Air Data System Research Articles

Laser-based air data system for aircraft control using Raman and elastic backscatter for the measurement of temperature, density, pressure, moisture, and particle backscatter coefficient

Flight safety in all weather conditions demands exact and reliable determination of flight-critical air parameters. Air speed, temperature, density, and pressure are essential for aircraft control. Conventional air data systems can be impacted by probe failure caused by mechanical damage from hail, volcanic ash, and icing. While optical air speed measurement methods have been discussed elsewhere, in this paper, a new concept for optically measuring the air temperature, density, pressure, moisture, and particle backscatter is presented, being independent on assumptions on the atmospheric state and eliminating the drawbacks of conventional aircraft probes by providing a different measurement principle. The concept is based on a laser emitting laser pulses into the atmosphere through a window and detecting the signals backscattered from a fixed region just outside the disturbed area of the fuselage flows. With four receiver channels, different spectral portions of the backscattered light are extracted. The measurement principle of air temperature and density is based on extracting two signals out of the rotational Raman (RR) backscatter signal of air molecules. For measuring the water vapor mixing ratio-and thus the density of the moist air-a water vapor Raman channel is included. The fourth channel serves to detect the elastic backscatter signal, which is essential for extending the measurements into clouds. This channel contributes to the detection of aerosols, which is interesting for developing a future volcanic ash warning system for aircraft. Detailed and realistic optimization and performance calculations have been performed based on the parameters of a first prototype of such a measurement system. The impact and correction of systematic error sources, such as solar background at daytime and elastic signal cross talk appearing in optically dense clouds, have been investigated. The results of the simulations show the high potential of the proposed system for reliable operation in different atmospheric conditions. Based on a laser emitting pulses at a wavelength of 532 nm with 200 mJ pulse energy, the expected measurement precisions (1-σ statistical uncertainty) are <0.6 K for temperature, <0.3% for density, and <0.4% for pressure for the detection of a single laser pulse at a flight altitude of 13,000 m at daytime. The errors will be smaller during nighttime or at lower altitudes. Even in optically very dense clouds with backscatter ratios of 10,000 and RR filters suppressing the elastic backscatter by 6 orders of magnitude, total errors of <1.4 K, <0.4%, and <0.9%, are expected, respectively. The calculations show that aerospace accuracy standards will be met with even lower pulse energies of 75 mJ for pressure and 18 mJ for temperature measurements when the backscatter signals of 10 laser pulses are averaged. Using laser sources at 355 nm will lead to a further reduction of the necessary pulse energies by more than a factor of 3.

Effects of Pressure Ports Layout on Angle of Attack and Sideslip Estimation in the Flush Air Data System

Flush air data system (FADS) have been successfully used on the nose tip of large manned/unmanned air vehicles instead of a traditional noseboom air data system. In order to integrate FADS with strapdown inertial navigation, high accuracy of angle of attack and sideslip is required. The estimated accuracy of angle of attack and sideslip in three types of FADS, which have different pressure ports layout, is compared using the nonlinear least squares theory. Evaluation function is provided to evaluate the accuracy of angle of attack and sideslip in different pressure ports layout. The results show that more sensors and radiation-type can provide high accuracy.

Analysis of requirements to the measurement channels of helicopter air data system based on a stationary combined aerometric receiver

The structural and functional scheme of helicopter air data system based on a stationary combined aerometric receiver using the aerometric field information of the main rotor vortex column is considered. According to the algorithms of information signal formation, the requirements to metrological characteristics of primary information sensors for the measurement channel system are substantiated.

