Aerodynamics and Design for Ultra-Low Reynolds Number Flight

FIGURE 6.10 Carbon-fiber two-blade rotors, inch scale.
6.4 Comparison of Total Thrust and Power
6.4.1 Two-Blade Ten Inch Diameter Rotor
Chapter 6
Global metrics, the total rotor thrust and power required, are both the principal points of
interest in design and the simplest to obtain experimentally. Whether or not they form a
concrete and comprehensive measure of accuracy will be a topic of later discussion. The
first comparison of analysis and experiment is for the ten inch two-blade rotor. The
larger scale greatly increases the confidence in the as-built geometry and the lower
rotational speeds, typically around 2000 RPM, diminish the likelihood of structural
deflection. The measured forces and torques increase by a factor of ten, reducing the
effect of approximately constant magnitude measurement errors.
Close agreement is obtained in both thrust and rotor power required for this design. The
maximum difference in thrust is approximately 10% at the highest tested RPM,
corresponding to a less than 5% difference in power required. One point of note to be
expanded on later is the indication of stalled tips when analyzed with the contracting
wake model. The rotor was designed with the Prandtl tip loss model and at that point
had no indication of stall. The thrust comparison for three rotor samples and the rapid
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