Avionics Bus

Without getting into the merits of an E-bus, anybody care to comment on the necessity of an avionics bus. I think Bob N. says they're old-fashioned and not needed, but I'm wondering what others have to say on the subject. George, you're up first.

If your are talking about an avionics master switch, I have one and would not be without it. It allows me to turn off all avionics with one switch and not have to readjust the volume of each radio everytime. I don't want the avionics on while starting. Also, my avionics master is a DPDT switch with the starter button wired thru the other side so that with the avionics on, the starter won't operate. By doing this, if the starter button is hit accidentally while in flight, nothing happens.
Mel...DAR

Grt Efis

I have one as I have fitted Grand Rapids EFIS and the manufacturer advises against having the system on and powered from the main battery whilst starting.
I fitted a small Gel Cell to power Avionics Bus during starting.
Pete.

I agree with Mel. Despite what one might consider regarding the existence of the phantom "electrical spike", you can't beat the convenience of turning all the radios off with one switch. Now, if you can combine the convenience with some good electrical energy savings in an emergency ala the essential bus, that's killing two birds with one stone!

Avionics Battery

Avionics/E bus

If you're following a Bob Nuckolls approach, like me, he recommends that "if you really want an avionics master" (and I do), put a switch in the line that feeds the E-bus from the Primary bus (either before or after the diode). Since the E-bus also has a feed direct to the battery throught the E-bus switch, the 'Avionics Master' is not a single point of failure.

Dennis Glaeser
7A Fuselage

Little Diodes

Yep.
Done that.
So if I loose the main power, I have a while before everything goes black.
VFR Day only.
Pete.

Yes to avionics master

Boy you guys take the fun out of it. Good posts I agree 100%. In fact my ICOM A200 says "DO NOT turn ON power until the engine has been started."

Plus convince as said

Avoiding single switch failure point can be done with two switches in parallel, Or as Bob shows a second switch (emergency) E-feed direct to battery with anti back-feed diode, makes it a winner.

99 out of 100 avionics shops recommend an avionics master.


As far as single point failures Bob N., God Bless him, but he does go crazy with it. You could go with just a double pole single throw switch in parallel. It is like two separate switches. Granted you are going thru the master relay but how often does that happen. (Every RV has many single point failure points, one prop, one crank shaft, one left/right wing spar, one brain between our ears. How many buss'es does a single engine plane need? "Yea, he crashed, the prop fell off and the wing followed shortly, but his avionics are still working. )

I mean he is right, and its better to have two switches and a second path direct to the battery (E-buss), not thru the master relay. However for a day VFR only no fancy avionics or EFIS its way overkill.

Really switches are very reliable. If you get an high end Mil spec toggle its going to last the life of the plane. Once you "MAKE" the contact its not likely going to die suddenly, I think. Switch damage is done on the make/break throw. Once you're hooked up, you're good to go. However I do have the E-bus concept. Why not? With electronic engine and flight instruments it's warranted.

George

Compass, Map and Watch.

I'm with you George.
KISS.
If everything fails, I am sure I can fly with no ASI.
I can judge my altitude by looking out the window.
And with a Compass, Map and a Watch I can find some where to land.

DAY VFR means look out the window. Mind you it is always sunny in Aus. Well, except in Victoria.................... where I live.
Pete.

Thanks to all who offered advice on this and especially to Mel, whose idea for an avionics/starter safety interlock I'm going to blatantly STEAL!!!

for an avionics/starter safety interlock

Click to expand...

Does this mean that if for some reason you had to restart in flight you wuld have to turn off all the avionics/EFIS etc. Or are you planning a 2nd battery with an avionics bus?

Lateral

Oooh!
A lateral thinker.

Yes, that is one consideration of having the starter wired through the avionics master. But, how often do you need to "restart" during flight. If the engine stops during flight, it stopped for a reason. The prop will continue to windmill, so the starter is not needed. If the prop stops, you have a real problem and the starter probably isn't going to help anyway. If you think this will be a problem in your case then I recommend that you not do it. For me it's been working for 13 years.
Mel...DAR

EFIS? I ain't got no stinkin' EFIS. Switch off the avionics, hit the start button, avionics back on. No big deal. Besides, if you restart without turning off the radios and such, isn't there a chance you'll toast them?