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Main
Date: 28 Aug 2007 09:27:02
From: Luke
Subject: Aerodynamics of Split Blade forks
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There's a brief article, authored by Lennard Zinn, on Split Blade
Forks at the Velonews.com website. Makes for interesting reading.
http://velonews.com/tech/report/articles/13170.0.html
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Date: 23 Oct 2007 10:43:04
From:
Subject: Re: Aerodynamics of Split Blade forks
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On Aug 29, 4:45 am, "Tom \"Johnny Sunset\" Sherman"
<sunsetss0...@iinvalid.com > wrote:
> Dorfus Dippintush wrote:
> > Luke wrote:
> >> There's a brief article, authored by LennardZinn, onSplitBlade
> >> Forks at the Velonews.com website. Makes for interesting reading.
>
> >>http://velonews.com/tech/report/articles/13170.0.html
>
> > I'm skeptical. One large shape is nearly always more efficient than
> > multiple small ones. That's why we have such big ships on the seas
> > instead of lots of small ones, and it's why we don't see biplanes around
> > any more.
>
> That is why I ride a bicycle with a mono-strut instead of afork. :)
>
> --
> Tom Sherman - Holstein-Friesland Bovinia
> A Real Cyclist [TM] keeps at least one bicycle in the bedroom.
>
> --
> Posted via a free Usenet account fromhttp://www.teranews.com
umm. we have big ships cause they can carry more than little ones. bi-
planes can about because at the time they couldnt make a single wing
that was long and stiff enough that didnt weigh to much but now we can.
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Date: 23 Oct 2007 12:27:46
From: Ted Bennett
Subject: Re: Aerodynamics of Split Blade forks
|
ben@bikedoc.co.uk wrote:
> umm. we have big ships cause they can carry more than little ones. bi-
> planes can about because at the time they couldnt make a single wing
> that was long and stiff enough that didnt weigh to much but now we can.
Don't they teach English over there any more?
--
Ted Bennett
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Date: 24 Oct 2007 03:55:36
From: Tom Sherman
Subject: Re: Aerodynamics of Split Blade forks
|
Ted Bennett wrote:
> ben@bikedoc.co.uk wrote:
>
>> umm. we have big ships cause they can carry more than little ones. bi-
>> planes can about because at the time they couldnt make a single wing
>> that was long and stiff enough that didnt weigh to much but now we can.
>
> Don't they teach English over there any more?
>
He has the "jim beam" keyboard that does not do capital letters. ;)
--
Tom Sherman - Holstein-Friesland Bovinia
Beer - It's not just for breakfast anymore!
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Date: 06 Sep 2007 21:47:46
From: datakoll
Subject: Re: Aerodynamics of Split Blade forks
|
The two wing device I saw was at the wing's rear not the front:
backwards right? To laminar flow the trailing turbulence. Middle
Cretaceous.
Did it work? Qualitative answer was no. But that was very pre-digital.
Digital visual and software analysis is the take off point.
Impressive! At GP Germany? A small u shaped hoop wing on top the front
wing meant to control turbulence into the front disc area, was crushed
off. The car immediately slowed. The loss was noted by announcers as:
"oooohhhh! The thingee fell off let's see what happens"
A device similar to the fork idea. Speed differential? Tunnel cars for
road courses were doubtful several years ago as the speed weren't
thought fast enough below 190 but I was surprised tuning into the F2
races finding tunnel cars with F1 going tunnel next year.
Digital quantification? If 9 grams less front weight gets it down the
road faster than why not an airfoil? How much fork air equals 9 grams
at what speeds? 28 versus 32 versus 36.
http://www.aerodynwindtunnel.com/
www.jayski.com/pages/windtunnel.htm
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Date: 06 Sep 2007 05:28:01
From:
Subject: Re: Aerodynamics of Split Blade forks
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On Sep 4, 11:33 pm, Michael Press <rub...@pacbell.net > wrote:
> In article
> <1188943835.919472.238...@r29g2000hsg.googlegroups.com>
> ,
>
>
>
> Tom_A <theanha...@yahoo.com> wrote:
> > On Aug 28, 6:27 am, Luke <lucasirag...@rogers.com> wrote:
> > > There's a brief article, authored by Lennard Zinn, on Split Blade
> > > Forks at the Velonews.com website. Makes for interesting reading.
