Increasing Flight Speed Research Articles

Enhanced flight performance and adaptive evolution of Mesozoic giant cicadas.

Insects have evolved diverse ecological flight behaviors and adaptations that played a key role in their large-scale evolutionary patterns. However, the evolution of their flight performance is poorly understood because reconstructing flight abilities of extinct insects is highly challenging. Here, we propose an integrated approach to reveal the evolution of flight performance of Palaeontinidae (giant cicadas), a Mesozoic arboreal insect clade with large bodies and wings. Our analyses unveil a faunal turnover from early to late Palaeontinidae during the latest Jurassic-earliest Cretaceous, accompanied by a morphological adaptive shift and remarkable improvement in flight abilities including increased flight speed and enhanced maneuverability. The adaptive aerodynamic evolution of Palaeontinidae may have been stimulated by the rise of early birds, supporting the hypothesis of an aerial evolutionary arms race (Air Race) between Palaeontinidae and birds. Our results provide a potential example of predator-induced morphological and behavioral macroevolution and contribute to our understanding of how powered flight has shaped animal evolution.

Effects of Wake Separation on Aerodynamic Interference Between Rotors in Urban Low-Altitude UAV Formation Flight

In recent years, unmanned aerial vehicle (UAV) formation flight has become an effective strategy for urban air mobility (UAM). However, close rotor separation during formation flight leads to complex aerodynamic interference between rotors, significantly affecting UAV flight performance and operational safety. This study systematically examines the effects of axial and lateral rotor separation on the rotor’s thrust performance through wind tunnel experiments. The tests simulate horizontal, vertical, and hovering states by generating relative airflow in the wind tunnel, focusing primarily on the thrust coefficient changes of the bottom rotor at various separations. The results are compared with a single rotor operating under the same conditions without wake interference. Additionally, computational fluid dynamics (CFD) simulations using the Fluent software were conducted to investigate the effect of wake interactions by analyzing the velocity flow field between the two rotors in different separations. Both the experimental and simulation results demonstrate that rotor aerodynamic performance is notably influenced by wake interactions. Under hovering and vertical states, substantial aerodynamic interference occurs in the region directly beneath the top rotor, within 1D ≤ Z ≤ 3D. This interference gradually diminishes as the rotor separation increases. Additionally, the thrust coefficient of the bottom rotor decreases with increasing flight speed due to the wake, and at higher flight speeds, the wake tends to contract. When the lateral separation is X = 0D, the mid-sectional flow field of the two rotors exhibits symmetry; however, with lateral separation, the symmetry of the bottom rotor’s wake velocity field is disrupted. During the horizontal flight, the rotor wake tilts backward due to the relative airflow, and the extent of this influence is governed by both rotor rotational speed and flight velocity. Therefore, when UAVs operate in formation, it is crucial to account for these factors affecting aerodynamic performance, and rotor separation must be optimized to enhance flight safety and efficiency.

Computational fluid dynamics analysis of aerodynamic characteristics in long-endurance unmanned aerial vehicles

Long-endurance unmanned aerial vehicles (UAVs) play an increasingly important role in various aspects of societal life. In response to the national emphasis on air force development, a study on the aerodynamic characteristics of long-endurance UAVs was conducted. This paper utilizes SolidWorks software to construct a geometric model based on the MQ-9 UAV, and a CFD method to establish a simulation model for UAV cruising flight. The aerodynamic coefficients, required thrust, and total mass during UAV cruise were calculated, and the variation of aerodynamic coefficients as airflow passes through the UAV was described. A comparative analysis was performed on the effects of different angles of attack, flight speeds, and flight altitudes on aerodynamic efficiency. The study results indicate that at an altitude of 10 km, with a 0° angle of attack, the UAV achieves a lift coefficient of 0.8888, a drag coefficient of 0.0679, and a lift-to-drag ratio of 13.0988. The required thrust is approximately 2236 N, and the total flight mass is approximately 3090 Kg. The angle of attack has the greatest impact on aerodynamic efficiency, followed by flight altitude, while flight speed has the least impact on aerodynamic performance. The lift-to-drag ratio initially increases sharply and then decreases rapidly with increasing angle of attack. It is recommended to control the angle of attack within the range of 0°–6°. The lift-to-drag ratio increases slowly with increasing flight speed, suggesting that the flight speed should be maintained near the maximum cruise speed. The lift-to-drag ratio generally decreases with increasing flight altitude, and it is recommended to maintain the flight altitude within the range of 9 km–11 km.

