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Old 08-23-2003 | 04:24 PM
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LouW
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From: Moreland, GA
Default Thrust Figures

For models, I believe you’ll fine the calculations are a dead end street.
As I’m sure you are aware, the formula for thrust is:

Thrust=Tc (density ratio) (velocity squared) (diameter squared)

Where Tc is the propeller coefficient. This term is empirically determined and requires considerable test data. It not only depends on the propeller but the shape of the body it is attached to. Unfortunately since power curves for model engines are not generally available (except for single points) nor are propeller characteristics readily found. A usable figure for Tc is just not possible.

Your best bet would be to contact the engineering department of a propeller manufacture and see if they have any test data they would be willing to share. Both APC propellers and Bolly props have done considerable testing in development of their lines although the approach of each is different. However I believe you will find that most of their work is in flight test rather than static thrust.

Any data you are able to acquire will only be applicable to the propellers tested. Attempts to extrapolate to propellers of other designs, or manufacturers are at best a wild guess.

Aerodynamics is an empirical discipline. Sprinkled through all the complicated formulas that make it seem like science, there are “coefficients” derived from test data that make them work. For full scale aircraft there is a very large body of such data that enables the designer to design with confidence, but us modelers are left pretty much to a cut and try approach.