Multi sensor data fusion based approach for the calibration of airdata systems

AbstractAccurate and reliable airdata systems are critical for aircraft flight control system. In this paper, both extended Kalman filter (EKF) and unscented Kalman filter (UKF) based various multi sensor data fusion methods are applied to dynamic manoeuvres with rapid variations in the aircraft motion to calibrate the angle-of-attack (AOA) and angle-of-sideslip (AOSS) and are compared. The main goal of the investigations reported is to obtain online accurate flow angles from the measured vane deflection and differential pressures from probes sensitive to flow angles even in the adverse effect of wind or turbulence. The proposed algorithms are applied to both simulated as well as flight test data. Investigations are initially made using simulated flight data that include external winds and turbulence effects. When performance of the sensor fusion methods based on both EKF and UKF are compared, UKF is found to be better. The same procedures are then applied to flight test data of a high performance fighter aircraft. The results are verified with results obtained using proven an offline method, namely, output error method (OEM) for flight-path reconstruction (FPR) using ESTIMA software package. The consistently good results obtained using sensor data fusion approaches proposed in this paper establish that these approaches are of great value for online implementations.

An Integrated Air Data / GPS Navigation System for Helicopters

In this study, the integration of two navigation systems Air Data System (ADS) and Global Positioning System (GPS) was aimed. ADS is a widely used navigation system which measures static and total air pressure and the air temperature. ADS has high sampling frequency and poor accuracy, on the other hand, another navigation system GPS has high accuracy compared to ADS but lower sampling frequency.Kalman Filter is used to integrate and minimize the errors of the two navigation systems. By this integration a navigation system with high sampling frequency and high accuracy is aimed. Another object is to calculate the wind speed with high accuracy.

Robust Fault Detection for Commercial Transport Air Data Probes

AbstractAir data probes provide essential sensing capabilities to aircraft. The loss or corruption of air data measurements due to sensor faults jeopardizes an aircraft and its passengers. To address such faults, sensor hardware redundancy is typically combined with a voting system to detect and discard erroneous measurements. This approach relies on redundancy, which may lead to unacceptable increases in system weight and cost. This paper presents an alternative, model-based approach to fault detection for a non-redundant air data system. The model-based fault detection strategy uses robust linear filtering methods to reject exogenous disturbances, e.g. wind, and provide robustness to model errors. The proposed algorithm is applied to NASA's Generic Transport Model aircraft with an air data system modeled based on manufacturer data provided by Goodrich Corporation. The fault detection filters are designed using linearized models at one flight condition. The detection performance is evaluated at a particular reference flight condition using linear analysis and nonlinear simulations.

Methodology of construction and models of informative signals for a stationary miltichannel flow aerometric receiver of the helicopter air data system

Methodology of constructing a stationary multichannel flow aerometric receiver using the effects of deceleration and throttling of an incoming airflow and their circular transformation in the yaw plane is considered. The mathematical models and algorithms for processing primary informative signals entering along the channels of speed, altitude, angles of attack and slip of the helicopter air data system constructed on the basis of the aerometric receiver being proposed are obtained.

A parametric synthesis technique for a stationary multichannel flow-type aerometric receiver in the helicopter air data system

The statement and a technique for solving a problem of parametric synthesis and rational choice of structural parameters for a stationary multichannel flow-type aerometric receiver using the results of the experiment being planned are clarified. The scheme of a design model and a receiver structure that provide an increase in noise immunity and extension of working velocities in the helicopter air data system are described.

Calibration of Airdata Systems Using Extended Kalman Filtering Technique

One of the aims of air data systems is the determination of flight parameters angles of attack and angle of sideslip from measurements of local pressures and of local flow angles on wings or fuselage using a proper set of sensors. The active and integrated use of flight parameters in a full-authority flight control system imposes requirements for accurate and reliable air data, which are critical to maintain control. In this paper, a methodology based on the data fusion using Extended Kalman Filter technique is applied to dynamic maneuvers with rapid variations in the aircraft motion to calibrate angle of attack and angle of sideslip. The main goal of the investigations reported in this paper is to obtain online accurate flow angles from the measured vane deflection and difference pressures from probes sensitive to flow angles even in the adverse effect of wind or turbulence. The investigations are initially made on simulated flight data with wind and turbulence effects and it is showed that both alpha and beta estimates are accurate. The same procedure is then extended to flight test data of a high performance fighter aircraft. It has been shown using these results that sensor data fusion approach proposed in this paper is of great value in online implementation.