>
> > >http://velonews.com/tech/report/articles/13170.0.html
>
> > Mark Drela and I have exchanged a few emails on this subject and
> > here's his take on the whole thing (posted with his permission):
>
> > "When the VN article came out, I assumed that Oval Concepts
> > made a new fork according to my plots.
> > But when I checked their website, it appears that
> > they are still peddling their old fork, which is
> > completely ill-conceived --- the shape is all wrong,
> > and the slot goes the wrong way.
>
> > >I'm just trying to reasonably judge the claims made
> > >by Oval Concepts that your "study"
> > >validates the claims they make for their fork.
>
> > My "study" was of my own fork design, not theirs.
> > I never analyzed their fork.
> > So they are grossly misrepresenting what I did
> > and what their fork is supposed to do.
> > It's false advertising, in a nutshell.
>
> Assuming, and I have no reason to do otherwise, what
> you say is so; then they are making money from your
> reputation while destroying it. Put a lawyer on them.
>
> --
> Michael Press
They're running this nonsense on their web page too:
http://www.ovalconcepts.com/news.php?id_news=83
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Date: 05 Sep 2007 14:53:55
From: datakoll
Subject: Re: Aerodynamics of Split Blade forks
|
are the chinese tooling up?
the two wing idea surfaced years ago in FI, was abandoned then as
casuing drag for the monohull but today on the multipull doodad
ferrari, see and enlarge bottom right corner image-
http://www.formula1.com/gallery/race/2007/776/
of which all are familiar, right?
on the front wing
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Date: 06 Sep 2007 18:27:57
From: Dorfus Dippintush
Subject: Re: Aerodynamics of Split Blade forks
|
datakoll wrote:
> are the chinese tooling up?
>
> the two wing idea surfaced years ago in FI, was abandoned then as
> casuing drag for the monohull but today on the multipull doodad
> ferrari, see and enlarge bottom right corner image-
> http://www.formula1.com/gallery/race/2007/776/
> of which all are familiar, right?
> on the front wing
>
Yeah but they have to abide by car design rules covering wing location
and area and also they are after down-force. On a bike you just want the
least wind resistance.
Dorfus
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Date: 04 Sep 2007 15:10:35
From: Tom_A
Subject: Re: Aerodynamics of Split Blade forks
|
On Aug 28, 6:27 am, Luke <lucasirag...@rogers.com > wrote:
> There's a brief article, authored by Lennard Zinn, on Split Blade
> Forks at the Velonews.com website. Makes for interesting reading.
>
> http://velonews.com/tech/report/articles/13170.0.html
Mark Drela and I have exchanged a few emails on this subject and
here's his take on the whole thing (posted with his permission):
"When the VN article came out, I assumed that Oval Concepts
made a new fork according to my plots.
But when I checked their website, it appears that
they are still peddling their old fork, which is
completely ill-conceived --- the shape is all wrong,
and the slot goes the wrong way.
>I'm just trying to reasonably judge the claims made
>by Oval Concepts that your "study"
>validates the claims they make for their fork.
My "study" was of my own fork design, not theirs.
I never analyzed their fork.
So they are grossly misrepresenting what I did
and what their fork is supposed to do.
It's false advertising, in a nutshell.
MD"
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Date: 05 Sep 2007 03:33:46
From: Michael Press
Subject: Re: Aerodynamics of Split Blade forks
|
In article
<1188943835.919472.238660@r29g2000hsg.googlegroups.com >
,
Tom_A <theanhalts@yahoo.com > wrote:
> On Aug 28, 6:27 am, Luke <lucasirag...@rogers.com> wrote:
> > There's a brief article, authored by Lennard Zinn, on Split Blade
> > Forks at the Velonews.com website. Makes for interesting reading.
> >
> > http://velonews.com/tech/report/articles/13170.0.html
>
> Mark Drela and I have exchanged a few emails on this subject and
> here's his take on the whole thing (posted with his permission):
>
> "When the VN article came out, I assumed that Oval Concepts
> made a new fork according to my plots.
> But when I checked their website, it appears that
> they are still peddling their old fork, which is
> completely ill-conceived --- the shape is all wrong,
> and the slot goes the wrong way.
>
>
> >I'm just trying to reasonably judge the claims made
> >by Oval Concepts that your "study"
> >validates the claims they make for their fork.
