Constant Altitude Research Articles

Energy-optimal trajectory planning for solar-powered aircraft using soft actor-critic

High-Altitude Long-Endurance (HALE) solar-powered Unmanned Aircraft Vehicles (UAVs) can utilize solar energy as power source and maintain extremely long cruise endurance, which has attracted extensive attentions from researchers. Trajectory optimization is a promising way to achieve superior flight time because of the finite solar energy absorbed in a day. In this work, a method of trajectory optimization and guidance for HALE solar-powered aircraft based on a Reinforcement Learning (RL) framework is introduced. According to flight and environment information, a neural network controller outputs commands of thrust, attack angle, and bank angle to realize an autonomous flight based on energy maximization. The validity of the proposed method was evaluated in a 5-km radius area in simulation, and results have shown that after one day-night cycle, the battery energy of the RL-controller was improved by 31% and 17% compared with those of a Steady-State (SS) strategy with a constant speed and a constant altitude and a kind of state-machine strategy, respectively. In addition, results of an uninterrupted flight test have shown that the endurance of the RL controller was longer than those of the control cases.

Steps to build a DIY low-cost fixed-wing drone for biodiversity conservation.

Despite the proved usefulness of drones in biodiversity studies, acquisition costs and difficulties in operating, maintaining and repairing these systems constrain their integration in conservation projects, particularly for low-income countries. Here we present the steps necessary to build a low-cost fixed-wing drone for environmental applications in large areas, along with instructions to increase the reliability of the system and testing its performance. Inspired by DIY (Do It Yourself) and open source models, this work prioritizes simplicity and accounts for cost-benefit for the researcher. The DIY fixed-wing drone developed has electric propulsion, can perform pre-programmed flight, can carry up to 500 g payload capacity with 65 minutes flight duration and flies at a maximum distance of 20 km. It is equipped with a RGB (Red, Green and Blue) sensor capable of obtaining 2.8 cm per pixel Ground Sample Distance (GSD) resolution at a constant altitude of 100 m above ground level (AGL). The total cost was $995 which is substantially less than the average value of similar commercial drones used in biodiversity studies. We performed 12 flight tests in auto mode using the developed model in protected areas in Brazil, obtaining RGB images that allowed us to identify deforestation spots smaller than 5 m2 and medium-sized animals. Building DIY drones requires some technical knowledge and demands more time than buying a commercial ready-to-fly system, but as proved here, it can be less expensive, which is often crucial in conservation projects.

Dynamic Transition Corridors and Control Strategy of a Rotor-Blown-Wing Tail-Sitter

Transition maneuvers are inherent challenges for tail-sitters because of the widely varying flight speed and pitch attitude. This paper investigates the dynamic model, the transition corridors, and the control strategy of a rotor-blown-wing (RBW) tail-sitter. Because the existing equilibrium transition corridor (ETC) cannot reflect system evolution trends of transition flights, a novel dynamic front transition corridor (DFTC) and a novel dynamic back transition corridor (DBTC) are developed. Compared with the ETC, the DFTC and DBTC are governed by dynamic nonequilibrium rules, thus covering transition trajectories more completely. Because excessive large altitude climb should be avoided in transition flights, the developed corridors are then enhanced by a climb velocity constraint. The effects of model mismatches on the enhanced DFTC and DBTC are analyzed. Based on the enhanced DFTC and DBTC, the transition strategy and controller are constructed by extracting typical features of the optimal transition trajectories. The transition robustness is increased by keeping the transition trajectory in the middle of the enhanced DFTC/DBTC. Numerical results indicate that the derived small altitude climb transition is more robust and natural than the constant altitude transition and the large altitude climb transition. Flight test results demonstrate the design principles of the RBW tail-sitter, the transition strategy, and the controller.

Flight management system for hydrogen-powered aircraft in cruise

The minimization of the Direct Operating Cost (DOC) for hydrogen-powered aircraft is formulated in this paper as an optimal control problem and is solved based on Pontryagin's minimum principle. As a consequence, the optimum cruise flight speed is determined assuming cruising at a constant altitude. The optimization criterion corresponds to the minimization of a functional representing the trade-off between the cost of hydrogen fuel and time-dependent costs, which are related by a parameter denoted by cost index. The value of this parameter is introduced by a pilot into the Flight Management System (FMS) of the aircraft. The HY4 aircraft model is used to obtain numerical results for the proposed methodology.

