Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Tue, 14 Jan 2003 10:16:46 -0500
Message-ID: <redirect-1983021@logan.com>
From: Bob Pastusek <rpastusek@htii.com>
Subject: RE: [LML] Wing Incidence
In-reply-to: <list-1982093@logan.com>
Reply-to: rpastusek@htii.com
MIME-version: 1.0
Content-type: text/plain; charset=iso-8859-1
Content-transfer-encoding: 7BIT
Importance: Normal

Mike Hutchins noted:

I am a bit surprised to learn that people are "finding" that their wing
incidence is different from side to side by as much as 2 degrees or that the
wing twist (washout) varies by more than 0.5 degrees...

Mike,

Jim White and I spend a considerable time checking and measuring our (closed
at the factory )wings for these things, both before and after mounting on
our IV-P's. My conclusion after spending many hours on this was that the
wings were identical within the measuring accuracy of our instruments/tools.
(Estimated to be approx 0.2 degrees). We spent some time and effort setting
the incidence and rake identical for both wings, and discovered in the
process that the basic fuselage is bowed about 1/4" in the center to the
right of the centerline. This turns out to be unimportant for anything we
could determine, but it did give us fits for a while... I believe we mounted
both wings within 0.2 degrees of the specified incidence, and both are set
to the same incidence within the measuring accuracy of our tools. As noted
elsewhere in the forum, if there is a discrepancy in washout between the
wings, I'd adjust the rear spar mounting to provide equal incidence at the
tips and then check the incidence at the roots. A small discrepancy at the
root will not matter, but if there is one, you might back out a small part
of the difference, recognizing that the rolling moment will be based on how
much lift the ends of the wings generate. The book has you measure/set
incidence at the roots, but make up a wingtip profile/form and make them as
close to equal as you can.

You didn't ask, but I cut off the Lancair-provided hinge section that's
provided as a trim tab, and remade a trim tab within the left aileron that
is 1.5 times larger than the original hinge section. This was based on the
observation from flying several IV's built to spec that have marginal trim
control in roll. That is, even a moderate fuel imbalance can't be trimmed
out.

I'd strongly  recommend you take advantage of the factory wing closing
option for several reasons, only one is to take advantage of their
well-aligned and very substantial jigs.

Hope this helps, Bob Pastusek

#############################################################
For archives see the LML website: http://www.lancaironline.net/maillist.html
LML members receive a 10% discount at http://www.buildersbooks.com