Dutch Roll

[SelwayKid]

So what is your understanding of a Dutch Roll? It is interesting to me
the various understandings of this manuever, how it is performed and
its origins.
I've got my own that I was taught by a CFI over 45 years ago and have
taught to virtually every student I've had over the years, including
helicopters.
Ol Shy & Bashful CFI - Airplanes and Rotorcraft Helicopters,
Instrument Rotorcraft and Airplanes, Multiengine, Gold Seal (1967)

[Bob Moore]

(SelwayKid) wrote

> So what is your understanding of a Dutch Roll? It is interesting to me
> the various understandings of this manuever, how it is performed and
> its origins.
> I've got my own that I was taught by a CFI over 45 years ago and have
> taught to virtually every student I've had over the years, including
> helicopters.

Well....a Dutch Roll is probably not what you understand it to be,
particularly if you have not flown swept-wing transport aircraft.
The aileron/rudder drill sometimes taught to student pilots is not
a Dutch Roll.

Copied from the following web site:

http://142.26.194.131/aerodynamics1/Stability/Page5.html

Dutch Roll
Many swept wing aircraft suffer a dynamic instability problem known as
Dutch Roll.

Dutch roll happens when the aircraft has relatively strong static
lateral stability (usually due to the swept wings) and somewhat weak
directional stability (relatively.) In a Dutch roll the aircraft begins
to yaw due to a gust or other input. The yaw is slow damping out so the
aircraft begins to roll before the yaw is stopped (due to the increased
speed of the advancing wing and the increased lift due to the swept wing
effect.)

By the time the yaw stops and begins to swing back toward zero slip the
aircraft has developed a considerable roll rate and due to momentum plus
the slip angle the aircraft continues to roll even once the nose has
begun returning to the original slip angle.

Eventually the yaw overshoots the zero slip angle causing the wings to
begin rolling back in the opposite direction.

The whole procedure repeats, sometimes with large motions, sometimes
with just a small churning motion. Like all dynamic stability problems,
Dutch roll is much worse at high altitudes where the air is less dense.

Dutch roll is almost certain to happen in a jet aircraft if the Yaw
dampener is turned off at high altitude. Therefore, the first thing to
check if an aircraft begins to exhibit Dutch roll is that the Yaw
Dampener is on. The pilot should then try to minimize the yawing
oscillations by blocking the rudder pedals (i.e. hold the rudder pedals
in the neutral position.) Next apply aileron (spoiler) control opposite
to the roll. The best technique to use is short jabs of ailerons applied
opposite to the roll. Try to give one quick jab on each cycle (i.e. turn
the wheel toward the rising wing, then return it to neutral.) Finally
accelerate to a higher speed, where directional stability will be
better, or descend into more dense air, for the same reason.

Bob Moore
ATP B-707 B-727
FI Airplanes/Instruments

[Todd Pattist]

Bob Moore > wrote:

>Well....a Dutch Roll is probably not what you understand it to be,
>particularly if you have not flown swept-wing transport aircraft.

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


Todd Pattist
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

[Greg Esres]

<<The term is correctly used>>

Can you specify on what basis you determine that the term is used
"correctly"?

It's true that the piloting community uses "Dutch Roll" in the way the
OP did, but the piloting community uses lots of words with implied
meanings at odds with the aerodynamic literature. This usage
interferes with their ability to gain a more sophisticated
understanding later on, due, I suppose, to the law of primacy.

I agree with Bob Moore (and Bill Kershner, et al) that Dutch Roll
shouldn't be used in this context.

[Darrell]

Dutch roll is roll due to yaw in a swept wing aircraft. It is more
pronounced than that experienced in a relatively straight wing aircraft.
Also, since swept wing aircraft are more frequently flown at high altitudes
where the air is thinner and mach transitions can occur it is generally
considered only a swept wing phenomenon. see
http://142.26.194.131/aerodynamics1/Stability/Page5.html

--

B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"SelwayKid" > wrote in message
m...
> So what is your understanding of a Dutch Roll? It is interesting to me
> the various understandings of this manuever, how it is performed and
> its origins.
> I've got my own that I was taught by a CFI over 45 years ago and have
> taught to virtually every student I've had over the years, including
> helicopters.
> Ol Shy & Bashful CFI - Airplanes and Rotorcraft Helicopters,
> Instrument Rotorcraft and Airplanes, Multiengine, Gold Seal (1967)

[Todd Pattist]

Greg Esres > wrote:

>Can you specify on what basis you determine that the term is used
>"correctly"?

