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Putting together a G3X system

SgtZim

Well Known Member
I'm in the early stage of (paper) wiring up my G3X system and would like to open this up as a thread - I invite advice and critiques, and I'll share the information as I get answers from the G3Xperts.

My planned system:
GDU 460 - 1
G5 - 2
GTR 20 - 1
GEA 24 engine interface
GAD 29 acars / data concentrator
GMA 240 audio panel
GMC 307 autopilot panel
GSA 28 - 2 servos
GSU 25 adhars
GMU

GNC 255A
GTN 625

My preliminary interconnect drawing (based on the Garmin basic drawing):
156c9ed4-1908-429c-9343-c190d1196159_zps3t8kopl7.jpg


I just sent an email to [email protected] with a question about the connections between the GDU and the GTN nav. I asked about the diagram on page 24-25 of the G3X manual that shows two RS232 connections to two separate GDUs. One is the MXMAP format channel, and the other is a Connext channel. I asked if I need both channels to my single GDU. If it requires two channels, I am out of serial channels to the GDU which has 5 max.

I have also asked about routing the GNC 255 to the GAD 29 instead of using a serial channel to the GDU. I'll post the answers I get as I get them.

I find this stuff fascinating, but it do make your head buzz once in a while and I can see why a lot of folks go to Stein and others to have it done. :)
 
Just wondering why you went with the GTN625 and a GNC-255A when a GTN-650 would do all the same with less room and wiring and I believe less cost too.

Thanks,

Jay
 
Just wondering why you went with the GTN625 and a GNC-255A when a GTN-650 would do all the same with less room and wiring and I believe less cost too.

Thanks,

Jay

Hi Jay, the deal at the time - the gtn 625 was much cheaper when bought with a g3x system, and no discount was offered on a 650 or 750. I think I would have spent close to $2000 more for a 650. Yes it would be easier, but hey, 2 grand, and if something breaks I'll still have a nav in the plane while the other box gets fixed.
 
I just sent an email to [email protected] with a question about the connections between the GDU and the GTN nav. I asked about the diagram on page 24-25 of the G3X manual that shows two RS232 connections to two separate GDUs. One is the MXMAP format channel, and the other is a Connext channel. I asked if I need both channels to my single GDU. If it requires two channels, I am out of serial channels to the GDU which has 5 max.

Hello SgtZim,

Nice system you are putting together.

Just a quick note to mention that your GDU 460 display has 6 serial ports, not 5.

As shown on page 23-19 of the Rev. AA G3X Installation Manual, the 6th serial port is on 9 pin connector P4601. This serial port is designed to be used for the backup data path for your GSU25 #1 and is permanently programmed for the "Garmin Instrument Data" format for this purpose.

If you are running low on serial ports, you can also consider only connecting the GMC 307 autopilot control panel to the roll servo and not to the display. There isn't a lot of benefit to connecting the GMC 307 to the display. The connection to the roll servo is the important connection and the only one that matters if your GDU 460 becomes unavailable and you need to operate your autopilot using the G5 and the GMC 307.

One additional comment. We noticed you had a GMA 240 audio panel in your list. This is a great audio panel, but you might also consider the new GMA 245 if you have not yet purchased the GMA 240.

Front.jpg


Thanks,
Steve
 
Last edited:
Hey Steve,
What is the benefit to connecting the 307 to the display. I've been doing that, but would love to get rid of unnecessary connections.
 
Hey Steve,
What is the benefit to connecting the 307 to the display. I've been doing that, but would love to get rid of unnecessary connections.

Hello Jon,

It is mostly just another data path. If you were to lose the RS-232 connection from the GMC 307 to the roll servo, you could still use the GMC 307 if you have the backup data path to the display. The GDU 4XX touch screen autopilot controller is, of course, a backup against loss of the GMC 307 making it less important to have a backup RS-232 data path.

Thanks,
Steve
 
Hello Jon,

It is mostly just another data path. If you were to lose the RS-232 connection from the GMC 307 to the roll servo, you could still use the GMC 307 if you have the backup data path to the display. The GDU 4XX touch screen autopilot controller is, of course, a backup against loss of the GMC 307 making it less important to have a backup RS-232 data path.

Thanks,
Steve

Thanks Steve!
 
