of twisted tethers
to drive groundGen?

~~~~Tether-Twist Quest~~~~

[For a contrast cousin: RRKs]

File:ADN animation.gif

I find Charles Max Fry clearly teaching AWECS torque tube as one of his taught options; so torque transmission from kited systems went into public domain for AWECS at least a couple of decades ago, if not sooner via basic torque-tube transmission of torque..., even the torque of a shaft of a generator driven by prime movers of various sorts....something used in 1800s.

Click image for full Fry instruction:


Jan. 2, 2011     M2801  Many years ago, BF Goodrich developed a rubber tube "torsion bar". If you pump a rubber hose with air pressure, torsional strength increases. It may be possible for a very long, lightweight, fiber-reinforced tube that is pressurized with air to point skyward . . . . with multiple propellers attached to it. Pressurizing an inflatable structure does increase its structural rigidity and torsional strength. 
Harry                                               [ ]

March 16, 2010 at M1340 

While twisting line is one way to transmit energy, there are clear practical limitations. Hockles, kinksloops, & bird cages are common partial failure modesSampson Rope, a technology leader in DyneemaŽ ship hawsers, asserts on its website that "high twist levels adversely affect the residual strength & should be avoided".

Twisting line concentrates stress on a just a few fibers, which fail progressively. Then there is the fact that twisted line pulls with great mechanical advantage, the basis for a "Spanish windlass", so an AWE kite or aerostat must pull against very powerful downforce or the line promptly supercoils into a twisted wad. These problems can be somewhat mitigated by thicker heavier line but this severely limits scaling potential compared to simply pulling or pumping a thinner less abused line. Still, for a small novelty AWE demo, a kite tether based on a "rubber-band motor" or the Thessalian witch's jynx (spinning disk string toy) [[Jinx ?]] will do fun micropower. An advantage is high rpm. There are old posts touching on this topic.        DaveS

Related former posts: M767     M744  

Abrasion and Twist Effects on High-Performance Synthetic Ropes for Towing Applications


March 16, 2010 at M1341

I pulled together some numbers for the weight of loop transmission vs electric conductors, and the loop looks like a clear winner. If somebody wants to have a particular tether material or voltage compared, let me know, or I'll go with 400 V and 1,000' of transmission, with solid aluminum conductors, vs Spectra line.

Regarding the option of a straight pull vs a drive shaft, I'd like to see the figures for Doug's favorite shafting, which we can take as optimized for this year. On an old HPV I did the numbers for, even chain drive was six times lighter than shaft drive, but I had different constraints. Still, J.E. Gordon points out that Nature almost always manages to avoid any serious need to resist torques, which is why ski bindings are so tricky. Drawing some rough analogies, we can compare a simple drive shaft to a loop fairly easily, I think.

As Doug points out, the loop system wants to reel itself in, but this is easily solved by always leaving some tension on the return run. AWE always requires some vertical tension, and it is of great benefit to either mechanical transmission system. On the loop scheme, one just uses large enough pulleys at high enough speeds to get the ft per min up and the lbs down to a safe figure for the HP expected.

A simple case of a drive shaft might take those same two tethers, and make them into a ladder with rigid struts to space them apart. Then, after launch, they could be twisted by the turbine. If the vertical tension and turbine RPM were adjusted nicely, you'd get a DNA-like double helix at 45 deg. If the working diameters and speeds were the same, the "shaft" would have the advantage of having two working members instead of one side of the loop. Against that, it would loose 29% to the angle vector, the same amount of length, and the weight of the separator struts. It would also experience far more wind resistance due to its own motion, but that would be partly cured by a full-round construction. If its diameter were reduced, and speed increased, it might tend to require great rigidity to avoid whipping. Perhaps some damper rings would act as center-steady bearings in the sky?

I'd be happy to compare numbers for the best hardware folks want to specify, from the shelf or not.

Bob Stuart 

March 21, 2010  "I would point out that the "DNA" helix (twisting rope ladder) without compressible strength would also tend to pull the machine down from the sky, however it may be that upward/downwind thrust would always be greater." Doug Selsam

PS: "P.S. I might point out that "the twist method" is the ONLY method actually used in millions of real wind turbines today. In reality, it's not just "A method", It's "THE method". In fact it is so common and taken for granted that I don't know if anyone has seen the need to name it before! :)" Doug Selsam

March 21, 2010 "There are being considered some wide multi-sub-tether schemes with three-rung-per-station segment with axial segmental struts to give compression strength when occasionally needed; smart tethering may well play a part that communicates with lifting bodies and generator or pump load-taking. JpF

March 17, 2010

While I applaud the micro independent individual set up, I do envision larger applications. The time is nigh, the weather is breaking and the fun begins; I do hope for a breakthrough on the tether front: some inside the box, some outside the circle and others off planet thinking will help us there.

Can you make a numeric list of what's available in the young art of tethers, then maybe we can explore each from there, DaveS?  All ears hears. 

March 17, 2010

Some actual achievements of torsional tether in AWE in its water analogue are several.

  • DaveS has a video up of a short groundGen driven by water turbine through a flexible drive shaft. 

