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We investigate the problem of the Lévy flight foraging hypothesis in an ecological niche described by a bounded region of space, with either absorbing or reflecting boundary conditions. To this end, we consider a forager diffusing according to a fractional heat equation in a bounded domain and we define several efficiency functionals whose optimality is discussed in relation to the fractional exponent s 2 (0, 1) of the diffusive equation. Such an equation is taken to be the spectral fractional heat equation (with Dirichlet or Neumann boundary conditions). We analyze the biological scenarios in which a target is close to the forager or far from it. In particular, for all the efficiency functionals considered here, we show that if the target is close enough to the forager, then the most rewarding search strategy will be in a small neighborhood of s D 0. Interestingly, we show that s D 0 is a global pessimizer for some of the efficiency functionals. From this, together with the aforementioned optimality results, we deduce that the most rewarding strategy can be unsafe or unreliable in practice, given its proximity with the pessimizing exponent, thus the forager may opt for a less performant, but safer, hunting method. However, the biological literature has already collected several pieces of evidence of foragers diffusing with very low Lévy exponents, often in relation with a high energetic content of the prey. It is thereby suggestive to relate these patterns, which are induced by distributions with a very fat tail, with a high-risk/high-gain strategy, in which the forager adopts a potentially very profitable, but also potentially completely unrewarding, strategy due to the high value of the possible outcome. [ABSTRACT FROM AUTHOR]

Highlights • The natural-mode structure of mosquitoes is the same as that of many other insects. • The different aerodynamic mechanisms of mosquitoes do not change the major aerodynamic derivatives. • The leg-spreading only have a small quantitative effect on the eigenvalues. Abstract The flight of mosquitoes is unusual compared with many other insects, such as fruit-flies and honey bees: mosquitoes fly with their legs spread; they also have rather short stroke amplitude, hence use different aerodynamic mechanisms to produce lift. Could their flight-stability properties be different from those of other insects? Here, we first measured wing kinematics and morphological parameters of two hovering mosquitoes, and then use the method of computational fluid dynamics to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis to study their stability properties. We found that their natural-mode structure is the same as that of many other insects: for the longitudinal motion, one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode; for the lateral motion: an unstable divergence mode, a stable oscillatory mode and a stable subsidence mode. The different aerodynamic mechanisms of mosquitoes do not change the major aerodynamic derivatives. The spread legs of mosquitoes have great effect on the moments of inertia and make the eigenvalue of the stable lateral mode much smaller. However, the leg-spreading has only a small quantitative effect on the unstable eigenvalues: the magnitudes of the eigenvalues in the two unstable modes, or the growth rate of the disturbances, are reduced by approximately 11%, compared to those calculated without considering the spread legs. [ABSTRACT FROM AUTHOR]

In order to improve the takeoff and landing aerodynamic characteristics of flying wing unmanned aircrafts, a novel low speed control device called the belly-flap is introduced. Low speed aerodynamic characteristics of the flying wing unmanned aircraft is studied by using CFD. The aerodynamic optimization design on the locations, deflection angles, and solidity of the belly-flap is carried out. The lift-off lift coefficient and moment coefficient are increased by the help of the belly-flap, and the takeoff and landing aerodynamic characteristics of the unmanned aircraft are improved. [ABSTRACT FROM AUTHOR]

In this study, we will give an overview of lessons learned during the radiometric calibration of the airborne, high-power Ka-band cloud radar on board the German research aircraft HALO. Within this context, a number of flight experiments over Europe and over the tropical and extra-tropical North-Atlantic have been conducted, where the ocean surface backscatter was used as an external reference reflector. Measurements of signal linearity and signal saturation complement this characterization. To validate the external calibration, joint flights of HALO and the French Falcon 20 aircraft, which was equipped with the RASTA cloud radar at 94 GHz and underflights of the spaceborne CloudSat at 94 GHz have been conducted. Finally, the influence of different radar wavelengths was explored with numerical studies. [ABSTRACT FROM AUTHOR]

This paper presents the development and extensive testing of the Transformer aircraft, a multimission UAV capable of symmetric and asymmetric span morphing. The UAV utilises a novel actuation system based on a rack and pinion mechanism to achieve span extensions up to 50%. The Transformer can morph symmetrically to enhance flight performance and asymmetrically to provide roll control. Extensive mechanical testing followed by wind-tunnel testing in the RJ Mitchell Wind-tunnel at the University of Southampton were conducted to ensure structural integrity and assess the behaviour of the UAV. Finally, a series of flight-testing were performed and the flight mechanics aspects associated with both symmetric and asymmetric span morphing were investigated. [ABSTRACT FROM AUTHOR]

