Tethered Airfoils for Renewable Energy using Wind Power, Wind Generators

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  Ships that have sails can tack over water, but ships equipped with high tech inflatable kites, Tethered  Airfoils, could do it more efficiently and at greater speed.  If a hydrofoil replaced the ship, these craft could tack  to any destination and arrive faster than the speed of the wind.  Tethered Airfoils could also act as Air Tugs causing freighters to tack across oceans and save as much as 15 billion dollars of fuel costs annually.  A pair of  Tethered Airfoils could tack in the air by having one airfoil in higher faster winds and the other airfoil in lower  slower winds.  If one airfoil were in the jet stream and the other just below it, then the craft could tack hundreds of miles an hour without consuming fuel and yet be able to transport people and freight anywhere around the world between unimproved open fields.  Also by tacking, it would be possible to maintain position in the jet  stream and use an on board wind turbine to generate electricity with which to synthesize helium, then transport  the helium to a power station.  Over Japan, 3.72 Kilowatts (4.99 horsepower), flow through each square foot of  the jet stream.  This is equivalent to 714 Kilowatts (958 horsepower) flowing through an area the size of a soccer  goal.  However, the power that a wind turbine generates is proportional to the area that it sweeps per unit time. So a small turbine could generate considerable power in the jet stream if it sweeps through a large area in a  short period of time.

These are the dreams of Wayne German, a software engineer by vocation, and an aeronautical  engineer by avocation.  After more than twenty years of dreaming and researching Wayne submitted an article, “Tethered Airfoils: An Enabling Technology”, to the Flight Research Institute which was a non-profit offshoot of  Boeing.  On the strength of that one paper alone Wayne was invited to become a Project Leader at the Flight Research Institute, and the Retired Chief of Product Development at Boeing and a Retired Engineering  Supervisor at Boeing, both volunteered to participate on the project.  Proposals were sent to organizations and  foundations to obtain funding to develop prototypes, but without a track record no funds were received.

Wayne’s colleagues at the Flight Research Institute wrote in their review of some of these proposals:

"As a result of our studies of your invention we have concluded that your concept is  fundamentally sound and we believe that your goals can be achieved by step-by-step  demonstrations and that each step can be accomplished within a reasonable effort."

It is now Wayne’s belief that much of this early prototype development can be done by knowledgeable  people volunteering their time and/or resources to participate as members of the Tethered Airfoil Research And Development group (TARAD) over the Internet, if not in person.  Particular skills that would be required would be   knowledge in aeronautics, mechanics, software, electronics, marketing, proposal writing, website development,  project leading, management, public relations, and assisting all of the above (i.e. students or other motivated individuals).  Knowledgeable retired individuals would particularly be encouraged to participate.  Project issues  would be determined by voting.  Wayne believes that a number of these goals could be accomplished with just a  few thousand dollars, if not hundreds of dollars.

Wayne believes Oregon would be a good state in which to begin these developments for the following  reasons:
1)    Oregon has beaches where four-wheel drives could pull very large kites at constant velocity to monitor their  design and the functioning of their control surfaces.
2)    At the Yakima Test Firing Range Wayne has an agreement in principle to be able to fly kites as high as the jet  stream -- free from any possible aircraft interference.
3)    The Columbia River Gorge would be an excellent place to test the ability to cause a boat to tack over water.  Any   kite system that can successfully tack in the Gorge can tack anywhere.
4)    We have technical people from Boeing and Intel nearby to provide guidance and input, and
5)    The Evergreen Aviation Museum in McMinnville Oregon may offer facilities and a place to meet.

The first three goals that Wayne would like to accomplish in Tethered Airfoil development would be to:
1)    Develop methods to construct Tethered Airfoil wings, and methods to manipulate their control  surfaces,
2)    Use a Tethered Airfoil to tack into the wind and with the wind with a small motorboat or kayak, and
3)    Demonstrate that a Tethered Airfoil can generate more electricity flying downwind at a high angle of attack than it consumes flying back upwind at a low angle of attack, and then demonstrate that a Tethered Airfoil  can generate far more energy flying corkscrews and figure 8’s downwind instead.

 If you have questions, or comments, or wish to participate, or receive a copy of the paper “Tethered   Airfoils: An Enabling Technology” you are encouraged to contact Wayne German.
 Contact Wayne German about Tethered Airfoils Here

(This is a text version of a Word document of the same name.  You
may request it at the email address below.)

By Wayne German
October 22, 2003

   1. Overview

   Occasionally, new technologies are developed that meet global needs
and generate considerable revenues in the process.  Widely recognized
examples are the light bulb, transistor, radio, television, computer,
automobile, and airplane.  The intent of this paper is to introduce another
technology, Tethered Airfoils, whose potential to generate revenue
exceeds all of these.  The development, marketing, and deployment of this
technology could yield the cheapest and cleanest means of: 1) electrical
power generation, 2) shipping, 3) transportation, and 4) communication
(radio signal relaying).

   Each of these four areas could be revolutionized by the introduction
of products that incorporate Tethered Airfoils.  For the purpose of this
paper, Tethered Airfoils are aerodynamically efficient inflatable kites
in the shape of wings that have lift to drag ratios of ten to one or
greater.  Unless stated otherwise, they are extremely light when inflated
with air and lighter-than-air when inflated with helium or hydrogen.
These airfoils have on board power and autopilots for stable, remotely
controllable flight.  Most importantly, they provide a means of
harnessing wind power to provide the mechanical power required to generate
electricity, synthesize fuel, or provide propulsion.

   2.  The Potentials of Tethered Airfoil Technology

  The potential applications for Tethered Airfoil technology are
numerous.  Some of the applications that should be possible are listed below.
The applications that could most easily be developed are listed first
followed by those that would require more skill and experience.

2.1. Wind power generators that use reciprocating airfoils to produce
electricity on the ground.
2.2. Water pumps that use reciprocating airfoils to pump water for
irrigation.
2.3. Sailing craft that have a Tethered Airfoil to tack into the wind
or with the wind -- the airfoil    being held aloft by aerodynamic
lift, or buoyancy (helium or hydrogen), or both.
2.4. Recreational airships that fly over water without fuel by tacking
in the air while being attached by tether to submerged hydrofoils.
2.5. Paraglider wings and ultralight aircraft that could use buoyant
lift, and/or the methods of manufacture that will be discussed later in
this proposal to greatly reduce cost.
2.6. Passive self-regulation of altitude using highly pressurized
lighter-than-air structures.
2.7. Ship and vessel propulsion assistance with minor retrofitting.
2.8. Energy conserving tugs that could deploy Tethered Airfoils to pull
unmodified vessels across oceans.
2.9. Land Based High altitude wind power generators that use
reciprocating Tethered Airfoils to tap winds as high as the jet stream to produce
electricity at a generator on the ground.
2.10. Sea Based wind power generators (low or high altitude) to produce
electricity at a boat or barge.
2.11. Flight without fuel over land or water by using an airfoil at
lower altitude tethered to another airfoil at a higher altitude to harness
the power available in the differential velocities of the two
altitudes.
2.12. Radio signal relaying by hovering indefinitely in the air while
using excess wind to generate electricity to relay radio signals.
3. Conceptual Descriptions of Products Incorporating Tethered Airfoil
Technology

   3.1. Wind Power Generators

Wind power generating systems can be developed using reciprocating
Tethered Airfoils.  Using two airfoils and a tether that passes from one
airfoil through an electrical generator on the ground to the other
airfoil, power could be generated if one airfoil flew at a high angle of
attack (nose up) while the other flew at a low angle of attack (nose into
the wind or slightly down).  The airfoil flying at a high angle of
attack would have greater lift and drag, which would cause it to be blown
downwind and upward while pulling the other airfoil upwind and downward.
Electricity would be generated as the cable is pulled and the generator
is forced to spin.

