From: "R & A Colebrook" <rossann@azstarnet.com>
To: "Lancair List" <lancair.list@olsusa.com>
Subject: CG LIMITS
Date: Tue, 14 Dec 1999 13:11:35 -0700
Message-ID: <01bf466f$891608a0$1b27c5a9@rossann.olympus.net>
Mime-Version: 1.0

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Here is a flight test tip for what it is worth.

I found it useful to make a few landings during my flight test program with
the flaps reflexed.  Our airplanes are only one simple electrical failure
(relays, microswitches, connectors, power supply)  from being stuck with the
flaps reflexed when descending from cruise.  The landings were made with the
most aft CG that I plan to use.  The reflexed flaps give a nose up pitch,
reducing some of down load on the horizontal tail.  The effect on
controllability is much the same as moving the CG still further aft.
Depending on your tolerance for squirreliness on approach you may wish to
select the aft CG limit for your airplane farther forward than Lancair
permits, to allow for this failure mode.

If you want to test a still worse case under controlled condition, make
these landing with the maximum asymmetric fuel load you plan to allow, with
the left wing heavy.  The reflexed flaps shift lift from the inboard to the
outboard portion of the wing where the ailerons are.  This gives less margin
from stall to pick up a wing dropped by a.gust.  I suggest left wing heavy
because that is the hard one to pick up because of P factor when power is
used.  I found this effect to be significant on my 235.

All this is a bunch of what-ifs, but it is better to try it on calm day on a
long wide runway than to have to do it for the first time some day when the
only place available is a short field with a stiff crosswind.

I think this is a good case for use of Jim Frantz' AOA system, though he has
never mentioned it for this case. An indication for a safe stall margin for
slow speed with the flaps reflexed is built into the calibration of the
system independent of airplane weight.

Ross W. Colebrook N7828


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