A prototype 250ram diameter, Electromagnetic Tip-Driven Propeller 0gTDP) unit has been designed, built and tested in a towing tank at zero advance and for a range of advance speeds. The aims have been to assess the performance, efficiency and general practicalities of such a propulsor for use on underwater vehicles. An overview is given of the design of the prototype, highlighting problems which were enccountered and methods used to overcome them. The testing procedure is also described and performance results presented.
The idea of driving a propeller via its blade tips is not new, but only a limited amount of work has been published on soch units. The work which has been covered mainly discusses mechanical drives rather than electrical, which offer additional sealing and gearing problems. It is probably due to these limitations that the idea has not been used in practical applications. Radojcic (1997), however, proposed some mechanical drives, some even with contra-rotating propellers, and explained that latest developments in material technology and motor design now mean that such drive methodss are viable alternatives, particularly in specialised applications such as underwater vehicles. The thrusters on an underwater vehicle are required to provide a flexible means of maneeuvring, and should be capable of a good response to inputs from the controller. It is also of benefit if the propulsors provide equal thrust in both forward and reverse directions. This illustrates a further area where a tip-driven propeller would be advantageous. The use of an electromagnetic drive aims to overcome some of the limitations associated with mechanical drives. With the absence of any physical contact between the drive system and the propulsor, the need for the extra sealing mechanism is eliminated.