Full scale aerodynamic wind tunnel testing, numerical simulation of high dimensional (full-order) aerodynamic models or flight testing are some of the fundamental but complex steps in the various design phases of recent civil transport aircrafts. Current aircraft aerodynamic designs have increase in complexity (multidisciplinary, multi-objective or multi-fidelity) and need to address the challenges posed by the nonlinearity of the objective functions and constraints, uncertainty quantification in aerodynamic problems or the restrained computational budgets. With the aim to reduce the computational burden and generate low-cost but accurate models that mimic those full order models at different values of the design variables, Recent progresses have witnessed the introduction, in real-time and many-query analyses, of surrogate-based approaches as rapid and cheaper to simulate models. In this paper, a comprehensive and state-of-the art survey on common surrogate modeling techniques and surrogate-based optimization methods is given, with an emphasis on models selection and validation, dimensionality reduction, sensitivity analyses, constraints handling or infill and stopping criteria. Benefits, drawbacks and comparative discussions in applying those methods are described. Furthermore, the paper familiarizes the readers with surrogate models that have been successfully applied to the general field of fluid dynamics, but not yet in the aerospace industry. Additionally, the review revisits the most popular sampling strategies used in conducting physical and simulation-based experiments in aircraft aerodynamic design. Attractive or smart designs infrequently used in the field and discussions on advanced sampling methodologies are presented, to give a glance on the various efficient possibilities to a priori sample the parameter space. Closing remarks foster on future perspectives, challenges and shortcomings associated with the use of surrogate models by aircraft industrial aerodynamicists, despite their increased interest among the research communities. [ABSTRACT FROM AUTHOR]

The flight mechanics, stability, and control of a helicopter undergoing rotor span morphing is examined. A span-morphing variant of the UH-60A Black Hawk helicopter at 18,300 lb gross weight is developed. A model-following dynamic inversion controller is implemented, and radius change is introduced as an additional feed-forward component into the control laws, with the aircraft model being updated with respect to flight condition. The flapping and inflow modes of the rotor exhibit significant movement as span changes, but relatively little movement is observed in the rigid-body modes. Closed-loop poles associated with the low-frequency aircraft modes are observed to be robust to change in rotor span, eliminating the need for model updates during the morphing process. The error compensators in the control laws use proportional-integral- derivative control for roll and pitch attitude and proportional-integral (PI) control for lateral and longitudinal ground speed, but require proportional-double integral compensator control for vertical speed and yaw rate to avoid altitude loss and heading drift observed with only PI control, during span morphing. Detailed simulations results are presented for 40 kt cruise, and velocities of 80 and 120 kt are also considered. From a baseline rotor radius of 26.8 ft, retraction to 22.8 ft, as well as extension to 31.5 ft, is considered, nominally over a 60-s duration. The controller is observed to regulate the aircraft operating state well over the nominal duration and is still effective when duration is reduced to 30 s. [ABSTRACT FROM AUTHOR]

Dynamic impact tests with a FAA Hybrid III 50th percentile crash dummy in seats with and without a stroking energyabsorbing mechanism were conducted to assess the effectiveness of memory foam cushions in mitigating impact to the occupant during an aircraft crash. Polyurethane foam (PU) cushions were also tested for comparison. The results obtained when using a rigid seat indicated that for an 8.3-m/s impact, lumbar spinal injury would occur. Memory cushions could reduce lumbar force by up to 34%. For an impact speed of 6 m/s, a memory cushion could mitigate the impact to a tolerable level, while the injury would still occur with the PU cushions. The results with the energy-absorbing seats showed that for an 8.3-m/s impact speed, the seat with over 125 mm (5 inches) stroking length is able to prevent injury. Relatively softer memory cushions reduced lumbar force by over 15% compared with the PU cushions. With a stoke length of 75 mm (3 inches), bottom-out occurred and occupant lumbar spinal injury would occur. Relatively higher stiffness memory cushions reduced lumbar force by approximately 20%. [ABSTRACT FROM AUTHOR]