As the airfoil having the lower angle of attack approaches sufficiently
close to the generator, remote control could cause it to assume a high
angle of attack and cause the airfoil further downwind to assume a low
angle of attack.  This would cause the upwind airfoil to fly downwind
and the downwind airfoil to fly upwind.  Periodically changing the
angles of attack would, therefore, cause the two airfoils to reciprocate in
the sky producing power on the ground.  Between strokes, as the
airfoils change their angles of attack, and as the cable changes its direction
of travel, there would be a brief time when no power would be
generated.  Therefore, in Tethered Airfoil wind farms the flights of all the
airfoils should be synchronized so that as few as possible would change
direction at the same time.  This would ensure that the power generated
at the farm would be as even and continuous as possible.

Note that only the pitch, or angle of attack, would have to be
controlled remotely -- not the yaw and roll.  This should make the design and
development straightforward.  Adjusting the tether bridle position fore
and aft should provide the level of control required for this
application.  The Tethered Airfoil could be designed to passively correct for
yaw and roll -- much the same way that single string kites do today.

A single Tethered Airfoil could produce electricity if a flywheel or
external electrical power is used to winch the airfoil in on the upwind
stroke.  The airfoil would produce more power on the downwind stroke
flying in a high lift, high drag mode than would be required to winch it
back in on the upwind stroke.

The amount of power that a Tethered Airfoil could generate is not
proportional to the size of the airfoil.  It is proportional to the area
swept by the airfoil per unit time -- just as in wind turbines.  A small
airfoil that quickly traverses a large area would generate more power.
But Tethered Airfoils could generate far more power than wind turbines
because they could sweep a greater area for an equivalent cost since
they would not have the cost of the tower, nor be limited to the sizes
that towers can accommodate.

Unlike standard wind turbines, Tethered Airfoils would not require
expensive towers, specially designed low speed generators, and would not be
subject to the strong vibrations that have so often caused premature
failures.  Most importantly, they could fly at higher altitudes to
harness more powerful winds.  On average, over flat land, the wind is twice
as powerful at every five-fold increase in altitude.  So a Tethered
Airfoil flying at only 500 feet would encounter twice the wind power as a
wind turbine 100 feet off the ground.  At a half mile the Tethered
Airfoil would encounter more than four times as much wind power.  This
effect can be greatly magnified by terrain that causes the air to be
funneled -- as is generally found at the best wind farm sites.

Obviously, Tethered Airfoils that fly at high altitude would need to be
assigned their own airspace a safe distance away from commercial flight
paths.  They might obtain permission to fly in the restricted airspace
over wilderness areas because they do not pollute or make noise.
Alternatively, the vast areas that exist offshore would provide excellent
sites for both low and high altitude wind farming (as will be discussed)
later.  But initially, windy rural areas would provide good lower
altitude proving grounds.

Inflated with helium, these Tethered Airfoils would simply float up in
exceptionally calm winds.  But in places, such as Minnesota, where the
winds are constant and strong close to the ground it may prove
practical to develop Tethered Airfoil Generators that rely exclusively on
aerodynamic lift rather than buoyant lift.  Inflated only with air, they
could be developed to automatically launch from a stand when the winds
blow sufficiently strong and be winched down quick enough to maintain
controllable flight when the winds are exceptionally calm.

While the jet stream offers the greatest potential power per unit area,
it may be more practical to fly larger Tethered Airfoils at lower
altitudes.  This would reduce the cost and drag of the tethers, but would
require larger or more numerous airfoils to generate a like amount of
power.

Even in typical installations, wind power used in conjunction with
hydropower or fossil fuel plants could reduce the long-term rates at which
these plants use water or fuel.  These plants on the other hand, could
provide backup power during periods of calm winds when these wind power
generators would produce little or no power.

   3.2. Water Pumps

Tethered Airfoils can be used to pump water as well as to generate
electricity.  The specific application of pumping water is mentioned here
for three reasons.  First, it would not require a generator.  Pulling
the tether could drive the pump directly.  Second, water pumps do not
require a consistent power source.  If the winds cause short-term
variations in the amount of water that is pumped there is no problem provided
that daily or weekly quotas are met.  Third, many nations require or
could benefit by the use of good cheap water pumps.

Many underdeveloped nations need power to pump irrigation water.
Studies conducted in Sri Lanka, Kenya, Cape Verda, and the Sudan show that
windmills can be cost effective compared with diesel engines for pumping
water.  If windmills are considered cost effective, Tethered Airfoils
should prove superior because they can extract power from much stronger
winds and sweep through a far greater airspace.  (As mentioned
previously, the power that may be generated is proportional to the area swept
per unit time).

   3.3. Custom Sailing Craft

A lighter-than-air Tethered Airfoil and a watercraft having a small
wetted surface could be tethered together to make a very fast and
efficient sailing craft.  Canoes and kayaks with centerboards or catamaran
hulls would make good choices.  Tethered Airfoils suitable for this purpose
would need to have remotely controllable pitch and roll so that they
could fly "out to the side" as well as downwind.  These Tethered Airfoils
would not require remotely controllable yaw.  These airfoils could be
designed (perhaps with a delta wing shape) to ensure that the Tethered
Airfoil would always fly with nearly zero yaw with respect to the wind.
(The purpose for flying "out to the side" is to generate a force
perpendicular to the direction of the wind just as sails do when tacking into
the wind.)

The Tethered Airfoils that have been discussed previously require pitch
control only (nose up or down) The purpose of this control is to: 1)
generate varying tether tensions by adjusting the lift and drag
characteristics of these airfoils, or 2) to adjust the height of the Tethered
Airfoils in the sky.  Tethered Airfoils that could be used to provide
propulsion into the wind (as well as with the wind) require roll control
as well.  These airfoils must be able to fly out to the side as well as
overhead and downwind.  The best Tethered Airfoil for this purpose
would be one that could be directed to assume a relative position in the
sky with respect to a hull -- in response to remote control -- and then
hold that position indefinitely without requiring power.  It appears
that such control may be possible (and patentable).

