Stall strips vs. Washout

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

wrote in message
oups.com...

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.

Not correct. The wing is not built "straight" and then twisted. It is built
with the "twist" jigged in.

Rich S.

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

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
-------
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

Tom,

You're the one guy that's offered information that supported my
hypothesis. Having an actual twist seems like the last thing you'd
want to do on a "go fast" airplane like the Lancair.

Having the taper and different airfoils is a way of affecting stall
behaviour rather that providing an actual twist which wasn't an end in
itself, simply a method used in the past to achieve an end (stall
performance).

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.

Constant cord (Hershey Bar) wings need no twist, or stall strips, as they
stall naturally on the inboard section, with the tips remaining flying to
the end. They are not as efficient at high speeds as elliptical or tapered
wings, but that is seldom the mission of planes that have constant cord
wings.
--
Jim in NC

"Morgans" wrote in message
...

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.

Constant cord (Hershey Bar) wings need no twist, or stall strips, as they
stall naturally on the inboard section, with the tips remaining flying to
the end. They are not as efficient at high speeds as elliptical or
tapered
wings, but that is seldom the mission of planes that have constant cord
wings.
--
Jim in NC

This may be a good generalization, but I can think of at least two
exceptions. The Grumman AA-1 and the Piper Tomahawk. I've never paid much
attention to the Grumman AA-5, but I wouldn't be surprised to see 'em there
either.

KB

"Kyle Boatright" wrote

This may be a good generalization, but I can think of at least two
exceptions. The Grumman AA-1 and the Piper Tomahawk. I've never paid
much
attention to the Grumman AA-5, but I wouldn't be surprised to see 'em
there
either.

KB

An exception to what? Surprised to see what, where? You gotta incude more
hints, unless you want to play 20 questions! :-)
--
Jim in NC

"Morgans" wrote in message
...

An exception to what?

My guess would be your statement that "They (constant chord wings) are not
as efficient at high speeds as elliptical or tapered wings, but that is
seldom the mission of planes that have constant cord wings".

Surprised to see what, where?

I'll bet he's referring to stall strips as mentioned in:

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

Constant cord (Hershey Bar) wings need no twist, or stall strips, as they
stall naturally on the inboard section. . .

But he is a bit obtuse with his referents. :-)

Rich S.

Sorry about that. I'm gonna blame nasty sinus infection combined with a
mixture of meds.

My follow-up was directed at JSMorgan's comments on hershey bar wings and
stall strips:

"Constant cord (Hershey Bar) wings need no twist, or stall strips, as they
stall naturally on the inboard section"

Like I was trying to say last night, the AA-1 and Tomahawk both have hershey
bar wings and stall strips.

KB


"Morgans" wrote in message
...

"Kyle Boatright" wrote

This may be a good generalization, but I can think of at least two
exceptions. The Grumman AA-1 and the Piper Tomahawk. I've never paid
much
attention to the Grumman AA-5, but I wouldn't be surprised to see 'em
there
either.

KB

An exception to what? Surprised to see what, where? You gotta incude
more
hints, unless you want to play 20 questions! :-)
--
Jim in NC