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Elec System Integration - Comments?

Strike69

Strike69

Active Member
The drawing below is my planned electrical system - VP-X, Garmin G3X EFIS, and dual p-mags. The stick mixer takes the various stick functions from both cockpits and provides one signal (for each function) to the system.

The starter system is a little non-traditional. I am planning a stick starter button instead of the traditional keyed starter. To provide a margin of safety to keep the prop from turning unintentionally/inadvertently, I designed a relay to require both the key to be in and turned to both AND the start push energized and depressed.

ElectricalSystemv3_zps081a3c07.jpg


Any comments, gotchas, or things i have missed are welcome.

Thanks
Strike
 
Seems perfectly "safe" to me - if the extra relays fail, you are "safely" on the ground....

Just remember that the more active components you add to a system, the more potential failure points you have that can prevent the function from operating.
 
Strike69 said:
The starter system is a little non-traditional. I am planning a stick starter button instead of the traditional keyed starter. To provide a margin of safety to keep the prop from turning unintentionally/inadvertently, I designed a relay to require both the key to be in and turned to both AND the start push energized and depressed.
Click to expand...
I'd strongly recommend having two buttons that have to be actuated at the same time, one for each hand, if you're pursuing a stick mounted starter. With the keyswitch in the "both" position, where it will live while in flight, your start button on the stick is live full-time, where you could bump it with your hand, knee, AF/D, paper map, iPad, etc. while in flight.

I suggest adding a button to your throttle, to make it fully HOTAS. Or add a button to a bulkhead near your throttle hand, so you can reach it during start. Wire them in series, so you have to push both to get a complete circuit for the starter.

Personally I wouldn't use a keyswitch either. One solid toggle for each mag, and get rid of the flopping keychain during aerobatics.

Oh, and finally, I don't think you want to be starting on "both"... Or is that okay with P-Mags?
 
Snowflake said:
I'd strongly recommend having two buttons that have to be actuated at the same time, one for each hand, if you're pursuing a stick mounted starter. With the keyswitch in the "both" position, where it will live while in flight, your start button on the stick is live full-time, where you could bump it with your hand, knee, AF/D, paper map, iPad, etc. while in flight.

I suggest adding a button to your throttle, to make it fully HOTAS. Or add a button to a bulkhead near your throttle hand, so you can reach it during start. Wire them in series, so you have to push both to get a complete circuit for the starter.

Personally I wouldn't use a keyswitch either. One solid toggle for each mag, and get rid of the flopping keychain during aerobatics.

Oh, and finally, I don't think you want to be starting on "both"... Or is that okay with P-Mags?
Click to expand...

The Starter Switch being "Live" in flight is a non-issue. VP-X disables it after the engine starts.
 
8CW said:
The Starter Switch being "Live" in flight is a non-issue. VP-X disables it after the engine starts.
Click to expand...

You'd still want a two-point interlock on the ground before you start. While it's parked, while you're working on it in the hangar, etc.

You want to avoid a single point of failure causing a safety issue... In a conventional setup, you have to accidentally turn on your master, and then accidentally turn your keyswitch to "start" to turn the prop. Two things have to "fail," and at least one is unlikely (turning a key by accident).

In the proposed setup, I believe the start button is unprotected on the stick. So if you're in the cockpit working on something, and accidentally hit your master, your starter is now live with an exposed pushbutton to activate it. Depending on which button it is, it might not even be prominently marked. How many people sit in a cockpit and grab hold of a stick like that, and immediately wonder "what do these buttons do?"
 
What is the advantage to having a stick mounted start switch?

Or is it "Because I Can" ? :)
 
Having a pushbutton on the throttle and one on the stick and requiring that they both be pushed for start ensures that your hands are where they should be (at the controls) during startup. Stick back, throttle positioned, etc. I'd like mine set up that way but don't have a throttle that's conducive to a pushbutton.

Also, while flying, a relight is quicker if you don't have to let go of the controls and find the starter on the panel. Perhaps useful for people flying aerobatics or formation.
 