Aerodynamic interference and unsteady loads for a trimming intermeshing rotor compound propeller helicopter at level forward flight

Traditional trim methods for isolated rotor helicopters are not suitable for intermeshing rotor compound propeller helicopters (IRcPHs) due to inherent structural differences. This study aims to establish a novel trim method for an intermeshing rotor with an auxiliary propeller. First, the relationship between the rotor cyclic pitch and the flapping response in the fully articulated rotor system with hinged extension is derived. The study then formulates the equilibrium state equations and the corresponding flight conditions for trimming the IRcPH in level forward flight. In addition, the unsteady vortex lattice method is employed to calculate the periodic averaging states on the rotor disk and correct for induced losses in flight dynamics. Finally, the paper focuses on the aerodynamic interference, blade–vortex interaction, and harmonic load patterns of the IRcPH, serving as a guide for rotor active control systems. Results show that the positions of the mutual aerodynamic interference occur constantly at 160° and 340° azimuths on the intermeshing rotor disk, serving as the phase basis for suppressing vibration. Moreover, the propeller enters the comfort zone as the forward flight speed increases, and the loads only have frequency orders of (2/nw)/rev with respect to the main frequency of the intermeshing rotor.

Developmental plasticity of melanisation in a beetle reveals sex‐specific responses and performance costs

Abstract Dark pigmentation of adults resulting from cold exposure during development is ubiquitous among insects. Yet the costs associated with the developmental plasticity of melanisation have been explored only for a handful of species. We explored two hypotheses relating to colour plasticity of insects. First, if melanin pigments are costly to synthesise and require allocation of resources, increased melanisation should be negatively associated with performance traits (the cost hypothesis). Second, given the positive association between melanisation and immune responses or desiccation resistance in some species, melanisation and performance may co‐vary positively (the positive covariance hypothesis). Furthermore, given the typical differences in reproductive effort and activity between females and males, we expect these performance–melanisation relationships to differ between sexes. We assessed whether temperature‐induced melanisation of the globally invasive beetle Harmonia axyridis f. succinea (Pallas) (Coleoptera: Coccinellidae) was related to standard metabolic rate and flight performance while accounting for developmental temperature and family affiliation. Melanisation explained little variation in standard metabolic rate at most temperatures tested (15, 20, 25, 30 and 35°C). For flight performance and after the cold‐rearing regime, lighter coloured female beetles had increased flight speed compared with darker females, whereas the opposite was found in males. In addition, in warm‐reared beetles, darker individuals had lower mean flight speeds. The results suggest that at least some flight performance costs are associated with developmentally induced melanisation, supporting the cost hypothesis. Disparities in these relationships between males and females suggest that the drivers underlying variation in melanisation differ between sexes. Importantly, variation in melanisation was more acute for females reared in the warm regime compared with equally treated males and to cold‐reared individuals. We propose new directions to test hypotheses pertaining to the maintenance of colour variation and performance between sexes in nature.

植保无人机喷头角度对雾滴沉积分布的影响

During the field application of pesticides by plant protection UAV, due to the interference of meteorological factors or operating parameters, the deposition effect of droplets is poor. In order to explore the impact of the nozzle angle of plant protection UAV on droplet deposition distribution, this article is based on field experiments and collects data on different flight speeds (1, 3, 5 m/s) and nozzle angles (±60°, ±45°, ±30°, 0°), and performs variance analysis and regression analysis on the test results. The results showed that adjusting the nozzle angle had a significant effect on the amount of droplet deposition and deposition uniformity. Compared with 0°, the nozzle angle of -30° increased the amount of deposition by 76.94% and 61.04% at flight speeds of 1.2 m/s and 3 m/s, respectively. The flight speed had a significant effect on the amount of droplet deposition, and the increase in flight speed decreased the amount of droplet deposition by 55.97%-77.06% and had no significant effect on the uniformity of droplet deposition. This study provides a reference for improving the droplet deposition effect of plant protection UAV field pesticide application operations.

