JAXAshby wrote in message
...
jim, the 'bernouli's" say the air is one unit at the leading
edge of the wing,
and because it travels a shorter distance along the straight
bottom surface
than the longer top surface it therefore means the air along
the top *had to*
speed up to "catch up" with the air on the bottom, therefore
less pressure.

Bernouilli may have said that. I didn't. And I like symmetrical
aerofoils, like rudders and keels, or ones that work well upside
down as well as the right way up.

This is not true. it does not HAVE to.

I'm not proposing that the air 'has to catch up'. I'm just saying
that if it loses pressure, it's got to gain speed (or disperse
energy in some other way).

The most efficient wing surface out there is a thin sheet
shaped into an "S",
with the top forward part of the "S" the leading edge and the
bottom rear part
the trailing edge.

Indentical distances for air to travel and the most lift
available for the
drag. (problem: andy particular "S" only works for one
airspeed)

Now I think the device you're proposing is designed to add a
downward speed to the air, then subtract that speed, leaving no
net change in downward speed. Is that correct? If so, you're
proposing that a net force can be generated by displacing air
through a distance, rather than adding momentum to it.
Interesting.

I haven't heard of this design in aerodymamics before except in
the context of windmills. I can see how such a device would
generate a magnificent torque (lift at the front, cancelled by
'anti-lift' at the rear). This torque would have to be stabilised
by a net lifting body on a lever arm for any practical
application. But I am very out of date in this subject, so a few
questions first:

Has it been written up anywhere?
Do you know any practical applications?

For sure, I wouldn't want to fly upside down with this one. Nor
use it for a keel.

Instead of thinking of "low" pressure and "high" pressure,
think of what low
and high means. high has more air molecules pressing against
the surface at
higher molecular speeds. low has fewer molecules and/or lower
molecular speed
of those molecules.

Yup. Got that. Brownian motion or some similar name and all that.
But I don't see what difference it makes.

To create lift (by changing the momentum of the passing air)
there must be low pressure above the wing compared to the
pressure below the wing.

reword this using impact of molecules instead of low/high
pressure and see what
happens.

Right:

'to create lift there must be fewer molecules at lower molecular
speeds above the wing compared to the higher number of molecules
at higher molecular speeds below the wing'.

So?

Jax, I hope you're not making the mistake of confusing the
temperature/pressure linked random motion of molecules with the
mean speed of a flow pattern!

My point remains: 'there are fewer molecules at lower [random]
molecular speeds above the wing' - so what did they sacrifice
their energy to? My argument is that it could only go to an
increased mean stream speed. Are you denying this? or am I out of
date here as well?

JimB

I haven't heard of this design ("S" shaped airfoils) in aerodymamics before
....

first semester aero eng books have had it for decades. It is not a practical
airfoil, but it shows why foils lift.

JAXAshby wrote in message
...
I haven't heard of this design ("S" shaped airfoils) in
aerodymamics before

Naughty Jax.

You've mis-quoted me by adding the bit in brackets. In full:

"Now I think the device you're proposing is designed to add a
downward speed to the air, then subtract that speed, leaving no
net change in downward speed. Is that correct? If so, you're
proposing that a net force can be generated by displacing air
through a distance, rather than adding momentum to it.
Interesting.

*I haven't heard of this design in aerodymamics before* except in
the context of windmills. I can see how such a device would
generate a magnificent torque (lift at the front, cancelled by
'anti-lift' at the rear)."

The design I was referring to was the technique of creating lift
without adding downward momentum to the passing air, and I have
asked if my understanding of your device (the S foil) and its
working is correct.

Because, I always thought that if there was a force, you had a
linked change in momentum.

So (unless I mis-understand you) you're proposing a revision of
the basic laws of physics.

Explain please. Without mis-quoting.

JimB

JAXAshby wrote in message
...
I haven't heard of this design ("S" shaped airfoils) in
aerodymamics before

Naughty Jax.

You've mis-quoted me by adding the bit in brackets. In full:

"Now I think the device you're proposing is designed to add a
downward speed to the air, then subtract that speed, leaving no
net change in downward speed. Is that correct? If so, you're
proposing that a net force can be generated by displacing air
through a distance, rather than adding momentum to it.
Interesting.

*I haven't heard of this design in aerodymamics before* except in
the context of windmills. I can see how such a device would
generate a magnificent torque (lift at the front, cancelled by
'anti-lift' at the rear)."

