An accurate knowledge of the unsteady aerodynamic forces acting on a bio-inspired, flapping-wing micro air vehicle (FWMAV) is crucial in the design development and optimization cycle. Two different types of experimental approaches are often used: determination of forces from position data obtained from external optical tracking during free flight, or direct measurements of forces by attaching the FWMAV to a force transducer in a wind-tunnel. This study compares the quality of the forces obtained from both methods as applied to a 17.4 gram FWMAV capable of controlled flight. A comprehensive analysis of various error sources is performed. The effects of different factors, e.g., measurement errors, error propagation, numerical differentiation, filtering frequency selection, and structural eigenmode interference, are assessed. For the forces obtained from free flight experiments it is shown that a data acquisition frequency below 200 Hz and an accuracy in the position measurements lower than ± 0.2 mm may considerably hinder determination of the unsteady forces. In general, the force component parallel to the fuselage determined by the two methods compares well for identical flight conditions; however, a significant difference was observed for the forces along the stroke plane of the wings. This was found to originate from the restrictions applied by the clamp to the dynamic oscillations observed in free flight and from the structural resonance of the clamped FWMAV structure, which generates loads that cannot be distinguished from the external forces. Furthermore, the clamping position was found to have a pronounced influence on the eigenmodes of the structure, and this effect should be taken into account for accurate force measurements.

https://iopscience.iop.org/article/10.1088/1748-3190/10/5/056004/pdf

Error analysis and assessment of unsteady forces acting on a flapping wing micro air vehicle: free flight versus wind-tunnel experimental methods.

Flapping-wing aerodynamic models that are accurate, computationally efficient and physically meaningful, are challenging to obtain. Such models are essential to design flapping-wing micro air vehicles and to develop advanced controllers enhancing the autonomy of such vehicles. In this work, a phenomenological model is developed for the time-resolved aerodynamic forces on clap-and-fling ornithopters. The model is based on quasi-steady theory and accounts for inertial, circulatory, added mass and viscous forces. It extends existing quasi-steady approaches by: including a fling circulation factor to account for unsteady wing-wing interaction, considering real platform-specific wing kinematics and different flight regimes. The model parameters are estimated from wind tunnel measurements conducted on a real test platform. Comparison to wind tunnel data shows that the model predicts the lift forces on the test platform accurately, and accounts for wing-wing interaction effectively. Additionally, validation tests with real free-flight data show that lift forces can be predicted with considerable accuracy in different flight regimes. The complete parameter-varying model represents a wide range of flight conditions, is computationally simple, physically meaningful and requires few measurements. It is therefore potentially useful for both control design and preliminary conceptual studies for developing new platforms.

Quasi-steady aerodynamic model of clap-and-fling flapping MAV and validation using free-flight data.

Several formulations have been proposed to model the dynamics of ornithopters, with inconclusive results regarding the need for complex kinematic formulations. Furthermore, the impact of assumptions made in the collected results was never assessed by comparing simulations with real flight data. In this study two dynamic models of a Flapping Wing Micro Aerial Vehicle (FWMAV) were derived and compared: a) single rigid body aircraft equations of motion and b) Virtual Work Principle derivation for multiple rigid body flapping kinematics. The aerodynamic forces and moments were compared by feeding the states that were reconstructed from the position and attitude data of a 17 gram free flying FWMAV into the dynamic equations of both formulations. To understand the applicability of rigid body formulations to FWMAVs, six wing-to-body mass ratios and two wing configurations were studied using real flight data. The results show that rigid body models are valid for the aerodynamic reconstruction of FWMAVs with four wings in ‘X’ configuration and two-winged FWMAV with a total wing-to-body mass ratio below 24% and 5.6%, respectively, without considerable information loss.

/pdf/rigid-body-kinematics-versus-flapping-kinematics-of-a-56kwlqusgb.pdf

Rigid-Body Kinematics Versus Flapping Kinematics of a Flapping Wing Micro Air Vehicle

A three-dimensional (3D) trajectory detection framework using two high-speed cameras for the flapping flexible wing of a micro-air-vehicle (MAV) is presented. This MAV, which is called the “Golden Snitch”, has a successful flight record of 8 minutes. We embed the flexible wingskin with a nine light emitting diode (LED) array as the light enhancing marker and capsulate it with parylene (poly-para-xylylene) as the protection layer. We confirm an oblique figure of eight trajectory of this MAV's wing with time-varying coordinate data. The corresponding aerofoil of the main wings' profiles was subjected to the time-varying coordinate data, yielding a resolution of a 1/70 wing beating cycle of 15Hz flapping. The trajectory information is first demonstrated as the moving boundaries of an unsteady flow simulation around a flapping flexible wing.

https://journals.sagepub.com/doi/pdf/10.5772/56565

3D Flapping Trajectory of a Micro-Air-Vehicle and its Application to Unsteady Flow Simulation

Recently, unmanned aerial vehicles (UAVs) or drones have emerged as a ubiquitous and integral part of our society. They appear in great diversity in a multiplicity of applications for economic, commercial, leisure, military and academic purposes. The drone industry has seen a sharp uptake in the last decade as a model to manufacture and deliver convergence, offering synergy by incorporating multiple technologies. It is due to technological trends and rapid advancements in control, miniaturization, and computerization, which culminate in secure, lightweight, robust, more-accessible and cost-efficient UAVs. UAVs support implicit particularities including access to disaster-stricken zones, swift mobility, airborne missions and payload features. Despite these appealing benefits, UAVs face limitations in operability due to several critical concerns in terms of flight autonomy, path planning, battery endurance, flight time and limited payload carrying capability, as intuitively it is not recommended to load heavy objects such as batteries. As a result, the primary goal of this research is to provide insights into the potentials of UAVs, as well as their characteristics and functionality issues. This study provides a comprehensive review of UAVs, types, swarms, classifications, charging methods and regulations. Moreover, application scenarios, potential challenges and security issues are also examined. Finally, future research directions are identified to further hone the research work. We believe these insights will serve as guidelines and motivations for relevant researchers. 

/pdf/unmanned-aerial-vehicles-uavs-practical-aspects-applications-1daaaq4t.pdf

Unmanned aerial vehicles (UAVs): practical aspects, applications, open challenges, security issues, and future trends

A deep reinforcement learning based method for real-time path planning and dynamic obstacle avoidance

The dynamics of a flapping-wing micro aerial vehicle (MAV) is studied in this paper. The MEMS Laboratory in Tamkang University has been developing flapping-wing MAVs for several years. Based on the developed flapping-wing MAV, the dynamics is studied and compared with flight test data. For a flapping wing, the average aerodynamic forces over one flapping period are usually formulated as a function of advance ratio. In this paper the averaging theory is applied to show the validity of this method. Consequently, the dynamics of a flapping-wing MAV longer than a flapping period can be analyzed using the same methodology as what we have done to a fixed-wing aircraft. Physical parameters are also obtained using experiment data, or through computer aid design programs. With the developed model and found parameters, numerical simulations of potential motions are proposed. Although several papers have discussed similar topics, comparing the numerical simulation with flight test data demonstrate the validity of our assumptions and derivations. The developed model can be further utilized in flight control and autonomous flight in the future.

W. C. Lu

Papers

A deep reinforcement learning based method for real-time path planning and dynamic obstacle avoidance

Dynamics of Flapping-Wing MAVs: Application to the Tamkang Golden Snitch