Message-ID: <3746FAC2.81B44A37@mc.net>
Date: Sat, 22 May 1999 13:43:14 -0500
From: jerry@mc.net
Reply-To: jerry@mc.net
To: Lancair Mail List <lancair.list@olsusa.com>
Subject: Trim Systems
Mime-Version: 1.0

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The connectors thread got me on to one of my pet topics.....TRIM SYSTEMS.
I don't want to muddy the connectors thread so I've changed the subject
title with this note.   To come right down to the solution though, if all
electrical components were inside the cockpit and therefore in reach for
maintenance we would not have a concern for connectors.  Also the manual
elevator trim wheel has much going for it to simplify the build.

To all who plan external trim as their goal for building a "straight" flying
machine.

The second best trim system is the one not needed. So its best to build
straight flying     machines and sometimes that seems to "happen" and
happily so.

The best trim system is the one the builder has to add after the first few
flights.  One for the rudder and/or for the heavy wing.   It is obvious, we
all must plan for and build-in, the elevator trim system.

There is no useful purpose served building trim systems which are not known
to be needed.  This begs the question then:  Why build these systems when it
is not certain the controls will need the system.

This discussion will be confined to the aileron trim system.
For every ounce of weight the trim system adds to the aileron it has to be
balanced with many times that weight in lead.  So leave the ailerons alone
with so called "big airplane" or store bought general aviation type airplane
trim tab systems.  Keep it simple, gentlemen. Be more effective by using the
systems the fighter jets, 727, 747 and others use.  These jets use a new
neutral position trim system.  If the left wing is heavy the trim system
finds a new neutral position for the stick.  A position which causes the
wings to remain level even though the stick is now off center a trifle.  Let
it be know, the ailerons in these airplanes are hydraulically actuated.  A
trim tab on the aileron simply would not be able to drive the aileron
against the hydraulic lock existing in the system.
The device that causes the stick to move off center is an electric servo
driving the control linkage which then drives hydraulic valves, driving the
ailerons.

In the Lancair 320 it could be a MAC servo pulling on bungee cords attached
to the bottom of the stick's push rod control.  The results of two or three
clicks on the aileron trim button would be witnessed in the movement of the
control sticks going from one position to another.  This new position then
becomes the new neutral position for both ailerons.

Of course the advantages  to this approach are obvious.  There is no
intensive labor to create a cosmetically beautiful aileron trim tab or servo
mounting cover and all the nut plates associated with those needs.  The
aileron has nothing inside and no tab to drag through the air, we have also
left a lot of lead at home, on the shelf, where it belongs.

The attendant advantage is the aileron trim is not in the airplane if it is
not needed and best of all can be added later with no loss of
effectiveness.  It hides under the seats, out of sight, easy to work on,
with no labor intensive highly fitted and painted covers.

The spin-off advantage.......the stick is spring-loaded to the aileron
center position which gives an elegance and sophistication to a deserving
and classy airplane.

If there are any questions about this approach please state them to the List
and I'll respond to that in kind.  Everyone will then get the whole mystery
solved, if this has generated any mystery.

Jerry Grimmonpre'


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