ROLES OF SCIENCE AND ENGINEERING IN NINETEENTH-CENTURY AERODYNAMICS

To understand the relationship of science and engineering to aerodynamics in the twentieth-century, we need to examine briefly the completely different relationship that existed during the nineteenth-century.

The history of aerodynamics before the twentieth-century is buried in the history of the more general discipline of fluid dynamics. Consistent with the evolution of classical physics, the basic aspects of the science of fluid dynamics were reasonably well understood by 1890. Meaningful experiments in fluid dynamics started with Edme Mariotte and Christiaan Huygens, both members of the Paris Academy of Science, who independently demonstrated by 1690 the important result that the force on a body moving through a fluid varies as the square of the velocity. The relationship between pressure and velocity in a moving fluid was studied experimentally by Henri Pitot, a French civil engineer in the 1730’s. Later in the eighteenth-century, the experimental tradition in fluid dynamics was extended by John Smeaton and Benjamin Robins in England, using whirling arms as test facilities. Finally, by the end of the nineteenth-century, the basic understanding of the effects of friction on fluid flows was greatly enhanced by the experiments of Osborne Reynolds at Manchester. These are just some examples. In parallel, the rational theoretical study of fluid mechanics began with Isaac Newton’s Principia in 1687. By 1755 Leonhard Euler had developed the partial differential equations describing the flow of a frictionless fluid – the well-known “Euler Equations” which are used extensively in modern aerodynamics. The theoretical basis of fluid mechanics was further enhanced by the vortex concepts of Hermann Von Helmholtz in Germany during the mid-nineteenth-century. Finally, the partial differential equations for the flow of a fluid with friction – the more realistic case – were developed independently by the frenchman Henri Navier in 1822 and the englishman George Stokes in 1845. These equations, called the Navier-Stokes equations, are the most fundamental basis for the theoretical study of fluid dynamics. They were well-established more than 150 years ago.

Thus, by the end of the nineteenth-century, the basic principles underlying classical fluid dynamics were well established. The progress in this discipline culminated in a complete formulation and understanding of the detailed equations of motion for a viscous fluid flow (the Navier-Stokes equations), as well as the beginnings of a quantitative, experimental data base on basic fluid phenomena, including the transition from laminar to turbulent flow. In essence, fluid dynamics was in step with the rest of classical physics at the end of the nineteenth-century – a science that was perceived at that time as being well-known, somewhat mature, with nothing more to be learned. Also, it is important to note that this science was predominately developed (at least in the nineteenth-century) by scholars who were university educated, and who were mainly part of the academic community.

The transfer of this state-of-the-art in fluid dynamics to the investigation of powered flight was, on the other hand, virtually non-existent. The idea of powered flight was considered fanciful by the established scientific community – an idea that was not appropriate for serious intellectual pursuits. Even Lord Rayleigh, who came closer than any of the scientific giants of the nineteenth-century to showing interest in powered flight, contributed nothing tangible to applied aerodynamics. This situation can not be more emphatically stated than appears in the following paragraph from the Fifth Annual Report of the Aeronautical Society of Great Britain in 1870:

“Now let us consider the nature of the mud in which I have said we are stuck. The cause of our standstill, briefly stated, seems to be this: men do not consider the subject of ‘aerostation’ or ‘avia­tion’ to be a real science, but bring forward wild, impracticable, unmechanical, and unmathematical schemes, wasting the time of the Society, and causing us to be looked upon as a laughing stock by an incredulous and skeptical public.”

Clearly, there was a “technology transfer problem” in regard to the science of fluid dynamics applied to powered flight. For this reason, applied aerodynamics in the nineteenth-century followed its own, somewhat independent path. It was developed by a group of self-educated (but generally we//-educated) enthusiasts, driven by the vision of flying machines. These people, most of whom had no formal education at the university level, represented the early beginnings of the profession of aeronautical engineering.

For example, this community of self-educated engineers was typified by the following: George Cayley, who in 1799 enunciated the basic concept of the modem configuration airplane; Francis Wenham, who in 1871 built the first wind tunnel; Horatio Phillips, who in 1884 built the second wind tunnel and used it to test cambered (curved) airfoil shapes which he later patented; Otto Lilienthal (who did have a bachelors degree in Mechanical Engineering), who carried out the first meaningful, systematic series of experimental measurements of the aerodynamic properties of cambered airfoils,4 and later designed and flew extensively the first successful human-carrying gliders (1892 – 1896); and Samuel Langley, 3rd Secretary of the Smithsonian Institution, who carried out an exhaustive series of well-planned and well-executed aerodynamic experiments on rectangular, flat plates,5 but who had two spectacular failures in 1903 when a piloted flying machine of his design crashed in the Potomac river.

Langley clearly stated the prevailing attitude in his Memoir published posthumously in 1911.6

“The whole subject of mechanical flight was so far from having attracted the general attention of physicists or engineers, that it was generally considered to be a field fitted rather for the pursuits of the charlatan than for those of the man of science. Consequently, he who was bold enough to enter it, found almost none of those experimental data which are ready to hand in every recognized and reputable field of scientific labor.”

Langley considered himself one of the bold ones. This is particularly relevant because in the United States at the end of the nineteenth century the position of Secretary of the Smithsonian was considered by many as the most prestigious scientific position in the country. Here we have, by definition, Langley as the most prestigious scientist in the United States, and he is turning the tables on the scientific community by devoting himself to the quest for powered flight.

However, the prevailing attitude abruptly changed in the space of ten years, beginning in 1894.