"cavelamb" wrote in message
m...

Can we at least agree that the floating boat actually does raise the water
level?

Absolutely. To the same extent that lighting a match increases global
warming. ;-)
--
KLC Lewis

WISCONSIN
Where It's So Cool Outside, Nobody Stays Indoors Napping
www.KLCLewisStudios.com

KLC Lewis wrote:
"cavelamb" wrote in message
m...
Can we at least agree that the floating boat actually does raise the water
level?

Absolutely. To the same extent that lighting a match increases global
warming. ;-)


Actually, KC, it took considerably more energy to MAKE that match
than it gives off.

Entropy is still increasing.

On Tue, 29 Sep 2009 07:02:36 -0700 (PDT), Roger Long
wrote:

On Sep 29, 7:32*am, Goofball_star_dot_etal
wrote:

There are numerous examples of equating inconsistant units. Here is one
example of gobeldygook:

The reaction to these presentations on the web is always the same.
The professionals, especially teachers, like them and they gather all
sorts of nit picks from others. That particular bit of gobeldygook
came from an article published in a leading aviation Emagazine and,
last I heard, was being used as an introduction to the subject in at
least one college course.

These are not intended to be physics texts. There are plenty of
those. The intent is to provide a plain language viceral
understanding of the basic principles. Units and terms most
recognizable to the reader with little prior knowledge are preferable
in a quick and light treatment.

Why this kind of thing worthwhile? I've had a whole career (I'm
hardly "budding") to watch people with naval architectural degrees and
complete understanding of the math and unit consistency come to
really bone headed conclusions that have greatly hampered the
commercial and educational sail industries because they didn't start
with a gut understanding of the physics and let numbers and anal
attention to unit consistency lead them to absurd conclusions. If
they had first understood the subject on this kind of level, they
might have made better use of the mathematical tools. Most college
courses and texts start right off with the math.

These articles are just starting points and not intended to be much
above the level of Sunday newpaper supplement stuff. Professionals
tend to see them for what they are and their limited value and net
posters as opportunities to show how smart they are. Happy to have
provided the opportunity.


Roger, you appear to be re-inventing the wheel. Here is the definition
of buoyancy taken from the Webster dictionary - note the edition date:

2. (Physics) The upward pressure exerted upon a floating body
by a fluid, which is equal to the weight of the body;
hence, also, the weight of a floating body, as measured by
the volume of fluid displaced.
[1913 Webster]

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

On the capsize issue, it seems to me that this should be addressed the same way
that the FAA did for load limits (G factors).

Differentiate by heeling moments - ie sail area and wind strength.

Rather than trying to say that a particular layout is "safe", determine the
allowable wind strength for different sail arrangements.

Top sails, sky sails and lighter kites for lighter conditions and strip down
for higher (Or Rated) winds.

On Sep 29, 8:12*pm, Bruce In Bangkok
wrote:

Roger, you appear to be re-inventing the wheel.

I sure hope I am. There isn't supposed to be anything new here.
We're talking about physics after all. It's just supposed to be an
entertaining discussion that makes the subject a bit more accessible
than a physics textbook and emphasizes points that I have encountered
a lot of confusion about, even among people who have advanced
degrees. Read through to the last section. The situation with
sailing vessels arose because USCG naval architects understood all the
math (and how to keep their units consistent but never held in their
mind a gut level understanding of what the number actually represented
and who boats act in the real world.

--
Roger Long

On Sep 29, 11:04*pm, cavelamb wrote:
On the capsize issue, it seems to me that this should be addressed the same way
that the FAA did for load limits (G factors).

Differentiate by heeling moments - ie sail area and wind strength.

Rather than trying to say that a particular layout is "safe", determine the
allowable wind strength for different sail arrangements.

Top sails, sky sails and lighter kites for lighter conditions and strip down
for higher (Or Rated) winds.

That actually doesn't work. The real issue, which has never been
addressed properly by regulation, is unexpected wind increases and the
rate of vessel response. Having the proper sail set for a specific
wind velocity isn't going to make you safe if there is a squall
bearing down that you are not prepared for. Current USCG regulations
for sailing passenger vessels will let you have a vessel that can be
capsized by that squall by reducing the sail plan to an unusably small
area for normal conditions. At the same time, the will prevent the
certification, in many cases, of a vessel that would be knocked down
by the squall but recover without flooding. It's crazy. Be sure to
read the last section of the stability site.

