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brettt777

Member
Hi. I am new to this forum. I am the avionics tech here at International Jets in Gadsden Alabama. We service and maintain about 70 L-39s in the US, Canada and Austrailia. We have started doing other types of A/C in the last year as well, but the Albatros is still our main stay right now. Anyway, more and more of our customers are getting into the "glass" cockpit thing. The problem is, some of the popular existing systems use AHRS units that won't stand up to the abuse an L-39 can give out (+8/-4 Gs, 200 degrees/second roll rate). While not all of our customers push the aircraft to these limits, there are some that do. In the past, when the only real option for a good EFIS was the Chelton system, they used aftermarket AHRS units; first the Crossbow which wasn't adequate at all, the the Pinpoint GADAHRS which is quite expensive but pretty much bulletproof. Since Chelton systems worked with an aftermarket AHRS unit, I am wondering if a Garmin or Avidyne EFIS would use something else besides the factory unit. What little info I have been able to get out of Garmin tells me that the G600 AHRS will handle the 200 degree/second roll rate but the data rate from the AHRS to the EFIS itself will only go up to 128 degrees/second which is totaly inadequate for the L-39. I also have a source that tells me that the new G3X system will use the same AHRS as the G600. I have several customers right now that would be interested in one of these Garmin systems if it had an adequate AHRS. So, I am wondering if I could install one of these Garmin systems with say, a pinpoint GADAHRS unit.
 
I can't tell you much about the Garmin unit, but the specs you quote are close to those of the GRT AHRS. If you're really searching for options, give Greg a call - he'll honestly tell you if it might work or not.

Paul
 
brettt777 said:
.... So, I am wondering if I could install one of these Garmin systems with say, a pinpoint GADAHRS unit.
Click to expand...

If I understand you correctly, you want to install a Garmin G3X but with a Pinpoint GADAHRS--Why in the world would you want to do that?

Garmin seems to be centering most of their certified EFIS around the GRS 77 (AHRS). This AHRS is used in the G500, G600, G900X & G1000. I do not believe the G3X uses the GRS 77. The G3X was designed primarily for Light Sport and Experimentals and the AHRS is probably not up to the challenge of an L-39.

I have no doubt that the GRS 77 could handle the performance of the L-39. Choosing however to replace a GRS 77 in favor of an uncertified Pinpoint GADAHRS is the part that doesn?t make sense to me.

A G500 using the GRS 77 seems to represent better value for the L-39. With the limited panel space of the L-39, even an Aspen EFD-1000 would make more sense than a than a "cobbled together" G3X/Pinpoint system.
 
w1curtis said:
I have no doubt that the GRS 77 could handle the performance of the L-39. Choosing however to replace a GRS 77 in favor of an uncertified Pinpoint GADAHRS is the part that doesn?t make sense to me.

A G500 using the GRS 77 seems to represent better value for the L-39. With the limited panel space of the L-39, even an Aspen EFD-1000 would make more sense than a than a "cobbled together" G3X/Pinpoint system.
Click to expand...

I have a good source that tells me that the GRS-77 will NOT handle the L-39s performance and that the G3X system will use the same unit.
I also know the Aspen EFIS WILL handle the L-39. I have seen them installed in Extra 300s and the like with no problems whatsoever.
I would hardly call a G3X/Pinpoint combination a "cobbled together" system. The Pinpoint is what Cheltons have been using quite successfully, even in the L-39. I would just like to know if the Pinpoint will adapt to a Garmin or other brand the same way it works with the Cheltons. I don't even know for sure if anyone would want such a system as the Pinpoints are quite expensive but I would like to know if it is an option.
 
Ironflight said:
I can't tell you much about the Garmin unit, but the specs you quote are close to those of the GRT AHRS. If you're really searching for options, give Greg a call - he'll honestly tell you if it might work or not.

Paul
Click to expand...

