Dutch Roll

"Cub Driver" wrote in message
...
It's also properly
used for the motion of a ship with a following sea.

Actually, a ship with a following sea pitches up and down, and in the
worst case is pooped.

A ship with a sea off the stern wallows, but is still pitching. It's a
corkscrew motion, say rolling to port while diving down, then rolling
to starboard while climbing up. Very sick-making.

Whoa there Dan, you're beginning to sound a little like Douglas Eagleson!

Allen

Todd Pattist wrote

The term is correctly used for both the intentional flight
maneuver that you think he's thinking of (alternating motion
on the roll axis without corresponding yaw) and the dynamic
instability problem you describe below.

Neither of my three Flight Instruction manuals, Jeppesen, FAA,
and Kershner make any mention of a "Dutch Roll" co-ordination
maneuver.

From http://www.mountainflying.com/adverse2.htm

Adverse Yaw - 2
TRAINING MANEUVER
(This is sometimes improperly called a "Dutch roll")
A training maneuver, called the training roll or coordination roll,
is often introduced early during primary flight training to teach
the pilot to cope with adverse yaw. It is mostly forgotten after
the private certificate is obtained. Many instructors consider the
training roll maneuver to be of greater importance in teaching some
one to fly than chandelles, lazy eights, or other commercial pilot
maneuvers. A pilot getting into a different airplane can determine
the amount of rudder that is required for proper coordination with
the ailerons by using this maneuver.
-------------------------------------------------------------------

From William Kershner's "The Flight Instructor's Manual"

And, for Pete's sake, don't call this maneuver a "Dutch roll."
Dutch roll, a stability and control term, is a condition of a
coupling of lateral-directional oscillations with the nose yawing
as the airplane rolls from bank to bank; the object here is to
keep the nose on the point."
--------------------------------------------------------------------

Bob Moore

I just asked my daughter the blue-water sailor about this. She never
heard of Dutch roll, but thought it perhaps came from the motion of a
round-bottomed boat popular when the Dutch ruled the ocean waves
(think Henry Hudson).

She confirmed that a boat can oscillate off a set heading in certain
combinations of wind and wave. Sometimes, she said, it might be
impossible to steer 210 without moving the wheel constantly. But if
you change to 212, you can hold the course just fine.

She called the motion fishtailing

On Mon, 03 May 2004 17:04:16 -0400, Cub Driver
wrote:

It's also properly
used for the motion of a ship with a following sea.

Actually, a ship with a following sea pitches up and down, and in the
worst case is pooped.

A ship with a sea off the stern wallows, but is still pitching. It's a
corkscrew motion, say rolling to port while diving down, then rolling
to starboard while climbing up. Very sick-making.

I never though of either motion as a Dutch roll, and it is not really
similar to Dutch roll in an aircraft.

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

Cub Driver wrote:

I just asked my daughter the blue-water sailor about this. She never
heard of Dutch roll, but thought it perhaps came from the motion of a
round-bottomed boat popular when the Dutch ruled the ocean waves
(think Henry Hudson).

Yes, that's the origin. The Dutch had a need for large
cargo and shallow draft, so Dutch-built ships tended to
perform a pronounced pitch-yaw-roll motion in following
seas. It's the origin of the "Dutch Roll" label used in
aerodynamics.
Todd Pattist
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

"Julian Scarfe" wrote in message ...
"Todd Pattist" wrote in message
...

Language has a tendency to go its own way and get labeled as
correct or incorrect after the fact :-)

I spent a while writing the physics bit of the New Penguin Dictionary of
Science. The hardest part was knowing whether to be prescriptive (tell them
what the usage *should* be) or descriptive (describe what the common usage
*is*). It's a judgement call in almost every case -- for example, I had no
qualms about defining "weight" quite carefully to distinguish it from
"mass", even though many people say "weight" when they mean "mass".

You are confused if you think you made a correct "should be" call on
this.

When we say our bag of sugar has, as it might be labeled in the U.S.,
a "net weight" of 10 lb (4.54 kg), where the pound is of course a unit
of mass officially defined as 4.5359237 kg, that is absoloutely
correct and proper, well justified in linguistics, in history, and in
the law.

