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Safety links in tether-set assemblies
for kiting systems

Disclaimer: This folder is a work in progress and is not a finished treatise nor a guide. This folder is but a place for exploratory study.  Tethering humans in kite systems is a most grave matter where death and serious injury may too easily be a result of incomplete engineering or safety practice. Work with experienced tether and tow people, especially when human life is involved, like in man-lifting in kite systems, towing manned hang gliders, towing gliders and sailplanes, parakiting, etc.
(files are being built by interested persons)
Most recent edit: Wednesday October 24, 2012

Definition:   A kite consists of a tether set together with components at both ends of the tether set wherein the end components and tether set reside in media that end up having the tether with a positive tension. Thus, components at the end of a kite's tether set experience resistive forces that may tend to destroy intended form and integrities.  To keep a kite operating as intended over-tension is to be avoided.  

The most simple kite is simply a simple tether with the tether's end points as simple end components; if such a tether-simple kite is placed in flowing media that involves flow differences on the simple tether-kite to give over-tension to part of the tether, then the tether will become damaged and perhaps fully break.

Damage in a tether component may or may not be evident with cursory inspection. A dream of a tether reporting its real time structure status remains yet a dream; several research centers are advancing on smart ropes, smart lines, smart tethers; the hope is to be alerted to changing structural integrity, changing ability to be all that the engineers want for the tether. To protect components in a working system, a quality-controlled safety link system might be incorporated in the macro system; comprehensive awareness of occurrences following the dislocation in the safety link system is a safety-critical matter; when human life is involved, then extreme exploration of all possibilities of post-dislocation of safety links should be explored and respected. Recoil of tensed components are historical sources of post-safety-link functioning; recoiled parts can kill humans or animals or destroy valuable parts of the environment. Safety links are not the only way to mitigate over-tension in kite systems; one may want to fully explore alternatives (porosity change, shape change, power change, direction change, angle of attack change, payout or length change, braking amount change, etc.).   Interested persons are invited to advance these notes.

Arrangements differ

  • Over-tension may lead to destruction of components at either end of a kite's tether set. One avenue of mitigation is the safety-link options. Other mitigations may involve change of action of driving or resistive components, e.g., change of angle of attack of a wing, change of powered propulsion of a powered tug component, or change of the amount of contact with the flowing media (water or air) by contact amount, porosity; perhaps shape or morphing of working components may be involved in over-tension mitigation.
  • Tether-set assemblies may be simple or complex. The coupling of various lines may be torsionally balanced or not.
  • Waves, oscillations, resonant vibrations, etc. may play in tensed systems and kites. Shock waves arrive into machines or systems from many sources, some more important than others per application.
  • In the kite system of simple hang gliding with pilot body tethered to wing, the hang lines and potential pilot-position-limit lines are tethers that may not have specific separate safety links as those lines may be specified to be last to break in a flight system.  
             However, in the activity of secondarily kiting the hang glider for launch purpose by use of a towing tether driven by a vehicle or winch or other prime mover (powered aircraft, ultralight, ship, boat, scooter, powered winch, set of friends, dog team, horse, etc.), the total system is more complex and human life is involved. Bridle lines become part of the macro kite tether set; connectors, safety links, tow line, line-fall-arrest devices, and active towing device bring in complexities to be respected. Tether dynamics comes to play; compression  or longitudinal waves may play a part in the tether set between the tug component and the hang glider component. The system safety call is to have a procedure to respect failure of any component in the system; but a safety link may be chosen to bring probabilities forward to favor dislocation of the safety link before other components fail.  Each combination of component failure or operation anomaly ought to be explored carefully and mitigations designed and practiced.  Tension limits, air speed limits, minimums, maximums, timing, etc. become part of the operational cares.
Discussion places, perhaps with open banter:
  • Recoil and related environment
  • Fail modes and resulting geometries and consequential environment upon fail
  • Material
  • Design
  • Inspection
  • Any smarts about conditions?
  • Quality control
  • Standards in manufacturing
  • Components couple with safety link form an environment that matters. Safety critical studies over each arrangement is recommended; when a safety link dislocates, then recoil, lashing, wrap, slap, etc. along with momentum exchanges in coupled parts affect safety. Protection of humans and components are involved. What are the experiences with safety links in each environment and arrangement?
  • Coupled components and torques of those components
  • Shock sources and sizes on a weak link prior to its breaking within an operation? What are the effects on a weak link from those shocks?  Replacement schedule? Inspection. Destruction testing and recording of results.
  • http://en.wikipedia.org/wiki/Aerial_rigging