moschops

Hiya folks.

Having recently decided to get myself in gear and progress my mad skillz
a bit, I picked up the BPA canopy handling manual, as read now by n00bs
eager to get their CH1/CH2/FAA a/FAA b and probably lots of other people.

To my horror, I found it repeated the oft cited mistake that the
principal lift is provided via the Bernoulli principle. My fear is that
skydivers trusting in this could ultimately expect a lifting force
significantly different to that they actually get, with the resulting
safety hazard.

Before I start a crusade on this, I'd welcome people's thoughts on the
matter. The CHM is available on the BPA website for those of you yet to
peruse it.

Moschops

Dave

Mos (Mick?)

I definitely recommend you start a crusade on this. If n00bs were to
expect what you describe, the consequences could be unspeakable.

Dave


moschops wrote:
> Hiya folks.
>
> Having recently decided to get myself in gear and progress my mad skillz
> a bit, I picked up the BPA canopy handling manual, as read now by n00bs
> eager to get their CH1/CH2/FAA a/FAA b and probably lots of other people.
>
> To my horror, I found it repeated the oft cited mistake that the
> principal lift is provided via the Bernoulli principle. My fear is that
> skydivers trusting in this could ultimately expect a lifting force
> significantly different to that they actually get, with the resulting
> safety hazard.
>
> Before I start a crusade on this, I'd welcome people's thoughts on the
> matter. The CHM is available on the BPA website for those of you yet to
> peruse it.
>
> Moschops

moschops

> moschops wrote:
>> Hiya folks.
>>
>> Having recently decided to get myself in gear and progress my mad skillz
>> a bit, I picked up the BPA canopy handling manual, as read now by n00bs
>> eager to get their CH1/CH2/FAA a/FAA b and probably lots of other people.
>>
>> To my horror, I found it repeated the oft cited mistake that the
>> principal lift is provided via the Bernoulli principle. My fear is that
>> skydivers trusting in this could ultimately expect a lifting force
>> significantly different to that they actually get, with the resulting
>> safety hazard.
>>
>> Before I start a crusade on this, I'd welcome people's thoughts on the
>> matter. The CHM is available on the BPA website for those of you yet to
>> peruse it.
>>
>> Moschops
>

Dave wrote:
> Mos (Mick?)
>
> I definitely recommend you start a crusade on this. If n00bs were to
> expect what you describe, the consequences could be unspeakable.
>
> Dave
>
>

Nuts - I thought I managed to squelch this thread title before it got
off my PC - the subject line is wrong. Anyone wishing to contribute
please add your very welcome comments to the message entitled "BPA
Canopy Handling manual technical error".

In particular, anyone who thinks I am in fact in error. If I'm looking
to correct an error I should definitely check that I'm right beforehand!

Moschops

luugnutes

On Sun, 07 Jan 2007 22:31:05 +0000, moschops <moschop@madasafish.com>
wrote:

> In particular, anyone who thinks I am in fact in error. If I'm looking
> to correct an error I should definitely check that I'm right beforehand!

You should email to ask the canopy manufacturers for their opinions in
the matter ... you might be surprised.

moschops

luugnutes wrote:
> On Sun, 07 Jan 2007 22:31:05 +0000, moschops <moschop@madasafish.com>
> wrote:
>
>> In particular, anyone who thinks I am in fact in error. If I'm looking
>> to correct an error I should definitely check that I'm right beforehand!
>
> You should email to ask the canopy manufacturers for their opinions in
> the matter ... you might be surprised.

They seem surprisingly reticent. Nonetheless, I believe that that on a
given wing, the Bernoulli effect is far and away not the principle
source of lift.

'Chops

luugnutes

On Mon, 08 Jan 2007 17:13:53 +0000, moschops <moschop@madasafish.com>
wrote:

> > You should email to ask the canopy manufacturers for their opinions in
> > the matter ... you might be surprised.
>
> They seem surprisingly reticent. Nonetheless, I believe that that on a
> given wing, the Bernoulli effect is far and away not the principle
> source of lift.

Mass displacement is certainly a sizable factor, but without Bernoulli
principle resulting from a well-formed wing, the rejoining of the
laminar flow aft of any wing will break down into disorganization and
reduce the mass displacement to the point where the wing won't lift at
all. They're both necessary, as one without the other just won't work.

