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For those braves before me ? GMU 11 installation

Bavafa

Well Known Member
I have two questions regarding the installation of GMU11 which will be in a RV14A. I am planning on installing it in the left wing tip but open to other ideas if a better location can be suggested.
First question - with a number of nut plats in that holds the wingtip, should I expect issues? Second but more difficult question, the manual indicates of a .5 degree from the longitude of the plane forward direction. How realistic is to come up with that kind of accuracy? Sure, I can determine the centerline of the plane and draw a line for that on the floor of my hanger. How does one transfer that to the wingtip?
If such accuracy is required, what is the purpose of the calibration? Is the calibration just to get and account for errors that is caused by magnetic field or is there any adjustment for the inaccuracy in the installation?
 
I have two questions regarding the installation of GMU11 which will be in a RV14A. I am planning on installing it in the left wing tip but open to other ideas if a better location can be suggested.
First question - with a number of nut plats in that holds the wingtip, should I expect issues? Second but more difficult question, the manual indicates of a .5 degree from the longitude of the plane forward direction. How realistic is to come up with that kind of accuracy? Sure, I can determine the centerline of the plane and draw a line for that on the floor of my hanger. How does one transfer that to the wingtip?
If such accuracy is required, what is the purpose of the calibration? Is the calibration just to get and account for errors that is caused by magnetic field or is there any adjustment for the inaccuracy in the installation?

Hello Mehrdad,

There is some good information in this recent thread about the importance of good GMU 11 installation alignment if you haven't seen it.

Thanks,
Steve
 
Most of us install in the Vans' specified location without any problems.

I had a bad GMU11 and that caused some grief, I couldn't get it to calibrate. Once I got a replacement, it calibrated easily the first time and has worked flawlessly.

Edit: SteinAir/Garmin replaced it for me without any hassle, thanks again to both :)
 
Does anyone know if all of the Van's planes have their outer wing webs parallel to the aircraft centerline? I know the sweep angle is under 1*

It certainly seems that that the webs are square to the spar and the spar is square to the fuse, except for the sweep angle.

Larry
 
Be Aware...

After spending a bunch of time at the Garmin tent at Oshkosh, many questions were answered. I thought I had my basic avionics figured out...then I went to Stein's booth and asked them what they thought of my G3X setup. We talked awhile and it was brought to light that the GMU communicates via the CAN bus. Normally not a problem in the RV aircraft, however, there is a LIMIT on the total length of the CAN bus. The guys at SteinAir recommended using the GMU 22 in the RV-10 due to the lengths involved. Apparently, when you add all of the lengths up for the CAN bus it starts to get near the limit. The GMU 22 communicates using a different method so that distance is saved whereas the GMU 11 adds to the length. It is also why I will be mounting my Remote Comm2 radio behind the panel.

I am just in the planning stage of my system, and not completely familiar with it all yet but thought it might be a good topic of discussion for those rolling their own system without the help of a shop.

Just wanted to put it out there...
 
...then I went to Stein's booth and asked them what they thought of my G3X setup. We talked awhile and it was brought to light that the GMU communicates via the CAN bus. Normally not a problem in the RV aircraft, however, there is a LIMIT on the total length of the CAN bus.

Just wanted to put it out there...

The "ISO 11898 Standard specifications are given for a maximum signaling rate of 1 Mbps with a bus length of 40 m and a maximum of 30 nodes."

HOW could anyone get more than 40 meters of CAN bus in an RV aircraft?
 
Well...

That is not the information I received, it was more like 60 feet...

If you add it up in the -10, you have the pitch servo at 11 feet, the roll servo about 11 feet, the GMU if tailcone mounted is about 12 feet, yaw servo is 12 feet, plus at the little runs behind the panel...

You can think what you want. I am having SteinAir do my wiring and they have done a bunch of RVs. That's where the info came from...
 
That is not the information I received, it was more like 60 feet...

If you add it up in the -10, you have the pitch servo at 11 feet, the roll servo about 11 feet, the GMU if tailcone mounted is about 12 feet, yaw servo is 12 feet, plus at the little runs behind the panel...

