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Attitude Issues

Postby MidgetMustang » Tue Feb 11, 2014 11:28 am

Hello All,

I have a 1st generation Sport WS in a Midget Mustang. I've been struggling with the attitude indication since the aircraft's first flight in 2009. The attitude information seems reliable at times. Then, just as I start to feel that its working well, it will show some crazy indication while the plane is just cruising along straight and level. I have never noticed a problem when i'm maneuvering the plane, it only seems to be an issue in steady state.

I've aligned the magnetometer orientation with the EFIS very carefully and confirmed it countless times. I've also completed all of the magnetometer location interference exercises that GRT describes and the results are quite good. I updated the software several times, but it never had any impact.

I have received some technical support from GRT that was focused on the location of the magnetometer. It is located in the top of the fuselage (behind my head about 2 feet). I have been somewhat resistant to completely relocating it because I have so few options and the current location was carefully planned to comply with all the guidelines when the plane was being built. It's a small aircraft. The wings are only 7 feet long. Finding a spot that is clear of landing gear torque tubes, aileron control rods, counterweights and fuel looks to be very challenging. If I really thought relocating the magnetometer would solve the issue, I would.

My Midget is one of a matching pair. My dad's plane and mine are nearly identical. His magnetometer location is the same as mine and his attitude indication is rock solid. We have swapped our sport units and magnetometers. The problem stays with my airframe.

Has anyone had an attitude problem that was solved by doing something other than moving the magnetometer? I remember others struggling with similar issues on the old Yahoo forum, but I never noted any solutions.

Any thoughts?
Posts: 4
Joined: Tue Feb 11, 2014 10:25 am

Re: Attitude Issues

Postby JimB » Thu Feb 20, 2014 2:15 pm

We had problems with the mag heading changing in flight. Didn't happen often and we couldn't make it happen on command. Eventually we relocated the magnetometer and that solved the problem.

I think our problem was actually caused by radiation from the comm antenna. The new location is 10 - 12 feet from the antenna, the original location was about 6 feet. What makes trouble shooting difficult is that the EFIS will compensate to some extent and then it finally can't compensate (gets overwhelmed) and the error will show.

We did improve our situation to some extent prior to moving the magnetometer by shielding. We ran shielded wires to the magnetometer with the shield connected to the metal portion of the DB9 connector. We wrapped the magnetometer in aluminum foil with the foil also connected to the shield and metal portion of the DB9. And we tried a DB9 filter which you can purchase from DigiKey or the like. Look for one that is effective at frequencies around the comm band, 120 - 130 mHz. If you need more info let me know and I'll look up what we used.

Hope this helps - I know it's different than what you asked but no one else has responded!

PS we also found that having our ELT close to our comm antenna caused the comm radio to not squelch properly. Just a wild guess but try flying without the ELT installed if you have one.

Jim & Heather
Europa XS, Dual HS Sport
Posts: 76
Joined: Tue Mar 12, 2013 12:52 am

Re: Attitude Issues

Postby MidgetMustang » Sat Apr 12, 2014 11:33 am

Thanks Jim,

I'm jealous of your 10 foot clearance. The only way I could get anything 10 feet apart would be to mount them each in a wing tip.

Posts: 4
Joined: Tue Feb 11, 2014 10:25 am

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