Real-time Aircraft Research Articles

Real-time aircraft noise likeness detector

Abstract One of the most difficult tasks involved in the process of noise monitoring near airports is related to the automatic detection and classification of aircraft noise events. These tasks can be solved by applying pattern recognition techniques to the audio signal captured by a microphone. But now the problem is caused by the background noise, which is present in real environments. This paper proposes a real-time method for continuously tracking the similarity of the input sound and the aircraft’s sounds. Using these facilities, the monitoring unit will be able to mark aircraft events, or to make measurements only when aircraft sound is louder than background noise. A one-class approach has been applied to this detection-by-classification method. Using the default setup, 93% of the aircraft’s events which held an SNR of 6–8 dB were detected, for 30 different locations with diverse soundscapes.

Real-Time Dynamic Modeling: Data Information Requirements and Flight-Test Results

Practical aspects of identifying dynamic models for aircraft in real time were studied. Topics include formulation of an equation-error method in the frequency domain to estimate non-dimensional stability and control derivatives in real time, data information content for accurate modeling results, and data information management techniques such as data forgetting, incorporating prior information, and optimized excitation. Real-time dynamic modeling was applied to simulation data and flight test data from a modified F-15B fighter aircraft, and to operational flight data from a subscale jet transport aircraft. Estimated parameter standard errors, prediction cases, and comparisons with results from a batch output-error method in the time domain were used to demonstrate the accuracy of the identified real-time models.

Hardware-in-the-Loop Testing of a Fuel Cell Aircraft Powerplant

This paper presents the experimental methods and test results of a hardware-in-the-loop simulation of the powerplant for a small-scale fuel-cell-powered unmanned aerial vehicle. In this study, the hardware associated with the powerplant, power train, energy storage, and control systems operates dynamically as a component within a real-time aircraft simulation routine. Control signals, electrical loads, and mechanical loads are applied to the hardware to emulate the conditions of operation of the unmanned aerial vehicle powerplant during flight. Experimental results from hardware-in-the-loop testing of the fuel cell power train are presented with uncertainty analysis and discussion. These results show new aspects of the performance of fuel cell unmanned aerial vehicle powerplants, including the powerplant performance during long-endurance missions, power train subsystem power consumption, and unmodeled fuel cell dynamics. A comparison of the measured powerplant performance to experimental results from the literature shows that the fuel cell powerplant can outperform advanced electrochemical energy storage and internal combustion powerplants at the scale of the hardware-in-the-loop aircraft.

Analysis of Departure and Arrival Profiles Using Real-Time Aircraft Data

The quantity and rate of fuel burned during aircraft operations forms the basis of all emission inventories at airports. The international standard for calculating fuel burn and emissions produced is the landing and takeoff cycle of the International Civil Aviation Organization and forms the basis for many emission inventory models and emission charging schemes at airports. The acquisition of real-time aircraft flight data recorder information provided a unique opportunity to compare actual operational fuel flows and times in mode to the International Civil Aviation Organization standard. For departures, there is tremendous variety in fuel flow patterns, rates of fuel flow, and times in mode. Only 67% of the flights analyzed show a classic transition from takeoff to climbout. Most of the remaining flights showed essentially flat-line fuel flow profiles. All aircraft showed some fuel flow rates indicative of reduced-thrust departures. The certificated values for departure fuel burn matched favorably to the real-time totals for four-engine aircraft. However, for the twin-engine aircraft in this study, total departure fuel burn was grossly overpredicted, due to shorter observed departure times in mode. The average approach times in mode were slightly higher than the International Civil Aviation Organization norm, but approach fuel flow rates were significantly lower, yielding lower total fuel burn values. In general, total fuel burn for both departures and arrivals is overestimated by the International Civil Aviation Organization method.

Real time aircraft fly-over noise discrimination

A method for measuring aircraft noise time history with automatic elimination of simultaneous urban noise is presented in this paper. A 3 m-long 12-microphone sparse array has been proven to give good performance in a wide range of urban placements. Nowadays, urban placements have to be avoided because their background noise has a great influence on the measurements made by sound level meters or single microphones. Because of the small device size and low number of microphones (that make it so easy to set up), the resolution of the device is not high enough to provide a clean aircraft noise time history by only applying frequency domain beamforming to the spatial cross-correlations of the microphones’ signals. Therefore, a new step to the processing algorithm has been added to eliminate this handicap.