>
> My "study" was of my own fork design, not theirs.
> I never analyzed their fork.
> So they are grossly misrepresenting what I did
> and what their fork is supposed to do.
> It's false advertising, in a nutshell.
Assuming, and I have no reason to do otherwise, what
you say is so; then they are making money from your
reputation while destroying it. Put a lawyer on them.
--
Michael Press
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Date: 30 Aug 2007 22:28:11
From: Tom_A
Subject: Re: Aerodynamics of Split Blade forks
|
On Aug 30, 7:46 pm, dr...@mit.edu (Mark Drela) wrote:
> In article <1188522367.912368.201...@q3g2000prf.googlegroups.com>, Tom_A <theanha...@yahoo.com> writes:> Am I missing something, but is the centerline of the fork at the
> > bottom of the page in your diagrams?
>
> Correct. Bottom of the plot is the centerline plane. Only one fork is shown.
>
> > If so, isn't the configuration
> > of the direction of the slots in the Oval Concepts fork in the
> > opposite direction than in your diagram? (i.e. "outside-in" vs. your
> > "inside-out"?)
>
> The airflow is left to right, with the flow through the slot
> going from the center outward. I've never seen one of their forks.
> I assume they made their fork cross sections like in the plot.
>
Look here:
http://www.ovalconcepts.com/productsGenereDett.php?idGenere=10&idCat=2
You might have to click on the link to the fork page which has
multiple views. Looks to me like the "entrance" of the slot is on the
outside of the fork leg.
> > Also...did your calculation of the speed increase through the standard
> > forks take into account the wheel itself (moving in the opposite
> > direction) in that space?
>
> No. The fork assumes a wheel with thin tension-type spokes.
> Such spokes fill up a very small fraction of the volume between
> the forks, so they are ignored in the calculation.
>
> With a disk wheel, this fork would not work as intended.
Aaah...I see. How about a deep section aerodynamic wheel? Something,
let's say 50-100mm deep? Obviously, the ends of the spokes on a wheel
like that won't be traveling at 2x bike speed so the potential savings
will be reduced. Does the deep section of the rim act like a disc in
that portion of the fork (i.e. near the crown?)...which means it
wouldn't "work as intended" in that portion?
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Date: 30 Aug 2007 18:06:07
From: Tom_A
Subject: Re: Aerodynamics of Split Blade forks
|
On Aug 30, 3:54 pm, dr...@mit.edu (Mark Drela) wrote:
> In article <46d746e...@news.peopletelecom.com.au>, Dorfus Dippintush <Dorfus.Dippint...@kippinbot.com> writes:
>
> > From my understanding of air flow, if the air moving through the forks
> > is moving faster then it would suck air INTO the slots rather than out,
> > the same as a carburettor sucks fuel in, and didn't Bernoulli
> > demonstrate that a moving liquid creates a low pressure?
>
> The lifting fork blades reduce the velocity and hence increase
> the pressure along the centerline. The air flows out of the slot.
>
> In any case, the flow though the slot merely provides a way
> to generate the necessary lift without massive flow separation.
> It's not central to the concept.
>
> > Secondly, any non symmetrical airfoil shape will have more drag than a
> > symmetrical airfoil, so even if you reduce airflow through the fork
> > you're going to increase the overall drag from the fork legs.
>
> Yes, but the rules require that each structural member have a thickness/chord
> ratio of at least 1/3. So it's legal to replace one 3x1" fork blade with two
> 1.5x0.75" fork blades. Normally this wouldn't help much, but the two smaller
> fork blades can cooperate via the slot to give an effectively
> more slender airfoil (compare figures A and C in the article).
> But they can cooperate only if there's some net lift.
> The lift also reduces spoke drag as a bonus.
Mark,
Am I missing something, but is the centerline of the fork at the
bottom of the page in your diagrams? If so, isn't the configuration
of the direction of the slots in the Oval Concepts fork in the
opposite direction than in your diagram? (i.e. "outside-in" vs. your
"inside-out"?)
Also...did your calculation of the speed increase through the standard
forks take into account the wheel itself (moving in the opposite
direction) in that space?
