Magnus Effect Propulsion System
Popular Science Monthly (February
1925): A Sailing Ship Without Sails: New Wonder of the Seas
Popular Science Monthly (August
1926): “We Can Trick the Wind into Saving Billions!"
Popular Science Monthly (September
1926): You Can Build a Rotor Yacht
Popular Science Monthly (September
1925): America’s First Rotor Boat
Popular Science (January 1984): Spin
Sail Harnesses Mysterious Magnus Effect for Ship Propulsion
Anton Flettner: Patents
Popular Science Monthly (February 1925)
A Sailing Ship Without Sails: New Wonder
of the Seas
By G.B. Seybold
Huge spinning cylinders harness the wind --- Inventor plans to
take strange vessel across the ocean this year.
From the wharves at Kiel, Germany, the schooner Buckau recently
put out to sea, a ship without sails or steam Like a ghost ship
it moved mysteriously through the water with no apparent means
The astounded spectators on shore knew that the boat was an old
2000-ton steel vessel and that previously 500 square yards of
canvas had been needed to propel her. But now she was denuded of
all sails, masts, and rigging. Instead, two strange cylinders,
resembling giant smoke-stacks, rose from her deck. But no smoke
was pouring from them and no engine noise was heard. There was
no churning of screws. Yet the ship plowed its way through the
rough waters of the Baltic, ad at nearly twice its former speed.
For several weeks the secret o the strange ship with the great
towers was closely guarded. People were told only that the craft
was equipped with a Flettner rotor, a new invention, the work of
Anton Flettner, director of the Institute of Aerodynamics at
When finally the explanation came, the world gasped in
amazement. For Dr Flettner calmly announced that he had returned
to the wind as a source of energy. He had harnessed it in a new
way. He had developed an invention that may permit ocean liners
to reduce their crews two-thirds and save 90 percent in fuel. He
and these spinning surfaces, presented to the wind, provided a
means of propulsion. This statement, after steamboats,
oil-driven ships, and electrically operated ships had relegated
sailing vessels into dim obscurity, immediately challenged
international attention. Several authorities, including
officials of a great steamship line, pronounced the invention
the most startling maritime development since Fulton’s
steamboat. Others were more skeptical, asking how the Buckau
would perform in a heavy sea, and are yet to be convinced of the
value of the invention. They also pointed out that the most that
can be claimed for the new ship is that it will apply to better
advantage the power available for a ship supplied with sails. It
cannot replace, in any case, the ship driven by steam or
internal-combustion engines. In the United States most experts
have adopted an attitude of watchful waiting with regard to the
The scientific principle upon which Dr Flettner based his
invention has been known for nearly three-quarters of a century.
Briefly, this is that a cylinder revolving in the wind will
exert pressure at right angles to the current. This principle,
known as the Magnus law, can be understood readily by any one
who is familiar with baseball. The giant cylinders, or rotors,
spinning in the wind, increase air pressure on one side and
suction on the other, just as the surface of a rapidly spinning
baseball from the hand of a pitcher piles up a difference of
pressure on its two sides that deflects the ball into a curve.
In the case of the baseball, of course, the equivalent of wind
is produced by the swift passage of the ball from pitcher to
Each of the two spinning towers on the Buckau rests on a
fixed pivot and moves on ball bearings. The towers are built of
sheet iron about one-half inch thick, are 60 feet high and 9
feet in diameter. Two electric motors of 10 horsepower each,
placed inside the pivots, drive the towers. Current for the
motors is generated by a Diesel engine. The total weight of the
complete mechanism --- towers, engine and motors --- is about
15,000 pounds, just one-fifth the weight of the discarded sails
and rigging on the same ship.
In propelling a sailing boat, suction, rather than pressure,
Flettner explains, is the important factor in producing motive
power. His aim was to produce artificially, by means of the
revolving towers, a greater suction power than that produced on
the vessel equipped with sails.
When wind strikes a sail, it divides equally, and in this
division there results what is called a circular current. This
works with the original current of wind on one side of the sail
and against it on the other side. On the other side where the
current whirling around the sail is added to the original
current, suction or pulling force is created, while on the other
side the clashing of the two currents results in a pressure or
pushing force. Of the two forces, suction is the greater factor
in making the boat move forward.
The revolving cylinders on the sailless boat impel it on
exactly the same principle as sails do, but more effectively, it
is claimed, because a greater suction power is produced. As the
wind hits one of the rotating towers from the side, one side of
the cylindrical surface naturally is going against it. There is
very little friction on the side where the surface goes with the
wind, and much friction on the other side.
The wind chooses the easier pathway, avoiding the side
producing friction, and most of it goes in the direction in
which the cylinder was originally traveling. Because the moving
cylinder offers less resistance than a rigid sail, the wind,
whirling around a cylinder, produces a much greater circular
current than is created around a sail. Thus the suction is
greatly increased, the inventor asserts, and the boat moves more
swiftly than one with sails.
Twenty horsepower is produced by the two motors that spin the
towers at the rate of 120 rpm. They take out of the wind about
1000 horsepower. The inventor claims that each tower produces
about 15 times as much propulsive power as that of a similar
surface of canvas. An auxiliary engine is used for getting the
ship in and out of the harbor.
