True Airspeed Research Articles

A Flight Control System for Small Unmanned Aerial Vehicle

The program adaptation of the controller for the flight control system (FCS) of an unmanned aerial vehicle (UAV) is considered. Linearized flight dynamic models depend mainly on the true airspeed of the UAV, which is measured by the onboard air data system. This enables its use for program adaptation of the FCS over the full range of altitudes and velocities, which define the flight operating range. FCS with program adaptation, based on static feedback (SF), is selected. The SF parameters for every sub-range of the true airspeed are determined using the linear matrix inequality approach in the case of discrete systems for synthesis of a suboptimal robust H∞-controller. The use of the Lagrange interpolation between true airspeed sub-ranges provides continuous adaptation. The efficiency of the proposed approach is shown against an example of the heading stabilization system.

Attitude and airdata estimation

Accurate attitude estimation is essential for basic flying and stable control of Unmanned Aerial Vehicles (UAV). The Extended Kalman Filter (EKF) is a potential candidate to fuse multiple low-cost sensor information for attitude estimation of UAVs. The estimation of Angle of Attack (AoA), Angle of Side Slip (AoSS), True Air Speed (TAS) is essential to design a better control law for the UAVs. This paper demonstrates the application of EKF for attitude estimation, AoA, AoSS and TAS estimation. The important contribution of the paper is that the demonstration is carried out using kinematic simulation platform for various maneuvers to understand the limitations of EKF for the application.

Feasibility Study on Modeling of Flight Time Prediction Uncertainty using Flight and Meteorological Conditions

A precise flight time uncertainty prediction is expected to enable a more efficient air traffic management. According to an uncertainty propagation equation derived from a physical model, the flight time uncertainty increases as a function of ground speed and the variances of true air speed and head wind speed. These factors also depend on the flight and meteorological conditions. It is expected possible to improve the uncertainty prediction accuracy by appropriately taking these factors into its modeling. Through the clustering analysis of the actual flight and weather forecast data, the feasibility of the flight time uncertainty modeling using the flight speed and weather forecast information is clearly demonstrated.

Predicting Abnormal Runway Occupancy Times and Observing Related Precursors

Accidents on the runway triggered the development and implementation of mitigation strategies. Therefore, the airline industry is moving toward proactive risk management, which aims to identify and predict risk precursors and to mitigate risks before accidents occur. For certain predictions machine learning techniques can be used. Although many studies have explored and applied novel machine learning techniques on different radar and A-SMGCS data, the identification and prediction of abnormal runway occupancy times and the observation of related precursors are not well developed. In our previous papers, three existing methods were introduced, lasso, multi-layer perception, and neural networks, to predict the taxi-out time on the taxiway and the time to fly and true airspeed profile on final approach. This paper presents a new machine learning method where the existing machine learning techniques are combined for predicting the abnormal runway occupancy times of unique radar data patterns. Additionally the regression tree method is used in this study to observe the key related precursors extracted from the top 10 features. Compared with existing methods, the new method no longer requires predefined criteria or domain knowledge. Tests were conducted using final approach radar data and A-SMGCS runway data consisting of 78,321 flights at Paris Charles de Gaulle airport and were benchmarked against 500,000 flights at Vienna airport.

Gyroscopic drift compensation by using low cost sensors for improved attitude determination

Desire of inexpensive Electro-Optic and Micro-Electro-Mechanical System (MEMS) inertial sensors has drastically been increased in the recent times for both military and commercial applications. Beside the traditional applications, reduced cost of such sensors has opened new domains in personal navigation. This paper provides a framework for attitude estimation using miniaturized and cost-effective Inertial Measurement Units (IMU). Sensor fusion of gyroscope, accelerometer and True Air Speed (TAS) sensor helps in minimizing the characteristic time growing error present in gyroscopic integrated data. A novel approach of TAS model development is implemented to generate true air speed data in the absence of TAS sensor. The presence of linear acceleration is estimated and eliminated by means of gyroscope and TAS model. Due to the slight difference in two direction vectors, an error function is estimated and constantly compensated by using a Proportional-Integral (PI) block. Coarse tuning of PI gains is applied and simulated results are produced to assess the filter performance by using real vehicle data. It has been presented that the proposed filter can be used to compute a reasonably accurate attitude solution by using low cost inertial sensors when external aiding is unavailable or not useful.