The civil light helicopter domain has not fully benefited yet from the advantages system identification methods can offer. The aim of this paper is to show that system identification methods are mature enough to be successfully implemented in the civil helicopter domain. To achieve this goal, a Robinson R44 Raven II is identified in this work. The identification focuses on the hover trim condition. A lean frequency domain identification method is adopted. Furthermore, a new procedure is proposed to limit the sensitivity of the state-space minimization algorithm to initial parametric values and bounds. The resulting state-space model presents good predictive capabilities and is able to capture high-frequency rotor-body dynamics. The model is also validated with the help of a helicopter pilot by performing closed-loop control task maneuvers in theMPI CyberMotion Simulator. The overall validation shows that the implemented model is suitable for handling qualities studies, high-frequency control system designs, and realistic simulations that involve piloted closed-loop control tasks. [ABSTRACT FROM AUTHOR]

The paper describes a methodology to extract a linearized state-space dynamic inflowmodel from a generic and high-fidelity aerodynamic analysis for single- and coaxial helicopter rotor systems. Both hover and forward flight are studied, including maneuvering, and the results are demonstrated by a free-wake analysis. The proposed methodology, which is founded on a uniquely tailored single frequency analysis, is computationally efficient and provides the entire frequency-domain behavior of the wake inflow states. Besides being able to incorporate any advanced computational tool, the presentmethodology takes advantage of exact wake states and thus adequately encompasses high-frequency responses. The paper also presents an extension of the methodology to the case where states of higher harmonics are required and to the case of heaving, rolling, and pitching rotor disk. For a single-rotor system, the results resemble the well-known classical dynamic inflow model. For a coaxial rotor system in hover, the high mutual couplings between the rotors are clearly demonstrated and affect the resulting system matrices. An important feature of the present methodology lies in the fact that the entire formulation is a nondimensional one, and the inflow analysis is completely separated from the loads analysis, which enables a consistent generalization of the results. [ABSTRACT FROM AUTHOR]

The elastic deformation of modern projectiles with large slenderness ratio cannot be ignored with the increasing of flight speed and maneuverability. Unsteady Reynolds-averaged Navier–Stokes (URANS) Equations are solved through CFD technique in this paper. Based on the frame of unstructured mesh, techniques of rigid-motion mesh and inverse-distance-weighted (IDW) morphing mesh are adopted to treat the rigid motion caused by flight dynamics and flexible structure deformation due to aeroelasticity, respectively. Moreover, the six degree of freedom (SDOF) dynamic equations and static aeroelastic equation are solved through the aerodynamic coupling. Numerical results of both free flight case and aeroelastic case calculated by the in-house code agree well with the experimental data, validating the numerical method. A projectile model with X–X configuration is constructed to investigate the effect of elastic deformation on the flight dynamics. Comparison results show that the longitudinal oscillation is more affected by the elastic deformation than the centroid motion, and the oscillation cycle of the orientation angle increases. Furthermore, the trajectories of rigid models with various centroid locations are simulated, illustrating that the elastic deformation could move the aerodynamic center forward and weaken the margin of the static stability margin. In the end, detailed analysis and comparison of the pressure distribution indicates the mechanism by which the elastic deformation leads to the movement of the aerodynamic center and changes the flight dynamic characteristics of the flexible projectile. [ABSTRACT FROM AUTHOR]

Over the last decades, there has been great interest in understanding the aerodynamics of flapping flight and development of flapping wing Micro Air Vehicles (FWMAVs). The camber deformation and twisting has been demonstrated quantitatively in a number of insects, but making artificial wings that mimic those features is a challenge. This paper reports the development and characterization of artificial wings that can reproduce camber and twisting deformations. By replacing the elastic material at the wing root vein, the root vein would bend upward and inward generating an angle of attack, camber, and twisting deformations while the wing was flapping due to the aerodynamic forces acting on the wing. The flapping wing apparatus was employed to study the flexible wing kinematics and aerodynamics of real scale insect wings. Multidisciplinary experiments were conducted to provide the natural frequency, the force production, three-dimensional wing kinematics, and the effects of wing flexibility experienced by the flexible wings. The results have shown that the present artificial wing was able to mimic the two important features of insect wings: twisting and camber generation. From the force measurement, it is found that the wing with the uniform deformation showed the higher lift/power generation in the flapping wing system. The present developed artificial wing suggests a new guideline for the bio-inspired wing of the FWMAV. [ABSTRACT FROM AUTHOR]

We present the circuitry design and plans of a photogate and accompanying Arduino board with coding for a data recording program used with a flight mill apparatus. These are being used to test the flight capacity of Halyomorpha halys Stål (Hemiptera: Pentatomidae) under various environmental conditions. [ABSTRACT FROM AUTHOR]

