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Where can I find reliable figures about the best glides of Lilienthal and the Wright Brothers (1902 - 1903)?

From the sources below it would appear that Lilienthal's most advanced glider was far superior to that built by the Wright brothers in 1902 as the German apparatus was able to fly 1148 ft while the machine made by the Wrights only 600 ft.

It seems like the wind tunnel tests done by the Wright brothers in 1901-1902 to find optimal wings did not lead to improvements in lowering the glide angle and so increasing the flight distance.

1)"Finally Lilienthal become so skilled that he could make his glides in air velocities of 33 feet per second ... Lilienthal carried out more than 1,000 glides and attained distances of 1,148 ft. at a gliding angle of 4 degree from the hill."

Source: John H. D. Blanke, "Pioneers in Gliding", Popular Aviation, pag. 74 - 77, May 1928

2) "World Record Holders
The improved performance of the 1902 glider finally enabled the Wright brothers to gain extensive practice in the air. During September and October, they made between 700 and 1,000 glides. Flights of 500 feet were common, and a few topped 600 feet. Orville enthusiastically wrote home of their success, “we now hold all records!”"

Source: Inventing a Flying Machine

I'm asking about which glider that had better glide ratio because the Lift/Drag ratio is essential: the higher it is the longer the glide and the less powerful and lighter an engine is needed to make the glider fly horizontally.

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    $\begingroup$ could you please define "advanced"? $\endgroup$ – Federico Oct 6 '15 at 12:57
  • $\begingroup$ You seem to have answered your own question. Why do you think your existing sources are unreliable? $\endgroup$ – user11516 Oct 7 '15 at 0:24
  • $\begingroup$ Airsick , At least one source is unreliable as long as "a few topped 600 feet. Orville enthusiastically wrote home ... “we now hold all records!"" comes into conflict with "Lilienthal ... attained distances of 1,148 ft."". $\endgroup$ – Robert Werner Oct 7 '15 at 6:32
  • $\begingroup$ Raw gliding distance isn't a useful measure of gliding ability. You also need to take into account launch height and wind velocity. $\endgroup$ – Mark Mar 4 at 21:04
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Otto Lilienthal saw flying as something similar to bicycling: A sport and an opportunity to spend time out in Mother nature. Therefore, he designed all his airplanes such that they would fit through the door of a standard Reichsbahn freight wagon. He used a central truss (Gestellkreuz) to which willow stakes could be bolted such that they would fold backwards. He covered this structure with waxed cotton cloth and used wooden ribs to shape the airfoil of these wings. Consequently, the wingspan of his designs was limited.

The next limitation was his way of controlling his aircraft only by weight shifting. Since his hands were already busy with holding on to the aircraft, he could not use them to move control surfaces. His drawings and his correspondence show that he considered control surfaces and even ailerons, but he did not incorporate them into his designs.

Only his type 18 glider had a rectanguar inner wing which could be pulled close using a scissor link spar. However, with the bigger wing his weight shifting control showed its limits, as this did not lend itself to controlling gliders with bigger wingspans.

Another limit was his insistence that his aircraft would not need a runway or a launching device. Instead, he would grab handles in the Gestellkreuz, stand upright and use his legs as a landing gear. This limited not only the size, but also the wing loading of his designs.

The Wrigths, on the other hand, strived for the mechanically simplest and most lightweight designs and arrived at a biplane of constant chord and much higher aspect ratio. The 1902 glider could already be flown in a prone position and the pilot could control it with control surfaces.

Drag area of the human body in different poses

Drag area of the human body in different poses, from Sieghart Hoerner's Fluid Dynamic Drag. The pilot of the Wright flyer caused only one fifth of the drag of the pilot in Lilienthal's designs.

Because the wingspan of the Wright glider was much higher (9.6 m versus 6.7 m for Lilienthal's Normalsegelapparat) and the much higher drag of the pilot's position in case of the Lilienthal design, the Wright glider certainly had a much better glide ratio.

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The Lilienthal reference says 4 degree gliding angle from the hill, in air velocities up to 33 feet/second- (presumably wind speed relative to the ground?) Neither reference gives the net change in altitude, and the wind speed, and ground speed at launch, for a specific flight of a particular distance. That's what's needed. From Lilienthal's gliding angle of 4 degrees one could imagine distance to descent ratio of 14.3:1, (slope=1/sin(4 degrees)) but we don't know if the 4 degree slope is in still air, a 33 fps head wind, a 33 fps tail wind, or something else.

("Wait!", you say, "tail wind?" Sure. If distance from launching point is the figure off merit, you'd be a fool NOT to take a tail wind.)

As far as computing glide ratio, the raw facts aren't here to compute it with certainty for either glider. And slope lift (air driven upward by hitting terrain) ought to at least be checked if not factored in, as well.

Its possible that a comprehensive table of air foils from the early days might have both the final glider airfoils for the Wrights and Lilienthal. And those air foils would have L/D ratios, but those are NOT the same as the gliding ratios of actual airplanes. The performance of the vehicles included not just the wing L/D but the parasitic drag of the whole structure and the wing loading. Which brings us back to the height of the descent and the distance covered.

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