Analysis of the Aircraft Motion at the Overcritical Angles of Attack: Errors of On-Board Measurements and Simulation of the Deviated Thrust Vector

The article deals with the problems of the flight test data analysis concerning the flights at higher then critical angles of attack in order to improve the mathematical model of an aircraft's motion. The paper presents a technique for validation and correction of the on-board measurements for this type of motion. Regarding the use of the vector control during such maneuvers, the article considers the mathematical model of the forces and torques generated by the thrust vectoring. Examples of the data processing of the modern maneuverable aircraft's flight tests are presented to confirm the efficiency of the proposed models and methods. The validation of the on-board measurements, above all, the aerometric measurements, is based on the equations of the aircraft spatial motion. It is assumed that the correct values of the motion parameters must satisfy the system of the nonlinear differential equations known from the flight dynamics. This approach has already proved its efficiency in the analysis of the flight data in the operational range of the angles of attack. The signals obtained through the simulation are used to correct the measurements in case of errors. The article presents examples of detection and correction of errors in the measurement channels for a true airspeed and angle of attack. This paper also proposes two versions of the model capable of calculation the projections of the forces and torques on the aircraft principal axes. The first version is derived from the evident geometrical considerations, the second one is based on Rodrigues' vector rotation formula known in the theoretical mechanics. A numerical comparison confirmed correctness of both obtained models. These models were also verified by processing of the flight tests data.

四次元航法における飛行時間のばらつきのモデル化

The feasibility of the flight time uncertainty modeling in 4-dimensional trajectory is discussed. The flight time uncertainty causes due to the difference between both the estimated and actual wind speeds and the control input and the output of the flight speed. According to the standard deviation analyses using the actual operation data, it has been demonstrated that the model of the flight time standard deviation is able to describe the tendency of its magnitude. It is further clarified that the correlation between the true air speed and the estimated wind speed should also be considered in the modeling to improve its accuracy. It is indispensable to take this correlation into consideration in the uncertainty modeling in the 4-dimensional trajectory operation.

Thermodynamic correction of particle concentrations measured by underwing probes on fast-flying aircraft

Abstract. Particle concentration measurements with underwing probes on aircraft are impacted by air compression upstream of the instrument body as a function of flight velocity. In particular, for fast-flying aircraft the necessity arises to account for compression of the air sample volume. Hence, a correction procedure is needed to invert measured particle number concentrations to ambient conditions that is commonly applicable to different instruments to gain comparable results. In the compression region where the detection of particles occurs (i.e. under factual measurement conditions), pressure and temperature of the air sample are increased compared to ambient (undisturbed) conditions in certain distance away from the aircraft. Conventional procedures for scaling the measured number densities to ambient conditions presume that the air volume probed per time interval is determined by the aircraft speed (true air speed, TAS). However, particle imaging instruments equipped with pitot tubes measuring the probe air speed (PAS) of each underwing probe reveal PAS values systematically below those of the TAS. We conclude that the deviation between PAS and TAS is mainly caused by the compression of the probed air sample. From measurements during two missions in 2014 with the German Gulfstream G-550 (HALO – High Altitude LOng range) research aircraft we develop a procedure to correct the measured particle concentration to ambient conditions using a thermodynamic approach. With the provided equation, the corresponding concentration correction factor ξ is applicable to the high-frequency measurements of the underwing probes, each of which is equipped with its own air speed sensor (e.g. a pitot tube). ξ values of 1 to 0.85 are calculated for air speeds (i.e. TAS) between 60 and 250 m s−1. For different instruments at individual wing position the calculated ξ values exhibit strong consistency, which allows for a parameterisation of ξ as a function of TAS for the current HALO underwing probe configuration. The ability of cloud particles to adopt changes of air speed between ambient and measurement conditions depends on the cloud particles' inertia as a function of particle size (diameter Dp). The suggested inertia correction factor μ (Dp) for liquid cloud drops ranges between 1 (for Dp < 70 µm) and 0.8 (for 100 µm < Dp < 225 µm) but it needs to be applied carefully with respect to the particles' phase and nature. The correction of measured concentration by both factors, ξ and μ (Dp), yields higher ambient particle concentration by about 10–25 % compared to conventional procedures – an improvement which can be considered as significant for many research applications. The calculated ξ values are specifically related to the considered HALO underwing probe arrangement and may differ for other aircraft. Moreover, suggested corrections may not cover all impacts originating from high flight velocities and from interferences between the instruments and e.g. the aircraft wings and/or fuselage. Consequently, it is important that PAS (as a function of TAS) is individually measured by each probe deployed underneath the wings of a fast-flying aircraft.

