If I have two AHRS can I get rid of my vacuum system?

[Fly_M20R]

Well.... got quite tied up with work so unable to make the promised video with my 275's.  It is on my TO DO list for sure!!

[NJMac]

On 5/27/2021 at 11:24 PM, Ragsf15e said:

 or dynon pocket panel.

+1 for the pocket panel.  

[midlifeflyer]

On 5/27/2021 at 6:09 PM, Fly_M20R said:

If you have a Flightstream 210 to allow for ADS-B traffic and Wx to be sent to your iPad (Garmin Pilot or Foreflight) and also sync flight plans then it has a built-in AHRS which can be displayed on the Sythetic Vision page of Garmin Pilot (not sure about Foreflight). Great backup AI as long as you have avionics master on. The Flightstream 510 will also send Attitude info to the iPad "from a compatible flight deck or display".

CK

It works with Foreflight.

[Fly_M20R]

3 hours ago, midlifeflyer said:

It works with Foreflight.

Perfect!

[midlifeflyer]

12 hours ago, Fly_M20R said:

Perfect!

It's probably a testament to Foreflight's market share. It's the only non-Garmin EFB FlightStream and Connext talk to. 

[PT20J]

I have a good vacuum pump. An overhauled RC Allen vacuum AI is only $595 from Spruce. Might be cheap insurance if my new G3X and G5 were to simultaneously give up their desire to function properly. Seems like overkill, but still…

[RobertGary1]

1 hour ago, PT20J said:

I have a good vacuum pump. An overhauled RC Allen vacuum AI is only $595 from Spruce. Might be cheap insurance if my new G3X and G5 were to simultaneously give up their desire to function properly. Seems like overkill, but still…

It also eliminates the single point of failure with the pitot system. The electronic AHRS use pitot to correct drift. 

[aviatoreb]

I kept my electric mechanic AI.  Those are getting pretty cheap to buy these days too if you don't already have one.  But I removed the vacuum.

[Ragsf15e]

11 minutes ago, aviatoreb said:

I kept my electric mechanic AI.  Those are getting pretty cheap to buy these days too if you don't already have one.  But I removed the vacuum.

Is it battery backed up?  What model is it?

After this thread, I wouldn’t mind having some type of backup, but I’m skeptical of going all the way back to the vacuum pump.

[aviatoreb]

51 minutes ago, Ragsf15e said:

Is it battery backed up?  What model is it?

After this thread, I wouldn’t mind having some type of backup, but I’m skeptical of going all the way back to the vacuum pump.

They do have battery backups available.  Mine is an RC.  I don't have an independent backup, but I do have two big 35amp hour batteries in my tail.  I figured the failure mode which would take out my former vacuum would likely not take out my alternator AND my entire electrical so access to the ships batteries.  I am rethinking this now since everything is electric.  However, the failure mode we are worrying about here, which is software based again will likely not take out my alternator and also entire electrical system.  I am open to critique on this point!

Anyway a separate stand alone battery is available that can drive the RC which I do not currently have.

[Ragsf15e]

49 minutes ago, aviatoreb said:

They do have battery backups available.  Mine is an RC.  I don't have an independent backup, but I do have two big 35amp hour batteries in my tail.  I figured the failure mode which would take out my former vacuum would likely not take out my alternator AND my entire electrical so access to the ships batteries.  I am rethinking this now since everything is electric.  However, the failure mode we are worrying about here, which is software based again will likely not take out my alternator and also entire electrical system.  I am open to critique on this point!

Anyway a separate stand alone battery is available that can drive the RC which I do not currently have.

Thanks.  Yeah I think the failure mode is fairly unlikely, especially since you have two batteries and maybe dual alternators?  I guess the thing that spooked me is that a total electrical failure would take out my gps input to the G5s as well as the pitot heat which could take out the airspeed input.  I’d like to think the G5s would keep working, but this thread has made me rethink that.

