Lift over foils
 

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

Lift over foils
 

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

Lift over foils
 

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

Lift over foils
 

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

Lift over foils
 

"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.

Lift over foils
 

"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.

Lift over foils
 

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

nah. that's barroom talk after the three beer. It won't design any airfoils
at all.

Lift over foils
 

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

nah. that's barroom talk after the three beer. It won't design any airfoils
at all.

Lift over foils
 

JAXAshby wrote in message
...
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

nah. that's barroom talk after the three beer. It won't
design any airfoils
at all.

So, you don't agree that a change in momentum [of air] is needed
to create a [lift] force?

This seems to confirm that you live in a different universe from
the rest of us, Jax .

JimB

Lift over foils
 

JAXAshby wrote in message
...
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

nah. that's barroom talk after the three beer. It won't
design any airfoils
at all.

So, you don't agree that a change in momentum [of air] is needed
to create a [lift] force?

This seems to confirm that you live in a different universe from
the rest of us, Jax .

JimB