grid heading
- Thread starter mhmenon
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Not sure to be perfectly honest. Our EFIS systems only deal with magnetic heading. If I had reason to fly up there though, I'd probably be have a few GPS systems in my bag 
Canadian_JOY
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OK, I'll take a shot at this since I've had to fly 'grid' more than I'd like to admit...
Picture this... Here you are, sitting on the runway in the far north in Nunavut, east of the magnetic north pole. Let's assume you want to fly back home to the sunny south. While you've got your airplane pointed down the centreline of Runway 18, your compass is telling you that North is off your right wingtip. Obviously this isn't of much help, especially when you know that as you continue to fly southward that same compass will say that North is fairly quickly moving toward the tail of your airplane. That is, when it's not pointing toward the local iron ore deposit which may be off the nose, under you, or behind you! In this region a magnetic compass is, well, not too reliable.
Enter GRID mode! While sitting on Runway 18 you align your compass to a heading of 180 and select grid mode. This effectively is telling your compass system to act more like a precision DG than a magnetic compass. Now as you fly all compass movement will be relative to that initial 180 heading that you selected. And you'll actually be able to fly along in a straight line, rather than in the arcing route that would result from following a magnetic compass.
This mode of operation is something I'd really like to see offered in the Dynon EFIS product. Firstly, it would help in areas of compass unreliability. Secondly, it could be used as a "DG Mode" in the event the EDC fails while you're away from home base. It would at least give you heading information sufficient to limp home. Given the number of "EDC Not Found" complaints on this message forum it sounds to me like this second reason would be the better one to use in justifying the business case.
Dear Dynon - any chances of making this happen?
Mark
(Davis DA-2A C-GJOY)
Picture this... Here you are, sitting on the runway in the far north in Nunavut, east of the magnetic north pole. Let's assume you want to fly back home to the sunny south. While you've got your airplane pointed down the centreline of Runway 18, your compass is telling you that North is off your right wingtip. Obviously this isn't of much help, especially when you know that as you continue to fly southward that same compass will say that North is fairly quickly moving toward the tail of your airplane. That is, when it's not pointing toward the local iron ore deposit which may be off the nose, under you, or behind you! In this region a magnetic compass is, well, not too reliable.
Enter GRID mode! While sitting on Runway 18 you align your compass to a heading of 180 and select grid mode. This effectively is telling your compass system to act more like a precision DG than a magnetic compass. Now as you fly all compass movement will be relative to that initial 180 heading that you selected. And you'll actually be able to fly along in a straight line, rather than in the arcing route that would result from following a magnetic compass.
This mode of operation is something I'd really like to see offered in the Dynon EFIS product. Firstly, it would help in areas of compass unreliability. Secondly, it could be used as a "DG Mode" in the event the EDC fails while you're away from home base. It would at least give you heading information sufficient to limp home. Given the number of "EDC Not Found" complaints on this message forum it sounds to me like this second reason would be the better one to use in justifying the business case.
Dear Dynon - any chances of making this happen?
Mark
(Davis DA-2A C-GJOY)
- Joined
- Mar 23, 2005
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- 13,226
Honestly? No chance we'll do it.
You need a DG with almost zero drift to make this work, and EFIS systems like ours don't have zero drift. You need $10,000+ sensors to do that. We use the compass sensor to help us cancel out the drift, so we can't do heading without it. The miracle of modern, inexpensive EFIS systems is using other sensors and calculations to fix the issues with inexpensive gyros. Even the $20,000+ certifed ADAHRS units do this.
From what I hear even really good, expensive DG's in military airplanes still cause them to be off by a few miles per hour if they navigate only by the DG, so this is still an issue.
We have the EDC not found problem fixed with our latest firmware, so this isn't really a problem anymore. They fail for real very, very rarely.
Doesn't everyone just type in their destination in the GPS nowadays?
You need a DG with almost zero drift to make this work, and EFIS systems like ours don't have zero drift. You need $10,000+ sensors to do that. We use the compass sensor to help us cancel out the drift, so we can't do heading without it. The miracle of modern, inexpensive EFIS systems is using other sensors and calculations to fix the issues with inexpensive gyros. Even the $20,000+ certifed ADAHRS units do this.
From what I hear even really good, expensive DG's in military airplanes still cause them to be off by a few miles per hour if they navigate only by the DG, so this is still an issue.
We have the EDC not found problem fixed with our latest firmware, so this isn't really a problem anymore. They fail for real very, very rarely.
Doesn't everyone just type in their destination in the GPS nowadays?
Canadian_JOY
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Dear Dynon Support,
Bingo, you've hit the nail on the head! You've stated that you need a DG with almost zero drift to make this work. The reality is that virtually all light aircraft currently operating within the region of compass unreliability are currently using their cheapo panel-mounted DG, be it electric or vacuum operated. Pilots set the DG to runway heading, then fly off into the wild blue yonder based on the heading reference provided by their trusty DG. And as for GPS, well, I've had more GPS receivers fail than any human should, so I want something to act as a backup. A grid-reference DG is a great way to provide this safety net.
Gyros precess - that's a given. Even the expensive ones precess. The 'gold standard' C-12 compass system used in military and commercial aircraft likewise drift. This is a given, a known. Anybody who flies grid has to make an attempt to calibrate the drift rate and use that drift rate to manually correct the indicated heading. Believe me, I've done this more times than I care to admit. Fly the airplane down south where magnetic compass can be somewhat relied upon, and set 'grid', then fly for an hour, and re-select "magnetic". This allows one to see how many degrees the gyro has drifted within a specific time. In this manner we can calibrate the precession out of our navigation equation.
Now over to Dynon. How much does the solid state heading gyro precess in terms of degrees per hour, worst case? If it's not absolutely horrible (ie less than 15 degrees per hour), there's no reason why a grid reference function shouldn't be offered. Clear wording of the pilot's guide would have to be used to ensure people understand how to use it, as has always been the case. And a clear indication of 'grid mode' on the EFIS would be required. Might I suggest placing the word "GRID" beside the heading reading?
In all honesty, this is a function which is fairly easy to implement. I find it difficult to believe that Dynon, who's concentration seems to be on packing huge functionality into small packages, hasn't already implemented a DG function.
(Just as an aside. For those of us who do wander around in the north it's an incredibly good feeling to have a backup system. GPS is a godsent device for polar navigators, but those receivers do fail. In that featureless terrain where maps are of no use whatsover, having a DG to guide you back home is very comforting, because it's no fun spending a night out on the tundra!)
Thanks for your consideration!
Mark.
Bingo, you've hit the nail on the head! You've stated that you need a DG with almost zero drift to make this work. The reality is that virtually all light aircraft currently operating within the region of compass unreliability are currently using their cheapo panel-mounted DG, be it electric or vacuum operated. Pilots set the DG to runway heading, then fly off into the wild blue yonder based on the heading reference provided by their trusty DG. And as for GPS, well, I've had more GPS receivers fail than any human should, so I want something to act as a backup. A grid-reference DG is a great way to provide this safety net.
Gyros precess - that's a given. Even the expensive ones precess. The 'gold standard' C-12 compass system used in military and commercial aircraft likewise drift. This is a given, a known. Anybody who flies grid has to make an attempt to calibrate the drift rate and use that drift rate to manually correct the indicated heading. Believe me, I've done this more times than I care to admit. Fly the airplane down south where magnetic compass can be somewhat relied upon, and set 'grid', then fly for an hour, and re-select "magnetic". This allows one to see how many degrees the gyro has drifted within a specific time. In this manner we can calibrate the precession out of our navigation equation.
Now over to Dynon. How much does the solid state heading gyro precess in terms of degrees per hour, worst case? If it's not absolutely horrible (ie less than 15 degrees per hour), there's no reason why a grid reference function shouldn't be offered. Clear wording of the pilot's guide would have to be used to ensure people understand how to use it, as has always been the case. And a clear indication of 'grid mode' on the EFIS would be required. Might I suggest placing the word "GRID" beside the heading reading?
In all honesty, this is a function which is fairly easy to implement. I find it difficult to believe that Dynon, who's concentration seems to be on packing huge functionality into small packages, hasn't already implemented a DG function.
(Just as an aside. For those of us who do wander around in the north it's an incredibly good feeling to have a backup system. GPS is a godsent device for polar navigators, but those receivers do fail. In that featureless terrain where maps are of no use whatsover, having a DG to guide you back home is very comforting, because it's no fun spending a night out on the tundra!)
Thanks for your consideration!
Mark.
balajimc
Smooth sea never makes a skillfull sailor
Hi, What is "DG" here?
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- Mar 23, 2005
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"Directional Gyro"