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Rare-earth magnet safety link assemblies   
(Tommy)    "Tommy Link"

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)

  • TommyT:
    Meanwhile have fun brainstorming

    Joe, ever think to use rare earth magnets as a weaklink?
    Tommy                                Sept. 2, 2011

    In other kite applications magnets are considered in tether parts for generation.
    But it looks like you have the kite hang glider towing safety link "Tommy" link for the rare-earth option for exploring!


    In first blush on the Tommy Link I am flashing on mini-soft cover protectors. And variations to consider: slide, face-to-face, graded plates that tune the G level wanted (magnet standardized, but facing plate grade for total strength wanted); seems like an avenue for the dial-a-G-safety-link direction also. Must explore the Tommy Link!

  • v
Parameters and aspects
  • Recoil protection. Covers with slight overhang.
  • Dirt clearance. Keep it clean and dry.
  • Inspection
  • Testing could be done just prior to flight.
  • Slide or face-to-face? Study each.
  • Cam-break switch for release
  • Consider pilot-controlled release systems using the Tommy Link principles. Pull cam breaks tethering.
  • Age-stamp the assembly. What degrades high-quality magnets?   Fail mode seems to be in the wanted direction: weakening.
  • Dial-a-strength or G level by various methods. Perhaps graded film interleave? Perhaps dialed-face area? Perhaps graded face plates?  Calibrated breaking points?  Tommy Link might lend itself to various calibration methods; explore.
  • No more buying of cord;
  • no more knots;
  • different quality control.
  • Maybe a totally simpler system.
  • Time saver. 
  • Consistency.
  • Consider axially magnetized rod magnet with ring magnet; compare with face holders and the cleaning issue.
  • Strength of break can be tested easily with weights.
  • Unmanned testing. RC.  Rigs.  Photographing recoils.
  • Magnet shape choice could be fine tuned.  First look at standard commercially available products for the assemblies to be explored.
  • Wrapping cases
  • What side would the magnet be?  Far toward tug or close-side to HG?  Would it ever matter?  The mass of the magnet may be much larger than the mass of the opposing iron plate; this may lead to keeping the magnet on the tug side, as recoil at HG-pilot side would deal with less mass. And maybe pilots in queque could have plates that give calibration for their personal G needs.  
  • Quick clean at each use. Non-destructive pull test just before use.
  • Two magnets or just one and a iron-facing plate or tube, etc., depending on the final shapes wanted.
  • Mounting or connecting the magnet to the tether assembly?
  • Keep items that may be injured by magnetic fields away from the magnet.   Procedure for storing the Tommy Link?
  • Coloring the Tommy Link assembly with red and magnetism symbol.  Keep away from certain electronic devices. What are the distances for the caution?
  • Test the consistency-of-opening of the Tommy Link against the consistency-of-opening of other safety links.  Cycles? Abuse and then cycles?   Dust abuse and cycles?   Finger oil?   Dew?  Grit?  Clear case for seeing dirt.   Manual test. Perhaps strain gauge could be handy for immediate kpre-flight test.
  • Note that destruction does not occur upon pull testing; integrity remains.
  • Life of the Tommy Link?
  • Game: fishing pole with string with magnet on end of string; players "fish" for objects that have iron-based receivers on the objects. The objects are contacted when aim is good. Contact made and the objects may be reeled into the player. Player pulls hard enough to release the object. Player gets to keep the object.  Do this in reverse for safety-link for HG towing, perhaps.
  • Release forces?
  • Encased magnet?
  • Magnet safety:
  • Magnet glossaries
  • Calculators:
  • http://energykitesystems.net/Tethers/SafetyLinks/RareEarthMagnets/TommyLink1.jpg  Considering an encapsulation that prevents slap contact upon re-mounting the two parts of the Tommy Link; clean proofing and then re-mount; ease re-mount; proofing. Then use. An indicator could prove depth reach of the re-mount. To prevent slap engagement, I envision a peristaltic tube that slow engagement, but permits full engagement; if the tube of engagement is clear vinyl then visual confirmation could be made; also, if a indicator mark was available on the inserting iron, then that would be nice redundancy; the pull test just before use would be a third redundancy check. Air-release hole also might be employed might also be employed here. Wanted: prevent slap join of magnetic working surfaces.
  • Pull force can vary significantly as a result of surface conditions.
  • http://www.kjmagnetics.com/magdir.asp  axially magnetized
  • Magnet-to-magnet gives more hold force than magnet to steel plate.
  • How to "see" that separation distance is cleanly zero? Or cleanly holding graded non-magnetic separator that might be used in calibrated dislocation force?  Perhaps test up to 90% and, if passed, then accept it; thus the hold is there up to the tested amount, at least.
General study toward the Tommy Link: