Multiple OAT's and GPS antennas

[TuomoMooneyFlying]

My JPI has an OAT, if I go the G5 route it will have another OAT. Same for 530 GPS antenna, my NAV2 has also GPS antenna, G5 will also have an antenna?

So the question is, can’t these devices share antennas?

[hais]

I think they would need to certify that combination, probably no incentive for that. 

[Ragsf15e]

53 minutes ago, TuomoMooneyFlying said:

My JPI has an OAT, if I go the G5 route it will have another OAT. Same for 530 GPS antenna, my NAV2 has also GPS antenna, G5 will also have an antenna?

So the question is, can’t these devices share antennas?

I agree that it’s a pia.  I have a jpi temp probe and g5s… i opted not to put an additional temp probe on the g5s, so I don’t get TAS and winds.  Apparently the jpi probe and garmin probe are different.  Worst part is, the jpi does share the temp to my 430W, but that can’t be shared to g5s (which get other data from the 430w)?.  And yes, my airplane came with two gps antenna and only one is used.

[Andy95W]

2 hours ago, TuomoMooneyFlying said:

My JPI has an OAT, if I go the G5 route it will have another OAT. Same for 530 GPS antenna, my NAV2 has also GPS antenna, G5 will also have an antenna?

So the question is, can’t these devices share antennas?

The G5 doesn’t need a GPS antenna, it gets its location data from one of your NAVs (as long as it’s a WAAS unit).

1 hour ago, Ragsf15e said:

I agree that it’s a pia.  I have a jpi temp probe and g5s… i opted not to put an additional temp probe on the g5s, so I don’t get TAS and winds.  Apparently the jpi probe and garmin probe are different.  Worst part is, the jpi does share the temp to my 430W, but that can’t be shared to g5s (which get other data from the 430w)?.  And yes, my airplane came with two gps antenna and only one is used.

The wind speed/direction on the G5 is well worth the additional probe, mainly because it also gives you Density Altitude in the summertime when you’re on the ground before takeoff.

[Ragsf15e]

1 hour ago, Andy95W said:

The G5 doesn’t need a GPS antenna, it gets its location data from one of your NAVs (as long as it’s a WAAS unit).

The wind speed/direction on the G5 is well worth the additional probe, mainly because it also gives you Density Altitude in the summertime when you’re on the ground before takeoff.

Yes, I would like it.  Funny thing is, I get the DA and winds from the 430W because it gets the oat from the jpi and the heading from the g5.  It’s just a couple more knob turns, so the info is already there in an actual garmin device.

[ArtVandelay]

Worst part is, the jpi does share the temp to my 430W, but that can’t be shared to g5s (which get other data from the 430w)?.

The JPI can share the OAT along with fuel data with 430 (at least it does for the GTNs).

[FlyingDude]

6 hours ago, Ragsf15e said:

oat from the jpi

They installed my jpi oat probe in the right air scoop on the fuselage whereas g5 probe is far out on the wing: there's always a 5-10C difference!!! Sometimes I feel like moving the jpi probe to the panel and call it IAT...

[Pinecone]

They installed a temp probe for my JPI 830, even through I have OAT from the GPS/Aspen/G55.

[Vance Harral]

The G5 is primarily a CANBUS device, so any temperature data it receives has to be transmitted over that network.  The main reason it can't get temperature data from existing probes is that those probes and/or the devices they connect to don't have a CANBUS interface to talk to the G5.

The probes themselves aren't CANBUS devices either, but Garmin provides the GAD13 device to bridge analog temperature probe data to the CANBUS network.  It's technically possible you could gang an existing temperature probe in parallel to a GAD13 and whatever it normally talks to; but I don't know the impedance implications of that, and you're into experimental territory anyway.

As others have pointed out, you probably don't need an additional GPS antenna to install a G5 or two.  They have a coax connector for an antenna, but they can also be set up to receive location data from a WAAS navigator over an RS-232 connection (which is independent from the CANBUS interface), and the latter is how most are installed.  The other curious trick is that in many installations, the GPS receiver in a G5 will acquire satellites even with no antenna attached to the coax connection on the back.  The installation manual doesn't allow exploiting this in a certified installation, but it's interesting.

We have the temperature probe in our G5 installation, so we get OAT, density altitude, TAS, winds aloft, etc.  It's kind of a fun gimmick, but I wouldn't agonize over adding the OAT probe if you don't have one.  What I've found in practice is that the TAS and winds aloft are only accurate during a long, steady state experiment.  It tends to be inaccurate when maneuvering (my guess is it's displaying a weighted average of samples over time).  So it's frankly not that much help for tactical things like picking a wind correction angle in a holding pattern or approach leg.  You can do just as well with GPS ground speed and ground track.  Seeing density altitude while taxiing out is kind of cute.  But pilots smart enough to understand the implications of DA already know the DA from math and/or the ubiquitous AWOS warnings.  The G5 doesn't display the DA in flight (at least not by default), so it's not going to help you understand the likelihood of getting over a tall rock.  I don't regret the extra time and effort of installing the OAT probe, but with a few hours under our belts flying with it, it just turns out that like many of these things, it doesn't really make an operational difference.

[Ragsf15e]

7 hours ago, ArtVandelay said:

The JPI can share the OAT along with fuel data with 430 (at least it does for the GTNs).

