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glastar(at)gmx.net
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 Posted: Thu Sep 18, 2014 6:30 am Post subject: Garmin AHRS drifting |
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Interesting read I've got today, seems to have an impact on Garmin
G1000, G1000H, G950, G900X, G500, G500H, G600 when after power up the
aircraft is moved the first 10 seconds.
Was not aware of this http://ad.easa.europa.eu/ad/SAFO14004
So does the G3X then have a different platform?
Cheers Werner
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peter(at)sportingaero.com
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| Posted: Thu Sep 18, 2014 11:00 am Post subject: Garmin AHRS drifting |
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> So does the G3X then have a different platform?
Yes, the G3X uses a GSU 73 or GSU 25 ADAHRS, not the GRS 77/77H that is the subject of the AD. However the G3X is not certified so cannot be the subject of an AD. It seems unlikely that the GSU 73 or 25 use fundamentally different algorithms than the GRS77, so will probably exhibit similar performance if abused.
Peter
On 18/09/2014 15:28, Werner Schneider wrote:
[quote]--> AeroElectric-List message posted by: Werner Schneider <glastar(at)gmx.net> (glastar(at)gmx.net)
Interesting read I've got today, seems to have an impact on Garmin G1000, G1000H, G950, G900X, G500, G500H, G600 when after power up the aircraft is moved the first 10 seconds.
Was not aware of this http://ad.easa.europa.eu/ad/SAFO14004
So does the G3X then have a different platform?
Cheers Werner
[b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Thu Sep 18, 2014 12:04 pm Post subject: Garmin AHRS drifting |
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At 13:59 2014-09-18, you wrote:
| Quote: | > So does the G3X then have a different platform?
Yes, the G3X uses a GSU 73 or GSU 25 ADAHRS, not the GRS 77/77H that
is the subject of the AD. However the G3X is not certified so cannot
be the subject of an AD. It seems unlikely that the GSU 73 or 25 use
fundamentally different algorithms than the GRS77, so will probably
exhibit similar performance if abused.
Peter
|
All modern AHRS systems have shed their 'iron' gyros
representing horizontal and heading references in favor
of rotational rate sensors.
When I was working the GP180 program at Lear wayyyy back when,
a supplier (I think it was King Radio) came in to pitch their
latest and greatest offering to the new airplane.
One of the presenters made kind of a show of opening a
briefcase-like container on the table and turning on
a switch. A light came on. He then proceeded to the next
phase of his presentation. After a time, the 'briefcase'
began to emit a 'ticking' sound . . . about one tick per
second. We were all looking at the thing with some concern
but the guy at the view graph projector seemed oblivious
to attention being paid to the ticking box on the table.
At some point he smiled and said, "Oh yeah, that briefcase
contains one of our new laser-ring gyros. It outputs a stream
of pulses proportional to rotation . . . that ticking you
hear is a measure of its present rotational speed."
"But sir . . . it's not moving!!"
"Ahhh . . . but it is . . . those ticks are marking rotation
of the earth."'
This was my first introduction into some of the engineering
and physics upon which the modern gyro-less systems are
based. Assuming that you can measure rotation rate or position
about any axis with precision, you can use that to replace
a spinning gyro assuming further that you KNOW from what orientation
from which you began making measurements. This means that from the
time you power up the system there will be an interval
of time for the software to stand up and say, "yeah . . .
I know where the horizon is and I've got a lock on present
yaw orientation in space . . . but until you give
me some GPS course data or some magnetometer data corrected
for deviation, I'm not going to know what our heading
orientation is . . . "
That laser ring gyro took several minutes to stand up.
It was a positional sensor with drift that was essentially
zero. Modern MEMS sensors are rate sensors. You have to
integrate rate over time to deduce the difference in
angle. Drifts and offsets are low but not zero. Hence
the necessity to stand still while the byte thrashers
decide when they're ready to go flying . . . or even
taxiing. They'll first wash out offset by assuming that
you're standing still. Once you move, data coming from
other sources will wash out calibration issues . . . and
it always takes some amount of time. 10 seconds is pretty
quick and I'm having a little trouble putting my arms around
the impatience for getting under way or perhaps already
being under way when the system gets powered up.