How does the manual in question address the matter, or is it too long
to post?

moschops

luugnutes wrote:
> On Mon, 08 Jan 2007 17:13:53 +0000, moschops <moschop@madasafish.com>
> wrote:
>
>>> You should email to ask the canopy manufacturers for their opinions in
>>> the matter ... you might be surprised.
>> They seem surprisingly reticent. Nonetheless, I believe that that on a
>> given wing, the Bernoulli effect is far and away not the principle
>> source of lift.
>
> Mass displacement is certainly a sizable factor, but without Bernoulli
> principle resulting from a well-formed wing, the rejoining of the
> laminar flow aft of any wing will break down into disorganization and
> reduce the mass displacement to the point where the wing won't lift at
> all. They're both necessary, as one without the other just won't work.
>
> How does the manual in question address the matter, or is it too long
> to post?
>

The canopy handling manual can be found tucked away on the
www.bpa.org.uk website. It ascribes the whole lift action to the
Bernoulli effect.

As I understood it, lack of laminar flow results in turbulence adjacent
to the wing, leading to a loss of lift - as you phrased it above, it
seems that any Bernoulli effect providing lift is a happy byproduct of
trying to ensure this laminar flow. Also, surely we don't want a smooth
flow behind the wing; we want to take a big chunk of air and push it
down. If we leave the air effectively undisturbed, we'll get no lift.

I must admit that I haven't sat down and measured the relative sizes of
the top and bottom of my canopy, but I don't recall the top being
significantly longer, front to back, than the underside, which is a key
part of the shape of a fixed wing as on an aircraft.

Chops

Jim White

moschops wrote:

> luugnutes wrote:
> > On Mon, 08 Jan 2007 17:13:53 +0000, moschops <moschop@madasafish.com>
> > wrote:
> >
> >>> You should email to ask the canopy manufacturers for their opinions in
> >>> the matter ... you might be surprised.
> >> They seem surprisingly reticent. Nonetheless, I believe that that on a
> >> given wing, the Bernoulli effect is far and away not the principle
> >> source of lift.
> >
> > Mass displacement is certainly a sizable factor, but without Bernoulli
> > principle resulting from a well-formed wing, the rejoining of the
> > laminar flow aft of any wing will break down into disorganization and
> > reduce the mass displacement to the point where the wing won't lift at
> > all. They're both necessary, as one without the other just won't work.
> >
> > How does the manual in question address the matter, or is it too long
> > to post?
> >
>
> The canopy handling manual can be found tucked away on the
> www.bpa.org.uk website. It ascribes the whole lift action to the
> Bernoulli effect.
>
> As I understood it, lack of laminar flow results in turbulence adjacent
> to the wing, leading to a loss of lift - as you phrased it above, it
> seems that any Bernoulli effect providing lift is a happy byproduct of
> trying to ensure this laminar flow. Also, surely we don't want a smooth
> flow behind the wing; we want to take a big chunk of air and push it
> down. If we leave the air effectively undisturbed, we'll get no lift.
>
> I must admit that I haven't sat down and measured the relative sizes of
> the top and bottom of my canopy, but I don't recall the top being
> significantly longer, front to back, than the underside, which is a key
> part of the shape of a fixed wing as on an aircraft.
>
> Chops

I think were getting a bit confused here so here my pennies worth.

Bernoulli's principle states that in an ideal fluid (low speed air is a
good approximation), with no work being performed on the fluid, an
increase in velocity occurs simultaneously with decrease in pressure or
gravitational energy.

This means that if the top surface of the canopy ( or wing) is longer
than the bottom. The air passing over the top has further to travel and
therefore speeds up, leading to a reduction in air pressure above the
wing. Giving us lift.

The boundary layer is the layer of air between the canopy (or wing) and
the free airsteam

Laminar flown is part of the boundary layer and is a very thin layer of
smooth airflow with regular stream lines.

Turbulance is found to the rear of the laminar flow and is where the
streamlines break up and become disturbed. This creates drag. If the
angle of attack is increased ( pulling down both toggles and lifting
the leading edge ) the turbulant area moves forward and will cause the
canopy ( or wing) to stall.

Hope this helps or talk to a pilot for more info.

