Message-ID: <000f01bfe129$510edae0$146c5da6@djpryan.ruralnet.net>
From: "DON J RYAN" <djpryan@ria.net>
To: "LANCAIR LIST" <lancair.list@olsusa.com>
Subject: AUTOPILOT DIVE, N15EG
Date: Wed, 28 Jun 2000 12:48:49 -0500
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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I reported the sudden dive, with negative g forces last Jan.  At the time I
suspected the autopilot, since I was cruising at 9500 ft using the S-Tec
altitude hold. I was reasonably certain that I had to overcome the autopilot
to stop the dive. The upset was especially violent since I was not holding
the stick. The first investigation did not find any problem with the
autopilot and left some uncertainity regarding the cause of the upset.

A clue was furnished on my next cross country from BPT to LHX. I was at
10500, a little cool and pulled the heater on. Immediately the plane tried
the dive manuever, but this time I did have a grip on the stick and averted
a major upset.  Subsequently, it appears that the problem was with the
heater cable passing over a terminal strip.  Clearance from an uninsulated
bolt with several leads attached was about 1/32".  I insulated the cable
with some FEP tubing and have had no further upsets.

Tracing of the leads to be certain that one of them was from the autopilot
was very difficult and not successful due to the lack of ID at the terminal
strip. However, another clue, my uMonitor also had failed to record the
proper flight time on the first upset.  Apparently this can be caused by low
voltage and I can trace that lead from the terminal strip bolt to the
uMonitor.

It would appear the builder completed the instrument panel with the terminal
strip before completing the heater cable. The terminal strip was not secured
to the nose wheel well. Of course, the short of these leads could have been
avoided by proper insulation or by proper placement of the cable or terminal
strip.

A warning to those of us who will have some else complete the instrument
panel. Any of the various engine control cables can short out instruments.


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Please send your photos and drawings to marvkaye@olsusa.com.
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