Gliding Flight Research Articles

区分線形近似を用いた動的計画法による軌道最適化

The feasibility in optimal control applications is increasing in recent years with rapid improvement of computational capability. User-friendly practical tools are highly required to meet complex design requirements in the field of aerospace engineering and dynamic programming is regarded as a powerful tool that satisfies these necessities. On the contrary, dynamic programming possesses a drawback so called ‘menace of the expanding grid’ or dimensional difference problem in applications where the number of control variables is fewer than that of state variables. This paper proposes a unique method to approach this issue and reviews its validity and feasibility by discussing a classical problem of Linear Quadratic Regulator (LQR) and an optimal gliding flight of an airplane that the analytically given exact solutions are checked for clarity.

An Approximate Optimal Maximum Range Guidance Scheme for Subsonic Unpowered Gliding Vehicles

This study investigates the maximum gliding range problems of subsonic unpowered gliding vehicles and proposes an approximate optimal maximum range guidance scheme. First, the gliding flight path angle corresponding to constant dynamic pressure is derived. A lift-to-drag ratio(L/D)inversely proportional to the dynamic pressure is then proven. On this basis, the calculation method of an optimal dynamic pressure (ODP) profile with a maximumL/Dthroughout the flight is presented. A guidance scheme for tracking the ODP profile, which uses the flight path angle as control variable, is then designed. The maximum ranges of the unpowered gliding vehicle obtained by the proposed guidance scheme and pseudospectral method are compared. Results show that the guidance scheme provides an accurate approximation of the optimal results, and the errors are less than 2%. The proposed guidance scheme is easy to implement and is not influenced by wind compared with numerical schemes.

수심 제한을 고려한 수중 글라이더 경로 최적화

In this study, the problem of trajectory optimization for underwater gliders considering depth constraints is discussed. Typically, underwater gliders are controlled to dive and climb in a saw-tooth pattern at constant gliding angles. This approach is effective and close to optimal for deep water applications. However, the optimal path deviates from the saw-tooth path in shallow water conditions. This study focuses on finding more efficient gliding paths that can minimize the traverse time in the horizontal plane when the water depth is limited. The trajectory optimization problem is formulated into a minimum time control problem with inequality path constraints and hydrodynamic drag effects. A numerical approach based on the pseudo-spectral method is adopted as a solution approach, and the simulation results are presented.

Pteromys

This paper introduces novel interactive techniques for designing original hand-launched free-flight glider airplanes which can actually fly. The aerodynamic properties of a glider aircraft depend on their shape, imposing significant design constraints. We present a compact and efficient representation of glider aerodynamics that can be fit to real-world conditions using a data-driven method. To do so, we acquire a sample set of glider flight trajectories using a video camera and the system learns a nonlinear relationship between forces on the wing and wing shape. Our acquisition system is much simpler to construct than a wind tunnel, but using it we can efficiently discover a wing model for simple gliding aircraft. Our resulting model can handle general free-form wing shapes and yet agrees sufficiently well with the acquired airplane flight trajectories. Based on this compact aerodynamics model, we present a design tool in which the wing configuration created by a user is interactively optimized to maximize flight-ability. To demonstrate the effectiveness of our tool for glider design by novice users, we compare it with a traditional design workflow.

Assessing the potential of autonomous submarine gliders for ecosystem monitoring across multiple trophic levels (plankton to cetaceans) and pollutants in shallow shelf seas

A combination of scientific, economic, technological and policy drivers is behind a recent upsurge in the use of marine autonomous systems (and accompanying miniaturized sensors) for environmental mapping and monitoring. Increased spatial–temporal resolution and coverage of data, at reduced cost, is particularly vital for effective spatial management of highly dynamic and heterogeneous shelf environments. This proof-of-concept study involves integration of a novel combination of sensors onto buoyancy-driven submarine gliders, in order to assess their suitability for ecosystem monitoring in shelf waters at a variety of trophic levels. Two shallow-water Slocum gliders were equipped with CTD and fluorometer to measure physical properties and chlorophyll, respectively. One glider was also equipped with a single-frequency echosounder to collect information on zooplankton and fish distribution. The other glider carried a Passive Acoustic Monitoring system to detect and record cetacean vocalizations, and a passive sampler to detect chemical contaminants in the water column. The two gliders were deployed together off southwest UK in autumn 2013, and targeted a known tidal-mixing front west of the Isles of Scilly. The gliders’ mission took about 40 days, with each glider travelling distances of >1000 km and undertaking >2500 dives to depths of up to 100 m. Controlling glider flight and alignment of the two glider trajectories proved to be particularly challenging due to strong tidal flows. However, the gliders continued to collect data in poor weather when an accompanying research vessel was unable to operate. In addition, all glider sensors generated useful data, with particularly interesting initial results relating to subsurface chlorophyll maxima and numerous fish/cetacean detections within the water column. The broader implications of this study for marine ecosystem monitoring with submarine gliders are discussed.

