run away or some other craziness that you could offline them with a single switch and keep the rest of your avionics up. I've not flown enough with autopilot to have experienced an issue, plus I thought you could override the servos with sheer force. So I think between having a power switch on the 307, the VPX menus and ultimately the Avionics Switch.. I should be fine.

In my training of auto pilot use, the first line of defense for a run away trim condition is the auto pilot disconnect. I have that on the stick. The second level response if for some reason the disconnect doesn't work is to turn off the autopilot. The last line of defense is to pull the breaker. That for me would be to kill the secondary avionics (I have the avionics segregated into three groups using three VPX switches). So avionics two will kill the autopilot and both autopilot servos without killing flight critical electronics.

With the Garmin GSA28 auto trim feature you would not like the result of fighting the servo for any length of time. The servo will automatically run the trim to it's limit opposing what the servo sees as continued force against it's control. In the end you would be fighting the trim position combined with the servo force.

More than once on the 182 I fly I have engaged the autopilot only to find the plane turning in a direction I hadn't anticipated. So naturally I pulled against the autopilot. As the auto trim kicked in the forces grew quickly. A quick poke of the disconnect button (I have never had to pull the breaker) and I was left with a badly out of trim aircraft. Re-tirm, then figure out what I missed in the settings. Usually it was the autopilot set to follow a VOR rather than the GPS I had anticipated ... Not a run away servo, however a similar outcome.

So I guess I amend my earlier comment. A way to quickly kill power to the autopilot and/or the autopilot servos is needed just in case for some reason your disconnect button fails to work (it is a momentary ground to the disconnect pin). So as you point out, a discrete switch for only the servos is not necessary.

[Av8rRob]

One possible option I plan on using for a stick mounted starter button is a panel mounted switch. This could be a three position off-arm-start. That would disable the stick button when its not wanted and allow a backup means of starting.

[Carl Froehlich]

Originally Posted by Av8rRob

One possible option I plan on using for a stick mounted starter button is a panel mounted switch. This could be a three position off-arm-start. That would disable the stick button when its not wanted and allow a backup means of starting.

There is another consideration. Few if any stick grip switches can handle the current needed to operate the starter solenoid. On my first RV I started off with the bottom blue pinkie switch on the Infinity Grip as the starter button. The button itself operated a 12vdc relay that then provided power to the starter solenoid. I even added a key switch on the side panel as a ?park the plane and prevent someone from starting it? feature.

As I said before however, I disconnected the grip starter switch early in Phase One after the second time I bumped it while the engine was running. I replaced it with a simple start button on the side panel. On the RV-10 I just used a traditional start button on the side panel, no relay. I wil do that again on the new RV-8 project. Here is the start switch I used - along with the bezel: http://www.steinair.com/product/starter-switch/

I use a separate locking toggle switch for each ignition.

Carl

[AviatorJ]

In the name of simplification I made the next iteration of my choices. I decided to go back to the original idea of having the boring regular ACS style key switch... It's not as exciting as a push start, nor is it as neat as having lots of cool toggles to mess with... but in the end it will be an easy transition from my 172 to the RV-10... cause it's the same.

For batteries and alternator I'm sticking with a single main battery and the IBBS backup. The IBBS is independent of the VPX so if there's an issue with it then I'll at least have 1 G3X, EFIS, GTN650 and comms. Then if that all goes out then I have the G5... for my flying that's a good balance of safety and simplicity. I am going to go ahead and have the extra alternator as well. The charging system is actually something I've had go out in the 172... twice.

I removed a few other things as well, like the AP Power switch and the 2nd ADAHRS... The G5 if on the CAN bus can supply the G3Xs with that info, functioning as the backup.

So now I'm working on updating the schematic and might change it even more. I need to now figure out what to do with the pinky button.... Maybe an Airhorn?

[bluskydreamin]

Originally Posted by AviatorJ

In the name of simplification I made the next iteration of my choices. I decided to go back to the original idea of having the boring regular ACS style key switch... It's not as exciting as a push start, nor is it as neat as having lots of cool toggles to mess with... but in the end it will be an easy transition from my 172 to the RV-10... cause it's the same.

For batteries and alternator I'm sticking with a single main battery and the IBBS backup. The IBBS is independent of the VPX so if there's an issue with it then I'll at least have 1 G3X, EFIS, GTN650 and comms. Then if that all goes out then I have the G5... for my flying that's a good balance of safety and simplicity. I am going to go ahead and have the extra alternator as well. The charging system is actually something I've had go out in the 172... twice.

I removed a few other things as well, like the AP Power switch and the 2nd ADAHRS... The G5 if on the CAN bus can supply the G3Xs with that info, functioning as the backup.

So now I'm working on updating the schematic and might change it even more. I need to now figure out what to do with the pinky button.... Maybe an Airhorn?

Justin - was looking at your panel idea layout on your site. I don't think the G5 can be mounted in the angled portion of the panel. It's manual calls out a mounting surface square to the spar so the yaw indication is accurate. Don't know if this has changed or not.

[AviatorJ]

Originally Posted by bluskydreamin

Justin - was looking at your panel idea layout on your site. I don't think the G5 can be mounted in the angled portion of the panel. It's manual calls out a mounting surface square to the spar so the yaw indication is accurate. Don't know if this has changed or not.

That is a bit of a concern. When I posted a pic on f my panel idea last year that came up. There was at least one other guy who was doing the same thing, so I'll follow up with him and see if he had any issues.

[Greenley]

I spoke to Garmin about the angle of the G5, they said it must be square to the direction of travel. This was in issue as I had the aerosport panel with the angled section was I was planning to mount the G5. I ended up working with Stein to create a recessed angled mount for the G5 that put square to the cabin, but is a little of difficult to see from the left seat.