The development of physics based analysis to predict the hover performance of a micro rotor system meant for a hover capable micro air vehicle for studying the role of blade geometric parameters (such as planform, twist etc.) is discussed. The analysis is developed using blade element theory using lookup table for the sectional airfoil properties taken from literature. The rotor induced inflow is obtained using blade element momentum theory. The use of taper seems beneficial in improving the hover efficiency for lower values of thrust coefficient. For rotors operating at high thrust conditions, high negative twist is desirable. There is no unique blade geometry which performs well under all thrust conditions. This well validated analysis can be used for design of hover capable micro air vehicles. [ABSTRACT FROM AUTHOR]

Operational data recorded from five agricultural aircraft are used to compare their flight loads. Four of the airframes were used as single-engine air tankers, whereas the fifth was flown exclusively for agricultural applications. The data collectively consisted of 454 h of flight time from firefighting and 100 h from the agricultural operation. Gust and maneuver vertical load factors are separated using the two-second rule, and their cumulative occurrences are presented per 1000 h. The flight load spectra are presented for the overall flight and for individual phases. Gust loads are shown to behave similarly for all missions. Air tankers are shown to be subject to a large load factor during the drop phase, which occurs once or twice per flight. In the case of agricultural missions, the positive load factors do not reach very high values but occur at much larger frequencies. It is also shown that the load factor alone is not a sufficient indicator of the stresses exerted on the structure due to the large changes in the aircraft weight. [ABSTRACT FROM AUTHOR]

A computational method involving evolutionary-based optimization to provide an optimal set of higher-harmonic deployment schedules for a multisegment trailing-edge flap is investigated. The trailing-edge flap is added to the UH-60A's rotor, with the flap's span, deflection angles, and start/end deployment azimuth positions all optimized to minimize the total rotor power and the resulting hub vibratory loads. The formal optimization effort is carried out through the coupling of a comprehensive analysis code and one of two evolutionary algorithm-based optimizers. With regard to a single-segment flap, peak power savings over the flight envelope reached 9.5% (at an advance ratio of 0.30) with associated out-of-plane and in-plane hub vibration reductions of 66 and 22%, respectively. The dual-segment trailing-edge flap optimization with a span limitation yielded power savings of 8.9% at the same flight condition. Multi-objective optimizations were performed at a target flight condition with an advance ratio of 0.3 for a total of four objectives: minimizing rotor power and all three hub vibratory loads. One optimum solution found 6.7% power savings, 68% out-of-plane hub vibration reductions, and 53% in-plane hub vibration reductions. [ABSTRACT FROM AUTHOR]

Within an immunity-based architecture for aircraft fault detection, identification and evaluation, a structured, non-self approach has been designed and implemented to classify and quantify the type and severity of different aircraft actuators, sensors, structural components and engine failures. The methodology relies on a hierarchical multi-self strategy with heuristic selection of sub-selves and formulation of a mapping logic algorithm, in which specific detectors of specific selves are mapped against failures based on their capability to selectively capture the dynamic fingerprint of abnormal conditions in all their aspects. Immune negative and positive selection mechanisms have been used within the process. Data from a motion-based six-degrees-of-freedom flight simulator were used to evaluate the performance in terms of percentage identification rates for a set of 2D non-self projections under several upset conditions. [ABSTRACT FROM AUTHOR]

Comprehensive aircraft observations are used to characterise surface roughness over the Arctic marginal ice zone (MIZ) and consequently make recommendations for the parametrisation of surface momentum exchange in the MIZ. These observations were gathered in the Barents Sea and Fram Strait from two aircraft as part of the Aerosol-Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) project. They represent a doubling of the total number of such aircraft observations currently available over the Arctic MIZ. The eddy covariance method is used to derive estimates of the 10m neutral drag coefficient (CDN10) from turbulent wind velocity measurements, and a novel method using albedo and surface temperature is employed to derive ice fraction. Peak surface roughness is found at ice fractions in the range 0.6 to 0.8 (with a mean interquartile range in CDN10 of 1.25 to 2.85×10-3/. CDN10 as a function of ice fraction is found to be well approximated by the negatively skewed distribution provided by a leading parametrisation scheme (Lüpkes et al., 2012) tailored for sea-ice drag over the MIZ in which the two constituent components of drag - skin and form drag - are separately quantified. Current parametrisation schemes used in the weather and climate models are compared with our results and the majority are found to be physically unjustified and unrepresentative. The Lüpkes et al. (2012) scheme is recommended in a computationally simple form, with adjusted parameter settings. A good agreement holds for subsets of the data from different locations, despite differences in sea-ice conditions. Ice conditions in the Barents Sea, characterised by small, unconsolidated ice floes, are found to be associated with higher CDN10 values - especially at the higher ice fractions - than those of Fram Strait, where typically larger, smoother floes are observed. Consequently, the important influence of sea-ice morphology and floe size on surface roughness is recognised, and improvement in the representation of this in parametrisation schemes is suggested for future study. [ABSTRACT FROM AUTHOR]