Thanks again,
Tom
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Date: 31 Aug 2007 02:46:36
From: Mark Drela
Subject: Re: Aerodynamics of Split Blade forks
|
In article <1188522367.912368.201570@q3g2000prf.googlegroups.com >, Tom_A <theanhalts@yahoo.com> writes:
> Am I missing something, but is the centerline of the fork at the
> bottom of the page in your diagrams?
Correct. Bottom of the plot is the centerline plane. Only one fork is shown.
> If so, isn't the configuration
> of the direction of the slots in the Oval Concepts fork in the
> opposite direction than in your diagram? (i.e. "outside-in" vs. your
> "inside-out"?)
The airflow is left to right, with the flow through the slot
going from the center outward. I've never seen one of their forks.
I assume they made their fork cross sections like in the plot.
> Also...did your calculation of the speed increase through the standard
> forks take into account the wheel itself (moving in the opposite
> direction) in that space?
No. The fork assumes a wheel with thin tension-type spokes.
Such spokes fill up a very small fraction of the volume between
the forks, so they are ignored in the calculation.
With a disk wheel, this fork would not work as intended.
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Date: 30 Aug 2007 16:50:29
From: almost_fast@yahoo.com
Subject: Re: Aerodynamics of Split Blade forks
|
On Aug 30, 4:39 pm, Tom_A <theanha...@yahoo.com > wrote:
> On Aug 30, 10:16 am, dr...@mit.edu (Mark Drela) wrote:
>
>
>
>
>
> > FWIW, Zinn's explanation of how this fork works is incredibly convoluted.
> > The concept is simple:
>
> > Conventional fork blades form a venturi between them,
> > so the spokes see a brief 1.2x larger headwind when
> > they pass through the fork (Figures A, B).
> > This implies a brief 1.2^3 = 1.7x larger power loss,
> > giving a _very_ significant average power loss increase
> > (most of the spoke power loss occurs between 2 and 10 o'clock
> > on the wheel).
>
> > By making the fork blades into airfoils which lift outward,
> > the centerline velocity is _decreased_ by 0.9x (Figure D),
> > which makes the local spoke drag power loss 0.9^3 = 0.7x smaller
> > as they pass between the fork blades.
>
> > That's the basic idea. The reason for the 2-element
> > airfoil fork is that it's the only way to make the
> > fork blades have sufficient outward lift, without
> > an excessive fork drag increase. This increase
> > would counteract the spoke drag benefit. Zinn's
> > explanation of how this works ("slot sucks the air out", etc)
> > makes no sense, but then again a correct explanation
> > wouldn't make much sense to a non-aero audience either.
>
> > BTW, Zinn seems to be relying on 3rd-hand information.
> > I had nothing to do with the tunnel tests. One of the
> > italian teams and Cervelo was in our tunnel doing tests.
> > While I was rubbernecking I hit on the idea of the
> > outward-lifting fork. I quickly cooked up the
> > 2-element fork with some CFD calculations,
> > and handed them the plots you see in the article.
> > It's kind of amusing to see my penciled doodles
> > and annotations on some of the plots.
>
> > So I really have no idea if it actually works or not.
> > If the fork blades lift as the CFD predicts, the
> > momentary spoke power between the forks is reduced
> > by a factor of 0.7/1.7 = 0.4x, which is pretty huge.
> > The net effective wheel drag reduction will of course
> > be more modest.
>
> Thanks for the explanation Mark. That actually makes a LOT more sense
> to me...then again, I'm an engineer...
>
> So, what you're saying is that there isn't an actual report from this
> "study" that Oval Concepts claims you've done? Dang, I was hoping to
> find a copy of it somewhere.
>
> I also take this to mean that (to your knowledge at least) there's
> never been a "head to head" (or would that be "fork to fork"?) test in
> the tunnel to determine the magnitude of the savings in the "real
> world"?
>
> - Show quoted text -
I gotta believe Lance's F1 team must have compared forks at some
point... Wish we could get those numbers!
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Date: 30 Aug 2007 14:39:11
From: Tom_A
Subject: Re: Aerodynamics of Split Blade forks
|
On Aug 30, 10:16 am, dr...@mit.edu (Mark Drela) wrote:
> FWIW, Zinn's explanation of how this fork works is incredibly convoluted.
> The concept is simple:
>
> Conventional fork blades form a venturi between them,
> so the spokes see a brief 1.2x larger headwind when
> they pass through the fork (Figures A, B).
