if you have read them, why don't you understand them?

wait a minute! just yesterday you were claiming to make your living as a"fluid
flow" expert, as in a plumber fixing toilets. Change careers since then?

Unmasked at last! After all these years! Yep, I'm an idiot and a fraud who
can't read, and I nearly got away with it for my whole career! Damn. Just
make me a promise - don't tell my department head. Please? OK?
You win, I can't possibly compete in this battle of the minds.
(Just a tiny little secret between us - I happen to have Richard Feynman's
works, papers and lectures in a book case about three feet behind me and
have read them all. So what?)

"JAXAshby" wrote in message
...
derek, you are idiot who can't read. Accept what I said, along with what
Feynman said, or not. your choice, but I will suggest that should you
decide
from your own totally ignorant knowledge base on the subject that everyone
in
sight will consider you an idiot.

now, dereck, should you wish to continue to look foolish do not bother to
ask
who Feynmann was.

I have no intention of getting into a fight here - but I didn't see
anywhere in my post, that which you claimed I said, nor do I ask you to
teach me anything. The point is simply that when somebody makes a claim
about a physics, as you have in a previous thread concerning steering
ability in reverse, that person should be able to back up that claim by
pointing to references or giving the fundamentals behind the assertion.
Give me a reasonable explanation and I'll accept what you say.
I suggest the following experiment that may settle the debate. Take
a
battery powered toy boat and fix it to a mid-hull pivot so that it can
rotate but not move forward or back. Place it in the bathtub. Examine
the
effects of rudder angle in both forward and reverse on the rotation (yaw)
of
the boat. Eliminate the effects of prop-walk by looking for changes
with
rudder angle. My prediction: a small but measurable effect in reverse -
much
more pronounced in forward. I built such a boat for my grandson when he
was living with us last year - if I can find it I'll try it this
afternoon.
Now here's my simplified argument (in words not math). The turning
torque exerted on a boat comes about from fluid flow across the offset
rudder, generating lift,drag, etc. The flow might come from 1) boat
motion
forwards or backwards, 2) currents, either global (around the hull) or
local
(just around the rudder). Of course the effects will not be identical
when
the keel/hull is taken into account.
There seems to be no argument about what happens in forward - a
"plume"
of flow, albeit with turbulence and vortices etc, will flow aft over the
rudder and the asymmetry of the flow over the two sides will exert a
torque
to turn the boat - even when the boat is not moving.
In reverse, that "plume" is directed forward along the keel, and the
question becomes: what is the flow pattern aft of the propellor, and is
any
localized flow taking place over the rudder? Flow is continuous ie
in-flow
= out-flow. But to answer the turning question we must determine whether
how much flow comes in to the propellor circumferentially and how much
axially, and more importantly - how far aft any axial flow pattern
exists.
The answer will all depend on the geometry of the boat, what the distance
is
between the rudder and the propellor, the existence of a skeg, blade
geometry of the propellor etc. On my present boat the propellor is a
long way from the skeg hung rudder and I have very little turning ability
in
reverse until I really get moving. At low speeds the dominant turning
effect is the windage of the hull, and the wind will determine which way
she
will turn regardless of the helm. (That has caused some really
interesting
situations backing out of the slip.) On my previous boat, however, the
propellor was much closer to the balanced rudder and I could swing the
stern
either way with no way-on with a burst of reverse and the helm over. I
didn't have to worry about prop-walk at all on that boat, I had great
control in reverse.
So the answer is - there is no answer.


"JAXAshby" wrote in message
...
derek, you show yourself to be a fraud when you write that you a.) have
no
idea
whatsoever as to what "asymetrical thrust" is, and b.) you can't see
where
the
dynamics of fluid flow in air has anything to do with the dynamics of
fluid
flow in water.

derek, it is not my job to teach you the basics of what you profess to
be
your
area of expertise.

did you say you teach at DeVry?

You know, some of us here actually spend their professional lives
studying
and teaching the laws of fluid dynamics, fluid mechanics, physics,
etc.
You would do your cause a great deal of good if you were to provide a
few
basic principles to support your claims, you know the sort of thing:
conservation laws, momentum exchange, torque and force balances,
basics
of
aero/hydrodynamic interactions at inclined surfaces, lift, drag,
circulation
flow etc. How about just writing a few basic equations for us? You
can
solve the continuum problem if you like, or I'll even settle for a FEM
(Finite Element Model) numerical analysis. I would be delighted to go
over
your analyses with my colleagues, who knows - we might just get a
paper
in a
respected journal out of this, because your arguments sound like we
might
be
on to a brand new phenomenon that has evaded all us scientists and
engineers
for centuries.
I look forward to you publishing your quantitative arguments here
for
us
all to read, analyze and digest.
I promise I won't be rude to you like some of those other nasty,
ignorant
people on this board.

With the very best and kindest of wishes,
Derek Rowell
p.s For the life of me I can't see the conection between the aircraft
article and boats in reverse. Oh well...

"JAXAshby" wrote in message
...
from aircraft, but the same happens on boats, just not as
catastrophically

http://www.mindspring.com/~cramskill/propefct.htm