Propellers represent an interesting application of the principles of aerodynamics. The basic physics of propeller operation can be modeled as a rotating wing section using classical blade element analysis procedure, which can also include flows induced by the propeller motion itself. Performance testing of small-scale powered propellers in modest size educational wind tunnels could yield important verification of these analysis tools, and also provide valuable experimental insight into important aspects of propeller design for the engineering laboratory. To provide useful data, measurements of propeller performance must include not only rotation speed and thrust, but also torque. These variables need to be investigated as a function of the imposed wind tunnel airspeed, which represents the forward speed of a powered propeller in flight. Rotation speed is easily measured using a variety of simple optical (including stroboscopic) techniques and thrust simply corresponds to the axial force measurement obtained directly from the typical “sting” balance used with educational wind tunnels. However, commercial devices for practical torque measurement can be quite expensive and are also typically of much higher torque range than that achieved by small-scale propellers designed for model airplane use, which limits their usefulness in the educational engineering wind tunnel laboratory. This paper presents a simple and inexpensive strain gage based device designed for measurement of low level torque developed by small-scale powered propellers. The operating principles of the torque measurement device are described, along with static calibration test results and experimental measurements of the performance characteristics of a small-scale electric motor driven powered propeller using our educational wind tunnel test facility. The torque sensor can be combined with rapid prototyping propeller design to allow investigation of a wide variety of propeller design features. Additional planned improvements and other wind tunnel applications for the torque measurement device are also discussed in the paper.

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