ahrs and vibration

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oaklandaviator
Posts: 4
Joined: Tue May 05, 2015 12:07 am

ahrs and vibration

Post by oaklandaviator »

I have an hx system installed in an RV-8. The ahrs is mounted on the bulkhead behind the instrument panel (back of the forward baggage compartment). When the engine is off, the unit initializes very quickly, but with the engine on it can take a long time to initialize. Additionally, the autopilot servos were jumping around in roll quite a bit and it seems they are following slightly erratic attitude indications. Has anyone else had this problem and if so, any ideas on reducing the vibrations to the ahrs? When trying to turn off the landing lights the other day I accidentally hit the radio master in flight. Took over half an hour of flying to finally reinitialize. Glad it was vfr.
jclark
Posts: 80
Joined: Mon Dec 10, 2012 12:15 am

Re: ahrs and vibration

Post by jclark »

You should call GRT on this.

I have assisted with or installed in my plane, the AHRS right behind the panel (aft of the baggage compartment on the right side) and IN the baggage compartment all the way on the left side. I am referenceing RV8's in these cases.

In neither case have I witnessed what you mention. In both cases, they are though firmly bolted to the airframe.


James
oaklandaviator
Posts: 4
Joined: Tue May 05, 2015 12:07 am

Re: ahrs and vibration

Post by oaklandaviator »

Thanks. I'll call them and see what they say.
oaklandaviator
Posts: 4
Joined: Tue May 05, 2015 12:07 am

Re: ahrs and vibration

Post by oaklandaviator »

After relocating the AHRS unit to behind the cockpit and adding a battery backup, I can say the initialization issues are cured, but the in flight ahrs performance is abysmal. The ball jumps from left to right wildly and causes the attitude indicator to move with it. FD/autopilot follows this movement. Is worse at certain rpm settings. I'm beginning to think the ball is sensing backwards. Any ideas would be appreciated.
Bobturner
Posts: 444
Joined: Mon Mar 11, 2013 6:34 pm

Re: ahrs and vibration

Post by Bobturner »

Backwards? One of the modules has an arrow on it which must face forward. Make sure it's not backwards or upside down!
jclark
Posts: 80
Joined: Mon Dec 10, 2012 12:15 am

Re: ahrs and vibration

Post by jclark »

This may sound like a strange question, but .....

Are you sure the magnetometer is connected?
And if so, where is it?
Does the heading **seem** to be about right?

Do you have multiple or a single power source to it?

Is it mounted in a manner that is "consistent" in all three spatial "planes"?

James
oaklandaviator
Posts: 4
Joined: Tue May 05, 2015 12:07 am

Re: ahrs and vibration

Post by oaklandaviator »

Thanks for the responses. I haven't checked the forum recently!

We originally mounted the AHRS behind the instrument panel but has vibration issues and moved it to a mount behind the rear baggage compartment. Now it is just as bad, if not worse. It isn't backwards and works fine when the engine is off. Worst performance of the unit is at 2500 rpm (fixed pitch RV-8). At 2500 rpm the slip ball bounces from stop to stop and the attitude goes to 30 degree back indications left and right while the plane is straight and level. Power up or down and the oscillations subside greatly, but totally not trustworthy for IFR.

It is single power source to all components and the magnetometer is connected and calibrated. I'm thinking there is a sensor problem in the AHRS.

Anybody else have this or a similar problem with the adaptive AHRS?
330drvr
Posts: 69
Joined: Sun Mar 24, 2013 5:30 pm

Re: ahrs and vibration

Post by 330drvr »

I am very pleased with my dual adaptive AHRS (and spare GPS). I would talk to GRT. I did have an issue when first installed and Greg and Jeff worked the problem until fully resoved.
RV-7A
Dual HX, Mini X, dual adaptive AHRS, GRT EIS
GRT_Jeff
Posts: 802
Joined: Tue Dec 11, 2012 12:11 am

Re: ahrs and vibration

Post by GRT_Jeff »

We've made a couple changes that improve performance in vibration and turbulence. These changes are in version 61 for the Adaptive AHRS and Mini AHRS. This version will be posted to the web site soon. For now, here is a direct link to the update:

Download AHRSUp-46-61.dat
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