In this paper, a new control structure for a quad-rotor helicopter that employs the least squares method is introduced. This proposed algorithm solves the overdetermined problem of the control input for the translational motion of a quad-rotor helicopter. The algorithm allows all six degrees of freedom to be considered to calculate the control input. The sliding mode controller is applied to achieve robust tracking and stabilization. A saturation function is designed around a boundary layer to reduce the chattering phenomenon that is a common problem in sliding mode control. In order to improve the tracking performance, an integral sliding surface is designed. An energy saving effect because of chattering reduction is also evaluated. First, the dynamics of the quad-rotor helicopter is derived by the Newton–Euler formulation for a rigid body. Second, a constant plus proportional reaching law is introduced to increase the reaching rate of the sliding mode controller. Global stability of the proposed control strategy is guaranteed based on the Lyapunov׳s stability theory. Finally, the robustness and effectiveness of the proposed control system are demonstrated experimentally under wind gusts, and are compared with a regular sliding mode controller, a proportional–differential controller, and a proportional–integral–differential controller. [ABSTRACT FROM AUTHOR]

The article discusses improvement in the performance of the optimal two stage extended Kalman filter using an iterated optimal two-stage extended Kalman filter. Topics discussed include influence of disturbances such as turbulence, use of flight data to validate the proposed approaches for inertial measurement unit (IMU) fault identification, and influence of the IMU sensor faults.

In recent years European airspace has become increasingly congested and airlines can now observe that en-route capacity constraints are the fastest growing source of flight delays. In 2010 this source of delay accounted for 19% of all flight delays in Europe and has been increasing with an average yearly rate of 17% from 2005 to 2010. This paper suggests and evaluates an approach to how disruption management can be combined with flight planning in order to create more proactive handling of the kind of disruptions, which are caused by congested airspace. The approach is evaluated using data from a medium size European carrier and estimates a lower bound saving of several million USD. [ABSTRACT FROM AUTHOR]

The paper presents the problem of searching for the right amount of time needed to wait for a passenger who is late for boarding a plane. This problem, although practically ignored by airline and handling agents' operational manuals, is common and very important for flight punctuality, and thus for both passenger satisfaction and the financial performance of air transport companies. The discrete Dynamic Programming task for finding the minimum amount of time wasted on waiting for a late passenger, depending on the moment in time in which the passenger arrives, is formally defined in this paper. The task is solved based on sample data. Dependence of the results on the average period of time needed to find the luggage of a passenger who did not arrive for boarding is examined. The paper also presents the preliminary results of the impact of the random variable describing the arrival time of the last passenger on the moment when the decision to stop waiting should be made. The function, which allows to determine the expected value of that lost time, was specified for different moments of the end of waiting by taking into account the random characteristics of the arrival of the last passenger. The obtained results show that in each of the analyzed cases there is a global minimum of that function. The moment for which the minimum occurs can be considered as the optimal (in terms of time wasted on waiting) moment to stop waiting for the late passenger. [ABSTRACT FROM AUTHOR]

The Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) provides measurements over the wavelength range 5 to 28:5 µm. MIRI has, within a single "package," four key scientific functions: photometric imaging, coronagraphy, single-source low-spectral resolving power (R ~ 100) spectroscopy, and medium-resolving power (R ~ 1500 to 3500) integral field spectroscopy. An associated cooler system maintains MIRI at its operating temperature of <6:7 K. This paper describes the driving principles behind the design of MIRI, the primary design parameters, and their realization in terms of the "as-built" instrument. It also describes the test program that led to delivery of the tested and calibrated Flight Model to NASA in 2012, and the confirmation after delivery of the key interface requirements. [ABSTRACT FROM AUTHOR]