When the two cylinders are turning at the same speed and the
helm is not put on, the Flettner ship sails normally at right
angles to the wind. Changing the speed of one cylinder is said
to alter the ship’s course just as changing the helm would.
N.W. Akimoff, general manager of the Akimoff Propeller Company,
Philadelphia, recently has given an explanation of the Magnus
Law as applied top the Flettner ship. He begins by considering
what would occur if the two cylinders on the Buckau were
stationary and the longest dimension of the ship were at right
angles to the wind. In that case, says Mr Akimoff, the wind
going around each cylinder would be evenly divided so that there
would be no action on the ship.
Then, suppose there were no wind, but that the cylinders were
spinning at the rate of 120 rpm.
The layers of air directly in contact with the moving
cylindrical surface would revolve with practically the same
velocity as the cylinder.
But in the case of the Flettner ship, there is a combination of
the two preceding cases --- the cylinders spinning and at the
same time wind acting upon the ship. Then on one side of the
cylinder, the velocity of the wind is opposed by the velocity of
the air adjoining the cylinder, thus retarding the velocity of
the wind. This means an increase in pressure.
On the other side of the cylinder, the opposite is true. The
velocity of the wind combines with the velocity of the air
layers next the cylinders, resulting in a decrease in pressure.
On one side of the cylinder there is an increase of pressure, on
the opposite side a decrease, so that there results a strong
force from the stronger to the weaker pressure. This causes the
ship to move forward.
The magnitude of this effect, Mr Akimoff says, may be computed
by multiplying the following quantities: the density of the air,
the velocity of the wind, the peripheral or surface velocity of
each cylinder, the circumference of each cylinder, and the
height of each cylinder. In the case of the Buckau, considering
the velocity of the wind at 40 feet/second, the forward thrust
due to the moving cylinder would be 12,000 pounds. Actually,
this would be reduced, on account of various losses, to the
extent of 10 percent.
Tests are said to have demonstrated that nearly double the
speed made by a sailing vessel equipped with sails can be made
by one with the rotor equipment. ON its trial voyage the Buckau
developed an average speed of 4.5 knots (5.2 mph) in unfavorable
weather and in later tests the ship was able to make 8 knots
The inventor estimates that with a vessel somewhat larger than
the Buckau, it would take only 18 days to sail across the
Atlantic. He is planning to make the trip late this year after
A notable feature of the ship is said to be its ease in
changing direction. With its towers reversed it is possible for
it to sail backward. A three-bladed rudder enables it to turn
around on its own length. Any change in course can be made
without coming to a stop or slackening the speed.
Supporting Flettner’s claim to practicality is his own
reputation. Anton Flettner is not a newcomer in marine
invention. He is recognized by scientists as an experimenter
along original lines. An automatic rudder that he invented a few
years ago is widely known and used.
Prof. Albert Einstein, originator of the theory of relativity,
has pronounced the rotor principle of great practical
importance. The Hamburg American Steamship Company, for example,
became so convinced of its economic value that it has decided to
use the rotors in 10 new freighters of 10,000 tons each to be
employed on its East Asia route.
On the East Asia route, wind conditions are so favorable to the
operation of the rotor ships that the company hopes tosave fuel
amounting to 60 percent of that consumed now. Ships equipped
with the device sailing from Germany to Brazil will make a
saving of 50 percent, it is estimated, while those to New York
will save from 35 to 40 percent.
One of the largest shipping companies in the world is reported
to be comtemplating using rotor ships as oil-tankers, and
steamship lines even are considering them as possibilities for
The inventor himself does not assert that his device will be a
substitute for steam or electric power on the high seas. But he
declares that while the speed of an ocean liner equipped with
revolving towers would not be increased, the invention would
save a large percentage of its coal and oil, resulting in a
great saving in storage space, as well as in the cost of fuel.
An extremely important line of inquiry developing in the
consideration of this device, is whether it will be possible to
store electrical energy, created by the rapidly revolving
cylinders, in batteries for future use. If this is possible, the
world will have a remarkable new means for producing electrical
current. Wind, the vast, unknown, unmeasured element, could be
harnessed in this easy way to propel anything from farm
machinery to an electric power plant.
Flettner has hinted of this. Wind power, he says, eventually
may supersede both coal and water power on account of its
Popular Science Monthly (August 1926)
“We Can Trick the Wind into Saving
by Robert E. Martin
That is the Rotor Ship’s Real Significance, Believes its
Inventor --- A Boy’s Idea Amazes the World.