One more example of a check-list forsaken . . .
Bob . . .
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peter(at)sportingaero.com
Guest
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| Posted: Thu Sep 18, 2014 12:57 pm Post subject: Garmin AHRS drifting |
|
|
The first aircraft I worked on had a 'iron' gyro platform that had to be
spun up to speed and then 'torqued' until the gyro axes were
perpendicular to the earth by aligning the vertical axis with gravity. A
good align, taking at least 5 minutes (something longer) resulted in a
gyro drift of 1nm per hour ... and it cost tens of thousands of $$$! The
equipment available today is remarkable - no discernible drift after a
10 second align, amazing! I'm using an AFS EFIS that takes around a
minute to align - I though that was rather good.
Peter
On 18/09/2014 21:02, Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 13:59 2014-09-18, you wrote:
> > So does the G3X then have a different platform?
>
> Yes, the G3X uses a GSU 73 or GSU 25 ADAHRS, not the GRS 77/77H that
> is the subject of the AD. However the G3X is not certified so cannot
> be the subject of an AD. It seems unlikely that the GSU 73 or 25 use
> fundamentally different algorithms than the GRS77, so will probably
> exhibit similar performance if abused.
>
> Peter
All modern AHRS systems have shed their 'iron' gyros
representing horizontal and heading references in favor
of rotational rate sensors.
When I was working the GP180 program at Lear wayyyy back when,
a supplier (I think it was King Radio) came in to pitch their
latest and greatest offering to the new airplane.
One of the presenters made kind of a show of opening a
briefcase-like container on the table and turning on
a switch. A light came on. He then proceeded to the next
phase of his presentation. After a time, the 'briefcase'
began to emit a 'ticking' sound . . . about one tick per
second. We were all looking at the thing with some concern
but the guy at the view graph projector seemed oblivious
to attention being paid to the ticking box on the table.
At some point he smiled and said, "Oh yeah, that briefcase
contains one of our new laser-ring gyros. It outputs a stream
of pulses proportional to rotation . . . that ticking you
hear is a measure of its present rotational speed."
"But sir . . . it's not moving!!"
"Ahhh . . . but it is . . . those ticks are marking rotation
of the earth."'
This was my first introduction into some of the engineering
and physics upon which the modern gyro-less systems are
based. Assuming that you can measure rotation rate or position
about any axis with precision, you can use that to replace
a spinning gyro assuming further that you KNOW from what orientation
from which you began making measurements. This means that from the
time you power up the system there will be an interval
of time for the software to stand up and say, "yeah . . .
I know where the horizon is and I've got a lock on present
yaw orientation in space . . . but until you give
me some GPS course data or some magnetometer data corrected
for deviation, I'm not going to know what our heading
orientation is . . . "
That laser ring gyro took several minutes to stand up.
It was a positional sensor with drift that was essentially
zero. Modern MEMS sensors are rate sensors. You have to
integrate rate over time to deduce the difference in
angle. Drifts and offsets are low but not zero. Hence
the necessity to stand still while the byte thrashers
decide when they're ready to go flying . . . or even
taxiing. They'll first wash out offset by assuming that
you're standing still. Once you move, data coming from
other sources will wash out calibration issues . . . and
it always takes some amount of time. 10 seconds is pretty
quick and I'm having a little trouble putting my arms around
the impatience for getting under way or perhaps already
being under way when the system gets powered up.
One more example of a check-list forsaken . . .
Bob . . .
|
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jluckey(at)pacbell.net
Guest
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| Posted: Thu Sep 18, 2014 1:33 pm Post subject: Garmin AHRS drifting |
|
|
So how does a modern AHRS re-initialize after an airborne re-boot? (perhaps due to some electrical failure)
Magnetometer?
-Jeff
On Thursday, September 18, 2014 2:09 PM, Peter Pengilly <peter(at)sportingaero.com> wrote:
--> AeroElectric-List message posted by: Peter Pengilly <peter(at)sportingaero.com (peter(at)sportingaero.com)>
The first aircraft I worked on had a 'iron' gyro platform that had to be
spun up to speed and then 'torqued' until the gyro axes were
perpendicular to the earth by aligning the vertical axis with gravity. A
good align, taking at least 5 minutes (something longer) resulted in a
gyro drift of 1nm per hour ... and it cost tens of thousands of $$$! The
equipment available today is remarkable - no discernible drift after a
10 second align, amazing! I'm using an AFS EFIS that takes around a
minute to align - I though that was rather good.
