Message-ID: <001301c04fe8$352b21c0$c8b188ce@pavilion>
From: "J. N. Cameron" <toucan@The-I.net>
To: "Lancair List" <lancair.list@olsusa.com>
Subject: Nose-heaviness in the ES -- mystery solved?
Date: Thu, 16 Nov 2000 10:13:47 -0600
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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    Here's a great example of why following the (badly outdated) manuals is
not always a good idea.  I've just finished putting my wings in place on my
FB ES. [Note:  The wing mating option, I think, is gone -- all the FB's now
have it.]  After putting my 3/4" stainless pins in place, which I use up
until final assembly to save the wing bolts, I checked the incidence angle
of the wing.  The manual calls for +2 degrees, and lo and behold, the actual
angle is +0.6 to +0.7 degrees.  Short of tearing out the shear box and
building it all over again, you're stuck with whatever the factory jigs give
you.  My last ES, by the way, was similar, although I can't recall the exact
incidence angle.

    Now, the interesting part.  If you follow the manual, you will already
have bonded your HStab in place before fitting the wings on.  The manual
calls for a 0 degree incidence angle for the HStab, although the recent
advice from the factory is "anywhere from 0 to -0.6", with the latter number
preferred.  Let's say you follow the manual that's still being supplied, set
your HStab incidence to 0 degrees, then fit the wings later.  The relative
incidence of the HStab relative to the wings will now be about -0.7, whereas
if everything is the way it's supposed to be (+2 for wings, 0 to -0.6 for
HStab) the relative incidence should be -2 to -2.6 degrees.  In other words,
following the manual sequence will result in a plane that's out of rig, with
the whole HStab exerting a down trim force.

    So, if you've got a FB ES, fit your wings on, check the incidence, then
set the HStab to give the right incidence relative to whatever the wings
turn out to be.  The worst you'll have is a fuselage that's angled a  degree
or so up or down, but that should have a lot less influence on flying
qualities than an out-of-rig HStab.  I have a hunch that the reason the
factory changed their advice on HStab incidence is that the wing incidence
is too low; canting the HStab down a bit would compensate and help counter
the "nose-heavy" feel of a lot of the completed ES's.  Some builders have
also increased the size of the elevator trim tab, but again, with the right
incidence angles, it's probably not needed.  The "nose-heavy" feel is
probably nothing to do with weight  -- with the battery in back, the c.g.
comes out right within the design envelope, even with the IO-550 and the
Hartzell prop.

    Now, if we could get the jigs tweaked the right way, and the manual
re-written . . . (are you guys listening up there?)

Jim Cameron,  ES #2 in progress


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