Jim

One question for you.

Who explain what the Angle of Incidence is ?

luugnutes

On 9 Jan 2007 05:27:20 -0800, "Jim White" <jcwhite526@hotmail.com>
wrote:

> I think were getting a bit confused here so here my pennies worth.

You sure *are* confused.

moschops

Jim White wrote:
The air passing over the top has further to travel and
> therefore speeds up, leading to a reduction in air pressure above the
> wing. Giving us lift.

But is this the primary source of lift on a canopy?

Chops

moschops

I spent some of today at work deriving equations of motion for a canopy
in flight. Took a while, but eventually the people learn and go to a
different counter. Most of them only want to buy stamps anyway.

A chap who is part of a parachute research group answered my eMail and
recommended an aerodynamics textbook, which should help.

Moschops

luugnutes

On Wed, 10 Jan 2007 21:58:21 +0000, moschops <moschop@madasafish.com>
wrote:

> I spent some of today at work deriving equations of motion for a canopy
> in flight. Took a while, ...

Why go to so much diversion to investigate your original idea? Just
use one of the vectored forms of the Bernoulli equation, assume an
"average" wing chord and "angle of attack", assume an "average" speed,
then calculate the pressure difference between the top and bottom
skins.

Integrate that difference over a unit area of the wing, then to make
life easy, just multiply that integral result over the size of the
wing. The upward force per unit area minus the downward gravitational
force of the entire package distibuted over the entire wing area is
the answer to your question.

You'll be surprised, I'm sure, and come to an understanding of why the
lift component is stated as it is in the manual.

moschops

luugnutes wrote:
> On Wed, 10 Jan 2007 21:58:21 +0000, moschops <moschop@madasafish.com>
> wrote:
>
>> I spent some of today at work deriving equations of motion for a canopy
>> in flight. Took a while, ...
>
> Why go to so much diversion to investigate your original idea? Just
> use one of the vectored forms of the Bernoulli equation, assume an
> "average" wing chord and "angle of attack", assume an "average" speed,
> then calculate the pressure difference between the top and bottom
> skins.
>
> Integrate that difference over a unit area of the wing, then to make
> life easy, just multiply that integral result over the size of the
> wing. The upward force per unit area minus the downward gravitational
> force of the entire package distibuted over the entire wing area is
> the answer to your question.
>
> You'll be surprised, I'm sure, and come to an understanding of why the
> lift component is stated as it is in the manual.

To do this I'll need to know the different areas of the top and
underside of the canopy. Do you happen to have any values?

Chops

Mick Cooper

"moschops" <moschop@madasafish.com> wrote in message
news:Vb6dnYBiHe8stDnYRVnytQA@brightview.co.uk...
> Jim White wrote:
> The air passing over the top has further to travel and
>> therefore speeds up, leading to a reduction in air pressure above the
>> wing. Giving us lift.
>
> But is this the primary source of lift on a canopy?
>
> Chops

http://en.wikipedia.org/wiki/Lift_%28force%29

Mick Cooper

"luugnutes" <dferree@privy.much> wrote in message
newsvvaq2tf9stq8jljo8cjp2r8gioc066ev2@4ax.com...
> On Wed, 10 Jan 2007 21:58:21 +0000, moschops <moschop@madasafish.com>
> wrote:
>
>> I spent some of today at work deriving equations of motion for a canopy
>> in flight. Took a while, ...
>
> Why go to so much diversion to investigate your original idea? Just
> use one of the vectored forms of the Bernoulli equation, assume an
> "average" wing chord and "angle of attack", assume an "average" speed,
> then calculate the pressure difference between the top and bottom
> skins.
>
> Integrate that difference over a unit area of the wing, then to make
> life easy, just multiply that integral result over the size of the
> wing. The upward force per unit area minus the downward gravitational
> force of the entire package distibuted over the entire wing area is
> the answer to your question.
>
> You'll be surprised, I'm sure, and come to an understanding of why the
> lift component is stated as it is in the manual.

I'm sure we'd all be surprised using your mickey mouse approach to
mathematics and physics

all thats missing is the line that says

and then multiply by the number you first thought of.