Air data systems - integrated multi system wireless networks

Aircraft data networks are fast becoming more of a necessity due to their support for user mobility. Many aircraft manufacturers are planning to deploy data networks within their airplanes and provide internet connectivity to their passengers. While a data network within the aircraft and passenger access to it causes some security concerns, it open up some safety enhancement opportunities. With internet connectivity within the airplane, the activity within the airplane can be monitored in real-time from the ground station. Also, using the high bandwidth satellite links, the flight critical data could be downloaded to a server in the ground station in real-time flight or periodically, thereby enabling real-time flight status monitoring. In a multi-system environment where a mobile node can utilize multiple interfaces and simultaneously connect to multiple providers, new opportunities exist for efficient location management strategies spanning heterogeneous cellular wireless networks. An integrated framework is developed for location management in such a multi-system, fourth generation (4G) wireless networks. This information-theoretic framework allows each individual sub-system to operate fairly independently, and does not require the knowledge of individual sub-network topologies. An efficient location management in such a loosely coupled network is designed by having a mobile node view its movement as a vector-valued sequence, and then transmit this sequence in an entropy coded form to the network. Ill. 2, bibl. 8 (in English; summaries in English, Russian and Lithuanian).

MEMS 압력센서를 이용한 고성능 무인항공기용 공력자료시스템의 개발과 검증

본 연구에서는 무인항공기의 대기속도 및 압력고도를 측정하는 공력자료시스템(ADS)을 개발하였다. ADS는 비행제어시스템에 항공기 속도와 고도를 제공함으로써 실속속도 이하에서의 비행을 막고 고도유지 비행을 가능하게 하는 시스템이다. 무인항공기의 속도와 고도를 정확하게 측정하는 것은 비행성능을 확인하고 항공기의 안전성을 보장하기 위한 중요한 부분이다. 본 논문에서 개발된 ADS는 MEMS 압력센서, 저역통과필터, 마이크로 컨트롤러 그리고 피토튜브로 구성되어 있다. 온도보정과 압력보정을 통해 ADS 데이터의 오차를 줄였으며 비행시험에서 GPS 데이터와 ADS 데이터를 비교하였다. The air data system(ADS) was developed for unmanned aerial vehicle(UAV) in this paper. Generally, the ADS helps flight control computer(FCC) to control the UAV above the stall speed and to hold the given altitude. The accurate measurement of airspeed and altitude of UAV is important because it indicates a flight performance and assures a safe flight. The ADS consists of MEMS pressure sensors, a lowpass filter, a micro controller unit and a pitot-tube. The ADS errors were reduced by pressure and temperature compensation of MEMS sensors. Finally, the altitude and airspeed data of the ADS was compared with GPS data in the flight test.

Omnidirectional integrated helicopter air data system based on the stationary multichannel aerometric transducer

In this paper, a problem of measuring the altitude-speed helicopter performance in the range of low and near-zero flight velocities is considered. The structural functional scheme of the omnidirectional helicopter air data system based on the stationary aerometric multichannel transducer (AMT) as well as the jet-convective measuring channels is shown and algorithms for the formation of the system output signals are presented. In order to extend the lower bound of operating speeds, it is proposed that the omnidirectional system be integrated with the aeromechanical measuring computer system that realizes the VIMI method with Luenberger’s observer. Also given is the algorithm support and the accuracy of the integrated system operation is estimated.

CFD 해석 및 최적화 기법을 이용한 피토관 형상설계

Accurate measurement of speed and altitude of flying vehicles in air data system remains a critical technical issue. A highly reliable Pitot-static probe is required to obtain air data such as total pressure and static pressure. In this study, an analysis of the characteristics of flowfield around the Pitot-static probe was performed by using a Navier-Stokes CFD code. In addition, for the purpose of finding an optimal configuration, a technique based on the response surface method is applied to the problem with design parameters including shape of the nose section and cone angle. It is shown that the optimal configuration fulfills the MIL specification in wider range of high angles of attack.

