I had this problem last year where the AHRS (SP-4) on my odyssey would randomly drop out. the problem seemed to go away all summer, but is now back that it's winter again. reading the documentation there is a heater in it and I'm now thinking that heater might be failing and maybe that's why it's not working? I live in Minnesota so winter flight temps are typically in the 0-30 degree Fahrenheit range.
I did move it behind the baggage wall in my RV-7 before last winter, which would be in colder air than when I had it behind the panel in the cockpit close to the cabin heater vent. Is it possible the heater is working and just being overpowered by the cold air? One reason I suspect this is sometimes it will come back on line during taxi after landing, my thinking is that the less airflow allows the heater to catch back up and get the temp back in range?
Anyway, is there any diagnostics I can do from the odyssey to see if it really is a temp issue? any downside to adding some sort of insulation over the AHRS and compass, I'm currently thinking about zip tying some microfiber towels around them.
Thanks,
Chris
AHRS(SP-4) heater failing?
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Re: AHRS(SP-4) heater failing?
Just a quick thought, do you have a hot air gun or any girls in your family have a small hand hair dryer or you can buy one those hot/cold packs you put in the fridge or in hot water.
With the aircraft on the ground and during a pretty cold day. I would try warming the SP-4 up to see if the unit starts to work.
If the SP-4 start to work, let it cool down until it stops working, do this a few time to make sure lack of heat is your answer.
Then knowing this is the problem for sure, if you like you could ask Rainer on this forum how hard would it be to have it fixed or replaced.
Cheers
JimJab
With the aircraft on the ground and during a pretty cold day. I would try warming the SP-4 up to see if the unit starts to work.
If the SP-4 start to work, let it cool down until it stops working, do this a few time to make sure lack of heat is your answer.
Then knowing this is the problem for sure, if you like you could ask Rainer on this forum how hard would it be to have it fixed or replaced.
Cheers
JimJab
Older MGL units
Re: AHRS(SP-4) heater failing?
There is a heater in the unit that kicks in if temps inside the unit are below about 10 degrees C. This is to reduce temperature related bias drift of the gyros into a narrower band. The bias is temperature compensated during manufacturing (we cool them down and then slowly raise them to a hot temperature recording what the bias does so a correction can be applied. Each of the three gyros has its own temperature measuring system directly on the chip.
Due to this the bias is pretty stable even at very low temps, even without the heater.
Failure of the heater will not stop the system from working at all - have a look at the little red LED on the SP-4. If that is flashing all is well. It should be flashing in a double flash. If it does that it means it is connected to an EFIS and is receiving data from the EFIS (mostly velocity information). If you see only a single flash at regular intervals then it means the SP-4 is working but there is no data received at all.
Check your airtalk cable and connections - I'm pretty sure there is something going on there. Metals have the habit of contracting when it gets cold - so this can cause a contact between two metal surfaces (such as a connector or bad solder joint) to separate.
Due to this the bias is pretty stable even at very low temps, even without the heater.
Failure of the heater will not stop the system from working at all - have a look at the little red LED on the SP-4. If that is flashing all is well. It should be flashing in a double flash. If it does that it means it is connected to an EFIS and is receiving data from the EFIS (mostly velocity information). If you see only a single flash at regular intervals then it means the SP-4 is working but there is no data received at all.
Check your airtalk cable and connections - I'm pretty sure there is something going on there. Metals have the habit of contracting when it gets cold - so this can cause a contact between two metal surfaces (such as a connector or bad solder joint) to separate.
Re: AHRS(SP-4) heater failing?
Thanks Rainer, when it drops out it has the red x on the Odyssey for horizon and slip; from what you said it sounds like the heater isn't my issue then. will go to work on double checking cabling and connections and checking the status light.