We have just completed our RV-12 and done the first flight. The surprise for me was that in the shutdown procedure, the engine is shut down with the avionics still live. I've had several airplanes over the years ... Bonanza, Cessna 150s and 172s, etc., and it was always preached to me to shut down the avionics first so that any voltage spike that might come from engine shutdown wouldn't damage the electronics. We even installed an Avionics Master Switch. So why do the RVs do it in the reverse. What am I missing here?
Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Shutdown engine before avionics
- Thread starter jveatch
- Start date
Old Wive's Tale
Read what Bob Nuckolls has to say Bob wrote the book by which many RVs are wired.
Below is quote from Bob's post:
Actually, the av master was borne on a compelling
but flawed premise . . .
About 1966, when transistors were starting to show
up in aircraft radios (pnp germanium with 30v ratings)
Cessna (and I suspect others . . . don't know for sure
but I was at Cessna) were experiencing a rash of radio
failures in new, ready-to-deliver airplanes . . .
. . .and yes . . . it seems that radios left ON during
engine start were the most affected. It was surmised
that a 'spike' from the starter got 'em. It stood to
good reason. That starter thingy draws hundreds of amps,
was very inductive . . . it HAD to be a potential source
of inductive 'kick back' deleterious to those relatively
fragile.
The Avionics Master was borne . . . and yes . . . the
failures went away. In retrospect, it was not an
inductive 'spike' that got the radios but brownout.
The 'Airplane Patch' east of the plant would park hundreds
of airplanes waiting for delivery . . . none of which had
guaranteed battery integrity . . . a 6v sag to the 14v radio
during a starter 'grunt' was the most likely cause. Further,
while DO-160 (and its predecessors DO-138 and DO-108)
was definitely around, it was not as rigorous with
respect to bus voltage aberrations.
In years since, solid state devices have become very
robust in that they are designed to EXPECT the very
abuse that rolled a NavCom 300 T.U. in 1967.
By the time yours truly was designing transistors into
airplanes in the 1975 time frame, the idea that I would
want to 'take it off the bus' during an engine start
was rather humorous . . . the industry had learned
how to live in the vehicular DC power environment.
It was no big deal . . . yet the seeds of concern for
'spiking' a radio persisted as did the avionics master
switch.
Bob . . .
Read what Bob Nuckolls has to say Bob wrote the book by which many RVs are wired.
Below is quote from Bob's post:
Actually, the av master was borne on a compelling
but flawed premise . . .
About 1966, when transistors were starting to show
up in aircraft radios (pnp germanium with 30v ratings)
Cessna (and I suspect others . . . don't know for sure
but I was at Cessna) were experiencing a rash of radio
failures in new, ready-to-deliver airplanes . . .
. . .and yes . . . it seems that radios left ON during
engine start were the most affected. It was surmised
that a 'spike' from the starter got 'em. It stood to
good reason. That starter thingy draws hundreds of amps,
was very inductive . . . it HAD to be a potential source
of inductive 'kick back' deleterious to those relatively
fragile.
The Avionics Master was borne . . . and yes . . . the
failures went away. In retrospect, it was not an
inductive 'spike' that got the radios but brownout.
The 'Airplane Patch' east of the plant would park hundreds
of airplanes waiting for delivery . . . none of which had
guaranteed battery integrity . . . a 6v sag to the 14v radio
during a starter 'grunt' was the most likely cause. Further,
while DO-160 (and its predecessors DO-138 and DO-108)
was definitely around, it was not as rigorous with
respect to bus voltage aberrations.
In years since, solid state devices have become very
robust in that they are designed to EXPECT the very
abuse that rolled a NavCom 300 T.U. in 1967.
By the time yours truly was designing transistors into
airplanes in the 1975 time frame, the idea that I would
want to 'take it off the bus' during an engine start
was rather humorous . . . the industry had learned
how to live in the vehicular DC power environment.
It was no big deal . . . yet the seeds of concern for
'spiking' a radio persisted as did the avionics master
switch.
Bob . . .
Canadian_JOY
Well Known Member
With all due respect to Mr. Nuckolls, an Avionics Master switch still has a very important roll to play in a modern aircraft instrument panel.
A brief check of Garmin's flat-rate repair fees will show that an Avionics Master can prevent the very expensive replacement of the individual power switches on many of our "modern" radios.
As for when the radios should be powered on and off, well, that's highly dependent on the electrical system of the aircraft in which they're installed. Many modern electrical systems have sufficient over-voltage protection to ensure potentially-damaging over-voltage conditions will not be experienced by our radios.
