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Enhancing Real Time Monitoring Support for Safe Envelope Expansion
Optimization of Dynamical Systems 4th International Conference on Advances in Control and 4th International Conference on Advances in Control and 4th International Conference on Advances in Control and February 1-5, of 2016. NIT Tiruchirappalli, India Optimization Dynamical Systems Optimization of Dynamical Systems Available online at www.sciencedirect.com Optimization Dynamical Systems February 1-5, of 2016. NIT Tiruchirappalli, India February 1-5, 2016. NIT Tiruchirappalli, India February 1-5, 2016. NIT Tiruchirappalli, India
ScienceDirect
49-1 (2016) 254–259 Enhancing Real TimeIFAC-PapersOnLine Monitoring Support for Safe Envelope Expansion Enhancing Real Time Monitoring Support for Safe Envelope Expansion Enhancing Time Support for Envelope Expansion Enhancing Real RealKhadeeja Time Monitoring Monitoring Support for Safe Safe Envelope Nusrath TK*, Dushyant Kaliyari*, Jatinder Singh* Expansion
Khadeeja Dushyant Kaliyari*, V Patel** Khadeeja Nusrath Nusrath TK*, TK*,Vijay Dushyant Kaliyari*, Jatinder Jatinder Singh* Singh* Khadeeja Nusrath TK*, Dushyant Kaliyari*, Jatinder Singh* Vijay V Patel** Vijay V Patel** Vijay VBangalore Patel** (e-mail: [email protected]) *National Aerospace Laboratories, *National Aerospace Laboratories, Bangalore (e-mail: [email protected]) **Aeronautical Development Agency, Bangalore *National Aerospace Aerospace Laboratories, Laboratories, Bangalore Bangalore (e-mail: [email protected]) *National (e-mail: [email protected]) **Aeronautical Development Agency, Bangalore **Aeronautical Development Development Agency, Agency, Bangalore Bangalore **Aeronautical Abstract: The paper describes a few simulation techniques implemented to support flight testing Abstract: Thesafe paper describes a few fewof simulation simulation techniques implemented to support support flight testing testing activities and envelope expansion a high performance fighter aircraft. One of the important tasks Abstract: The paper describes techniques implemented to flight Abstract: The paper describes aa few simulation techniques implemented to support flight testing activities and safe envelope expansion of a high performance fighter aircraft. One of the important tasks of flight testing is to safely carry out parameter identification flight tests at the edge of the flight envelope activities and and safe safe envelope envelope expansion expansion of of aa high high performance performance fighter fighter aircraft. aircraft. One One of of the the important important tasks tasks activities of flight testing is to safely carry out parameter identification flight tests at the edge of the flight envelope (maximum angle-of-attack). Wind tunnel data updated on the basis of these flight tests is used to upgrade of flight flight testing testing is is to to safely safely carry carry out out parameter parameter identification identification flight flight tests tests at at the edge edge of of the the flight flight envelope envelope of (maximum angle-of-attack). Wind tunnelfor data updated onclose the basis basis of these thesethe flight tests tests always is used used presents to upgrade upgrade the aircraft flight control design. Flying theupdated first time to envelope boundaries an (maximum angle-of-attack). Wind tunnel data on the of flight is to (maximum angle-of-attack). Wind tunnel data updated on the basis of these flight tests is used to upgrade the aircraft flight control design. Flying for the first time close to envelope boundaries always presents an extra degreeflight of uncertainty due toFlying the nonlinear flight dynamics. This uncertainty needsalways to be removed by the aircraft control design. for the first time close to envelope boundaries presents an the aircraft flight control design. Flying for the first time close toThis envelope boundaries always presents ana extra degree of uncertainty due to the nonlinear flight dynamics. uncertainty needs to be removed by gradually expanding flight envelope through flight tests. Parameter Excursion Boundaries (PEBs) offer extra degree degree of of uncertainty uncertainty due due to to the the nonlinear nonlinear flight flight dynamics. dynamics. This This uncertainty uncertainty needs needs to to be be removed removed by by extra gradually expanding expanding flight envelope through flight tests. Parameter Parameter Excursion Boundaries (PEBs) offer offer convenient option to flight monitor the critical safety parameters in real-time during envelope expansion. PEBsaa gradually envelope through flight tests. Excursion Boundaries (PEBs) gradually envelope flight tests.for Parameter Excursion Boundaries (PEBs) offer convenient option to flight monitor the critical critical safety parameters inspecified real-time duringcondition envelope expansion. PEBsa decide theexpanding safe limits of excursion ofthrough these parameters ain flight and configuration. convenient option to monitor the safety parameters real-time during envelope expansion. PEBs convenient option to monitor the critical safety parameters in real-time during envelope expansion. PEBs decide the safe safecase, limits of excursion excursion ofprocess these parameters parameters for aa maneuvers specified flight flight condition and configuration. In the present batch simulationof of the relevant to becondition carried out during the flight decide the limits of these for specified and configuration. decide the safecase, limits of