Stall strips vs. Washout

Stall strips are used to fix a design shortcoming. No engineer
wants to design a wing that stalls sooner than absolutely necessary,
but some wings didn't behave as predicted and the stall strip was meant
to induce stall on the inboard wing areas and get the nose to drop
before the ailerons lost authority. The Tomahawk has a reputation for
some nasty stall/spin behavior, and I imagine the stall strips were
meant to alleviate it somewhat. The Bonanza has them, too. With newer
computer-generated airflow modelling it's easier to spot deficiencies
before the wing is built.

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).

In article ,
Roger wrote:

On Mon, 21 Feb 2005 17:42:36 -0500, "Morgans"
wrote:


wrote in message
roups.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.

The old "Hershey Bar Wing" Cherokees are the only planes I've flow
that I could put into a stall, keep it in the stall, and still make
turns using the ailerons. Many airplanes don't like that and in
particular the Bo series of planes are likely to roll over with which
ever wing you try to raise going down instead. It's amazing how fast
they can put the greasy side up.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com


The old Meyers 200 was another plane that you could hold in a stall and
rock the wings with the ailerons without falling off into a spin. It
also had about 3 deg of wing twist.

Some aeroplanes have stall strips just to give stall warning, by make the
h-tail vibrate from the turbulence.

some Hershey-bar wings have twist to improve its handling.

most all taper wing have some washout in form of twist or aerodynamically or
a combination of the two.

aerodynamic washout can be achieved by using an airfoil at the tip with more
camber, or more nose camber (drop nose)

Messersmith was probably one of the first to use a combination of twist and
a more cambered tip airfoil, it is made so the zero-lift line at tip have a
small amount of twist compered to the root airfoils zero-lift line, the cord
line have then a larger amount of twist. At high speed the tip will not
produce negative lift due to the small difference in zero-lift line.

Jan Carlsson
www.jcpropellerdesign.com

Sure you don't want the wing to stall before absolutely necessary, but
that is in effect what is done with having washout- making the inboard
section of the wing stall before it absolutely had to. They felt it
was preferable to do that so at the artificially early stall you'd
still have aileron control.

"Kyle Boatright" wrote


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

KB

The AA-1 had them more to make the high speed stall more noticeable, as I
recall reading , somewhere.

The AA-1 was hot little number, for that HP, and people changing to it from
slower designs could have hardly ever have produced a real mean high speed
stall in their earlier planes, as most other designs of that HP and period
were close to 50% slower.

The stall strips were there to get the pilot's attention, earlier, before
they got into trouble.

Or so I recall reading.

Tomahawks just were nasty to handle in a stall, because of the T-tail way
out of the prop blast, and they need to stall earlier to keep elevator
control? I'm guessing about that one, just from what I have heard.
--
Jim in NC

"Morgans" wrote in message
...

snip

Tomahawks just were nasty to handle in a stall, because of the T-tail way
out of the prop blast, and they need to stall earlier to keep elevator
control? I'm guessing about that one, just from what I have heard.
--
Jim in NC



I recall the following story from the early 1970's.

It seems that the #2 American light aircraft manufacturer wanted to compete
with the Cezzna 150 so they built the little Axe prototype with a clean wing
using a nifty new NASA wing section and then asked some CFI's to fly it.
The CFI's said, "Nice little airplane - good performance and very
forgiving." "But, we think a trainer should spin more easily."

So, #2 modified their prototype with stall strips on the OUTBOARD wing
leading edge and asked the CFI's to fly it again. They said, "Man, will
that thing spin - nice trainer".

So, #2 laid off it's design team and built a bunch of Axes. However,
reports started coming in almost immediately of smoking craters as CFI's and
their students spun them in.

#2 needed a quick fix so, in the tradition of American Business Management,
it hired some consultants. The consultants looked in their "How to Fix an
Airplane" comic book for the section on "Bad Stall Behavior". The comic
book said, "Add stall strips to the INBOARD wing leading edge."

There was nothing in the comic book saying, "Remove outboard stall strips."

That's why the Axe has both inboard AND outboard stall strips - and why it
flies like an anvil.

Bill Daniels

wrote:
Sure you don't want the wing to stall before absolutely necessary, but
that is in effect what is done with having washout- making the inboard
section of the wing stall before it absolutely had to. They felt it
was preferable to do that so at the artificially early stall you'd
still have aileron control.


Not exactly accurate. It more like, you know the plane is going to
stall at some point, but you'd like the pilot to know about it before it
happens. The twist lets the lift drop out slowly as the wing begins to
buffet. Before the spin happens, it is hoped that the pilot will have
awakened and lowered the nose a little.

wrote:
Sure you don't want the wing to stall before absolutely necessary, but
that is in effect what is done with having washout- making the inboard
section of the wing stall before it absolutely had to. They felt it
was preferable to do that so at the artificially early stall you'd
still have aileron control.

Yeah -- to put it another way: Putting down an aileron effectively
raises the angle of attack of the outboard part of the wing. So, if you
are near the stall, aileron movement causes the outboard part of the
up-going wing to stall, dropping that wing.

A bit of washout will cure this bad behaviour by having both wings stall
at about the same time.

Frank

Tomahawks just were nasty to handle in a stall, because of the T-tail way
out of the prop blast, and they need to stall earlier to keep elevator
control? I'm guessing about that one, just from what I have heard.
--
Jim in NC


Gotta dispel this myth. As the former owner of a T-tail airplane, I can
assure you that the traumahawk's troubles were not merely the result of a
T-tail. The overall design just was not that good.

T-tail vs. Cruciform is just like high vs. low wing.

Piper wanted a T-tail because they thought it would sell more planes. Had
they wanted a high wing I suspect at the time they would have done just as
poorly. You can't just move the horizontal stab and attach it differently
any more than you can do so with the wings. They did, and it didn't work
well.