Simply that it seems to be successfully used for both
meanings without any real confusion I can detect. CFI's
suggesting coordination exercises are using the OP's meaning
and aerodynamicists are talking about the dynamic
instability problem.

I suspect the OP had never heard the aerodynamic definition,
and the first reply he got assumed the same thing, so in
this group, it's likely to have the coordination exercise
definition. If you think it's "incorrect" while I think
it's "correct" that's interesting, but I suspect it's too
late to stop it from being used the way it is currently
being used, even if we wanted to.

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

BTW, do you think the coordination exercise label was
initially adopted by someone who'd heard of the aerodynamic
usage, but didn't understand it, or do you think they
developed independently?

>It's true that the piloting community uses "Dutch Roll" in the way the
>OP did, but the piloting community uses lots of words with implied
>meanings at odds with the aerodynamic literature. This usage
>interferes with their ability to gain a more sophisticated
>understanding later on, due, I suppose, to the law of primacy.

I didn't have any problem when I first learned of another
usage. I'd already learned the nautical usage, so the two
aviation usages were just added into the mix. I believe int
h law of primacy, but we're talking intellectual stuff here,
not how to react when your wing falls off :-)

>
>I agree with Bob Moore (and Bill Kershner, et al) that Dutch Roll
>shouldn't be used in this context.

Todd Pattist
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

[Greg Esres]

<< If you think it's "incorrect" while I think
it's "correct" that's interesting, >>

No, no, just "non-standard". "Correct" is a fuzzy term. ;-)

<<BTW, do you think the coordination exercise label was
initially adopted by someone who'd heard of the aerodynamic
usage, but didn't understand it, or do you think they
developed independently? >>

Hmmm....interesting question. Seems low probability they'd develop
independently. The originator of the term might well have understood
the stability use of the term, but since the motions bear a
resemblence to each other, might have used it anyway.

Actually, I had never heard of the term in a nautical sense (I'm not a
boater.) Given that boating is older than aviating, seems more likely
that the term was originally use to describe a motion without regard
to its origin. (Or is the boating use a stability issue too?)

But now that it exists as a stability issue in aviation, it seems
prudent to use it only in that sense. I can't tell you how many hours
of confusion it has caused me in the past when the author of an
aerodynamics text used a word carelessly and sent me along dead-end
trails.

Possibly an analogy is the description of the 4 left-turning
tendencies of an airplane. Collectively they're often called
"torque", but only one is caused by the torque of the engine, and is
also called torque. So is calling p-factor "torque" incorrect? Not,
I suppose in the sense that it creates torque around the vertical
axis, and the engine torque creates torque around the longitudinal
axis. But this generated ambiguity in the word "torque" makes it a
bit confusing to talk about the subject.

[Julian Scarfe]

"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". But
should I really make a fuss about the difference between "spectrograph" and
"spectrometer" when everyone uses the terms interchangeably?

I guess "Dutch Roll" is pretty close to the line.

Julian

[Todd Pattist]

"Julian Scarfe" > wrote:

>I guess "Dutch Roll" is pretty close to the line.

I encountered the term first in sailing. Then I ran into
the term used for the aviation coordination exercise and I
have to admit that it seemed odd as the motions weren't
really all that similar. Then I ran into the technical
aerodynamic usage, which describes a motion more similar to
the nautical motion. I suppose if I'd encountered the
technical aviation usage first, I might have felt the
coordination usage was "wrong," but I've never looked at it
like that. I've always seen it as the same adopted name for
two distinct things.

Todd Pattist
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

[Cub Driver]

>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

[Allen]

"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

[Bob Moore]

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

[Cub Driver]

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

[Todd Pattist]

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.

[Gene Nygaard]

"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

[Jim Buckridge]

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

Mmmmm.... Duuuutch Rooooool

[PS2727]

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.

[Cub Driver]

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

[Cub Driver]

>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

[Dennis O'Connor]

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.

[CV]

Gene Nygaard wrote:

> "Julian Scarfe" > wrote in message >...
>>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.

Well, perhaps you missed the fact that he was writing definitions for
a dictionary of _science_ ?