Personally, I've installed a fail-safe Avionics Master contactor in our aircraft. Time will tell whether or not it is a good or bad idea. My critical avionics are on an Essential Buss with a stone-simple buss master switch. Simple is good.
A brief check of Garmin's flat-rate repair fees will show that an Avionics Master can prevent the very expensive replacement of the individual power switches on many of our "modern" radios.
As for when the radios should be powered on and off, well, that's highly dependent on the electrical system of the aircraft in which they're installed. Many modern electrical systems have sufficient over-voltage protection to ensure potentially-damaging over-voltage conditions will not be experienced by our radios.
Personally, I've installed a fail-safe Avionics Master contactor in our aircraft. Time will tell whether or not it is a good or bad idea. My critical avionics are on an Essential Buss with a stone-simple buss master switch. Simple is good.
The only reason I can think of to turn the radios off whatsoever is to save the battery when the engine is not running. I hardly ever turn my radios off. Systems like Skyview are designed to operate under engine start conditions, so really really no reason to turn it off or even have a switch to turn it off. Typical flat panel systems with fully integrated coms,navs (think G1000) and so on stay on whenever the battery master is turned on.
My checklist has the avionics switch off before the master. However, the avionics switch does not control the PFD. But it does include the radio and MFD.
Here's an excerpt from the checklist (specific to G3X equipped RV12):
Throttle IDLE
ELT CHECK OFF
Ignition A OFF - Ignition B OFF
Hobbs RECORD
Avionics Master OFF
Master OFF
Here's an excerpt from the checklist (specific to G3X equipped RV12):
Throttle IDLE
ELT CHECK OFF
Ignition A OFF - Ignition B OFF
Hobbs RECORD
Avionics Master OFF
Master OFF
Bill_H
Well Known Member
Leave a memory stick connected to the Skyview at all times. It has to be there if you want to take an inflight screenshot. But at the end of the flight, after your shutdown, download your flight logs into it.
I ran a USB extender cable from one of the rear USB ports on the Skyview into a hole in the glovebox. Don't like the port that sticks straight down from the panel. To use that one, you should use a very short USB stick.
I ran a USB extender cable from one of the rear USB ports on the Skyview into a hole in the glovebox. Don't like the port that sticks straight down from the panel. To use that one, you should use a very short USB stick.
RFSchaller
Well Known Member
I will preface my remarks with an admission I'm not an avionics expert. So, FWIW:
I would be more concerned about having the avionics online during start up than shutdown due to the potential for voltage spikes. However, I have my D180 and D100 online when I start the engine and have never had an issue in almost 4 years and 400 hours.
My switch configuration proceeds from left to right on startup and shutdown, so the master is on, then the avionics is on before engine start and the master is off and then the avionics is off after engine shutdown in my routine.
I would be more concerned about having the avionics online during start up than shutdown due to the potential for voltage spikes. However, I have my D180 and D100 online when I start the engine and have never had an issue in almost 4 years and 400 hours.
My switch configuration proceeds from left to right on startup and shutdown, so the master is on, then the avionics is on before engine start and the master is off and then the avionics is off after engine shutdown in my routine.
Dgamble
Well Known Member
That, or get a flat USB multi-port. I have a four-port that fits very nicely under the panel, flush with the instrument panel. It currently hosts the Dynon WiFi dongle and my Seattle Maps memory stick.
tomkk
Well Known Member
I was under the impression that Skyview could only see one memory stick regardless of how many were plugged in. Not so?
Dgamble
Well Known Member
I'm not sure. One port has the WiFi, one has memory, and the other two are only there because a 4-port was the smallest hub Walmart had. I was wondering if the WiFi dongle would confuse it, but it hasn't since I moved up to Version 13 of the firmware.
I have found that the system operates fine with multiple ports being used (wifi, and Sectional charts on separate sticks), but it causes problems if you leave them installed and attempt to do an internal database or firmware update.
When doing those tasks, we remove all other USB sticks and then replace them when finished.
When doing those tasks, we remove all other USB sticks and then replace them when finished.
I've been installing monthly Dynon database updates with the WiFi USB installed in the back of the Skyview. Haven't seen any problem and WiFi worked okay inflight immediately afterwards.
I did remove the WiFi USB when I upgraded the Firmware to 13.03.
So, should I still remove the WiFi before each monthly update because that's rather a pain.
If it works, I see no reason to remove it.
We remove them all because we have had problems. Maybe the one with the sectional subscription is what causes the problem... I haven't bothered to isolate which one was the problem.
