Date: Wed, 26 May 1999 23:38:30 +0200
To: "jerry@mc.net" <jerry@mc.net>,
    "Lancair Mail List" <lancair.list@olsusa.com>
From: "colmar" <jones@colmar.demon.nl>
Importance: medium
Priority: normal
Message-Id: <927754710-0-jones@colmar.demon.nl>
Subject: Re:Bob Weight
Mime-Version: 1.0

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The bob weight is there to increase the g/stick force by pushing back on the
stick when, (like everything else including pilot),  the bob weight experiences
the g force arising from the original stick motion (or from turbulence). It
becomes effectively heavier than the elevator spring was trimmed to balance out,
and pushes back against the pilot's disturbing action. (He was probably about to
leave a deposit on his leather, anyway!) 
Therefore, I deduce (but have not tested) that the same reverse force back on
the stick can be achieved for less actual bob weight, by increasing the length
of the lever arm between the CG of the bob weight and the center of rotation,
while keeping the other lever arm (from center of rotation to push rod center
line) the same. Of course you may have to make room for this longer arm by
moving/sculpting the baggage area close-out panel. ( I have been too lazy to try
it) 

I don't see how any other type of resistance devise can have the same g-related
action on the stick. 
I also don't see why you think the bob weight mechanism itself is any cause for
the noise of the elevator spring - quite the opposite - the bob-weight acts to
REDUCE the spring motion which the pilot is attempting to make, and will exert
it's intended resistive force independent of the stick motion but related only
to the change of g-force it feels (which does arise from a stick motion of
course)

 The best solution I have found to the noise of the spring motion, in addition
to plenty of grease of course, is to rotate slightly the clamp which attaches
the trim push rod to the elevator push rod so that the fixation of the back end
of the trim push rod is better in line with the (average) height of its front
end, determined by the trim lever arc. This way the Al. tube down the center of
the spring has less opportunity to rub against the spring.

Incidentally, based on some (unquantifed) test flying with different Lancairs
here in Holland, we suspect that the stability characteristics are very
susceptible to any non-linearity in the elevator control system; and this comes
down to the spring trim device and the bob weight. So I think it is worth taking
some trouble to eliminate the noise and friction to get as nearly a pure spring
as possible, but I certainly would not think of introducing any other kind of
"resistive" device into the control system. 

Colin Jones (PH-COL)    


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Subject: Bob Weight
Author: jerry@mc.net
Date:  26/05/99 20:00

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For the List......

Has anyone discovered, used, created or heard of a lighter weight device
substitute for the bob weight?

It seems a resistance device could be created to serve the same purpose.
Something like artificial feel without the screeching feel of  steel springs
stretching.  Something with "G load" sensitivity to create the same feel of
the bob weight?  Something as simple as the bob weight.

Jerry Grimmonpre'     L320

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