Aerodynamic Theories

Several theories on propeller aerodynamics have been put forward by different authors. The theories include the vortex, general momentum, axial momentum and the blade element theory. The blade element is the most widely accepted theory, along with parts of the axial momentum theory, leaving the vortex and general momentum theories to fall by the wayside.

In 1865, the Scottish engineer and scientist William George Rankine (1820-1872) founded the axial momentum theory while working on the theory of ship’s propellers. At a later date further work and development on the axial momentum theory, was covered by Robert Edmund Froude (1846­1924) also an engineer. The blade element theory was first introduced by William Froude (1810-1879) the father of R. E. Froude, an engineer and naval architect in 1878, when he also was working on ship’s propeller theories. Note the theory of ship and aircraft propellers is virtually the same, because air at subsonic speed behaves very similar to flowing water.

Stefan Drzeweicke (1844-1938) further developed the blade element theory from 1892 onwards and he has been credited with the majority of the research work. The axial momentum theory, also known as the Rankine-Froude theory after its two authors, deals with the energy change given to the air mass after it passes through the propeller disc. It also includes the effect of the rotational propwash, the friction drag of the propeller blades and the loss of energy in the propwash caused by the interference of the engine nacelle or the fuselage, amongst other factors The blade element theory deals with the forces acting on the propeller as it moves through the air at a uniform velocity. It also includes the blade’s shape and number of blades and assumes the propeller blade to be made from an infinite number of blade elements, hence the name blade element theory. Theodore Theodorsen (1897-1978) of NACA also performed aircraft propeller research, circa 1930s. The diagrams in this book represent the blade element theory

After the Wright brothers’ initial success, further testing and advances in prop design by other engineers led to the first generation of propellers. Lucian Chauviere (1876-1966), a French aeronautical engineer, is noted for introducing his Integrale aircraft propellers of advanced design, (he introduced the laminated propeller mentioned above) the forerunner of all propellers to follow. Louise Bleriot (1872-1936) had a Chauviere propeller mounted on his Bleriot XI monoplane for his cross-channel flight in 1909. During the First World War, Chauviere’s company produced about 25% of the propellers manufactured for allied aircraft.