Return-Path: <marv@lancaironline.net>
Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Thu, 16 Jan 2003 10:17:39 -0500
Message-ID: <redirect-1990338@logan.com>
X-Original-Return-Path: <Christopher.Zavatson@udlp.com>
Received: from mailrelay.udlp.com ([207.109.1.10] verified)
  by logan.com (CommuniGate Pro SMTP 4.0.5)
  with ESMTP id 1990356 for lml@lancaironline.net; Thu, 16 Jan 2003 10:15:07 -0500
Received: from asdmngwia.mpls.udlp.com (asdmngwia.mpls.udlp.com [10.1.62.22])
	by mailrelay.udlp.com (8.12.6/8.12.6) with ESMTP id h0GFEpDG001567
	for <lml@lancaironline.net>; Thu, 16 Jan 2003 09:14:51 -0600
Received: from DM-MN-06-MTA by asdmngwia.mpls.udlp.com
	with Novell_GroupWise; Thu, 16 Jan 2003 09:14:45 -0600
X-Original-Message-Id: <se267805.024@asdmngwia.mpls.udlp.com>
X-Mailer: Novell GroupWise Internet Agent 6.0.1
X-Original-Date: Thu, 16 Jan 2003 09:14:20 -0600
From: "Christopher Zavatson" <Christopher.Zavatson@udlp.com>
X-Original-To: <lml@lancaironline.net>
Subject: [LML] Re: Wing Loading mysteries
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
X-Spam-Status: No, hits=0.5 required=7.0
	tests=DISCLAIMER,QUOTED_EMAIL_TEXT,SPAM_PHRASE_00_01
	version=2.42

Scott,
<<All I know is that the faster I go, the more I must trim nose down,
not nose up.>>

As it should be.  You are trimming to a lower AOA and the tail
effectiveness increases faster that pitching moment of the wing with
increase in air speed.

<<Luckily, the rear seat passenger, if any, sat on the middle of the CG
range.  
If I think about it hard enough,  trim via reflexing the flap may not
be the 
best idea since the tail is being unloaded>>

There is nothing wrong with unloading the tail in this fashion.  You
were mearly changing the pitching moment and the zero lift line of the
wing until everything balanced out.  Now, if you kept throwing sand bags
into the the tail cone to achieve the same result you might run into
difficulty.

One thing I forgot to mention earlier is that the 25%MAC point is not
the same thing as "center of lift".  The quarter chord point of the mean
aerodynamic chord is a convenient location to use for stability
calculations because at this point Cm (pitching moment coeficient) is
nearly constant for any value of Cl (lift coeficient).  In other words,
the moment coeficient is independent of angle of attack.  This quarter
chord point is also referred to as the aerodynamic center of the wing. 
The "center of lift" moves with changes of AOA which makes it very
inconvenient to use. The quarter chord happens to be near the CG
location of most GA planes, but it is entirely possible to have a
completely stable aircraft with the CG at 50% of the MAC.  For the
aircraft to have positive stabilty the CG must remain ahead of the
neutral point of the aircraft.
As a side note, a few years ago I compared the static longitudinal
stability of a the MKII tail with that of the small tail.  The MKII buys
you about 1.5 inches rearward CG range.  In other words  to reduce the
static longitudinal stability to that of the original tail you must move
the CG back 1.5 inches.(Disclaimer:  I didn't have exact dimensions for
the small tail so this may be off a little) Lancair did not change the
official CG range rearward for the MKII and thus built in greater
longitudinal stability.
A few other tidbits.  My experience has shown that any up or down pitch
of the engine has little effect unless the angle is quite large (a few
degrees) If, however, the prop wash impinges on the horizontal
stabilizer with any significant angle it can have a  large impact in
pitch, moreso at slower flight speeds where the difference between
airspeed of the plane and velocity of the propwash is greater.
The actual angle of attack of the horizontal stabilizer is also
influenced by the down wash of the wing.   Looking out the window at the
horizontal stabilizer gives a  false indication of its angle of attack
as you cannot see the actual local flow.
-Hope all this doesn't make your headache any worse.
<<Oh, my head is starting to hurt. >>
It is good to see these topics on the list. -gets people thinking about
how these things stay up there in the first place.
Chris Zavatson
N91CZ
360std

>>> Sky2high@aol.com 01/14/03 06:36PM >>>
In a message dated 1/14/2003 7:58:34 PM Central Standard Time, 
marv@lancaironline.net writes:

> Don't forget about the pitching moment about the MAC.  Cm is fairly
> small for our airfoil (-.05) and the reflex will reduce it further
but
> it still amounts to a significant down force requirement for the
tail.
> 

Chris,

Yeah, I talked to Jack Webb today.  There are many variables.  But, let
us 
not forget that the engine is pitched up a bit and there is some
fuselage 
effect since my cowl and canopy want to be badly sucked upwards.  All I
know 
is that the faster I go, the more I must trim nose down, not nose up.

I built a tube and fabric (Quad Cities Challenger II, sold long ago)
with 
flaperons. I used a linear motor to operate the "flap" part of the
flaperons. 
 This became the pitch trim - no tab on the elevator.

Luckily, the rear seat passenger, if any, sat on the middle of the CG
range.  
If I think about it hard enough,  trim via reflexing the flap may not
be the 
best idea since the tail is being unloaded.  Speed via drag reduction
was not 
a consideration.  Oh, my head is starting to hurt. 

Scott Krueger
N92EX