Even in the modern age of steam and electricity and gasoline
engines, the wind still howls as hard as ever. As a source of
driving power, the wind remains quite as available and quite as
cheap as it was in the beginning of time. It still blows
everywhere without cost, and it is free to anyone who will use
Notwithstanding many generations of dependence on the wind,
most of us were ready to lose sight of these facts when, a few
weeks ago, a 31-years old inventive genius blew in from Germany
to remind us most forcibly of their truth. His reminder was in
the form of as strange a ship as ever sailed the sea --- a craft
with odd spinning funnels that caught the breezes and harnessed
As Anton Fletner’s rotor ship, the Baden-Baden, sailed into New
York harbor, welcoming crowds regarded her at first as some kind
of mysterious freak of invention. Since then, this strange
vessel and her young inventor have remained to demonstrate to
the foremost power-using nation on Earth that the wind, as a
cheap and efficient source of usable energy, is far from being a
We were beginning to think it was. After mariners for thousands
of years had set bellying sails to the breezes, we saw the
sailing ships vanish from te seas. After enturies of whirlin
windmills, we saw the picturesque towers falling to decay, and
the wide wings tattered and dejected. Served instead by
tremendously efficient power drawn from the coal and oil of the
earth and from the discoveries of electricity --- with out motor
cars, motor ships and all the rest --- we were ready to place
wind power among the has-beens of history.
It remained for the genius of Anton Flettner to reawaken us ---
to prove that it is not the wind itself, but rather man’s method
of capturing the wind, that has run out of date. What he has
done is simply to find a new and better way.
The rotor ship Baden-Baden, which astonished thousands of us
during it visits to American ports, is the first application of
Flettner’s revolutionary ideas. It is only a beginning.
Its real importance lies not so much in its immediate proof that
wind power can be used effectively as a fuel-saving auxiliary
for steamships and motor ships, as in te vast possibilities it
offers in te future for cheaper power on land as well as on sea.
Flettner’s invention, as described in detail in the February
1925 issue of Popular Science Monthly, is simply the application
of the scientific principle, known for nearly three-quarters of
a century, that a cylinder rotating in the wind exerts a force
at right angles to the wind. On the side of the cylinder moving
against the wind, the air piles up and exerts pressure. On the
opposite side suction is created, exerting a pull. Of the total
forces on the cylinder, about 7/8 is due to suction, and 1/8 to
pressure. And this force, Flettner has found, is ten times as
great as that produced by an equal area of canvas sail.
‘Blue coal’ is the name applied by the inventor to the
wind-fuel he has thus harnessed for the use of mankind. “It is
wonderfully cheap", he tells us, “and it is available to the
world in billions of horsepower".
Just when, where, and how extensively it will be available not
even Flettner himself has been able to predict with certainty.
The idea is still in its babyhood. Its possibilities seem almost
limitless. We do know, however, that the first Flettner rotor
windmill is being operated by the city of Berlin and is reported
to be at least 30 percent more efficient than the best of the
old-time wind sail-mills; also that a second rotor-mill, capable
of developing 2000 or more horsepower, is being completed. We
know too, that the same principle recently has been applied by
certain American automobile manufacturers in rotor ventilators
for closed cars; that Flettner is working on other industrial
applications, and that he even predicts that rotors eventually
may replace the wings on airplanes. Finally, we know that the
world is eager for just such a source of cheap power, for the
irrigation and reclamation of vast desert lands, and for
industry in regions where water power is unavailable.
Billions of horsepower absolutely free! Anton Flettner seems to
have been born with a genius to sense the wasted force of
howling gales, and to devote his inventive mind to their
mastery. Sprung from a long line of seafaring men, his first
dreams of invention began when, as a boy, he sailed before the
mast in his father’s ships. To him the elements were an endless
source of wonder. When a hurricane struck his vessel off the
Gold Coast, he was inspired by the tremendous power lost in the
gale. Conceiving a plan for a wind turbine, he drew rough
sketches --- enough to convince him that he would need wider
technical knowledge before he could carry his dream to
completion. He left the sea and went to school. For five years
he devoted himself to physics and higher mathematics, first at
Frankfurt-am-Main, near his birthplace, then at Berlin.
His first creation was an invention which not only failed but
nearly ended in disaster. It was a metal sail, somewhat like an
airplane wing, designed as a substitute for canvas. He strung it
on the rigging of a small boat and set out. In a light breeze
the boat almost capsized, and its frightened creator quickly
sped back to port. Yet this first attempt, futile though it was,
at least marked a step toward the invention of the metal rotors
which eventually were to drive the Baden-Baden.
Another boyhood invention which also merely missed a tragedy,
was a method of wireless control of moving objects at a
distance. Anton, then a youth of 17, could find only one man who
saw any use for it. That man was the owner of a circus. He
commissioned Flettner to build a device that could put a
riderless horse through its paces at a distance. The machinery
was to be hidden in the saddle.
On the first trial the horse displayed a strong dislike for the
mysterious saddle. It bucked so violently that it jounced the
delicate control mechanism out of order. Left to its own
devices, the machine began to jerk and whip the reins with such
wild abandon that the horse jumped a fence and ran away. That
was the end of wireless control for Flettner for the time being,
although in later years, during the world war, he was to develop
a system for radio control of army tanks and airplanes which
went through paces that amazed high army officers.
Meanwhile, during his search for a new way of capturing the
wind, Flettner hit upon the idea of a free-swinging rudder, one
of the most valuable of all his inventions. At the outset this
startling departure from the common hinged ruder met only with
ridicule. Technical experts scoffed at the idea that a rudder,
free to swing on its axis like a weather vane, could possibly
influence the course of a ship. In fact, experts in the German
patent office refused the young inventor a patent, accompanying
their refusal with a lengthy document containing complicated
mathematical calculations to prove that the rudder could not
“All right", said Flettner. “I’ll prove their calculations are
wrong. And he did He has lived to see his invention installed on
more than a hundred ships, arge and small, and on at least 500
airplanes. Today his rudder is being is being adopted by
shjipbuilders the world over. The secret f its operation is a
small panel, or fin, set into the tail of the rudder. This fin,
rather than the main rudder, is controlled by the navigator. He
simply swings the fin; the fin steers the rudder; the rudder
steers the ship.