excursion ofprocess these parameters for a online specified flight condition and configuration. In the present batch simulation of the relevant maneuvers to be carried out during the flight flight tests was used to generate the PEBs. Apart from this, parameter estimation tool was also In the the present present case, case, batch batch simulation simulation process process of of the the relevant relevant maneuvers maneuvers to to be be carried carried out out during during the the In flight tests was used to generate the PEBs. Apart from this, online parameter estimation tool was also . developed for improving the flight test efficiency and for assuring pilot and vehicle safety tests was was used used to to generate generate the the PEBs. PEBs. Apart Apart from from this, this, online online parameter parameter estimation estimation tool tool was was also also tests . developed for improving the flight test efficiency and for assuring pilot and vehicle safety .. Flight developed for improving theFederation flight test test efficiency and forBoundary, assuring pilot and vehicle safety Keywords: Real-Time Monitoring, Parameter Excursion Parameter Estimation, Test © 2016, IFAC (International of Automatic Control) Hosting by and Elsevier Ltd.safety All rights reserved. developed for improving the flight efficiency and for assuring pilot vehicle Keywords: Real-Time Monitoring, Parameter Excursion Boundary, Parameter Estimation, Flight Test Keywords: Real-Time Monitoring, Parameter Excursion Boundary, Parameter Estimation, Flight Keywords: Real-Time Monitoring, Parameter Excursion Boundary, Parameter Estimation, Flight Test Test using only ground-based simulators to cover the envelope using only ground-based simulators to cover the envelope and select maneuvers for flight tests [Tormalm Magnus et. al using only ground-based simulators to cover the envelope using only ground-based simulators toaerodata cover Magnus the envelope and select maneuvers for flight tests [Tormalm et. al (2000)]. A real-time online model and control tool 1. INTRODUCTION and select for flight tests [Tormalm Magnus et. al and selectAmaneuvers maneuvers for of flight testsand [Tormalm Magnus et. al (2000)]. real-time online model aerodata control tool 1. INTRODUCTION (ROMAC), comprising complete simulation model of (2000)]. A real-time online model and aerodata control tool INTRODUCTION A common practice1. followed by the aircraft industry is to (2000)]. A real-time online model and aerodata control tool 1. INTRODUCTION (ROMAC), comprising of complete simulation model of Gripen aircraft, was run of in complete real-time using telemetry input (ROMAC), comprising simulation model of A common followed by the is to use system practice identification tools to aircraft validateindustry the aircraft (ROMAC), comprising of complete simulation model of A common practice followed by the aircraft industry is to Gripen aircraft, was run in real-time input data from the flying test aircraft using and telemetry the simulation A common practice followed by the aircraft industry is to Gripen aircraft, was run in real-time using telemetry input use system identification tools to validate the aircraft aerodynamic database from flight tests. Parameter Gripen aircraft, was run in real-time using telemetry input use system identification tools to validate the aircraft data from the flying test aircraft and the simulation trajectories compared with the flight test data [Klas use system identification tools toapplied validate theParameter aircraft data from the flying test aircraft and the simulation aerodynamic database from tests. Identification (PID) techniques areflight to data gathered data from et. the test and the data simulation aerodynamic database from flight tests. Parameter trajectories compared with the flight test [Klas Andersson al flying (2002)]. At aircraft Daimler Chrysler Aerospace aerodynamic database from flight tests. Parameter trajectories compared with the flight test data [Klas Identification (PID) techniques are applied to data gathered within the flight envelope and, to a certain level, beyond the trajectories compared with the flight test data [Klas Identification (PID) techniques are applied to data gathered Andersson et. al (2002)]. At Daimler Chrysler Aerospace (DASA), the envelope expansion process was supported by Identification (PID) techniques are applied to data gathered Andersson et. al (2002)]. At Daimler Chrysler Aerospace within the flight envelope and, to a certain level, beyond the full operational clearance envelope boundaries. To extract Andersson et. al (2002)]. At Daimler Chrysler Aerospace within the flight envelope and, to a certain level, beyond the (DASA), the envelope expansion process was supported by “Parallel Simulation” comprising of a non-linear simulation within the flight clearance envelope and, to a flight certain level, beyond the (DASA), the envelope expansion process was supported by full operational envelope boundaries. To extract the aerodynamic parameters from data, flight data is (DASA),that the was envelope expansion process waswhile supported by full operational clearance envelope boundaries. To extract “Parallel Simulation” comprising of a non-linear simulation model operated simultaneously the test full operational clearance envelope boundaries. To extract “Parallel Simulation” comprising of a non-linear simulation the aerodynamic parameters from flight data, flight data is gathered from specially designed system identification and “Parallel