Welcome to the mysterious and arcane world of propellers. Most aviators dismiss the propeller as a merely adequate device that performs its given task. There is little interest in its function or efficacy. Glibly dismissing it as “a rotating wing,” they intuitively sense and avoid its complexity.
The curious, however, soon learn of the two most-often quoted numbers for a propeller, the “pitch” and the diameter. The mystery of how these two numbers miraculously define the operating characteristics of this marvelous device have driven this author to further investigation; how can the synergy of such an organic shape and its interaction with the air be synthesized and distilled into just two numbers to specify all its important characteristics and to declare the appropriate marriage of propeller to engine and airframe and operating conditions?
In fact, the answer is, they can’t. The answer is nowhere near that simple.
The propeller is at once both the most important and the least studied aerodynamic surface or device in aeronautics. Books abound that teach the finer points of aerodynamics and airplane design, yet their treatment of propellers is, at best, cursory. Few engineers have attempted to learn the nuances of propellers. Fewer still have undertaken to publish, and none have been comprehensive in their treatment of the topic.
The most recent publications in the field are dated. Weick’s Airplane Propeller Design was published in 1930; Theodorsen’s Theory of Propellers dates to 1948. The only important books published since have been in the marine propulsion industry. And NASA has been largely absent from the roles of researcher and cataloger that their predecessor, the N.A.C.A., seemed to be so good at.
The present work attempts to address the need for clear explanations that can foster fundamental understanding of what a propeller is, what it does, and how it works. The work is aimed squarely at the world light airplane design and manufacturing base, and the American homebuilt airplane community. If one can design an airplane, one ought, at the least, to understand the principles involved in the design or selection of that airplane’s propeller to the same extent that one might understand the longitudinal stability criteria used to select that airplane’s Center of Gravity location.