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- Notice the slack lines a and b in Fig.75. indicating gliding upon just de-anchored hung lines; the lines hanging in gliding had mass that help to power the hang gliding.
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Attentive opening to Otto Lilienthal's book
Birdflightfinds global mechanical art awareness that might be under-appreciated relative to
boomed bi-conical flex-wing kite hang gliders.
Appreciating and respecting Otto's flex-wing awareness space seems like the least we could do to honor our hang glider roots. So, All
are invited to visit any and all that we might know about Otto and such mechanical space. He placed such matter by publishing into the
pool of public domain for use by further tinkerers, designers, builders, and users. Just what did Otto and his brother Gustav put forward?
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Boomed sails for kite hang gliders in simplicity was visited in experimental ways by Otto and Gustav, his brother. That Otto is most
known for his highly ribbed taut wings seems to have let his more simple explorations be under-appreciated art. May this possible
oversight be mended by attention of Hawks.
He knew of wings of sail with "cross-stay". Two leading edges and a cross or spreader "stay". Ref: page 92.
He noted that the spreader or "cross-stay" provided a reduction of lift compared to absenting the "cross-stay".
He also called the spreader or "cross-stay" a "cross-rib". He showed the standard cross kite of leading edges that were curved and
showed how its cross-rib dimpled the sail upon impacted the flow of air; he noted strongly that the deformed sail with the cross-rib of such standard kite was a means of not having performances available from more bird-like wings. Then immediately he taught in the next figure Fig. 72 a flexible-wing kite with two leading edges and a keel with no spreader bar or cross-rib disturbing the aerocurve of the sail; he illustrated the bi-conical sailform that would show up in later decades in Bach patent and Wanner patent and others. Otto did not seem to have the light of the fully limp Rogallo wing, but Otto was teaching in his published share about simple boom-stayed flexible wing kite gliders.
Otto noted on page 92 about the shaped of each of the two lobes of sail:
"shows there is only one larger curvature to either side of the axis, a curvature which endows the kite with a more favorable shape, since it is a closer approximation to the uniformly curved birds' wings." The keel of the kite-glider was his "
axis" beam. His teachings on the two pages tended to the higher-aspect-ratio "anachronistic stiffened Rogallo kite-glider."
Otto on page 92 also refers to the "Japanese kite" which is to be carefully explored for meaning to him in his time; identifying just what kite he had in mind on his writing under quotaton of that term "Japanese kite" would be interesting. It has been suggested that Otto may have had the
Tosa Dako in mind.
On page 93 Otto would provide back the equivalent of a frontal spreader by special construction of the leading edge booms fixing on a widened keel complex; he was apparently wanting to keep things clean drag-wise. They obtained very high L/D results. They fully got handsome results for L/D with the flex-wing boom stiffened. BUT THEY IMMEDIATELY SAW SOME NEXT STEPS that would give even better L/D: "Still better results are attainable when making the wings of stiff material, so as not to have to depend upon the wind for their curvature; a number of curved light ribs running crossways to the wings ensure the proper curvature of the covering." Hence we see quick move or progress from the standard-rog-like wing to advance flying wings helped by curved battens or ribs in the sail; Fig 75. In relatively short order the Lilienthal Brothers paced through the global mechanical arts key to recreational kite-hang gliding. Simple boomed sails on up to whatever stiffening one wanted by shaped ribs in the "shirting." Add the
W. Simon art and presto, full precursor to our later "Renaissance" of participation that was largely affected by the NASA and the related attention over the works of Rogallo and scores of associates.
On page 93: "and we released the cords"
.... So, with free-flying cords hanging free, the kite-gliders descended into the wind "without descending, travelling faster than we could when running as fast as possible against the wind." So, they glided and soared the hang gliders of these flexible-wing sorts .... and shared the teaching to the world in a published book. Their aim was to finally have powered kite-gliders, but they spent years toward the mastery of piloting hang gliders. Many would say "Rogallo wings" ... and for some good leadership reasons; but nod to the fundamental arts over stiffened-flexible-sails for kite-hang gliders would bring Otto Brothers forward front and center for attention.
For the above reasons, WHGA has awarded the Lilienthal Brothers a place in the
Flex-Wing Hang Glider Gold Air Award.
That the brothers Lilienthal went fast ahead to stiffened and shaped wings for carrying Otto's body should not bury the stark flex-wing kite hang-glider global mechanical arts that they set into the public domain by teaching and publishing. Perhaps this attention could help any overlooking that may have been done in hang glider mechanical history.
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