A Tethered Airfoil should be able to passively maintain a new relative
position in the air in response to a single radio control request to
change the tether bridle position, flaps, wing warping, or center of
gravity.  Using this technique to change the attitude of the airfoil would
cause the airfoil to select a different position in the sky.  This, in
turn, would cause the tether to be pulled in a different direction --
causing a new tack to be taken.  If the airfoil could maintain this new
position indefinitely after it had made these changes, it would be
highly desirable, because power would only be required when changing tacks
-- not to maintain the course of a tack.  Even more important, is the
fact that if it could passively self-correct it's own position it would
be immune to brief system power failures or shutdowns.  It would still
continue to fly just as well on the same tack.

Members of the Flight Research Institute have demonstrated the
feasibility of water skiing upwind or downwind with a Tethered Airfoil at the
Columbia River Gorge.  They also won first place in a speed sailing
competition in England -- racing against craft having similar sail area.
Even though the airfoil and hydrofoil were inefficient off-the-shelf
kites and skis, they won by the greatest margin of the day.

While the principle of tacking into the wind with Tethered Airfoils may
sound unique, it has actually been accomplished and documented as early
as 1827 by G. Pocock.  (The Samoans used it even earlier.)  It appears
that as soon as Orville and Wilbur Wright showed that it was possible
to fly without a tether, virtually all scientific research into the
applications of Tethered Airfoil flight ceased.  Back then, the only way
that an operator could remotely control a Tethered Airfoil, was by
applying varying tensions on additional drag-inducing cables.  The winds that
kept the airfoil aloft also acted upon these control cables.  When a
wind gust would cause an airfoil to start diving to one side, different
tensions would result in the control cables.  Often, these different
tensions would cause the airfoil to dive even more.  These airfoils often
flew out of control and crashed.  What is surprising, is that in 176
years nothing has changed.

Tethered Airfoils that rely on cables for their control will always be
unreliable and prone to crash.  To the best of my knowledge, no one has
yet put an inexpensive autopilot and an aerodynamically efficient
Tethered Airfoil together.  I hope to work with others to be the first to
achieve this goal.  With such equipment there is no reason why Tethered
Airfoils would not be every bit as stable, controllable, reliable, and
useful as airplanes.

Tethered Airfoils could provide propulsion for small boats.  Attached
to the gunwales negligible listing moment would be generated.  In fact,
traveling with the wind, the airfoil could help pull the hull of
smaller boats out of the water, thereby reducing drag.  Motor boats,
sailboats, hydrofoils, canoes, kayaks, sailboarders, skiers (both water and
snow) -- all could be accommodated with a handful of different models.
Unlike sails, Tethered Airfoils need not be custom made for each boat or
application.  No heavy masts, ballast, special ship design, or
expensive retrofitting would be required.  Like sails on a sailboat, Tethered
Airfoils could provide power for all points of tack except dead into the
wind.  They would be better than sails because they would have an
aerodynamically superior shape -- higher lift to drag ratios -- and
therefore be able to tack much closer into the wind.  They would also have
access to the stronger winds aloft.  They would have one cable, requiring
one winch, and take up no deck space (mounted externally to a track on
the gunwales).

Over land, the available wind power doubles with every five-fold
increase in altitude.  This factor can be much greater over water when the
wind causes the waves to crest and the waves cause more pronounced
boundary layer effects.  So Tethered Airfoils could tap much more powerful
winds than sails.

If a motor boat were outfitted with a Tethered Airfoil that flew at 500
feet (where the winds at sea are often three to four times as strong as
at the top of most masts and towers) it could outrun most sailboats --
without engine power.  Naturally, If the winds became too strong the
airfoil could be tied down or deflated.  For example, fishing fleets
could race to their fishing grounds with their airfoils at high altitude
and troll with their airfoils slightly overhead.

Motor boats under power could use Tethered Airfoils to provide a
component of thrust in the direction they wished to travel.  Suppose that a
captain desired to travel east and decided to use an airfoil to help
reduce fuel consumption.  Suppose further that the wind was blowing such
that his Tethered Airfoil pulled strongest in a northeasterly direction.
He could accomplish his goal by directing the motors to cause an
equally powerful thrust in a southeasterly direction.  If the captain wished
to travel east at 20 knots, the motors would only need to propel the
boat at 14 knots.  Depending on the ship and the sea conditions, this
thirty percent reduction in motor propulsion speed could result in a fifty
percent reduction in fuel consumption -- yet he could travel just as
fast as if he had used motor power only.

It is typically reported that by assisting propulsion with standard
sails, fuel consumption can be reduced by a fourth.  But since Tethered
Airfoils can harness winds having greater power, Tethered Airfoils could
save much more fuel.  Since Tethered Airfoils could be attached at the
gunwales they could never pull the boat over -- just along.  So, unlike
sails, Tethered Airfoils would never need to be furled to prevent
capsizing.  Tethered Airfoils should always be able to make use of the best
winds -- at altitudes where there is over four times as much power
available.

The Tethered Airfoils for sailing applications could be inflated with
lighter-than-air gases such as helium or hydrogen so that they would
simply float up in exceptionally calm winds.  Alternatively, they could be
inflated with air in which case they would need to launch and land as
the winds would permit.  As the winds would become strong enough, or as
a boat having an alternative propulsion source would pull, an air
inflated Tethered Airfoil could be launched by letting out the tether.  To
land the airfoil when desired, or in the event of exceptionally calm
winds, a winch could pull the Tether back in again at a sufficient
velocity to maintain stable flight.

Airfoils that are inflated with air would be advantageous because they
could readily be deflated and conveniently stored on board when not in
use.  Also, there is additional cost and logistics involved in
obtaining, storing, and transferring lighter-than-air gases.  As elegant as it
would be to have lighter-than-air Tethered Airfoils pull boats, in
general it would probably be more practical to use air inflated Tethered
Airfoils.

   3.4. Recreational Airships that Fly Over Water without Fuel

As soon as Tethered Airfoils are developed that can pull hydrofoils
reliably, passengers could fly in gondolas attached to airfoils rather
than sail in hulls over the water.  The principles of operation would be
just the same.  The only difference is that the hydrofoil would now be
remotely controlled rather than the airfoil.  Such a craft should have a
much smoother ride.  The tether would dampen Wave action before it was
transmitted to the gondola.  In the event that the wind stopped, the
gondola would simply float -- being held up by the buoyant lift of the
lighter-than-air airfoil.

This configuration could render a truly efficient sailing craft because
a lighter-than-air airfoil could support the passengers, cargo, and all
other components of the craft except for the hydrofoil that would be
required for tacking.  In other words, the craft could be made very
efficient by the elimination of the hull and all unnecessary water drag.
Having a high sail, very little drag, and always being "up on the
hydrofoils" such a craft could sail even in the lightest of winds.  For truly
high speed, the airfoil could fly at high altitudes.  For passenger
comfort without cabin pressurization, the gondola could be attached to the
tether a reasonable distance above the ocean.

Nearly this same level of comfort and efficiency could be obtained by
using Tethered Airfoils that are inflated with air.  In this case, the
Tethered Airfoil and gondola would have to launch and land as the winds
would permit.  But this would probably not be a very big penalty
because they would land when the winds would provide little or no propulsion
and when the water would be calm.   The one disadvantage in using air
rather a lighter-than-air gas to inflate the airfoil is that some of the
aerodynamic and hydrodynamic lift generated by the airfoil and
hydrofoil would have to be used to lift the gondola and wing.  Normally, a
relatively small percentage of the power would be required to lift the
gondola and wing.  The vast majority of the power would still be available
to provide propulsion.

