Tethered free flying wings

The following is an outline of an idea that I have been working on for
some time, for the sake of brevity I have omitted details at this stage,
they will follow. The primary purpose of this post is to publish this
idea, for the usual reasons, though discussion, debate, criticism and
advice would be appreciated, it should be a simple concept for most
people to grasp. It is my intention to write a paper on this in a few
months time.

Space related applications might be far better air launch platforms and
vehicle recovery systems, even planes for Mars. Energy related
applications include the possibility of far more effective and efficient
wind turbines and aircraft.

Introduction
The ongoing development of traction kites and unmanned air vehicles has
raised the possibility of some alternate solutions to some of the most
basic of aerodynamic design problems. Possible advantage lies in the
separation of wing from body via a load carrying tether, this allows the
wing to otherwise fly, and generate lift, independently of the body.
It also enables loads to be distributed in tension, avoiding much of the
need for heavy structure and the weight and cost so incurred. Powered
free flying wings of this kind will likely have sufficient thrust to
weight ratios to take off and land vertically, and by circling, take off
and land their payloads vertically. The following is a outline of some
of the possible applications of such free flying tethered wings to
aircraft, wind turbines, kite sailing, and other technologies, and some
of the potential advantages there of.

Aircraft
An airplane utilising the free flying wing concept might consist of a
streamlined body, in which payload and fuel are stored, with retractable
landing gear sufficient for VTOL and taxiing purposes, and perhaps
landing pads on the top of the body suitable for holding free flying
wings when not in use. Likely multiple wings will be used so as to
balance rotating tether loads and for the purposes of redundancy. Fuel,
electrical power, and control, will likely be transmitted within the
line fairing with the wing capable of a degree of autonomy in case of
emergency, numerous safety features could be added. Such aircraft could
be built with payloads ranging from a few grams, to a few thousands of
tons.

Compared to a standard air plane such aircraft would have VTOL and a
significantly lower mass fraction, resulting in much greater range,
payload, efficiency, and much lower cost. Primarily this is due to the
elimination of a large part of the aircrafts structure and weight, which
no longer serves any purpose.

Such an aircraft would have similar advantages over a helicopter with
additional advantages in the elimination of the heavy gear box and the
additional capacity for high speed flight. For a given amount of lift a
free flying wing is far lighter than a rotor, and by being far less
constrained by effective rotor diameter greatly improved hover
performance, and much higher efficiency is possible. In effect, such an
aircraft might even hover more efficiently than it could fly
horizontally, due to the reduction in body drag. The heavy lift
capacity, perhaps into the thousands of tons, of such a large helicopter
might be particularly useful.

Wind turbines
The free flying wing approach might offer especially great advantage
with regard to power generation from the wind. With VTOL, such a wing
could be developed to launch and land autonomously and due to the high
flying speed should be able to survive extreme wind strengths without
even needing to land. In comparison to a standard wind turbine, the
tower is replaced by a line with the free flying wing replacing the
rotor tip, eliminating most of the blade. The large low speed generator
and gearbox are replaced by a small high speed generator/motor direct
coupled to a small propeller or ducted fan. This is sufficient for
VTOL, electrical power is transmitted via a cable within the line
fairing. Even with the much higher speed operation the generator is the
dominant cost, there is significant advantage in using lower performance
generator designs of far lower cost. The dominant generator cost also
favours the use of a larger wing that can generate in much lower wind
speeds, further, such a system is able to operate at much higher
altitude where the wind is generally stronger. Wind turbines typically
have a utility of around 25%, with the capacity to generate in much
lighter winds, this system would operate far more of the time. A
further advantage is the capacity to scale up to very large sizes, units
in the hundreds of megawatts at least, should be possible, this is not
possible with current wind turbines.

A comparative analysis would tend to infer that this system should be
able to generate electricity for about a tenth the cost of standard wind
turbines, direct cost analysis would tend to confer with this. It has
the potential to be significantly less expensive than other mainstream
electricity production. This does not, however, account for the cost of
a site, power transmission, and social and environmental costs.

Parachutes
An interesting application for an unpowered free flying wing is as a
parachute or even paraglider. While structurally similar such a wing
can be made much smaller than a parachute due to the much higher flight
speeds, and can be made of high performance materials. For these
reasons an arch style wing system especially, can be made much lighter
than a comparable parachute. By using such a free flying wing as a
gyrocopter reasonable glide rates are possible, in effect the gyrocopter
mode trades glide rate, or lift to drag ratio, for lift. With this
system it is possible to combine a flared landing, as per a paraglider,
with pitch control and energy storage in the wing's speed, for highly
effective and controlled vertical landings.

Kite sailing
In recent times high performance kite development has been greatly
pushed by kite traction and kitesurfing in particular. Considerable
effort is now going into the development of kite sailing, this is in
many ways driving the development of the free flying wing concept.
Traditional problems for kite sailing are launching, landing, power
control and light wind operation. Light wind operation is particularly
difficult because it necessitates extremely light weight construction.
One possibility is to use the wind turbine type solution, this enables
launching and landing, and the capacity to motor the wing in light
winds. It also enables power generation for use on board and if used in
conjunction with a diesel electric type ship, the capacity to sail
directly into the wind, avoiding the need to tack. The free flying wing
enables a comprehensive solution to power control and lends itself to
control by autopilot.

Aerostats
Another possible application for free flying wings is as aerostats. For
example, a wing might be flown high over a city providing everything
from communications to surveillance services. Power might be
transmitted up the line, enabling it to generate power when the wind
blows, and to be powered when it does not.

Water application
It would seem possible to use free flying wings to generate power from
water currents, rivers, tides, even ocean currents, in much the same way
as a wind power generation system would work. While the free flying
wing approach is very effective at extracting energy from such flows the
available energy is not as great as one would think. While water is far
more dense than air it is the speed of the flow and available area that
is really important. The power available is proportional to the speed
of the flow cubed, this makes wind power more attractive, especially as
the available areas are much greater. There are also issues with regard
to impacting submerged objects, even so, this could be a significant
application for free flying wings.

This system might also be used in place of water propellers, they would
be particularly useful in applications requiring high thrust at low
speed, they might also be useful with regard to manoeuvring. Pitch, yaw
and roll mitigation might also be possible, this can actually use the
energy of waves to power forward motion. In this way wave energy power
schemes could also be developed.

Pete