  Micro aerial vehicles are making a large impact in applications such as
search-and-rescue, package delivery, and recreation. Unfortunately, these
diminutive drones are currently constrained to carrying small payloads, in
large part because they use propellers optimized for larger aircraft and
inviscid flow regimes. Fully realizing the potential of emerging microflyers
requires next-generation propellers that are specifically designed for
low-Reynolds number conditions and that include new features advantageous in
highly viscous flows. One aspect that has received limited attention in the
literature is the addition of roughness to propeller blades as a method of
reducing drag and increasing thrust. To investigate this possibility, we used
large eddy simulation to conduct a numerical investigation of smooth and rough
propellers. Our results indicate that roughness produces a 2% increase in
thrust and a 5% decrease in power relative to a baseline smooth propeller
operating at the same Reynolds number of Rec = 6500, held constant by
rotational speed. We corroborated our numerical findings using
thrust-stand-based experiments of 3D-printed propellers identical to those of
the numerical simulations. Our study confirms that surface roughness is an
additional parameter within the design space for micro-propellers that will
lead to unprecedented drone efficiencies and payloads.
