Aerodynamics and Design for Ultra-Low Reynolds Number Flight

Chapter 6
method with the contracted ring wake and angular momentum swirl model have been
used as a common method of comparison.
The resulting chord and incidence distributions are provided in Figures 6.42 and 6.43.
The largest differences are seen in the inboard half of each blade. The average wake
deficit case is identical to the as-built and tested four-blade 2.5cm diameter rotor. The
other two viscous swirl models predict much lower viscous swirl velocities and reduce
any penalty associated with blockage due to high local solidity, this permits and makes
desirable an increase in chord closer to the hub. With the reduced blockage and solidity
penalty, the optimizer increases the total lifting area and increases the Reynolds number
at the inboard stations, lowering the section drag coefficient.
140
x/R
0.4
0.2
0.0
-0.2
Gaussian Wake
Avg. Wake Deficit
Angular Momentum
-0.4
0.0 0.2 0.4 0.6 0.8 1.0
r/R
FIGURE 6.42 Blade planforms obtained by applying the rapid design tool with three different
viscous swirl models in conjunction with the classical Prandtl tip loss correction.