Retrieval algorithm for the column CO<sub>2</sub> mixing ratio from pulsed multi-wavelength lidar measurements

Abstract. The retrieval algorithm for CO2 column mixing ratio from measurements of a pulsed multi-wavelength integrated path differential absorption (IPDA) lidar is described. The lidar samples the shape of the 1572.33 nm CO2 absorption line at multiple wavelengths. The algorithm uses a least-squares fit between the CO2 line shape computed from a layered atmosphere model and that sampled by the lidar. In addition to the column-average CO2 dry-air mole fraction (XCO2), several other parameters are also solved simultaneously from the fit. These include the Doppler shift at the received laser signal wavelength, the product of the surface reflectivity and atmospheric transmission, and a linear trend in the lidar receiver's spectral response. The algorithm can also be used to solve for the average water vapor mixing ratio, which produces a secondary absorption in the wings of the CO2 absorption line under humid conditions. The least-squares fit is linearized about the expected XCO2 value, which allows the use of a standard linear least-squares fitting method and software tools. The standard deviation of the retrieved XCO2 is obtained from the covariance matrix of the fit. The averaging kernel is also provided similarly to that used for passive trace-gas column measurements. Examples are presented of using the algorithm to retrieve XCO2 from measurements of the NASA Goddard airborne CO2 Sounder lidar that were made at constant altitude and during spiral-down profile maneuvers.

Determination of the flight trajectory in terms of emission and fuel consumption minimization

The present-day world is characterized by the intense development of air transport. However, along with it, significant problems appear. Among these problems, the most important are those relating to safety and negative impact of air transport on the environment. Air transport efficiency and profitability issues, although not critical, must also be taken into account because they decide about the intensity of development of this branch of transport. There are currently two large programs in Europe oriented at improving safety, environmental, and efficiency indicators. These are SESAR 2020 and Clean Sky 2, being a continuation of previous ones. One of the ways to reduce negative impact of air transport on the environment and improve its efficiency is to reduce fuel consumption and pollutants emissions resulting from fuel combustion. To find solutions with the abovementioned features, it is necessary to have sufficiently accurate models to estimate the amount of fuel consumed and the amount of pollutants emitted. Developing a sufficiently accurate model to determine fuel consumption and pollutants emission was performed. Due to the specificity of the missions carried out by passenger aircraft, the focus was on the cruise stage when aircraft flies at a constant altitude with a constant air speed. The result of the analysis was the development of methodology for fuel consumption and emission of main pollutants in cruise conditions. Specific fuel consumption is calculated for the thrust required for horizontal flight at cruising altitude. Emission indexes for CO, NOx, HC, and CO2 for the cruise have been determined based on known indexes for the landing and take-off cycle phase, after applying appropriate corrections. An illustration of the application of the developed methodology was the optimization of a medium-sized transport aircraft trajectory on a selected connection to determine a trajectory characterized by a minimum emission value taking into account weather conditions.