Doh

moschops

Mick Cooper wrote:
> "moschops" <moschop@madasafish.com> wrote in message
> news:Vb6dnYBiHe8stDnYRVnytQA@brightview.co.uk...
>> Jim White wrote:
>> The air passing over the top has further to travel and
>>> therefore speeds up, leading to a reduction in air pressure above the
>>> wing. Giving us lift.
>> But is this the primary source of lift on a canopy?
>>
>> Chops
>
> http://en.wikipedia.org/wiki/Lift_%28force%29
>
>

This doesn't actually provide the answers we're looking for. It just
states the obvious - that more pressure under a wing than on top of the
wing creates lift.

Mick Cooper

"moschops" <moschop@madasafish.com> wrote in message
news:38SdnYHR7MeBMTvYRVnyjAA@brightview.com...
> Mick Cooper wrote:
>> "moschops" <moschop@madasafish.com> wrote in message
>> news:Vb6dnYBiHe8stDnYRVnytQA@brightview.co.uk...
>>> Jim White wrote:
>>> The air passing over the top has further to travel and
>>>> therefore speeds up, leading to a reduction in air pressure above the
>>>> wing. Giving us lift.
>>> But is this the primary source of lift on a canopy?
>>>
>>> Chops
>>
>> http://en.wikipedia.org/wiki/Lift_%28force%29
>>
>>
>
> This doesn't actually provide the answers we're looking for. It just
> states the obvious - that more pressure under a wing than on top of the
> wing creates lift.

I know

what it does is to propose that your original assessment was indeed true -
and that there is more to the whole scenario than meets the generally
accepted scenario.

You can work out the reality - all you have to do then is to prove it......

luugnutes

On Thu, 11 Jan 2007 17:58:12 +0000, moschops <moschop@madasafish.com>
wrote:

> > Why go to so much diversion to investigate your original idea? Just
> > use one of the vectored forms of the Bernoulli equation, assume an
> > "average" wing chord and "angle of attack", assume an "average" speed,
> > then calculate the pressure difference between the top and bottom
> > skins.
> >
> > Integrate that difference over a unit area of the wing, then to make
> > life easy, just multiply that integral result over the size of the
> > wing. ...
>
> To do this I'll need to know the different areas of the top and
> underside of the canopy. Do you happen to have any values?

You don't need to know the areas beyond the chord cross-section.
Choose an arbitray one close to what you might normally jump. The
difference in length over the top and under the bottom are what
determine the relative velocity over each, since under "ideal"
conditions a parcel of air that is split at the leading edge will
rejoin as the same parcel at the trailing edge. Thus the parcel over
the top has a greater velocity than the parcel under the bottom.

moschops

Mick Cooper wrote:
> "moschops" <moschop@madasafish.com> wrote in message
> news:38SdnYHR7MeBMTvYRVnyjAA@brightview.com...
>> Mick Cooper wrote:
>>> "moschops" <moschop@madasafish.com> wrote in message
>>> news:Vb6dnYBiHe8stDnYRVnytQA@brightview.co.uk...
>>>> Jim White wrote:
>>>> The air passing over the top has further to travel and
>>>>> therefore speeds up, leading to a reduction in air pressure above the
>>>>> wing. Giving us lift.
>>>> But is this the primary source of lift on a canopy?
>>>>
>>>> Chops
>>> http://en.wikipedia.org/wiki/Lift_%28force%29
>>>
>>>
>> This doesn't actually provide the answers we're looking for. It just
>> states the obvious - that more pressure under a wing than on top of the
>> wing creates lift.
>
> I know
>
> what it does is to propose that your original assessment was indeed true -
> and that there is more to the whole scenario than meets the generally
> accepted scenario.
>
> You can work out the reality - all you have to do then is to prove it......
>
>

Perhaps by constructing and jumping a canopy designed to have zero lift
from the Bernoulli effect...

moschops

luugnutes wrote:
> On Thu, 11 Jan 2007 17:58:12 +0000, moschops <moschop@madasafish.com>
> wrote:
>
>>> Why go to so much diversion to investigate your original idea? Just
>>> use one of the vectored forms of the Bernoulli equation, assume an
>>> "average" wing chord and "angle of attack", assume an "average" speed,
>>> then calculate the pressure difference between the top and bottom
>>> skins.
>>>
>>> Integrate that difference over a unit area of the wing, then to make
>>> life easy, just multiply that integral result over the size of the
>>> wing. ...
>> To do this I'll need to know the different areas of the top and
>> underside of the canopy. Do you happen to have any values?
>
> You don't need to know the areas beyond the chord cross-section.
> Choose an arbitray one close to what you might normally jump. The
> difference in length over the top and under the bottom are what
> determine the relative velocity over each, since under "ideal"
> conditions a parcel of air that is split at the leading edge will
> rejoin as the same parcel at the trailing edge. Thus the parcel over
> the top has a greater velocity than the parcel under the bottom.

