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

Hexagonal ring origami is a type of foldable structure that has impressive packing abilities and can be tessellated into two-dimensional or three-dimensional surfaces without any gap or overlap. It can be folded under bending or twisting loads into a peach core-shaped configuration with only 10.6% of its initial area. However, in applications of large-scale foldable structures, folding by bending or twisting is usually technically difficult. Here, we propose strategies to facilitate easy snap-folding of the hexagonal ring by a simple point load or localized twist or squeeze. This is enabled by two geometric modifications made to the hexagonal ring: introducing residual strain and creating pre-twisted edges. By combining theoretical modeling, finite element simulations, and experiments, we systematically investigate the snap-folding behaviors of modified hexagonal rings with residual strain and pre-twisted edges. It is found that the geometric modifications promote easy snap-folding of the hexagonal ring by different mechanisms: introducing residual strain can significantly decrease the energy barrier and thus reduce the required moment to snap-fold the ring, while creating pre-twisted edges allows for easy out-of-plane deformation which is a necessary condition for a ring to fold. Combining the two methods further enables the snap-folding of the hexagonal ring by a point load or localized twist or squeeze. To demonstrate the easy folding of large assemblies of the modified rings, we construct dome and pyramid assemblies that can be snap-folded from their initial three-dimensional states to significantly lower-volume final states by a simple compression at the rings’ corners. We envision that the proposed geometric modification strategies can provide a new perspective on the rational design of easy-to-fold ring origami-based foldable functional structures with extremely high packing ratios. 

Easy snap-folding of hexagonal ring origami by geometric modifications


 Origami has emerged as a powerful mechanism for designing functional foldable and deployable structures. Among various origami patterns, a large class of origami exhibits rotational symmetry, which possesses the advantages of elegant geometric shapes, axisymmetric contraction/expansion, and omnidirectional deployability, etc. Due to these merits, origami with rotational symmetry has found widespread applications in various engineering fields such as foldable emergency shelters, deformable wheels, deployable medical stents, and deployable solar panels. To guide the rational design of origami-based deployable structures and functional devices, numerous works in recent years have been devoted to understanding the geometric designs and mechanical behaviors of rotationally symmetric origami. In this review, we classify origami structures with rotational symmetry into three categories according to the dimensional transitions between their deployed and folded states as three-dimensional to three-dimensional, three-dimensional to two-dimensional, and two-dimensional to two-dimensional. Based on these three categories, we systematically review the geometric designs of their origami patterns and the mechanical behaviors during their folding motions. We summarize the existing theories and numerical methods for analyzing and designing these origami structures. Also, potential directions and future challenges of rotationally symmetric origami mechanics and applications are discussed. This review can provide guidelines for origami with rotational symmetry to achieve more functional applications across a wide range of length scales.

Origami with Rotational Symmetry: A Review on Their Mechanics and Design

Origami inspired structures are largely being recognized as efficient deployable structures that can serve multidisciplinary applications. This research focuses on the geometric analyses and quasistatic behavior of toroidal folding patterns based on the four-fold line origami concept. A sequential design process is presented to develop four-fold line toroidal origami structures from a flat sheet of paper, followed by a generalized design algorithm based on the mathematical formulation of the design process. The availability of the geometric design space is calculated considering the limiting values of the design parameters. Geometric analyses is performed to investigate the influence of design parameters on the packaging parameters and availability of the design space. A novel experimental setup is developed, and methodology is introduced to investigate the quasistatic behavior of the single story toroidal patterns. Then, this experimental approach is utilized to characterize the single story toroidal Miura-ori patterns (TMOPs) on the basis of their quasistatic behavior. Moreover, the quasistatic behavior of multi story TMOPs is investigated experimentally. • Mathematical model to develop toroidal Miura-ori patterns is proposed. • Geometric analyses for folded configuration and availability of design space. • Experimental methodology to investigate the quasistatic deployment behavior. • Experimental Characterization based on quasistatic Behavior. 

Geometric analyses and experimental characterization of toroidal Miura-ori structures

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).