There is no conflict, really, between the call he made, in that context,
and the everyday meaning you go on to defend, and quite convincingly so.

> 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.

Absolutely.

> 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.

Not quite, though you have a point. What we measure with a balance
is the relationship of the force due to gravity of the object we
want to weigh, to that of a reference object of a known weight.
We are measuring relations between "weights", as the term is
understood in physics. To illustrate this, in the absence of gravity
we could not measure mass in this way (well, we might contrive a way
to use inertial forces, but we'd still be measuring forces).

Where you do have a point is in the sense that this method will give
consistent results whether performed on earth, on the moon, or in any
other gravitational field. Spring-based scales of course measure
absolute weight and will only give correct (mass) results in a
standard gravitational field eg. on the earth's surface.
In both cases we express the result in units of mass.

> 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."

Agreed. It's not really a case of either being wrong. It's just that
in physics there is a need to differentiate and keep the two concepts
apart, while in everyday life there is normally no such need.

Most people (even physicists, I imagine), quite correctly and
appropriately, say "weight" in everyday contexts, when referring
to something that is really "mass", as the concept is understood
in physics. They are not saying anything different from what
they mean. They are merely applying a level of differentiation
of concepts, appropriate to the situation at hand.

> 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.

If the weight and the gravitation are known, the mass can be determined,
so the above sentence is quite correct in any context, even as strictly
understood in physics.

CV

[GeorgeB]

On Wed, 05 May 2004 13:57:13 +0200, CV > wrote:

>Not quite, though you have a point. What we measure with a balance
>is the relationship of the force due to gravity of the object we
>want to weigh, to that of a reference object of a known weight.
>We are measuring relations between "weights", as the term is
>understood in physics.

There is another issue using this method ... in very critical work,
one compares the volumes of the 2 objects on a balance to correct for
the density of air. The air has lift as did Archimedes system to
determine if some crown was pure gold <g> (is that the coirrect
reference?)

[Don Tuite]

On Wed, 05 May 2004 21:51:30 -0400, GeorgeB > wrote:

>On Wed, 05 May 2004 13:57:13 +0200, CV > wrote:
>
>>Not quite, though you have a point. What we measure with a balance
>>is the relationship of the force due to gravity of the object we
>>want to weigh, to that of a reference object of a known weight.
>>We are measuring relations between "weights", as the term is
>>understood in physics.
>
>There is another issue using this method ... in very critical work,
>one compares the volumes of the 2 objects on a balance to correct for
>the density of air. The air has lift as did Archimedes system to
>determine if some crown was pure gold <g> (is that the coirrect
>reference?)

Yep, but I think you meant to say bouyancy.

Don

[Julian Scarfe]

> > 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".

"Gene Nygaard" > wrote in message
om...

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

I think you illustrate the dilemma rather well! Are there *any* correct
"should be" calls? If so, what makes them "correct"?

I would note however, the words "should be" in the passage below, which you
quote:

'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.'

:-)

Julian

[Gene Nygaard]

On Wed, 05 May 2004 13:57:13 +0200, CV > wrote:

>Gene Nygaard wrote:
>
>> "Julian Scarfe" > wrote in message >...
>>>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.
>
>Well, perhaps you missed the fact that he was writing definitions for
>a dictionary of _science_ ?
]
Yes, of science. NOt of the mechanics section of an introductory
physics textbook.

Furthermore, it is often easiest to explain a jargon meaning by
showing how that usage is distinguished from normal usage.

>There is no conflict, really, between the call he made, in that context,
>and the everyday meaning you go on to defend, and quite convincingly so.
>
>> 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.
>
>Absolutely.
>
>> 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.
>
>Not quite, though you have a point. What we measure with a balance
>is the relationship of the force due to gravity of the object we
>want to weigh, to that of a reference object of a known weight.
>We are measuring relations between "weights", as the term is
>understood in physics. To illustrate this, in the absence of gravity
>we could not measure mass in this way (well, we might contrive a way
>to use inertial forces, but we'd still be measuring forces).

Pretty strange notion of what it means "to measure" something.

If I have measured forces, then suppose I weighed a gold coin on one
of these balances at Hammerfest, Norway, and it weighed 19 dwt 20 gr
(nearly a troy ounce; the troy units of weight are always units of
mass, never units of force). How much force is it exerting due to
gravity?

