Further technical details, for those who are interested, warning, this
is otherwise boring.

Theory
The lift of a wing is proportional to the velocity squared, as such a
wing is very speed dependent, generating little useful lift at low
speed. For helicopters and wind turbines this means that the inner part
of the blade, which is travelling at a proportionately slower speed, is
generating significantly less lift, in effect, the tip does most of the
work. For airplanes this means that a high takeoff speed is generally
necessary. Sail craft likewise have little lift at low speed, being
slow to accelerate and build up apparent wind.

Within typical operating ranges, the lift to drag ratio, or efficiency,
of a wing is largely independent of speed, such that higher speed wings
can be smaller, for a given lifting force, without costing efficiency,
though power increases in proportion to speed. The general design
difficulty, is in overcoming this low speed regime without compromising
overall design. Generally this design compromise requires a wing which
is too small for efficient low speed operation, and to large for
effective high speed operation.

The other significant advantage of a free flying wing is that
structurally they can use distributed support from beneath via tensile
members. Such bridles, as in a paraglider, parachute, or kite, can be
very light and inexpensive, providing distributed support and largely
eliminating the need for internal wing spars. This is a very
significant thing enabling major weight reductions. An interesting
consequence of this is the avoidance of this scaling constraint which
currently limits larger aircraft. Free flying wings capable of lifting
a thousand ton would seem theoretically possible, with the possibility
of using multiple wings, partially for redundancy, truly large payloads
should be possible, though perhaps not optimal.

A further limitation of rotors as per helicopters and wind turbines, is
the slow rotational speed which comes with large diameter, requiring
complex and heavy power transmission systems. Because a free flying
wing, can be flying at high speed, a small high speed propeller or
ducted fan can be used. While there are inefficiencies involved in
doing this, they are not great, and this avoids the low speed gearing
problem. In this mode, a free flying wing can to some extent be thought
of as a free flying rotor tip, without the same limitations in diameter.

In addition to enabling the predominate use of tensile load carrying
members where heavy structural members in compression or bending were
previously often required this approach enables the speed, and hence
lift, of the wing to be actively controlled independently of the body.

For an aircraft this might enable vertical takeoff and landing, also,
using a bridle to distribute load a much lighter wing, less limited by
scale, should be possible. Compared to a helicopter this might allow
the elimination of the gearing necessary for low rotational speed and
much of the inner rotor, also, the adoption of much larger rotor
diameters. Wind turbines might be similarly advantaged with the added
capacity of self erection and operation at much higher altitudes,
without a tower.

Construction
The lift generated from a free flying wing is utilised some distance
beneath the wing via tensile members, this enables the spanwise lift to
be supported via tensile members instead of the traditional and heavy
wing spar. Paragliders, parachutes, and kites exemplify this form of
wing and so provide considerable insight into what their design and
construction might entail. The task at hand is to transfer the lift
force from the skin of the wing through to the payload in a light and
effective fashion which little compromises the overall aerodynamics.
The first step in this load transmission is in collecting this lifting
force from the skin of the wing, this raises a number of possibilities.
Generally kites support this lifting force by transmitting it in tension
along the wings skin, while this generally distorts the skin shape,
seriously compromising the aerodynamics, it has the advantage of being
very light weight, a necessity for low speed flying. Aircraft tend to
use a rigid skin structure which is internally supported by heavy
structural members, this does not aerodynamically compromise the skin
shape, at the expense of weight. Obviously, there are also a number of
hybrid solutions to this problem, for example the use of ram air
inflation to support the skin structure in a paraglider, and the use of
a fabric skin stretched over a rigid spar and rib internal wing
structure in many older and lighter weight aircraft.

The two wing types that suggest themselves are a standard type rigid
flying wing, bridled much like a paraglider, though likely with fewer
fared bridles, and the arch style wing where the bridles are effectively
internalised with load distributed spanwise under tension from each tip.
The advantage of the arc style wing is that the skin can function in
tension with out compromising the skin shape, this avoids the need for a
rigid skin structure and the majority of the weight and cost there of.
The major disadvantage of the arc style wing is that conventional wisdom
would infer that lift coefficient corresponds roughly to the projected
area when flying, which is somewhat less than the wing area when laid
out flat. Interestingly, for a given aspect ratio, the arch style wings
tend to have a higher lift to drag ratio than conventional soft wings,
likely, this is due to the elimination of bridle drag. Initial
calculations would infer that a five to ten fold weight and cost
reduction might be possible over a standard type bridled rigid wing, but
there are a number of uncertainties, this is a field in need of further
study. A bridled rigid wing might ultimately achieve a weight of 2%
that of the load carrying capacity, an arc style wing might get well
below one percent. Note that some applications favour low wing loadings
that can invoke a skin thickness below the minimum gauge constraints of
some materials, this can constrain such designs.

For a rigid wing, to first approximation, doubling the number of bridles
halves the internal structure required. This eventually reaches a point
of diminishing returns as bridle drag scales with line diameter while
the bridle load scales with line diameter squared. Experimental and
theoretical evidence to date would infer that wings with high lift to
drag ratios are going to require a degree of bridle and line faring in
order to realise high efficiency. Current high performance kites and
paragliders are already constrained by this limitation. The development
of fared lines that are aerodynamically stable might be interesting.
The dynamics of line twist in conjunction with aerodynamic feedback will
need to be mitigated to stop strumming. The centre of line tension will
likely want to be significantly forward of the centre of pressure of the
fared section to aid this stability, though there are other
possibilities like the addition of tail planes to active control
systems. These problems will likely govern the design and construction
of such fared lines. Some basic construction methods are to use a
standard line with a foam trailing edge faring, or a pulltruded glass or
carbon fibre section in which the trailing edge is hollow, so as to keep
the centre of tension forward. Interestingly, such a hollow trailing
edge section is sufficiently large for the insertion of high voltage
power cables or fuel lines sufficient to power such flying wings.

Pete.