> This implies a brief 1.2^3 = 1.7x larger power loss,
> giving a _very_ significant average power loss increase
> (most of the spoke power loss occurs between 2 and 10 o'clock
> on the wheel).
>
> By making the fork blades into airfoils which lift outward,
> the centerline velocity is _decreased_ by 0.9x (Figure D),
> which makes the local spoke drag power loss 0.9^3 = 0.7x smaller
> as they pass between the fork blades.
>
> That's the basic idea. The reason for the 2-element
> airfoil fork is that it's the only way to make the
> fork blades have sufficient outward lift, without
> an excessive fork drag increase. This increase
> would counteract the spoke drag benefit. Zinn's
> explanation of how this works ("slot sucks the air out", etc)
> makes no sense, but then again a correct explanation
> wouldn't make much sense to a non-aero audience either.
>
> BTW, Zinn seems to be relying on 3rd-hand information.
> I had nothing to do with the tunnel tests. One of the
> italian teams and Cervelo was in our tunnel doing tests.
> While I was rubbernecking I hit on the idea of the
> outward-lifting fork. I quickly cooked up the
> 2-element fork with some CFD calculations,
> and handed them the plots you see in the article.
> It's kind of amusing to see my penciled doodles
> and annotations on some of the plots.
>
> So I really have no idea if it actually works or not.
> If the fork blades lift as the CFD predicts, the
> momentary spoke power between the forks is reduced
> by a factor of 0.7/1.7 = 0.4x, which is pretty huge.
> The net effective wheel drag reduction will of course
> be more modest.
Thanks for the explanation Mark. That actually makes a LOT more sense
to me...then again, I'm an engineer...
So, what you're saying is that there isn't an actual report from this
"study" that Oval Concepts claims you've done? Dang, I was hoping to
find a copy of it somewhere.
I also take this to mean that (to your knowledge at least) there's
never been a "head to head" (or would that be "fork to fork"?) test in
the tunnel to determine the magnitude of the savings in the "real
world"?
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Date: 30 Aug 2007 22:40:02
From: Mark Drela
Subject: Re: Aerodynamics of Split Blade forks
|
In article <1188509951.971195.103990@q3g2000prf.googlegroups.com >, Tom_A <theanhalts@yahoo.com> writes:
> I also take this to mean that (to your knowledge at least) there's
> never been a "head to head" (or would that be "fork to fork"?) test in
> the tunnel to determine the magnitude of the savings in the "real
> world"?
Dunno. They may have tested it, or the claims may be estimates
from the CFD results. It seems like whoever Zinn talked to wasn't
sure about what was done either.
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Date: 29 Aug 2007 07:05:51
From: Dorfus Dippintush
Subject: Re: Aerodynamics of Split Blade forks
|
Luke wrote:
> There's a brief article, authored by Lennard Zinn, on Split Blade
> Forks at the Velonews.com website. Makes for interesting reading.
>
> http://velonews.com/tech/report/articles/13170.0.html
I'm skeptical. One large shape is nearly always more efficient than
multiple small ones. That's why we have such big ships on the seas
instead of lots of small ones, and it's why we don't see biplanes around
any more.
Supposedly this design moves air away from the front wheel but it
doesn't say how much energy is expended in drag to do that.
Dorfus
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| | |
Date: 29 Aug 2007 17:39:21
From: Kinky Cowboy
Subject: Re: Aerodynamics of Split Blade forks
|
On Wed, 29 Aug 2007 07:05:51 +0800, Dorfus Dippintush
<Dorfus.Dippintush@kippinbot.com > wrote:
>Luke wrote:
>> There's a brief article, authored by Lennard Zinn, on Split Blade
>> Forks at the Velonews.com website. Makes for interesting reading.
>>
>> http://velonews.com/tech/report/articles/13170.0.html
>
>I'm skeptical. One large shape is nearly always more efficient than
>multiple small ones. That's why we have such big ships on the seas
>instead of lots of small ones, and it's why we don't see biplanes around
>any more.
Have you ever seen a racing Catamaran/Trimaran? Much faster than a
mono-hull, whether sailed or motor powered. Have you seen a modern GP
car? A lot of small aerodynamic elements contribute to reducing drag
while providing maximum downforce.
Aircraft have been using slots to direct and control flow over the
wings since the biplane age to prevent stalling, a major cause of
increased drag.