Robust Nonlinear Model Predictive Control With Partial State Information

A nonlinear controller methodology is developed based on nonlinear model predictive control and set-membership estimation, resulting in a controller which is robust to model uncertainties and bounded noise sources. The model predictive control makes direct use of the estimated bounds of the states and model parameters through integration as constraints in the optimization problem. This results in lower computation times and the ability to satisfy constraints with partial state information. Stability of the integrated estimation and control algorithm is guaranteed through the use of a contractive terminal cost. Real time implementation is developed through a unique sequential quadratic programming solver, which develops an initial feasible solution very quickly, and continues to optimize as time allows. The estimation and control algorithm is demonstrated in software simulation, hardware simulation, and in uninhabited aircraft flight tests. A formation flight example consisting of two aircraft is presented, showing how the controller can maintain a formation within given constraints and avoid collisions while in the presence of noise. Real time flight control results for an autonomous airplane demonstrate the capability of the algorithms to control a nonlinear aircraft in real time around a suddenly appearing threat, thus avoiding collisions.

Simulation and Flight Test of Autonomous Aircraft Estimation, Planning, and Control Algorithms

The development, summary, and validation of real time autonomous estimation, planning, and control algorithms for nonlinear aircraft are presented. Two square root estimation algorithms are developed and used to estimate the state dynamics, parameters, and uncertainty bounds of a nonlinear aircraft in real time. A square root sigma point filter approximates the uncertain state using a finite set of points, while a square root extended set-membership filter bounds the states and parameters of the nonlinear system using ellipsoidal sets. The estimation methods are integrated into online optimized model predictive control methodology for fast reconfigurable control, and a path planner based on streamlines for fast path planning around obstacles and for target pursuit. The performances of the estimation, planning, and control techniques are tested in flight using the SeaScan autonomous aircraft. The SeaScan platform is briefly described, and real time hardware in the loop and flight data are presented for a variety of applications using each of the algorithms.

Linear Programming and Language Processing for Human-Unmanned Aerial-Vehicle Team Missions

This paper presents a manned-vehicle/unmanned-aerial-vehicle (UAV) mission system that enables an operator in a manned aircraft to issue mission level commands to an autonomous aircraft in real time. A natural language interface allows the manned and unmanned vehicle to communicate in languages understood by both agents. A task scheduler transforms the commands into a dynamic mission plan consisting of task waypoints. These are then given to a mixed-integer linear programming (MILP)-based trajectory optimizer, which safely guides the vehicle through a partially known environment in real time. The MILP trajectory planning formulation and its implementation are discussed in detail. Integrated simulation and June 2004 flight-test results that used an F-15 and an autonomous T-33 equipped with Boeing’s unmanned combat air vehicle (UCAV) avionics package are presented. These activities were part of the Capstone Demonstration of the Defense Advanced Research Projects Agency-sponsored Software Enabled Control effort. The flight tests mark the first time that an onboard MILPbased guidance system was used to control a UAV. They also mark the first time that a natural language interface was used by a manned vehicle to task a UAV in real time.

Real-Time Parameter Estimation in the Frequency Domain

A method for real-time estimation of parameters in a linear dynamic state space model was developed and studied. The application is aircraft dynamic model parameter estimation from measured data in flight for indirect adaptive or reconfigurable control. Equation error in the frequency domain was used with a recursive Fourier transform for the real-time data analysis. Linear and nonlinear simulation examples and flight test data from the F-18 High Alpha Research Vehicle HARV) were used to demonstrate that the technique produces accurate model parameter estimates with appropriate error bounds. Parameter estimates converged in less than 1 cycle of the dominant dynamic mode natural frequencies, using control surface inputs measured in flight during ordinary piloted maneuvers. The real-time parameter estimation method has low computational requirements, and could be implemented aboard an aircraft in real time.

The Application of Oct-Tree Terrain Models to Real-Time Aircraft Flight Path Planning

This paper outlines a technique to represent terrain using tree structures, based on Morton ordering to avoid the use of pointers. This approach enables terrain data to be organised in a hierarchical form affording a trade-off between the speed of access to the terrain database and resolution of the terrain data extracted from the tree. A set of database access algorithms is developed that form the basis of path extraction needed for real-time mission management. Several examples are presented to illustrate the performance of the routeing algorithms developed in the paper.