Then I take it to Quito, Ecuador, and it weighs 19 dwt 20 gr. How
much force is it exerting due to gravity here, where the acceleration
of free fall is much less?

If it makes it easier for you, change that to 30.84 g. How much force
does it exert at each place?

If we've measured forces, you should be able to tell me that. But we
haven't "measured" these forces.

>Where you do have a point is in the sense that this method will give
>consistent results whether performed on earth, on the moon, or in any
>other gravitational field. Spring-based scales of course measure
>absolute weight and will only give correct (mass) results in a
>standard gravitational field eg. on the earth's surface.
>In both cases we express the result in units of mass.
>
>> 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."
>
>Agreed. It's not really a case of either being wrong. It's just that
>in physics there is a need to differentiate and keep the two concepts
>apart, while in everyday life there is normally no such need.

But the usage in commerce is much more consistent and uniform than the
usage in science.

>Most people (even physicists, I imagine), quite correctly and
>appropriately, say "weight" in everyday contexts, when referring
>to something that is really "mass", as the concept is understood
>in physics. They are not saying anything different from what
>they mean. They are merely applying a level of differentiation
>of concepts, appropriate to the situation at hand.
>
>> 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.
>
>If the weight and the gravitation are known, the mass can be determined,
>so the above sentence is quite correct in any context, even as strictly
>understood in physics.

Sure, introduce some new big "ifs" not in the original.

As in my example with the gold coin, usually the "gravitation" is not
known. Furthermore, "weighing" the object doesn't give you a "weight"
which is different from mass, as your statement assumes.

The statement in that standard is intended to reflect the fact that
chemists especially, and physicists as well, consider the use of the
verb form acceptable in situations were many would not accept using
the noun "weight" to express the result when they "weigh" something.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

[Greg Esres]

<<I think you illustrate the dilemma rather well! Are there *any*
correct "should be" calls? If so, what makes them "correct"?>>

Precise words => precise thoughts => precise understandings => precise
behavior.

Historical precedent be damned. ;-) Most of history is an example
of slopping thinking.

[Gene Nygaard]

On Thu, 06 May 2004 14:48:08 GMT, Greg Esres >
wrote:

><<I think you illustrate the dilemma rather well! Are there *any*
>correct "should be" calls? If so, what makes them "correct"?>>
>
>Precise words => precise thoughts => precise understandings => precise
>behavior.

So go find yourself a precise word.

Maybe you can borrow one from Norwegian; the physicists using that
language had more sense than those using English. They didn't choose
"vekt"--the cognate of the English "weight"--for their jargon word for
the force due to gravity. Instead, they chose an entirely different
word, "tyngde."

>Historical precedent be damned. ;-) Most of history is an example
>of slopping thinking.

The meaning of "weight" is much more consistent and uniform in
commerce than it is "in science."

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

[CV]

Gene Nygaard wrote:
>>Well, perhaps you missed the fact that he was writing definitions for
>>a dictionary of _science_ ?
>
> ]
> Yes, of science. NOt of the mechanics section of an introductory
> physics textbook.

Is physics not science ?

>>Not quite, though you have a point. What we measure with a balance
>>is the relationship of the force due to gravity of the object we
>>want to weigh, to that of a reference object of a known weight.
>>We are measuring relations between "weights", as the term is
>>understood in physics. To illustrate this, in the absence of gravity
>>we could not measure mass in this way (well, we might contrive a way
>>to use inertial forces, but we'd still be measuring forces).
>
> Pretty strange notion of what it means "to measure" something.
>
> If I have measured forces, then suppose I weighed a gold coin on one
> of these balances at Hammerfest, Norway, and it weighed 19 dwt 20 gr
> (nearly a troy ounce; the troy units of weight are always units of
> mass, never units of force). How much force is it exerting due to
> gravity?
>
> Then I take it to Quito, Ecuador, and it weighs 19 dwt 20 gr. How
> much force is it exerting due to gravity here, where the acceleration
> of free fall is much less?
>
> If it makes it easier for you, change that to 30.84 g. How much force
> does it exert at each place?
>
> If we've measured forces, you should be able to tell me that. But we
> haven't "measured" these forces.

Partly true. We have not measured their absolute values. We are not even
interested in them. We have measured the relationship between two forces,
which allows us to determine the mass.