As the winds would start to pick up, this craft could be launched by
releasing tether from a spool in the hydrofoil.  In many cases this would
be sufficient to cause the gondola and wing to take to the air.  But if
the winds at low altitude were insufficient, the gondola and the
airfoil would float on the water downwind from the hydrofoil.  When the
tether would be let out sufficiently, the tether could be winched back in
briefly and strongly to cause enough tension in the tether between the
hydrofoil and the airfoil to pull the airfoil into the sky.  Once in the
sky, under the influence of greater wind power, the winch could stop
pulling and gradually let out more tether so that the gondola and airfoil
could ascend to the altitudes that would allow tacking.

   3.5. Paraglider Wings and Ultralight Aircraft

Tethered Airfoil construction techniques should enable the construction
of high performance inflatable paraglider wings and ultralight
aircraft.  Standard Paraglider wings are ram-air inflated.  This causes drag to
be generated at the leading edge.  Also during flight, standard
paraglider wings can easily be deformed into less efficient shapes.  Tethered
Airfoils should be at least as light, but they should form much more
rigid and well-defined airfoil shapes.  It should also be possible to use
these techniques to make inflatable ultralight aircraft.

   3.6. Passive Self-Regulation of Altitude

Using the proprietary construction methods that will be discussed near
the end of this paper, highly pressurized lighter-than-air balloons (or
airfoils) could be manufactured that could passively stabilize their
altitudes in free-flight without being restrained by tethers.  These
construction methods could be used to make lighter-than-air balloons that
would prevent the internal gases from expanding as the balloons would
rise.  As a consequence, if these balloons were free to ascend or descend
they would come to rest at the altitude that would have the same
density as the over-all balloon.  If these balloons rose higher -- perhaps
due to momentary gusts -- they would be heavier than the surrounding air
so they would settle back down.  Likewise, if they were lower, they
would be lighter than the surrounding air so they would rise.  They would
always passively return to the altitude whose density is equal to that
of the balloon.  In short, they would require no monitoring, control,
or power to automatically self-regulate their own altitudes.  If they
were in no hurry they could float to destinations downwind consuming no
power.  This might be a useful plan in hauling freight inexpensively.

This technique was once used to make a weather balloon that passively
stayed aloft for numerous circumnavigations of the globe.
Interestingly, this technique has never been used to maintain the altitude of
lighter-than-air man-lifting balloons.

To date, all lighter-than-air man-lifting balloons require continual
monitoring and adjustments of altitude.  This is because the air in these
balloons expand during ascent and compress during decent.  If they
start upward, they continue upward at an accelerating rate, until helium is
released to cause them to descend again to the desired height.  But
once they start to descend they continue to descend at an accelerating
rate, until ballast is released to cause them to ascend again.  These
balloons continually rise and fall requiring continual releases of helium
and ballast to compensate.

In standard airships or blimps, the lifting gas is free to expand or
compress to come to equilibrium with the surrounding air.  So as the
airship descends, the gases compress.  This would cause the airship
envelope to become limp were it not for ballonets.  Ballonets are special
internal air pressure compensating balloons that inflate during descents to
maintain a small but uniform positive pressure in the airship.
Unfortunately, a ballonet requires a fan to maintain a slight positive
pressure.  The fan in turn requires a power source.  Present day airships do
not regulate altitude by alternately releasing helium and ballast like
balloons.  That would be too costly.  Instead, they use the aerodynamic
forces of thrusters to maintain altitudes when the airship has a
different density than the surrounding air.  These thrusters are used to
provide an upward force when the airship is heavier than the surrounding
air and a downward force when the airship is lighter.  This method
requires engines that continually consume fuel.

It would be better if airships were designed to withstand high internal
pressures (such as up to 5 psi).  To ascend, air could be released from
an internal ballonet.  The loss of this air, and the expansion of the
helium that would result in the adjacent chambers, would lower the
overall density of the airship, which would cause it to rise to the altitude
having the same density -- and no higher.  To descend, a fan would be
required to draw air back into the ballonet.  This additional air, and
the compression of the helium that would result, would cause the airship
to descend to the altitude that would have the same density -- and no
lower.

Such an airship would never need to discard helium or ballast, or
consume fuel to maintain a specific altitude.  It could also be smaller
because it would not need the extra buoyancy required to lift ballast or
the additional fuel required to maintain altitude.  In the course of
adjusting altitude, this airship would only need to consume power when
using the fan to draw in additional air to descend.  It would require no
power to maintain a specific altitude or ascend.  It could float
indefinitely downwind at a specific altitude without requiring any altitude
monitoring or control.

   3.7. Ship and Vessel Propulsion Assistance

If freighters and ocean going vessels used even relatively simple and
inefficient Tethered Airfoils they could realize dramatic reductions in
the costs of fuel.  When traveling the direction that the jet stream
blows (eastward in the Northern Hemisphere) the vessels could pull large
Tethered Airfoils into the jet stream.  Once in the jet stream, these
airfoils could simply pull the vessels downwind.  A 50 percent reduction in
the cost of fuel one direction on a large freighter would save hundreds
of thousands of dollars annually.  Efficient Tethered Airfoils might be
able to save significantly more because they could provide propulsion
assistance on the return upwind trip as well.

Some freighters have been designed to use metal sails to provide
propulsion assistance with the wind or into the wind.  They are designed to
save as much as 60 percent of the cost of the fuel.  Like all sails,
these metal sails cause the vessels to list to one side when the winds
blow.  Listing causes all decks and cargo bays to have sloping floors.  To
prevent capsizing, the metal sails are "furled" by folding.  They
require special ship designs to accommodate the masts, ballasts, and the
forces that the sails generate.

Tethered Airfoils in contrast could provide greater power from higher
altitudes and yet cause negligible listing.  Little or no retrofitting
would be required because Tethered Airfoils could pull the vessels at
the same attachment points that tugs would use.  Even if these Tethered
Airfoils were not lighter-than-air they could be self-launched into the
apparent wind generated by these ships at sail.

Between territorial waters there are no governmental bodies that
regulate how high Tethered Airfoils would be allowed to fly.  As low as a ten
percent reduction in the worldwide consumption of fuel by freighters
would save billions of dollars annually -- not to mention the
environmental benefit of reduced pollution and less global warming.

   3.8. Energy Conserving Tugs

Special tugs could be designed for the express purpose of manipulating
Tethered Airfoils to pull ships across oceans.  This would have the
advantage that the large vessels would not have to manipulate the Tethered
Airfoils directly.  All the tasks associated with providing propulsion
assistance could be handled by a tug specially designed to do the job.
Tethered Airfoils suitable for this purpose would probably not have to
be lighter-than-air.  The tug could sail into the wind, pulling even a
heavier Tethered Airfoil into the air.  A heavier-than-air airfoil
would have to fly exclusively by aerodynamic lift, but it could still land
safely even in calm winds by being pulled in fast enough to ensure
stable flight back down.