If two adjacent parcels are split by the canopy and rejoin post-canopy,
effectively undisturbed by the canopy, they provide no lift whatsoever.

Do you have some numbers? I've never measured the dimensions of a canopy.

Chops

luugnutes

On Thu, 11 Jan 2007 23:16:23 +0000, moschops <moschop@madasafish.com>
wrote:

> > You don't need to know the areas beyond the chord cross-section.
> > Choose an arbitray one close to what you might normally jump. The
> > difference in length over the top and under the bottom are what
> > determine the relative velocity over each, since under "ideal"
> > conditions a parcel of air that is split at the leading edge will
> > rejoin as the same parcel at the trailing edge. Thus the parcel over
> > the top has a greater velocity than the parcel under the bottom.
>
> If two adjacent parcels are split by the canopy and rejoin post-canopy,
> effectively undisturbed by the canopy, they provide no lift whatsoever.

<sigh> Back to math 328 for you then, if you can't understand what the
equation is saying.

bye bye.

Mick Cooper

"moschops" <moschop@madasafish.com> wrote in message
news:RbidnaEEIfRGWTvYRVnyvgA@brightview.com...
>>
>> You can work out the reality - all you have to do then is to prove
>> it......
>
> Perhaps by constructing and jumping a canopy designed to have zero lift
> from the Bernoulli effect...

Id like to do DZ control the day you try.

moschops

luugnutes wrote:
> On Thu, 11 Jan 2007 23:16:23 +0000, moschops <moschop@madasafish.com>
> wrote:
>
>>> You don't need to know the areas beyond the chord cross-section.
>>> Choose an arbitray one close to what you might normally jump. The
>>> difference in length over the top and under the bottom are what
>>> determine the relative velocity over each, since under "ideal"
>>> conditions a parcel of air that is split at the leading edge will
>>> rejoin as the same parcel at the trailing edge. Thus the parcel over
>>> the top has a greater velocity than the parcel under the bottom.
>> If two adjacent parcels are split by the canopy and rejoin post-canopy,
>> effectively undisturbed by the canopy, they provide no lift whatsoever.
>
> <sigh> Back to math 328 for you then, if you can't understand what the
> equation is saying.
>
> bye bye.

You have demonstrated a fatal lack of understanding of the conservation
of momentum. I shall take my advice from other sources, thank you.

Mick Cooper

"moschops" <moschop@madasafish.com> wrote in message
news:TICdnQC4JZDkQjrYnZ2dnUVZ8tzinZ2d@brightview.c om...
> luugnutes wrote:
>> On Thu, 11 Jan 2007 23:16:23 +0000, moschops <moschop@madasafish.com>
>> wrote:
>>
>>>> You don't need to know the areas beyond the chord cross-section.
>>>> Choose an arbitray one close to what you might normally jump. The
>>>> difference in length over the top and under the bottom are what
>>>> determine the relative velocity over each, since under "ideal"
>>>> conditions a parcel of air that is split at the leading edge will
>>>> rejoin as the same parcel at the trailing edge. Thus the parcel over
>>>> the top has a greater velocity than the parcel under the bottom.
>>> If two adjacent parcels are split by the canopy and rejoin post-canopy,
>>> effectively undisturbed by the canopy, they provide no lift whatsoever.
>>
>> <sigh> Back to math 328 for you then, if you can't understand what the
>> equation is saying.
>>
>> bye bye.
>
> You have demonstrated a fatal lack of understanding of the conservation of
> momentum. I shall take my advice from other sources, thank you.

don't worry - he's never let his complete and utter lack of comprehension of
any subject get in the way of proffering a totally inaccurate opinion.