I don't know whether Oval's fork is as good as they claim, but your
skepticism needs to based on something a bit more substantial than
"Oil tankers are monohulls, therefore slotted forks produce more drag
than solid ones" :-)
Kinky Cowboy*
*Batteries not included
May contain traces of nuts
Your milage may vary
|
| | | |
Date: 30 Aug 2007 15:33:10
From: Dorfus Dippintush
Subject: Re: Aerodynamics of Split Blade forks
|
Kinky Cowboy wrote:
> On Wed, 29 Aug 2007 07:05:51 +0800, Dorfus Dippintush
> <Dorfus.Dippintush@kippinbot.com> wrote:
>
>> Luke wrote:
>>> There's a brief article, authored by Lennard Zinn, on Split Blade
>>> Forks at the Velonews.com website. Makes for interesting reading.
>>>
>>> http://velonews.com/tech/report/articles/13170.0.html
>> I'm skeptical. One large shape is nearly always more efficient than
>> multiple small ones. That's why we have such big ships on the seas
>> instead of lots of small ones, and it's why we don't see biplanes around
>> any more.
>
> Have you ever seen a racing Catamaran/Trimaran? Much faster than a
> mono-hull, whether sailed or motor powered. Have you seen a modern GP
> car? A lot of small aerodynamic elements contribute to reducing drag
> while providing maximum downforce.
Catamarans are faster because they are lighter, relying on wide spread
pontoons for stability rather than ballast.
>
> Aircraft have been using slots to direct and control flow over the
> wings since the biplane age to prevent stalling, a major cause of
> increased drag.
>
> I don't know whether Oval's fork is as good as they claim, but your
> skepticism needs to based on something a bit more substantial than
> "Oil tankers are monohulls, therefore slotted forks produce more drag
> than solid ones" :-)
Do some reading about Reynolds numbers and you'll find there is a
scientific reason for what I'm saying.
>
> Kinky Cowboy*
>
> *Batteries not included
> May contain traces of nuts
> Your milage may vary
>
Dorfus
|
| | | | |
Date: 30 Aug 2007 10:18:17
From: Michael Press
Subject: Re: Aerodynamics of Split Blade forks
|
In article <46d672d5$1_5@news.peopletelecom.com.au >,
Dorfus Dippintush <Dorfus.Dippintush@kippinbot.com >
wrote:
> Catamarans are faster because they are lighter, relying on wide spread
> pontoons for stability rather than ballast.
For small values of stability. :)
There is a reason for the buoyant sphere rigged
on the peak of the catamarran mast.
--
Michael Press
|
| | | | |
Date: 30 Aug 2007 17:16:49
From: Mark Drela
Subject: Re: Aerodynamics of Split Blade forks
|
FWIW, Zinn's explanation of how this fork works is incredibly convoluted.
The concept is simple:
Conventional fork blades form a venturi between them,
so the spokes see a brief 1.2x larger headwind when
they pass through the fork (Figures A, B).
This implies a brief 1.2^3 = 1.7x larger power loss,
giving a _very_ significant average power loss increase
(most of the spoke power loss occurs between 2 and 10 o'clock
on the wheel).
By making the fork blades into airfoils which lift outward,
the centerline velocity is _decreased_ by 0.9x (Figure D),
which makes the local spoke drag power loss 0.9^3 = 0.7x smaller
as they pass between the fork blades.
That's the basic idea. The reason for the 2-element
airfoil fork is that it's the only way to make the
fork blades have sufficient outward lift, without
an excessive fork drag increase. This increase
would counteract the spoke drag benefit. Zinn's
explanation of how this works ("slot sucks the air out", etc)
makes no sense, but then again a correct explanation
wouldn't make much sense to a non-aero audience either.
BTW, Zinn seems to be relying on 3rd-hand information.
I had nothing to do with the tunnel tests. One of the
italian teams and Cervelo was in our tunnel doing tests.
While I was rubbernecking I hit on the idea of the
outward-lifting fork. I quickly cooked up the
2-element fork with some CFD calculations,
and handed them the plots you see in the article.
It's kind of amusing to see my penciled doodles
and annotations on some of the plots.
So I really have no idea if it actually works or not.
If the fork blades lift as the CFD predicts, the
momentary spoke power between the forks is reduced
by a factor of 0.7/1.7 = 0.4x, which is pretty huge.
