Otto Lilienthal's
(Aeronautical) Bibliography

An Annotated Overview

1873
"Theorie des Vogelflugs" (Theory of Bird Flight)

Lecture at the Business Association Potsdam
(The manuscript of the lecture is preserved in the "Deutsches Museum"
in Munich (DM))

Lilienthal's first known lecture was a scientific program. Lilienthal deals especially with the criticism of the balloon and with the necessity of studying bird flight. He demonstrates wing flapping models. Lilienthal refers to the "Aeronautical Society of Great Britain", which the Lilienthal brothers had joined, and to the lack of such a society in Germany: "The art of flight cannot be invented in the same way that gunpowder was. For this reason it is a pity that the English and not the more theoretical Germans had the idea to found an aeronautical society...."

1886
"Über leichte Motoren und ihre Verwendung für die Luftschiffahrt"
(About Light Engines and Their Use in Aerial Navigation)

Lecture at the "Verein zur Förderung der Luftschiffahrt" (Society for Promoting Aerial Navigation), Berlin, June, 5.(VzFdL)

Lilienthal gives a report on models with engine power. Apart from other things he reports on a mechanical pigeon that has a coil spring engine and natural wings weighing 50 g and a steam engine weighing 1500 g producing 1/4 HP that he built himself.

1888
"Der Kraftaufwand beim Vogelflug" (The Energy Involved in Bird Flight)

(The manuscript of the lecture is preserved in the DM in Munich)

In a series of three lectures in 1888-89 Lilienthal reports the results of his research in bird flight and measurements of the force of air.
The minutes recorded: "The interest of the Society in Mr. Lilienthal's interesting experiments was demonstrated by a standing ovation upon a motion by the chairman."

The lecture reports the essential part of the book, Lilienthal published in 1889:

1889
"Der Vogelflug als Grundlage der Fliegekunst"
(Bird flight as a Basis of Aviation);

The second edition was published in 1910 with an additional chapter by Gustav Lilienthal.
The third edition was published in 1938 as a facsimile of the first edition with Lilienthal's corrections in handwriting and with a foreword by the Professor of Aerodynamics Ludwig Prandtl.
Russian edition "poljot ptiz", St. Petersburg, 1905
English edition (translated from the 2nd edition) "Bird flight as a Basis of Aviation", New York, 1911

With this book Lilienthal finished his flight physical preliminary research studies of flight. Now he believed that he had the necessary knowledge to start building a man carrying apparatus. In addition to the development of the physics of flight the book contains a summary of all experiments, that Lilienthal carried out during the last twenty years, a chapter with rules for the construction of aeroplanes his further programm, a water-colour, 80 woodcuts from his own hands and two sections of poetry. One of them is the often quoted poem about the stork and selections often appear on memorials to Lilienthal.

Lilienthal presents his knowledge in articles and lectures in a variety of popular and scientific forms. The most important lectures take place at the "Deutscher Verein zur Förderung der Luftschiffahrt" (German Society for Advancement of Airship Travel) VzFdL. The voice of the society is the "Zeitschrift für Luftschiffahrt" ZfL (Journal of Aviation).

In addition, Lilienthal publishes frequently in the popular weekly magazine "Prometheus".

1890
"Der Flug der Vögel und des Menschen durch die Sonnenwärme"
(The Flight of Birds and Humans By Using the Warmth of the Sun)

Prometheus Nr.55, page 35

Lilienthal sees essential factors for energy conservation in bird flight not only in the curved wings but in an ascending wind component. Even though the title indicates a description of thermal updrafts, Lilienthal sees a lifting component as a general phenomenon of the wind.

"Über die Möglichkeit des freien Fluges"
(About the Possibility of Free Flight)

Lecture at the "Verein zur Förderung des Gewerbefleißes in Preußen"
(Society for Promoting Diligence in Business in Prussia), June, 2.

 

1891
"Über Theorie und Praxis des freien Fluges"
(About Theory and Practice of Free Flight)

Lecture in front of VzFdL, ZfL Nr.7/8 page 153

Lilienthal proceeds to experiment with man-carrying gliders according to his plans described earlier in his book. Obviously he was dissatisfied with his success: "Free flight establishes a scope of work for human diligence, that distinguishes like no other the way that success stands in an unfavourable ratio to the pains taken over." Lilienthal starts his article, "But still one thing is certain: we will not get anywhere just by talking and there is little research to do on the simple whirling arm device. We have to go on and we must try to be alone in the air on a real flight…. The transition to flight practise is therefore a necessary connection for building up our whole knowledge of aviation."

