Bill,
Could you advise a source where one could find info on "aerodynamic"
twist? As I understand it, newer designs like the Lancair Legacy do not
have a geometric twist but use different airfoils and taper to provide
the twist. Thanks
Tom
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Bill Daniels wrote:
Wing twist, whether geometric or aerodynamic via a change in airfoil
spanwise is designed in. Stall strips are added later if the
original
design proves to have unacceptable stall characteristics.

Stall strips hurt performance and should be avoided if at all
possible. You
NEVER see stall strips on a sailplane. Careful selection of outboard
wing
sections can produce very sweet stall behavior.

Twist, is usually an aerodynamic benefit across the whole speed
range. It
helps maintain an elliptical spanwise distribution of lift.

Bill Daniels


wrote in message
oups.com...
I've noticed a lot of aircraft are designed to use washout at the
tips
to control stall behaviour. The idea as it was explained was that
they
wanted the inboard part of the wing to stall before the outboard
part
so aileron authority could be maintained a little longer.

I've also seen mention of stall strips being installed inboard to
try
to affect the same thing.

It seems to me that trying to impart a twist of only a few degrees
into
a structure that large, and have it maintain that twist under load
and
over time (as opposed to jigged on a bench) is a fairly hard thing
to
do correctly.

Also, with the washout, aren't you in effect constantly flying
around
with the whole wing at a non-optimal AOA since each part of the
wing is
slightly different AOA as you move out on the span?

Since airfoils are a trade off, among other things, of lift, drag,
and
range of AOA, wouldn't it be better to extend the stall strip
approach
to just having a progressive (or piece wise) airfoil cross section
with
a sharper leading edge in-board moving out to a smooth rounded
leading
edge near the tips (and ailerons)? So you have a lower drag,
reduced
AOA range inboard, and higher drag albiet wider range AOA outboard.
And have no twist in the wing.

Discuss