Particle-Image Velocimetry and Force Measurements of Leading-Edge Serrations on Owl-Based Wing Models

High-resolution Particle-Image Velocimetry (PIV) and time-resolved force measurements were performed to analyze the impact of the comb-like structure on the leading edge of barn owl wings on the flow field and overall aerodynamic performance. The Reynolds number was varied in the range of 40,000 to 120,000 and the range of angle of attack was 0° to 6° for the PIV and −15° to +20° for the force measurements to cover the full flight envelope of the owl. As a reference, a wind-tunnel model which possessed a geometry based on the shape of a typical barn owl wing without any owl-specific adaptations was built, and measurements were performed in the aforementioned Reynolds number and angle of attack range. This clean wing model shows a separation bubble in the distal part of the wing at higher angles of attack. Two types of comb-like structures, i.e., artificial serrations, were manufactured to model the owl's leading edge with respect to its length, thickness, and material properties. The artificial structures were able to reduce the size of the separation region and additionally cause a more uniform size of the vortical structures shed by the separation bubble within the Reynolds number range investigated, resulting in stable gliding flight independent of the flight velocity. However, due to increased drag coefficients in conjunction with similar lift coefficients, the overall aerodynamic performance, i.e., lift-to-drag ratio is reduced for the serrated models. Nevertheless, especially at lower Reynolds numbers the stabilizing effect of the uniform vortex size outperforms the lower aerodynamic performance.

Dissipation measurements using temperature microstructure from an underwater glider

Microstructure measurements of temperature and current shear are made using an autonomous underwater glider. The glider is equipped with fast-response thermistors and airfoil shear probes, providing measurements of dissipation rate of temperature variance, χ, and of turbulent kinetic energy, ε, respectively. Furthermore, by fitting the temperature gradient variance spectra to a theoretical model, an independent measurement of ε is obtained. Both Batchelor (εB) and Kraichnan (εK) theoretical forms are used. Shear probe measurements are reported elsewhere; here, the thermistor-derived εB and εK are compared to the shear probe results, demonstrating the possibility of dissipation measurements using gliders equipped with thermistors only. A total of 152 dive and climb profiles are used, collected during a one-week mission in the Faroe Bank Channel, sampling the turbulent dense overflow plume and the ambient water above. Measurement of ε with thermistors using a glider requires careful consideration of data quality. Data are screened for glider flight properties, measurement noise, and the quality of fits to the theoretical models. Resulting dissipation rates from the two independent methods compare well for dissipation rates below 2×10−7 W kg−1. For more energetic turbulence, thermistors underestimate dissipation rates significantly, caused primarily by increased uncertainty in the time response correction. Batchelor and Kraichnan spectral models give very similar results. Concurrent measurements of ε and χ are used to compute the dissipation flux coefficient Γ (or so-called apparent mixing efficiency). A wide range of values is found, with a mode value of Γ≈0.14, in agreement with previous studies. Gliders prove to be suitable platforms for ocean microstructure measurements, complementary to existing methods.

Optimal soaring via Hamilton-Jacobi-Bellman equations

Competition glider flying is a game of stochastic optimization, in which mathematics and quantitative strategies have historically played an important role. We address the problem of uncertain future atmospheric conditions by constructing a nonlinear Hamilton–Jacobi–Bellman equation for the optimal speed to fly, with a free boundary describing the climb/cruise decision. We consider two different forms of knowledge about future atmospheric conditions, the first in which the pilot has complete foreknowledge and the second in which the state of the atmosphere is a Markov process discovered by flying through it. We compute an accurate numerical solution by designing a robust monotone finite difference method. The results obtained are of direct applicability for glider flight. Copyright © 2014 John Wiley & Sons, Ltd.