When the fin is set at an angle to the rudder, it swings the
latter to a position where water pressure on rudder and fin are
balanced, Even if the impact of a bid wave temperoraily upsets
this equilibrium, the rudder immediately returns to its former
position of balance.
The increased safety and economy of such an arrangement are
obvious. Control of the Flettner rudder requires on about 5
percent of the power needed to manipulate an equally large
rudder of the old type. Even a ship of 1000 tons may be steered
From the difficulties he encountered in convincing experts of
the practicability of the rudder, Flettner knew that he would
have even greater trouble to put over the rotor ship idea, which
he eventually developed out of the failure of his metal sail. He
was not far wrong. When he tried to explain the rotor to
technical men he found that either they would not, or could not
understand it. Only when he built a small working model of his
rotor ship, spinning the rotors by clockwork, did he convince
them that it would work. And not until the Baden-Baden sailed
6200 miles across the Atlantic, using on 12 tons of fuel oil, as
compared with 45 tons for a motor ship of the same size without
rotors, did he convince skeptics of its economy.
This economy, he expects, will be demonstrated even more
strikingly by the new 3000-ton 3-rotor ship Barbara recently
launched by the German government. Her first long cruise
will bring her to the United States some time in October.
Ion the application of the rotor principle to windmills,
Flettner sees even a more valuable source of cheap power. The
first rotor mill in Berlin is designed to turn an electric light
and power plant. It consists of a wind wheel, some 60 feet in
diameter, with four spokes, and on each spoke is mounted a
conical rotor which is spin by a small electric motor deriving
its power from a central generator in the windmill tower. The
arrangement is such that the wind, always blowing at right
angles to the wheel, exerts a side pressure on the revolving
rotors. Not only is the force of the wind on the cylinders ten
times as great as it would be in sails of the same area, but the
rotors respond to the slightest breezes.
To utilize the wind still further, Flettner now proposes to
attach to the outer ends of the spokes four secondary windmills
resembling small airplanes with streamlined bodies and
propellers set against the wind. Motors driven by these small
propellers, the inventor has found, will develop 64 times the
speed of the main rotor arms.
Whether “blue coal" ever will supplant black coal in industry
and commerce remains for the future to decide. In Germany, where
nearly 75 percent of the available water power is now devoted to
useful purposes, engineers are predicting that before long the
nation will be obtaining a large part of its electrical energy
from the wind. Government Electrical Engineer Foerster, in a
recent statement in Berlin, predicted that “the time is not far
off when forests of windmills will be centralized in various
parts of the country to supply power and light to nearby cities
For the present time, Anton Flettner has succeeded, at least,
in arousing the world to the wealth that howls about our
Popular Science Monthly (September 1926)
You Can Build a Rotor Yacht
By Ernest Welleck
Hints on Using Flettner’s Marvelous Ideas in a Miniature
Judging from the interest that so many readers of the Home
Workshop family have taken in the building of ship models, it is
reasonable to assume that they will be doubly interested in
building on a small scale a working model of a rotor ship, Anton
Flettner’s sensational invention.
Although the rotor and its application for propelling ships and
windmills, as described last month in Popular Science Monthly,
are protected by patents in all civilized countries, those who
make miniature rotors need not fear suit for infringement. The
inventor, during his recent visit to New York, cheerfully
extended his permission for Home Workshoppers to build such
models. At the same time he expressed the confident belief that
the building of small rotor ship models not only will give the
builders pleasure, but also will teach them intensely
interesting lessons in aerodynmaics.
Before Mr Flettner built his first rotor ship, the Buckau, now
Baden-Baden, he prepared the round by several months of
experiments with models. He established by tests that the
potential propelling power of a rotor cylinder of a given
projection surface is equal to that of a sail or sails with an
area ten times as treat. The theory of this was explained last
month and is again indicated diagrammatically in Figure 4.
As rotors may be used on any ship, practically any hull design
may be chosen for the rotor ship model. Those among the
workshoppers who have had experience in building sailing models
with find no difficulty in making a suitable hull…
Anyone who has built several ship models and wishes to change
on of them into a rotor ship may do this easily by removing the
masts and sails and putting in their place one or two rotor
The rotor cylinders may be made of stiff paper, cardboard or
thin sheet metal. The dimensions for a hull 2 ft long are given
in Figure 5. If the hull is made larger or smaller, the rotor
dimensions should be changed proportionally.
The rotor or rotors always should be in a vertical position
when the ship is on an even keel.
In a model built for looks only, the placing of the rotor or
rotors is a simple matter. Each cylinder is provided with a
spindle which passes through the centers of the two end plates.
The lower end of the spindle is inserted in a hole in the deck
of the ship or in a small cylindrical base, slightly larger in
diameter than the cylinder of the rotor and about 1/2 inch high.