Hello SgtZim,

Nice system you are putting together.

Just a quick note to mention that your GDU 460 display has 6 serial ports, not 5.

As shown on page 23-19 of the Rev. AA G3X Installation Manual, the 6th serial port is on 9 pin connector P4601. This serial port is designed to be used for the backup data path for your GSU25 #1 and is permanently programmed for the "Garmin Instrument Data" format for this purpose.

If you are running low on serial ports, you can also consider only connecting the GMC 307 autopilot control panel to the roll servo and not to the display. There isn't a lot of benefit to connecting the GMC 307 to the display. The connection to the roll servo is the important connection and the only one that matters if your GDU 460 becomes unavailable and you need to operate your autopilot using the G5 and the GMC 307.

One additional comment. We noticed you had a GMA 240 audio panel in your list. This is a great audio panel, but you might also consider the new GMA 245 if you have not yet purchased the GMA 240.

Front.jpg


Thanks,
Steve

Thanks Steve!

That does clear up things a lot. And yes I'm out of serial ports - dropping the connection from the GDU to the GMC 307 would help. Jonathan at Garmin (email) has been helping clear things up too.

He said I do need two ports from the GDU to the GTN 625, one for MXMAP data and one for Connext - so my total ports that could be connected to the GDU are:

GSU 25 - I will connect with the dedicated port on P4601
GTX 45R for traffic and weather info
GTN 625 MXMAP channel
GTN 625 Connext channel
GNC 255A control and display of vor/loc info - Nav 2
GEA 24 redundant path for engine data
GMC 307 - will probably skip this one if all functionality is good through the roll servo connection.

Thanks again for all the helpful information and tips.

Another couple of open questions to you experts....

I'm currently planning on bolting the GSU 25 to the GDU - though Garmin is not endorsing this - I had done a quickie survey here a couple of months ago and the few RV-8 guys that responded did not think it would be an issue.

Anyone have a bad experience with this on an 8? My thinking is that the narrow cockpit / panel seems like it should be pretty solid. I'm not sure where else to mount the GSU that would be more solid and not vibrating.

Also, The Garmin "certified" manuals for the GTN and the GNC go into detail about prepping the mating surfaces of the radio racks and the instrument panel.... cleaning and alodining, then checking the resistance between radio rack and panel with a milliohm meter. Overkill? or worth the extra mile?
 
panel build

Here's the panel being built so far:

panel%20front_zps62pujsky.jpg


panelback_zpsrtpkl1ap.jpg


Still mulling over switches and their locations.

I'd kind of like an extra master caution and a master warning - but would need to be able to cancel / dim them quickly at night.
 
Thoughts

I was wondering why you need the audio panel, the GTR-20 has an intercom built in with stereo.

Also, why two G5s?
 
The intercom on the GTR-20/200 is single-COM. His Audio panel will allow him to switch between the two COM units, and also the NAV audio.
 
Great info here; I'm in the process of planning out my -7 panel in G3X colors as well. It's great to get some collective intelligence.

Garmin: thanks for chiming in!
 
Lights

Another interesting option with these units is possibly a lighting bus. However, the method seems to vary between the GDU, and the non G3X boxes.

The external dimming on the G3X uses a reference voltage
The GNC has "hi/lo" pins out to a "display dimmer"
The GTN is similar to the GNC
The GMA audio panel has 2 lo pins and a hi pin
The G5s have only photocell control

The non G3X manuals have lots of warnings to not hook these up wrong, but are light on "how to". This really makes me appreciate the G3X engineers and writers 👍🏾

I don't see myself doing a lot of night IFR, but nows the time to set this up if it's worth doing.

Tips, comments?
 
Here is my panel. Stein did the build for me and advised on what I needed. I can't wait to get it in the air.
g3x2_zps6787783a.jpg
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Let me know if you want details. I have a VP Sport power system.
 
Here is my panel. Stein did the build for me and advised on what I needed. I can't wait to get it in the air.
Let me know if you want details. I have a VP Sport power system.

Looks great, What is the smallish rectangle device on the right?
 
The real small at far fight is the ELT display. To the right of the 2 screens is the radio and the AP. I have second guessed myself about a thousand times on having both screens together and then the radio on the right. I guess I will find out when I get it in the air!