I offer a novel solution to Zeno's paradox of The Arrow by introducing nilpotent infinitesimal lengths of time. Nilpotents are nonzero numbers that yield zero when multiplied by themselves a certain number of times. Zeno's Arrow goes like this: during the present, a flying arrow is moving in virtue of its being in flight. However, if the present is a single point in time, then the arrow is frozen in place during that time. Therefore, the arrow is both moving and at rest. In 'Zeno's Arrow, Divisible Infinitesimals, and Chrysippus,' White suggests using an infinitesimal value as the length of the present. Contra Zeno, this allows the arrow to be moving in the present, rather than frozen in place. In this paper, I follow the basic outline of White's solution but argue that his solution suffers from arbitrariness and a related theoretical artificiality in relation to the system of infinitesimals he invokes, viz. in relation to the hyperreal infinitesimals of nonstandard analysis. After arguing that any solution to the paradox must satisfy certain theoretical requirements, I examine White's solution alongside two nilpotent solutions. One of these solutions is inspired by F.W. Lawvere's Smooth Infinitesimal Analysis and the other is inspired by Paolo Giordano's ring of Fermat Reals. I argue that Giordano's nilpotents supply the best answer to Zeno's paradox. [ABSTRACT FROM AUTHOR]

Purpose -- This paper aims to propose a method for measuring the rotation of moving body during parabolic flight using camera. Design/methodology/approach -- An orthogonal matrix used to calculate the Euler angles of rotation is solved by means of singular value decomposition. The translation velocity and position of moving body are measured by a binocular camera system. Findings -- The experiment is executed in a jet aircraft to simulate micro-gravity during parabolic flight. And the human moving body is regarded as a rigid body. The results show that this method can calculate the angles effectively. Practical implications -- This work is useful for calculation and monitoring body's motion in space. Originality/value -- The paper gives a method which measures the rotation of a rigid body under the microgravity by a binocular camera to modify the measurement error of the interferometer. [ABSTRACT FROM AUTHOR]

An aircraft and landing gear loads model was developed to assess the Margin of Safety (MS) in main landing gear components such as the main fitting, sliding tube and shock absorber upper diaphragm tube. Using a technique of Bayesian sensitivity analysis, a number of flight parameters were varied in the aircraft and landing gear loads model to gain an understanding of the sensitivity of the MS of the main landing gear components to the individual flight parameters in symmetric two-point landings. The significant flight parameters to the main fitting MS, sliding tube bending moment MS and shock absorber upper diaphragm tube MS include: longitudinal tyre-runway friction coefficient, aircraft vertical descent velocity, aircraft Euler pitch angle and aircraft mass. It was also shown that shock absorber servicing state and tyre pressure do not contribute significantly to the MS. [ABSTRACT FROM AUTHOR]

To reduce aircraft emissions to the atmosphere, the fuel burn from aircraft has to be reduced. For long flights, the cruise is the phase where the most significant reduction can be obtained. A new horizontal profile optimisation methodology to achieve lower emissions is described in this article. The impact of wind during a flight can reduce the flight time, either by taking advantage of tailwinds or by avoiding headwinds. A set of alternative trajectories are evaluated to determine the quickest flight time, and therefore, the lowest fuel burn. To determine the expected amount of fuel reduction, the performance databases used on actual FMS devices, were used. These databases represent the flight performance of commercial aircraft. [ABSTRACT FROM AUTHOR]

The paper presents the estimation of lateral-directional aerodynamic derivatives (parameters) using conventional and neural based methods from real flight data of Hansa-3 aircraft. The conventional methods such as least squares (LS) and maximum likelihood (ML) require an a priori postulation of mathematical model to estimate the parameters. Whereas the neural-based method such as Neural-Gauss-Newton (NGN) is an algorithm that utilises feed forward neural network and Gauss-Newton optimisation to estimate the parameters and does not require any a priori postulation of mathematical model or solution of equations of motion. In the paper, the LS, ML and NGN methods are applied to lateral-directional flight data in order to estimate parameters. The results obtained in terms of lateral-directional aerodynamic derivatives are reasonably accurate to establish LS, ML and NGN as parameter estimation methods along with NGN method having an additional advantage of non-requirement of a priori mathematical model. The paper also highlights the effect of different types of control inputs on parameter estimation. For this, three types of control inputs were used to generate real flight data. The ailerons and rudder were deflected in the first, the ailerons were deflected while keeping rudder at trim condition in the second and the rudder was deflected while keeping ailerons at trim condition in the third type of control input to generate the real flight data. The paper presents the effect of three different types of control inputs in terms of aerodynamic parameters estimated through conventional and neural based methods using flight data generated through these inputs. [ABSTRACT FROM AUTHOR]