When a working model is attempted, some means for turning the
rotor or rotors at a rate of 100 to 150 rpm must be provided. If
one is content to sail the model in only one direction in
relation to the wind, that is, with the wind either to port or
starboard, it is sufficient to have the rotation in one
direction. To allow the boat to be sailed back and forth across
a pond, the mechanism must allow the direction of rotation to be
The selection for the source of power for the rotor must be
left to the ingenuity of the builder of the model. The most
primitive and cheapest, but not the most satisfactory power
plant, is undoubtedly a rubber-band motor similar to that used
to rotate the propellers of small airplane models.
One type consists of a rod about 1 ft long, with a fixed disk
at one end and a rotatable disk at the other. Through holes near
the periphery of each disk rubber bands are threaded from one
disk to the other. At one end the rod is provided with a crank
handle and a ratchet wheel. When the crank is turned, the rubber
bands are twisted around the rod, which is held in place by the
ratchet when the required tension has been reached. The tension
of the twisted rubber bands would cause the rotatable disk at
the other end of the rod to revolve as the crank is set in
motion, were it not for the fact that it is held by a trigger.
When the trigger is released, the wheel begins to turn and, as
it is geared to a small cogwheel on the propeller shaft, it
imparts to the propeller a rapid whirling motion. A similar
contrivance may be stowed away in the hold of the ship model and
geared to the shaft of the rotor to give the required speed.
The spring-actuated mechanism of an old alarm clock may be used
to better advantage for operating the rotor.
With some ingenuity a speed governor may be installed, and a
gear shift may be interposed between the drive wheel or shaft of
the power source and the spindle of the rotor, so that the rotor
cylinder may be rotated in either direction.
Anyone who possesses a small electric motor driven by a
miniature battery may consider himself particularly fortunate,
because, wit this power plant in te hold of the model and geared
to the rotor spindle, his ship will be able to undertake much
These suggestions, which by no means exhaust the possible means
for supplying the required motive power, make it obvious that it
would be impractical to give definite directions for installing
all of these motors or hooking them up with the rotor. These
problems, different in each individual case, must be solved by
the workshopper who undertakes to build a working model of a
If the works of an alarm clock or a mechanical toy are
selected, they should be placed as low as possible in the hold
of the ship, so that they will act as ballast and add to the
stability of the ship. In placing the works, it must be
remembered that they must be wound from time to time. Do not
locate them so that it will become necessary to dismantle the
model to wind up the spring.
Another problem is presented by the hooking of the driving
mechanism with the rotor to give the proper speed. The simplest
scheme is illustrated in Figure 2. In a fair wind the rotor
should make about 100 rpm; in a gentle breeze, about 150.
On the Baden-Baden the rotors are driven by individual electric
motors, the speed of which can be regulated and controlled from
the bridge. The best that can be done in a rotor ship model is
to provide for a maximum speed of 150 rpm and devise some means
--- on either the rotor or the driving shaft --- for reducing
the speed of the rotor if the wind is stroner.
Without a gear shift to make it possible to turn the rotor
cylinder either clockwise of counter-clockwise, the ship model
can sail only in wind coming from one direction. If you imagine
the rotor turning clockwise, for example, your ship can sail
only when the wind comes from the left side, facing the bow.
Wind coming from the right would drive the ship backwards.
Popular Science Monthly (September 1925)
America’s First Rotor Boat
Naval Officers Embody New Ideas in Odd Craft.
The interest with which the strange rotor ship designed by
Anton Flettner was greeted a few months ago, when it sailed out
into the Baltic Sea, little surpassed that of the
spectators who recently watched the trial voyage of the
first rotor ship built in America, on the Charles River at
Cambridge, Mass. This American boat, constructed by two young
naval officers, was the first actual demonstration in this
country of how a revolving metal tower can replace canvas sails.
Lt. Joseph Kiernan and W. Hastings. Students in naval
architecture at the Massachusetts Institute of Technology, were
greatly interested in reports of the rotor ship. They decided to
build one for themselves. They acquired an abandoned navy cutter
about 30 feet long and 8 feet wide, and with discarded materials
from other boats fixed up the rotor apparatus.
In designing the tower they used data gathered in exhaustive
experiments in aviation at Langley Field, VA, where for some
time the US Army has been studying the application of the Magnus
theory of air pressures to aircraft. The American boat employs
the Magnus effect, just as the German boat does.
The Magnus principle, as applied to a rotor boat, may be
expressed as follows:
The wind hitting the side of a rotating cylinder goes around
with the cylinder. Decreased air friction on one side of the
cylinder creates suction, and increased friction on the other
side causes pressure. These two forces together, move the boat.
The American boat differs in several respects, however, from
Flettner’s craft. While the German inventor used two cylinders
on his 600-ton boat, the Americans decided to use only one on
their cutter. They believed that when two cylinders were used,
one interfered with the other’s action. Flettner also apparently
has come to this conclusion, for he is experimenting now with a
single-tower system of propulsion as indicated by one of his
latest designs --- a rotor yacht that recently appeared in
Germany in competition with sailing yachts.