Here is a better picture with the panel in the plane.

panel_zpssn7wu6uf.jpg
[/URL][/IMG]
 
update

I'm plugging along, making detailed lists and notes on each LRU and every connecting pin that I will use and where each one connects to. Following Bob Knuckolls' advice to "make your mistakes on paper first".

I had a question for the G3Xpert about how to connect and configure a GTX 45R transponder to the GDU. The wording on how to configure their respective serial ports was worded differently.

Steve responded:

The current G3X Installation Manual is Rev. AA and it includes all the wiring and configuration guidance you need for the GTX 45R on page 24-21. (see below)

The serial port connection from the GSU25 to the transponder is also used to control the transponder.

Let us know if you have further questions.

Thanks,

Steve

(I try to keep current on revisions, but I think this time I was just reading the wrong copy.)


Thanks to Steve and Jonathan at Garmin! They are awesome, and respond quickly to clear things up!

So, I endorse reading, taking notes, checking revisions, reading again, and asking questions.

Now for the Q and request for A section: I'm still unclear about how an external lighting bus is supposed to work. The Garmin manual says there are several commercially available dimmers but does not comment about desired or required parameters. The lighting bus is supposed to "follow" a supplied voltage to control the lights via a lighting bus HI and a LO pin on the connectors. Components that can accept 14 or 28 volt systems have wiring options to use one or the other.

I experimented today with my GMC 307 - wired power to it and tried out the lighting bus inputs - connected to my Van's supplied dimmer unit I will use for cabin area lights. The dimmer puts out between 1.12 and about 10.99 volts as you turn the pot. I wired the variable volt wire from the dimmer to the GMC 307 "lighting bus HI" pin, and grounded the "lighting bus LO" pin per directions. I did not see any response or control of the lights as I turned the pot up or down. Could be an issue using the PWM dimmer, or maybe it has to be configured in the GDU program?

I'm not really worried about it - but I'd still kind of like to get all the lights on the GMA audio panel to work - it has to have external lighting control to get power to light the text labeling. Other than this, all the other boxes seem to do a good job auto dimming from their own photocells.

Thanks again for the tips and comments!

Bruce
 
Thanks again for the tips and comments!

Bruce


Hey Bruce,

Just curious as to why the G5s are on the left vs the right? As a former single seat guy your free hand should be the left one without the A/P on. For that reason it seems to make more sense to have the GTN and GNC on the left. I'm working on upgrading the panel on my -4 and wondering if there's something I haven't thought of before I pull the trigger.

Thanks.
 
Thread hi jack

So i am also putting a G3x system together. Here are my plans tell me what are better options:
G3x touch dual screen
GMA245R remote audio panel
GTN650 certified GPS/VOR/ILS
GTX45R remote ADBS transponder with weather
GMC307 autopilot control panel
G5 backup flight instruments
Wiskey compass
Archer vor antenna

Does this give me what i want:
ADSB
GPS approaches to mins
Dual com (One with second monitoring)
Autopilot
Intercomm

If i wanted to add a second com how would i do that?
What am I missing?
 
GTR 20 would give you a remote second com radio. I am opting for GTN 625(on sale currently with G3X purchase for $5500) and a GNC 255A for redundancy purposes. If all you have is the 650 and it goes T.U. you're out of IFR approach options.
 
Thanks

GTR 20 would give you a remote second com radio. I am opting for GTN 625(on sale currently with G3X purchase for $5500) and a GNC 255A for redundancy purposes. If all you have is the 650 and it goes T.U. you're out of IFR approach options.

Thanks. I will make this change.
 
Photo cells vs. Dimmer Pot

SgtZim (Bruce),

I am currently installing a G3X with all the bells and whistles into my RV-4. Due to limited panel space in my -4, the only mounted avioncs in the panel will be the GDU460, GTN650, and GMC307. I have planned to use the photo cells in the GTN650 as well as the GDU460 for night-time dimming. It now occurs to me that the lighting on the GMC307 buttons may not follow the brightness settings from the photo cells on the display. Do you have any info from your install that could help here? I would prefer not to have to hook up a pot just for the GMC307 button light brightness if I could avoid it. Thanks! Great looking panel by the way!



I'm plugging along, making detailed lists and notes on each LRU and every connecting pin that I will use and where each one connects to. Following Bob Knuckolls' advice to "make your mistakes on paper first".