Within this work a monolithically integrated low-power dual-lock-in amplifier (LIA) with integrated photodiodes is presented. This structure as a whole defines an opto-sensitive single-pixel sensor, being fabricated in a 0.35 µm 1P4M CMOS process with integrated PIN photodiodes. Since two correlators are exploited, the sensor is able to detect the modulated optical signal in the frequency domain, as well as its phase, which can be used in numerous applications. Among the others, the time-of-flight and interferometry based distance measurement system can benefit from this structure. The single pixel occupies an active area of 120 × 100 µm at 58 % fill factor. The measurement results show that a dynamic range of 27 dB could be achieved at a modulation frequency of 10 MHz. While the bandwidth of the LIA is adjustable, a signal can be detected up to a modulation frequency of 35 MHz and beyond dependent on the received optical power. [ABSTRACT FROM AUTHOR]

The force equalization of a hybrid actuation system combining one servo-hydraulic actuator and one electro-mechanical actuator operated in position control and in active/active mode is addressed for safety critical applications such as primary flight controls. In a first step, an accurate virtual test bench is built to facilitate the analysis of force fighting and the assessment of the performance and robustness of the proposed force equalization strategies. It is validated from real experiments performed for the aileron actuator of a single-aisle commercial aircraft. Static force equalization is achieved first by adding equalization offsets in the position control loops as a function of the integral of the force difference between actuators. In order to keep a high level of segregation, the authority for this action is limited to 4% of the total actuator stroke. The dynamic force equalization is performed by forcing the two actuators to follow the same path. Thus, a trajectory generator is introduced to output the required position, velocity and acceleration from the position set point with realistic reproduction of the actuator power limits. Feedforward actions are used to compensate the major and invariant effects such as servo-hydraulic actuators functional flow and electro-mechanical actuator inertial torque. In this way, the pursuit errors are significantly reduced without decreasing robustness. Then, the accurate virtual test bench is used to assess the robustness of the force equalization strategy by analyzing the sensitivity of performance indicators to parameters and operating conditions. It is shown that the proposed force equalization scheme meets all the requirements, including segregation, robustness and simplicity. [ABSTRACT FROM PUBLISHER]

A dynamic model of a twin ducted-fan vertical takeoff and landing aircraft, the Martin Jetpack, has been developed to study and improve the understanding of the flight mechanics involved with this novel aircraft concept. This article describes the flight mechanics of a twin ducted-fan aircraft and explains in detail the modeling of the forces and moments contributed by the twin ducted-fans, body aerodynamics, control surfaces, gyration, and landing gear interactions. Also, a novel model for the movement of the duct center of pressure has been developed, which allows for the complex duct pitching moment to be predicted. Employing the conventional aircraft modeling methodology, a system of ordinary differential equations that describes the behavior of the aircraft is developed. The equations are solved in real-time using MATLAB–Simulink software to simulate the response to given inputs. A comparison of the flight data with both steady-state (trimmed) and dynamic simulations shows good agreement, which validates the novel duct center of pressure model. The validated model allows the aircraft designer/engineer to efficiently evaluate the sizing of key aerodynamic features and various control methodologies to aid in the design and flying of the Martin Jetpack. [ABSTRACT FROM PUBLISHER]

When an observer lifts two objects with the same weight but different sizes, the smaller object is consistently reported to feel heavier than the larger object even after repeated trials. Here we explored the effect of reduced and increased gravity on this perceptual size-mass illusion. Experiments were performed on board the CNES Airbus A300 Zero-G during parabolic flights eliciting repeated exposures to short periods of zero g, 0.16 g, 0.38 g, one g, and 1.8 g. Subjects were asked to assess perceived heaviness by actively oscillating objects with various sizes and masses. The results showed that a perceptual size-mass illusion was clearly present at all gravity levels. During the oscillations, the peak arm acceleration varied as a function of the gravity level, irrespective of the mass and size of the objects. In other words we did not observe a sensorimotor size-mass illusion. These findings confirm dissociation between the sensorimotor and perceptual systems for determining object mass. In addition, they suggest that astronauts on the Moon or Mars with the eyes closed will be able to accurately determine the relative difference in mass between objects. [ABSTRACT FROM AUTHOR]

