Reply-To: <glcasey@gte.net>
Reply-To: lancair.list@olsusa.com
From: "Gary Casey" <glcasey@gte.net>
To: <lancair.list@olsusa.com>
Subject: Nose strut rake angle
Date: Thu, 17 Jan 2002 05:22:18 -0800
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<<It seems to me that the vertical strut should be angled forward at least 5
degrees more. If this were the case, the entire weight of the engine and
airframe forward of the main wheels would have to be overcome in order for
the nose wheel to retract when the aircraft is on the ground.>>

The nose strut, unfortunately for your concern, is also the steering pivot
for the nose wheel.  The inclination of this strut, called the "rake angle"
by bicycle types is critical in achieving shimmy-free operation of the nose
wheel.  The other critical dimension is "trail", which is the distance from
the pivot axis to the center of the tire contact patch at ground level and
these two interact to make up the steering and stability characteristics of
the nose wheel.  Not to say that the designed geometry is perfect, it is a
lot easier to mess it up than fix it.  One way to change the design to
improve the situation would be to move the retraction pivot back.
Unfortunately, this would result in the gear leg being further down when
retracted, so the pivot point has to be move back AND upward to get the same
position retracted.  Oops, that will move the gear further back when
retracted and there may not be room to do that.  A better solution might be
to concentrate your efforts on a more rugged down-lock.  There are a number
of designs used in production aircraft that mechanically lock the link until
positive pressure is in the retract line of the system.  Look at the nose
gear of a Skylane RG - it has no over-center link at all, but relies on the
cylinder itself, with help from a mechanical latch, to hold the gear down.
My 177 just has a spring that holds the link over-center (and there have
been nose gear collapses).

Gary Casey
ES, gear down and locked


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