GTX 345R AHRS via Bluetooth?

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Lou
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GTX 345R AHRS via Bluetooth?

Post by Lou »

Are any DA40 owners able to confirm that they are receiving Bluetooth AHRS from the GTX 345R to their iPad ? I am having a discussion with my avionics guy who says that he doesn’t think that it can be enabled due to the vertical mount. Neither of us is sure, but it seems others are getting this data.

I have good Bluetooth connectivity otherwise.

Any info, help or advice would be great. Thanks.
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Rich
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Re: GTX 345R AHRS via Bluetooth?

Post by Rich »

Which iPad app are you using? Is there a setting for the 345 to "use as GPS"?

Most devices like this do require a proper orientation along the longitudinal axis to work as AHRS source. True for Stratus and FS210 (which is working for me).
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Re: GTX 345R AHRS via Bluetooth?

Post by smoss »

works fine for me via Garmin Pilot and Foreflight. During the install of the GTX there was a calibration process we did to level and center the AHRS.
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Re: GTX 345R AHRS via Bluetooth?

Post by Lou »

I get the GPS no problem. It just the attitude information that’s not coming through. Thanks - I’ll pass this along.
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arksat
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Re: GTX 345R AHRS via Bluetooth?

Post by arksat »

When I installed 345R, I couldn't get AHRS attitude on ForeFlight/Garmin Pilot even though iPad is connected and ADS-B traffic is displayed.
Brought my plane back to the shop and it turned out they didn't do the calibration process correctly. It started working then.

But honestly I don't really use it with several reasons. I found it's not so stable (drift a lot). GPS altitude doesn't take into account the altimeter settings. GPS ground speed is not really IAS... etc.
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Re: GTX 345R AHRS via Bluetooth?

Post by Rich »

arksat wrote: Wed Mar 04, 2020 2:23 am But honestly I don't really use it with several reasons. I found it's not so stable (drift a lot). GPS altitude doesn't take into account the altimeter settings. GPS ground speed is not really IAS... etc.
I haven't yet tried my FS210 functionality in this area, but the Stratus/FF has never demonstrated any instability.

Keep in mind that altimeter setting is calibrated to the ISA lapse rate. It's really only precisely accurate at ground level of the reporting station. So there is an indeterminate inaccuracy with respect to your "real" altitude. This works fine for traffic control, since all such altimeters have that same behavior.

For me the FF AHRS is used as a backup for instrument failure (primarily the AI) and to give me a profile view of traffic. Having steam gauges means I'm likely to retain the use of mechanical AI and Altimeter. These types of gauges have no real history of sudden failures.
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Rich
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Re: GTX 345R AHRS via Bluetooth?

Post by Rich »

I tested out the AHRS function of my FS210 and, like Tosh, I find the attitude behavior unusable. It's not so much drift that I sense, it's more like instability. That is, over and incorrect reactions:

- Left turn onto runway, the unit shows a 20-30 degree bank and stays that way throughout the takeoff run.
- There was some light-moderate turbulence today. Holding attitude, there were airspeed excursions. Increasing speed would cause the AI to show significant nose-down. Decreasing speed, nose-up.
- Yaw activity in turbulence would cause non-existent banking action.

In short, the bank indication seemed to behave like a turn coordinator. Pitch indication is consistent with theoretical behavior for an AI but much, much exaggerated.

These look like software-correctable damping weaknesses. But for now I will explore if I can go back to using the Stratus for the AHRS function. I haven't seen anything like this with the Stratus.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: GTX 345R AHRS via Bluetooth?

Post by smoss »

My GTX345R AHRS works great, no drift or instability. Great backup in case of any failures.
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Re: GTX 345R AHRS via Bluetooth?

Post by Antoine »

Strange... my FS210 works perfectly. Attitude, heading, everything is perfect.
It is true that GPS derived ground speed is not very useful and even potentially dangerous if not understood for what it is, but the altitude indication of a WAAS GPS is more useful and accurate by design than the primitive barometric approximation.
As always: use with care and know what you are doing.
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Re: GTX 345R AHRS via Bluetooth?

Post by Lou »

I agree bad attitude info is worse than none. I had mixed success with the Stratux AHRS and concluded it was more dangerous than helpful. I am surprised to hear there are mixed results with the GTX345. One would think Garmin would get this right.

It comes down to enabling all the functionality so that it’s there. I’ll get it calibrated when it goes in for annual at the end of this month.
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