Abstract: Mathematical representations of human control behaviour have played a very important part in manned aviation, especially in the definition of aircraft handling qualities requirements. New challenges posed by advances in aerospace technologies, such as fly-by-wire flight control, large flexible airframes and flight simulation, have led to increasingly complex mathematical representations of pilot behaviour. However, all these areas tend to be investigated separately and in parallel with human factors studies. The motivation behind this review is to promote discussion between the flight dynamicists and other engineers and scientists on the methods of modelling and simulation of today's pilot. A review of pilot model components used for flight control system design that focuses specifically on physiological and manual control aspects is presented in this paper. Models of varying complexity that are considered to be the state-of-the-art within the flight control and handling qualities engineering community are discussed. These include simple sensory models, biomechanics models and complex nonlinear pilot manual control models. In each area, the challenges posed by inter-subject variations and the need to understand the aircraft as a complex man–machine system are highlighted. However, the presented discussion is limited to a thin slice of this field thought to be fundamental to modelling manual control dynamics exhibited by aircraft pilots. [Copyright &y& Elsevier]

Abstract: Fluid shifts toward the upper body may cause differences in the blood flow of the upper and lower limbs under microgravity compared to that under gravity conditions. Blood flow was compared between the upper and lower limbs in a sitting position under different gravity levels generated by parabolic flight of an airplane. The blood flow of both the upper and lower limbs increased immediately after 0 G. Thereafter, the blood flow of both the upper and lower limbs returned to the normal level observed under 1 G. The blood flow of the upper limbs remained at the normal level during 0 G and after 1.5 G, whereas the blood flow of the lower limbs decreased during 0 G. The decreased blood flow of the lower limbs recovered to the normal level after 1.5 G. We concluded that decreased blood flow, under microgravity conditions, is observed in the lower limbs, but not in the upper limbs. [Copyright &y& Elsevier]

From flight data obtained on a fruit bat, Cynopterus brachyotis, a kinematic model for straight-line flapping motion is extracted and analyzed in a computational fluid dynamics (CFD) framework to gain insight into the complexity of bat flight. The intricate functional mechanics and architecture of the bat wings set it apart from other vertebrate flight. The extracted kinematic model is simulated for a range of Reynolds numbers, to observe the effect these phenomena have on the unsteady transient mechanisms of the flow produced by the flapping wings. The Strouhal number calculated from the data is high indicating that the oscillatory motion dominates the flow physics. From the obtained data, the bat exhibits fine control of its mechanics by actively varying wing camber, wing area, torsional rotation of the wing, forward and backward translational sweep of the wing, and wing conformation to dictate the fluid dynamics. As is common in flapping flight, the primary force generation is through the attached unsteady vortices on the wing surface. The bat through varying the wing camber and the wing area modulates this force output. The power requirement for the kinematics is analyzed and correlated with the aerodynamic performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The present work is concerned with the shape optimization of flapping wings in forward flight. The analysis is performed by combining a gradient-based optimizer with the unsteady vortex lattice method (UVLM). We describe the UVLM simulation procedure and provide the first methodology to select properly the mesh and time-step sizes to achieve invariant UVLM simulation results under mesh refinement. Our objective is to identify a set of optimized shapes that maximize the propulsive efficiency, defined as the ratio of the propulsive power over the aerodynamic power, under lift, thrust, and area constraints. Several parameters affecting flight performance are investigated and their impact is described. These include the wingʼs aspect ratio, camber line, and curvature of the leading and trailing edges. This study provides guidance for shape design of engineered flying systems. [Copyright &y& Elsevier]

Aeroelastic and aero-viscoelastic phenomena arising from the high flexibility of modern flight vehicles are examined, and governing relations are formulated and solved. In particular, the :ime dependent flight velocities associated with maneuvers and with in-plane bending are considered, which necessitate new derivations of the Theodorsen function, unsteady aerodynamic relations and ;quations of motion. Under these conditions, simple harmonic motion (SHM) is no longer achievable md different flutter criteria based directly on motion stability are presented. The viscoelastic problem, af importance to composites and other media, is formulated in terms of integral partial differential îquations with variable nonlinear coefficients. Their solutions and evaluations are discussed in detail. 3ne interesting departure from linear elastic and/or viscoelastic constant flight velocity responses emerged which, for some configurations, indicates the presence of flutter in the in-plane bending node while the other bending (plunging) and torsional modes both remain stable. [ABSTRACT FROM AUTHOR]