The cylinder designed by Lts. Hastings and Kiernan for the
American craft is 3-1/2 ft in diameter and 9-1/2 ft high. This
is smaller in proportion that the tower used in the original
Flettner ship, and it revolves at greater speed. On the Flettner
ship, at the top of each of the cylinders, was a rim projecting
about 14 inches. The purpose of this was to maintain the suction
and pressure zones extending up and down the opposite sides of
the cylinder, and to prevent air from entering these zones from
above and disturbing them. These rims revolved with the
The disk used on the top of the American rotor tower is
stationary. The rotor tower is mounted in the middle of the boat
on a ball-bearing base and is supported by an interior column.
It is driven by a 5-hp motor located at its base.
In the first test of the boat on the Charles River, its
estimated speed was about 3 knots (3-1/2 mph). With the tower
rotating at 260 rpm in a 15-mile wind, the designers believe
their boat will attain a speed of 7 knots (8 mph). They estimate
that it would require 10 ho to drive a boat of the same size 6
mph by propeller. Its development is an indication of future
Popular Science (January 1984)
Spin Sail Harnesses Mysterious Magnus
Effect for Ship Propulsion
The Magnus Effect was discovered in 1852, and a ship using
it was sailed across the Atlantic in 1926. Its inventor
predicted that it would launch a new age of wind-powered
ships. But cheap oil sank that idea. Now, with oil prices up,
the Magnus Effect ship is back. Its design has been worked out
for ships of all classes, and instrumented tests have proved
the device’s effectiveness. The day of the rotor-assisted
windship may at last be at hand.
By C. P. Gilmore
The sky was blue and the wind fresh fine morning recently as I
stepped aboard the yacht Tracker. The 42-foot craft with a
strange, giant cylinder mounted on the forward deck was hanging
at anchor in Edgartown Harbor in Martha’s Vineyard, Mass.
A pair of legs protruded from beneath the tower, as though the
thing was in the process of eating a man and only his legs
remained. That wasn’t the case, of course. Lloyd Bergeson,
president of Wind Ship Development Corporation, explained that
his son, Henry, an engineer, was making a change. The hull
vibrated when the tower rotated at several hundred rpm, and
Henry was bolting in a brace to stop the vibration. He crawled
from under the tower and announced that the rig was ready for a
test. Then he started up a lawn-mower sized engine just aft of
As the engine pu-putted to life and the tower began to rotate,
the 17-ton Tracker suddenly lurched forward and to the right and
was soon straining against the anchor. I thought it was going to
drag the anchor ad, with no one at the helm, go crashing through
the scores of yachts moored throughout the harbor. Lloyd
Bergeson, grinning widely, shouted, “Underway under rotor
That was my introduction to the Flettner rotor. Even though I
understood the principle, it was hard to believe that that rotor
spinning on the bow had actually propelled the boat forward. Yet
the fact was undeniable; the yacht had lurched forward as though
the diesel engine below decks had been started and shifted into
Bergeson mounted the rotor on the tracker to prove to the
maritime community that the age of wind-assisted shipping is
about to return and that ships using strange spinning towers on
their decks can save enormous amounts of fuel as they ply the
world’s oceans. He has formed Wind Ship to promote the idea. And
the world, apparently, is beginning to listen.
Physicists call the force that moves the Tracker the Magnus
Effect. It was discovered in 1852 by a German physicist, Gustav
Magnus, who was trying to find out why spinning artillery shells
sometimes curved in unpredictable ways.
What Magnus discovered is that a sphere or cylinder spinning in
a moving airstream develops a force at right angle to the
direction of the moving air (se diagram). I discovered in
Edgartown Harbor that the force has amazing power. It can
develop hundreds of pounds of thrust on a craft the size of the
The first attempt to drive a ship with the Magnus effect was
made in the 1920s by another German physicist, Anton Flettner.
He mounted two spinning cylinders, which have since been called
Flettner rotors, on a schooner and sailed the ship across the
Atlantic under rotor power in the spring of 1926.
Despite the fact that Flettner’s rotor ship worked and at least
one other rotor ship went into commercial service, the idea
gradually died. “The shipping industry didn’t care about saving
energy", said Bergeson. “Oil was a dime a barrel and was
replacing coal. And about that time Flettner turned to designing
planes for Hitler".
Flettner Rotor Revived
In the early 1970s Thomas Hanson, a west Coast engineer who had
been working on helicopter design, turned his attention to wind
turbines. He discovered Flettner’s work and became convinced
that many of the problems of large wind machines could be solved
by using Flettner’s rotors in place of the usual blades. The
result of this work appeared on the cover of Popular Science
last August (1983).
Enter Bergeson. A naval architect with a degree from MIT, he
had spent his life in the shipbuilding industry, supervising the
production of nuclear submarines for General Dynamics and
functioning as general manager of two major shipyards.
The 66-year old Bergeson stood on the deck of the Tracker,
looking across the harbor with a sailor’s squint. “I had always
wanted to sail across the Atlantic single-handed", he said when
I asked how he got interested in sail-assisted shipping. “So in
1978 I did it". He sailed his 43-foot yacht, the Cockatoo II, to
Norway by himself.