That's the original meaning of the word "weight," which entered the
English language meaning the quantity measured with a balance, used to
measure goods sold by weight in commerce. We measures mass, as that
term is used in physics jargon today, with a balance--not the force
due to gravity. Of course, they couldn't have called this "weight" by
today's physics term, because "mass" didn't have that meaning until
half a millennium or thereabouts after "weight" had this meaning.

In other words, it isn't a case of us saying the wrong thing. We mean
to say "weight"; we mean "weight" in a quite legitimate and proper
meaning of the word; it just happens to be the same quantity that
physicists happen to call "mass" in their jargon--but we don't
normally "mean" something different from what we "say."

You can argue that we should give up this word, to which we have a
prior claim by about 800 years, if you want to. But if you are too
stupid to realize that these are indeed *different meanings* in the
first place, then you will never expend the effort that would be
needed to accomplish this change.

Furthermore, if you hope to accomplish this change, you had darned
sure better offer us a verb as well as a noun, something we can utter
in public without embarrassing ourselves. Currently, there is a
difference between the use of the noun "weight" with different
meanings each used fairly consistently in different contexts, and the
verb "to weight" which is correctly used in any context to mean "to
determine the mass of" or "to have a mass of" as well as the "to exert
a force due to gravity of." That verb and noun distinction is
expressed fairly clearly in The National Standard of Canada,
CAN/CSA-Z234.1-89 Canadian Metric Practice Guide, January 1989:

5.7.3 Considerable confusion exists in the use of the term "weight."
In commercial and everyday use, the term "weight" nearly always means
mass. In science and technology, "weight" has primarily meant a force
due to gravity. In scientific and technical work, the term "weight"
should be replaced by the term "mass" or "force," depending on the
application.

5.7.4 The use of the verb "to weigh" meaning "to determine the mass
of," e.g., "I weighed this object and determined its mass to be 5 kg,"
is correct.

end quote

More on the noun usage:

NPL FAQ
http://www.npl.co.uk/force/faqs/forcemassdiffs.html

Weight
In the trading of goods, weight is taken to mean the same as mass, and
is measured in kilograms. Scientifically however, it is normal to
state that the weight of a body is the gravitational force acting on
it and hence it should be measured in newtons, and this force depends
on the local acceleration due to gravity. To add to the confusion, a
weight (or weightpiece) is a calibrated mass normally made from a
dense metal, and weighing is generally defined as a process for
determining the mass of an object.

So, unfortunately, weight has three meanings and care should always be
taken to appreciate which one is meant in a particular context.

end quote

NIST Guide for the Use of the International System of Units (SI)
http://physics.nist.gov/Pubs/SP811/

Thus the SI unit of the quantity weight used in this
sense is the kilogram (kg) and the verb "to weigh" means
"to determine the mass of" or "to have a mass of".

Examples: the child's weight is 23 kg
the briefcase weighs 6 kg
Net wt. 227 g



Gene Nygaard

(SelwayKid) wrote:
So what is your understanding of a Dutch Roll?

Mmmmm.... Duuuutch Rooooool

I'd like to throw my 2 cents into this scholarly disucssion.
The device which dampens the yaw is called a yaw damper, not a yaw dampener.
There, I feel better.

On 4 May 2004 06:11:13 -0700, (Gene Nygaard)
wrote:

In other words, it isn't a case of us saying the wrong thing. We mean
to say "weight"; we mean "weight" in a quite legitimate and proper
meaning of the word; it just happens to be the same quantity that
physicists happen to call "mass" in their jargon--but we don't
normally "mean" something different from what we "say."

I have the same problem with Down Syndrome, Hansen's Disease, and
other politically correct terms that have been imposed on me over the
years.

Nice argument, by the way!

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

I just asked my daughter the blue-water sailor about this. She never
heard of Dutch roll, but thought it perhaps came from the motion of a
round-bottomed boat popular when the Dutch ruled the ocean waves
(think Henry Hudson).

Okay, last night I asked my son-in-law. He pointed out that if there
is anything bad in nautical usage, it gets the adjective Dutch. (Not
just nautical, I suppose. There is also Dutch treat, which was
considered de trop when I was a lad but which has since evidently
become acceptable.)

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

Hmmm, a trisomy 21 defect patient with leprosy who is a facile typist of
complex prose - I'm impressed...

dr. denny

"Cub Driver" wrote in I have the same problem
with Down Syndrome, Hansen's Disease, and
other politically correct terms that have been imposed on me over the
years.