Real-time implementation of an algorithm for self-repairing control systems based on LQG optimization

In this paper a self-repairing real-time control (SRC) system based on LQG (Linear Quadratic Gaussian) optimization is proposed. Its transputer implementation and a real-time aircraft application are presented. The SRC system is composed of the monitoring of the control system, the detection and diagnosis of the failure and the reconfiguration of the control laws. The proposed SRC system is suitable for real-time operation because of the parallel nature of its architecture. The INMOS multitransputer implementation of the SRC applied to an aircraft model provides 56 per cent efficiency compared to a single-transputer implementation.

Coherent lidar airborne wind sensor II: flight-test results at 2 and 10 μm

The use of airborne laser radar (lidar) to measure wind velocities and to detect turbulence in front of an aircraft in real time can significantly increase fuel efficiency, flight safety, and terminal area capacity. We describe the flight-test results for two coherent lidar airborne shear sensor (CLASS) systems and discuss their agreement with our theoretical simulations. The 10.6-μm CO(2) system (CLASS-10) is a flying brassboard; the 2.02-μm Tm:YAG solid-state system (CLASS-2) is configured in a rugged, light-weight, high-performance package. Both lidars have shown a wind measurement accuracy of better than 1 m/s.

The shipboard exposure testing of aircraft materials

The aircraft carrier environment provides the most severe conditions to which naval aircraft materials are exposed. The combination of humidity, temperature, salt content from the water vapor, and sulfur dioxide from aircraft exhausts creates an extremely corrosive environment. Under these conditions, unprotected high-strength aluminum alloys exhibit extensive exfoliation during relatively short periods of exposure. Although various ASTM standards have been established to characterize corrosion (ranging from exfoliation to general corrosion and pitting), there is no laboratory test that compares with real-time aircraft exposure. Still, accelerated laboratory tests have been devised that well simulate the exposure of aluminum alloys in the natural environment, although there is no real correlation for aluminum-lithium alloys. Considering these factors, this paper compares the results of shipboard exposure testing with those obtained from laboratory accelerated tests.

Optical design of a wide-angle simulator probe

An optical design concept is presented for a wide field of view camera, used to take pictures of a model board, which are displayed to the pilot of a simulated aircraft in real time. The concept achieves mapping functions and perspectives in three separate images that match the display system properties over 140 deg field of view. This enables fast feedback of the model board images to the pilot by avoiding the need for computer correction of optical distortion. The geometry of the lens system also ensures good uniformity of brightness over the wide field of view. The provision of three axes of angular movement and computer optical design techniques are discussed. The general design and fabrication of a prototype is described.

Expert system for real-time aircraft monitoring

Real-time aircraft testing is increasing in both frequency and complexity. Greater demands are being placed on flight test engineers to simultaneously monitor aircraft systems during flight and to perform problem analysis real time. This has caused a rise in requirements for automated and intelligent monitoring systems. The use of state-of-the-art off-the-shelf hardware and software has provided a cost effective base for supporting development of real-time expert systems to aid in these monitoring tasks. A brief introduction to the telemetry environment is given. This is followed by descriptions of some specific applications including a propulsion monitor. The final section discusses some aspects of knowledge engineering and an inherent conflict between knowledge engineering and software engineering.

Elimination of directional wave spectrum contamination from noise in elevation measurements

The Surface Contour Radar (SCR) is a 36-GHz computer-controlled airborne radar which generates a false-color-coded elevation map of the sea surface below the aircraft in real time, and can routinely produce ocean directional wave spectra with post-flight data processing which have much higher angular resolution than pitch-and-roll buoys. The SCR range measurements are not error-free and the resulting errors in the elevations corrupt the directional wave spectrum. This paper presents a technique for eliminating that contamination.

An Application of Manned Simulation in Crew Station Conceptual Development

The McDonnell Aircraft Company's Manned Air Combat Simulator is being used in the early design and evaluation phases of an advanced real-time reconnaissance aircraft. The cockpit arrangement and control logic have been implemented in the engineering development simulator. To date there have been two formal human factors evaluations of the system under simulated operational conditions. This presentation outlines the procedures used, the results, and their impact upon the design.

Application of CCD Technology to Produce Imagery from Radar Data

A real-time aircraft synthetic-aperture radar (SAR) image processor using charge-coupled device (CCD) technology has been developed. Both range and azimuth convolution are accomplished using CCD transversal filtering in the analog domain. The computational equivalency of a CCD transversal filter to comparatively more complex digital processing implementations provides significant reductions in processor power, weight, size, and cost requirements. This paper describes the results of the aircraft CCD SAR image-processor development work to date.