|Longline Control & XC
Shuttling of Sweeping Kites
Directing sweeping kites by pulling lines from the
ground is the simplest cheapest control actuation method. At distances
of a few hundred meters where common direct multiline kite control is
too mushy AWECS designers have been forced to resort to radio-controlled
pods with batteries and servos. This adds flying weight, capital/operating/maintenance costs,
and failure modes (dead batteries,
communications gaps, worn-out servos, etc.). A related problem is how to
shuttle a kite XC crosswind on tracks or cableways where control lines
must somehow keep up the chase. This post describes methods extending
direct multiline control to higher altitudes and crosswind shuttling.
Driving a string pulley loop set crosswind between two anchors is a
powerful way to tap a shuttling powerkite. A stock generator with a
pulley-wheel can be so driven but a direct kite control method of a
shuttling kite has been elusive. A pair of string pulley loops moving in
tandem can do the job. The "upwind loop" is connected to the forward
lines (A, B) brought together aloft as a bridle junction. The downwind
loop is connected to a pulley/control-bar thingy at the bridle junction
to toggle brake lines (D) left or right, retarding or advancing the loop
relative to its partner. Both loops drive the generator shaft at one end
of travel while a pulley pair at the other end varies the moving loops
relative to each other. To operate use either cross-linked
heddle pulleys with reins or a pulley T-bar moved by a joystick or
steering wheel. Photos and sketches
are pending, so have fun imagining
thingies and layouts.
A general principle for controlling long-line kites is to use the
thinnest low-stretch lines (esp.
UHMWPE) for control lines. Catenary
mush is minimized and can be reduced further by a small tensioning drogue
on a pulley self-flying partway up the line. Such tensioning robs a bit
of raw performance, but less than a control pod up to considerable
distance. Tensioning reduces control lag so much that crisp control over
many hundreds of meters is enabled.
Misc. Tips: The use of reins to a control bar, such as control draft
animals, allows personnel to stay "out of the bite" of dangerous ground
tackle. Another bar-trick is to "float" a control bar to the brake lines
unconnected to the main anchor "working line" to fore-lines, but you
must stay near that anchor point.
~Dave Santos July
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