Sail area is only one of several factors effecting heeling moment.
Siimple course changes that create luffing cause dramatic reductions
in heeling moment as any sailor knows. So does easing sheets and
reefing.

Every properly operated sailboat on the wind will have its sailplan
and trim adjusted to bring it to a normal heel angle. There is then
some larger angle at which bad things can happen such as water
entering open hatches or capsizing in the case of the wide flat
vessels the USCG rules favor. It is the margin between those two
angles, and its relationship to the possible speed of response to
sudden wind increases that is the critical factor. This is
independent of the total sail area. Sailing at 10 degree heel with a
large sail plan in a 15 knot wind that suddenly doubles in strength is
very much the same as sailing at the same angle with a sail reduced by
reefing or striking individual sails in a 30 knot wind that suddenly
doubles in strength. Proper regulation might require sail reductions
at some specifice heel angle as SOP and would insure sufficient margin
between this angle and the angle of downflooding or capsizing. This
is independent of the maximum total sail that might be carried. It's
a matter of hull design, not sail plan. USCG rules let you operate,
and indeed even promote the operation, of dangerous hulls with total
sail area restrictions that are irrelevant to actual safety in the
winds where accidents are most likely to occur.

All of this is very statistical and you can only get a handle on what
is required by population analysis of a large number of vessels that
draws a line between the ones that have capsized and those that have
not. One of the few intelligent things the Coast Guard did in the
history of sail regulation was recognize this fact and attempt such an
analysis. Unfortunately, they couldn't find data on any capsizes so
they just threw a lot of absurd dynamic theory at the problem and came
up with a mess that plagues large sailing vessel regulation to this
day. I conducted a much larger population study in the early 1980's
for the USCG and ASTA joint task force on sailing school vessel
regulations. We had data on vessels that had capsized by that time so
we were able to justify some improvements in the regulation of
educational vessels but it was no help to the commercial fleet that
still operates under the original crazy criteria. We still had to
work within the existing USCG methods though so sailing school vessels
still have the flawed emphasis on total sail area.

I took all the data I had at hand as a result of this project and
performed another population analysis that evaluated only hull
characteristics and put no restrictions on total sail that could be
carried or even measured sail plan at all. This created the same,
actually better, distinction between successful vessels and casualties
than the application of the USCG methods. A draft of this paper sent
to a friend and fellow researcher in England led to many of the
principles being incorporated in their much more rational set of
regulations for large sailing vessels. I got too busy though trying
to make a living, keep my business going, and start being a father to
ever finish up the paper for publication.

--
Roger Long

Roger Long wrote:
On Sep 29, 11:04 pm, cavelamb wrote:
On the capsize issue, it seems to me that this should be addressed the same way
that the FAA did for load limits (G factors).

Differentiate by heeling moments - ie sail area and wind strength.

Rather than trying to say that a particular layout is "safe", determine the
allowable wind strength for different sail arrangements.

Top sails, sky sails and lighter kites for lighter conditions and strip down
for higher (Or Rated) winds.

That actually doesn't work. The real issue, which has never been
addressed properly by regulation, is unexpected wind increases and the
rate of vessel response. Having the proper sail set for a specific
wind velocity isn't going to make you safe if there is a squall
bearing down that you are not prepared for. Current USCG regulations
for sailing passenger vessels will let you have a vessel that can be
capsized by that squall by reducing the sail plan to an unusably small
area for normal conditions. At the same time, the will prevent the
certification, in many cases, of a vessel that would be knocked down
by the squall but recover without flooding. It's crazy. Be sure to
read the last section of the stability site.


I think I get your point now.

FAR 25, which covers load factors and gust loading in commercial aircraft
doesn't have to deal with flooding and the resultant stability changes!

Roger Long wrote:
On Sep 29, 7:32 am, Goofball_star_dot_etal
wrote:

There are numerous examples of equating inconsistant units. Here is one
example of gobeldygook:

The reaction to these presentations on the web is always the same.
The professionals, especially teachers, like them and they gather all
sorts of nit picks from others. That particular bit of gobeldygook
came from an article published in a leading aviation Emagazine and,
last I heard, was being used as an introduction to the subject in at
least one college course.

These are not intended to be physics texts. There are plenty of
those. The intent is to provide a plain language viceral
understanding of the basic principles. Units and terms most
recognizable to the reader with little prior knowledge are preferable
in a quick and light treatment.