Computational analysis of the fluid–structure interactions of a synthetic badminton shuttlecock

Fluid–structure interactions of a synthetic badminton shuttlecock at various flight speeds are investigated computationally. The cork of the shuttlecock is held fixed and its skirt is free to deform. The cross-sectional area of the skirt decreases with an increase in flight speed leading to a significant reduction in the drag compared to that for an undeformed shuttlecock. Four regimes of deformation, with an increase in speed, are identified. The deformation is steady and axisymmetric in regime 1. Beyond a certain speed, which is referred to as “buckling speed,” the deformation is in regime 2. The skirt assumes a non-axisymmetric shape with a significant increase in its rate of deformation with speed. It undergoes vibration in regime 3. The amplitude of vibration increases with increased speed. In regime 4, the vibrations are modulated atop a lower frequency wave that travels circumferentially along the skirt. Compared to a rigid shuttlecock at the same flow speed, the streamwise vortex structures inside the skirt are weaker in a deformed shuttlecock. The decrease in the drag coefficient with an increase in speed is due to a decrease in the cross-sectional area of the skirt as well as a reduction in the entrainment of the flow through the gaps in the skirt area. The computational results are in good agreement with the available experimental measurements. The effect of the elastic modulus of the material and various structural reinforcements is studied.

MODEL OF THE FLAT FAIRING ANTENNA DIELECTRIC LAYER WITH AERODYNAMIC HEATING

To protect the antenna systems of modern aircraft, radio-transparent dielectric fairings are widely used. At low flight speeds, when designing and evaluating the characteristics of the fairing-antenna, it is assumed that the dielectric constant is a constant value and does not depend on the aircraft's flight speed. As the flight speed increases, as a result of aerodynamic heating of the fairing, its dielectric permeability changes, which leads to errors in the processing of received signals. Currently, to take into account the effect of dielectric coatings heating when designing antenna systems, the temperature of the fairing wall is averaged over its thickness. This method during maneuvering and at high flight speeds leads to large errors in determining the characteristics of the fairing antenna since the nature of the temperature distribution along the thickness of the fairing wall is not taken into account. A new approach to the analysis of dielectric layers with their uneven heating along the thickness is proposed. The obtained results make it possible to adjust the signal processing algorithms with analog and digital matrices, as a result of taking into account the emerging heat flows affecting the fairing of the aviation antenna, which leads to the improvement of the characteristics of the antenna systems.

Mosquito swarms shear harden

Recently Cavagna et al. (Sci Rep 13(1): 8745, 2023) documented the swarming behaviors of laboratory-based Anopheles gambiae mosquitoes. Here key observations from this 3D-video tracking study are reproduced by a minimally structured (maximum entropy) stochastic trajectory model. The modelling shows that in contrast with midge swarms which are a form of collective behavior, unperturbed mosquito swarms are more like collections of individuals that independently circulate around a fixed location. The modelling predicts the observed response Anopheles gambiae mosquitoes in wild swarms to varying wind speeds (Butail et al. in J Med Entomol 50(3): 552–559, 2013). It is shown that this response can be attributed to shear hardening. This is because mosquitoes are found to be attracted to the centre of the swarm by an effective force that increases with increasing flight speed. Mosquitoes can therefore better resist the influence of environmental disturbances by increasing their flight speeds. This contrasts with other emergent mechanical-like properties of swarming which arise accidentally without a change in an individual’s behavior. The new results add to the growing realization that perturbations can drive swarms into more robust states.

Variability of small multirotor aircraft noise measurements

Experimental procedures are developed to measure and characterize the variability of noise radiated by small multirotor aircraft during outdoor flight. These procedures were applied to characterize the noise of a Tarot X8 octocopter. Large (up to 10 dB) variations in A-weighted sound pressure level (SPL) are observed between repeated measurements of the same flight conditions. However, the measured peak SPLs are found to be insensitive to changes in flight speed. This results in a reduction of sound exposure level with increasing flight speed. The A-weighted sound exposure level varies by as much as 6 dB across repeated overflights. Variability in noise is assessed both across repeated runs of the same condition and within a run using an array of microphones parallel to the flight track. Variability is found to increase as the distance between the microphone and aircraft increases. Variations within a run are significant (2.2 dB) and are similar to the variation in peak SPLs observed between runs (2.5 dB).

