The aerodynamic characteristics of water rockets are analyzed experimentally by wind tunnel testing. Aerodynamic devices such as vortex generators and dimples are tested and their effectiveness to the flight performance of water rocket is discussed. Attaching vortex generators suppresses the unsteady body fluttering. Dimpling the nose reduces the drag coefficient in high angles of attack. Robust design approach is applied to water rocket design for flight stability and optimum water rocket configuration is determined. Semi-sphere nose is found to be effective for flight stability and it is desirable for the safety of landing point. Stiffed fin attachment is required for fins to work properly as aerodynamic device and it enhances the flight stability of water rockets.
Axial-gap permanent magnet (PM) motors have an air gap in the axial direction and produce more torque than conventional radial-gap motors, especially with flat structures. However, eddy-current loss in the magnets cannot be disregarded since axial-gap PM motors generally have a surface permanent magnet (SPM) rotor and an open slot structure. Furthermore, the open slot structure causes large amounts of torque ripple. We report here a method for decreasing the eddy-current loss by mounting a soft magnetic composite (SMC) onto the magnets. We also propose a method for reducing the torque ripple by adjusting both the pole arc angle of the magnets and the spatial phase difference between the two rotors.
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