Actualy I have a customer that wants to replace his Blue Mountain systems with something else in one of his L-39s, maybe both. He spoke with a GRT rep at Oshkosh. They told him straight up that the GRT AHRS would handle those specs. So that might be an option as well, and most likely considerably less expensive than the Pinpoint. I believe I will give Greg a call tomorrow.
 
Have a look at MGL's

Hi Brett,

Welcome to these forums.
I think you should talk to Rainier Lamers from MGL Avionics. He often posts to this forum.
In the mean time, you might be interested by this document that gives the specs of their SP-5 AHRS that I think is the most adequate to your application.
Hope this helps
 
FlyingArcher said:
Hi Brett,

Welcome to these forums.
I think you should talk to Rainier Lamers from MGL Avionics. He often posts to this forum.
In the mean time, you might be interested by this document that gives the specs of their SP-5 AHRS that I think is the most adequate to your application.
Hope this helps
Click to expand...

Yes I would tend to agree, the SP-5 is the most affordable solution, yet it uses the same British Aerospace designed gyros that are used in medium range certified applications (like the Crossbow AHRS-500 for example). These gyros are pretty decent and adequate for most applications, even more demanding ones. We combined them with the algorithms used in our SP-4 which uses low cost gyros and thus needs a lot more trickery to perform (took us many years to get to this stage). Combining this with a good gyro makes the good gyro even better.
The system is rated for 200 degees/second around each axis and can measure G-force in the Z axis up to 18G and 6G in the other two axis (sideways and backwards/forwards acceleration) - more than adequate for any possible application.
The communications protocol for this is in the public domain so it can be used for any 3rd party application.

Rainier
CEO MGL Avionics
 
I know a couple of things about Garmin products, but I haven't finished my coffee yet this morning so I still have my RV builder's hat on. :) So without recommending or endorsing any particular product or manufacturer, let me clarify a few points:

1. The G500/G600 system uses the certified GRS 77 AHRS. The GSU 73 sensor unit used in G3X system contains a different, non-certified AHRS that is quite similar in design to the certified GRS 77. Neither system is capable of being used with a different AHRS other than the one that it was designed to work with.

2. Both the GRS 77 and GSU 73 AHRS have a max roll rate specification of 200 deg/sec. The 128 deg/sec limitation mentioned above is actually an ARINC 429 limitation, and applies only to the GRS 77. The G3X system does not use ARINC 429 to send AHRS data to the displays, and does not have this limitation - so whoever said this is the case was probably thinking of something else.

3. High-performance jets and aerobatic aircraft can be challenging for any attitude instrument, whether electronic or mechanical. Regardless of who makes it, it's possible that an EFIS (or iron gyro) designed to exceed the requirements of the vast majority of general aviation and sport flying applications might not have such high performance margins when used in something like a Pitts or L-39. A careful analysis of equipment specifications, including but not limited to such things as ability to realign in flight, is certainly called for.

good luck,
mcb
 
mburch said:
1. The G500/G600 system uses the certified GRS 77 AHRS. The GSU 73 sensor unit used in G3X system contains a different, non-certified AHRS that is quite similar in design to the certified GRS 77. Neither system is capable of being used with a different AHRS other than the one that it was designed to work with.

2. Both the GRS 77 and GSU 73 AHRS have a max roll rate specification of 200 deg/sec. The 128 deg/sec limitation mentioned above is actually an ARINC 429 limitation, and applies only to the GRS 77. The G3X system does not use ARINC 429 to send AHRS data to the displays, and does not have this limitation - so whoever said this is the case was probably thinking of something else.
Click to expand...

So you are saying that the Garmin systems will use only the specified Garmin AHRS, correct? That is one question answered and I thank you for that.

You are also saying that the data limitations on the GRS 77 is because of the ARINC 429 data transfer and not an issue with the AHRS itself? I was told, not necessarily on good authority, that the G3X system used the same AHRS but you are sure that it doesn't, correct? And since the AHRS that it does use doesn't use ARINC 429 for data transfer, the 128 degrees/second would not be a factor. This clarifies alot for me, thank you.
 
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