   3.9. Land Based High Altitude Wind Power Generators

Most appealing is the prospect of harnessing winds in the jet stream
where the wind power is often hundreds of times greater than at the top of
masts and towers.  Technical and political hurdles would have to be
overcome, but as Tethered Airfoil technology matures and gains acceptance
jetstream wind farming may prove practical.

At each site, the local terrain and the proximity to the jet stream will
determine whether it would be best to fly more airfoils at lower
altitude or fewer airfoils at higher altitude.  Mountains or other land
formations that funnel wind may favor lower altitudes.  One such mountain
range exists in Hawaii.  This range runs perpendicular to the prevailing
winds and funnels winds up and over.  (Hawaii also has expensive
electricity and a state government that has recently invested millions in
wind energy development in a single year.)

Obviously, Tethered Airfoils that fly at high altitude would need to be
assigned their own airspace.  They could be assigned airspace far from
the commercial flight paths.  In rural Kansas, for example, strong
constant winds at ground level would assure that the Tethered Airfoils
could self-launch and self-land inflated only with air.  Alternatively,
they might obtain permission to fly in the restricted airspace over
wilderness areas because they do not pollute or make noise.

Many Third World countries are crossed by the jet streams of the
northern and southern hemispheres.  They might desire to relinquish airspace
to produce inexpensive electrical power.  If the winds at ground level
are insufficient to launch these Tethered Airfoils, they could be
filled with helium or hydrogen so they would always be in flight even in
calm winds.

(Ever since the Hindenburg blew up, people have been reluctant to use
hydrogen in lighter-than-air aircraft, but it should be noted that the
Hindenburg contained the hydrogen in "gold beater's skin" -- the
intestines of calves beaten thin -- nothing to be compared with today's
multi-layered plastic films.)

A number of articles have been written about the feasibility of
developing wind power generating systems that could tap the power of the
jetstream.  But the systems described in these research papers consist of
wind turbines mounted on large metal wings that are tethered with special
power conducting cables.  The wings use the turbines as thrusters for
launching and landing.  The complexity and manufacturing costs are
staggering; yet the amortized costs of the electrical power generation are
considered favorable (in the 7.5 - 9.5 cent per kilowatt range nearly
twenty five years ago).

   However, it would be much simpler and less expensive to design a system
      that would:

   1)      have an ordinary land based generator,
2)      have inexpensive inflatable fabrics that can be quickly deflated and
    stored away during periods of excessive wind,
4)      bounce rather than crash in an accident,
5)      contain virtually no costly and fragile high tech components,
6)      require no heavy turbines or metal cables to conduct lightning,
7)      never need to land during light winds,
8)      provide a much greater return on investment because the same costs
    could be used to construct larger Tethered Airfoils that could extract
    power from a greater area.

Over much of the United States the average potential power of the air
that flows through one square meter of the jet stream exceeds 10
kilowatts.  Drag on the tether and airfoil(s) will, of course, limit how much
of this potential power can be converted into mechanical or electrical
power.  Greater potential exists over Maine where during a winter month
(when the need for power is greatest) the average power available per
square meter exceeds 30 kilowatts (or 40 horsepower).  The greatest wind
power in the world is found near Tokyo Japan where the average power
exceeds 60 kilowatts (or 80 horsepower) per square meter in the winter.

As stated before, the power generated would be proportional to the area
swept by the airfoil per unit time, so if an ideal Tethered Airfoil
that is one square meter in area were to fly in the jet stream near Tokyo
it would be able to generate 600 kilowatts of power on the average
providing it could quickly and efficiently traverse an area ten times its
size and extract all of the power available.  However, due to technical
limitations, even a perfect wind turbine can only extract 60 percent of
the wind power available.  In this case, the weight and the drag of the
tether would limit efficiencies far more.  Even so, an airfoil that had
an area the size of a standard desk top (3 feet by 6 feet) and that
extracted only 10 percent of the power in an area five times it's size
would be able to generate 50 kilowatts on the average -- enough to provide
power for 50 homes -- and yet be inexpensive, deflatable, and readily
portable.  At a cost of 10 cents per kilowatt, very modest by Japanese
standards, this small airfoil would generate gross revenue of 43,800
dollars per year.

Japan has expensive electricity and no indigenous fuel supply.  It has
few hydroelectric facilities and little land to set aside for solar
power generators or wind turbines.  The people of Japan fear nuclear power
due to the bombing at Hiroshima and a near catastrophic accident at one
of their nuclear plants.  So harvesting the power in the winds offshore
may be the most desirable means of generating electricity for their
nation.

   3.10. Sea Based High Altitude Wind Power Generators

Studies have pointed out the potential of generating electrical power
using wind turbines at sea.  A major expense outlined in these studies
is the cost of installing and maintaining the stationary platforms and
towers required to hold the turbines in the air.  Tethered Airfoils do
not require tall towers or large platforms.  Instead, small boats or
barges could contain generators and be able to automatically launch,
coordinate the flights, and retrieve the airfoils.  Since the winds at sea
are generally strong, these airfoils could fly totally by aerodynamic
lift, so they would not require lighter-than-air gases.  Using the
methods of manufacturing that will be discussed, these airfoils could
momentarily bend and deform in the heaviest winds -- rather than break and
fracture.

Since these Tethered Airfoils could fly as high as the jet stream,
where the wind power is often 30 to 100 times as great, and since they
would not require tall towers or large platforms, and since they could be
made with inexpensive fabrics and low tech components, the cost of the
power that the Tethered Airfoils could produce should be much less.
Within 200 miles of shore both ocean and airspace would have to be
reserved, but permission to reserve this space should not be difficult to
obtain because Tethered Airfoils do not pollute or make noise and they
could not easily damage people or property at sea if they are assigned
their own space.  More than 200 miles offshore, outside of territorial
boundaries, they could fly without obtaining permission from anyone.  In
fact, with limited taxation (or no taxation in the case of Liberian
registry), and no property cost -- save for a power cable right-of-way
connecting the wind farm to the land, this might be the most cost effective
alternative.  (Lights, radar, and automated radio warning systems could
warn approaching craft.)

There is a method of generating electricity from the winds at sea that
would not require power cables to transmit the electricity to land.  In
this case, boats at anchor or sailing the seas could deploy
reciprocating Tethered Airfoils.  The electricity generated could be used to
electrolyze seawater to generate hydrogen that could be stored in onboard
tanks.  Later these tanks could be transferred to power stations where
fuel cells or conventional steam turbines could use the hydrogen to
generate electricity.  Therefore, boats could ply the waters off countries
such as Japan to harvest wind power for the purpose of synthesizing
hydrogen to sell: 1) to local power stations to generate electricity, or 2)
as an automobile fuel.