Wave-slope soaring of the brown pelican

BackgroundFrom the laboratory at Scripps Institution of Oceanography, it is common to see the brown pelican (Pelecanus occidentalis) traveling along the crests of ocean waves just offshore of the surf-zone. When flying in this manner, the birds can travel long distances without flapping, centimeters above the ocean’s surface. Here we derive a theoretical framework for assessing the energetic savings related to this behavior, ‘wave-slope soaring,’ in which an organism in flight takes advantage of localized updrafts caused by traveling ocean surface gravity waves.MethodsThe energy cost of steady, constant altitude flight in and out of ground effect are analyzed as controls. Potential flow theory is used to quantify the ocean wave-induced wind associated with near-shoaling, weakly nonlinear, shallow water ocean surface gravity waves moving through an atmosphere initially at rest. Using perturbation theory and the Green’s function for Laplace’s equation in 2D with Dirichlet boundary conditions, we obtain integrals for the horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave. Wave-slope soaring flight is then analyzed using an energetics-based approach for waves under a range of ocean conditions and the body plan of P. occidentalis.ResultsFor ground effect flight, we calculate a ∼15 - 25% reduction in cost of transport as compared with steady, level flight out of ground effect. When wave-slope soaring is employed at flight heights ∼2m in typical ocean conditions (2m wave height, 15s period), we calculate 60-70% reduction in cost of transport as compared with flight in ground effect. A relatively small increase in swell amplitude or decrease in flight height allows up to 100% of the cost of transport to be offset by wave-slope soaring behavior.ConclusionsThe theoretical development presented here suggests there are energy savings associated with wave-slope soaring. Individual brown pelicans may significantly decrease their cost of transport utilizing this mode of flight under typical ocean conditions. Thus wave-slope soaring may provide fitness benefit to these highly mobile organisms that depend on patchy prey distribution over large home ranges.

Analysis of Imaging Quality of New Laser Communication System on Missile in the Aerodynamic Environment

We study the influence of altitude and speed on aero-optic imaging quality degradation of new laser communication system “Multi-Aperture Transmission and Diversity Reception” of surface-to-air missile. The 3D modeling and meshing of surface-to-air missile are obtained by ANSYS software. The density field distribution around the optical system was analyzed by FLUENT and the nonuniform refractive-index field around is calculated, in view of the Gladstone–Dale relation. The point spread function (PSF), Strehl ratio (SR), encircled energy, and modulation transfer function (MTF) are provided for the imaging quality evaluation of optical system. The altitude ranges from 0 to 20 km, and the speeds of missile are 5 and 3 Ma. The results show that, at the constant speed, with increase in the altitude, the refraction index and the radius of dispersion spot including 80% energy are gradually decreasing; the SR results and the curve of MTF are gradually increasing, and the PSF is concentrated. At the constant altitude, with increase in the speed, the aerodynamic flow field becomes more and more complex. Therefore, the higher the altitude, the better the receiving quality, and the smaller the speed, the better the receiving quality.

Impact of middle atmospheric humidity on boundary layer turbulence and clouds

An attempt is made to connect the moisture present above the boundary layer and its association with the cloud development and boundary layer turbulence using Large Eddy Simulation (LES) and aircraft observations. The dry boundary layer (BL) with shallow clouds observed during Cloud-Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over the arid Indian peninsula is investigated in this study. The constant altitude aircraft observations at different elevations are used to verify LES derived fluxes and variances. LES simulations with the drier conditions above BL resulted in deeper, warmer and drier BL with an enhanced boundary layer turbulent kinetic energy. A dynamic feedback from dry air intrusion into the BL resulted in energetic BL eddies in the dry conditions and a doubling of moisture exchange coefficients. The liquid water content in cloud updrafts rather than in downdrafts were depleted significantly in dry conditions. LES sensitivity indicates that the middle atmospheric water vapor alone could influence the shallow to deep cumulus cloud transitions in the monsoon regime in a dramatic way, by changing the population of cumulus, congestus or deep cumulus clouds. A 30% drying above the BL could drastically reduce the liquid water path and cloud albedo by 10–15%.

Precipitation cloud identification based on faster-RCNN for Doppler weather radar

Precipitation clouds are visible aggregates of hydrometeor in the air that floating in the atmosphere after condensation, which can be divided into stratiform cloud and convective cloud. Different precipitation clouds often accompany different precipitation processes. Accurate identification of precipitation clouds is significant for the prediction of severe precipitation processes. Traditional identification methods mostly depend on the differences of radar reflectivity distribution morphology between stratiform and convective precipitation clouds in three-dimensional space. However, all of them have a common shortcoming that the radial velocity data detected by Doppler Weather Radar has not been applied to the identification of precipitation clouds because it is insensitive to the convective movement in the vertical direction. This paper proposes a new method for precipitation clouds identification based on deep learning algorithm, which is according the distribution morphology of multiple radar data. It mainly includes three parts, which are Constant Altitude Plan Position Indicator data (CAPPI) interpolation for radar reflectivity, Radial projection of the ground horizontal wind field by using radial velocity data, and the precipitation clouds identification based on Faster-RCNN. The testing result shows that the method proposed in this paper performs better than the traditional methods in terms of precision. Moreover, this method boasts great advantages in running time and adaptive ability.