EXPERT: An atmospheric re-entry test-bed

In recognition of the importance of an independent European access to the International Space Station (ISS) and in preparation for the future needs of exploration missions, ESA is conducting parallel activities to generate flight data using atmospheric re-entry test-beds and to identify vehicle design solutions for human and cargo transportation vehicles serving the ISS and beyond. The EXPERT (European eXPErimental Re-entry Test-bed) vehicle represents the major on-going development in the first class of activities. Its results may also benefit in due time scientific missions to planets with an atmosphere and future reusable launcher programmes. The objective of EXPERT is to provide a test-bed for the validation of aerothermodynamics models, codes and ground test facilities in a representative flight environment, to improve the understanding of issues related to analysis, testing and extrapolation to flight. The vehicle will be launched on a sub-orbital trajectory using a Volna missile. The EXPERT concept is based on a symmetrical re-entry capsule whose shape is composed of simple geometrical elements. The suborbital trajectory will reach 120 km altitude and a re-entry velocity of 5–6 km / s . The dimensions of the capsule are 1.6 m high and 1.3 m diameter; the overall mass is in the range of 250–350 kg , depending upon the mission parameters and the payload/instrumentation complement. A consistent number of scientific experiments are foreseen on-board, from innovative air data system to shock wave/boundary layer interaction, from sharp hot structures characterisation to natural and induced regime transition. Currently the project is approaching completion of the phase B, with Alenia Spazio leading the industrial team and CIRA coordinating the scientific payload development under ESA contract.

AN UNDERGRADUATE-STUDENT AUTONOMOUS VIDEO-SURVEILANCE UAV PROJECT

This paper reports on a one-year, multidisciplinary, undergraduate project, involving the design, development, testing, and evaluation of a low-cost, unmanned aerial vehicle (UAV) system. The UAV system, including ground station and support software, was developed to autonomously perform video surveillance at low altitude. The ultimate focus of the team was to compete in an international undergraduate student competition. Presented are the competition requirements, systems design and testing, and the competition results. The UAV system was developed using on off-the-shelf components plus some custom-designed software. The vehicle selected was a radio-controlled (RC) hobby-class airframe. On-board sensors included gyros, accelerometers, GPS, and an airdata system. The video-surveillance payload consisted of a digital video camera. Telemetry included navigation-and-control uplink and downlink, plus video downlink. The system is operated from the ground by two students - one responsible for navigation and control, and the other for payload control. The ground station consists of two laptop computers and communication equipment.

Frequency Response Model for Branched Pneumatic Sensing Systems

A frequency response model for branched pneumatic sensors is developed. A typical application is prediction of pneumatic latency and attenuation in aircraft airdata systems, where pneumatic lines are branched to feed a variety of instruments, navigation systems, and pilot displays. The model is developed using small perturbations of the unsteady Navier-Stokes equations. The linearized equations are radially averaged and expressed in the frequency domain. The result is one-dimensional boundary value problem where the pressure oscillation for a given frequency is expressed as a function of position within the sensor. Assuming constant tube geometry and gas properties along an arbitrarily small tubing element allows a closed-form solution of the boundary value equations. This solution becomes a fundamental building block for solving the frequency response of more complex pneumatic geometries. The analysis process employed is similar to applying Kirchhoff's laws to analyze complex electrical circuits. The model predictions are compared against experimental data generated for a simple two-branch configuration. Comparisons for both symmetrical and unbalanced branches are presented. Experiment setup and procedures are described. The comparisons show that the model accurately predicts both the magnitude and phase frequency response of dominant and reflected wave harmonics within each branch of the system.

