Adjusted ADAHRS

The inclinometer on my SkyView has always shown nearly 1/2 ball out to the left, even when the fuselage was absolutely level.  After doing some research, it looked like the only way to adjust this was to shim the ADAHRS until in showed a centered ball with the fuselage level.  I used my shop crane to raise the tail to a level attitude and put my aircraft jacks under the jacking points on the wings to hold the plane rigid in the roll axis and to make minute adjustments to the lateral level of the plane.

After getting the longerons level, I used the wing jacks to adjust the lateral angle until my digital level showed 0.0 when placed across the seat back support.  I then zeroed the smaller digital level I have and placed it on the ADAHRS.  Sure enough, it showed about 0.5º angle with the left edge low (exactly as a left ball would indicate).

I removed the attachment screws holding down the ADAHRS and fabricated some small aluminum shims to fit under the left edge.  After some experimentation, I found that I needed a 0.048″ thick shim to center the ball.  Now the ball is nearly perfectly centered.  I’m really surprised how sensitive this is.  Varying the shim thickness by just a few thousandths made a visible difference in the position of the ball.  Given that my digital angle is only accurate to 0.1º, it’s really hard to get this accurate since I can now move the ball from one vertical mark to the other while still reading 0.0º on my digital level.

While I had the plane in the level attitude, I was curious how much ground clearance I have from the propeller tip.  This is the best case without any further gear compression.  If I were to bounce a wheel landing or raise the tail too far, this clearance could diminish significantly.

Greg also stopped by with his Windows laptop so we could make a few adjustments to my VP-X.  My Windows laptop is acting up (surprise, surprise), so I haven’t been able to use it to connect.  We configured the Wig-Wag function, set up intermediate stops on the flaps (and configured the VP-X to use them instead of requiring me to hold the flap switch until they reach the position I want), and turned off current monitoring on the fuel pump.  I still need to adjust the flap airspeeds, but I forgot at the time.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.