Buoyancy is Imaginary
 

On Oct 1, 11:36*am, Goofball_star_dot_etal
wrote:


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".

For the record: I have never claimed to be an expert on aerodynamics
and I'm not. I'm just a writer. I've also never claimed to have
"discovered" anything new about the subject as has often been
claimed. I wrote a couple of articles on the subject once that an
aviation magazine published and a professor of aerodynamics found
useful as an introduction to the subject.

I'll also agree BTW that the web page with the circulation animation
isn't very good. I'd forgotten it was there until you brought it up.
The text isn't from the article but something I threw together quickly
to present the animation (which is from wind tunnel photographs and
not my interpretation of any physics) when the question of flow around
sails came up here quite a while ago. The page isn't linked on my web
site and therefore not really "published". Some of your comments are
valid and I'm going to rewrite it if I ever decide to provide a direct
link to it.

--
Roger Long

Buoyancy is Imaginary
 

Roger Long wrote:
On Oct 1, 11:36 am, Goofball_star_dot_etal
wrote:

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".

For the record: I have never claimed to be an expert on aerodynamics
and I'm not. I'm just a writer. I've also never claimed to have
"discovered" anything new about the subject as has often been
claimed. I wrote a couple of articles on the subject once that an
aviation magazine published and a professor of aerodynamics found
useful as an introduction to the subject.

I'll also agree BTW that the web page with the circulation animation
isn't very good. I'd forgotten it was there until you brought it up.
The text isn't from the article but something I threw together quickly
to present the animation (which is from wind tunnel photographs and
not my interpretation of any physics) when the question of flow around
sails came up here quite a while ago. The page isn't linked on my web
site and therefore not really "published". Some of your comments are
valid and I'm going to rewrite it if I ever decide to provide a direct
link to it.

--
Roger Long


There is a lot to like about your animations and presentations. I
particulary like "Removancy". It is expressions like "energy forces"
that spoil it for me. It does not mean anything, outside perhaps a seance.

My home PC is bust so you will have peace over the weekend.

Work is not Imaginary (was Buoyancy is Imaginary)
 

Goofball_star_dot_etal wrote:
....
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.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

....but I won't beat the topic down....
:-)

Brian W

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Oct 2, 8:02*pm, brian whatcott wrote:
Goofball_star_dot_etal wrote:

...

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.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

...but I won't beat the topic down....
:-)

Brian W

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.
How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote:

How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.

There are limits to that. If you get knocked down hard enough and
fast enough, the boom will hit the water and prevent the mainsail from
being eased. That's where the fun starts, and some boats will tend
to stay on their beam ends once they get knocked flat with the mast in
the water.

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Oct 2, 8:42*pm, Frogwatch wrote:

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.

That was a huge issue and we did a lot of analysis on it back during
the sailing school vessel research in the early 80's. The sail and
rig forces caused by wave motion and rolling often exceed the forces
that would cause knockdown although only for brief periods. If you
put "fuses" in the rig, you would have stuff breaking constantly.

--
Roger Long

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote:

On Oct 2, 8:02*pm, brian whatcott wrote:
Goofball_star_dot_etal wrote:

...

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.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

...but I won't beat the topic down....
:-)

Brian W

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.
How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.


Not really a problem to design a boat that won't be knocked down. Good
form or ballast stability and a small rig.

Of course, as soon as the bloke buys this no-knock-down marvel he will
get a cruising gennaker, a storm spinnaker and fit a topmast so he can
fly a topsail. Probably it is impossible to build a vessel that is
impossible to knock down if the owner is in any way adventurous.

After all they once built an airplane that wouldn't spin and wouldn't
stall. It wasn't immensely popular.

Even full rigged ships quite frequently could send down their topmasts
in bad weather.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

Work is not Imaginary (was Buoyancy is Imaginary)
 

On Fri, 2 Oct 2009 17:42:17 -0700 (PDT), Frogwatch
wrote:

On Oct 2, 8:02*pm, brian whatcott wrote:
Goofball_star_dot_etal wrote:

...

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.

If I push a sled over snow with force F for distance D
it's usually accounted that the work I did ON the sled is F X D

...but I won't beat the topic down....
:-)

Brian W

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.
How many boats get knocked down anyway? I mean cruising boats, racers
intend to be on the edge. My own boat, a 28' S2, if a sudden gust
came up, I'd never be able to hold the tiller and she'd round up into
the wind before getting knocked down.

Guess again!

Work is not Imaginary (was Buoyancy is Imaginary)
 

Roger Long wrote:
On Oct 2, 8:42 pm, Frogwatch wrote:

In regard to sudden gusts, why not use a breakaway strap like some
rock climbers use whose stitches break at some load allowing the sail
to be let out all the way.

That was a huge issue and we did a lot of analysis on it back during
the sailing school vessel research in the early 80's. The sail and
rig forces caused by wave motion and rolling often exceed the forces
that would cause knockdown although only for brief periods. If you
put "fuses" in the rig, you would have stuff breaking constantly.

Most of the Nonsuch's (unstayed catboats) were built with aluminum masts
that tapered near the top. The marketing folks made a big point of how
the tip would flex to leeward and spill wind in gusts. Indeed, it
worked well and was helpful since it was easy to overpower the large
mainsail in gusty weather. (I learned to reef before going out, since
it was a lot easier to shake out than take in a reef!)

At the end of the production run they shifted to fiberglass masts that
were stiffer. The marketing folks stressed how this gave better
pointing ability in strong wind.