Conceptual design of windplanes
Conceptual design of windplanes (pdf)
4.11.5 Optimal airfoils
Airfoils used in airborne wind energy are designed to maximize the metric CL³ / CD²
(Bauer et al. (2018); Thedens et al. (2019); Tucker (2020); De Fezza and Barber (2022); Ran
griz and Kheiri (2023); Porta Ko et al. (2023) among others) and thus to be operated at
high lift coefficients.
About Bauer et al. (2018):
Just before (also page 291):
[…] which falsely suggests that a maximization of the glide ratio of the main wing’s airfoil maximizes the power while the actual value of CL has little influence.
Florian Bauer’s perspective tends to favor a high lift coefficient (CL), even though the CL/CD ratio is relatively lower than that of a conventional rigid wing, such as the one envisioned by Filippo Trevisi, whose approach aligns with more standard perspective in 4.11.5:
This metric points to multi-elements airfoils to achieve high lift coefficients, close to stall. These airfoils are complex to be designed, manufactured and operated. Using this metric is a consequence of optimizing the design per wing area and not per wingspan.
If we design the system per wingspan and consider the optimal aspect ratio, we find
that the airfoils which maximize the aerodynamic efficiency CL / Cd are required.
See also 4.1, where a high value of CL (CL/CD)², so CL³ / CD², is achieved with also a high CL and a low CL/CD:
See also the discussion on High lift coefficient and biplane kite - Engineering / Blade design - AWESystems Forum