| Topic for open discussion: z-factor
(specific power) / (wing thickness) |
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Aug 8, 2020, post by Dave Santos
z-Factor is primarily an explanatory number to relate wing types from SS to rigid-composite. Its strongly corelated precedent number in aerodynamics is Wing Loading: the ratio of an aircraft's weight to its wing area. One of my many mentors across aerospace was George Parks, a savant from youth who designed and built countless world-champion RC gliders, with peers like Paul McCready. George and I built many crazy sUAS concepts in the '80s and '90s, and every one flew just as intended. George's number-one Number for an experimental design was lowest possible Wing Loading. In classic kites, Lowest Wing Loading is also the most important performance parameter. All expert kitemakers know it, if not the respective mathematical aerodynamics, including top intuitive empirical power-kite designers. And yet, most AWE researchers completely disregard Lowest Wing-loading in favor of highest L/D or piling on parasitic-flying-mass, like eVTOL capability and avionics.
The modern SS power kite or paraglider has the Lowest Wing-Loading of any utility wing. The lightest models (62gr/m2) are less than half the Wing-Loading of a Monarch Butterfly (168gr/m2), the Lowest Wing-Loading charted
on WP. Note the WP paraglider number includes pilot payload mass, but
an unloaded AWES SS kite is far less loaded and is maximally "floaty". Lowest Wing-Loading is
a very useful AWES property during lulls, where minimum sink-rate wins,
with lowest wind velocity for sustained flight (zero-point energy of
flight) and lowest cut-in (AWE free-energy and capacity-factor).
All champion kite foilboarders know these things. Dave Culp was teaching AWE players SS Lowest Wing-Loading superiority a generation ago. The SS NASA Power Wing and Barish's first PG was based on Lowest Wing-Loading, over 50 years ago. z-Factor based on wing-thickness is simply another way of expressing the virtue of Lowest Wing-Loading, for reasoning better about optimal AWES wing selection
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| August 6, 2020, post by Dave Santos Key Kite-Number Identified: Specific-Power by Wing-Thickness z-factor
Specific-Power by Area is a popular top figure of merit in AWE R&D, that has led to a lot of hot kiteplane designs, of relatively higher mass, velocity, and risk, but poor scalability and wishful survival-to-payback. Specific-Power by Mass is the dominant number in classical aerospace, but its not been a popular design-driver in experimental AWE. Only slowly and weakly have academic AWE theorists addressed Mass Factors. Mass is a function of x,y,z, Volume and material Density. Wing Thickness, the z-axis, represents the engineering trade-offs between composite wings at the thickest highest-mass extreme, and Single-Skin kites. A new Kite Number identified is Specific-Power by Wing-Thickness. SS kites offer the highest value for this number. kPower proposes this "z-factor" as most-predictive number for megascale AWES viability. |