Simulation” comprising of a non-linear simulation the aerodynamic parameters from flight data, flight data is model that test aircraft was was up inoperated the air simultaneously for flight tests while [Oelkerthe Hansthe aerodynamic parameters from system flight data, flight dataand is model was operated simultaneously while the test gathered from specially designed identification performance maneuvers performed throughout the envelope. model that that was operated simultaneously while theHanstest gathered from specially designed system identification and aircraft was up in the air for flight tests [Oelker Christoph et. al (2000)]. Different real-time parameter gathered from specially designed system identification and aircraft was up in the air for flight tests [Oelker Hansperformance maneuvers performed throughout the envelope. A reliable Decision Support System (DSS) during these aircraft was up in the air for flight tests [Oelker Hansperformance maneuvers performed throughout the envelope. Christoph et. al (2000)]. Different real-time parameter estimation techniques have been used toreal-time speed up parameter the flight performance maneuvers performed throughout the Christoph et. Different A reliable Support System (DSS) during these flight tests isDecision crucial for carefree manoeuvring andenvelope. efficient Christoph et. al al (2000)]. (2000)]. Different real-time parameter A reliable Decision Support System (DSS) during these estimation techniques have been used to speed up theduring flight testing by analysing the aerodynamic characteristics A reliable Decision Support System (DSS) during these estimation techniques have been used to speed up flight tests is crucial for carefree manoeuvring and efficient flight test data gathering. estimation techniques have been used to speed up the theof flight flight tests is crucial for carefree manoeuvring and efficient testing by analysing the aerodynamic characteristics during the conduct of flight tests and making the results data flight tests is crucial for carefree manoeuvring and efficient by analysing the aerodynamic characteristics during testing flight test data gathering. testing by analysing the aerodynamic characteristics during flight test data gathering. the conduct of flight tests and making the results of data analysis available for post flight debrief [Christoph Deiler flight gathering. the conduct of tests and making the results data There test aredata different schemes employed in the telemetry the conduct of flight flight tests and making the results of ofDeiler data analysis available for post flight debrief [Christoph (2012), Timothy J. Spaulding et. al (2011)]. analysis available for post flight debrief [Christoph Deiler There are different schemes employed in the telemetry station to provide support to the pilot for maximum analysis available for post flight debrief [Christoph Deiler There are different schemes employed in the telemetry (2012), Timothy Timothy J. J. Spaulding Spaulding et. There are different schemes employed in for the telemetry (2012), et. al al (2011)]. (2011)]. station to provide the pilot maximum performance without support the risk to of ending up in an out-ofstation to provide support to the pilot for maximum (2012), Timothy J. Spaulding et. al (2011)]. station to provide support to the pilot for maximum performance without the risk of ending up in an out-ofcontrol situation. Flight simulators have been generally used This paper discusses the techniques developed to support performance without the risk ending up in an out-of performance the risk of of and ending up generally in the an present out-ofcontrol situation. Flight simulators have been used flight for flight test without planning, execution safety. In This paper discusses the techniques developed to support data gathering and safe flight envelope expansion of a control situation. Flight simulators have been generally used This paper discusses the techniques developed to control situation. Flight tools simulators have beenspread generally used for flight test planning, execution safety. In the present This paper discusses thesafe techniques developed to support support scenario, simulation haveand wide use in flight data gathering and flight envelope expansion of high performance fly-by-wire aircraft. These algorithms areaa for flight test planning, execution and safety. In the present flight data and flight envelope expansion of for flight test planning, execution andwide safety.spread In during the use present scenario, simulation tools have in flightperformance dataatgathering gathering and safe safe flight envelope expansion ofare supporting carefree manoeuvring, especially the high fly-by-wire aircraft. These algorithms installed the telemetry station for real-time monitoring ofa scenario, simulation tools have wide spread use in high performance fly-by-wire aircraft. These algorithms are scenario, simulation tools Real-time have wide spread use the in supporting carefree manoeuvring, especially during high performance fly-by-wire aircraft. These algorithms are flight envelope expansion. or near real-time installed at the telemetry station for real-time monitoring of the critical flight parameters during flight testing. The paper supporting carefree manoeuvring, especially during the installed at the telemetry station for real-time monitoring of supporting carefree manoeuvring, especially during flight envelope expansion. Real-time or near real-time installed at flight the telemetry station