Research on operating characteristics of single-spool turbojet enginewith the afterburner AL-21F

The single-spool, single-thread, turbojet engine with afterburner AL-21F has been used on fighter aircraft for a long time, but there are few studies on this engine in Vietnam. This article uses the theoretical approach, calibrates according to the technical description and actual operation, combined with specialised software such as GasTurb and GSP to calculate engine thermodynamic parameters in some actual flight conditions. The obtained results showed that, when the flight speed increases, the specific fuel consumption increases linearly, while the initial engine thrust decreases and reaches the minimum value at M=0.3÷0.5, then continue to increase and reach the maximum at the speed limit. When increasing the height, the speed and regulating spool speed of the engine remain the same, the engine thrust decreases as well as the specific fuel consumption increases. When increasing the rotor rotation speed, the engine thrust increases linearly but the specific fuel consumption decreases gradually and remains almost the same at engine rpm above 85%. The results allowed for a better understanding of the operating process of the AL-21F engine in particular and turbojet engines in general or used to build simulation models operating close to reality.

Aerodynamic explanation of flight speed limits in hawkmoth-like flapping-wing insects

It has long been unknown why the hawkmoth's maximum forward flying speed is much lower than the theoretical prediction based on its body mass. Our computational fluid dynamics study revealed that as a hawkmoth's flight speed increases, its wings inevitably generate a significant amount of negative lift during the upstroke, which renders the hawkmoth incapable of sustaining steady forward flight. A similar trend has also been observed for other insects, including fruit flies and bumblebees. However, birds and other flying vertebrates are able to overcome this limitation by flexing their wings during the upstroke.

Gull dynamic pitch stability is controlled by wing morphing

Birds perform astounding aerial maneuvers by actuating their shoulder, elbow, and wrist joints to morph their wing shape. This maneuverability is desirable for similar-sized uncrewed aerial vehicles (UAVs) and can be analyzed through the lens of dynamic flight stability. Quantifying avian dynamic stability is challenging as it is dictated by aerodynamics and inertia, which must both account for birds' complex and variable morphology. To date, avian dynamic stability across flight conditions remains largely unknown. Here, we fill this gap by quantifying how a gull can use wing morphing to adjust its longitudinal dynamic response. We found that it was necessary to adjust the shoulder angle to achieve trimmed flight and that most trimmed configurations were longitudinally stable except for configurations with high wrist angles. Our results showed that as flight speed increases, the gull could fold or sweep its wings backward to trim. Further, a trimmed gull can use its wing joints to control the frequencies and damping ratios of the longitudinal oscillatory modes. We found a more damped phugoid mode than similar-sized UAVs, possibly reducing speed sensitivity to perturbations, such as gusts. Although most configurations had controllable short-period flying qualities, the heavily damped phugoid mode indicates a sluggish response to control inputs, which may be overcome while maneuvering by morphing into an unstable flight configuration. Our study shows that gulls use their shoulder, wrist, and elbow joints to negotiate trade-offs in stability and control and points the way forward for designing UAVs with avian-like maneuverability.

A CFD-Based Examination of Rotor-Rotor Separation Effects on Interactional Aerodynamics for eVTOL Aircraft

This study systematically investigates the aerodynamic interactions of a two-rotor system with a front rotor and an aft rotor aligned with the direction of flow. The rotors are 5.5 ftdiameter fixed-pitch rotors operating at approximately 12 lb/ft2 disk loading, representative of large eVTOL aircraft. Fluid flow is simulated using the commercial Navier–Stokes solver, AcuSolve, with a detached eddy simulation (DES) model. Simulations were performed nominally at 40 kt edgewise flight for nine cases corresponding to three values of longitudinal hub–hub separation (2.5R, 3R, 3.5R) and three values of vertical offset (0, 0.25 R, 0.5 R ). Aft rotor performance was compared to an isolated rotor operating in the same conditions in order to quantify the effects of rotor–rotor interaction. For the cases where the aft rotor is closest to the front rotor (2.5R longitudinal offset, zero vertical offset), the aft rotor produced 8.4% less thrust and required 13.4% higher torque than a rotor in isolation. When vertical rotor separation was increased, interactional aerodynamic effects decreased. For a 2.5R longitudinal offset, increasing the vertical offset to 0.5 R decreased the lift deficit to 4.6% and the torque penalty to 6.8%. Increasing the longitudinal offset to 3.5R (while keeping the vertical offset at zero) also reduced interactional aerodynamic effects, but reductions in lift deficit and torque penalty were smaller than those observed with 0.5R vertical offset. Reducing disk loading was found to strengthen interactional aerodynamic effects, with an 11.5% thrust deficit at 6 lb/ft2 compared to 9.0% at 12 lb/ft2. An increase in flight speed also increased interactional aerodynamic penalties from 5.4% thrust deficit at 20 kt to 12.2% at 60 kt. The increased interactional aerodynamic penalties with the reduction in disk loading and increase in flight speed were both attributed to an increase in wake skew angle and the resulting decrease in separation between the aft rotor disk and front rotor wake.

