(published posthumously in the Aero Club of America Bulletin, Sept. 1912, after Wilbur Wright died on May 30.)
By Wilbur Wright
Of all the men who attacked the flying problem in the 19th century, Otto Lilienthal was easily the most important. His greatness appeared in every phase of the problem. No one equaled him in power to draw new recruits to the cause; no one equaled him in fullness and dearness of understanding of the principles of flight; no one did so much to convince the world of the advantages of curved wing surfaces; and no one did so much to transfer the problem of human flight to the open air where it belonged.
As a missionary he was wonderful. He presented the cause of human flight to his readers so earnestly, so attractively, and so convincingly that it was difficult for anyone to resist the temptation to make an attempt at it himself, even though his sober judgment and the misfortunes of all predecessors warned him to avoid touching it. If Lilienthal had done nothing more than this he still would have been one of the greatest contributors to the final success. But he was much more than a mere missionary.
As a scientific investigator none of his contemporaries was his equal. He set forth the advantages of arched wings in such convincing manner as to make him the real originator of this feature. Others had noted that bird wings were arched, and had speculated on the possibility that an arched wing was superior to an absolutely true plane, but Lilienthal demonstrated the reason why it was better, and changed mere speculation into accepted knowledge. He also devoted an enormous amount of time and patience to experiments with test surfaces for the purpose of determining the best shapes for wings and for the amount of pressures to be obtained at the various angles of incidence. For nearly twenty years his tables and charts were the best to be found in print. His work in this line alone would have been sufficient to place Lilienthal in the front rank, yet there still remains to be mentioned his greatest contribution to the cause.
Lilienthal was the real founder of out-of-door experimenting. 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 othcrs were reported to have made feeble attempts to glide, but their failures were so complete that nothing of value resulted.
Lilienthal pursued the undertaking so persistently and intelligently that although his own death and that of Pilcher for a time caused a cessation of this mode of experiment, nevertheless his efforts constituted the greatest contribution to final success that had been made by any of the nineteenth century group of workers.
When the general excellence of the work of Lilienthal is considered, the question arises as to whether or not he would have solved the problem of human flight if his untimely death in 1896 had not interrupted his efforts. Many people believe that success was almost within his grasp. Others think that he had limitations which rendered such an outcome at least doubtful. One of the greatest difficulties of the problem has been little understood by the world at large. This was the fact that those who aspired to solve the problem were constantly pursued by expense, danger, and time. In order to succeed it was not only necessary to make progress, but it was necessary to make progress at a sufficient rate to reach the goal before money gave out, or before accident intervened, or before the portion of life allowable for such work was past. The problem was so vast and many sided that no one could hope to win unless he possessed unusual ability to grasp the essential points, and ignore the nonessentials. It was necessary to have a genius for solving almost innumerable difficult problems with a minimum expenditure of time, a minimum expenditure of money, and a minimum risk of accident.
A study of the failures of the nineteenth century shows clearly that none of the important workers stood still, but that the rate of progress was so slow that each one was overcome and removed from the race by one of the causes just mentioned before the goal was reached. If they had possessed the faculty of doing things more quickly, more simply, and less expensively, they might not have been overtaken by old age, lack of funds, or accident. Some were traveling at a rate which would have required fifty years or more to reach success. Others were spending money at a rate which would have necessitated an expenditure of millions of dollars in order to complete the task. When the detailed story is written of the means by which success in human flight was finally attained, it will be seen that this success was not won by spending more time than others had spent, nor by spending more money than others had spent, nor by taking greater risks than others had taken.
Those who failed for lack of time had already used more time than was necessary; those who failed for lack of money had already spent more money than was necessary; and those who were cut off by accident had previously enjoyed many lucky escapes as reasonably could be expected.
Lilienthal progressed, but not very rapidly. His tables of pressures and resistances of arched aeroplane surfaces were the results of years of experiment and were the best in existence, yet they were not sufficiently accurate to enable anyone to construct a machine with full assurance that it would give exactly the expected results. Under such conditions progress could not but be slow. His methods of controlling balance both laterally and longitudinally were exceedingly crude and quite insufficient. Although he experimented for six successive years 1891-1896 with gliding machines, he was using at the end the same inadequate method of control with which he started. His rate of progress during these years makes it doubtful whether he would have achieved full success in the near future if his life had been spared, but whatever his limitations may have been, he was without question the greatest of the precursors, and the world owes to him a great debt.