Adjusting an HSI compass

BigBadLou

BigBadLou

Final Approach
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Lou
Howdy, gents.
Since I just acquired a new (to me) airplane with a new panel, I will be posting some MX questions.

First one (I guess the most important one to me) pertains to the HSI. It is the S-TEC brand and it seems it was installed at the same time as the S-TEC S50 A/P.

The HSI is not aligned with the magnetic compass. On the ground or in flight. Since I have not flown the aircraft extensively (that is coming, believe me :) ) and I flew it only in gorgeous CAVU VMC, I do not have much to report but at least I know that the HSI shows more north on a westerly and also easterly heading. I am not sure whether I worded that correctly so here's what I noticed in plain numbers: flying west on hdg 280, the HSI indicated close to 300. Flying east on hdg 100, the HSI indicated approx. 090.

The S-TEC HSI comes with a control panel that allows for E-W and N-S corrections (via trimpots). However, I could not find (by Googling) any good document that discusses how to properly correct the HSI hdg using these trimpots. I understand this would be a job for an avionics guy but I'd like to have the adjustment procedure myself so that I can watch him do it and check his work. (yeah, I know, pretty bad case of CDO)

Does anybody have a good reference to the calibration procedure?

Thank you in advance for USEFUL replies and I will be posting more MX questions as they come. :)
 
Are you sure the compass isn't off?

On a compass rose my HSI is dead on, my compass and vertical card compass were not even close when mounted on the glareshield. I had my A&P relocate the compass to the top of the windscreen and all is well.
 
GlennAB1 said:
First thing, make sure you don'the have any ferrous hardware close to the Flux sensor. Like within 3 feet.
Click to expand...

This. I'd also add that - depending on where your flux gate is - you should check to see whether any of the wiring runs nearby. Especially flashing beacon wiring. Voice of experience.
 
Thank you for the useful replies, gentlemen.
And thank you for educating me on the name of the compass part. Didn't know it was called the "flux". Great.
I will have to go through all the new papers that hopefully contain information about the installation of the flux gate. I realize it cannot be anywhere near ferrous materials, I sure hope they installed it far away from those.
Fred, good question, very good question. Fortunately I am smart enough to have checked that already. :D We checked it with rwy alignment.
James, thank you, that is exactly the manual I found and downloaded. Useless for calibration. I will ask my mechanic whether he has one.
WSuffa, true, that would cause a problem. We already checked that, we turned off all electrical with no change.

And sorry for all the replies without quotes, I still have not figured out how to do a multi-quote in this new slow funky UI. :)
 
GlennAB1 said:
Note: They are commonly referred to as "Flux gate" or "Flux valve". They sense the earth's magnetic Flux lines.
Click to expand...

But not a flux capacitor. And it you get above 88 MPH no big flash and bang and time travel. ;-)

Good luck getting it sorted out.
 
This procedure is done by adjusting the pots on the slaving panel (as you mentioned) and someone outside the aircraft with a wet compass aligned to the center line of the aircraft. You will face North and adjust the N-S pot, then face E, adjust E-W pot, then South (N-S), lastly..West (E-W). Prior to any compass alignment, turn on your nav and beacon lights to ensure there isn't any interference. Something possibly threw off your alignment. Just want to check out all possibilities so it doesn't happen again.
 
Bricktop said:
This procedure is done by adjusting the pots on the slaving panel (as you mentioned) and someone outside the aircraft with a wet compass aligned to the center line of the aircraft. You will face North and adjust the N-S pot, then face E, adjust E-W pot, then South (N-S), lastly..West (E-W). Prior to any compass alignment, turn on your nav and beacon lights to ensure there isn't any interference. Something possibly threw off your alignment. Just want to check out all possibilities so it doesn't happen again.
Click to expand...
That will get you close, don't sign it off that way though. You need a compass rose.
 
We don't have a compass rose, we perform this procedure at request with ATC on a runway. Having a individual with a calibrated wet compass aligned with the centerline of the aircraft is highly accurate and acceptable for sign off. I was just giving the OP an idea of how this is accomplished. Of course seek qualified avionic technicians to perform the task.
 
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