How do Continuous Climb Operations affect the capacity of a Terminal Manoeuvre Area

Continuous climb operations are the following step to optimise departure trajectories with the goals of minimizing fuel consumption and pollutants and noise emissions in the airports neighbourhood, although due to intrinsic nature of these procedures, the integration of these procedures need to develop a new framework for airline operators and air traffic control. Based on the BADA model developed by EUROCONTROL, three activities have been carried out: simulation of several continuous climbs for three aircraft types (Light, Medium and Heavy), analysation of different applied separations throughout the climb from the runway up to cruise level and, as third activity, definition of new separation minima to ensure that the minimum separations are not violated with this new procedures along the climb. In this work are presented the results of modelling three continuous climb type (constant true airspeed, constant climb angle and constant vertical speed) and new time-based separations for most used models in Palma TMA, which will be the case-study scenario. Finally, this theoretical analysis has been applied to a real scenario in Palma de Mallorca TMA in order to compare how the capacity deals with the introduction of this new procedure to standard departures, standard departures are understood as a departure with a level-off at a determined altitude and with the possibility to be affected by any ATC action. First outcomes are promising because capacity, theoretically, would not be grossly diminished, which could initially be expected based on previous studies on continuous descent approaches, although these results should be considered cautiously due to the fact that the model lacks several factors of associated uncertainty for a real climb. DOI: http://dx.doi.org/10.4995/CIT2016.2016.3525

1.5 μm lidar anemometer for true air speed, angle of sideslip, and angle of attack measurements on-board Piaggio P180 aircraft

Lidar (light detection and ranging) is a well-established measurement method for the prediction of atmospheric motions through velocity measurements. Recent advances in 1.5 μm Lidars show that the technology is mature, offers great ease of use, and is reliable and compact. A 1.5 μm airborne Lidar appears to be a good candidate for airborne in-flight measurement systems. It allows measurements remotely, outside aircraft aerodynamic disturbance, and absolute air speed (no need for calibration) with great precision in all aircraft flight domains.In the framework of the EU AIM2 project, the ONERA task has consisted of developing and testing a 1.5 μm anemometer sensor for in-flight airspeed measurements. The objective of this work is to demonstrate that the 1.5 μm Lidar sensor can increase the quality of the data acquisition procedure for aircraft flight test certification.This article presents the 1.5 μm anemometer sensor dedicated to in-flight airspeed measurements and describes the flight tests performed successfully on-board the Piaggio P180 aircraft. Lidar air data have been graphically compared to the air data provided by the aircraft flight test instrumentation (FTI) in the reference frame of the Lidar sensor head. Very good agreement of true air speed (TAS) by a fraction of ms−1, angle of sideslip (AOS), and angle of attack (AOA) by a fraction of degree were observed.

A simulator of the aircraft air data system

This paper considers the purpose, principles of construction, algorithms of generating output signals and the functional diagram of a simulator of aircraft air signals that is built based on the vortex sensor of aerodynamic angle and true airspeed.

Optimal Control Framework for Cruise Economy Mode of Flight Management Systems

The main contribution of this paper is to propose optimal and suboptimal control solutions to the cruise economy mode problem in a flight management system for flights below the drag divergence Mach number. The problem is formulated as an optimization of a functional that trades off the fuel and time-related costs of a flight using a (crew-supplied) cost index CI. A novel approach is proposed based on solving the problem analytically using a combination of Pontryagin’s maximum principle and the Hamilton–Jacobi–Bellman equation. A suboptimal analytical solution for the true airspeed is obtained in state feedback form, which reduces to the well-known optimal solution for maximum range when the cost index vanishes. An analytical solution for the speed target as a function of the cost index gives physical insight, allows one to analytically compute sensitivities, and eliminates the need to have a performance database to store the optimal speed schedules in the system. An extension shows that the approach is valid when the aircraft is turning with a small bank angle. Overall, this work provides not only a very efficient means of implementing the optimal speed schedules in an onboard flight management system for flights below the divergence Mach number, but also extends the theory of aircraft performance to the more general case based on a nonzero cost index. The new results are compared with flight simulation data for an A320 Airbus aircraft.

