klaus(at)utdallas.edu
Guest
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 Posted: Mon Sep 11, 2006 8:45 am Post subject: Warning Sign of Bungee Cord Failure in 601 |
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Hi,
One sign of a failing nose gear bungee is reduced tension of the rudder
cables
when the plane is empty. The reduction is due to the angle of the
nose gear tube relative to the surface defined by the rudder cables. In
the 601,
that angle is less than 90 degrees when the nose gear is as far extended as
possible, which is the case when the plane is empty, assuming a Rotax
engine is installed. As a result, the cable tension is maximum at that
point.
When the bungee begins to fail, the nose
gear moves up a bit from the stop when the plane is empty, and the
tension of the rudder cables is reduced. An easy way
to test whether reduced cable tension is due to failing of the bungee,
is as follows. A friend steps onto the wing aft of the spar, as if
climbing into
the plane. This unloads the nose gear and causes it to move down toward
the stop
if it was not at the stop originally. Any such nose gear
movement increases the rudder cable
tension, which can be easily checked near the bellcrank of the rudder.
If a change is detected, then this is a warning sign of bungee failure.
These facts motivate the following recommendation.
1. During the preflight check, one should always test the tension
of the rudder cables at the rudder bellcrank.
2. If the cable tension has dropped, one should NOT retension
the cables, but should investigate the cause. Most likely, the nose
gear bungee is beginning to fail.
In my plane the bungee has been failing every 500 hrs,
most recently when I reached 1000 hrs TTAE. In each case,
the bungee began to fail on the hook behind the nose gear tube,
a hard-to-inspect location. On the other hand, the rudder cable
test was a reliable indicator.
Best wishes,
Klaus
--
Klaus Truemper
Professor Emeritus of Computer Science
University of Texas at Dallas
Erik Jonsson School of Engineering and
Computer Science EC31
P.O. Box 830688
Richardson, TX 75083-0688
(972) 883-2712
klaus(at)utdallas.edu
www.utdallas.edu/~klaus
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