for real-time monitoring of parameter estimation techniques have also been used the for the critical parameters during flight testing. The paper is organized as follows: Section 2 of the paper describes the flight envelope expansion. Real-time or near real-time the critical flight parameters during flight testing. The paper flight envelope expansion. Real-time or near real-time parameter estimation techniques have also been used for the critical flight parameters during flight testing. The paper ensuring the safety and efficiency during the flight testing at is organized as follows: Section 2 of the paper describes the batch simulation process used tothegenerate parameter parameter estimation techniques have also been used is organized as Section 2 paper describes the parameter estimation techniques have been testing used for for ensuring the safety and efficiency the flight at is organized as follows: follows: Section 2 of of thethe paper describes the extreme flight regimes [Kaliyari, Dduring et. al also (2014)]. batch simulation process used to generate parameter excursion boundaries (PEBs) for critical safety ensuring the safety and efficiency during the flight testing at batch simulation process used to generate parameter ensuring the safety and efficiency during the flight testing at extreme flight regimes [Kaliyari, D et. al (2014)]. batch simulation process used to generate parameter excursion (PEBs) critical safety parameters. boundaries Section 3 explains thefor use the of online parameter extreme flight regimes [Kaliyari, D al excursion boundaries (PEBs) for the critical safety extreme regimes [Kaliyari, D et. et.literature al (2014)]. (2014)]. excursion boundaries (PEBs) foruse the critical safety There is flight enough information in open to suggest the parameters. Section 3 explains the of online parameter estimation techniques for improving the flight test efficiency parameters. Section 3 explains the use of online parameter There is enough information in open literature to suggest the parameters. Section 3 explains the use of online parameter use of desktop simulators for ensuring safety during flight estimation techniques for improving the flight test efficiency during envelope expansion. Concluding remarks are There is enough information in open to suggest the estimation techniques for improving the efficiency There isdesktop enough information in ensuring open literature literature toduring suggest the use of simulators safety flight estimation techniques forthe improving the flight flight test test efficiency testing. The introduction offor desktop simulations for JAS39 during envelope expansion. Concluding remarks are provided in Section 4 of paper. use of desktop simulators for ensuring safety during flight during envelope expansion. Concluding use of desktop for ensuring safety during flight testing. The of desktop simulations for JAS39 during envelope expansion. Concluding remarks remarks are are Gripen led introduction tosimulators significantly higher coverage of the provided in Section 4 of the paper. testing. The introduction of desktop simulations for JAS39 provided in Section 4 of the paper. testing. The introduction of desktop simulations for of JAS39 Gripen led to significantly higher coverage the provided in Section 4 of the paper. operational flight envelope compared to the approach of Gripen to higher of Gripen led led flight to significantly significantly higher tocoverage coverage of the the operational envelope compared the approach of operational flight envelope compared to the approach operational flight envelope compared to the approach of of Copyright © 2016 IFAC 254 2405-8963 © 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Copyright 2016 responsibility IFAC 254Control. Peer review© of International Federation of Automatic Copyright ©under 2016 IFAC 254 Copyright © 2016 IFAC 254 10.1016/j.ifacol.2016.03.062
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2. PARAMETER EXCURSION BOUNDARIES (PEBs)
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(AOA) and sideslip, at higher AOAs from wind up turns, keeping all other parameters within safe limits. The input type is decided based on the energy spectrum of the input signals [Jategaonkar, R.V. (2006)]. Optimal input design for data gathering from parameter identification (PID) maneuvers is discussed in Section 2.1.
During the critical flight tests at the edges of flight envelope, it is always desirable to have pre-defined excursion boundaries for the critical flight parameters pertaining to each configuration and flight condition to be test flown. These excursion boundaries are used in the telemetry to monitor the exceedence in the critical parameters, if any, during flight tests. Parameter Excursion Boundaries (PEBs) can be thought of as a “set of pre-defined boundaries of some critical flight parameters (such as angle-of-attack, sideslip, etc.), for a given flight test condition and configuration, that assist in deciding the safe limits of excursions for these parameters”. The aim of PEBs is to have a set of boundaries that would allow safe envelope expansion without having to stop the flight envelope expansion process prematurely because of tolerable model inaccuracies. Parameters monitored online through PEBs include control surface deflections, angle-ofattack, angle-of-sideslip, Mach number, roll rate, yaw rate and their steady state (trim) values. Figure 1 gives a schematic of the process of generating PEBs for real-time telemetry monitoring.
