CoolIP index                                                          Most recent edit: Wednesday October 24, 2012

* See legal note below.

Inverse Figure Eights?

In reviewing TUDelft videos a curious fact jumps out, that they are flying figure eights in the opposite direction from what is common. Rather than crossing the kite power-zone in a dive, they use the power zone to climb and then dive toward the edge of the window. The result is a smoother power output during the "long-cycle" extended reel-out phase. By contrast, we see NASA Langley tracing figure eights in the "normal" way, diving across the power zone in a huge surge, but other than that, the two prestige aerospace teams are exploring similar long-cycle reeling hardware configurations.

Its rather harder to fly TUDelft's pattern, as it goes counter to passive "Dutch Roll" oscillation, and so requires a tighter active control loop, but it is thus possible to keep the tether more consistently loaded near its working limit. Who better than the Dutch to add a new twist to Dutch Roll? NASA, KiteGen, and many others flying the old eights face an interesting fork in the design space, to follow TUDelft's example in optimizing long reeling, or to switch to a short cycle of power stroke phase during the dive surge, with elastic recovery phase at the upper edges of the window.

WPI and KiteLab Group have explored the conventional-eight all short-cycle design and found a high power potential without a long recovery phase, but with high sensitivity to optimal harmonic tuning, to getting the kite and transmission "in the groove."  As Massimo pointed out, there is no magic ratio for practical downwinding, and short-stroke eight systems really like the "grunt" force of minimal downwind travel. Elastic (or balance mass) return is part of these designs, and the challenge is to perfect a self-regulating (self-tuning) cycle across a wide wind range. Its not that hard.

Here is KiteLab's old passive Dutch Roll demonstrator representing a normal eight pattern with short-stroke tug cycling:

CoolIP*                      ~Dave Santos                 24March2012                    AWES5882

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

Terms and aspects:   

  • v

Related links and concepts:


Commentary is welcome:


*Legal Note: coolIP is hereby defined as a Creative-Commons Unported NonCommercial Share-Alike License, so now we are integrated with the latest standard cooperative IP model, but "coolIP" remains a nice shorthand.