Lilienthal compares flying to swimming and cycling in order to make his point: "Even swimming has a distinctive theory…. Someone who has no knowledge of swimming and learned the theory well and has done land drills, will drown in all probability if he is in the situation to use his theoretical knowledge practically for the first time in order to save his life."

Shortly afterwards Lilienthal announces the success that the Frenchman Ferdinand Ferber would later call the beginning of human flight.

"Ueber meine diesjährigen Flugversuche"
(About My Flight Attempts This Year)

Lecture at VzFdL, ZfL Nr.12 page 286
English Translation of the original text:

 

1892
"Über die Mechanik im Dienste der Flugtechnik"
(About the Mechanics Servicing Aviation)

ZfL Nr.11 page 180

Lilienthal tries to clarify the laws of physics with strong words: "The unpleasant pamphlets of aviation hot-headers have expanded the specialized literature with an enormous number of unproductive thoughts. Ignorance, bigotry and arrogance have given a disadvantageous character to the whole flight technical literature…. The layman went on with his emotional mechanics in abundance and tried to explain the flight process in his way. Of course all this had to be printed."

In the following years Lilienthal made regular reports with photographs to the society about his attempts to fly.

"Einiges aus meiner Fliegepraxis"
(A few Things Out of my Flying Practise)

Lecture in front of VzFdL, October, 17.

Lilienthal reports on flying distances up to 200 feet.

"Ueber den Segelflug und seine Nachahmung"
(About Sailing Flight and Its Imitation)

ZfL Nr.11 page 277

A summary is published in "American Engineer and Railroad Journal" Vol. 7 (1893) at page 342

Lilienthal reports on dangerous flight situations, the limits of bird flight imitation and the use of natural wind as he has experienced these in his practical experiments: "What is the most ingenious man-made flying machine compared to those wings powered by nature's power? … The imitative wing of man is and always will be ... a poor instrument and still I can confirm by use of man-made flying devices that practise and experience will do their part in order to remove, step by step, certain imperfections and to improve considerably safety dealing with the wind."
Also, he mentions his most important safety method that he has kept through his entire flying practise, the possibility of letting oneself fall out of the apparatus while flying above and against the direction of the wind onto a smooth slop. "The area surrounding Berlin is unfortunately poor in good places for practising Sailing Flight. The ideal is a sandy, round, sloping hill with a height of at least 20 meters, which allows a jump in all directions." In 1894 Lilienthal creates such an artificial hill out of a slagheap near his flat.

1893
"Die Flugmaschinen des Mr. Hargrave" (Mr. Hargrave's Flying Machines)

ZfL Nr.12, page 114

Lilienthal gives a detailed report on light wing-flapping-engines, which were created by the Australian Lawrence Hargrave, because adding a wing-flapping-mechanism was one of Lilienthal's future goals.

"Die Tragfähigkeit gewölbter Flächen beim praktischen Segelfluge"
(The Carrying Capacity of Arched Surfaces in Sailing Flight)

ZfL Nr.11, page 259
The article was published in "Aeronautics" Nr.1/7, page 92 as well as in full by Octave Chanute: "Progress in Flying Machines", New York, 1894, Appendix
(scanned in G. Bradshaws "to fly is everything")
and in abbreviated form in "L'Aeronaute" 27/1(1894), page 10 as "Essais de planement dans l'air"

In November 1893 Lilienthal reports with satisfaction on enormous progress. Two enclosed pictures show a man flying high above the landscape of the Rhinow hills. In two other pictures his Berlin flight-station, a new tower for jumping off, can be seen. After a short time this building failed to meet his requirements and was replaced with the "flight hill" in Lichterfelde one year later. In the face of success he mentions objections by the prominent critics Helmholtz and Reuleaux: "In those days one had by government decree through a scholarly commission established that man just can't fly...."

Lilienthal describes:
His new collapsible wing construction;
The principle of the tail of the flying machine and flight control, and
The experience of flight in updraft that carried him higher than he started.
"I gave up the large wing span of my early gliders step by step."