Study on influence of forced vibration of cooling channel on flow and heat transfer of hydrocarbon fuel at supercritical pressure

The cooling channel of a scramjet is the fundamental structure of the active thermal protection for an engine. Till now, studies have focused mainly on the steady-state flow and heat transfer process in the cooling channel. However, the vibration intensity of an engine increases sharply as the flight speed increases, because of which, the flow and heat exchange mechanisms based on the cooling channel under stable conditions cannot be applied under vibration. In this study, experimental methods are used to study the characteristics of the forced vibration of a cooling channel on the flow and heat transfer of hydrocarbon fuel at supercritical pressure. In addition, the influences of different vibration frequencies and vibration amplitudes on the flow and heat transfer are analyzed. The research results show that at supercritical pressure, when the fuel temperature is below the critical temperature and the inner wall temperature is above the critical temperature, external vibrations would enhance the heat transfer characteristics of the cooling channel. However, when the pressure and temperature are unstable, the forced vibration of the cooling channel would suppress the instability of temperature and pressure while strengthening the heat exchange.

Acoustic deterrents influence foraging activity, flight and echolocation behaviour of free-flying bats.

ABSTRACTAcoustic deterrents have shown potential as a viable mitigation measure to reduce human impacts on bats; however, the mechanisms underpinning acoustic deterrence of bats have yet to be explored. Bats avoid ambient ultrasound in their environment and alter their echolocation calls in response to masking noise. Using stereo thermal videogrammetry and acoustic methods, we tested predictions that: (i) bats would avoid acoustic deterrents and forage and social call less in a ‘treated airspace’; (ii) deterrents would cause bats to fly with more direct flight paths akin to commuting behaviour and in line with a reduction in foraging activity, resulting in increased flight speed and decreased flight tortuosity; and (iii) bats would alter their echolocation call structure in response to the masking deterrent sound. As predicted, overall bat activity was reduced by 30% and we recorded a significant reduction in counts of Pipistrellus pygmaeus (27%), Myotis spp. (probably M. daubentonii) (26%), and Nyctalus spp. and Eptesicus spp. (68%) passes. Pipistrellus pygmaeus feeding buzzes were also reduced by the deterrent in relation to general activity (by 38%); however, social calls were not (only 23% reduction). Bats also increased their flight speed and reduced the tortuosity of their flight paths, and P. pygmaeus reduced echolocation call bandwidth and start frequency of calls in response to deterrent playback, probably owing to the masking effect of the sound. Deterrence could therefore be used to remove bats from areas where they forage, for example wind turbines and roads, where they may be under threat from direct mortality.

The effect of flight state parameters on the performance of photovoltaic modules in solar aircraft

Based on the power generation model of photovoltaic modules, the effects of flight speed, altitude, time and area in solar aircraft on the performance of photovoltaic modules have been studied. As the flight speed increases, the power generated by the module increases but tends to saturate. When the conversion efficiency of photovoltaic modules is improved, the required power of the solar aircraft and the power generated by the photovoltaic modules are balanced at a faster flight speed. The power generated by the modules increases with the flight altitude but tends to saturate due to the drop of air temperature and the surface temperature of the module. The higher the altitude, the smaller is the atmospheric density, and atmospheric permeability, and the greater is the solar radiation intensity, and thus the power generated by the module increases. The power generated by the components is the strongest at noon. Battery performance is the strongest in summer and the weakest in winter, as the module’s performance is mainly determined by the intensity of solar radiation. Finally, the energy distribution of solar aircraft and long-time space flight has been discussed.
 J. Bangladesh Acad. Sci. 45(1); 73-83: June 2021