Airborne turbines driving short flexible torsion tethers can be understood:

  • Spinning tails driving an aloft small generator
  • Doug Selsam has a segmented series of lifted rotors driving a multipart tether to drive groundGen.
  • Doug Selsam also instructs large diameter working tethers of various sorts.
  • And Doug Selsam  instructs in his patent large diameter open-mesh Darrieus structures that double as a tether to two anchors, one out and one near.
  • View the KiteGen carousel as a complex set of tethers twisting a large ground-plate or ring to drive either ring generator or central generator shaft. Here the tether set is made of separated ropes.  The kite elements turn the tether elements around and around; the groundGen mines that turning and relieves the twisting; meanwhile, the tether elements are each not going through local twist.

March 17, 2010
The gyro with the counter-rotating rotors is an interesting concept . . . there is a tail-less helicopter known as a "Manx" that uses concentric counter-rotating rotors . . . like the radio controlled toy.
Piasecki built a helicopter with inter-meshing, counter-rotating rotors . . . that concept allow for gigantic rotors and it also allows for each drive-shaft to drive a flexible torque-tube or twist-drive mechanism that could carry power to ground-level alternators. 


Doug Selsam holding generator receiving torque from pilot-kited series of rotors
 twisting-turning the shaft of the generator.  SuperTurbineŽ




In ten AWECS scales (microAWE to free-flight) what are the potentials of aloft twisting of tethers in order to have tether untwisting drive ground generators?  What are the challenges? The theoretical limits of effective energy generation from such a method category? 

In early 2009 such twist method was listed in a methods collection for AWE online (now seated in AWE Sector).  It might be easy to quit the quest with fears of torsional-knotting-tangle failures. However, a comprehensive analysis of the category may be worthy of attention.

Spiraling kites, looping kites, in-tether rotors, helicity gobblers, spinning kites, barrel-rolling kites, off-end-reel let-outs, rotating tails-twist piped to main tether, etc. can put extra twist in kite-held or aerostat-held tethers.  If twist is deliberately designed to enter into an AWECS tether with deliberate intention of mining that tether twist for doing ground work, then what are the possibilities for practical execution?  What materials at what scale?  Niche uses?   

Hold off comparing energy gains against other methods while this twist category is mastered to its limits and well analyzed and described. For some, this will be an interesting challenge; some may make a life's business from the category; others may see this quest as a dilution or distraction from what they may see as more profitable methods. But it might be neat to have the method well described for all. 

Instead of installing a relieving swivel, consider installing a relieving-working-mining generator.  What is the physical theoretical Betz-like limit for this category? Where will be the failures and how smart might be a tether to handle the challenges? Twist limiters? Calm-section smart reactions?  Best materials? Controls? Life of the tether? Heat? Structure of best tether per use? Open-mesh tethers? Aerodynamically-working tethers? Full-Magnus-effect rotating tethers? Bladed tethers? Large-diameter airy lifting rotating tethers? Twist thresholds?  Flexible drive shafts. Long torsion tubes doubling as system tether? High-tension cables?  Encased pre-stressed tether?  Smart anti-buckling tether? Open-mesh torsion case?  Darrieus flying flex-shaft doubling as tether?

Yes, Dave Lang is invited to this tether-in-focus party, as well as all others.  Top scientific analysis and practical experience are invited to the Tether-Twist Quest (TTQ).  Who will do the twist? Why? Where? When? At what scale? Free aloft ended? Double-end-anchoring?  Wide-collector of multiple tethers of one system? World-records in this method? Not to forget that in an extreme sense conventional turbines are do the twist with a "tether" that is frequently a hard and rigid direct driveshaft to a generator. And consider how a multi-part tether system is doing a large twist in the KiteGen carousel arrangement with a sub-tether doing a twisting!

CoopIP                         JpF

On wide separated multi-strand tether complexes with open center and stack wings, have smart controls to fly segments in order to keep macro tether complex turning in all of its parts at the same rate. This has not been modeled yet.  CoopIP   JpF

Some attending links:

Your favorite links for the TTQ project party are invited:


Flexible Rotary Torque Transmission Cable

Tethers anchored at both ends:

Rotate image clockwise is needed here.

Definitions of hockles on the Web:


Rough-draft notes:

Keywords towards this topic:
Tether, tether types, tether material, tether structure, fiber-based tethers, flexible drive shaft tethers, ladder-like tethers, multi-tether tether complexes, high-tension, low-tension, torque, loops, hockles, kinks, tangles, bird cages, rigidity, tension meter, twist measuring, torque measuring, untwisting, sudden relaxation, high modulus polyethylene (HMPE) synthetic ropes, retirement criteria of synthetic fiber ropes, abrasion, tensile fatigue, shock loading, drum compression, twist, concept: building kite to fit a given bridle, shear, shear stress, strain, torsion, torque, rotation, tension, torsion equation, open-mesh shafts, flying open-mesh shaft, tether set, Hockling,

Following list is clipped from Simple determination of the maximum axial and torsional energy dissipation in large diameter spiral strands  with extensive references

Note: OCR errors may be found in this Reference List extracted from the full text article. ACM has opted to expose the complete List rather than only correct and linked references.

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