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Propeller Pitch Distribution For Control Line Models


This is a help file for the computer program  WProp.exe . A program that can be executed on Windows95®, Windows98®, or Windows NT® (including Windows 2000).

The program was designed to provide a pitch distribution for racing or speed event control line aircraft. The primary features of this kind of model in flight are extended periods of flight at constant engine and airspeed, moderately low disc loading, and propeller rotational speeds that can produce Mach numbers in the transonic regime.

These characteristics lend themselves to a kind of analysis that is somewhat less complex than the general combined vortex and blade element theory solutions. In addition, estimates of propeller torque, thrust, and other characteristics are much less relevant than the pitch distribution. Propellers are often trimmed in diameter to let the engine run at the best speed and the general size of propeller is known. The best pitch distribution, however, is not accurately known. In particular the effect of Mach number is significant and is seldom accounted for or understood.

This program provides my estimate of a good pitch distribution. Although it ignores some second-order effects of inflow it is easier to use than the more general approach. The answers it provides are not far from those generated by a more complicated vortex + blade element program I have written.

This program and its associated files are free. It is intended that they be freely distributed by any one. The program and associated documents have been copyright in order to provide some protection against them being sold. The copyright details are found on the Copyright page. This set of HTML pages is to support the use of the program. More information on propellers in general, the effect of Mach Number, and other related topics from a model aircraft perspective may be found on my web site Microaeronautics under Aero Notes.

The Install Run  section tells you how to install the program and this help file and see a test case while Error Messages describes the few messages that might appear and what to do about them.

The Input Format section explains how to enter input data describing your problem. The Output section provides a description of the output screen that can be printed r saved as a binary file. This output corresponds to the input data. It contains all the input data and output data in SI and English units a brief explanation of each entry. This help file includes unit conversion pages to help generating input.

Special emphasis is placed on the airfoil characteristics as they relate to the way model builders measure propeller pitch. There are references to these discussions in the above two sections and they are important to the understanding of the results this program produces. See that pages: Airfoil Data ,    Reynolds Number ,  and   Mach Number  

Calculations contains a brief description of how some of the principal calculations are made. The descriptions explain the assumptions and limitations of the output. Several other pages linked to this page provide details on Mach Number, Inflow, Propeller Motion, and Efficiency. For more information at an engineering level the References section provides a few texts, most of which are available in paperback, and points to two URL's that discuss related subjects. The information in the URL's do not completely agree with the information here.