Serrated trailing edges for improving lift and drag characteristics of
Patent 5088665 Issued on February 18, 1992.
the apparatus includes a serrated panel having a plurality of span-wise,
periodic indentations, and means for connecting the serrated panel to
the trailing edge of the lifting surface. Preferably, the indentations
form a plurality of saw teeth having 60° included angles between
adjacent vertices, but other shapes of the indentations are possible.
The bumps are on the leading edge of flippers, and that=92s not the way
it=92s supposed to go.=94
...When you ride on an airplane, you don=92t see bumps on the leading
edge of the wing... he did not see a flat surface that would produce
smooth, aerodynamic flow...
...Drag and lift are familiar to anyone who ever stuck a hand out the
window of a moving car. Hold the hand parallel to the ground and it
will slice through the air. Cant it slightly and it will lift upwards.
The amount of lift grows in linear fashion as the angle of attack
increases=97up to a point. Too much and drag jerks the hand backwards.
This is how wings and flippers work. To maintain lift, we need to keep
air or water flowing over the wing. Normally, wings allow an 11 to 12
percent angle of attack.
More than that and you lose the lift. What happens is not enough air
is moving over the wing. The flow detaches from the surface of the
wing and creates an eddy current. You lose the pressure differential
between the upper and lower side of the wing and you stall...
...the marriage of the born and the made. By extracting the logical
principle of both life and machines, and applying each to the task of
building extremely complex systems, technicians are conjuring up
contraptions that are at once both made and alive. This marriage
between life and machines is one of convenience, because, in part, it
has been forced by our current technical limitations. For the world of
our own making has become so complicated that we must turn to the
world of the born to understand how to manage it. That is, the more
mechanical we make our fabricated environment, the more biological it
will eventually have to be if it is to work at all. Our future is
technological; but it will not be a world of gray steel. Rather our
technological future is headed toward a neo-biological civilization.
Nature has all along yielded her flesh to humans. First, we took
nature's materials as food, fibers, and shelter. Then we learned to
extract raw materials from her biosphere to create our own new
synthetic materials. Now Bios is yielding us her mind-we are taking
Clockwork logic-the logic of the machines-will only build simple
contraptions. Truly complex systems such as a cell, a meadow, an
economy, or a brain (natural or artificial) require a rigorous
nontechnological logic. We now see that no logic except bio-logic can
assemble a thinking device, or even a workable system of any
It is an astounding discovery that one can extract the logic of Bios
out of biology and have something useful. Although many philosophers
in the past have suspected one could abstract the laws of life and
apply them elsewhere, it wasn't until the complexity of computers and
human-made systems became as complicated as living things, that it was
possible to prove this. It's eerie how much of life can be
transferred. So far, some of the traits of the living that have
successfully been transported to mechanical systems are: self-
replication, self-governance, limited self-repair, mild evolution, and
partial learning. We have reason to believe yet more can be
synthesized and made into something new.
Yet at the same time that the logic of Bios is being imported into
machines, the logic of Technos is being imported into life.
The root of bioengineering is the desire to control the organic long
enough to improve it. Domesticated plants and animals are examples of
technos-logic applied to life. The wild aromatic root of the Queen
Anne's lace weed has been fine-tuned over generations by selective
herb gatherers until it has evolved into a sweet carrot of the garden;
the udders of wild bovines have been selectively enlarged in a
"unnatural" way to satisfy humans rather than calves. Milk cows and
carrots, therefore, are human inventions as much as steam engines and
gunpowder are. But milk cows and carrots are more indicative of the
kind of inventions humans will make in the future: products that are
grown rather than manufactured.
Genetic engineering is precisely what cattle breeders do when they
select better strains of Holsteins, only bioengineers employ more
precise and powerful control. While carrot and milk cow breeders had
to rely on diffuse organic evolution, modern genetic engineers can use
directed artificial evolution-purposeful design-which greatly
The overlap of the mechanical and the lifelike increases year by year.
Part of this bionic convergence is a matter of words. The meanings of
"mechanical" and "life" are both stretching until all complicated
things can be perceived as machines, and all self-sustaining machines
can be perceived as alive. Yet beyond semantics, two concrete trends
are happening: (1) Human-made things are behaving more lifelike, and
(2) Life is becoming more engineered. The apparent veil between the
organic and the manufactured has crumpled to reveal that the two
really are, and have always been, of one being. What should we call
that common soul between the organic communities we know of as
organisms and ecologies, and their manufactured counterparts of
robots, corporations, economies, and computer circuits? I call those
examples, both made and born, "vivisystems" for the lifelikeness each
kind of system holds.
In the following chapters I survey this unified bionic frontier. Many
of the vivisystems I report on are "artificial"-artifices of human
making-but in almost every case they are also real-experimentally
implemented rather than mere theory. The artificial vivisystems I
survey are all complex and grand: planetary telephone systems,
computer virus incubators, robot prototypes, virtual reality worlds,
synthetic animated characters, diverse artificial ecologies, and
computer models of the whole Earth.
