Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml@lancaironline.net
Date: Thu, 25 Sep 2003 20:33:44 -0400
Message-ID: <redirect-2604041@logan.com>
From: "Larry Henney" <LHenney@attg.net>
Subject: RE: [LML] Re: Gain a couple of knots
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In-Reply-To: <list-2602613@logan.com>

Eric,

One thing I think is correct when considering a CG adjusting system
would be that you want the elevators in line with the horizontal stab.
When I was building I was told by some compuserve Avsig guys that they
ran out of forward stick at higher speeds.  I have no idea how true that
statement may be.  However, as a result I tried to reduce my high speed
"anti-lift" by installing the horizontal tail at a less negative
incidence than specified.  I believe it called for 1/4 to 1/2 degree
nose down.  I really don't know how well I succeeded when I finally
installed the thing.  When measured with a smart level and compared to a
water level I found mine to be at both ends of the target.  

The long short of it is that my plane seems to go a little faster than
many LNC2's.  I too am convinced that reducing that tail drag would be
beneficial.  I have spent hours designing a trim tank as you describe.
My intent would perhaps be a little more conservative than yours in that
my tank would be empty for takeoff and landing.  I would have a simple
transfer system with two pumps.  Additionally, I intended to have a 1/2
dia dump valve in case of pump failure.

Here's the rub.  I think I'm sitting with a touch of forward stick or
down elevator in fast flight.  I look at the tail to see 1/8" up on the
elevator weights. Therefore, I surmised (somebody correct my narrow
shortsightedness pls) that adding weight aft may increase speed.
However, I think it would also increase drag through more forward stick
of a drooping elevator.  Thence, this may permit no actual speed
benefit.  Comments welcome....?

The long short of it is that if one were smart enough to properly assess
the affects of a shallower dive angle on the horizontal tail one might
make progress in this area.  Specifically, say we went with a zero of
plus 1/4 deg dive.  Then what would happen to the stall speed (and by
how much would it increase?).  Additionally, would the plane have enough
elevator authority to rotate to a take off attitude at reasonable
speeds.  Finally, are there other issues interrelated here?  The trim
tank (adjustable CG) might then be a very affective tool to perfect the
tail drag equation.  

I'd love some engineer to give us some insight into these thoughts.

Larry Henney