I had a question for the G3Xpert about how to connect and configure a GTX 45R transponder to the GDU. The wording on how to configure their respective serial ports was worded differently.

Steve responded:

The current G3X Installation Manual is Rev. AA and it includes all the wiring and configuration guidance you need for the GTX 45R on page 24-21. (see below)

The serial port connection from the GSU25 to the transponder is also used to control the transponder.

Let us know if you have further questions.

Thanks,

Steve

(I try to keep current on revisions, but I think this time I was just reading the wrong copy.)


Thanks to Steve and Jonathan at Garmin! They are awesome, and respond quickly to clear things up!

So, I endorse reading, taking notes, checking revisions, reading again, and asking questions.

Now for the Q and request for A section: I'm still unclear about how an external lighting bus is supposed to work. The Garmin manual says there are several commercially available dimmers but does not comment about desired or required parameters. The lighting bus is supposed to "follow" a supplied voltage to control the lights via a lighting bus HI and a LO pin on the connectors. Components that can accept 14 or 28 volt systems have wiring options to use one or the other.

I experimented today with my GMC 307 - wired power to it and tried out the lighting bus inputs - connected to my Van's supplied dimmer unit I will use for cabin area lights. The dimmer puts out between 1.12 and about 10.99 volts as you turn the pot. I wired the variable volt wire from the dimmer to the GMC 307 "lighting bus HI" pin, and grounded the "lighting bus LO" pin per directions. I did not see any response or control of the lights as I turned the pot up or down. Could be an issue using the PWM dimmer, or maybe it has to be configured in the GDU program?

I'm not really worried about it - but I'd still kind of like to get all the lights on the GMA audio panel to work - it has to have external lighting control to get power to light the text labeling. Other than this, all the other boxes seem to do a good job auto dimming from their own photocells.

Thanks again for the tips and comments!

Bruce
 
Photocells work great on everything, 307 included. Ok, so maybe the G5 could track a little closer to the G3X system out of the box, I?m guessing I could maybe get them closer with some tweaking. But yeah Devin, no need for any lighting controls IMHO, in 300ish hours behind it I?m happy just to let the photocells drive.

Fitz
 
photocells

Thanks for your comment Fitz. I was hoping the photocells would be all that's needed. I'm not confident I could have successfully connected all the Garmin boxes to a common lighting bus without buying the GAD27 (don't have the space anyway) Most of the main boxes are "tweakable" for lighting in their software if some are too dim or bright. I've also added a dimmable led strip under the glareshield and led area lights on the sides of front and back cockpit.
igo6Us.jpg
 
So, maybe I?m just a simpleton, or a guy with a -4 that doesn?t have room or weight for extra things, but why do folks install heated pitot on our planes?

I?m just curious, after a couple hundred hours in my plane I was pretty confident operating it sans airspeed in nearly any conditions, and now especially with a really nice ground speed readout and easily accessible surface wind speed data on the G3X. Makes a non-pitot approach even less of a pulse-raiser. Is it just peace of mind for some folks?

-Fitz
 
Heated pitot

Even flying VFR, if I am flying below a cloud deck up in the northern states, sometimes the pitot will get moisture or something a little colder inside. The heat drives out the moisture and any inadvertant icing. I have been a follower of Vlads adventures and when he went to Alaska, he stated in his writeup that the airspeed went wacky for a time without a heated pitot tube. JMHO
 
So, maybe I?m just a simpleton, or a guy with a -4 that doesn?t have room or weight for extra things, but why do folks install heated pitot on our planes?

I?m just curious, after a couple hundred hours in my plane I was pretty confident operating it sans airspeed in nearly any conditions, and now especially with a really nice ground speed readout and easily accessible surface wind speed data on the G3X. Makes a non-pitot approach even less of a pulse-raiser. Is it just peace of mind for some folks?

-Fitz

Some people also have redundancy in their systems. FAR 91.205 does not require a heated pitot or for that matter only applies to EXPERIMENTAL aircraft when operating NIGHT and or IFR.

Never used pitot heat in the last 20-years and or over 3,300 flying hours in my RV. Yes I did use pitot heat once in a Mooney on an IFR approach during that time but only once.
 
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