Efficiency of Lift Production in Flapping and Gliding Flight of Swifts

Many flying animals use both flapping and gliding flight as part of their routine behaviour. These two kinematic patterns impose conflicting requirements on wing design for aerodynamic efficiency and, in the absence of extreme morphing, wings cannot be optimised for both flight modes. In gliding flight, the wing experiences uniform incident flow and the optimal shape is a high aspect ratio wing with an elliptical planform. In flapping flight, on the other hand, the wing tip travels faster than the root, creating a spanwise velocity gradient. To compensate, the optimal wing shape should taper towards the tip (reducing the local chord) and/or twist from root to tip (reducing local angle of attack). We hypothesised that, if a bird is limited in its ability to morph its wings and adapt its wing shape to suit both flight modes, then a preference towards flapping flight optimization will be expected since this is the most energetically demanding flight mode. We tested this by studying a well-known flap-gliding species, the common swift, by measuring the wakes generated by two birds, one in gliding and one in flapping flight in a wind tunnel. We calculated span efficiency, the efficiency of lift production, and found that the flapping swift had consistently higher span efficiency than the gliding swift. This supports our hypothesis and suggests that even though swifts have been shown previously to increase their lift-to-drag ratio substantially when gliding, the wing morphology is tuned to be more aerodynamically efficient in generating lift during flapping. Since body drag can be assumed to be similar for both flapping and gliding, it follows that the higher total drag in flapping flight compared with gliding flight is primarily a consequence of an increase in wing profile drag due to the flapping motion, exceeding the reduction in induced drag.

Optimal Soaring via Hamilton-Jacobi-Bellman Equations

Competition glider flying is a game of stochastic optimization, in which mathematics and quantitative strategies have historically played an important role. We address the problem of uncertain future atmospheric conditions by constructing a nonlinear Hamilton-Jacobi-Bellman equation for the optimal speed to fly, with a free boundary describing the climb/cruise decision. We consider two different forms of knowledge about future atmospheric conditions, the first in which the pilot has complete foreknowledge and the second in which the state of the atmosphere is a Markov process discovered by flying through it. We compute an accurate numerical solution by designing a robust monotone finite difference method. The results obtained are of direct applicability for glider flight.

Aerodynamic characteristics of a feathered dinosaur measured using physical models. Effects of form on static stability and control effectiveness.

We report the effects of posture and morphology on the static aerodynamic stability and control effectiveness of physical models based on the feathered dinosaur, Microraptor gui, from the Cretaceous of China. Postures had similar lift and drag coefficients and were broadly similar when simplified metrics of gliding were considered, but they exhibited different stability characteristics depending on the position of the legs and the presence of feathers on the legs and the tail. Both stability and the function of appendages in generating maneuvering forces and torques changed as the glide angle or angle of attack were changed. These are significant because they represent an aerial environment that may have shifted during the evolution of directed aerial descent and other aerial behaviors. Certain movements were particularly effective (symmetric movements of the wings and tail in pitch, asymmetric wing movements, some tail movements). Other appendages altered their function from creating yaws at high angle of attack to rolls at low angle of attack, or reversed their function entirely. While M. gui lived after Archaeopteryx and likely represents a side experiment with feathered morphology, the general patterns of stability and control effectiveness suggested from the manipulations of forelimb, hindlimb and tail morphology here may help understand the evolution of flight control aerodynamics in vertebrates. Though these results rest on a single specimen, as further fossils with different morphologies are tested, the findings here could be applied in a phylogenetic context to reveal biomechanical constraints on extinct flyers arising from the need to maneuver.

The aerodynamic performance of the feathertail glider, Acrobates pygmaeus (Marsupialia: Acrobatidae)

Photographic and videographic investigations of the aerodynamic performance of four captive adult Acrobates pygmeus are described. During short (1–4 m) glides, steep angles of descent (>45°) and large angles of attack (up to 50°) were used mid-flight, and the possums failed to achieve steady velocities. During longer (>10 m) glides steady velocities of 5.3–7.5 m s–1 were achieved, and glide angles of 21–42° and angles of attack between 36° and 45° were used. The best (lowest) glide angles used at steady velocity were similar to those documented in sugar gliders, but involved lower air speeds. During steady gliding the forelimbs of Acrobates assumed an ‘elbows-out’ disposition similar to that of Petauroides volans, and unlike that of petaurid gliders. A glide polar for Acrobates shows that it uses lower air speeds and higher sinking speeds than other gliding animals for which polars are available (several birds and one bat). Few data on the radius of turn and sinking speed were obtained; nevertheless, in accord with theory, sinking speeds were higher during tighter turns. During flight the feather-like tail was used to generate pitching movements and adjust the angle of attack and hence glide angle. However, the control of turns seems to be achieved primarily through limb adjustments.