Yes, mine does that to the 430W.  Just can’t get it to the g5s as @Vance Harral explained.

[201Mooniac]

1 hour ago, Vance Harral said:

The G5 is primarily a CANBUS device, so any temperature data it receives has to be transmitted over that network.  The main reason it can't get temperature data from existing probes is that those probes and/or the devices they connect to don't have a CANBUS interface to talk to the G5.

When I had a G5 as backup to my G500TXi, the G5 got the temperature from the TXi over A429 so it is possible to get temp other than by CAN bus.

[201Mooniac]

The G5 antenna, if you would like it as backup to you WAAS position source, can be mounted under the glareshield so it is a really simple install.

[Vance Harral]

50 minutes ago, 201Mooniac said:

When I had a G5 as backup to my G500TXi, the G5 got the temperature from the TXi over A429

The G5 has no A429 inputs.  If you have a GAD29B - which many installations do - you can send A429 data to that, and it will convert to CANBUS and pass it along to the G5.  This works in the other direction too - e.g. our GTN gets air data from the G5 on A429 inputs - but this only works because the GAD29B is there to bridge the two busses.

I don't mean to be a pedant about it - it's not really incorrect to say a G5 can get temp data "via A429".  But for people trying to decide what they want and how much it's going to cost, it's important to understand the architecture.  A G5 has an RS-232 interface for GPS position data, and CANBUS for everything else.  Accordingly, any air data device that doesn't natively speak CANBUS will need a GAD bridge to communicate with the G5.

[201Mooniac]

1 hour ago, Vance Harral said:

The G5 has no A429 inputs.  If you have a GAD29B - which many installations do - you can send A429 data to that, and it will convert to CANBUS and pass it along to the G5.  This works in the other direction too - e.g. our GTN gets air data from the G5 on A429 inputs - but this only works because the GAD29B is there to bridge the two busses.

I don't mean to be a pedant about it - it's not really incorrect to say a G5 can get temp data "via A429".  But for people trying to decide what they want and how much it's going to cost, it's important to understand the architecture.  A G5 has an RS-232 interface for GPS position data, and CANBUS for everything else.  Accordingly, any air data device that doesn't natively speak CANBUS will need a GAD bridge to communicate with the G5.

You are of course correct.  If the G5 is connected to any navigator the GAD29(B) is already there.

[MoonFlyer68]

7 hours ago, FlyingDude said:

They installed my jpi oat probe in the right air scoop on the fuselage whereas g5 probe is far out on the wing: there's always a 5-10C difference!!! Sometimes I feel like moving the jpi probe to the panel and call it IAT...

They did the same thing with my JPI probe. One of these days I will rip it out and move it to the wing where the probe for my AV-30 is.

[TuomoMooneyFlying]

Thanks for all the responses! Sounds like I just need to get used to a bunch of probes sticking out. And I’ve got a non-WAAS 530 so the G5's will require it’s own WAAS antenna's. Ugh!

[FlyingDude]

On 2/21/2023 at 2:36 PM, MoonFlyer68 said:

They did the same thing with my JPI probe. One of these days I will rip it out and move it to the wing where the probe for my AV-30 is.

Why keep poking holes in your wing?  Do you really need OAT in your JPI?  Especially since you already have it on your AV-30?  

[jlunseth]

I have the same concern. Why do I need more than one temp probe. However some of the instruments that have been installed in my panel to date (such as a GI 275) require a compatible temp probe in order to receive the information needed by the instrument to make its computations, such as airspeed. OK, I guess. I want my instruments to work correctly. 

[MoonFlyer68]

6 hours ago, FlyingDude said:

Why keep poking holes in your wing?  Do you really need OAT in your JPI?  Especially since you already have it on your AV-30?  

I guess you're right. I was thinking that the JPI used that temperature readings as part of some calculations like the AV-30 does.  But now that you mention it, I think the JPI just displays the temperature but doesn't really need it for any other functions.

[flyboy0681]

On 2/21/2023 at 6:43 AM, FlyingDude said:

They installed my jpi oat probe in the right air scoop on the fuselage whereas g5 probe is far out on the wing: there's always a 5-10C difference!!! Sometimes I feel like moving the jpi probe to the panel and call it IAT...

The real question is, when the nose of the plane is out of the sun or the plane is in the hangar, do the two temperatures agree? If you know that the JPI is off, you can adjust an offset through the programming menu.

[ArtVandelay]

I guess you're right. I was thinking that the JPI used that temperature readings as part of some calculations like the AV-30 does.  But now that you mention it, I think the JPI just displays the temperature but doesn't really need it for any other functions.

I think it’s used for HP calculation.

[ArtVandelay]

If you know that the JPI is off, you can adjust an offset through the programming menu.

Only up to 6°, in my case that’s not quite enough, my is ~9° warmer with probe in the vent.

[MoonFlyer68]

13 hours ago, ArtVandelay said:

I think it’s used for HP calculation.

Checking the pilot guide, the OAT is used in the %HP calculations.  I will see if I can adjust it enough in the software to make it accurate.

[FlyingDude]

16 hours ago, flyboy0681 said:

when the nose of the plane is out of the sun or the plane is in the hangar, do the two temperatures agree?

Yes. All 3 of g5 and jpi probes and windshield-mounted thermometer. Checked it in the hangar...

Edit: also the wall mounted thermometer. 

Edited February 24, 2023 by FlyingDude
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