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Date: Thu, 08 Mar 2007 18:48:55 -0500
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Subject: LNC2 flap mod
From: "bob mackey" <n103md@yahoo.com>
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Marv considers Fowler flaps for an LNC2:
> It occurred to me that semi-fowler flaps on an LNC2 instead of the
> present rotating, hinged flaps might be a worthwhile modification.
...
> Have any of you attempted this mod or given it any serious thought?
> I'd sure like to get some input before committing to it.

Mark says:
> I'd be happy to have Legacy flaps if I could have Legacy wings too.
> (maybe I should just get a Legacy) :)

Marv:
I think Mark hits this nail on the head. At first glance, it
might be nice to have the greater lifting area and coefficient
of lift (Cl) associated with Fowler flaps. It might seem that
simply lowering the hinge point would do the trick. In going
from the 235 to the 320/360, the hinge point is lowered from
the top skin to the lower skin. In the Legacy the hinge point
drops another 4-5 inches.

When you look into the Legacy wing you'll also see some other
changes: larger bond areas, stiffer skins, heavier ribs.
Notice the Legacy's drag spar -- much stiffer than the LNC2's.
Even heavier areas around the flap hinge mounts. Also notice
that the airfoil is different, and the tail is bigger and on
a longer boom.

All those changes are there in part to accommodate the greater
torsional loads from the Fowler flap design. The deeper camber
with the Fowler flaps requires a different pressure distribution
on the top of the wing to be effective. The deeper downwash
behind the wing changes the airflow at the tail. The more effective
flaps move the center of lift aft, further increasing the
tail loading. Perhaps those effects contributed to
Greg Cole's decision to put the tail where it is on the Legacy.
You wouldn't want to learn on your test flight that lowering
the flaps causes the tail to stall as you approach full up elevator.

I'm not saying that Fowler flaps for a 320/360 is a bad idea,
but there are quite a few ramifications to consider. At the very
least I would want to build and test a model (real or computed)
to determine how the new airfoil would work, and what loads it
would impose on the airframe. A structural engineering model
(real or computed) should be tested to determine what changes
would be needed to carry those loads. The new load and angle of
attack requirements for the horizontal tail would be estimated
from a tufted model or 3D-CFD calculation and re-engineered.
Then the new design should be re-analyzed for aeroelastic (flutter)
effects. Finally, the real airframe should be load tested on the
ground to see if the new design achieved it's modeled stiffness
and strength.

Again, I'm not saying it is a bad idea, but it would
definitely be earning the "experimental" badge.

This one appears to have the hinge lowered an inch or so below the
bottom skin.
http://www.aoaircrafters.com/lancair360.asp
I'm curious what they did to transfer loads into the new
hinge points.