Performance Optimization of a Low-Altitude Skid-to-Turn Vehicle

The problem of performance optimization of a skid-to-turn vehicle is studied. The objective is to minimize the time required to steer the vehicle from an initial state at a nonzero altitude to a ground target state subject to constraints on altitude and crosstrack. A performance index is designed that enables the vehicle to fly at a constant low altitude for as long as possible while performing a bunt maneuver (negative sensed acceleration) as quickly as possible at the end of the trajectory. To implement the objective functional and incorporate all required constraints, a two-phase optimal control problem is developed. The key features of the two-phase optimal control problem are provided for various values of the objective functional weight and maximum allowable crosstrack. Finally, a sensitivity analysis is performed to assess the accuracy of the solutions obtained to the true optimal solution.

Analyses of three-dimensional weather radar data from volcanic eruption clouds

This paper demonstrates the advantages of three-dimensional (3D) analysis and visualization of weather radar data for studies on the inner structure of eruption columns and their 3D ash-fall distributions. The 3D data were collected using an operational X-band polarimetric radar located ~11 km from the Showa vent of Sakurajima, Japan. Three eruption cases were chosen for the analysis to study the effect of environmental wind conditions on the inner structure of an eruption column and horizontal ash-fall distributions at 1000 m height: a 3677-m-high eruption on 13 June 2013 under calm winds (Case 1), a 3982-m-high eruption on 7 October 2013 under strong winds (Case 2), and a 4520-m-high eruption on 18 August 2013 under moderate winds (Case 3). The Analytical Tools for Three-dimensional Weather Radar Data (ANT3D) package was developed and used for the construction of 3D constant altitude plan position indicator (3D CAPPI) data from eruption columns. The quantitative ash-fall analyses of 3D CAPPI data revealed that the total ash-fall amounts of the Case 1, Case 2, and Case 3 eruptions were 6.24 × 107, 9.99 × 107, and 6.71 × 107 kg, respectively, and the total ash-fall areas at the 1000-m height were 29.7, 151.3, and 107.7 km2, respectively. It was shown that the area of the maximum ash-fall amount at the 1000-m height depends on the environmental conditions. The accumulated ash-fall distribution area was limited to over and around the vent in the Case 1 eruption, whereas the ash distribution pattern was elongated to the downwind direction and multiple ash concentration maxima were formed in the Case 2 eruption probably due to the multiple eruptions. The accumulated ash-fall distribution was also elongated to the down wind direction in the Case 3 eruption but a single maximum concentration which was larger than that in the Case 2 eruption was found inland of Sakurajima. The 3D CAPPI data were visualized using techniques such as surface rendering, volume rendering, bird's eye viewing, and cross-sectional analysis. The 3D visualizations suggest that vertical size-sorting and aggregation occurred in the buoyancy-driven regions of the eruption columns in all three cases. The results of this study will contribute to the understanding of volcanic eruption column dynamics and horizontal ash-fall transportation.

Vector Magnetometry Using Remotely Piloted Aircraft Systems: An Example of Application for Planetary Exploration

Geomagnetic prospection is an efficient and environmentally friendly geophysical method for the analysis of the magnetic minerals’ distribution in the subsurface. High-resolution measurements require on-ground campaigns. However, these activities might imply high costs, risk and time consumption. Some more recent works have started to use magnetometers on-board remote piloted aircrafts. Normally, they fly at a constant altitude and use scalar probes. This configuration permits the determination of the magnitude of the magnetic field but not the direction, and requires advanced techniques for in-depth interpretation of the sources. In this manuscript, we describe the accommodation of a system for vector magnetometry in a drone whose flight altitude follows the elevation of the terrain. This singularity improves the capability of interpretation, including constraints in dating due to the record of the geomagnetic field. The work consists of the design, development and implementation of a solidary payload system anchored to the body of the platform in order to determine the vector magnetic field. It describes the details of the system and the performance characteristics obtained after the calibration, as well as its demonstration via a field campaign in the spatter deposits of Cerro Gordo volcano in Campos de Calatrava volcanic province in Spain.

