Most recent edit:
Monday December 17, 2012
* See legal note below.
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.
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
- corner-block line-tensioners
- loose line catenary
- aeroelastically tuned
- tension nodal points
- harmonic nodes
- passive stiffness
- active wingmill antinodes
- Related links and concepts:
- Commentary is welcome:
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