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

Deployable toroidal structures based on modified Kresling pattern

Abstract Background The Ilizarov method and fixator are clinically recognised for the treatment of fractures, limb salvage and deformity correction. There have been extensive studies determining the basic mechanism for fracture healing using this technique. It is generally accepted that circular frames optimise the mechanical environment by reducing shear strain across the fracture while maintaining axial micromotion so as to promote fracture healing. There have been several new hexapod-type frames introduced into the market over the past 20 years with little comparative research into their biomechanical properties and resultant effects on the fracture environment. Questions/purposes To investigate the biomechanical behaviours of the TrueLok-Hex (TL-HEX) and Taylor spatial frame (TSF) hexapod-type circular external fixators with comparison to traditional Ilizarov-type (TL-Ilizarov and TSF-Ilizarov) constructs and potential performance in vivo. Methods Testing was performed on standardised four-ring TSF and TL-HEX constructs matched by identical frames using Ilizarov threaded rod constructs for each set of components. All frames were tested under physiological levels of axial, bending and torsional loading. Load-deformation properties for each construct under each mode of loading were calculated and analysed statistically using ANOVA. Results Under axial loading, the Ilizarov construct utilising TL-HEX components demonstrated the greatest rigidity followed by the Ilizarov construct using TSF components. Under bending loads, the difference in rigidity between constructs was similar but less marked. Under torsional loading, both hexapod frames were seen to be significantly more rigid than the Ilizarov constructs. Overall deformation around neutral loading was much higher in the TSF frame due to an observed significant “toe-in” laxity in the strut universal joints. The remaining deformation of both hexapod frames was similar with a higher level of TL-HEX rigidity in axial loading and a higher level of TSF rigidity in bending and torsion. Conclusion In conclusion, both hexapod frame constructs were less rigid under axial loading but more rigid under bending and torsional loads than their comparative Ilizarov constructs. As a result of their Cardan universal joints, the TSF demonstrated greater overall planar strain due to the observed “toe-in” laxity around neutral loading while the TL-HEX, with ball-and-socket universal joints, demonstrated a minimal level of laxity. Beyond the initial deformation due to the preloaded laxity, both hexapod frames responded to loading in a similar manner. There were significant differences in the frames’ mechanical behaviour under different loading conditions but further research is required to determine whether these translate in vivo into clinical significance. How to cite this article Fenton C, Henderson D, Samchukov M, et al. Comparative Stiffness Characteristics of Ilizarov- and Hexapod-type External Frame Constructs. Strategies Trauma Limb Reconstr 2021;16(3):138–143.

/pdf/comparative-stiffness-characteristics-of-ilizarov-and-2675xn79.pdf

Comparative Stiffness Characteristics of Ilizarov- and Hexapod-type External Frame Constructs

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

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


 Origami inspired deployable structures have received significant attention due to their exceptional kinematic and mechanical characteristics. Specifically, the cylindrical Kresling origami pattern has been extensively investigated for its multi-stable properties in past studies. This study presents the design and analysis of a novel non-prismatic foldable/ deployable truss module inspired from the conical Kresling origami pattern. The intrinsic relationship between the kinematics and mechanics of non-prismatic foldable truss (NPFT) modules is investigated. First, the geometric design and the analytical modeling of the motion behavior of NPFT modules are presented, followed by the development of design maps considering a range of design parameters to demarcate the domains of qualitatively different deployment behavior. The numerical simulations were performed to validate the findings of analytical investigations. Later, the comparative analysis is presented to highlight the advancements of the proposed NPFT modules over conical Kresling truss structures. The programmability of the deployment characteristics of NPFT modules is investigated considering different design parameters and the influence of scaling. The outcomes demonstrate that the proposed design of NPFT modules offers enhanced deployable and tunable properties along with ease of manufacturing for reconfigurable truss structures.

Hemant Sharma

Papers

Deployable toroidal structures based on modified Kresling pattern

Comparative Stiffness Characteristics of Ilizarov- and Hexapod-type External Frame Constructs

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

Geometric analyses and experimental characterization of toroidal Miura-ori structures

Design and kinematics of origami inspired non-prismatic foldable truss modules