Peter
On 18/09/2014 21:02, Robert L. Nuckolls, III wrote:
| Quote: | --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 13:59 2014-09-18, you wrote:
> > So does the G3X then have a different platform?
>
> Yes, the G3X uses a GSU 73 or GSU 25 ADAHRS, not the GRS 77/77H that
> is the subject of the AD. However the G3X is not certified so cannot
> be the subject of an AD. It seems unlikely that the GSU 73 or 25 use
> fundamentally different algorithms than the GRS77, so will probably
> exhibit similar performance if abused.
>
> Peter
All modern AHRS systems have shed their 'iron' gyros
representing horizontal and heading references in favor
of rotational rate sensors.
When I was working the GP180 program at Lear wayyyy back when,
a supplier (I think it was King Radio) came in to pitch their
latest and greatest offering to the new airplane.
One of the presenters made kind of a show of opening a
briefcase-like container on the table and turning on
a switch. A light came on. He then proceeded to the next
phase of his presentation. After a time, the 'briefcase'
began to emit a 'ticking' sound . . . about one tick per
second. We were all looking at the thing with some concern
but the guy at the view graph projector seemed oblivious
to attention being paid to the ticking box on the table.
At some point he smiled and said, "Oh yeah, that briefcase
contains one of our new laser-ring gyros. It outputs a stream
of pulses proportional to rotation . . . that ticking you
hear is a measure of its present rotational speed."
"But sir . . . it's not moving!!"
"Ahhh . . . but it is . . . those ticks are marking rotation
of the earth."'
This was my first introduction into some of the engineering
and physics upon which the modern gyro-less systems are
based. Assuming that you can measure rotation rate or position
about any axis with precision, you can use that to replace
a spinning gyro assuming further that you KNOW from what orientation
from which you began making measurements. This means that from the
time you power up the system there will be an interval
of time for the software to stand up and say, "yeah . . .
I know where the horizon is and I've got a lock on present
yaw orientation in space . . . but until you give
me some GPS course data or some magnetometer data corrected
for deviation, I'm not going to know what our heading
orientation is . . . "
That laser ring gyro took several minutes to stand up.
It was a positional sensor with drift that was essentially
zero. Modern MEMS sensors are rate sensors. You have to
integrate rate over time to deduce the difference in
angle. Drifts and offsets are low but not zero. Hence
the necessity to stand still while the byte thrashers
decide when they're ready to go flying . . . or even
taxiing. They'll first wash out offset by assuming that
you're standing still. Once you move, data coming from
other sources will wash out calibration issues . . . and
it always takes some amount of time. 10
|
[quote][b]
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Kellym
Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ
|
| Posted: Thu Sep 18, 2014 1:43 pm Post subject: Garmin AHRS drifting |
|
|
Just to clarify a misconception....ADs most certainly can be issued on
non-certificated equipment. Not common, and up to aircraft
owner/operator to determine if it applies to their situation. Part 39
applies to ALL aircraft, not just type certificated aircraft. While it
is rare to issue one on an experimental airframe, the FAA does have the
authority, and often issues ADs on components used on both certificated
and experimental aircraft.
No different than if you have a Lycoming O-360-A1A engine on your
Puffmaster 1000, and an AD is issued on that engine. No different than a
King KX-170B...it was non-TSO, only met FCC requirements, not any
particular FAA standard, but it certainly could have an AD issued for
whatever. You can ignore the AD if you choose, but if you have an
accident where someone/something gets injured, do you want to be sitting
at the plaintiff's deposition explaining why you ignored the AD?
On 9/18/2014 1:02 PM, Robert L. Nuckolls, III wrote:
| Quote: |
<nuckolls.bob(at)aeroelectric.com>
At 13:59 2014-09-18, you wrote:
> > So does the G3X then have a different platform?