During the 31-day crossing, Bergeson thought about the shipping
industry and became convinced that enormous amounts of money
could be saved if ships used the wind to furnish some of their
propulsion. They’d still have engines. But why not also have
some sort of sail that would take advantage of wind when
conditions were right?
In 1979 he formed Wind Ship to promote the idea and, as his
first major project, undertook a study of sail power for the US
Maritime Administration. His report, published in 1981,
investigated different kinds of sail-assist schemes. It
concluded that properly designed sails could be built to operate
from the bridge with no additional crew, that they would be
easier to maneuver than conventional ones, that such rigs would
benefit both new ships and retrofitted ships, and they’d save a
lot of fuel.
Bergeson put his theory to the test in 1981. He designed a 3000
square foot sail for the 3100-ton dead weight ship Mini Lace, a
freighter operating in the Caribean out of New Orleans. His
calculations showed that fuel savings would average about 20
percent. After 18 months of operation, the ship’s owner
published the actual results. Savings had been a satisfying 24
percent. Other companies around the world had been experimenting
with sail assistm, notably the Japanese tanker Shinaitoku Maru
[PS, Dec. 1980], but none did so well as the Mini Lace.
Although the Mini Lace was a success, Bergeson’s original dtudy
had investigated different types of sails. He had concluded that
three --- including the cat rig used on the Mini Lace --- had
great promise. Another promising type was the wing sail, which
looks like an airplane wing standing on end. The third was the
Windmill to the Rescue
At about the time Wind Ship had done the preliminary
engineering of a rotor design that could be tested, BERGESON
HEARD ABOUT Hanson’s work with the wind turbine. It turned out
that the rotors Hanson had built were almost identical to those
Bergeson had calculated he would need, so a Hanson rotor was
shipped from California to Massachusetts, and the project became
a joint enterprise between Wind Ship and Hanson’s company,
I first saw the joint enterprise, the tracker, that morning in
Edgartown Harbor. The most striking thing about it, of course,
is that rotor. It’s 42 inches in diameter and 24 feet hih. It is
driven --- up to about 600 rpm --- by a hydraulic motor which in
turn is driven by a hydraulic pump turned by a small gas engine.
When the vibration problem had been solved, we got underway
with the craft’s owner, Dave Frantz, at the helm. We were the
center of attraction as we sailed between the rows of anchored
yachts. With Frantz in control, the Tracker moved majestically
through the anchorage at about 4 knots and put out into open
sea. With about an 18-knot wind, the boat moved easily at 6
knots under rotor power alone. By adding a little power from the
diesel, Frantz eased it up to a little over 7 knots.
Some funny things: You have to learn to sail all over again.
The best point of sail is a beam reach --- with the wind coming
directly from one side or the other --- because then the force
vector generated by the rotor is directly ahead. To tack, you
have to stop the rotor and start it again in the opposite
direction as you go through the wind. A rotor-powered boat can
sail to within 25 degrees of the wind. That compares with the
ability of a conventional sail-powered vessel to sail within
about 45 degrees o the wind. The most peculiar anomaly: As you
sail on a broad reach --- say 135 degrees to the wind --- the
vector moment is actually such that the boat heels into the
During the day I asked Bergeson how projected fuel savings for
the Tracker had worked out with actual findings. He said that
predictions were for a saving in the 20-20 percent range but
that they had not had an opportunity to make accurate
measurements. A week later, Tom Marriot, a member of the PS
auto-test crew, drove to Cape Cod with the PS precision
fuel-consumption measuring equipment and met the Tracker. Over
the next few weeks, with the measuring equipment aboard, the
Tracker went through a series of trials. The results are as
Power Mode --- Ave. Wind (Knots) --- Ave. Boat Speed (knots)
--- Ave Fuel Saving (%)
Rotor-Assist --- 16.1 --- 7.0 --- 44
Rotor-assist --- 12.9 --- 6.0 --- 27
Rotor Sailing --- 17.7 --- 5.3 --- 100
Under rotor power alone, the Tracker reached a maximum speed of
6.1 knots in an 18.4 knot wind and a true wind angle of 122
Bergeson is demonstrating the Tracker to fishing-boat owners,
talking to large shipping companies, and presenting scientific
papers at maritime conferences. And interest is growing. He now
has a Navy contract to study the conversion of a military
sea-lift ship to rotor-assisted propulsion. He is also
conducting similar studies for a number of independent shipping
companies, including major oil and cruise-ship companies.
The economic potential certainly is there. Bergeson has
calculated that the world’s shipping fleet consumes 730 million
barrels of petroleum a year at a cost of $30 billion. If only 20
percent of the world’s fleet adopted sail assist, the savings
would be on the order of 91 million barrels a year --- almost $3
The payback to an owner can be astonishingly quick. The entire
rig for the Mini Lace cost $250,000. But the owner’s records
show that the sailassit saves $48,000 worth of fuel a year. In
addition, average speed is increased by 5 percent, which means
that the ship can make more trips. Extra income from this source
was $9200. At that rate, the rig would pay for itself in a
little over 4 years. But there’s more. On the New
Orleans-Jamaica route, where winds are usually unfavorable, the
fuel savings was an incredible 36 percent, and the speed was up
18 percent. If the ship were used on similarly favorable routes,
the payback would fall to an astonishing 1.7 years.