You can think what you want. I am having SteinAir do my wiring and they have done a bunch of RVs. That's where the info came from...

There has been multiple update to this length and the latest I heard was 66 feet which it is not that hard to reach or exceed.
 
Hello Mehrdad,

There is some good information in this recent thread about the importance of good GMU 11 installation alignment if you haven't seen it.

Thanks,
Steve
Thank you Steve, I did look at that thread but was hoping for more info. Do you know if Garmin has a generic mount that allows for fine adjustment. Although it is not hard to make but if there is one available, why reinvent the wheel
 
Most of us install in the Vans' specified location without any problems.

I had a bad GMU11 and that caused some grief, I couldn't get it to calibrate. Once I got a replacement, it calibrated easily the first time and has worked flawlessly.

Edit: SteinAir/Garmin replaced it for me without any hassle, thanks again to both :)
Are you referring to the bracket in the second bay in the left wing? is there an easy way of mounting a GMU11 in that bracket and any issues?
I have read that the wing tip gets better results.
 
We talked awhile and it was brought to light that the GMU communicates via the CAN bus. Normally not a problem in the RV aircraft, however, there is a LIMIT on the total length of the CAN bus.

There are different types of length limits to CAN, overall length and stub length are the two we are concerned with. There is no reason we need long stub lengths (Garmin wants them under .3m) and overall length is not a problem in any RV. Overall bus length is limited to 20 meters at the high bit rates we use.

At those lengths you could start the linear backbone bus at one end of the left wing, go all the way to the end of the right wing, come back and go all the way to the tail with any RV. Which would also be unnecessary with any RV.
 
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so

So I guess the guys that are doing tons of RV setups don't know what they are talking about...

From the Install manual:

"2.3.1.3.5 CAN Bus Installation Guidelines
For maximum reliability of the CAN bus, the following guidelines should be followed:
• The CAN bus backbone must be a single linear path with exactly two distinct ends. CAN bus
connections should be “daisy chained” from device to device. Avoid “star” and “Y” topologies,
and do not use a hub device (see Figure 2-12).
• The overall length of the bus should not exceed 20 meters (66 feet).
• Keep all stub node connections as short as practical. The maximum length of any stub node
connection is 0.3 meters (1 foot)."


I think I will stick with the guys that are doing this for a living...YMMV
 
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Can Bus

A 10 might indeed require more length and I can't imagine the other models would require more.....but in my 9 I don't need to worry about a yaw dampener, so mine will likely start in the right wing with the GMU11 and end at the pitch servo just behind the baggage bulkhead, forming a wide U shape. Probably around 40 ft. This is what the G3X class recently recommended. Wonder if it can be configured similarly in the 10 or if the yaw dampener servo creates an issue for the length? It must.

Rocket man has the guidelines right on. The biggest things emphasized to us was to keep the bus linear and daisy chained and the node lengths shorter than a foot.
 
Gmu

...which is why Steiner recommends the gmu22 for the -10. It doesn?t use the CAN bus, so it doesn?t add to the length...
 
I was advised (by one of Stein's guys) to place the GMU22 in the -14's left wing ADAHRS mount and that's how I've configured my just-completed wing.

Why go with the GMU11 at all? What am I missing?
 
So I guess the guys that are doing tons of RV setups don't know what they are talking about...

From the Install manual:

"2.3.1.3.5 CAN Bus Installation Guidelines
For maximum reliability of the CAN bus, the following guidelines should be followed:
• The CAN bus backbone must be a single linear path with exactly two distinct ends. CAN bus
connections should be “daisy chained” from device to device. Avoid “star” and “Y” topologies,
and do not use a hub device (see Figure 2-12).
• The overall length of the bus should not exceed 20 meters (66 feet).
• Keep all stub node connections as short as practical. The maximum length of any stub node
connection is 0.3 meters (1 foot)."


I think I will stick with the guys that are doing this for a living...YMMV

With a total length AND span summed to around ~56 feet, it would take the world's most schizophrenic wire run to bust your quoted total length. Just wire it, the largest source of signal loss is going to be poor technique not the length (in supplied scenario).

-Guy with nominal signal loss in setup who apparently doesn't know what he's talking about.
 