>
> Yes, the G3X uses a GSU 73 or GSU 25 ADAHRS, not the GRS 77/77H that
> is the subject of the AD. However the G3X is not certified so cannot
> be the subject of an AD. It seems unlikely that the GSU 73 or 25 use
> fundamentally different algorithms than the GRS77, so will probably
> exhibit similar performance if abused.
>
|
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http://www.matronics.com/Navigator?AeroElectric-List |
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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD |
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peter(at)sportingaero.com
Guest
|
| Posted: Thu Sep 18, 2014 2:04 pm Post subject: Garmin AHRS drifting |
|
|
Yes, there have always been airborne re-alignment techniques. Once the platform has toppled a rough alignment can be done quickly (a few seconds as the pilot will be needing some information soonest) using combinations of (hopefully) reliable data, such as gravity, mag heading, GPS, airspeed (with OAT input), a stored position/velocity from a state model. Some of these are more reliable than others, hence the need for the pilot to fly level and unaccelerated for a while where possible, and also depends on the sophistication of the software algorithms (perhaps $$$ behind the developer).
I have never seen inside these algorithms, but I would hope they would compare the available data. Such as if heading is changing don't believe gravity, how does heading compare with GPS track (hopefully constant offset), how does GPS speed compare to airspeed/TAS (again constant offset?), and so on, to figure out what can be believed, and so get the best available alignment. Its never going to be quite as accurate as a ground align, but should be sufficient to get you on the ground without too much additional workload.
On 18/09/2014 22:32, Jeff Luckey wrote:
[quote] So how does a modern AHRS re-initialize after an airborne re-boot? (perhaps due to some electrical failure)
Magnetometer?
-Jeff
On Thursday, September 18, 2014 2:09 PM, Peter Pengilly <peter(at)sportingaero.com> (peter(at)sportingaero.com) wrote:
--> AeroElectric-List message posted by: Peter Pengilly <peter(at)sportingaero.com (peter(at)sportingaero.com)>
The first aircraft I worked on had a 'iron' gyro platform that had to be
spun up to speed and then 'torqued' until the gyro axes were
perpendicular to the earth by aligning the vertical axis with gravity. A
good align, taking at least 5 minutes (something longer) resulted in a
gyro drift of 1nm per hour ... and it cost tens of thousands of $$$! The
equipment available today is remarkable - no discernible drift after a
10 second align, amazing! I'm using an AFS EFIS that takes around a
minute to align - I though that was rather good.
Peter
On 18/09/2014 21:02, Robert L. Nuckolls, III wrote:
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
>
> At 13:59 2014-09-18, you wrote:
>> > So does the G3X then have a different platform?
>>
>> Yes, the G3X uses a GSU 73 or GSU 25 ADAHRS, not the GRS 77/77H that
>> is the subject of the AD. However the G3X is not certified so cannot
>> be the subject of an AD. It seems unlikely that the GSU 73 or 25 use
>> fundamentally different algorithms than the GRS77, so will probably
>> exhibit similar performance if abused.
>>
>> Peter
>
> All modern AHRS systems have shed their 'iron' gyros
> representing horizontal and heading references in favor
> of rotational rate sensors.
>
> When I was working the GP180 program at Lear wayyyy back when,
> a supplier (I think it was King Radio) came in to pitch their
> latest and greatest offering to the new airplane.
>
> One of the presenters made kind of a show of opening a
> briefcase-like container on the table and turning on
> a switch. A light came on. He then proceeded to the next
> phase of his presentation. After a time, the 'briefcase'
> began to emit a 'ticking' sound . . . about one tick per
> second. We were all looking at the thing with some concern
> but the guy at the view graph projector seemed oblivious
> to attention being paid to the ticking box on the table.
>
> At some point he smiled and said, "Oh yeah, that briefcase
> contains one of our new laser-ring gyros. It outputs a stream
> of pulses proportional to rotation . . . that ticking you
> hear is a measure of its present rotational speed."
>
> "But sir . . . it's not moving!!"
>
> "Ahhh . . . but it is . . . those ticks are marking rotation
> of the earth."'