He again gives reasons for his flight position that is essential for his safety on the still unsafe flights: "It seems to me to be inadvisable to extend the body in a stretched position …. Later one can possibly turn to that." Extension of flight through a mechanized flapping of the wings is, apart from flying practise in stronger wind, his next aim: "I have already finished a steam engine that should move the wings during my next attempts. It has an overall weight of 20 kg producing 2 hp, and is being adjusted for an operating time of half an hour."
He reduced the wing camber depth based on his practical experience from 1:18 to 1:20. As the only alternative to the flapping wing he sees "lifting and at the same time forward moving airscrews". It is noteworthy is that Lilienthal could not improve flight distance and control substantially during the next three years before his fatal crash.

"Zur Flugfrage"(The Problem of Flying)

"Prometheus" Nr. 204, page 753 and Nr. 205, page 769

A summary of the two above articles appears in "Prometheus". The second part was published in abbreviated form in the 1893 "Smithsonian Report," page 189

"Praktische Erfahrungen beim Segelfluge"
(Practical Experiences in Soaring)

"Prometheus" Nr.219, page 161 and Nr.220, page 182

The first part reports on the different developmental directions in flight technique from insect flight to the balloon. The second part continues the report of his work (The Problem of Flying).
The second part was published as "Practical Experiment in Soaring" in the 1893"Smithsonian Report," page 195

"Der Schwebeflug des Menschen" (Man's Sustained Flight)
is the title of a manuscript that was sold in New York in 1993. The content is only partly known. One part deals with the project of a reduced size, man-made flying-hill built in 1894 near Berlin. His experiences of Rhinow appeared in the article.

Shorter report "Über Schraubenflieger" (About Propeller Aircraft)

ZfL Nr.12, page 228

Lilienthal analyzes the opinions of the flight technicians Popper, Lössl and Jarolimek and why he thinks that propellers, in contrast to flapping wings, are not compatible with soaring.

1894
"Allgemeine Gesichtspunkte bei deren Herstellung und Anwendung von Flugapparaten"
(General Factors for Production and Use of Flying Machines)

in ZfL Nr. 6, page 143
published as "Die Flugapparate" (Flying Machines), Berlin 1894 in "L'Aeronaute " 27, Nr.12, page 270 as "Principes généraux a considerer dans la construction et l'emploi des appareils de vol"

Lilienthal already had given a lecture with demonstrations of his gliders at the society (VzFdL) on the 22nd of January. The name of this lecture is unknown. The page of a manuscript preserved in the DM "Praktische Flugversuche - Eine Anleitung zur Entwicklung des freien Fluges" (Practical Attempts to Fly - An Instruction for Developing Free Flight) possibly belongs to this report.

"Über die Geheimnisse des Vogelflugs" (About the Mystery of Bird Flight)

The lecture in front of the "Polytechnische Gesellschaft" (Polytechnic Society) on the 15th of November was printed in the magazine "Polytechnisches Zentrallblatt" Nr.56, page 59. The manuscript is also preserved at the DM.

In a popular lecture, Lilienthal talks about the ancient dream of human flight, contemporary flight toys and the studies of bird flight. He shows his flying devices and compares the problem of flight stability to learning to ride a unicycle. He gives a precise account of the flights he did in Rhinow during one year: approximately 1,100; each for more than 800 feet; losing 100 feet of height.
"In conclusion I want to ask you not to take my achievements for more than they are. In the photographic pictures, you can see me flying high above in the sky. One can get the impression that the problem is already solved. That is not at all the case. I have to admit that it will still take quite a lot of work to turn this simple gliding into a long distance human flight. The achievements so far are for human flight, nothing more than what the first insecure steps of a child mean to walking of men."

Lilienthal gave a very similar lecture to the Society of Architects Berlin, November 1894:
"Über die Grundlagen der Flugtechnik"
(About the Basics of Flight Technique)

published in "Deutsche Bauzeitung", Nr.28, page 566 and in "Berliner-Börsen-Zeitung", November, 7., manuscript preserved (DM)

With concise words he describes the three problems of flying: take-off, stability, landing (because of the necessary fast decrease in speed). The problem is the following: "that you can only learn to fly by practising, but you can only practise flying without breaking your neck if you understand flying!
That's why the problem of flying is still not solved." From this fact, he develops his own flight program: "Flying means: to take off with a flying machine. That we cannot do! Flying means further: to move through the air from one mountain top to another similar in height. That we cannot do either! But flying means as well to let oneself down through the air from the top of a hill to a valley. And that we can do. ... It is advisable to choose the simplest devices possible and renounce every motion mechanism. This will lead to ridge soaring for movement through the air which we must start in our practical attempts."