[aviatoreb]

17 hours ago, Ragsf15e said:

Thanks.  Yeah I think the failure mode is fairly unlikely, especially since you have two batteries and maybe dual alternators?  I guess the thing that spooked me is that a total electrical failure would take out my gps input to the G5s as well as the pitot heat which could take out the airspeed input.  I’d like to think the G5s would keep working, but this thread has made me rethink that.

Good points.  Anyway my thinking on backups was in terms of the failure modes associated with having a vacuum system.

My annual is coming up - I might have them add a battery inline to my RC mechanical gyro attitude.

[Fly_M20R]

I finally got to do the torture GI 275 flight!!

1) Pitot tube failed.... AHRS and AI worked perfectly fine with IAS red-x'd

2) To further evaluate, removed all GPS sources so that no speed data at all for the AHRS 530W and turned MFD/stby ADI off so its VFR GPS would not give data to the primary ADI). Still worked perfectly through TWO coordinated standard rate turns. It never red-x'd or tumbled!!

Shall publish video hopefully within a week. (It takes time to edit...)

My conclusion is the Garmin has "rocket scientists" writing the AHRS software!!

Chris

[aviatoreb]

1 hour ago, Fly_M20R said:

I finally got to do the torture GI 275 flight!!

1) Pitot tube was covered all the way with a rubber glove over the pitot cover and everything zip tied. No air whatsoever either through pitot or drain tube. AHRS and AI worked perfectly fine with IAS red-x'd

2) Then removed all GPS sources so that no speed data at all for the AHRS 530W and turned MFD/stby ADI off so its VFR GPS would not give data to the primary ADI). Still worked perfectly through TWO coordinated standard rate turns. It never red-x'd or tumbled!!

Shall publish video hopefully within a week. (It takes time to edit...)

My conclusion is the Garmin has "rocket scientists" writing the AHRS software!!

Chris

Thanks for doing that for us Chris!

[Fly_M20R]

Just now, aviatoreb said:

Thanks for doing that for us Chris!

Welcome!!

I was quite amazed at how they performed.

Chris

[EricJ]

1 hour ago, Fly_M20R said:

Shall publish video hopefully within a week. (It takes time to edit...)

If you really flew with your pitot system disabled I'd suggest removing any identifying information in the video.

[RobertGary1]

3 hours ago, Fly_M20R said:

I finally got to do the torture GI 275 flight!!

1) Pitot tube was covered all the way with a rubber glove over the pitot cover and everything zip tied. No air whatsoever either through pitot or drain tube. AHRS and AI worked perfectly fine with IAS red-x'd

2) Then removed all GPS sources so that no speed data at all for the AHRS 530W and turned MFD/stby ADI off so its VFR GPS would not give data to the primary ADI). Still worked perfectly through TWO coordinated standard rate turns. It never red-x'd or tumbled!!

Shall publish video hopefully within a week. (It takes time to edit...)

My conclusion is the Garmin has "rocket scientists" writing the AHRS software!!

Chris

That was my experience too. It was only after the third time the pitot failed that this happened. I suspect it may have been the high winds that day that made the difference.  

[aviatoreb]

2 hours ago, Fly_M20R said:

Welcome!!

I was quite amazed at how they performed.

Chris

Me too - I am really pleased of the outcome and thankful you took the bullet for the team.

[Yourpilotincommand]

I removed my vacuum pump. I have two G5’s. Shed a little bit of useless extra weight.

[RobertGary1]

58 minutes ago, Yourpilotincommand said:

I removed my vacuum pump. I have two G5’s. Shed a little bit of useless extra weight.

Just hope you don’t have the dual AHRS failure I did. 

[Ragsf15e]

On 6/19/2021 at 12:44 PM, Fly_M20R said:

I finally got to do the torture GI 275 flight!!

1) Pitot tube failed.... AHRS and AI worked perfectly fine with IAS red-x'd

2) To further evaluate, removed all GPS sources so that no speed data at all for the AHRS 530W and turned MFD/stby ADI off so its VFR GPS would not give data to the primary ADI). Still worked perfectly through TWO coordinated standard rate turns. It never red-x'd or tumbled!!

Shall publish video hopefully within a week. (It takes time to edit...)

My conclusion is the Garmin has "rocket scientists" writing the AHRS software!!

