G5 install in the home stretch. GMU11 question

[ragedracer1977]

Mounting it in the right wing.  Passes every test except the Nav lights.  There's a 200% error when I flip the switch on and off. Just a transient error, it doesn't "stay".  Only appears for an instant. 

It seems like the best way to correct that would be a twisted pair to the power and ground of the Nav light.  Move the ground to the firewall area and isolate it from the wing entirely.  I think it being grounded at the wing tip is what causes the interference. 

Thoughts?

Edited January 14, 2019 by ragedracer1977

[N201MKTurbo]

LED nav lights

[N201MKTurbo]

Incandescent lights have a much lower resistance when cold. When they are first turned on they draw a large current for a few milliseconds until the filament heats up. This large current is causing the interference.

Try to route the GMU11 wires away from the nav light wires. 

 

[ragedracer1977]

1 hour ago, N201MKTurbo said:

Incandescent lights have a much lower resistance when cold. When they are first turned on they draw a large current for a few milliseconds until the filament heats up. This large current is causing the interference.

Try to route the GMU11 wires away from the nav light wires. 

 

Can't get any farther away. The nav wire is a single unshielded wire that runs through the front most hole in the ribs.  I'm gonna try pulling new wire first, if that doesn't fix it, I guess it's LEDs!

[Marauder]

Can't get any farther away. The nav wire is a single unshielded wire that runs through the front most hole in the ribs.  I'm gonna try pulling new wire first, if that doesn't fix it, I guess it's LEDs!

I think running new wires is a cheaper alternative than the LEDs (although the LEDs are ). Were there any requirements for the magnometer for clearance from other wires? Is suspect it will be tough considering you’ll need to run those wires close to each other when you bring them in from the wing.


Sent from my iPad using Tapatalk Pro

[jetdriven]

You can pull wire for gmu11 behind the wheel well... there’s a little gap at the back of the rib that’s outboard of the wheel well you can sneak wire through there and then go to your magnetometer. 

And yes the twisted wire pair with the ground at the center of the airplane pretty much negates the EMI from it

Edited January 14, 2019 by jetdriven

[Aerodon]

I was advised to run new grounds from my tail nav and tail beacon to 'in front' of the GMU11.  I pre-emptively replaced the Cessna 'flasher' with one on the Whelen 'integrated flasher' because I just knew that was going to be a problem.  Passed the GMU11 test with nothing more than 15% of the limit first time.

 

Don

[Aerodon]

3 hours ago, ragedracer1977 said:

Can't get any farther away. The nav wire is a single unshielded wire that runs through the front most hole in the ribs.  I'm gonna try pulling new wire first, if that doesn't fix it, I guess it's LEDs!

LED's are not going to help, just sort your grounds out.

[bob865]

I need to ask a question....Is this 200% position error i.e. the direction needle swings? or 200% data transmission/communication error?

[ragedracer1977]

2 hours ago, bob865 said:

I need to ask a question....Is this 200% position error i.e. the direction needle swings? or 200% data transmission/communication error?

This is in the interference test.  And, I don't think it's the wires.  I think it's a field generated in the wing just for a fraction of a second when you power on/off the nav light.  I tested there with a 2' connection to the G5.  I had the G5 on a stool near me and my friends 12v power supply.  The wires were at least 2' apart.  I think it's the ground deal because it's transient. When the lights are on or off, theres no interference. Only on power on/off

[OR75]

what wing compartment is the GMU located ?

all the wires usually are run at the front of the wing

The GMU should be closer to the spar

 

[ragedracer1977]

It's behind the spar, just past the flap.  

[ragedracer1977]

I'm pulling new wire this afternoon. I'll let you know what happens

[BDPetersen]

Had interference issue with my installation emanating from the led beacon. Solution was running ground all the way to battery.

[jetdriven]

Most all the Mooney stuff is grounded at the location of the hardware. which heats the structure up with skin current and EMI.  pulling ground wire back to the center of the plane or ideally, the battery, greatly helps.

 

[EricJ]

+1 on LEDS.    There are plug-in replacements that meet the TSO specs for basic nav bulbs.   

Probably just re-opened a worm can, but that's fine.

[N201MKTurbo]

When there is a single conductor feeding the nav light and airframe ground, the current carrying wire makes a magnetic field concentrated around the wire. The magnetic field from the return path through the airframe is so spread out it doesn’t locally cancel, the magnetic field. By putting a return conductor (ground wire) in, it will generate a magnetic field exactly opposing the magnetic field of the feed wire. 

To be most effective all the ground current must flow through the ground wire instead of the airframe.

