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Abstract Some bird species fly inverted, or whiffle, to lose altitude. Inverted flight twists the primary flight feathers, creating gaps along the wing’s trailing edge and decreasing lift. It is speculated that feather rotation-inspired gaps could be used as control surfaces on uncrewed aerial vehicles (UAVs). When implemented on one semi-span of a UAV wing, the gaps produce roll due to the asymmetric lift distribution. However, the understanding of the fluid mechanics and actuation requirements of this novel gapped wing were rudimentary. Here, we use a commercial computational fluid dynamics solver to model a gapped wing, compare its analytically estimated work requirements to an aileron, and identify the impacts of key aerodynamic mechanisms. An experimental validation shows that the results agree well with previous findings. We also find that the gaps re-energize the boundary layer over the suction side of the trailing edge, delaying stall of the gapped wing. Further, the gaps produce vortices distributed along the wingspan. This vortex behavior creates a beneficial lift distribution that produces comparable roll and less yaw than the aileron. The gap vortices also inform the change in the control surface’s roll effectiveness across angle of attack. Finally, the flow within a gap recirculates and creates negative pressure coefficients on the majority of the gap face. The result is a suction force on the gap face that increases with angle of attack and requires work to hold the gaps open. Overall, the gapped wing requires higher actuation work than the aileron at low rolling moment coefficients. However, above rolling moment coefficients of 0.0182, the gapped wing requires less work and ultimately produces a higher maximum rolling moment coefficient. Despite the variable control effectiveness, the data suggest that the gapped wing could be a useful roll control surface for energy-constrained UAVs at high lift coefficients.
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Flight Dynamics of a Flying Wing Aircraft Featuring the Bell Spanload
Results of a previous aerodynamics study conducted over a wing that exhibits the Prandtl Bell Spanload were implemented into a simulation environment with the intent of studying unique flight characteristics that are theorized to be presented by this spanload. However, early simulations over the dynamics show that the yawing moment due to roll rate is of higher effect than the yaw moment due to aileron deflection angle. This over-prediction of the roll-yaw coupling term has been called into question. A new method is to be tested, which implements a compact vortex-lattice (CVLM) formulation, to show the difference between the flight dynamics predicted by this new method and the stability derivative method currently in use. The analysis utilizes two initial conditions to test the differences as the dynamics propagate through time. The first, a large initial bank angle, leads to the stabiltiy derivative method diverging while the CVLM results show this to not be the case. The second condition, a wind-field representative of a stable nocturnal boundary layer over the ground, leads to much more agreement between methods before divergence occurs due to a velocity higher than that of the stability derivative linearization point. It is then agreed that, since CVLM cannot predict stall effects and other nonlinear flight regions, a hybrid approach is proposed that takes advantage of the roll-yaw coupling prediction of the CVLM and the range of condition available to the stability derivative method.
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- Award ID(s):
- 1925147
- PAR ID:
- 10657821
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- ISBN:
- 978-1-62410-699-6
- Subject(s) / Keyword(s):
- Flight Dynamics Realistic Wind Field compact vortex-lattice
- Format(s):
- Medium: X
- Location:
- National Harbor, MD
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2023-2610