2.
Designed inputs are used in Real Time Simulator (RTS) to verify the extent of excursions in important flight parameters. If the excursions are found to be inadequate for parameter estimation studies, the inputs are redesigned using desktop simulator. Step1 is repeated till the magnitude of excursions in flight parameters from RTS is satisfactory.
3.
The designed FTP inputs are further used to carry out batch simulations at the desired flight conditions and configurations, with varying fuel conditions to study the effect of the movement of center-of-gravity (CG).
4.
For the defined configurations and flight conditions, parameter excursion boundaries are generated from the simulated trajectories in offline mode. The generated PEBs indicate the precincts of the flight parameters, both for the steady state (trim) flight as well as allowable manoeuvring area.
5.
PEBs are put into operation at telemetry station for real-time monitoring and safe envelope expansion during PID data gathering. The excursion boundaries for monitoring the flight test are selected based on the aircraft configuration and the test point trim condition to be executed during the sortie.
2.1 Optimal input design at envelope boundaries To perform Parameter Identification (PID) maneuvers at extreme boundary conditions (at high angles-of-attack, high load factor), the pilot needs to hold the target AOA at constant Mach for a sufficient duration. Generally “wind up turn” maneuver is used to achieve this than the pull-up maneuver. In pull-up maneuver, large speed variation occurs and the pilot is left with very small time window to execute the input. For the test aircraft considered, computer generated flight test inputs through flight test panel (FTP) are executed at the target AOA in windup turn. FTP inputs are designed in such a way that excite the flight parameters of interest within the permissible safe limits and yet provide sufficient information in the data to permit aerodynamic characterization.
Fig.1. Schematic for Parameter Excursion Boundary generation
Since the envelope expansion in the extreme pockets of flight envelope takes place with small increments in angleof-attack, the criterion used for designing FTP input was that the AOA excursion during PID maneuver should be at least 1.0 deg from the trim but should not exceed 1.5 deg to
The following steps are performed to generate the PEBs: 1.
Desktop simulation software is used to design suitable automated Flight Test Panel (FTP) inputs to get the desired excursions in angle-of-attack 255
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maneuvers for the desired range of angles-of-attack for which the envelope expansion is targeted. Fig. 3 gives the typical trajectory plot from the batch simulation process. It shows the magnitude of FTP inputs in pitch, roll and yaw axis and the corresponding excursions in AOA for 6 different cases, corresponding to 6 different trim angles-ofattack. Longitudinal Input Amplitude
Normalized PSD
ensure the safety. The FTP inputs normally selected for data gathering are either doublets or 3-2-1-1, based on the frequency range to be excited. This is determined based on the study of energy spectrum of these inputs [Jategaonkar, R.V. (2006)]. Fig. 2 provides typical energy spectra of different inputs such as pulse, doublet and 3-2-1-1. The FTP inputs are executed to excite the longitudinal, lateral and directional motion and observe the excursion in flight parameters. 1 Pulse Doublet 3211 Modified 3211
0.8 0.6 0.4
5
4
0.2 0 0
2 3 4 Normalized Frequency
5
3 2 Test Cases
Directional
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1
46
8
Time (s)
6 Alpha
1
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Fig.3. Batch Simulation
Fig.2. Energy spectra of different inputs
2.3 PEB generation from simulated responses
2.2 Batch simulation For PEBs
The flow chart in Fig. 4 gives the schematic representation of how simulated trajectories are used to generate excursion boundaries for the critical flight parameters. Simulated responses from all the test maneuvers at each Mach number are collated. Angular rates and control input surface deflections are sorted in ascending order of angle-of-attack. Minimum and maximum value of the parameters is picked at each angle-of-attack. Since lateral parameters and control surface deflections are maneuver dependent (clockwise/anticlockwise wind-up turn), larger of the minimum and maximum values are chosen to provide a symmetric excursion boundary.
