Message-ID: <39A6FFA2.ED3AFDC5@mc.net>
Date: Fri, 25 Aug 2000 18:22:10 -0500
From: jerry@mc.net
To: lancair.list@olsusa.com
Subject: Re: Circuit Breakers for Hydraulic Pump Relays
References: <86256946.0070FCB9.00@mail.firstar.com>
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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Theo_Green@firstar.com wrote:
> Runaway trim is a potential killer....
> Make sure the trim system is not able to cause this
> type of problem....
> I haven't figured it out yet, and I'm interested in suggestions too.

In our training, in our B727's, at United, we practiced runaway trim in the
simulator. Basically Boeing figured it this way ... which ever way the trim
ran the natural reaction, by the pilot, was to hold the controls in the
opposite direction.  This action stopped the runaway, mechanically, by
stopping the trim wheel, on the control pedestal.  With the trim stopped
mechanically the procedure called for the two trim switches to be turned
off.  These two trim switches opened the control circuit on the yokes and
the actuator circuit for the jack screws.

Similar switches could be installed in the Lancairs.  One switch would
provide a circuit to the nose up trim and the second switch would provide a
circuit to the nose down circuit.  If the pilot wanted nose up trim and was
pushing forward on the stick the nose up circuit would open.  If the pilot
wanted nose down trim and was pulling back on the stick the nose down
circuit would open.  With the stick in a no load position, the trim switches
would both be in the circuit closed position.  This will discipline a pilot
to fly with no pressure on the controls .... a good practice anyway.

This is how it could be switched and wired.  You all will have to figure out
the mechanics of the switches in relation to the neutral position of the
stick.  You will have to make it all come together for your individual
lifting machine.  Don't get them wired backwards or you will have two
surprises with a runaway trim.

Jerry Grimmonpre'   LNC2    McHenry,IL

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