Acoustotactic response of mosquitoes in untethered flight to incidental sound

Mosquitoes are vectors for some of the most devastating diseases on the planet. Given the centrality of acoustic sensing in the precopulatory behavior of these vectors, the use of an exogenous acoustic stimulus offers the potential of interfering with the courtship behavior of these insects. Previous research on the acoustotactic response of mosquitoes has been conducted on tethered preparations using low-intensity sound stimuli. To quantify differences in acoustotactic responses between mosquitos of distinct sex and species, we examined the effects of incidental sound stimuli on the flight behavior of free-flying male vs. female Aedes aegypti and Anopheles gambiae mosquitoes. The key variables were sound frequency (100–1000 Hz) and intensity (67–103 dB, measured at 12.5 cm from the source), and the acoustotactic response was measured in terms of the relative increase in flight speed in response to the stimulus. The data show, for the first time, significant sex- and species-specific differences in acoustotactic responses. A. aegypti exhibited a greater response to sound stimulus compared to An. gambiae, and the response also extended over a larger range of frequencies. Furthermore, the males of both species displayed a greater acoustotactic response than females, with An. gambiae females exhibiting minimal response to sound.

Females invest more energy in flight: flight characteristics of Platypus quercivorus (Murayama) revealed by a flight mill

ABSTRACT Dispersal flight is an essential component of the life history of bark and ambrosia beetles. Previous studies have shown considerable variation in flight distance between individual beetles; however, different factors drive this variation between species. Furthermore, when the ecological role of dispersal flight differs between sexes (i.e., males locate hosts and females follow), influencing factors might also vary. Here, we evaluated the factors driving variation in the dispersal flight distance of the ambrosia beetle Platypus quercivorus (Murayama) (Coleoptera: Curculionidae: Platypodinae), which is a vector insect of Raffaelea quercivora, the causal agent of the Japanese oak wilt, and we estimated sex-based differences for each influencing factor. A flight mill was used to measure flight distance, flight duration, and initial and terminal flight speed. Because flight speed was not constant during beetle flight, we estimated both initial and terminal flight speed, and assumed that initial flight speed represents a relative measure of energy allocated to flight. Flight distance was mainly determined by flight duration, with an average flight speed of 4.22 km/h for both sexes. Initial and terminal flight speed affected flight distance; however, these factors had contrasting effects between sexes. Specifically, a simultaneous increase in initial and terminal flight speed by males increased flight distance. In comparison, increased flight distance by females was mainly achieved by increasing the initial flight speed. These different patterns in increased flight speed likely reflect differences in the relative importance of flight in the life history of the two sexes.

Optimal Control of a Compound Rotorcraft for Engine Performance Enhancement

Abstract Demands for rotorcraft with increased flight speed, improved operational performance and reduced environmental impact have led to a drive in research and development of alternative concepts. Compound rotorcraft overcome the flight speed limitations of conventional helicopters with additional lifting and propulsive components. Further to operational benefits, these augmentations provide additional flight control parameters, resulting in control redundancy. This work aims to investigate the impact of optimal control strategies for a generic coaxial compound rotorcraft, equipped with turboshaft engines, targeting the minimization of mission fuel burn and gaseous emissions. The direct redundant controls considered are: (a) main rotor speed, (b) propeller speed, and (c) fuselage pitch attitude. A simulation tool for coaxial compound rotorcraft analysis has been developed and coupled to a zero-dimensional engine performance model and a stirred-reactor combustor model. First, experimental and flight test data were used to provide extensive validation of the developed models. A parametric analysis was then carried out to gain insight into the effect of the redundant controls. This was followed by the derivation of a generalized set of optimal redundant control allocations using a surrogate-assisted genetic algorithm. Application of the optimal redundant control allocations during realistic operational scenarios has demonstrated reductions in fuel burn and NOx of up to 6.93% and 8.74%, respectively. The developed method constitutes a rigorous approach to guide the design of control systems for future advanced rotorcraft.