Weight Characteristics of Measured Propellers

To estimate these torques one must know the engine speed and the moment of inertia of the propeller. While engine speeds are well known and accurate devices are available to measure speed, no moment of inertia data seems to have ever appeared in the literature. The measurements described below were made primarily in 1994 on a number of propellers. A large group of different propellers was assembled and weighed. From this group 21 propellers were chosen as representative of all diameters, shapes, and material in the larger group. A bifilar pendulum was constructed to measure the radius of gyration of each propeller.

The accuracy of each estimate was assessed as well as the error due to factors in the bifilar pendulum. From these measurements data were obtained that permit a fairly accurate estimate of gyro torques. This note presents the results of these measurements and discussed how the resulting data may be used to estimate gyro torques.

The first measurements were just geometry - number of blades, diameter, and some representative blade width -- and mass. Fifty propellers made of wood, plastic, glass filled plastic, and carbon fiber were measured. Some were new and some were old and out of production. The mass data are plotted in the figure below .

The graph below of weight and diameter for the tested propeller is in a mixed set of units. The propellers were weighed in grams but plotted against the marked diameter which was primarily in inch units. The different colors are for different types of material. For multi-blade propellers the weight has been changed to the weight for 2 blades. For example 2/3 of the weight of a 3 blade propeller is shown.

The next plot show how well the data are correlated on the basis of the scaling relationship for mass and dimension. See the discussion in the ScaleFactor article for details. The constant diameter cubed lines shows the characteristic density of the material from which the propellers were made.