Flux Compass 1981 K model

[placolla]

I have a 1981 M20K  with KFC 200 Silver package.  

 

My HSI started swing 30 degrees off from magnetic when slave to the remote flux compass.  This started after my annual.  It never had issues before.  A recent trip had the HSA alternately working on some legs and consistently off on the other legs by 30 degrees.

 

Any thoughts on what could be causing this?

 

Where is the flux compass in this make and model located in the plane?

 

 

[KSMooniac]

It is a KMT-112, and likely located in the left wing, but I can't remember inboard or outboard of the main gear.  You can open the inspection panels on the lower wing skin that aren't sealed (for the fuel tanks) and take a look.

[M20Kid]

I also have a 1981 M20K and I believe the compass for the HSI is located in the aft fuselage in the same compartment as the battery and autopilot servos.  I thought my HSI was indicating improperly on certain heading, but it turned out the wet compass in the cockpit was the culprit; the compass for the HSI was correct all along.  After my local avionics shop swung both compasses, they now read within a few degrees of each other on all headings.

 

As for intermittant causes, I wonder if a tool was left near the compass and it's shifting in flight.  Seems likely if it's intermittant right after an inspection.

[placolla]

Thanks Folks.  M20Kid- It would be interesting if it is in fact in the aft fuselage.  My ELT is not right after the inspection too, and I know that is located there.  I'm wondering if something possible is related to the two squawks.

[KSMooniac]

The KG102A Remote Gyro is in the tailcone on the avionics shelf, near the battery, autopilot computer (and pitch/trim servos), and other stuff.  The KMT 112 needs to be away from that stuff and it is in the left wing.  I just can't remember exactly where I found it when I cut up my '81 salvage.

[Guest]

I have a 1981 M20K  with KFC 200 Silver package.  

 

My HSI started swing 30 degrees off from magnetic when slave to the remote flux compass.  This started after my annual.  It never had issues before.  A recent trip had the HSA alternately working on some legs and consistently off on the other legs by 30 degrees.

 

Any thoughts on what could be causing this?

 

Where is the flux compass in this make and model located in the plane?

A hand full of new inspection cover screws magnetized with a screw driver may be the cause if its just after the annual.

Clarence

[Piloto]

It is likely located on the left wing in the mid wing skin section overlap, behind the main spar. The cover has screws instead of rivets. Unplug the connector and clean the contacts with contact cleaner. This may solve your problem.

 

José

[Aerodon]

Why assume its the KMT112 - could be your gyro and thats much easier to swap out with a loaner?  

 

Contact Bob at robert@aerolabaviation.com  to discussion you symptoms.  He has an overhauled KG102A of mine that we can trade?  I also have a KMT112 for you if thats the culprit.

 

 

Don

supercub180@gmail.com

[pinerunner]

A hand full of new inspection cover screws magnetized with a screw driver may be the cause if its just after the annual.

Clarence

This makes a lot of sense to me.  I used to do work on a very old magnetic sector mass spectrometer. The point being there was a special type of nonmagnetic stainless steel that had to be used for replacement parts or measurements would get screwed up. It makes sense to me that the inspection cover near the flux gate might require special screws that could easily swapped out by an unsuspecting mechanic doing the inspection and make trouble on certain headings. This looks like the type of problem that's easy to check if you know about it and also easy to overlook for a couple years of time and money while you check everything else.

[placolla]

Thanks all for the feedback!

[Jack Burson]

I had the same issue about a year ago - had to replace the flux box (located in the fuselage) - it's not cheap. Also, 1st replacement received was defective, the 2nd one fixed the problem...

[shamsbro]

I have a 1984 with similar problem. My HSI spins 180 degrees out (off heading) when in slaved mode. I replaced the KMT-112 (located in left wing, 3rd inspection plate out from gear door). The inspection plate was riveted (not screwed) which made swapping out the 112 a challenge. Alas, the problem is not fixed...

 

Any updates or advice as to what to do next?

[carusoam]

Welcome aboard Shams...

In the 90's they went with brass screws...equally non-magnetic with easy open pieces.

Made it a bit easier to clean all the connections.

Not sure if the O and the K got the same hardware, but that is the solution that worked on mine...

Best regards,

-a-

[jlunseth]

Its in the left wing. Servos for the AP are what you see in the aft compartment.

Is it possible your slaving indicator is switched to manual? Over on the far right of the panel, indicator with a small square button. If I recall correctly it has to be pushed in for the HSI to be slaved. I have never had any luck with it in manual mode, it acts weird like what you are describing.

[Alan Fox]

Generally speaking when a flux fails the reading is 60 degrees off in either direction...These do fail ....If the system works in the non slaved mode , it has to be in one of three components (assuming that the wiring is correct and in tact)  The Flux valve , the remote gyro , or the slaving accy....   The flux valve and slaving accy use the old style century barrel connectors , as Jose" stated you can try checking the connection on the flux , while you are there take a DVOM and check continuity on the flux itself.....There are 5 terminals , you should have continuity  between two pins (E and H ) , and the other three (A,B,D) ....  It is a very simple circuit and easy to check , also the gyro should supply 10 volts A/C voltage out to the flux for the stator (pins E and H ) .... I have all parts for this system , if needed...

[placolla]

I had discovered what was causing my problem.  The flux had not failed.  Instead it was picking up interference from my ELT which is located behind the rear seat.  When I corrected the ELT's issue the slaved compass worked properly.

[carusoam]

Thanks for the follow-up.

Best regards,

-a-