View Single Post
Old 03-17-2018, 03:40 PM
czechsix's Avatar
czechsix czechsix is offline
Join Date: Mar 2006
Location: Spring Hill, KS
Posts: 336

Originally Posted by Toobuilder View Post
Your panel looks fantastic, but for clarity the switches you have shown are personal choice - not "required". For example, I do not power my ECU's independantly, nor do I have a separate switch for the fuel pumps. I have a single "Engine On/Off" switch, and the Pri/Sec. The engine switch powers both ECU's, the coils, and a single fuel pump. Just like a car. My second fuel pump is in my old "boost pump" location on the throttle, and it is used exactly as we have been trained for generations: takeoff, landing, and "as required". There are many ways to skin this cat and personal choice is going to dictate what we are comfortable with.
I've been thinking a lot about switch configurations for the EFI system in my RV-14A. A few years ago I had the opportunity to spend a dozen hours flying an RV-12, and it really struck me how simple the airplane was to operate. There's no mixture or prop levers, no fuel selector, and the boost pump and nav lights came on with the master switch. For takeoff and landing it was just throttle and flaps!

So back to the EFI switching scheme, I'm thinking about having just two switches. The left switch would be DPDT with one circuit controlling power to ECU A, Coilpack1, and Pump1 and the second circuit controlling injector selection (injectors would be using ECU A when this switch is On and switch to ECU B when Off). The right switch would be SPST controlling power to ECU B, Coilpack2, and Pump2.

This really reduces the proliferation of switches related to the ignition/EFI from seven down to two. You can do a standard 'mag check' on run-up where you turn off one side of the system and verify that the engine runs on the other. If you have an engine problem in flight, you switch tanks and turn Off the left switch (because this moves injectors from ECU A to B). A bit unconventional perhaps but very simple and the left switch would be clearly marked (yellow) for this function.

Downsides would include running both fuel pumps all the time (don't know if this would substantially reduce reliability of the pumps, it would mean pulling another 4.5 A continuously but I'm planning dual alternators so not really worried about the electrical load). Also the left switch becomes a single point failure for the engine since it controls power to one side of the system AND switches injectors between ECUs...but I think it would be a very unlikely failure mode where one circuit of the DPDT switch fails open (loss of power to ECU A/coilpack1/Pump1) and the other circuit fails to actuate when you flip the switch off to move the injectors to ECU B. And if this failure mode is even possible, it would most likely happen when actuating the switch at the beginning or end of the flight, and not during flight when you would not normally be touching the switch.

One other downside to ganging everything together is troubleshooting...if something isn't working, it's a bit less obvious who the culprit is. The fuel pumps could be ruled out by looking at fuel pressure, so it would mainly be a question of ECU vs coil pack.

Has anybody used a switching scheme like this?
Mark Navratil
Spring Hill, KS
RV-8A N2D #80583 - built/flew/sold
RV-14A #140017 - wings complete, empacone in progress...

Last edited by czechsix : 03-18-2018 at 10:50 PM. Reason: minor wording clarification
Reply With Quote