Optimal air route flight conflict resolution based on receding horizon control

To deal with the air route flight conflicts caused by abnormal situations during four-dimensional based air traffic operation, the air route flight conflict resolution problem for two aircrafts was addressed. Based on the optimized static single heading angle or ground speed adjustment strategy, we proposed an optimized dynamic mixed conflict resolution strategy based on Receding Horizon Control (RHC), which considered the possibility of one aircraft's ground speed variation. In particular, the wind speed vector disturbance during conflict resolution might lead to a model mismatch, so the maximum likelihood estimation method and the Newton–Raphson iterative algorithm were employed to identify the wind speed vector using the aircraft true airspeed inputs and ground based trajectory measurements. Moreover, we considered the convergence of conflict resolution method based on RHC and proposed the pre-condition that local and global optimization resolution can be achieved. We compared three situations, i.e., static single strategy optimization, dynamic mixed strategy optimization using RHC with one aircraft's ground speed variation, and dynamic mixed strategy optimization using RHC with the wind speed vector disturbance. We demonstrated that the dynamic mixed strategy responds to one aircraft's ground speed disturbance quickly, and resolved conflict by track angle and ground speed adjustments in an effective manner after the wind speed vector being identified accurately.

Modeling the fuel flow-rate of transport aircraft during flight phases using genetic algorithm-optimized neural networks

Predicting the fuel consumption of transport aircraft is vital for minimizing the detrimental effects of fuel emissions on the environment, saving fuel energy sources, reducing flight costs, achieving more accurate aircraft trajectory prediction, and providing effective and seamless management of air traffic. In this study, a genetic algorithm-optimized neural network topology is designed to predict the fuel flow-rate of a transport aircraft using real flight data. This model incorporates the cruise flight phase and the fuel consumption dependency with respect to both the variation of true airspeed and altitude. Feed-forward backpropagation and Levenberg–Marquardt algorithms are applied, and a genetic algorithm is utilized to design the optimum network architecture regarding time and effort. The predicted fuel flow-rates closely match the real data for both neural network training algorithms. Backpropagation gives the best accuracy for the climb and cruise phases, whereas the Levenberg–Marquardt algorithm is optimal for the descent phase.

System of air signals of aircraft with stationary non-protrusive flow receiver

Features of constructing and information processing algorithms for the system of air signals of an aircraft with the stationary non-protrusive flow receiver, built on the basis of ion-beacon sensor of aerodynamic angle and true airspeed, are disclosed.

On the Discrepancy in Simultaneous Observations of the Structure Parameter of Temperature Using Scintillometers and Unmanned Aircraft

We elaborate on the preliminary results presented in Beyrich et al. (in Boundary-Layer Meteorol 144:83–112, 2012), who compared the structure parameter of temperature ( $${C_{T}^2}_{}$$ ) obtained with the unmanned meteorological mini aerial vehicle ( $$\text{ M }^{2}\text{ AV } $$ ) versus $${C_{T}^2}_{}$$ obtained with two large-aperture scintillometers (LASs) for a limited dataset from one single experiment (LITFASS-2009). They found that $${C_{T}^2}_{}$$ obtained from the $$\text{ M }^{2}\text{ AV } $$ data is significantly larger than that obtained from the LAS data. We investigate if similar differences can be found for the flights on the other six days during LITFASS-2009 and LITFASS-2010, and whether these differences can be reduced or explained through a more elaborate processing of both the LAS data and the $$\text{ M }^{2}\text{ AV } $$ data. This processing includes different corrections and measures to reduce the differences between the spatial and temporal averaging of the datasets. We conclude that the differences reported in Beyrich et al. can be found for other days as well. For the LAS-derived values the additional processing steps that have the largest effect are the saturation correction and the humidity correction. For the $$\text{ M }^{2}\text{ AV } $$ -derived values the most important step is the application of the scintillometer path-weighting function. Using the true air speed of the $$\text{ M }^{2}\text{ AV } $$ to convert from a temporal to a spatial structure function rather than the ground speed (as in Beyrich et al.) does not change the mean discrepancy, but it does affect $${C_{T}^2}_{}$$ values for individual flights. To investigate whether $${C_{T}^2}_{}$$ derived from the $$\text{ M }^{2}\text{ AV } $$ data depends on the fact that the underlying temperature dataset combines spatial and temporal sampling, we used large-eddy simulation data to analyze $${C_{T}^2}_{}$$ from virtual flights with different mean ground speeds. This analysis shows that $${C_{T}^2}_{}$$ does only slightly depends on the true air speed when averaged over many flights.