>
> This was my first introduction into some of the engineering
> and physics upon which the modern gyro-less systems are
> based. Assuming that you can measure rotation rate or position
> about any axis with precision, you can use that to replace
> a spinning gyro assuming further that you KNOW from what orientation
> from which you began making measurements. This means that from the
> time you power up the system there will be an interval
> of time for the software to stand up and say, "yeah . . .
> I know where the horizon is and I've got a lock on present
> yaw orientation in space . . . but until you give
> me some GPS course data or some magnetometer data corrected
> for deviation, I'm not going to know what our heading
> orientation is . . . "
>
> That laser ring gyro took several minutes to stand up.
> It was a positional sensor with drift that was essentially
> zero. Modern MEMS sensors are rate sensors. You have to
> integrate rate over time to deduce the difference in
> angle. Drifts and offsets are low but not zero. Hence
> the necessity to stand still while the byte thrashers
> decide when they're ready to go flying . . . or even
> taxiing. They'll first wash out offset by assuming that
> you're standing still. Once you move, data coming from
> other sources will wash out calibration issues . . . and
> it always takes some amount of time. 10
[b]
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peter(at)sportingaero.com
Guest
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| Posted: Thu Sep 18, 2014 2:11 pm Post subject: Garmin AHRS drifting |
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|
The situation in the US may be different to other countries. As I
understand it the CofA of an aircraft will not be valid if an AD is not
complied with. In the UK amateur built aircraft don't have a CofA, they
have a permit to fly. Therefore the CAA has to raise a Mandatory Permit
Directive to make ADs effective on permit aircraft.
On 18/09/2014 22:42, Kelly McMullen wrote:
| Quote: |
<kellym(at)aviating.com>
Just to clarify a misconception....ADs most certainly can be issued on
non-certificated equipment. Not common, and up to aircraft
owner/operator to determine if it applies to their situation. Part 39
applies to ALL aircraft, not just type certificated aircraft. While it
is rare to issue one on an experimental airframe, the FAA does have
the authority, and often issues ADs on components used on both
certificated and experimental aircraft.
No different than if you have a Lycoming O-360-A1A engine on your
Puffmaster 1000, and an AD is issued on that engine. No different than
a King KX-170B...it was non-TSO, only met FCC requirements, not any
particular FAA standard, but it certainly could have an AD issued for
whatever. You can ignore the AD if you choose, but if you have an
accident where someone/something gets injured, do you want to be
sitting at the plaintiff's deposition explaining why you ignored the AD?
On 9/18/2014 1:02 PM, Robert L. Nuckolls, III wrote:
>
> <nuckolls.bob(at)aeroelectric.com>
>
> At 13:59 2014-09-18, you wrote:
>> > So does the G3X then have a different platform?
>>
>> Yes, the G3X uses a GSU 73 or GSU 25 ADAHRS, not the GRS 77/77H that
>> is the subject of the AD. However the G3X is not certified so cannot
>> be the subject of an AD. It seems unlikely that the GSU 73 or 25 use
>> fundamentally different algorithms than the GRS77, so will probably
>> exhibit similar performance if abused.
>>
|
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mmayfield
Joined: 09 Oct 2009
Posts: 40
Location: NSW Central Coast, Australia
|
| Posted: Thu Sep 18, 2014 2:28 pm Post subject: Re: Garmin AHRS drifting |
|
|
Totally concur with the comment about ADs. An Airworthiness Directive can be issued on pretty much anything pertaining to safety of flight, whether it's "certified" equipment or not. That's certainly the case in my country at least.
Owner/builders of experimental aircraft are of course responsible for their own maintenance. But if you don't bother keeping up to date with ADs or decline to carry out an AD on an item in your plane, you could well be hung out to dry legally if anything goes wrong with that piece of equipment. Plus there's the obvious point that it simply makes good safety sense to just do it. It never ceases to amaze me that there are people out there who maintain the line that "I don't legally have to" when it comes to flight safety issues.
On the topic of IRS/AHRS alignment, 10 seconds is nothing! We used to have to wait at least 15 minutes for IRS alignment before even starting our engines on some early systems when I was in the military. Anyone complaining about having to be stationary without the engine running for a 10 second or even a 60 second alignment gets no sympathy from me! 
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