PREFACE
This text is a basic introduction to classical propeller theory. It offers the reader an intuitive grasp of the most important concepts. This allows sensible preliminary designs, well informed sanity checks on existing design proposals, and parameter studies from very basic data.
No prior knowledge is assumed except for high school physics, including a basic understanding of Newton's law and the concept of kinetic energy.
Historically, there seems to be a fresh attempt at writing an introductory text to propeller theory every few decades. The list of references gives the classical examples from the 1930's onward, through the 1950's and into the 1980's. They all cover the same basic ground as Glauert's 1935 classic synthesis in Durand, and the present text is no exception. However, there are two significant modernizations :
- a novel, exact viscous optimization.
- and a solid, simple lifting line code.
This text takes Glauert's optimization of the viscous drag to its logical conclusion. I believe this material is new.
This optimization by itself gives only a very minor increase in the efficiency of the propeller. But it is not just about dotting the i's in the theory. Somewhat unexpectedly, the viscous optimization gives a very noticeable modification to the blade shape, which may have some useful side benefits.
The viscous derivation also helps to get a better intuition of the balance between viscous and momentum loss, and on the optimal value for the tip speed ratio.
The text gives an exact, yet extremely simple lifting line code based on Lerbs's 1952 version of Goldstein's exact vortex solution. With laptops on every desk, this code is both easier and more exact than Prandtl's classical approximation for the tip loss. Prandtl's model is still discussed in some detail however, because it gives a useful intuitive understanding of the tip loss.
A running example for a typical lightplane serves as a guide for the order of magnitude of various effects.
The Propeller Theory text on this website was originally written as a small book which was never published.
I retained the preface to the book version, since it captures the orginal intention quite well.
-- P. Lammertse, 2025 --