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...which is why Steiner recommends the gmu22 for the -10. It doesn’t use the CAN bus, so it doesn’t add to the length...

Guess that depends who you talk to, and what your setup is. It was suggested to me to go with the GMU11. They did the harness as well and kept it down to 40' I beleive.

Why go with the GMU11 at all? What am I missing?

What I was told because it communicates on the CAN bus and I have a full Garmin layout that both G3X's and my G5t and whatever else needs it will retrieve the information.

I struggled a bit with where to mount it as well. After reading installation guidance and seeing what a few others did I decided to make essentially a tiny shelf hanging off a aluminium angle. I'm still debating how to fasten it onto the longeron. I'm hesitant to drill into the longeron so will either use some two-sided tape or my go to 3M adhesive which seems to lock anything I use it on in place. Took a few pictures prior to primer.

Here's one pre-trim. I ended up smoothing out the edges and making the front even.



Here it is just sitting in place. It's a snug fit.
 
Outside of the VPX, CO2 detector and a few random things everything else is Garmin. I have Dual G3X's, the 245 audio panel, the 507 AP head, GTN 650, Remote comm, remote transponder with ADS-B in/out, G5, their ARINC box and Engine monitoring system. I essentially never wanted any compatibility issues.
 
Setup

That is pretty much what I am doing. They were pretty certain about using the 22 over the 11 in my case. Wonder what is different...
 
I struggled a bit with where to mount it as well. After reading installation guidance and seeing what a few others did I decided to make essentially a tiny shelf hanging off a aluminium angle. I'm still debating how to fasten it onto the longeron. I'm hesitant to drill into the longeron so will either use some two-sided tape or my go to 3M adhesive which seems to lock anything I use it on in place. Took a few pictures prior to primer.

Here's one pre-trim. I ended up smoothing out the edges and making the front even.



Here it is just sitting in place. It's a snug fit.
I think that its going to bounce up and down a bit without a front support. I would add an additional aluminum angle up there. If you don't want to drill more holes in the longerons, just bed the angle supports down on some tank sealant and let it cure. I just did that on my -9A.. You will probably want to swap out the standard AN hardware mounting the seat belt cable attachments with non magnetic SS hardware.
 
I think that its going to bounce up and down a bit without a front support. I would add an additional aluminum angle up there. If you don't want to drill more holes in the longerons, just bed the angle supports down on some tank sealant and let it cure. I just did that on my -9A.. You will probably want to swap out the standard AN hardware mounting the seat belt cable attachments with non magnetic SS hardware.
You may want to double check the manual or consult with Garmin. It advises against installation near any servo so if you are planning on having an A/P servo, this location may not be a suitable one.
 
You may want to double check the manual or consult with Garmin. It advises against installation near any servo so if you are planning on having an A/P servo, this location may not be a suitable one.

I believe it suggests 10 feet from any type of servos. Unless you're going to mount these on a stick hanging off the plane you're going to be hard pressed to get this type of clearance.
 
I believe it suggests 10 feet from any type of servos. Unless you're going to mount these on a stick hanging off the plane you're going to be hard pressed to get this type of clearance.

Left wingtip seem to be a long enough stick, isn't it?
 
...You will probably want to swap out the standard AN hardware mounting the seat belt cable attachments with non magnetic SS hardware.

Check the material strength before you swap any critical hardware. The seatbelt and harness attach points standard AN bolts for a reason. Stainless hardware tends to be weaker than normal AN cad plated hardware.
 
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Ran into a CAN bus length issue with putting it in the wing. I'll be able to see if I have any calibration issues before I adhesive this mount down.
Please let us know what you find. I am also exceeding it by two feet, partly due to poor planning but I am told that two feet is not all that much since the pervious max length was around 100' and it had worked. This is at least what I have been told.
 
You may want to double check the manual or consult with Garmin. It advises against installation near any servo so if you are planning on having an A/P servo, this location may not be a suitable one.

Yeah,,,,,that would be great if practical but not doable in my -9. I have it mounted on the F-709 bulkhead which puts it "about" the same isolation distance from the pitch servo that I had on the RV-10, about 4 feet. I had it mounted on the bulkhead aft of the aft baggage bulkhead and had no problems with it there so I expect the same here.
 