We still depend on there being forces for this measurement to work.
Take your gold coin along on a flight on the Space Shuttle. In a
weightless state, your balance would not tell you anything, but
the coin would still have the same mass as in Hammerfest or Quito.

>>>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.
>>
>>If the weight and the gravitation are known, the mass can be determined,
>>so the above sentence is quite correct in any context, even as strictly
>>understood in physics.
>
> Sure, introduce some new big "ifs" not in the original.
>
> As in my example with the gold coin, usually the "gravitation" is not
> known. Furthermore, "weighing" the object doesn't give you a "weight"
> which is different from mass, as your statement assumes.

It might, and it might not, depending on the method of "weighing".
Use some kind of spring-based scales on your gold coin and it will.

> The statement in that standard is intended to reflect the fact that
> chemists especially, and physicists as well, consider the use of the
> verb form acceptable in situations were many would not accept using
> the noun "weight" to express the result when they "weigh" something.

Sure, an elaborate interpretation of what it was "intended to
reflect", to suit your purpose. Didn´t _someone_ just object
to introducing new stuff, not in the original ?

All the same, even in that context, those chemists and physicists
have a good reason for accepting one and not the other, which is
what my comment intended to point out.

CV

[Gene Nygaard]

On Fri, 07 May 2004 11:48:51 +0200, CV > wrote:

>Gene Nygaard wrote:
>>>Well, perhaps you missed the fact that he was writing definitions for
>>>a dictionary of _science_ ?
>>
>> ]
>> Yes, of science. NOt of the mechanics section of an introductory
>> physics textbook.
>
>Is physics not science ?

Sure. So what? That might be useful if you want to prove the meaning
we are discussing is _sometimes_ used in science. That's as far as
that logic gets you.

But if you look at the bigger picture, you don't have the consistency
you claimed. Not even in the rest of physics. Not even in real-world
application of those mechanics problems.

Yes, "weight" is sometimes used with that same meaning in other areas
in science. It is also used with other meanings in other areas of
science.

When I first learned about atomic weight, this was different in
physics than it was in chemistry--one based on the oxygen-16 isotope
having an atomic weight of 16, the other on the natural mixture of
oxygen on Earth having an atomic weight of 16.

Don't bull**** me about "molecular weight" and "atomic weight" not
being used any more. Just do a search of the Internet or of Usenet.
Go look at some of the thousands of periodic tables, many from
colleges and universities around the world, which give you the atomic
weight of the elements.

When the medical sciences talk about human body weight, they measure
mass in units of kilograms or pounds, not newtons and not kilograms
force and not pounds force.

It isn't any different if a zoologist talks about the weight of a
capybara or a hummingbird or an ostrich's egg.

What does weight mean when the NASA scientists and engineers tell us
that the weight of the Apollo 11 lunar module at liftoff of its ascent
stage was 10,776.6 lb? At the time, of course, it was only exerting a
force due to gravity of somewhere around 1800 lbf. This is normal
NASA usage; we still see it today in connection with the space
station. For the Apollo missions, NASA has recordings of the
conversations between astronauts and ground control in which the
astronauts are reading off these numbers, in those units of pounds
mass, and they are referring to this quantity as "weight" because
that's the way it was indicated on the readout from their onboard
computers.

An agronomist in the U.S. might use "bushels by weight" in assessing
the production from a test plot of soybeans. That is also "in
science."

Other scientists will measure "dry weight" of various quantities. It
is mass they are interested in, not force.

>>>Not quite, though you have a point. What we measure with a balance
>>>is the relationship of the force due to gravity of the object we
>>>want to weigh, to that of a reference object of a known weight.
>>>We are measuring relations between "weights", as the term is
>>>understood in physics. To illustrate this, in the absence of gravity
>>>we could not measure mass in this way (well, we might contrive a way
>>>to use inertial forces, but we'd still be measuring forces).
>>
>> Pretty strange notion of what it means "to measure" something.
>>
>> If I have measured forces, then suppose I weighed a gold coin on one
>> of these balances at Hammerfest, Norway, and it weighed 19 dwt 20 gr
>> (nearly a troy ounce; the troy units of weight are always units of
>> mass, never units of force). How much force is it exerting due to
>> gravity?
>>
>> Then I take it to Quito, Ecuador, and it weighs 19 dwt 20 gr. How
>> much force is it exerting due to gravity here, where the acceleration
>> of free fall is much less?
>>
>> If it makes it easier for you, change that to 30.84 g. How much force
>> does it exert at each place?
>>
>> If we've measured forces, you should be able to tell me that. But we
>> haven't "measured" these forces.
>
>Partly true. We have not measured their absolute values. We are not even
>interested in them. We have measured the relationship between two forces,
>which allows us to determine the mass.
>
>We still depend on there being forces for this measurement to work.
>Take your gold coin along on a flight on the Space Shuttle. In a
>weightless state, your balance would not tell you anything, but
>the coin would still have the same mass as in Hammerfest or Quito.

