Any Thoughts on EVERYTHING ON switch for take-off, landing, and emergencies at low alttitude?

[wsimpso1]

There has been the whole electrical reliability discussion over in Bob Nuckolls' AeroElectric Connection and in his list, and discussions on here about them. The basics are:

1. Things break;
2. When something breaks, your systems should be designed so no immediate hazard is created;
3. Things needed for comfortable termination are backed up or have special effort to ensure operation and availability;
4. Upgrading stuff is because your are tired of fixing stuff or want a new thing, NOT because it darn near killed you.

So, we followers of this thinking go about building our airplanes so that Important stuff is backed up. OK, good idea.

I am planning an electrically dependent engine. Following BN's path, the important things are installed in pairs, powered from always hot battery buses. Each of these things has a fuse, wires, a switch, the essential powered element, and a ground bus. Multiple places exist on each of four circuits that can turn off the engine in an instant. I have redundant circuits and components, but the thought of one of them going to sleep when less than 1000' AGL is scary. An engine failure would have to be followed by immediate action list of: Pitch over to get glide speed, pull alternate air, change the setting for each of two live switches, bring in the two backup switches, switch tanks, all while finding a place to put the beast and making the forced landing...

All those switches are fine and dandy for troubleshooting, and have really high probabilities of having combinations that will run the engine even with any single failure I can conceive. But below 1000' AGL, isn't that asking a lot of the human? For low altitude engine failure, and for that matter all ops below 1000' AGL, wouldn't we just want one switch that unconditionally energizes all of the pumps and ECU options?

What I have in mind is adding a parallel set of circuits using a single pole switch, diode isolated inputs from the always hot battery buses, and closes NO contacts in a 4PDT relays. Each set of contacts connects a diode isolated power and one essential element. Throw the switch and everything is under redundant power. Probably need diode isolation on the main circuits too.

Following through on thinking is:

• Walk Around Checklist includes:
  • Running each of the pumps from each of the switches;
  • Confirming plenty of fuel in each tank;
• Pre Take-Off Checklist includes:
  • Checking ignition halves;
  • Checking both ECU's with both main switches;
  • Setting the switch configuration for the flight;
  • Setting the ALL ON Switch
• Departure checklist turns off the ALL ON switch
• GUMPS check upon reaching downwind for landing includes setting the ALL ON Switch.

As a mechanical engineer, and only the lightest of preparation over 40 years ago in electronics, I do not know if diode isolation makes sense for the ALL ON switch and powered circuits. I think that they are needed or we may be trying to power a dead bus that is giving us trouble in the first place.

The alternative to a couple relays is a 4PDT switch rated to our current flows.

So, what do you guys think? Too much?

Billski

 

[AdrianS]

 

[Pops]

 

[Vigilant1]

 

[TFF]

 

[rv7charlie]

 

[wsimpso1]

 

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[gtae07]

 

[WonderousMountain]

 

[D Hillberg]

 

[dave wolfe]

 

[dwalker]

 

[Dan Thomas]

 

[blane.c]

 

[wsimpso1]

 

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[WonderousMountain]

 

[dwalker]

 

[Marc Zeitlin]