- All flight is based upon producing air pressure, all flight energy consists in overcoming air pressure.
- Der Vogelflug als Grundlage der Fliegekunst (1889); English edition: Birdflight As The Basis of Aviation (1911)
- I, too, have made it a lifelong task of mine to add a cultural element to my work, which should result in uniting countries and reconciling their people. Our experience of today's civilisation suffers from the fact that it only happens on the surface of the earth. We have invented barricades between our countries, custom regulations and constraints and complicated traffic laws and these are only possible because we are not in control of the 'kingdom of the air', and not as 'free as a bird'.
Numerous technicians in every state are doing their utmost to achieve the dream of free, unlimited flight and it is precisely here where changes can be made which would have a radical effect on our whole way of life. The borders between countries would lose their significance, because they could not be closed off from each other. Linguistic differences would disappear, as human mobility increased. National defence would cease to devour the best resources of nations as it would become impossible in itself. And the necessity of resolving disagreements among nations in some other way than by bloody battles would, in its turn, lead us to eternal peace.
We are getting closer to this goal. When we will reach it, I do not know.
- Letter to Moritz von Egidy (c. January 1894) - Original German text online
The Romance of Aeronautics (1912)
- Quotations of Lilienthal from The Romance of Aeronautics: An Interesting Account of the Growth & Achievements of All Kinds of Aerial Craft (1912) by Charles Cyril Turner, Ch. VII Lilienthal and Pilcher
- 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, as the necessary conditions can most easily be fulfilled when man flies individually.
- Variant translation: 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 the dexterity of the user.
- The increasing size of the apparatus makes the construction more difficult in securing lightness in the machine; therefore the building of small apparatus is to be recommended.
- The difficulty of rising into the air increases rapidly with the size of the apparatus. The uplifting of a single person, therefore, is more easily attained than that of a large flying machine loaded with several persons.
- Gradual development of flight should begin with the simplest apparatus and movements, and without time complication of dynamic means.
- The sailing flight of birds is the only form of flight which is carried on for some length of time without the expenditure of power.
- The contrivances which are necessary to counteract the wind effects can only be understood by actual practice in the wind.
- The supporting powers of time air and of the wind depend on the shape of the surfaces used, and the best forms can only be evolved by free flight through the air.
- The maintenance of equilibrium in forward flight is a matter of practice, and can only be learned by repeated personal experiment.
- Experience alone can teach us the best forms of construction for sailing apparatus in order that they may be of sufficient strength, very light, and most easily managed.
- By practice and experience a man can (if the wind be of the right strength) imitate the complete sailing flight of birds by availing himself of the slight upward trend of some winds, by performing circling sweeps, and by allowing the air to carry him.
- Actual practice in individual flight presents the best prospects for developing our capacity until it leads to perfected free flight.
Quotes about Lilienthal
- Particular honour belongs to those who believed in the possibility of mechanical flight when all the world was against them; not the visionaries because they hoped for it merely, but those who by sheer force of intellect perceived the means by which it could be accomplished and directed their experiments along the right path. ... The name of Lilienthal is now among the most honoured, but curiously his own countrymen were the last to recognize the value of his work.
- Charles Cyril Turner in The Romance of Aeronautics: An Interesting Account of the Growth & Achievements of All Kinds of Aerial Craft (1912), Ch. VII, Lilienthal and Pilcher
- Of all the men who attacked the flying problem in the 19th century, Otto Lilienthal was easily the most important. ... It is true that attempts at gliding had been made hundreds of years before him, and that in the nineteenth century, Cayley, Spencer, Wenham, Mouillard, and many others were reported to have made feeble attempts to glide, but their failures were so complete that nothing of value resulted.
- Wilbur Wright in Aero Club of America Bulletin (September 1912)