Preserved in the DM is a manuscript "Der Segelflug" (Soaring Flight) that adopts examples from the aforementioned lectures. The manuscript deals with the theoretical basis and existing theories of soaring flight. The manuscript seems to be intended for publishing but appears incomplete.

"Weshalb ist es so schwierig, das Fliegen zu erfinden?"
(Why is artificial flight so difficult?)

Prometheus 261, page 7,
published in "Aeronautics" (American Engineer and Railroad Journal) 68/12, page 575

In a short announcement Lilienthal reports on
"Maxims Flugmaschine" ("Maxim's Flying Machine")

ZfL 13, page 272

 

1895
"Das Flugproblem" (The Problem of Flying)

in "Naturwissenschaftliche-Technisch-Soziale Korrespondenz"
("Scientific-Technological-Social Correspondence")
The manuscript is preserved.(DM)

In the following articles technical and cultural visions play a large role. The Lilienthal brothers' great commitment is shown clearly in the reform movement in Germany around the turn of the century.
"Yes, If there were already money to be earned in flying, some would lose their indifference to the mystery of flight. But the greatest driving force behind technical progress, speculation, is not yet able to get things moving."
Lilienthal compares human flight with the rapidly developing electricity technology: "Like vultures swooping down upon the carcass, … the after-inventors and exploitative industrialists rush to the great ingenious thoughts."

Another obviously incomplete lecture manuscript is known as:
"Über den Fortschritt in der Flugtechnik"
(About the Progress in Flight Technique).

Through mention of the drafts of the airship men Andreè and Wölfert that were presented at the trade exhibition in Berlin it is known that the manuscript was written in 1895.
"What cultural progress could be achieved if we could use the free atmosphere for air travel, where no mountains, no woods, no water, no marsh obstruct our movements. You probably have imagined before that borders would lose their relevance completely, because one cannot barricade them in the sky. One can hardly imagine that customs duties and wars could still be possible. The immense progress of world traffic between peoples would make it necessary that the languages mix to a universal one. But it should not be my task to talk about the enormous upheaval in all spheres and to give you an outlook on the future in a way of enthusiasm. We rather want to see today's standard of flight technique in a sober light." An analysis of current interest in balloon technology and of bird flight research follows. The manuscript ends before it comes to the topic of the title.

"Der Kunstflug" (Aerobatics)

Chapter 9 in "Modebecks Taschenbuch für Flugtechniker und Luftschiffer", Berlin, 1895
(English edition: "Pocket - Book of Aeronautics, in Collaboration with O. Chanute and Others", London, 1907

In the first part, Lilienthal defines what he called aerobatics: "Artificial flight may be defined as that form of aviation in which a man flies at will in any direction, by means of an apparatus, attached to his body, the use of which requires personal skill. Artificial flight by a single individual is the proper beginning for all species of artificial flight. ... The maintenance of equilibrium in forward flight is a matter of practice, and can only be learned by repeated personal experiment."
The following report deals with wing profiles and gives instructions for personal aerobatics in which Lilienthal presents his exercises as a universally applicable training program.

"Unsere Lehrmeister im Schwebeflug" (Our Teachers in Soaring Flight)

"Prometheus" Nr.316, page 55
published in "The Aeronautical Annual", 1897, page 85
another handwritten translation by O. Chanute "Our Masters in Soaring" is preserved in the archives of the University of Chicago.

 

The article is an evaluation of a trip to study the stork-village Vehlin (Brandenburg), where Lilienthal counted 40 houses and 54 stork nests. Accompanied by the photographer Dr. Fülleborn Lilienthal wants to study the dynamic gliding of storks. Recently several pictures of this trip were donated to the museum from Lilienthal's estate.

"Fliegesport und Fliegepraxis" (Flying - Sports and Experience)

"Prometheus" Nr. 322, page 145, 169 and 323
Published with slight revisions in "Aeronautical Annual", Boston, 1896 as "Practical Experiments for the Development of Human Flight". The handwritten German manuscript of this article is displayed in the National Air and Space Museum in Washington.
English translation of the original text:

