Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency. To support our comparative approach, we began by surveying theoretical and experimental estimates of avian aerodynamic efficiency and investigating the uncertainty associated with each estimation method. We found that the methodology used by a study affects the estimated efficiency and can lead to incongruent conclusions on gliding bird aerodynamic efficiency. Our survey showed that studies on live birds gliding in wind tunnels provide a reliable minimum estimate of a birds' aerodynamic efficiency while simultaneously quantifying the wing configurations used in flight. Next, we surveyed the aeronautical literature to collect the published aerodynamic efficiencies of similar-sized, non-copter UAVs. The compiled information allowed a direct comparison of UAVs and gliding birds. Contrary to our expectation, we found that there is no definitive evidence that any gliding bird species is either more or less efficient than a comparable UAV. This non-result highlights a critical need for new technology and analytical advances that can reduce the uncertainty associated with estimating a gliding bird's aerodynamic efficiency. Nevertheless, our survey indicated that species flying within subcritical Reynolds number regimes may inspire UAV designs that can extend their operational range to efficiently operate in subcritical regimes. The survey results provided here point the way forward for research into avian gliding flight and enable informed UAV designs.

Aerodynamic efficiency of gliding birds vs comparable UAVs: a review

This paper concentrates on the design, analysis, and development of fixed-wing hand launch unmanned aerial vehicle (UAV). This flight can able to carry the payloads of 0.8. The design process involves the conceptual, preliminary, and detailed design. This paper involves the investigation of the aerodynamic characteristics over the wing to enhance the aerodynamic design of the UAV. This analysis includes estimating the best gliding ratio to increase the flight mission and attain the maximum altitude. This simulation will be performed for subsonic flow with Mach number 0.04202(14.3m/s). The manufacturing of the UAV is done using composite materials like glass fiber of both (1mm and 2 mm) thickness, carbon fiber of 2mm, and carbon rod is used for connecting the empennage to the fuselage. The detailed design has been done in CATIA V5 and the analysis of the wing has been done using XFLR, ANSYS (fluent). Keywords— Fixed-wing hand launch UAV, Design process, Aerodynamic characteristics, Gliding ratio, Manufacturing, Composite materials, Glass fiber, Carbon fiber, CATIA V5, XFLR, ANSYS (fluent).

/pdf/design-performance-analysis-of-wing-and-manufacturing-of-4xiwchr28v.pdf

Design, performance analysis of wing, and manufacturing of fixed wing hand launch unmanned aerial vehicle

This paper adresses the detailed overview and challenges facing while designing a low thrust to weight ration and high payload fraction unmanned aerial vehicles from the flight stability perspective. The main focus is to get sufficient pitch stiffness without using any external controllers in the process of achieving high payload fraction. Several Iterations are illustrated with different aerofoils like Eppler, NACA and S1223 to achieve required pitch stiffness. This paper also presents the longitudinal stability analysis and theoretical lateral and directional stability and control derivatives of the Mini UAV. Keywords— Mini UAV, XFLR5, Pitch Stiffness, Stability derivatives.

/pdf/design-and-fabrication-of-low-t-w-ratio-and-high-payload-arbuaky1n6.pdf

Design and fabrication of low t/w ratio and high payload fraction mini uav

The environment of the work done in this thesis are the smart cities. A smart city is an urban area that collects data in order to efficiently manage infrastructures and resources. The proposed architecture involves the use of three different systems: the autonomous vehicles, the non-autonomous vehicles and the cloud system. The autonomous vehicles have the purpose of acquiring information, the non-autonomous vehicles have the purpose of acquiring information and support the autonomous vehicles, the cloud system processes the monitoring data and execute the path algorithm. The path planner algorithm calculate the path optimizing a risk function, evaluated considering the cells of a risk map. In order to generate the risk map, four different layers are required: occupation layer, population density layer, sheltering factor layer and signal power layer. The aim of this thesis is to improve the performance of the path planning algorithms considering two aspects: considering the autonomous vehicle crash distance after a failure and automating the generation of the sheltering factor layer. The crash distance was considered differentiating fixed wing UAVs from rotary wing UAVs. For fixed wing, starting from the equilibrium equations of a body, a simple equation has been found. The equation is able to evaluate the crash distance knowing the aerodynamic efficiency and initial altitude of the UAV. The effect of the implementation of the crash distance on the risk map generation are analyzed, in particular it was found that the risk shows a more uniform distribution with larger values of crash distance. Vice versa, for smaller crash distances, the risk distribution in the risk map is less uniform, with areas characterized by a much higher risk value than others. For the rotary wing, the ballistic equations have been numerically integrated. The obtained trajectories have been compared, considering different values of mass, drag coefficient, altitude, initial velocity and reference surface. The results are presented in two forms, one specific and one more generic. In the specific case, knowing a priori all the characteristics of the UAV considered (mass, drag coefficient, reference surface and flying altitude), it is possible to obtain an equation that evaluate the crash distance as a function of the initial speed. In the second generic case, a table has been generated. This table contains numerous combinations of mass, drag coefficient, reference surface, flight altitude and speed associating each of them the corresponding crash distance. The automation of the generation of the sheltering factor layer was performed by training neural networks in order to solve the problem of image classification. A database was created considering open source satellite images. Two different networks have been trained. The first was made from scratch, in order to be very light and fast. This network considers only one channel of the input images and is composed of a small number of layers. The second network is an already existing neural network, in this case transfer learning has been performed. This network is more complex and the training much slower. In the first case, the training was not successful enough to be used for generating the sheltering factor layer. In fact, the trained network accuracy is relatively small and presents overfitting. Necessary improvements in order to increase this network performance are described, including the implementation of a variable learning rate and the consideration of all three image channels instead of only one. In the second case, the network gave satisfactory results. Accuracy is relatively high with no overfitting observed. The improvements that could increase the performance of this network mainly concern the database. In particular, using a better database with higher image resolution and quality is suggested as future developments.

Sheltering factor recognition via machine learning for fully autonomous UAV urban path planning

This paper attempts to bring out the challenges associated with the design of a high altitude mini UAV especially from the aerodynamics perspective. The mini UAV under consideration is a 2 kg class conventional, high wing and T-Tail configuration. A comparative study of various high lift airfoils has been done to illustrate that the selection of a suitable airfoil for high altitude applications is indeed an important part of the design activity and it shows that the wing loading of a UAV designed for high altitudes does not depend on the changes in air density alone. The chosen high lift low Reynolds number airfoil is found to have a minor effect on the aerodynamic parameters (Cl and Cd) with changes in Reynolds number. This paper also addresses the performance variation due to operation at off design condition such as at sea level.

https://nal-ir.nal.res.in/12109/1/cp135.pdf

C. S. Suraj

Papers

Design of a High Altitude Fixed Wing Mini UAV - Aerodynamic Challenges