The net effective wheel drag reduction will of course
be more modest.
|
| | | | | |
Date: 31 Aug 2007 06:38:07
From: Dorfus Dippintush
Subject: Re: Aerodynamics of Split Blade forks
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Mark Drela wrote:
> FWIW, Zinn's explanation of how this fork works is incredibly convoluted.
> The concept is simple:
>
> Conventional fork blades form a venturi between them,
> so the spokes see a brief 1.2x larger headwind when
> they pass through the fork (Figures A, B).
> This implies a brief 1.2^3 = 1.7x larger power loss,
> giving a _very_ significant average power loss increase
> (most of the spoke power loss occurs between 2 and 10 o'clock
> on the wheel).
>
> By making the fork blades into airfoils which lift outward,
> the centerline velocity is _decreased_ by 0.9x (Figure D),
> which makes the local spoke drag power loss 0.9^3 = 0.7x smaller
> as they pass between the fork blades.
>
>
> That's the basic idea. The reason for the 2-element
> airfoil fork is that it's the only way to make the
> fork blades have sufficient outward lift, without
> an excessive fork drag increase. This increase
> would counteract the spoke drag benefit. Zinn's
> explanation of how this works ("slot sucks the air out", etc)
> makes no sense, but then again a correct explanation
> wouldn't make much sense to a non-aero audience either.
>
>
> BTW, Zinn seems to be relying on 3rd-hand information.
> I had nothing to do with the tunnel tests. One of the
> italian teams and Cervelo was in our tunnel doing tests.
> While I was rubbernecking I hit on the idea of the
> outward-lifting fork. I quickly cooked up the
> 2-element fork with some CFD calculations,
> and handed them the plots you see in the article.
> It's kind of amusing to see my penciled doodles
> and annotations on some of the plots.
>
> So I really have no idea if it actually works or not.
> If the fork blades lift as the CFD predicts, the
> momentary spoke power between the forks is reduced
> by a factor of 0.7/1.7 = 0.4x, which is pretty huge.
> The net effective wheel drag reduction will of course
> be more modest.
>
>
>
>
From my understanding of air flow, if the air moving through the forks
is moving faster then it would suck air INTO the slots rather than out,
the same as a carburettor sucks fuel in, and didn't Bernoulli
demonstrate that a moving liquid creates a low pressure?
Secondly, any non symmetrical airfoil shape will have more drag than a
symmetrical airfoil, so even if you reduce airflow through the fork
you're going to increase the overall drag from the fork legs.
I don't have access to a wind tunnel so I have to assume things.
Dorfus
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Date: 30 Aug 2007 22:54:02
From: Mark Drela
Subject: Re: Aerodynamics of Split Blade forks
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In article <46d746ef_7@news.peopletelecom.com.au >, Dorfus Dippintush <Dorfus.Dippintush@kippinbot.com> writes:
> From my understanding of air flow, if the air moving through the forks
> is moving faster then it would suck air INTO the slots rather than out,
> the same as a carburettor sucks fuel in, and didn't Bernoulli
> demonstrate that a moving liquid creates a low pressure?
The lifting fork blades reduce the velocity and hence increase
the pressure along the centerline. The air flows out of the slot.
In any case, the flow though the slot merely provides a way
to generate the necessary lift without massive flow separation.
It's not central to the concept.
> Secondly, any non symmetrical airfoil shape will have more drag than a
> symmetrical airfoil, so even if you reduce airflow through the fork
> you're going to increase the overall drag from the fork legs.
Yes, but the rules require that each structural member have a thickness/chord
ratio of at least 1/3. So it's legal to replace one 3x1" fork blade with two
1.5x0.75" fork blades. Normally this wouldn't help much, but the two smaller
fork blades can cooperate via the slot to give an effectively
more slender airfoil (compare figures A and C in the article).
But they can cooperate only if there's some net lift.
The lift also reduces spoke drag as a bonus.
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Date: 28 Aug 2007 21:45:36
From: Tom \Johnny Sunset\ Sherman
Subject: Re: Aerodynamics of Split Blade forks
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Dorfus Dippintush wrote:
> Luke wrote:
>> There's a brief article, authored by Lennard Zinn, on Split Blade
>> Forks at the Velonews.com website. Makes for interesting reading.
