MGL Avionics User Forum

Looking for advice, suggestions....
1. My MX1 VSI reads about double the actual. At actual 0 fpm the MX1 reads close. At, say 750 fpm, the MX1 reads 1500 fpm. The manual says on page 54 that the VSI calibration factor does not normally need to be changed. Should I try adjusting it? Or is there something else to look at. My ASV1 VSI seems to be correct.
2. My MX1 and ASV1 altitudes read almost identical, but both are off about 250 feet low from actual. I seem to be able to adjust the cal factor on the MX1, but changing the altitude cal factor on the ASV1 results in an airspeed indication of about 60 mph when the airplane is not moving.

Any suggestions on what to look at?
Thank you,
Peter

I have the same problem. I'm just guessing at my numbers, but they are 1000 ft-ish off. On climb out, I see 1400-1500, and on final I see -1400 or -1500 fpm.

I haven't tried adjusting anything yet for fear of making it worse. Also, my static port is just vented inside the cabin... unsure if it matters, but I assume I'd just have steady wrong reading rather than such a wild swing.

Edit: I'd also like to add that my DA reading swings +/- 1000 feet even when sitting on the ground? Do you have this problem?

yes I see that as well...DA all over the place. I'm also seeing issues withe the slip indicator. It dances when the airplane isn't even moving. The compass is not reliable and can be 100 degrees or more off. As things stand now I use the MX1 for engine monitoring and the ASV1 for airspeed, altitude and VSI. I put the ASV1 in the Sonex B for backup...so glad I did.

Peter

Sounds like whatever the issue is, we have the same one.

My slip indicator is totally unreliable. The compass was also pretty crazy, but I relocated it to a better position and re-did the in-flight calibration procedure and that helped... but I am planning on doing another procedure to see if I can raise the fit % at all.

The only "steady" readings I get are the CHT's. I suspect it's a grounding issue, so today I rearranged some stuff and I have 0.2 ohm resistance between the bus and the engine block, and a separate .2 ohm resistance ground from the RDAC directly to the engine block. There are some posts here on the forum that says the RDAC needs its own ground, but I then found a diagram in the RDAC installation manual that showed the Rotax 912 tach ground wire should go to to that same point, so I did that. I also found a post from Ranier that said the RDAC should have High Gain ON, Ballast ON, Filter OFF on the dip switches. I will fly this configuration in the morning and report the results.

I am hoping it will fix some of the engine readings, but I suspect the DA and VSI are a separate issue.

Oh, do you also have the G Meter pop up inappropriately?

Yes i have the g meter gremlin as well. I redid the in flight compass calibration and nothing changed. Compass, slip, horizon, VSI etc just dont work at this point. I do have the V17 firmwear rev and that fixed my recording issues but revealed new ones.
Peter

Looks like for the Rotax that High Gain OFF, Ballast ON, Filter ON, is what works for me. And no shared ground for the RDAC.

Adam at Michigan Avionics mentioned vibration in regards to the G Meter and slip indicator... I'm not sure how I could fix that. My panel is already isolated with rubber mounts and I think that's probably the best I can do.

He also mentioned that he's heard about the VSI/DA problem from more than just me and asked for a video, so I sent one in:

https://youtube.com/shorts/oSMSw1AsZng

The ALT reading is mostly right. The field elevation at BQ1 is 445.

Quick points to consider...

- During the start up process the VSI finds its balance point until reach 0. This is a normal process of the system.

- To improve the reaction of the instrument against harmonic vibration excess, try adjusting the "Gyro coupling coefficient", under the following Menu: System setup menu / Internal Sensor setup / Internal IMU setup /Gyro coupling coefficient. Just a suggestion, but often works well.

- To make sure the VSI is correct reading, install the static port in a suitable spot. Misplacing the static port (or not installing it) may considerably degrade the response of the VSI. Actually it interferes with all readings, but the VSI is more noticeable.

Hope it might help somehow...

Good flights to all...

Thanks for the input Fabio! A couple questions for you:

Fabio Bolorino wrote: ↑Fri May 19, 2023 4:03 pm o improve the reaction of the instrument against harmonic vibration excess, try adjusting the "Gyro coupling coefficient", under the following Menu: System setup menu / Internal Sensor setup / Internal IMU setup /Gyro coupling coefficient. Just a suggestion, but often works well.

Is this something that can only be done between flights. For example does it require restarting the MX1, or can I continuously adjust it in flight?

Fabio Bolorino wrote: ↑Fri May 19, 2023 4:03 pm o make sure the VSI is correct reading, install the static port in a suitable spot. Misplacing the static port (or not installing it) may considerably degrade the response of the VSI. Actually it interferes with all readings, but the VSI is more noticeable.

This makes sense, but I'm just venting the static port behind the panel. I could absolutely install a port elsewhere, but it just didn't seem like it would matter on my plane. Have you seen the internal venting to be an issue? It's common on some other planes that aren't too different to mine.

Thanks for the help.

Did you get your MX1 VSI issue resolved and if so what was the fix? I know its not my static source because my ASV1 VSI readings are good. I still have the altitude issue, both devices reading 300 feet low. Its frustrating trying to get thru the EAA test cards when so much data is bad. I cant even get the basics, ie setting the altimeters to local pressure.

peter

Sadly I haven’t.

I don’t think static port location is going to make a huge difference, but I did install ports on either side of the boot cowl in order to have a more constant pressure. Static pressure absolutely can make a difference, as when using cabin pressure I could get different readings if I opened the doors, for instance…. But again I don’t think this is the cause of the problem.

Currently I think the best work around is calibrating the VSI using your GPS climb rate. A 750fpm climb on ForeFlight usually looks like 1700+ on the MX1. You can also use the ADSB Exchange site to see what your GPS climb rate is.

If you go to SYSTEM SETUP > INTERNAL SENSOR SETUP > VSI Calibration factor, you can change it from 100% to something that matches your actual climb rate. For me it's probably 60% or so.

Also of note, there's probably a sticker on the back of your MX1 that has factory calibration numbers and if those aren't the same as what's on this menu that could be a factor.

Rob

Edit: So far I can deal with the innaccurate VSI, I just wish that my dang slip indicator would stay centered but that thing has a mind of its own.