The design I was referring to was the technique of creating lift
without adding downward momentum to the passing air, and I have
asked if my understanding of your device (the S foil) and its
working is correct.

Because, I always thought that if there was a force, you had a
linked change in momentum.

So (unless I mis-understand you) you're proposing a revision of
the basic laws of physics.

Explain please. Without mis-quoting.

JimB

I haven't heard of this design ("S" shaped airfoils) in aerodymamics before
....

first semester aero eng books have had it for decades. It is not a practical
airfoil, but it shows why foils lift.

On Thu, 1 Apr 2004 10:33:19 +0100, "JimB"
wrote:

I'm not proposing that the air 'has to catch up'. I'm just saying
that if it loses pressure, it's got to gain speed (or disperse
energy in some other way).

==================================

Let's try for an intuitive approach using a flat plate (your hand, for
example). Imagine sticking your hand out the window of a moving car
and "flying" it through the air as most of us have probably done as a
kid until our parents yelled at us.

If you hand is more or less parallel to the ground, you have wind
resistance (drag), but no lift. Tilt you hand slightly upwards and
now the wind strikes the bottom of your palm and forces it upwards
(lift). The reason lift is created is that your hand is deflecting
molecules of air downwards (change in momentum), and the resultant
force is upwards. It's simple Newtonian mechanics.

On Thu, 01 Apr 2004 23:25:21 -0500, Wayne.B
wrote:

On Thu, 1 Apr 2004 10:33:19 +0100, "JimB"
wrote:

I'm not proposing that the air 'has to catch up'. I'm just saying
that if it loses pressure, it's got to gain speed (or disperse
energy in some other way).

==================================

Let's try for an intuitive approach using a flat plate (your hand, for
example). Imagine sticking your hand out the window of a moving car
and "flying" it through the air as most of us have probably done as a
kid until our parents yelled at us.

If you hand is more or less parallel to the ground, you have wind
resistance (drag), but no lift. Tilt you hand slightly upwards and
now the wind strikes the bottom of your palm and forces it upwards
(lift). The reason lift is created is that your hand is deflecting
molecules of air downwards (change in momentum), and the resultant
force is upwards. It's simple Newtonian mechanics.

Nothing wrong with this explanation, as far as it goes.
[Except possibly the idea that aerodynamics is
'simple Newtonian dynamics'. :-) ]

But to answer the question, "Why does 2/3 of the lift come from the
upper surface?" you might need to continue with some suggestion that
the faster flow over and above the upper surface meeting the slower
flow under and below the lower surface effectively turns the flow
downwards which provides that change of velocity which with the air
mass flow, provides the Newtonian mass rate times acceleration
called the ' momentum change' - is the lifting force

Brian W

"Why does 2/3 of the lift come from the
upper surface?"

it doesn't. 100% comes from the difference between the bottom and the top.
obviously, the bottom is greater when the foil has lift.

JAXAshby wrote in message
...
"Why does 2/3 of the lift come from the
upper surface?"

it doesn't.

Decades of aerodynamicists believe it does, based on the the
evidence of thousands of surface pressure measurements by a
variety of different methods, in flight and in wind tunnels.
They've designed aircraft and their structures, then flown them,
then tested them, based on this knowledge. Jax, I'm beginning to
believe you come from a different planet.

100% comes from the difference between the bottom and the top.

I'll go along with that self evident truth

obviously, the bottom is greater when the foil has lift.

Sure, the bottom has greater pressure than the top. You've just
said that. But your phrasing was designed to mislead people into
thinking that you'd said the 'bottom' contributed more lift than
the 'top' contributed. And I can't believe that's what you meant.

JimB

JAXAshby wrote in message
...
"Why does 2/3 of the lift come from the
upper surface?"

it doesn't.

Decades of aerodynamicists believe it does, based on the the
evidence of thousands of surface pressure measurements by a
variety of different methods, in flight and in wind tunnels.
They've designed aircraft and their structures, then flown them,
then tested them, based on this knowledge. Jax, I'm beginning to
believe you come from a different planet.

100% comes from the difference between the bottom and the top.

I'll go along with that self evident truth

obviously, the bottom is greater when the foil has lift.

Sure, the bottom has greater pressure than the top. You've just
said that. But your phrasing was designed to mislead people into
thinking that you'd said the 'bottom' contributed more lift than
the 'top' contributed. And I can't believe that's what you meant.

JimB