Influence of Accelerometer Location on Autopilot Stability of Reusable Launch Vehicle Attitude Control System

Fly-back phase of any Reusable Launch Vehicle (RLV), with wings, encounters ballistic flight in the absence of aerodynamic forces, in rare atmosphere at high re-entry altitude. Lifting vehicles enter the atmosphere at high angle of attack to increase the drag so that the vehicle velocity can be reduced. High angle of attack also increases the lift to balance the weight for equilibrium glide flight. During high altitude flight, angle of attack and side-slip estimations based on information from inertial sensors and modeled wind, are accurate enough to be used for feedback in attitude control. Once RLV descends below certain altitude and Mach number reduces below certain value, wind's contribution in angle of attack and side-slip becomes prominent and inertial navigation based estimates of these angles, no more remain accurate for their use in attitude control. To overcome this problem, normal and lateral accelerations are directly used in place of angle of attack and side-slip angle, respectively. Two aspect of control law design are covered in this paper which are applicable to descent flight of a typical RLV. First aspect is the impact of change in feedback signals from side-slip angle to lateral acceleration, on stability of lateral-directional dynamics. It is seen that the selection of feedback variables or sensors, significantly changes the achievable stability margins. Second aspect is the role of sensor placement w.r.t. CG, especially lateral accelerometer, on the stability of lateral-directional dynamics. This aspect of sensor placement is being discussed for the first time in any paper. It is seen that proper placement of accelerometer results in better stability margins.

Gliding performance in the yellow-bellied glider in low-canopy forest

Knowledge of the gliding performance of gliding mammals is fundamental to understanding how these species have adapted to their environment and is of increasing relevance to their conservation. I describe aspects of the glide performance of the yellow-bellied glider (Petaurus australis) based on 22 glides of 17 individuals within 20–30-m-high open forest in western Victoria. Gliders launched into a glide from a horizontal branch that was, on average, 2.8 m below the top of a tree, 5.2 m out from the main trunk and 18.5 m above the ground. Gliders landed on the trunks of trees 5.8 m above the ground. The mean horizontal glide distance was 25.2 ± 1.5 m (s.e.) (range = 19–45 m), producing a glide ratio (horizontal distance/height dropped) of 2.0 and a glide angle of 27.3°. These values are similar to those reported for other gliding petaurids in low-canopy forest. This knowledge should be used to guide the management of habitat connectivity for yellow-bellied gliders.

Comparison of flight test data with a computational fluid dynamics model of a Scottish Aviation Bulldog aircraft

AbstractThe following paper presents detailed aerodynamic data of a Scottish Aviation Bulldog light aircraft. The data is taken from the pre-stall region of the aircraft flight envelope through two flight test methods and from a geometrically accurate computational fluid dynamics (CFD) model of the full scale aircraft, which was meshed in Ansys ICEM CFD and solved in Ansys Fluent. The fidelity of the CFD model was achieved by development of a CATIA solid model with surfaces matching a spatial point cloud of the aircraft taken using a 3D laser scanner. Following a CFD verification process, a 3·4m hybrid mesh with a Spalart-Allmaras (SA) turbulence model was found to give the best overall lift and drag characteristics. Further detailed comparisons with the glide flight test data showed the CFD drag polar to have 63% lower zero lift drag, although this discrepancy was related to the simplification of the original CATIA surface model, which excluded the undercarriage, aerials and other protuberance drags. Inclusion of estimates of these sources of drag resulted in a match in zero lift drag to within 15% and a maximum lift to drag of 10:1 which was within 11% of the glide flight test result. The remaining drag discrepancy is attributed to other effects including trim drag and the surface finish of the actual aircraft.

Fabrication of silver nano coatings and investigation of their superhydrophobic and anticorrosion properties

Silver nano coatings were fabricated on zinc substrate by a facile method of replacement reaction. The coatings enhibit properties of superhydrophobicity and anticorrosion after being modified by dodecanethiol (DDT) and octadecanethiol (ODT). Contact angles on modified coating are 156.2° and 151.8°, respectively, and the glide angle is approximately 5°. Silver coatings superhydrophobicity is dominated by reaction time, concentration of AgNO3 and surface free energy. Finally, superhydrophobic and anticorrosion mechanisms of the coatings were analyzed and discussed.

A numerical investigation on the ground effect of a flapping-flying bird

The flight of a small bird under the influence of the ground effect is numerically investigated with a complete three-dimensional model including the bird's body and wings. The flight mode is not the conventional steady gliding flight but an unsteady flight consisting of flapping, twisting, and folding motions. As the bird approaches the ground, the average lift force gradually increases while the average drag force decreases. At a particular distance, the average lift force increases by approximately 47%, whereas the average drag force decreases by nearly 20%, relative to the absence of the ground effect. Because of the ground, the improved aerodynamic performance in flapping flight is much more significant than in steady flight, in which the modification of the lift-drag ratio is typically less than 10%. On the basis of the flow field, regardless of the presence or absence of the ground, there exists no evidence for an obstruction of a wing-tip vortex, which is a remarkable phenomenon and accounts for the improved performance in steady flight. The extent of the region of high pressure beneath the wing in the near-ground case seems to surpass that in the far-ground case, accounting for the greater lift and thrust forces in the near-ground case. This air cushion beneath the wing, known as the cram effect, is the dominant factor of the ground effect on a flapping bird.

