Aerodynamics and Design for Ultra-Low Reynolds Number Flight

At hover, with a mass of 153g, the entire system consumes ten Watts of power. The
Chapter 7
predicted and experimental results indicate 1.3 Watts of power required per rotor at this
thrust level indicating a total electro-mechanical efficiency of roughly 52%. This is a
tremendous increase over the performance of the 15g prototype and once again
demonstrates a key issue with developing electrically powered micro-rotorcraft: the
rapid degradation of electro-mechanical efficiencies at reduced physical scales.
7.5 Insights Gained, Limiting Technologies, and the
Potential for Future Development
With the goal of self-powered autonomous micro rotorcraft, the three prototypes span the
design space from 15g (considered infeasible with current technology), up to 65g (that
with further design refinement would represent the state-of the-art), finally increasing to
150g. The largest is a design that poses challenges in system integration and automated
flight control, but otherwise represents what can be accomplished with current consumer
level technology and hardware.
Experience with these three prototypes indicates that the cost of reduced scale on the
overall power requirements is severe. A summary of key sizing parameters and hover
power requirements for these rotorcraft is provided in Table 7.4. The data without
battery mass is included to indicate the lower bound on hover power required.
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