Bergeson is totally committed to the idea of sail assist and
thinks that it might come in three forms. The cat rig is useful
in some applications, as demonstrated b y the Mini Lace. But the
wind sail is more efficient and might be appropriate in many
application. And the Flettner rotor, he believes, is the most
efficient and can be smaller, lighter, and most trouble-free in
operation. “As far as I’m concerned, I’m interested in findgin
the best way for every application", Bergeson says. “In the
development of something like a nuclear submarine, you try two
or three things to see which is best. When it comes to these
sail schemes, I think they’re all winners. They are
complementary. I love ‘em all, and I see a future for all of
Anton FLETTNER PATENTS
Air vehicle with rotary wing
Balancing of aircraft
Arrangement for exchanging energy between a current and a
Method and device for the steering of ships
Device for steering aircraft
Counterbalance for rudders
Hélicoptère à rotors s'engageant par paires l'un dans
Anordning ved Flyvemaskiner med parvis i hinanden
Anordning ved Flybemaskiner med parvis i hinanden
Hubschrauber mit paarweise ineinander kämmenden Rotoren.
Doppelschrauber mit Fluegelanschlaegen
Doppelschrauber mit paarweise ineinanderkaemmenden
Vorrichtung zum selbsttaetigen Regeln des Schubes einer
Avion à ailes tournantes
Flyvemaskine med roterende Vinger.
Flugzeug mit umlaufenden Tragflügeln.
Dispositif d'affichage et de publicité
Anzeige- und Reklamevorrichtung.
Steering gear for vehicles
Lenkeinrichtung an Fahrzeugen, insbesondere
Dispositif de ventilation
Anordning ved afbalancerede Skibsror.
Procédé et arrangements pour gouverner des navires
Steueranordnung für Wasser- und Luftfahrzeuge.
Système de commande pour gouvernails munis de surfaces
Improved steering device for marine and aerial vessels
Rotor à ailes réglables
Mécanisme compensateur pour la manoeuvre de surfaces se
mouvant dans un milieu dépourvu de rigidité
Governing of surfaces moving within alpha nonrigid medium
Improvements relating to the steering planes of air-craft
Einrichtung zum Steuern von Schiffen
Hjälperor til Luftfartöjer
Styreror til Skibe
Indretning til Styring af Luftfartöjer.
Device for steering aircraft
Method and device for the steering of ships
Procédé et arrangements pour gouverner des navires
Durch Fernverstellung eines mitschwingenden
Hilfssteuerruders betätigbares Hauptsteuerruder.
MARINE STEERING DEVICE
DEVICE FOR STEERING SHIPS
DEVICE FOR STEERING AIR CRAFTS
Anton Flettner (November 1, 1885 in Eddersheim (today a
district of Hattersheim am Main) – December 29, 1961) was a
German aviation engineer and inventor. He made important
contributions to airplane and helicopter design.
During World War I, Flettner developed a device allowing to
raise or lower a plane's nose for better control, today known as
the "trim tab".
Following World War I, Flettner directed an aeronautical and
hydrodynamic research institute in Amsterdam.
In the 1920s, he bought a schooner and added two rotating
50-foot cylinders onto it, and thus was the first to build a
propulsion system based on the Magnus effect. The ship was named
Baden-Baden and crossed the Atlantic in 1926. It could outsail
normal schooners under moderate to heavy winds, but was finally
destroyed by a storm in 1931. A commercial ship, The Barbara,
was also built and sailed to the U.S.
During World War II, he headed the Flettner Aircraft
Corporation which specialized in helicopters.
Anton Flettner was also noted for his invention of the famous
Flettner rotary ventilator, widely used on buses, vans, boats,
campervans and trucks to assist cooling without the use of
energy - modern derivatives of his ventilator are still
manufactured in Britain by Flettner Ventilator Limited. The
helicopter invention was accomplished from his wealth from the
ventilator business, whose success also depended on the skill of
his wife, Lydia Freudenberg Flettner. Although Anton Flettner
built his helicopters for the German military, primarily for
navy spotter use, his wife was Jewish. He held a personal
relationship with Himmler who in turn had a lower ranked officer
and his men escort her family safely to Sweden for the duration
of WWII. His partner and confidant was Dr. Kurt Hohenemser, a
brilliant and thorough engineer from whom the details necessary
for the helicopter's success was derived. Dr. Hohenemser's
father was also Jewish, yet the pair remained unharmed during
their tenure together throughout the war as they worked to
develop the helicopter for military use.
While the final product, the Kolibri FL282 (Kolibri means
Hummingbird) was able to be factory assembled, Flettner and
Hohenemser insisted that they were the only ones who were
capable to assemble the complex intermeshing rotor gearbox
assembly. This bottleneck in production kept the FL282 from ever
gaining a serious military role.
After 1945, Flettner (along with many other aviation pioneers)
moved to America, where he started a new Flettner Aircraft
Corporation which developed helicopters for the U.S. military.
Flettner's company in the US was not commercially successful,
but his work was shared with the Army Air Corp. Many of the
Flettner designs are found in Kaman helicopters of later years.
Flettner died at 76 years of age in New York City on December