Not all of the electrical power that is used to synthesize hydrogen can
be reclaimed when the hydrogen is used to generate electricity again.
These processes are not a hundred percent efficient.  Also, the storage
and transportation of hydrogen presents other difficulties.  So it will
always cost more to synthesize, store, and transport hydrogen than use
wind generated electricity directly.  But hydrogen is the cleanest fuel
of all.  When hydrogen is used to generate electricity the output
"exhaust" is pure water.  Utilities pay a premium for electricity that is
generated without producing pollutants.  More importantly, electricity
that is stored in the form of hydrogen can be converted back to
electricity at times of peak demand when electricity can sell for over three
times as much as it normally does.  So, all of the costs associated with
converting electricity to hydrogen and back again can be more than
offset by selling the electricity at times of peak demand.  Moreover, the
conversion of wind power to hydrogen to electrical power could provide
backup power during periods of calm winds for other Tethered Airfoils
that provide more efficient direct power.

Wildcat oil miners risk much every time they attempt to sink a new hole
at sea.  Each hole could come up dry or cause much pollution.  Sea
based Tethered Airfoil wind farmers would risk much less and would have a
resource that would never run out.  The main risk in developing sea
based wind power generating systems is the risk incurred in developing the
first one.  After the methods of manufacture and deployment are
resolved, there is never a chance of finding a "dry hole''.  The patterns of
the jet stream are well known.  In the United States, the owners of
Tethered Airfoil wind power generating systems have another benefit: power
companies are obligated to buy the power produced by private individuals
or companies at fair market rates.  Having an obligated customer means
that this enterprise should be recession or depression proof.  Wildcat
oil miners, in contrast, have no such benefit.

   3.11 Flight without Fuel

Actually, there is not any reason why anything must drag through the
water or be attached to the land in order to make a system that can tack
using airfoils.  Two airfoils attached to opposite ends of the same
tether can accomplish the same thing.  If one airfoil is in faster moving
air at a higher altitude and the other airfoil is in slower moving air
at a lower altitude, then the craft can tack.  The principle is the
same as an airfoil attached to a hydrofoil.  The only difference is that
instead of using the hydrofoil as a rudder in the slow moving water,
another airfoil could be used as a rudder in the slow moving air.

If a passenger-containing gondola were attached to the lower of the two
airfoils, then the upper airfoil could ascend into the jet stream for
fast, silent flight.  This aircraft would require a sophisticated
autopilot because it could tack vertically as well as horizontally.
Fortunately, low cost integrated circuits and servomechanisms can be developed
that can perform all flight operations with little or no human
intervention.  As an example, autopilots could be pre-programmed to fly between
any two points on earth using sensors that receive information from the
Global Positioning System.  Using these sensors (and others) the
airfoils could continuously monitor their exact positions above the earth (to
within a few meters), their attitudes (pitch, yaw, and roll) and the
wind velocity and direction.  With this information, the autopilots could
cause the airfoils to automatically launch (causing the mooring cable
to become disconnected from the ground) fly to a pre-programmed
destination using a pre-determined route, then dock at a destination (flying
the mooring cable such that the ground end is caught by a waiting
receptacle).

In June of 1982, the Smithsonian magazine stated: "A kite flying across
the wind will fly faster than the speed of the wind.  If the
lift-to-drag ratio is ten to one, the kite theoretically can go ten times as fast
as the velocity of the wind.''  This article also stated: "The wind
blows hardest (more than 100 miles per hour) about 30,000 feet above the
ground in the jet stream.''

Taken together, these two facts would suggest that Tethered Airfoil
airships could fly faster than 1000 miles per hour! This is impressive but
not realistic.  At these speeds the long tether would have considerable
drag.  Furthermore, flying crosswind means that the craft would
generally be restricted to flying just north or south.  If the average
practical speed (due to limitations of tether length and drag) were only 5
percent of this theoretical maximum, if it were no greater than 50 miles
per hour, it would still be highly desirable because it would be flying
without fuel.

Since these airships would consume no fuel, they could prove very
competitive as haulers of airfreight, low cost air transportation, pleasure
craft, or sightseeing craft.  They would not need airports.  Moored to
the ground as helium filled kite-balloons, and perhaps using thrusters
to help maintain position, they could load and unload people or cargo
from open areas or the flat roofs of large buildings.  In the days of
the old airships it was said that: "You can fly in an airplane, or you
can voyage in a Zeppelin''.  Zeppelins of those days had ballrooms and
verandas in the sky.  There is no reason why these newer airships could
not be at least as gracious.

Since there is generally a large differential in velocities between the
winds in the jet stream and those below, if the cabin were pressurized,
and the lower airfoil was just below the jet stream, the tether required
for free flight could be made much shorter -- thereby reducing drag,
increasing speed, and freeing more airspace.  A commercial version of
this airship could have metalized plastics for the retention of
lighter-than-air gases and for good visual and radar tracking.

   3.13 Radio Signal Relaying

When it becomes possible to fly indefinitely by tacking in the air (as
was just described), it should be even easier to tack in order to stay
in the same general location.  When this feat is achieved it could lead
to the cheapest means of communication.  Small wind turbines could
generate on-board power that could be backed up by battery to provide a
consistent power source 24 hours a day.  This form of hovering would not
require the same aerodynamic efficiency as a craft designed to tack to
locations upwind.  Therefore, the on-board wind turbine should not
restrict operation.  Such wind turbines would introduce drag.  But if the
objective were to maintain position rather than to progress to locations
upwind, some additional drag could be accommodated.

Already, nations have expressed concern that there may not be enough
locations above the equator at which to position all the geosynchronous
communication satellites that the world may shortly need.  It should be
far cheaper to make geosynchronous craft that can tack in the air
without fuel.  They would not need to be positioned above the equator and
they could launch and land under their own power whenever it would be
desirable to perform maintenance.  Just a few of these flying high in the
jet stream could provide a network that could provide continental
coverage.  They could provide the cheapest means of mass communication.

Recently an aircraft named Helios demonstrated that it is possible to
fly at high altitude by the power harvested by solar cells alone.  This
is a very technically complex craft.  By contrast a Tethered Airfoil
craft could accomplish this feat with two simple inflated craft tethered
together.  It would not be restricted by the availability of sunlight.

   3.13 In-Flight Generation of Fuel

If it proves to be possible to tack in the air while generating power
from on-board wind turbines, commercial wind power generators could be
developed using this concept.  By tacking "in place" in the jet stream
they could generate electricity with which to produce hydrogen from
water.  Afterward, these craft could fly to power generating stations that
could use fuel cells to generate electricity from the hydrogen --
generating no pollution aside from water vapor.  Alternatively, the hydrogen
could be sold as a non-polluting automobile fuel.

   4. The Initial Objectives of Tethered Airfoil Research and Development
 

Currently, the support and endorsements for the development and
commercialization of Tethered Airfoil Technology are fairly balanced between
those who would want to see it initially used to generate electricity
and those who would want to see it initially used to propel efficient
sailing and flying craft.  Each has their relative merits.  Electrical
generators would have to overcome more political hurdles if they fly at
high altitudes, but sailing and flying craft would present more technical
challenges.  Electrical generators might provide a greater income long
term, but sailing and flying applications would probably find more
immediate acceptance.  In either case, the Tethered Airfoils that would be
best suited to these tasks would be airfoils that could maintain their
relative positions in the sky with respect to their mooring sites -
positions that could be specified, and could be changeable, by remote
control.  In other words, the best Tethered Airfoils for these applications
would be ones that could be programmed by remote control to fly to
specific locations left, right, up, or down in any wind.  These airfoils
should maintain nearly constant position until programmed to move to
another position.  Lastly, they should consume as little power as possible
to stay in a programmed position.