Check the material strength before you swap any critical hardware. The seatbelt and harness attach points standard AN bolts for a reason. Stainless hardware tends to be weaker than normal AN cad plated hardware.

Do you know of a reference chart to find this info? I plan on using the SS AN bolts from AS&S but can not find a reference for tensile strength on the web.
 
Do you know of a reference chart to find this info? I plan on using the SS AN bolts from AS&S but can not find a reference for tensile strength on the web.

The big 'ol thick Aircraft Spruce Catalog has that information for some of the hardware they sell. I can find several online resources which list the tensile (125,000 PSI) and shear strength (76,000 PSI) for regular cad plated steel AN hardware. Information on stainless depends on the alloy you're using. If you know the alloy, I bet the shear strength is online somewhere.
 
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Mcmaster

Mcmaster has good info if you know the alloy...SS is almost always softer but there ARE some alloys that are just as strong...
 
My take

In general i dont use stainless bolts for anything structural. Like mentioned above in general stainless is not as strong. I also have had stainless screws jam up in tapped threads; seems it is more prone to siezing than steel hardware. JMHO
 
SS

There are actually some SS alloys that perform as well or better than a standard AN bolt, however, it takes some research to find them and the available sizes and options are usually more limited. The price is also generally much higher, too.
 
What I was told because it communicates on the CAN bus and I have a full Garmin layout that both G3X's and my G5t and whatever else needs it will retrieve the information.

I'm doing essentially the same, all-Garmin, system and was advised by Stein's shop to go with the GMU22 for the -14. I'm not convinced that CAN bus offers any real-world advantages in our application and, since the GMU22 fits neatly into the left wing with zero fuss, I elected to go with it.

Once it's all up and running, I doubt that anyone would be able to discern from behind the stick whether there's an -11 or -22 in a given airplane.
 
Another Data Point

Benefits of the GMU 11 include:

-Price

-Weight

-It uses ships power instead of 5V from the GSU.

-Using the CAN BUS (and freeing up Serial Ports, which is less of an issue now that more and more LRU's are also using the CAN BUS).

-Mounting


Regarding the Can Bus, it is important to remember that the can bus is laid out as a backbone, with two distinct "terminations"/ends. When you have units spread throughout an airframe, the wiring doesn't have to make a bunch of jumps to and from your panel for every unit (as long as it is somewhat methodically designed.)


So, RV-10 Can Bus length might be in the 40-50ft range with wingtip and/or tail cone mounted LRU's.


Another data point regarding a tailcone install:
The GMU 11's in the factory demonstrator, and One Week Wonder RV-12iS's both sit about 32" away from dual fuel pumps and a roll servo. The interference tests conducted passed with flying colors ;) YMMV

All that being said, those guys at Stein do good work, and could very well be taking things into account that I've overlooked.
 
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I concurred with the thought a single angle wouldn't be secure enough. Added a second.

IMG_0578.JPG


Had to cut the back angle piece so I can get it past a set of frames. Will know in a week or so if it's going to have any interference issues.
 
So I guess the guys that are doing tons of RV setups don't know what they are talking about...

From the Install manual:

...

? The overall length of the bus should not exceed 20 meters (66 feet).

...

I think I will stick with the guys that are doing this for a living...YMMV

I edited my post changing 25 to 20 meters per Garmin's recommendation (I went from memory instead of looking up the value, an error I readily admit) but I stand by my post. 66 feet is achievable in any RV, even a 10.

There is also one big advantage to the GMU 11 no one has brought up. It's data is available to everyone, even if the ADAHRS to which the GMU 22 is connected fails.

Stein is great and they did a great job on my harness, but they are not gods.

They were very thankful when I pointed out the wiring error in the harness for the 14 (engineered by Van's) in how the servos were wired preventing correct three servo operation. I do know what I am talking about.

Mine was one of the first to use the Van's production drawing of the RV14 harness. I would have substituted the GMU 11 for the GMU 22 in a heart beat if it had been available.
 
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