>>
>> http://velonews.com/tech/report/articles/13170.0.html
>
> I'm skeptical. One large shape is nearly always more efficient than
> multiple small ones. That's why we have such big ships on the seas
> instead of lots of small ones, and it's why we don't see biplanes around
> any more.
That is why I ride a bicycle with a mono-strut instead of a fork. :)
--
Tom Sherman - Holstein-Friesland Bovinia
A Real Cyclist [TM] keeps at least one bicycle in the bedroom.
--
Posted via a free Usenet account from http://www.teranews.com
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Date: 28 Aug 2007 22:43:21
From: Carl Sundquist
Subject: Re: Aerodynamics of Split Blade forks
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"Tom "Johnny Sunset" Sherman" <sunsetss0003@iinvalid.com > wrote in message
news:46d4d1c3$0$16364$88260bb3@free.teranews.com...
> Dorfus Dippintush wrote:
>> Luke wrote:
>>> There's a brief article, authored by Lennard Zinn, on Split Blade
>>> Forks at the Velonews.com website. Makes for interesting reading.
>>>
>>> http://velonews.com/tech/report/articles/13170.0.html
>>
>> I'm skeptical. One large shape is nearly always more efficient than
>> multiple small ones. That's why we have such big ships on the seas
>> instead of lots of small ones, and it's why we don't see biplanes around
>> any more.
>
> That is why I ride a bicycle with a mono-strut instead of a fork. :)
http://www.velonews.com/tech/report/articles/12493.0.html
This is my favorite. Water filling the voids makes a smoother faster road?
When was the last time Zinn was drug tested? How about humid air being less
dense than dry air?
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Date: 29 Aug 2007 11:49:56
From: Dorfus Dippintush
Subject: Re: Aerodynamics of Split Blade forks
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Carl Sundquist wrote:
>
> "Tom "Johnny Sunset" Sherman" <sunsetss0003@iinvalid.com> wrote in
> message news:46d4d1c3$0$16364$88260bb3@free.teranews.com...
>> Dorfus Dippintush wrote:
>>> Luke wrote:
>>>> There's a brief article, authored by Lennard Zinn, on Split Blade
>>>> Forks at the Velonews.com website. Makes for interesting reading.
>>>>
>>>> http://velonews.com/tech/report/articles/13170.0.html
>>>
>>> I'm skeptical. One large shape is nearly always more efficient than
>>> multiple small ones. That's why we have such big ships on the seas
>>> instead of lots of small ones, and it's why we don't see biplanes
>>> around any more.
>>
>> That is why I ride a bicycle with a mono-strut instead of a fork. :)
>
> http://www.velonews.com/tech/report/articles/12493.0.html
>
> This is my favorite. Water filling the voids makes a smoother faster
> road? When was the last time Zinn was drug tested? How about humid air
> being less dense than dry air?
I read that and thought the same thing.
Dorfus
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Date: 28 Aug 2007 07:10:27
From: Qui si parla Campagnolo-www.vecchios.com
Subject: Re: Aerodynamics of Split Blade forks
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On Aug 28, 7:27 am, Luke <lucasirag...@rogers.com > wrote:
> There's a brief article, authored by Lennard Zinn, on Split Blade
> Forks at the Velonews.com website. Makes for interesting reading.
>
> http://velonews.com/tech/report/articles/13170.0.html
Also interesting are the 'palmares' of 2 of the riders in the
graph...makes the whole thing suspect.
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Date: 28 Aug 2007 13:39:12
From: Luke
Subject: Re: Aerodynamics of Split Blade forks
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In article <1188310227.922830.67150@e9g2000prf.googlegroups.com >, Qui
si parla Campagnolo-www.vecchios.com <peter@vecchios.com > wrote:
> On Aug 28, 7:27 am, Luke <lucasirag...@rogers.com> wrote:
> > There's a brief article, authored by Lennard Zinn, on Split Blade
> > Forks at the Velonews.com website. Makes for interesting reading.
> >
> > http://velonews.com/tech/report/articles/13170.0.html
>
> Also interesting are the 'palmares' of 2 of the riders in the
> graph...makes the whole thing suspect.
I don't follow. How do Vino's and Heras' self medicating tendencies
cast suspicion on Drela's test results? Why look for validation of the
forks' aerodynamic superiority in the riders' palmares, isn't that what
the test data are for?
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