Aerodynamics and Design for Ultra-Low Reynolds Number Flight

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Chapter 6
FIGURE 6.46 Blade planforms obtained by applying the rapid design tool with two different wake
models in conjunction with the angular momentum swirl correction.
The design using the Prandtl tip loss correction has already been described in the
previous section on viscous swirl model effects. As noted earlier, a primary issue with
this wake model is an increased risk of tip stall. The primary observed benefit of the
contracted ring wake model is an increase in tip loading relative to the predicted loading
using the Prandtl tip loss correction. For the design of rotors, this results in a reduction
in the tip incidence angle and consequently a reduction in the risk of tip stall. The two-
step method works around the planform issues of a pure contracted ring design, but still
benefits from the change in tip loading. The reduction in incidence is clearly visible in
Figure 6.47.
Contracted Ring
Two-Step Method
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