A relight? these are not turbine aircraft, and getting the prop to actually stop takes extraordinary actions on the part of the pilot. I can think of an incredibly unlikely set of events that would make it necessary to actually crank the engine in the air if it quit - just restore fuel or ignition, and it should go - the prop will already be turning.

Paul
 
Snowflake said:
...

Oh, and finally, I don't think you want to be starting on "both"... Or is that okay with P-Mags?
Click to expand...
There is no issue with starting an engine with P-mags on "both". The ignitions retard the timing to TDC when below 200 RPM. This means when the first cylinder fires, the engine is over 200 RPM and the timing moves to its operational setting. The “operational setting” is dependent on the timing curve selected.

Here is one question, do you want both of your ignitions to go through the VP-X? I have no experience with this system but you might want to think about putting your P-mags on traditional pullable breakers.

Two things to keep in mind regarding the P-mags; first, make sure to run the ground wires from Pin 1 to an engine case bolt and don’t use the same case bolt for both P-mags. Second, you might want to think about running serial data lines from the P-mags into the cockpit somewhere and terminate them with female DB-9 connectors as we describe on page 33 in the EICommander manual. That way, if you ever want to program them, you can plug your PC into them one at a time, without having to remove your cowl. Also, if you want to run the “A” curve, you can just put a jumper in male DB-9 connector and plug it in, no need to de-cowl.
 
Feedback

Bill - thanks for the explanation on how the p-mags work. I think there is a lot of confusion over this type of e-ignition with the number of systems that DO require a continuous electrical supply, while the p-mags do not. Once the p-mags reach ~900 RPM they are generating their own power internally. I have no issues with putting both p-mags through the VP-X. It has a Dual Buss architecture and the only time it would be a problem is during the start. If something is wrong with the VP-X preventing the start, I don't want to be flying anyway.

On the starter switch, I went with the stick mount for the aforementioned reason and because I can. I didn't want to use the traditional key start since this grounds the right p-lead and as explained, both p-mags are used for start resulting in a more efficient/smoother (and quicker?) ... so I understand.

Thanks for all the great comments. I have gained a few additional thoughts and tweaks to the system.

v/r
Strike
 
Ironflight said:
A relight? these are not turbine aircraft, and getting the prop to actually stop takes extraordinary actions on the part of the pilot. I can think of an incredibly unlikely set of events that would make it necessary to actually crank the engine in the air if it quit - just restore fuel or ignition, and it should go - the prop will already be turning.
Click to expand...
In most cases I agree. Two come to mind where it might not be true: one, a wood prop, which doesn't have the momentum that a metal one does to keep going (I have had wood props stop in homebuilts), and two, during aerobatics your airspeed and/or prop loading could stop a metal prop too. Getting it started turning again without a starter will require a slight dive to get your airspeed up.
 
Schematic

So, I'm starting to get my electrical system figured out. Where are you getting the schematic layout? Is there a program? I am planning on using a VP-X and have seen their planning tool, but haven't been able to get it to display (or print) a full schematic, just pin outs...

Thanks!
 
rocketman1988 said:
So, I'm starting to get my electrical system figured out. Where are you getting the schematic layout? Is there a program? I am planning on using a VP-X and have seen their planning tool, but haven't been able to get it to display (or print) a full schematic, just pin outs..
Click to expand...
The software from ExpressPCB is free, and quite feature-rich. Many RV owners have used it to document the electrical systems on their aircraft.
 
Schematic

Great point about the fuel boost pump. It was planned in the VP-X but not shown on the diagram. The Infinity Stick functions (in/out from the mixer) are trim, flaps, starter, PTT, autopilot disconnect, and fuel boost pump.

I am using a Plane Power Alternator which has an internal voltage regulator.

Here is what the avionics bay looks like so far. I built a bar this weekend to mount the VP-X ... only to find out it hung too low and interfered with the stick. 5 hours later ...

DSCN2069_zpsc710d45e.jpg


More to follow. Thanks for all the great comments. I am using Visio to generate the drawing. I'll revise and republish in a few days.

/r
Strike
 
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