Determining Aerodynamic Characteristics of a Micro Air Vehicle Using Motion Tracking

The aerodynamic performance of small-scale fixed-wing flight is not well understood, and flight data is needed to gain a better understanding of the aerodynamics of micro air vehicles. The flight characteristics of micro air vehicles are difficult to measure because the small size and low weight prevent the use of conventional onboard instrumentation systems. In this research, an offboard motion tracking system captured the motion trajectory during the flights of a small off-the-shelf radio-controlled airplane that weighed 14.44 g (0.5094 oz) and had a span of 37.47 cm (14.75 in.). The recorded motion-path time histories were analyzed to determine the aerodynamic characteristics of the airplane during unpowered flight. The results presented show the longitudinal aerodynamic characteristics of the micro air vehicle over a wide range of angles of attack at a nominal Reynolds number of 25,000. Specifically, lift and drag characteristics of the airplane were obtained from the analysis of the flight trajectories during quasi-steady nominal gliding flight, as well as unsteady high angle-of-attack flight. The nominal-gliding flights showed an almost linear lift curve and small unsteady effects that were in part due to the angle-of-attack rate. During the unsteady high angle-of-attack flight, as would be seen during perching maneuvers, deep stall maneuvers, and highly dynamic flight in confined spaces, the unsteady effects of rapid changes in the angle of attack significantly increased the lift coefficient during pitch-up maneuvers and then decreased the lift coefficient during pitch-down maneuvers. By using numerous flight tests in both regimes (nominal-gliding and unsteady high angle-of-attack flight), the results show the effect of the angular rate and expand on the limited existing work. The flight-test results presented show the influence of unsteady aerodynamic effects on the longitudinal aerodynamic characteristics of a micro air vehicle in both quasi-steady nominal gliding flight and unsteady high angle-of-attack flight.

Bio-inspired fabrication of well-oriented ZnO nanorod arrays film and its superhydrophobicity and superhydrophilicity

A highly oriented ZnO nanorod array film was fabricated on glass substrate by combinations of Sol–Gel and hydrothermal. The film exhibits perfect superhydrophobicity with a contact angle of 155° and a glide angle of 4° after being surface modified by fluoroalkylsilane, which is similar with wings’ property and structures of large yellow spots mosquitoes. Interestingly, the ZnO nanorods film were converted from superhydrophobicity into superhydrophilicity under ultraviolet light for 2 h due to the decomposition of fluoroalkyl chain of fluoroalkylsilane and the photosensitivity of ZnO surface. The transition mechanisms of wettability are discussed on the basis of correlated theories.

Elements of Underwater Glider Performance and Stability

AbstractUnderwater gliders are winged autonomous underwater vehicles (AUVs) that can be deployed for months at a time and travel thousands of kilometers. As with any vehicle, different applications impose different mission requirements that impact vehicle design. We investigate the relationship between a glider’s geometry and its performance and stability characteristics. Because our aim is to identify general trends rather than perform a detailed design optimization, we consider a generic glider shape: a cylindrical hull with trapezoidal wings. Geometric parameters of interest include the fineness ratio of the hull, the wing position and shape, and the position and size of the vertical stabilizer. We describe the results of parametric studies for steady wings-level flight, both at minimum glide angle and at maximum horizontal speed, as well as for steady turning flight. We describe the variation in required lung capacity and maximum lift-to-drag ratio corresponding to a given vehicle size and speed; we also consider range and endurance, given some initial supply of energy for propulsion. We investigate how the turning performance varies with wing and vertical stabilizer configuration. To support this analysis, we consider the glider as an 8-degree-of-freedom multibody system (a rigid body with a cylindrically actuated internal moving mass) and develop approximate expressions for turning flight in terms of geometry and control parameters. Moving from performance to stability and recognizing that a glider’s motion is well described in terms of small perturbations from wings-level equilibrium, we study stability as an eigenvalue problem for a rigid (actuators-fixed) flight vehicle. We present a number of root locus plots in terms of various geometric parameters that illuminate the design tradeoff between stability and control authority.