Air Data Computation in Fly-By-Wire Flight-Control Systems

The aim of air data systems is the determination of flight parameters (such as pressure altitude, Mach number, angles of attack and sideslip) from measurements of local pressures and of local flow angles on wings or fuselage provided by a proper set of sensors. The active and integrated use of flight parameters in a full-authority fly-bywire flight-control system imposes redundant system architecture to achieve an adequate level of reliability and safety. In this paper a methodology for air data computation is proposed that allows the flight parameters to be evaluated on the basis of data measured by four multifunction air data probes. It takes into account the effects of the modification of aircraft configuration during flight, as well as the effects of aircraft maneuver. Finally, it includes dedicated algorithms for the management of redundancy, which are able to detect possible system failures and to provide consolidated outputs. The methodology has been implemented in the Matlab/Simulink environment and a preliminary comparison of the results with flight test data showed satisfactory performance. Nomenclature a = asymptotic speed of sound C pfront i = frontal pressure coefficient of the ith probe C pslot i = slot pressure coefficient of the ith probe Config = aircraft configuration parameter d = (X s, 0, 0) = distance between the section of installation of the probes and the center of mass of the aircraft ffront = characteristic function of the stand alone probe for the frontal pressure fi = flow angle function of the ith probe f Li

Calibration and Data-Reduction Algorithms for Nonconventional Multihole Pressure Probes

The development of calibration and data-reduction algorithms for nonconventional multihole pressure probes is presented. The algorithms that have been developed in the past for conventional five- and seven-hole probes are not optimal for probes with port arrangements (on the probe tip) that are nonconventional. Conventional algorithms utilize the axisymmetry of the port distribution pattern to define the nondimensional pressure coefficients. These coefficients are typically defined specifically for these patterns, but fail to represent correctly different patterns of port arrangements, such as patterns without axisymmetry or regularity. The algorithms introduced can handle any pattern of port arrangement, from axisymmetric and regular to random. Moreover, they eliminate the need to separate the measurement domain of a probe to low-angle and high-angle regimes, typical in conventional five-and seven-hole-probe algorithms that require two different sets of pressure coefficient definitions and procedures. Additionally, the algorithms have been formulated such that they facilitate redundancy implementations, especially in applications where such redundancy is important, such as air-data systems. The developed algorithms are applied to a nonconventional probe, a nearly omnidirectional 18-hole probe, and demonstrate very high flow-measurement accuracy

Simulation of UAV Systems

The study described in this paper deals with the issue of a design tool for the autopilot of an Unmanned Aerial Vehicle (UAV) and the selection of the airdata and inertial system sensors. This project was processed in cooperation with VTUL a PVO o.z. [1]. The feature that distinguishes the autopilot requirements of a UAV (Figs. 1, 7, 8) from the flight systems of conventional manned aircraft is the paradox of controlling a high bandwidth dynamical system using sensors that are in harmony with the low cost low weight objectives that UAV designs are often expected to achieve. The principal function of the autopilot is flight stability, which establishes the UAV as a stable airborne platform that can operate at a precisely defined height. The main sensor for providing this height information is a barometric altimeter. The solution to the UAV autopilot design was realised with simulations using the facilities of Matlab® and in particular Simulink®[2].

MANAGING SENSOR HARDWARE REDUNDANCY ON A SMALL COMMERCIAL AIRCRAFT WITH H∞ FDI OBSERVERS

In this paper the problem of managing Hardware redundancy on the Attitude Heading System and the Air Data System of a small commercial aircraft is considered. The proposed approach is based on a bank of extended H∞ observers guaranteeing sensor fault detection and isolation in the presence of external disturbances and model uncertainties. Each observer is composed of an open loop nonlinear part replicating the system dynamics and a linear feedback action. Sufficient conditions for the synthesis of the feedback action are provided in terms of an LMI feasibility problem. Constraints on the position of the observer poles are added to fasten the residual generation dynamics and to avoid low damped and/or high frequency modes. Numerical simulations on the model of the AP-68 Vulcanair small commercial aircraft are presented.