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   LEI Scaling Law
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August 2, 2020, post by Dave Santos
to Roland, GONZALO, Tallak, editor

Tallak,

TUD preprint-
"Kitepower uses flexible leading edge inflatable kites, but these have a scaling disadvantage in that they become heavier with size. A single skin kite has the potential of negating this disadvantage while at the same time being more aerodynamically efficient. "

Ever since Wubbo passed, the TUD/AWEurope circle has erred by several premature technical down-selects, like single-line topology, control-pod dependence, kiteplane and LEI over-scaling, etc. There really has not been TUD due-diligence "argumentation" of these decisions, as the absence of written record shows. Instead, there is the clear written trail of Open AWE identification of these "no-go" choices, since 2007.

Roland now finds himself trying to correct course despite all the formal papers, textbooks, and conferences that presented more problematic paths as credible, like Makani's predicted-doomed architecture (on specific technical flaws). Roland has never intellectually engaged Open AWE advocacy of SS kites. kPower is not even on his map of AWE players. You and Roland are also complicit and acquiescent in New Forum censorship of the AWES technical debates involved.

The evidence of poor LEI scaling is long-standing nd extensive. The 100m2 prototype is an ideal source of scaling-law data. Roland should recognize the faithful AWE developers who first championed SS kites, like Dave Culp with KiteShip, and the NASA's 1960s NPW legacy. kPower is clearly the leading advocate-of-record of SS AWE kites, and should be respected as such. TUK has taken up the SS and lattice topology cause, and is actively in pre-publication, which should happen before the date JoeF has found for TUD's pivot.

We should all be collaborating in optimal experimental design, not playing venture capitalist commercialization roulette. kPower should be welcomed to contribute to RogerC's MSc belated TUD research, on merits.

Wubbo Lives,

dave

--------------

On Sunday, August 2, 2020, 12:13:18 PM CDT, Joe Faust <joefaust333@gmail.com> wrote:

Paper is apparently hidden until
the Embargo date      2020-12-21

Title
Single Skin Kite Airfoil Optimization for AWES

Author:    Coenen, Roger (TU Delft Aerospace Engineering)

Contributor::    Schmehl, Roland (mentor)

Degree granting institution:     Delft University of Technology

Date:   2018-12-21

Abstract
Airborne Wind Energy is a technology where wind energy is harvested with tethered flying devices. Kitepower uses flexible leading edge inflatable kites, but these have a scaling disadvantage in that they become heavier with size. A single skin kite has the potential of negating this disadvantage while at the same time being more aerodynamically efficient. An airfoil of this type is therefore investigated using Computational Fluid Dynamics and optimized using Surrogate Modelling techniques. A hybrid mesh was generated with hyperbolic extrusion and triangulation. The RANS solver that was used produced good results.The results of the optimization were unsatisfactory. The parametrization did not provide enough local control and unique airfoil shapes. The surrogate modelling approach is promising due to the computationally expensive CFD analyses.

Subject
Kites
Airfoil optimisation
CFD Optimization
CFD

To reference this document use:
http://resolver.tudelft.nl/uuid:fdcf8423-11f0-4b33-956e-3e761635ac41

Embargo date
2020-12-21

Part of collection
Student theses

Document type
master thesis

Rights
© 2018 Roger Coenen
August 2, 2020, post by Dave Santos
LEI Scaling

The problem seems to be thinking of aerospace scaling as a binary issue ("worthless", "does work")-

"You could not expect someone to readily accept a scaling limit of 30 sqm by your statement. That would mean Kitepower’s 100 sqm kite is worthless? I would rather believe that the 100 sqm kite does work, as they have much more to show for in terms of argumentation"

My heuristic expert claim is that 30m2 is perhaps the upper bound of a current LEI scaling sweet-spot, based on my evidence. Sure the 100m2 LEI will "work", just not well enough, in a narrower than desirable flight envelope. 

Where exactly is this "show" of "argumentation" for a 100m2 LEI? Like the M600, just because something is built does not prove it is not over its architecture's optimal scale, under engineering scaling laws. Instead, they can prove failures in testing.

We need folks who over-scale where a more informed expert would not bother. The failures are needed to show the world where the limits are. Lets see if the 100m2 LEI is proven or not.

The New Forum under Luke/Windy criteria is not a good place for serious technical kite discussion, given the petty limits on posting.

On Sunday, August 2, 2020, 08:54:18 AM CDT, dave santos <santos137@yahoo.com> wrote:


Tallak,

Pat Goodman, North's lead designer, wrote recently to me that 20m2 is the largest LEI he has ever designed. Why? Our common friend, Don Montague, tried a 50m2 LEI in light wind ten years ago,as carefully discussed on the old Forum. Don found it marginal. BrunoL seeks to up-pressure as racing parafoils win Darwinistically in foilboarding speed competition.

Go ahead and not believe that conventional LEIs above 30m2 really do suffer from scaling laws, and that the new scaling law identified (pressure-scaling) is not relevant.

My posting of LEI ideas that you objected to is removed. Good luck scaling your wing ideas. Good luck to Kitepower with its 100m2 LEI, that you believe in so.

dave
July 13, 2020, post by Dave Santos
LEI Scaling Law

Air-pressure does not inherently increase with LEI scale-up, therefore an LEI larger than about 30m2 becomes too floppy, or the tubes too thick, or the needed pressure too high.
==============================
Jul 14, 2020, post by Tallak Tveide

Thanks. I did not do any calculations myself. I expect what you say is true.

So LEI will only be appropriate for small systems. I can only think of sailboats right now. Three of these kites could produce almost 7 kW if they pulled 75 kgG at 3 m/s reelout. So for a small sailboat it should be feasible. Building such a kite with much higher glide number and tolerance for power could likely increase that a lot for that purpose, without touching the scaling limits of the design.
=====
July 17, post by Dave Santos

A comparable strutless LEI by Airush. Note that "power-to-weight" is clearly identified as the critical power-kite performance parameter, and mediocre "glide number" not worth mention.

AWES developers who have chosen lower power-to-mass wings in the desire for higher glide number find themselves sooner trapped by scaling law, tether drag, and crash-loss/hazard (uninsurability) limits. This has been known since Culp, pre-2004.

Airush: "unbeatable power to weight ratio"

They are of course comparing to other LEIs only. Parafoils do far better, and SS foils offer truly "unbeatable power to weight", scaling and inherent crashworthiness.

Airush Kiteboarding 
===============