The treatise is a popular account of the chapter "Aerobatics". Lilienthal's next development would be the establishment of soaring as a sport, which actually occurred in the 1920's. "It depends on finding methods to ensure safe attempts to fly and at the same time, be interesting entertainment for people keen on sports. … Indescribable is the attraction that flight guarantees. Healthier fresh air and exercise as well as a more stimulating sport is unimaginable.
The competitive drive during these exercises must lead to continuous improvement of the flying machines like we experienced with bicycles." Lilienthal mentions his own experiences that led to a constant improvement of his gliders. "My experiments basically go in two directions. On one hand I am trying to extend my successes in gliding through the air with fixed wing devices as I learn to use stronger wind to achieve long-lasting flight. On the other hand I am trying to be successful in dynamic flight with the help of flapping wings, which are simply added to my gliders. I am not able to present final results because the necessary equipment still needs improvement."
Lilienthal now has complete command of wind up to 7 m/s. "Nevertheless I came to the conviction that ... something must be done to perfect control and easy use of the flying machines." Lilienthal has what he considers a surprising success with the transition to biplanes. He can ascend without running from the launching point with a wind velocity of 10 m/s (36 km/h). "At the highest point of such an flight path, the glider occasionally comes to a standstill, so that I can discuss with the gentlemen who would like to take a picture of me about the right position for the photograph."
With regard to Langley's work ("The Internal Work of the Wind") he describes almost prophetically future soaring flight: "My effort…turns to… following and circling in the strong lifting breeze."
Finally, he makes an appeal to enlarge his "flight-hill" with private money: "Both the state in Moscow and private people in Boston are interested in establishing an institution for private flight testing on a large scale. It would be a pity if something like that can't be done in our fatherland because of a lack of entrepreneurial spirit."

"Die Profile der Segelflächen und ihre Wirkung"
(The Profiles of Soaring Airfoils and their Effect)

ZfL Nr.14/2,3; page 42
An extract was published as "At Rhinow" in "The Aeronautical Annual" 1897, page 92

Lilienthal sums up the results of his experiments of wing profiles (airfoils) and some new findings: "Nature seems to attach great importance to a smooth upper surface, at least you can see that clearly in the shape of the remige (flight feathers) that are always totally smooth. … From this one can conclude that the suction effect above the wings is of more importance than the pressure effect of the air on the underside of the wing."

"Über die Ermittlung der besten Flügelform"
(About the Determination of Best Shape of Wings)

in ZfL Nr.14/10, page 237
published as "La découverte des meilleures formes d' ailes" in "L'Aéronaute" 29/1 (1896), page 5
and as "K woprosu o mechanitschekoi letanii" translated from French into Russian with an obituary in "Inshenernyi shurnal" Nr.40 (Okt.1896), page 122
An extract was published as "The Best Shape of Wings" in "The Aeronautical Annual", 1897, page 95. The extract is about planned model experiments that are called "Lilienthal's Unfinished Work".

"That the feather-made structure of a wing gives special advantages to it that improves the lifting force, is already assumed but not yet proved. … That is why it is doubtful that we are doing something wrong when we stick to the easier, more practical construction of the bat wing when building flying machines."
Lilienthal refers to new bird research and to the usefulness of a thickening of the profile at the leading edge. The work on the wing profile is more important than the engine. For his further work, he sees two directions: the better control of the wing and the driving device. "The time-consuming improvements … of the machine equipment didn't lead me to specific results. On the other hand I was on better terms with the wind last summer..."
As an addition to the article "Flying - Sport and Experience," Lilienthal mentions his experimental apparatus from 1895 (wing warping, air resistance winglets, pre wing flap): "I am rejecting methods that should, through arbitrary changes in the form of the wings, increase the stability of flight, because other principles surprisingly have shown more promising results.": the biplane.
For optimising wing profiles (airfoils), he describes a program with models that is superior in accuracy when compared with well-known measuring methods: "I make these profiles out of stiff drawing paper, approximately 10 cm wide and 50 cm long." These should be launched from a high point in calm weather. By averaging the results of several measurements of the flight times the best profile should be determined.

1896
"Praktische Flugversuche" (Practical Attempts to Fly)

Lecture at the "Trade Exhibition" in Berlin on the 16th of June where Lilienthal displayed the products of his steam engine factory. It is the last known lecture before his crash.

"Moderne Raubritter" (modern robber barons)

screenplay for the "Ostendtheater. Lilienthal was a co-owner of this "peoples theatre".

In the years between 1890 and 1895, Lilienthal wrote several book reviews, articles, and reports for the ZfL and for the popular "Prometheus". Articles signed with "L." and "O.L." are ascribed to Lilienthal as well.

Between 1878 and 1895, he obtained several patents in different countries, including four with "flying machine" as the subject.