Covert-inspired Flaps for Flight Control
Engineering Challenges
Wind energy harvesting has become an essential sustainable alternative to fossil fuels, addressing issues related to climate change. Unlike terrestrial wind farms, airborne wind energy harvesting (AWEH) systems employ tethered kites at high altitudes to exploit stronger wind currents. These AWEH kites offer substantial benefits in terms of weight and infrastructure. However, their light and flexible nature presents difficulties in aerodynamic modeling and control surface design. This project investigates the feasibility of using bio-inspired coverts as flight control devices during both static and dynamic flight maneuvers and applies these bioinspired flaps to an actual energy-harvesting kite. Throughout this process, we utilize various tools to understand the physics and model the aerodynamics, including wind tunnel testing, particle image velocimetry, flight testing, and system identification.
a) Artist impression of Toyota’s Mothership kite performing multiple functions while harvesting wind energy b) Scaled-down proof of concept kite fitted with covert-inspired flaps for flight control
Nature's Inspiration
Birds are known for their ability to perform high Angle of Attack maneuvers. They can take off, land and perch using the same wing platform. Birds usually use large-scale deflections of the wings or tails or feathers to control their flight attitude. This project studies one of these feather groups, namely coverts, as flight control devices. They are usually studied as passive flow control devices (link other covert page here). In this project, we show the first evidence that actively deployable coverts have a large aerodynamic force and moment modulation range, which can be used for flight control.
BAM Approach
Coverts are modeled as flap surfaces attached to a NACA 2414 airfoil at different chordwise locations and deflected at various angles. The wing's angle of attack varies, and the free-stream conditions are set to a transitional Reynolds number, similar to that experienced by birds and small-scale UAVs. Force and moment data, along with flow field velocity and vorticity measurements, are acquired using a 6-axis force-torque transducer and particle image velocimetry in a controlled wind tunnel environment. After understanding and modeling the physics, we implemented the coverts on Toyota's wind energy harvesting kite and tested its performance in field flight tests.
caption a) wind tunnel schematic with the PIV setup and laser sheet shown b) wing setup integrated with the ATI force transducer and the rotary table. c) airfoil schematic showing the experimental parameter
Recent Results
Simultaneous deflection increased the lift and drag modulation range of covert-inspired flaps compared to deflections on the suction or pressure side alone. This additional effect can be incredibly useful for the attitude control of energy-harvesting kites. Additionally, we observed the sensitivities of the covert flaps to their location along the chord and their deflection angle. Our findings show that for maximum yaw control with minimal undesired roll, a 2080 flap configuration is optimal. Furthermore, we captured time-averaged velocity fields and explained the underlying physics of the mechanism of action. We applied our understanding to Toyota's energy-harvesting kite, where the coverts helped satisfy stability augmentation and maneuver requirements. Finally, we successfully identified the full aerodynamic model of the kite using specially designed maneuvers and system identification techniques tailored for this application.
Main effect plots for pre-stall lift (upper row) and drag (lower row) for every design parameter. The baseline is depicted with a dashed black line. The pressure side is indicated in red, the suction side in blue, and simultaneous deflection in solid black. The colored regions illustrate the range of responses.PIV velocity field for suction only (a,e), pressure only (b,f), simultaneous (c,g), and superposition (d,h) experiments. All velocity fields are measured except d and h, which are reconstructed from the suction side of a and e, superimposed to the pressure side of b and f, respectively. The dashed lines 1 through 6 indicate the limits of the wake for the different cases, and the white box highlights the difference in the wake between the simultaneous measured flow field and the superposition flow field.Time history of flow angles (a,b), angular rates (c), and designed deflection angle (d) for a steady state flight condition. The longitudinal body forces (e,f), and moments (g) with the true value represented by the solid line, the linear model with the dashed red line, and the non-linear model with the dashed blue line
Journal Papers
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Zekry, D., Nam, T., Gupta, R., Zhu, Y. and Wissa, A. Bioinspiration & Biomimetics 2023. Covert-inspired flaps: an experimental study to understand the interactions between upper and under-wing coverts.
Peer Reviewed Conference Papers
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Zekry, D., and Wissa, A. AIAA Scitech 2024. Identification of aerodynamic models for an energy-harvesting kite using multisine inputs and equation error. (UR)
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Zekry, D., and Wissa A. ASME SMASIS 2024. The physics of bio-inspired covert flaps as flight control devices. (A)
Conference Presentations
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Feather-inspired flight control for airborne wind energy harvesting. (IT) AIAA Scitech 2024
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Identification of aerodynamic models for an EHK using multisine inputs and equation error. (UR) AIAA Scitech 2024
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The physics of bio-inspired covert flaps as flight control devices. (A) ASME SMASIS 2024
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Feather-inspired flight control for airborne energy harvesting kites. NAWEA WindTech 2024
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Covert-inspired flaps as flight control surfaces for BWB aircraft. APS DFD 2023
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Coverts as bio-inspired flight control devices for tailless UAVs. ASME SMASIS 2022