Why this kind of thing worthwhile? I've had a whole career (I'm
hardly "budding") to watch people with naval architectural degrees and
complete understanding of the math and unit consistency come to
really bone headed conclusions that have greatly hampered the
commercial and educational sail industries because they didn't start
with a gut understanding of the physics and let numbers and anal
attention to unit consistency lead them to absurd conclusions. If
they had first understood the subject on this kind of level, they
might have made better use of the mathematical tools. Most college
courses and texts start right off with the math.

These articles are just starting points and not intended to be much
above the level of Sunday newpaper supplement stuff. Professionals
tend to see them for what they are and their limited value and net
posters as opportunities to show how smart they are. Happy to have
provided the opportunity.

--
Roger Long

The point is not that I am a "clever clogs" but that you publish stuff
as an "expert" and get it plain wrong. As it happens I am just "an oily
rag".

The vertcal force on an airfoil (lift) is equal to vertcal *rate of
increase of momentum* of the surrounding air. Not displacement, work or
anything else.

Force has the dimensions (MLT-2) the same as Mass (M) times acceleration
(L-2) (from F=ma)or the same as mass flow rate (MT-1) times velocity
(LT-1). M represents Mass, L length and T time. 1/T^2 is represented as
T-2 etc.

In the case of airfoils, turbines etc. there is not a fixed mass but a
mass flow. It is a lot easier to measure the pressures over an airfoil
than the increasing momentum of the air but they are two sides of the
same coin.

No work is done on a plane in level fight at constant speed. Its
potential energy is not increasing with height and its kinetic energy is
not increasing with velocity. The lift is equal to its weight and its
drag is equal to the thrust. All the power ends up heating the air,
although initially some goes into increasing the kinetic energy of the
air you cannot get at this number by looking at the lift, as you
suggest, since kinetic energy and momentum are not the same thing.

Context re-inserted:

"Note the net downwards displacement of the air. The essence of all
Newtonian physics is the symmetry of energy conservation (the equal and
opposite reaction business). The work done by accelerating the mass of
air downwards is exactly equal to the work required to keep the aircraft
aloft. The work required to shift it from left to right in the
animations is an important aspect of the drag that the engine must
overcome."

http://www.rogerlongboats.com/Circulation.htm

Goofball_star_dot_etal wrote:

/snip/
No work is done on a plane in level fight at constant speed. Its
potential energy is not increasing with height and its kinetic energy is
not increasing with velocity. The lift is equal to its weight and its
drag is equal to the thrust. All the power ends up heating the air,
although initially some goes into increasing the kinetic energy of the
air you cannot get at this number by looking at the lift, as you
suggest, since kinetic energy and momentum are not the same thing.


Hmmmm. a mostly reasonable review - but the idea that force times
distance is not equal to work is somewhat radical, don't you think?

And if the force (usually called thrust in this context,)which was
provided to oppose the drag on the plane due to its airspeed, is
multiplied with the airspeed rather than some air distance - the work
becomes the power expended in opposing drag.

But you knew that, I'm sure - you were just trying to provide a gut feel
for the physics, huh? :-)

Brian W

brian whatcott wrote:
Goofball_star_dot_etal wrote:

/snip/
No work is done on a plane in level fight at constant speed. Its
potential energy is not increasing with height and its kinetic energy
is not increasing with velocity. The lift is equal to its weight and
its drag is equal to the thrust. All the power ends up heating the
air, although initially some goes into increasing the kinetic energy
of the air you cannot get at this number by looking at the lift, as
you suggest, since kinetic energy and momentum are not the same thing.


Hmmmm. a mostly reasonable review - but the idea that force times
distance is not equal to work is somewhat radical, don't you think?


I said no work was done *on the (air)plane*. Since we only have the
airplane and the air, the work done by the thrust of the engine moving
the airplane through a distance all goes into the air as (kinetic)
energy or heat in its wake.

And if the force (usually called thrust in this context,)which was
provided to oppose the drag on the plane due to its airspeed, is
multiplied with the airspeed rather than some air distance - the work
becomes the power expended in opposing drag.

But you knew that, I'm sure

True.

- you were just trying to provide a gut feel
for the physics, huh? :-)

No I was responding to Roger's statement:

"The work done by accelerating the mass of air downwards is exactly
equal to the work required to keep the aircraft aloft"

I think he meant "force" but it is difficult to tell..