So you need to find a different tool when it doesn't work. A liquid
in glass thermometer won't work if it is so hot the glass melts, or so
cold the liquid freezes. But when it does work, we use it to measure
temperature.

NASA has found a different tool for the astronauts to use in weighing
themselves in space.

>>>>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.
>>>
>>>If the weight and the gravitation are known, the mass can be determined,
>>>so the above sentence is quite correct in any context, even as strictly
>>>understood in physics.
>>
>> Sure, introduce some new big "ifs" not in the original.
>>
>> As in my example with the gold coin, usually the "gravitation" is not
>> known. Furthermore, "weighing" the object doesn't give you a "weight"
>> which is different from mass, as your statement assumes.
>
>It might, and it might not, depending on the method of "weighing".
>Use some kind of spring-based scales on your gold coin and it will.

Okay, we've taken care of a couple of the simpler examples. Of
course, there's a reason you don't see gold buyers running around with
spring scales.

Now suppose I have one of those modern piezo-electric electronic load
cell scales, for use in commerce or for precise measurements in the
chemistry lab. Maybe it is used to weigh a bell pepper at the
supermarket, or a semi-load of wheat at the grain elevator, or a
package at the post office.

When it is set up, the manufacturer's representative makes sure that
it is set level, and goes "under the hood" to adjust it for use in
that location. It is, of course, the microprocessor that makes this
possible; making the adjustments is normally made more difficult than
it needs to be, to reduce that chances of tampering when no inspector
is around. He places a known test weight on the scale, and adjusts it
so that it reads the correct amount.

Then when a government inspector comes to test and certify the scale
(in commerce anyway--government doesn't worry about the chemistry
lab), this is done by placing test weights of known mass on the scale,
making sure that the readout is within the limits allowed for the
purpose for which it is used.

So what do those scales "measure"? They are tested and certified on
the basis of their accuracy in measuring mass in the very location in
which they are used, not on their accuracy in measuring force. We
never get any number we could assign to the precise amount of force
the weighed object does exert at that particular location.

Two such scales, properly calibrated, will give the same reading in
Hammerfest and in Quito. Properly adjusted force-measuring scales
would show a significantly different force due to gravity.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

[CHUCK ROAST]

Bob Moore > wrote

> Well....a Dutch Roll is probably not what you understand it to be,
> particularly if you have not flown swept-wing transport aircraft.
> The aileron/rudder drill sometimes taught to student pilots is not
> a Dutch Roll.

Well said Bob!

Chuck

[Teacherjh]

> The aileron/rudder drill sometimes taught to student pilots is not
> a Dutch Roll.

What is the proper name for that (other than "the aileron/rudder drill
sometimes taught to student pilots"

Jose

--
(for Email, make the obvious changes in my address)

[Achillus]

"Teacherjh" > wrote in message
...
> > The aileron/rudder drill sometimes taught to student pilots is not
> > a Dutch Roll.
>
> What is the proper name for that (other than "the aileron/rudder drill
> sometimes taught to student pilots"
>
> Jose
>
> --
> (for Email, make the obvious changes in my address)


5 proper names (acronyms) for that Dutch Roll aileron/rudder drill:


1. Dr Boffin's drill:

Stop Pilot Induced Occillation (SPIO)!


2. Miss Murphy's Drill:

Freeze Fingers & Feet (FF&F)!


3. Robby Robot's Drill:

Pleaze Engaze Yaw Damper (PEYD)!


4. Jack Ass's Drill:

Stop Stirring That Panhas (SSTP)!


5. Dutch Uncle's Drill:

U Betterr Stop Drrinking (UBSD)!

;-)