CoolIP index           


Curious Ultra-High RPM Rotary Tether Finding           UHrpmRT

Weight -to-power efficiency of rotating tether mechanical energy transmission, such as Selsam and SkyMill Italy have demoed, can be greatly increased by a higher rotation rate. If the tether can be rotated at ultra-high speed close to its aero-thermal limit (>100 k rpm) spectacular performance seems possible.

Of course an aero-turbine of itself cannot turn so fast by wind, so some sort of step-up gearing is needed. This is a weird mechanism with a critical dependence on maintaining a narrow range of tether tension to operate properly, but should be possible with the right controls. I wonder if DaveL's tether software can model this exotic mode. There are probably some very odd dynamics to discover; and failure-modes are likely pretty interesting.

CoolIP                       ~Dave Santos           May 14, 2011           M3562 

Comment and development of this topic will be occurring here.       
All, send notes, drawings, and photographs!

Terms and aspects:   

  • UHrpmRT     Ultra-high rpm Rotary-Tether    
  • aero-thermal limit, aerothermal, aerothermodynamics, aerodynamic heating,
  • step-up gearing  
  • range of tether tension
  • failure-modes

Related links:


Commentary is welcome:

  • Beware of using gearboxes where high amounts of power (over 1 MW) is concerned .  .  .  . gearboxes involve weight and expense.   ~ Harry                  May14, 2011    
  • Consider the very shroud of a rotary cable or tube as a stator with the cable as rotor to have the tether itself as an electric generator.      JpF        May14, 2011    
  • Harry is right about conventional gearboxes scaling poorly by weight & my use of "gearbox" is in the broadest sense; several methods of mechanical advantage do avoid gears. Also this particular idea is so far-out that its not (yet) serious. Joe's idea seems to be constrained by the low Re of the characteristic dimension of the tether cross-section fundamentally limiting the top "tip" speed and resulting RPM.
    I neglected to mention that this idea's best advantage is that one can greatly reduce the required tether tension for operation. High power-to-weight efficiency at low RPM is possible, but by a tether so tight that the amount of kite lift required is prohibitive.      ~DaveS                        May14, 2011    

  • The suggested consideration has the shroud of a tether be kept rotationally static by anchor and aloft hold while the interior shrouded part of the tether complex be rotated by wind-driven kite-lifted lofted elements; then the tether become an electric generator.    In your comment, DaveS, is that what you got from my first concept presentation, or did you envision something else for your comment?        JpF        May14, 2011    
  •  Yes a driveshaft carries more power at less torque at higher RPM, and a series
    of small rotors naturally spin the tether fast without a gearbox. The many
    small blades are the aerodynamic equivalent of many gear teeth. We've
    simplified it by making the turbine itself act as its own gearbox. That way the
    whole SuperturbineŽ has only a single moving part. Steady-state rotation -
    who knew? :)
    I'd share some characteristics of these long, fast driveshafts, but it would
    take all day of explaining.      DougS               May15, 2011      M3579