But the wildness of nature is the chief source for clarifying insights
into vivisystems, and probably the paramount source of more insights
to come. I report on new experimental work in ecosystem assembly,
restoration biology, coral reef replicas, social insects (bees and
ants), and complex closed systems such as the Biosphere 2 project in
Arizona, from wherein I write this prologue.
The vivisystems I examine in this book are nearly bottomless
complications, vast in range, and gigantic in nuance. From these
particular big systems I have appropriated unifying principles for all
large vivisystems; I call them the laws of god, and they are the
fundamentals shared by all self-sustaining, self-improving systems.
As we look at human efforts to create complex mechanical things, again
and again we return to nature for directions. Nature is thus more than
a diverse gene bank harboring undiscovered herbal cures for future
diseases-although it is certainly this. Nature is also a "meme bank,"
an idea factory. Vital, postindustrial paradigms are hidden in every
jungly ant hill. The billion-footed beast of living bugs and weeds,
and the aboriginal human cultures which have extracted meaning from
this life, are worth protecting, if for no other reason than for the
postmodern metaphors they still have not revealed. Destroying a
prairie destroys not only a reservoir of genes but also a treasure of
future metaphors, insight, and models for a neo-biological
| > It's surprising this wasn't discovered decades ago.
| It was..
| Serrated trailing edges for improving lift and drag characteristics of
| lifting surfaces
| Patent 5088665 Issued on February 18, 1992.
| the apparatus includes a serrated panel having a plurality of span-wise,
| periodic indentations, and means for connecting the serrated panel to
| the trailing edge of the lifting surface. Preferably, the indentations
| form a plurality of saw teeth having 60° included angles between
| adjacent vertices, but other shapes of the indentations are possible.
Very funny Ads by Google, totally unrelated to the patent.
I wonder if invalifts know what they are paying for?
The BAC 1-11 of the '60s had trailing edge "ridges".
| >Serrated trailing edges for improving lift and drag characteristics of
| >lifting surfaces
| >Patent 5088665 Issued on February 18, 1992.
| >the apparatus includes a serrated panel having a plurality of span-wise,
| >periodic indentations, and means for connecting the serrated panel to
| >the trailing edge of the lifting surface. Preferably, the indentations
| >form a plurality of saw teeth having 60° included angles between
| >adjacent vertices, but other shapes of the indentations are possible.
| You missed the crucial point of the OP. The serration are on the
| LEADING, not TRAILING edge!
Howle was not surprised that the tubercles improved lift. =93The big
surprise was that they increased lift without higher drag,=94 he said.
=93Ordinarily, if you want more lift, you pay the price in drag. That
was not the case here.=94The wind tunnel experiments enabled the team to
develop CFD models that showed why tubercles delayed stall. They
formed evenly spaced hills and valleys along the leading edge of the
flipper. The rounded hills created vortices that they deflected into
the valleys.Each valley was surrounded by two hills, and the vortices
from each hill had opposite spins. When they mixed in the valley, they
accelerated the flow of liquid to the back of the flipper. =93It was
like what happens in a pitching machine in a batting cage,=94 Fish said.
=93They have two large wheels spinning in opposite directions. When you
put a baseball between them, it accelerates it very
quickly.=94Ordinarily, the airflow over an airfoil separates from the
surface when the angle of attack rises above 11 or 12 percent. The
vortices, on the other hand, energized the airflow so that it adhered
to the surface all the way back to the trailing edge. The result was
more lift and less drag...
...=93The flippers act like wings, enabling them to bank and make
turns,=94 Fish said. =93Why do they need tubercles? They have to cant at
higher angles of attack to make the tight turn they need to
concentrate their prey. If their flippers stall, it would be like
going into a turn and hitting a patch of ice and being flung out
tangentially. If they were to stall, the bubble net would be too large
and their prey would get away.=94...
It would be nice to see a full blown study, Reynolds numbers, etc.
It may only work at lower speeds. Axial flow compressor blades don't
have ridges yet they are already at 95% efficiency. If it does work
at near sonic speeds, the higher angle of attack without separation
may have some value reducing the number of stages of an axial
For adjustable pitch props it should increase the pitch range.
Increasing the specific power of a gas turbine from 100 kW/kg to 120
kW/kg may be of dubious commercial value.
It may also have some application on sail design, i.e., a lot of pre
formed battens for tacking more closely into the wind, etc. If so cup
racers are already on it.
Powered para sail may be doing it without knowing it.
Well we just blew at least a half dozen patentable inventions.
If you don't have the time to persue a patent always say, "don't know
exactly how it would be done" so someone else can protect the
The real advantage may be each stage has a different size so reducing
the number of stages reduces a lot of design work + 5-axis machining.
A shorter rotor would be easier to spin balance as well.
The parasail's primary virtue, indeed the motive for inventing it, was
to eliminate supports such as wood, composite struts, and so-forth.
Check into the invention of the Jalbert Parasail (or parafoil) and the
story of his life toward the final invention. I know the story well. He
was my Uncle.