Typical kites stay in position without consuming power, but they cannot
maintain position to the left or right of their mooring location.  The
goal here would be to develop Tethered Airfoils that could stay in any
programmed position in the sky that kites could reasonably fly in.
These airfoils would require an autopilot, remote control electronics, and
servomechanisms.  These are areas that I would feel comfortable
developing.  What I need is help developing the best control theories and
mechanisms to maintain position at the lowest possible in-flight power
consumption.  But the first goal is to demonstrate a practical method of
being able to manufacture these Tethered Airfoils quickly and
economically.  It is for this reason that the objective of this initial unsolicited
proposal is to obtain funds to plan the development of a system that
could be used to manufacture Tethered Airfoils.   The proposal, itself,
is near the end of this paper.

   6.  Tethered Airfoil Generators Compared to Other Power Generating
Technologies

All of the current and proposed methods of energy generation or fuel
synthesis have their advantages and disadvantages.  Below the costs of
consuming oil are discussed.  Afterward, the advantages of Tethered
Airfoil Generators are discussed and compared against the current and
proposed methods of energy generation.  The intent is to lay a foundation
that will clearly establish our need for a cleaner, safer, cheaper source
of power other than that, which is currently available or proposed.

   6.1.  The Hidden Costs in Oil Consumption

According to the US Geological Survey (the branch of the government
that assesses oil reserves) virtually all of the oil that is known to
exist or is likely to be discovered in the United States will be consumed
within the next thirty years.  Currently, oil is cheap and abundant, yet
the purchase of foreign oil is the single biggest contributor to our
spiraling trade deficit and global indebtedness.  When oil is no longer
abundant it will no longer be cheap -- in which case our trade deficit
and indebtedness will likely soar.
 

Even in peacetime we spend considerable sums just to secure access to
Mideast oil.  According to an article in the April 1991 issue of
Scientific American, it is estimated that the Pentagon has spent between 15
and 54 billion dollars annually to secure access to Mideast oil -- before
the war in Iraq.  As long as we are dependent upon the consumption of
foreign oil we will continue to spend much money securing access to the
oil and safeguarding the remaining reserves.

In times of war we spend much more.  In the heart of an oil glut we
fought the war in Iraq to secure access to oil.  A quarter of a million
Iraqis died and over 60 billion dollars was spent by the allied forces
alone.  Shouldn't we expect that when global oil supplies diminish such
wars would become more common and widespread? Already, Middle Eastern
nations such as Iran are arming themselves to exert regional authority
and to prepare for such conflicts -- this time with nuclear weapons.  The
point is simple: our need for foreign oil compels us to spend
considerable sums to ensure our access to oil in peace time and to fight wars
when that access is threatened.

Perhaps most importantly, the consumption of oil or other fossil fuels
degrades the environment through smog, acid rain, the green house
effect, and inevitable wide spread accidents such as oil tanker spills.
Millions suffer and many die from respiratory illnesses, entire forests
are being decimated, and vast stretches of ocean are being laid waste.
According to the article in Scientific American, it is estimated that at
the current rate of oil consumption the environmental degradation,
increased health care, lost employment, and other factors cost the United
States between 100 to 300 billion dollars annually -- not to mention the
15 to 54 billion dollars that the pentagon spends in peace time to
secure access to Mideast oil -- nor the costs of fighting wars to secure
access to oil such as in Iraq.  These "hidden" costs are in addition to
the s paid at gas pumps.  World wide these incidental costs may
exceed one trillion dollars annually.  The world pays an enormous to
consume oil -- politically, economically, and environmentally.

   6.2.  Comparing Tethered Airfoil Electricity Generation and the Solar
Power

   Solar power has long been promoted as an energy source that is likely
to be used to meet much of the future demand for power.  Advocates of
solar power point out that it is clean, dependable, and uses a renewable
energy source.  While true, all of these claims can be made for
Tethered Airfoils Wind Power Generators as well.

Compared to solar energy sources, Tethered Airfoil Generators:

6.2.1. do not require expensive and inefficient energy storage and
retrieval systems to convert daytime power into nighttime electricity,

6.2.2. do not require much sun-favored land since they can share land
with agriculture (or go offshore to avoid the use of land altogether),

6.2.3. can efficiently generate power at far more sites throughout the
world (such as anywhere under the jet streams of the northern and
southern hemispheres or over the oceans where the installation of solar cell
arrays would be impractical, if not impossible),

6.2.4. can extract energy from a source that is hundreds of times more
powerful per unit area (10 kilowatts per square meter is often the
average power available in winds in the jet stream versus 100 watts of
solar power per square meter), and

6.2.5. are more efficient at extracting power (even windmills are
generally more than four times as efficient as solar cells in extracting
power)

6.2.6. could offer a greater return on investment by generating more
power at less cost.

   In short, Tethered Airfoils hold greater promise for economical and
ecological power generation than solar cells.

   6.3.  The Wind Turbine Alternative

   Currently wind turbines offer the most practical and cost effective
means of generating electricity from a renewable energy source, but
Tethered Airfoil Wind Power Generators promise to offer even a much more
cost effective solution.  Wind Turbines will probably always be more
efficient, but Tethered Airfoil Generators should be much less expensive to
install and maintain when generating the equal wattage.

    Unlike standard wind turbines, Tethered Airfoil Generators would not require:

   6.3.1. towers,
6.3.2. stationary platforms,
6.3.3. rigid, fragile blades,
6.3.4. airfoil sizes to be limited to the strengths of the towers,
6.3.5. expensive custom low speed generators,
6.3.6. sophisticated gear trains to survive high torsional loads,
6.3.7. operation in the slow and variable winds close to the earth, or
6.3.8. land.

   Tethered Airfoil Generators could use standard gear trains and
generators.  Since they would have no rotating blades they would not be
subject to the strong vibrations and torsional forces that have caused many
wind turbines to fail.  They would be constructed of inflatable fabrics
rather than rigid materials so they would bend and deform in excessive
winds rather than fracture and break.  Most importantly, they could fly
at higher altitudes where the winds are stronger and more constant.

   Generally over level terrain the velocity of the wind varies in
relation to the elevation above ground by the "one seventh power law":

  velocity_high / velocity_low = (elevation_high / elevation_low) ^ (1 / 7)

   The power available in the wind is proportional to the cube of the
velocity, so over level terrain the power in the wind varies in relation
to the elevation above ground by the "three sevenths power law":

  power_high / power_low = (elevation_high / elevation_low) ^ (3 / 7)

   From this equation comes the simple relationship that winds that are 5
times higher are very nearly twice as powerful.  Similarly, winds that
are 25 times higher are 4 times more powerful.  Thus, if Tethered
Airfoils were to fly just a half mile in the air above standard level
terrain they should encounter winds that would be over 4 times more powerful
than the winds encountered by turbines that were 30 meters (nearly 100
feet) above ground -- and over 6.5 times more powerful than turbines at
10 meters (nearly 33 feet).  These comparisons are for winds above
level terrain -- the general case.  Near mountain ridges, and other places
where the terrain funnels the air, the power available can increase far
more with changes in height.  Likewise, at sea, when strong breezes
blow, the power available in the winds varies more markedly with changes
in altitude.  This is because strong breezes make waves that effectively
slow the winds closer to the earth even more -- which causes a greater
change in velocity with height.