High-resolution measurement of cloud microphysics and turbulence at a mountaintop station

Abstract. Mountain research stations are advantageous not only for long-term sampling of cloud properties but also for measurements that are prohibitively difficult to perform on airborne platforms due to the large true air speed or adverse factors such as weight and complexity of the equipment necessary. Some cloud–turbulence measurements, especially Lagrangian in nature, fall into this category. We report results from simultaneous, high-resolution and collocated measurements of cloud microphysical and turbulence properties during several warm cloud events at the Umweltforschungsstation Schneefernerhaus (UFS) on Zugspitze in the German Alps. The data gathered were found to be representative of observations made with similar instrumentation in free clouds. The observed turbulence shared all features known for high-Reynolds-number flows: it exhibited approximately Gaussian fluctuations for all three velocity components, a clearly defined inertial subrange following Kolmogorov scaling (power spectrum, and second- and third-order Eulerian structure functions), and highly intermittent velocity gradients, as well as approximately lognormal kinetic energy dissipation rates. The clouds were observed to have liquid water contents on the order of 1 g m−3 and size distributions typical of continental clouds, sometimes exhibiting long positive tails indicative of large drop production through turbulent mixing or coalescence growth. Dimensionless parameters relevant to cloud–turbulence interactions, the Stokes number and settling parameter are in the range typically observed in atmospheric clouds. Observed fluctuations in droplet number concentration and diameter suggest a preference for inhomogeneous mixing. Finally, enhanced variance in liquid water content fluctuations is observed at high frequencies, and the scale break occurs at a value consistent with the independently estimated phase relaxation time from microphysical measurements.

Applicability of a Counterpropagating Laser Airspeed Sensor to Aircraft Flight Regimes

This paper presents the investigation of the applicability of a counterpropagating laser airspeed sensor system to measure airflow velocity in the subsonic-to-transonic aircraft flight regimes. The system uses the Doppler shift of an absorption line in the -band of molecular oxygen near 760 nm combined with an independent measurement of the static pressure and temperature to determine the true airspeed. The unique experimental arrangement using laser diodes allows the possibility for fully analog signal processing, while the size and weight of the system would be appropriate for most commercial aircraft or unmanned aerial vehicles flying today. Static pressure and velocity regimes were investigated in wind-tunnel tests from static pressures of 20 to 150 kPa (altitude equivalent 40,000 ft to subsea-level) and airspeeds of 5 to . It is concluded that counterpropagating laser airspeed sensor is a viable airspeed instrument for these aircraft flight regimes as well as a safety-enhancing possible alternative or supplement to pitot-based air data systems.

Turbulent Mixing in Shallow Trade Wind Cumuli: Dependence on Cloud Life Cycle

Abstract Helicopter-borne observations of the impact of turbulent mixing and cloud microphysical properties in shallow trade wind cumuli are presented. The measurements were collected during the Cloud, Aerosol, Radiation and Turbulence in the Trade Wind Regime over Barbados (CARRIBA) project. Basic meteorological parameters (3D wind vector, air temperature, and relative humidity), cloud condensation nuclei concentrations, and cloud microphysical parameters (droplet number, size distribution, and liquid water content) are measured by the Airborne Cloud Turbulence Observation System (ACTOS), which is fixed by a 160-m-long rope underneath a helicopter flying with a true airspeed of approximately 20 m s−1. Clouds at different evolutionary stages were sampled. A total of 300 clouds are classified into actively growing, decelerated, and dissolving clouds. The mixing process of these cloud categories is investigated by correlating the cloud droplet number concentration and cubed droplet mean volume diameter. A significant tendency to more inhomogeneous mixing with increasing cloud lifetime is observed. Furthermore, the mixing process and its effects on droplet number concentration, droplet size, and cloud liquid water content are statistically evaluated. It is found that, in dissolving clouds, liquid water content and droplet number concentration are decreased by about 50% compared to actively growing clouds. Conversely, the droplet size remains almost constant, which can be attributed to the existence of a humid shell around the cloud that prevents cloud droplets from rapid evaporation after entrainment of premoistened air. Moreover, signs of secondary activation are found, which results in a more difficult interpretation of observed mixing diagrams.

Fuel flow-rate modelling of transport aircraft for the climb flight using genetic algorithms

AbstractIn this study, development of a new fuel flow rate model for the climbing phase of flight was achieved using a genetic algorithm (GA) method. Two modelling approaches were performed using real flight data records (FDRs) from a medium-weight transport-category aircraft. The first model considered the dependency of fuel consumption only with respect to altitude, whereas the effects of both altitude and true airspeed (TAS) were included in the second model. The proposed models are improvements on existing models because the relationship between fuel flow rate, flight altitude, and TAS can be deduced using the derived formulations. Both modelling approaches were found to provide accurate results after performing an error analysis for fuel flow rate values. It was clear that incorporating the TAS effect into the second model enhanced the accuracy of the model, but the first model was also found to be appropriate for practical usage.