The overall goal of this project was to produce an adaptively flexible fixed pitch propeller using polymer composites. Polymer composites are generally used for their high weight to strength ratio, however they can also be utilized for functional applications with their bend-twist properties. Two models were investigated which included a full scale propeller as well as a ‘hydrowing’, which both were used for validating the FEA method. Internal goals of the project included determining properties that affect propeller behavior, model a propeller with the main desired property of untwisting (or negative twist), fabricate and prove practicality of a manufacturing method for the polymer composite propeller and hydrowing and confirm the FEA methods used through experimentation.
Simplified FEA modelling techniques were implemented and used to determine the effects of local stiffness changes in both models. This was used to develop carbon fiber layup designs for both the propeller and the hydrowing which gave the desired untwisting behavior in the propeller. FEA simulations of the final design for the propeller produced a maximum twist of -1.45 degree in the angle of attack of the propeller blade at full loading. A reproducible manufacturing method was chosen to successfully build both the propeller and the hydrowing. Geometrical accuracy of the fabricated propeller and the hydrowing was respectively within +1.45mm and +1.85mm at the largest deviating points while the majority was within +0.5mm.
Static load testing of the propeller gave results showing an average relative experimental error of 8.9% in load caused displacement while error in strain was 7.48% compared to FEA results. Static load testing of the hydrowing resulted in a 33.8% error compared to FEA results in load created displacement. The results from the propeller, although not perfect, were quite good and give confidence to trust the FEA methods that were used. This also means that with confident the propeller which was produced will behave with the designed amount of twist as stated earlier. The hydrowing had quite high error in results, however a closer look shows opportunities where potential fabrication or experimental mistakes were made, which if were corrected in future work could produce a much more accurate hydrowing blade.