CoolIP index                                                          Most recent edit: Monday December 17, 2012

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Stiffer Nodes (Max Power from Membrane Wing-Mills)

Over years of building and flight testing flapping membranes for power extraction, many design principles revealed themselves. Today's versions are better in every way. Nice airspace and planform geometries are worked out. Internal load-paths are aeroelastically tuned for certain firing. Battens run as they should to enhance membrane normal mode harmonics. Turbulators and inertial regulators are validated. Loads are variably matched. Most such refinements have been described. These "flipwings" made power, but did not quite yield the amazing power-to-weight suggested by predictions. A missing ingredient was needed.

The hint was the drogue corner-block line-tensioners that allowed flipwing pumping output to change direction back to the anchorpoint with far less loss than pumping damped around a loose line catenary to the suspended flipwing. This was noticed as a transverse wave dispersion problem, with the fix being to make the wave longitudinal by guy-lining it as a still node. It was now clear that a proper guy-lining of the nodal points acted on by the flipwing (as anti-node) allows maximum power-out. The new configuration, in the simplest case, has two pairs of flipwing node guylines to a pair of anchors, as an arch variant. Power is extracted as a two-phase pulsing at the anchors. For single anchor needs, the older flipwing method still gives useful power; the trick is to use more kite and drogue to tension nodal points.

The new AWES lesson here is to rig airborne harmonic nodes as stiff as practical for efficient lattice-pumping. We already knew the ground itself is the stiffest nodal medium, but the new understanding is how passive stiffness is the vital property for active wingmill antinodes to act against. The latest wingmill tests are almost daily validating the improved understanding. 2kiteSam has sewn several fine wingmill variants the last few months, and some of my weird cymatic Tyvek creatures will have to be seen on video to be believed.

  • CC BY-NC-SA (same as coolIP)                 ~Dave Santos              16 Dec. 2012              AirborneWindEnergy/message/8220

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

  • Terms and aspects:   
    • normal mode harmonics of membranes
    • anchorpoint
    • corner-block line-tensioners
    • loose line catenary
    • aeroelastically tuned                           wiki/Aeroelasticity
    • tension nodal points
    • harmonic nodes
    • passive stiffness
    • active wingmill antinodes

  • Related links and concepts:
  • Commentary is welcome:
    • v

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