   The purpose of these discussions is to show that Tethered Airfoils
could tap into winds that are much stronger than those accessible by
commercial wind turbines -- even if the Tethered Airfoils were to fly
relatively low.  But as the technology progresses, and as it becomes
practical to fly as high as the jet stream, then Tethered Airfoils could tap
into winds that can be hundreds of times more powerful.

   Besides being able to tap into much stronger winds, Tethered Airfoils
could also be more practically constructed and deployed in larger
sizes.  This would allow them to extract power from a greater area.
Compared to wind turbines, Tethered Airfoils would be more practical to scale
up to larger sizes for two reasons: 1) Within reasonable limits, key
materials are more economically manufactured, more readily available, and
easier to manipulate in larger sizes, and 2) Tethered Airfoils would
not have to be limited to the sizes that towers can accommodate.

   If wind turbine towers were made twice as tall then the blades could
be twice as long, and the turbine could extract power from an area four
times as great.  But the tower could require 16 times as much material
(and cost) to accommodate the greater load at the increased height.
This simple example shows the strict size limitations that towers impose
on wind turbines.  Tethered Airfoils, on the other hand, have no tower
and would channel all the force that they would generate directly to a
generator located on the ground.

   7.  The Advantages of Constructing Tethered Airfoils of Larger Size

   For nearly all of these applications, the economies of scale should
favor Tethered Airfoils of larger size.  If the linear dimensions
(length, width, and height) of a Tethered Airfoil were all to double, then the
volume and buoyant lifting forces would increase by a factor of eight.
Such an airfoil could support eight times as much payload during
periods of calm wind -- without requiring the use of a stronger tether.  The
payload or ballast of this airfoil could be adjusted to offset the
increases in buoyancy, so the tether would not have to increase in strength
to support the greater buoyant forces.

   If the linear dimensions of a Tethered Airfoil doubled, then the
surface area, aerodynamic lifting forces, and tether tensions would increase
by a factor of four.  This would necessitate the use of a tether that
is four times stronger, has a diameter twice as large, and a drag about
2.5 times greater.  (Tether drag increases faster than the diameter and
less than the cross-sectional area.)  Therefore, when the tether is the
predominant source of drag and when buoyant lift is small compared to
aerodynamic lift (as should normally be the case), each time the linear
dimensions are doubled, the overall lift-to-drag increases by a factor
of 1.6.  In other words, if a Tethered Airfoil had an overall
lift-to-drag ratio of 5.0, then doubling it's linear dimensions would yield a
lift-to-drag ratio of 8.0.  The point is, that larger Tethered Airfoils
are more efficient.  This means that craft that use larger Tethered
Airfoils could travel faster and closer into the wind.  Likewise, Tethered
Airfoil Wind Power Generators that use larger Tethered Airfoils could
fly higher, tapping into winds that are more powerful, or they could fly
at the same altitudes with a shorter tether since the tether could be
more vertical.  In these applications, the increased buoyancy would best
be used to provide additional lift so that the airfoil could fly still
higher using even less tether.  (It is assumed that the aerodynamic
lift would still be much larger than the buoyant lift so a stronger tether
would not be required to support the additional tension due to
buoyancy.)

   Perhaps, the greatest advantage in increasing Tethered Airfoil size is
that the materials that are proposed for Tethered Airfoil manufacture
are more readily available and economically produced in larger sizes.
Using proprietary construction techniques, larger airfoils would be
easier to manufacture (within limits) and more aerodynamically refined and
efficient -- again leading to higher lift-to-drag ratios, faster
speeds, and higher altitudes with less tether.

   8.  Technical Endorsements

   Many of the ideas that are disclosed in this paper have been reviewed
by some of the most widely recognized authorities on aerodynamics and
hydrodynamics:

8.1.    Bernard Smith, the Retired Technical Director of the Naval Weapons
Laboratory, has been a pioneer in the integration of airfoils with
hydrofoils to make efficient sailing craft.  When he reviewed an early
draft of these concepts he pointed out a few inaccuracies and yet wrote:

"Your paper has enough good ideas in it to be worth the effort required
to perfect it".

8.2.    Later, a revised paper that describes these ideas was sent to the
Flight Research Institute (FRI) for their evaluation.  (The FRI was a
non-profit experimental offshoot of Boeing Commercial Aircraft.) After
reading the paper, Jack Wimpress, the Retired Chief of Product
Development at Boeing, and Harry Higgins, a Retired Engineering Supervisor,
thought that the potential to generate electricity with reciprocating
Tethered Airfoils appeared promising.  They invited me to pursue this
technology as an Associate Project Leader under the auspices of the Flight
Research Institute (FRI) and offered their assistance and guidance (which
is gratefully acknowledged!).

They wrote a letter of endorsement concerning Tethered Airfoil Wind
Power Generators that says:

"As a result of our studies of your invention we have concluded that
your concept is fundamentally sound and we believe that your goals can be
achieved by step-by-step demonstrations and that each step can be
accomplished within a reasonable effort."

  Later they reconfirmed their willingness to provide assistance:

"We plan to continue our support of the Project in the areas of
technical guidance and account monitoring as we are able and as long as such
efforts will help you attain our goals.  Be advised that we are able to
call on professional support from both the University of Washington and
the Boeing Company in support of this work."

   To summarize then, the Flight Research Institute offered to assist
the Tethered Airfoil Development Project three ways: 1) by providing free
technical consultations and monitoring of project finances by some of
the most widely respected aeronautical design engineers and managers of
aeronautical development, 2) by providing free access to the best
aeronautical design and development computers at Boeing, and 3) by providing
tax deductions for money invested in development.

8.3.    Reiner Descher, a professor of aeronautics at the University of
Washington liked the concept of using lighter-than-air airfoils in
conjunction with hydrofoils to make efficient sailing craft -- and perhaps
also to pull freighters.  He said he would like to supervise at least one
graduate student who would spend a year technically and thoroughly
evaluating these proposals.  We hope to find the funding required to
support this work.

   Not too surprisingly, these three evaluators and endorsers have
differing opinions regarding which implementations of this technology should
prove to be most practical and profitable, and which should be pursued
first.  Smith, for example, believes that Tethered Airfoils could be
used as a means to pull freighters.  Wimpress and Higgins are more
skeptical about this application and would rather not offer their support to
pursue this objective initially.  Descher, on the other hand, believes
that it might be possible to design around the technical limitations
that Wimpress and Higgins foresee.  Also, Wimpress, and Higgins see more
potential in the development of Tethered Airfoil Wind Power Generators
than Smith.