REFLECTOR: anyone know the story behind this-musthavemissedit.....

[Al Gietzen]

Looking at the outside shape of the winglet and rudder, one will notice a
slight cuff (concave shape).  Builders sometimes mistakenly believe the
concave area should be filled in with micro in order to make a straight
surface along the winglet and rudder outside line.  Wrong.  The cuff is part
of the "wing" shape and is designed in this fashion for a purpose - and that
is, to allow the winglet to create lift in a horizontal direction towards
the fuselage.  The winglet forces mimic that of a person pushing the winglet
from the outside towards the fuselage.  This "loads" the winglet and adds to
stability.  It also creates a design that does not support flutter.  It is
very important that builders who build from the basic kit make absolutely
sure that the toe-in of the winglets are built according to the construction
manual.  Straight winglets and the absence of a slight concave line on the
outside of the winglet invite flutter.  This is what happened with Brendan
and the first "Brazil" set of wings.  The toe-in was reduced by a fraction
of an inch and the shape of the outside of the winglet did not feature a
concave feature.  It was just enough to begin winglet flutter, which once
started - could not be stopped once the rudder cables broke.

SB

 

Scott;

 

I put a straight edge on my Alan Shaw winglets, and find that the outside is
flat, no "slight concave line". I certainly don't want to be inviting
flutter.  I assume they have the correct 'toe-in' for a positive AOA; but
have no way of knowing.  How concerned should I be? I suppose a rudder
shimmed just slightly outward from flat would constitute slight concavity.  

 

Any cases of flutter with wings built by Alan?

 

Al

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