Altitude control of a remote-sensing balloon platform

This paper addresses the problem of altitude control of stratospheric balloon platforms. Over the last years, there has been an increasing interest in the development of balloon platforms with the ability of maneuvering and fluctuating at the stratosphere for different applications on the basis of remote-sensing. Considering the current trend of a high connected world with sensor grids spread in wide geographical areas, the interest in balloon platform applications has increased posing new challenges for future applications. One of the major problems encountered in this context is how to guarantee constant altitude sustainability. Although the technologies required to address this problem already exist, low cost and easy to launch solutions are still needed considering applications on a wide scale. In this work, a theoretical model of the balloon dynamic is presented and validated. A valve control loop mechanism is proposed for rubber balloons. The controller is tuned empirically and numerical simulations conducted for performance analysis and a case study in a real mission. The proposed solution contributes to increase the capacity of rubber balloons by proposing an altitude control system that allows fluctuation stages which, in general, are not common with this type of balloon.

Combustion analysis of porous radiant burner for commercial cooking applications

High efficiency and low efficiency were observed by using porous burner technology for commercial cooking. The whole research consists of survey of these three types of burners. Like burners diameter having convergent 100mm, straight 100mm and80mm divergent shape burner. LPG is the fuel i.e. liquid petroleum gas is used in the all experiment. The two zones combustion and preheating zones comprise by a porous burner. Preheating zone having steel balls of width 6.5mm where combustion zone has Sic matric of 10ppi was used. 150mm is the constant altitude of three burners comprise of combustion zone and having equivalence ratio from 0.10-0.60. The range at which burner was operated 79% is the maximum efficiency analyzed for porous burner having dimensions like 100mm diameter at power equal to 0.84 kW and equivalence ratio (Φ) equal to 0.49.

Construction of three-dimensional weather radar data from volcanic eruption clouds

Analysis tools of three-dimensional weather radar data (ANT3D) was originally developed at the National Research Institute for Earth Science and Disaster prevention (NIED) to retrieve three-dimensional (3D) precipitation and wind fields for convective storms. In 2013, Kagoshima University significantly revised ANT3D for analyses of volcanic eruption clouds, mainly to improve the temporal and spatial interpolation of radar data and estimation of the advection vector, which is required for temporal interpolation. Detailed information pertaining to these algorithms is listed as additional information in this paper.•Procedures necessary for the construction of three-dimensional (3D) volcanic cloud weather radar data are described.•An algorithm based on temporal and elevation angle interpolation methods was used to create 3D constant altitude plan position indicator (3D CAPPI) data with high temporal and spatial resolution.•Two programs (ANT3D_GUI and the CAPPI viewer) are provided for readers interested in analyzing volcanic eruption cloud radar data.

Power minimization of fixed-wing drones for Venus exploration in various altitudes

Venus has a harsh environment that makes its exploration especially difficult. Standard rovers like on Mars would not work as the intense temperature, and pressure would cause them to have a short operating time. At an altitude of about 55 km, Venus has an Earth-like atmosphere where a robotic system could survey for different features. A fixed-wing drone that can fly at this altitude would be practical. To obtain better information on Venus, the UAV can operate at lower altitudes until pressure and temperature operational limits are met. Then the drone can come back to an altitude of 55 km and alleviate until it is ready to go back into the lower altitudes. The atmospheric analysis is done to model Venus’ characteristics at lower altitudes between 0 km and 60 km. Functions are made that model the atmospheric properties of Venus, such as temperature, pressure, density, and viscosity. These modeled atmospheric properties are then used to investigate the wing and thrust loading of a fixed-wing UAV in Venus. The results from this wing and thrust loading investigation are that, as wing loading and altitude increase, thrust loading also increases. This general trend is not consistent for all flight modes. For the case analyzed, thrust loading decreases between 0 N/m2 and 16 N/m2, and increases between 17 N/m2 and 80 N/m2 for flight at a constant altitude and cruise speed. There is a specific wing loading that requires the minimum thrust loading for each flight mode and altitude. For flight at a constant altitude and cruise speed, the best wing loading to have is about 16.75 N/m2. For flight at accelerated climb speed, the best wing loading to have is as low as it can be, in this case, it is 10 N/m2. This study gives outlines for future steps of designing fixed-wing UAVs for Venus exploration.

