Correlating Propeller Performance with Kt/Kq Multipliers

A HydroComp Technical Report
Report 101

Product link: NavCad, SwiftCraft, PropExpert

The AU and M-AU (modified AU) propellers are a series of aerofoil blade section propellers popular in Japan and the Far East. The basic geometry of the series is quite similar to the Wageningen B-Series developed at NSMB.

Unlike the B-series, the thrust and torque performance has never been developed into polynomial expressions for the calculation of Kt and Kq. It is possible to adequately predict the performance of the AU/M-AU series through the use of Kt and Kq multipliers. Kt and Kq multipliers shift the predicted curves for the chosen series (B-series in this case), to make them closer to what is expected from the actual propeller (AU/M-AU). HydroComp has identified that to predict AU/M-AU series performance:

    • Series: B-series
    • Kt multiplier: 1.07
    • Kq multiplier: 1.07
    • Use suitable scale corrections and options as for the B-series

A plot of actual AU/M-AU performance compared to multiplier-corrected B-series performance is shown below. This was performed at model scale for a 5-bladed propeller with 0.80 expanded area ratio and pitch/diameter ratio of 0.80. The multiplier was chosen to minimize the error in the range of the maximum efficiency. The calculation tended to overpredict (less than 4%) below the point of maximum efficiency, and underpredict above.