[EricJ]

1 hour ago, N201MKTurbo said:

When there is a single conductor feeding the nav light and airframe ground, the current carrying wire makes a magnetic field concentrated around the wire. The magnetic field from the return path through the airframe is so spread out it doesn’t locally cancel, the magnetic field. By putting a return conductor (ground wire) in, it will generate a magnetic field exactly opposing the magnetic field of the feed wire. 

To be most effective all the ground current must flow through the ground wire instead of the airframe.

Yup, and make them a twisted pair like Brice suggested and it should help quite a bit.

An example twisted pair:

[Dream to fly]

20 hours ago, ragedracer1977 said:

Mounting it in the right wing.  Passes every test except the Nav lights.  There's a 200% error when I flip the switch on and off. Just a transient error, it doesn't "stay".  Only appears for an instant. 

It seems like the best way to correct that would be a twisted pair to the power and ground of the Nav light.  Move the ground to the firewall area and isolate it from the wing entirely.  I think it being grounded at the wing tip is what causes the interference. 

Thoughts?

Just asking because I am installing a G5 too.  Why did you go to the wing and not the tail?

[ragedracer1977]

Twisted pair did the trick.  Not even a bump when I turn the nav lights on and off.  

And I went with the wing, because why not.  I figured that would be better because there's a lot of steel in the tail (control rods) and I have my rotating beacon and strobe power supply back there.  Near the end of the wing seems liked the cleanest place.  And I don't know for sure, but I'm betting a servo gets mounted in the tail for the TruTrak.  

I have no idea where the aileron servo will go, but it won't be past the control rods in the wing.  Where I put it seems the least likely to have future interference.

[Dream to fly]

1 minute ago, ragedracer1977 said:

Twisted pair did the trick.  Not even a bump when I turn the nav lights on and off.  

And I went with the wing, because why not.  I figured that would be better because there's a lot of steel in the tail (control rods) and I have my rotating beacon and strobe power supply back there.  Near the end of the wing seems liked the cleanest place.  And I don't know for sure, but I'm betting a servo gets mounted in the tail for the TruTrak.  

I have no idea where the aileron servo will go, but it won't be past the control rods in the wing.  Where I put it seems the least likely to have future interference.

Thanks.   I might just have to relocate.  How did you mount it in the wing?

[ragedracer1977]

56 minutes ago, Dream to fly said:

Thanks.   I might just have to relocate.  How did you mount it in the wing?

That's next.  I had to make sure it would work there first.  I guess I'll just mount it to the wing skin.  That seems to meet all the requirements for pitcg, roll, and yaw.

[carusoam]

If we are still talking magnetometer location...

Mooney used to put them in the wing about halfway out, on the copilot side(I believe)... it is hiding under an access panel that is held in place with brass rivets.

So if you want to know which bay it is in... look for a Mooney with a nice BK HSI and check under the wing....   

The pilot side gets the Pitot tube and stall horn...

Not sure if there is a reason for these various locations...

 

Is the magnetic compass officially dead...?

 

Garmin GMU11 magnetometer (needs display of course) $275

https://buy.garmin.com/en-US/US/p/574236

 

Airpath compass....  $220

https://www.aircraftspruce.com/catalog/inpages/airpath_compass3.php?gclid=EAIaIQobChMI8776l_ft3wIVFeDICh2BiAKaEAQYByABEgKjW_D_BwE

 

Pretty small dollars for something so powerful.... and convenient.

Best regards,

-a-

[bob865]

10 hours ago, carusoam said:

Mooney used to put them in the wing about halfway out, on the copilot side(I believe)... it is hiding under an access panel that is held in place with brass rivets.

So if you want to know which bay it is in... look for a Mooney with a nice BK HSI and check under the wing....   

I wonder if it's in the same bay or nearby the temp probe.  On my plane the temp probe is mounted in the right wing about midway down.  Similar location you seem to be describing.

12 hours ago, ragedracer1977 said:

Twisted pair did the trick.  Not even a bump when I turn the nav lights on and off. 

Between the GMU and the G5 correct?  You didn't change the wiring on the light, right?

[Steve W]

2 hours ago, bob865 said:

I wonder if it's in the same bay or nearby the temp probe.  On my plane the temp probe is mounted in the right wing about midway down.  Similar location you seem to be describing.

Between the GMU and the G5 correct?  You didn't change the wiring on the light, right?

I haven't seen my magnetometer yet, I replaced my temp probe in that position for the JPI 900. (1994 M20J with King HSI) I should go look for the magnetometer.

And it's replacing the lighting wiring, the twisted pair means the power to the light and the return from the light cancel itself out and greatly reduce the magnetic interference. Twisted pair both reduces interference to the signals in the wires(the light doesn't care) but also reduces interference to things around those wires.

 

Edited January 15, 2019 by Steve W