Collaborative Target-Tracking Control Using Multiple Fixed-Wing Unmanned Aerial Vehicles with Constant Speeds

This paper considers a collaborative tracking control problem using a group of fixed-wing unmanned aerial vehicles (UAVs) with constant and nonidentical speeds. The dynamics of fixed-wing UAVs are modeled by unicycle-type equations with nonholonomic constraints, assuming that UAVs fly at constant altitudes in the nominal operation mode. The controller is designed such that all fixed-wing UAVs as a group can collaboratively track a desired target’s position and velocity. This paper first presents conditions on the relative speeds of tracking UAVs and the target to ensure that the tracking objective can be achieved when UAVs are subject to constant-speed constraints. A reference velocity is constructed that includes both the target’s velocity and position as feedback, which is to be tracked by the group centroid. In this way, all vehicles’ headings are controlled such that the group centroid follows a reference trajectory that successfully tracks the target’s trajectory. A spacing controller is further devised to ensure that all vehicles stay close to the group centroid trajectory. Tradeoffs in the controller design and performance limitations of the target tracking control due to the constant-speed constraint are also discussed in detail. Experimental results with three fixed-wing UAVs tracking a target rotorcraft are provided.

Effects of propeller flow on the longitudinal and lateral dynamics and model couplings of a fixed-wing micro air vehicle

This paper analyzes the effects of propeller flow on the linear coupled longitudinal and lateral dynamics of a 150 mm wingspan fixed wing micro air vehicle (MAV). The effects propeller flow on the lift, drag, pitching moment and side force is obtained through wind tunnel tests. The aerodynamic forces and moments are modeled as a function of angle of attack, sideslip angle, control surface deflection and propeller rotation per minute. The nonlinear six degrees of freedom model is linearized about straight and constant altitude flight conditions for different trim airspeed to obtain linear coupled longitudinal and lateral state space model. The eigenvalues and eigenvectors of linear coupled longitudinal and lateral state space model are compared with and without propeller flow effects. The variation in the natural frequencies and damping ratios of short period mode, phugoid mode and Dutch roll mode are analyzed for various trim airspeed. An increase in the natural frequency is observed for phugoid mode and Dutch roll mode with propeller effects. The stability of the spiral mode is enhanced by the propeller flow and also the response of the roll subsidence mode is faster with propeller effects. Detailed analysis of eigenvalues and eigenvectors shows the importance of incorporating propeller flow in analyzing the dynamics of the MAV.

Influence of atmospheric uncertainty, convective indicators, and cost-index on the leveled aircraft trajectory optimization problem

The existence of significant uncertainties in the models and systems required for trajectory prediction represents a major challenge for the Air traffic Management (ATM) system. Weather can be considered as one of the most relevant sources of uncertainty. Understanding and managing the impact of these uncertainties is necessary to increase the predictability of the ATM system. State-of-the-art probabilistic forecasts from Ensemble Prediction Systems are employed to characterize uncertainty in the wind and potential convective areas. A robust optimal control methodology to produce efficient and predictable aircraft trajectories in the presence of these uncertainties is presented. Aircraft motion is assumed to be at a constant altitude and variable speed, considering BADA4 as the aircraft performance model. A set of Pareto-optimal trajectories is obtained for different preferences among predictability, convective risk, and average cost index running a thorough parametric study on a North Atlantic crossing use case. Results show that the cost of reducing the arrival time window by 10 s. is between 100 and 200 kg or 3 and 6 min., depending on the cost-index. They also show that reducing the exposure to convection by 50 km is on the order of 5 and 10 min. or 100 and 200 kg. of average fuel consumption.