Chris

Definitely appreciate you doing that.

[Fly_M20R]

I have some selected frames from the video I am editing of the flight where I had no pitot input into the 275's:

1) No IAS, with GPS ground speed and TRK input from 530W and having both 275's on. Climbing to 5500 ft. Both working perfectly. MFD/Standby ADI unit went to Standby ADI and unable to change to other pages

2) Turning level at 5500 ft with 530W on and autopilot engaged in HDG and ALT hold modes. No issues whatsoever.

3). In Standard rate turn with 530W off and GS being provided by now active VFR GPS of bottom Standby ADI 275 unit.  In this case both have the GMU11 magnetometer provided by the top 275 ADI and GS by bottom VFR GPS. Stayed in turn attitude for 2 full coordinated turns without issues

4) In standard rate turn with 530W and PFD (ADI unit) off. Bottom Standby ADI unit has own VFR GPS active but no GMU11 magnetometer HDG input that goes through top unit. Note that now the heading strip reads TRK and not HDG. GS still available. In this case although there were no obvious issues with the bank or slip/skid bug the pitch did vary from above horizon to below horizon even if I stayed at the same altitude. It means that the AHRS unit does need GMU11 input to correct for gyro drift which was more obvious in pitch than bank. 

5) In standard rate turn with 530W and MFD/Standby ADI off. By turning the MFD/Standby ADI off it eliminated the VFR GPS and therefore the ADI had no GPS TRK or GS input. It only had the magnetometer (GMU11) for HDG. In this case it worked perfectly. My conclusion is that the AHRS works much better with magnetometer rather than GPS TRK. It does not seem to need speed input.

I hope to have the video out "soon"...

Chris

[carusoam]

Nice details Chris,

Thanks for sharing them.

Best regards,

-a-

[PT20J]

On 6/24/2021 at 5:55 PM, Fly_M20R said:

My conclusion is that the AHRS works much better with magnetometer rather than GPS TRK. It does not seem to need speed input.

I believe this is correct. As I understand it, a basic AHRS sensor has 3-axis accelerometers and 3-axis gyros. These are accurate for short periods but will drift over time and the amount of drift depends on the acceleration. So, they are better straight and level than maneuvering. Adding 3-axis magnetometers greatly improves accuracy with time and maneuvering. AHRS sensors are available with built-in magnetometers. I believe this is what Kelly uses in the RCA 2610 which does not need GPS or pitot/static inputs. If you have a magnetometer, GPS and pitot/static, you have a belt and suspenders approach and it should be very reliable. 

Garmin told me that the GTX 345 uses the same AHRS as other Garmin units. However, the GTX 345 has a GPS input but no pitot/static and no magnetometer inputs. My GTX 345 linked to Foreflight shows an accurate bank angle, but a 2 degree nose up in a level left turn and a 2 degree pitch down in a level right turn. If I turn off the GPS, it performs reasonably well in a left turn but pitches down 20 deg or so in a level right turn. 

Skip

 

[Fly_M20R]

7 hours ago, PT20J said:

I believe this is correct. As I understand it, a basic AHRS sensor has 3-axis accelerometers and 3-axis gyros. These are accurate for short periods but will drift over time and the amount of drift depends on the acceleration. So, they are better straight and level than maneuvering. Adding 3-axis magnetometers greatly improves accuracy with time and maneuvering. AHRS sensors are available with built-in magnetometers. I believe this is what Kelly uses in the RCA 2610 which does not need GPS or pitot/static inputs. If you have a magnetometer, GPS and pitot/static, you have a belt and suspenders approach and it should be very reliable. 

Garmin told me that the GTX 345 uses the same AHRS as other Garmin units. However, the GTX 345 has a GPS input but no pitot/static and no magnetometer inputs. My GTX 345 linked to Foreflight shows an accurate bank angle, but a 2 degree nose up in a level left turn and a 2 degree pitch down in a level right turn. If I turn off the GPS, it performs reasonably well in a left turn but pitches down 20 deg or so in a level right turn. 

Skip

 

Great insight!

Chris