Aerodynamics of Split Blade forks

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

On Aug 28, 7:27 am, 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

Also interesting are the 'palmares' of 2 of the riders in the
graph...makes the whole thing suspect.

In article om, Qui
si parla Campagnolo-www.vecchios.com wrote:

On Aug 28, 7:27 am, 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

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?

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

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

"Tom "Johnny Sunset" Sherman" wrote in message
.. .
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/...s/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?

Carl Sundquist wrote:

"Tom "Johnny Sunset" Sherman" wrote in
message .. .
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/...s/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

On Wed, 29 Aug 2007 07:05:51 +0800, 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.

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

Kinky Cowboy wrote:
On Wed, 29 Aug 2007 07:05:51 +0800, 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.

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

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.