This was achieved with the invention of the dimensionless Reynolds number by Osborne Reynolds. Reynolds also experimented with laminar to turbulent flow transition in 1883. Working from at least as early as 1796, when he constructed a model helicopter, until his death in 1857, Sir George Cayley is credited as the first person to identify the four aerodynamic forces of flight—weight, lift, drag, and thrust—and the relationships between them. Cayley is also credited as the first person to develop the modern fixed-wing aircraft concept; although da Vinci's notes contain drawings and descriptions of a fixed-wing heavier-than-air flight machine, da Vinci's notes were disorganized and scattered following his death, and his aerodynamics achievements were not rediscovered until after technology had progressed well beyond da Vinci's advances. By the late 19th century, two problems were identified before heavier-than-air flight could be realized. The first was the creation of low-drag, high-lift aerodynamic wings. The second problem was how to determine the power needed for sustained flight. During this time, the groundwork was laid down for modern day fluid dynamics and aerodynamics, with other less scientifically-inclined enthusiasts testing various flying machines with little success. In 1884, John J. Montgomery, an American trained in physics, began experimenting with glider designs. Using a water table with circulating water and a smoke chamber he began applying the physics of fluid dynamics to describe the motions of flow over curved surfaces such as airfoils. In 1889, Charles Renard, a French aeronautical engineer, became the first person to reasonably predict the power needed for sustained flight. Renard and German physicist Hermann von Helmholtz explored the wing loading (weight to wing-area ratio) of birds, eventually concluding that humans could not fly under their own power by attaching wings onto their arms. Otto Lilienthal, following the work of Sir George Cayley, was the first person to become highly successful with glider flights. Lilienthal believed that thin, curved airfoils would produce high lift and low drag. Octave Chanute's 1893 book, "Progress in Flying Machines", outlined all of the known research conducted around the world up to that point. Chanute's book provided a great service to those interested in aerodynamics and flying machines. With the information contained in Chanute's book, the personal assistance of Chanute himself, and research carried out in their own wind tunnel, the Wright brothers gained enough knowledge of aerodynamics to fly the first powered aircraft on December 17, 1903.