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
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