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View Full Version : Altrak failure resolution


Steve Brown
11-07-2007, 09:26 AM
Hi All,

I posted a while back about the Altrak in my RV9A failing. A few
people asked me to make an update when the whole thing was done.

Actually it turned out to be nothing more, apparently, than the pitch servo
shear screw breaking. If it were not for the fact that I broke off the
mounting screws inside the Altrak during removal, I could have just put a
new shear screw in and went flying.

Lucas at TruTrak was very helpful. I sent in the Altrak and the pitch servo
so they could remove the busted screws, replace the shear screw, and check
the whole thing out. They did, and found no problems. There was no charge
except for shipping because I wanted 2nd day arrival. He included a couple
of spare shear screws.

According to Lucas the best procedure in this case would be to first try
replacing the shear screw. There are three holes, so you can replace the
shear screw up to twice before having to pull the unit and get the old
screws out.

On installation I generally followed Sam Buchanan's recommendations for
installation + Included 6-32 machine screws with heads drilled for 0.02"
safety wire for the Altrak:

http://home.hiwaay.net/~sbuc/journal/altrak.htm (http://home.hiwaay.net/%7Esbuc/journal/altrak.htm)

Hopefully using safety wire rather than locktite will result in less
melodrama next time I remove the units.

Everything seemed to work ok on a short test flight. If I have any
additional near term problems I'm going to go looking for something
intermittent in the wiring.

My theory on why the pitch shear screw went first is that it gets more
abuse. I don't think the quick override check I do on the ground for both
pitch and roll is a problem for either. In flight the pitch gets much more
abuse during up & down drafts, which are sustained, compared to turbulence
induced roll which tends to be very transient. Also there have been several
times that I have overrode either pitch or roll in flight. Again the roll
is transient by definition unless you are turning circles, but climbing or
descending for a new altitude is sustained.