Simulation tools when used in conjunction with the actual flight testing, greatly improve the efficiency and effectiveness of flight test program [Dennis. O. Hines (2000)]. Simulation permits the flight envelope to be investigated and understood prior to flight testing. Since the number of possible maneuvers and flight conditions to be flown is generally very large, batch simulation eases the process of generating PEBs for various configurations for different prototypes. The desktop simulation model comprises of a 6DOF state-space model and other submodels for airdata, aerodynamics, rigid body and FCS etc. Aero data models are validated and updated in an incremental manner using system identification and parameter estimation techniques. The desktop simulation can be controlled interactively or with the use of scripts.
Club simulated responses of all the test cases at each Mach number (𝛼𝛼, 𝛽𝛽, 𝑀𝑀𝑎𝑎𝑐𝑐ℎ, 𝑝𝑝, 𝑞𝑞, 𝑟𝑟, 𝛿𝛿𝑎𝑎, 𝛿𝛿𝑒𝑒, 𝛿𝛿𝑟𝑟)
Sort the motion parameters w.r.t. 𝛼𝛼 ®
A Graphical User Interface developed in MATLAB is used to access the input file, which contains the state parameters, events and other configuration settings for running the desktop simulation. Provision is made to select the aerodynamic database corresponding to the configuration being test flown. Envelope points and parameters are specified and the maneuvers to be performed are selected. The model is trimmed, and the actual maneuver is simulated. The simulated time trajectories of all the parameters required for PEB creation are stored in an output file. Simulation using the same maneuver, flight condition and configuration is repeated for different fuel conditions to capture the effect of variation in center-of-gravity. The entire process is automated to simulate all the test
Obtain the minimum and maximum excursion of the parameters at each 𝛼𝛼
Adjust the min & max values to generate symmetric excursion of the parameters
Parameter Excursion Boundaries (𝛼𝛼 𝑣𝑣𝑠𝑠. 𝛽𝛽, 𝛼𝛼 𝑣𝑣𝑠𝑠. 𝛿𝛿𝑒𝑒, 𝛼𝛼 𝑣𝑣𝑠𝑠. 𝑝𝑝, 𝛽𝛽 𝑣𝑣𝑠𝑠. 𝛿𝛿𝑟𝑟, 𝑒𝑒𝑡𝑡𝑐𝑐.)
Fig.4. Generation of PEBs from simulated data 256
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This leads to a set of closed boundaries of flow angles v/s control surface deflection as well as angular rates. Similarly, trim boundaries are generated to verify the trim state of each test point during its execution in real-time.
3. ONLINE PARAMETER ESTIMATION TOOL Online estimation tools can provide an effective means of ensuring safety during flight testing and PID data gathering near envelope boundaries. Two approaches have been developed.
Fig. 5 provides the PEBs plotted in red along with the flight data plotted in green from the test maneuvers during a flight test sortie. These kinds of plots are used for data debrief and post flight data analysis.
a)
A direct comparison of the flight derived aerodynamic coefficients with those obtained from updated simulation tool (Coefficient Matching Approach) b) Real-time estimation of aircraft stability and control derivatives and their comparison with the linear models generated from apriori aerodynamic database using Recursive Parameter Estimation techniques.
0
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EXCURSION BOUNDARY 0
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3.1 Coefficient Matching Approach
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The simulation tool is continuously updated as the flight testing progresses. Close to the edge of the flight envelope, flight testing is carried out in small steps of AOA due to high degree of uncertainty in aerodynamic database at higher AOAs.
r (1unit = 20)
Aerodynamic force and moment coefficients are computed from flight measured angular rates and linear accelerations, and compared with the simulation output in real-time to check for the discrepancies in the coefficients. If the error is small and lies within the pre-defined tolerance bounds, the flight testing can proceed unhindered. Else, the aerodynamic database needs to be updated to account for the newly found trends in the error plots of the aerodynamic coefficients. It is desirable to do a timely update to the aerodynamic database so that the simulation matches the flight measured responses, particularly as the aircraft is flight tested close to the edge of the flight envelope.
Fig.5. PEBs with flight test data gathered for all the test points Fig.6 shows the screenshot of PEBs used for real-time monitoring while an FTP pitch doublet input is executed during wind up turn manuever. The PEBs page includes plots for elevator (DE) v/s AOA, roll rate (P) v/s AOA, yaw rate (R) v/s AOA. During the execution of the test, it can be noticed that the flight data plotted in green lie within the boundary and it helps in safe envelope expansion. If the flight parameters during the execution of maneuver deviate considerablly from the boundaries, the flight test can be aborted and the flight data is analysed to find out the cause of descripencies in the postulated model. Slight deviation from the PEBs are acceptable since the boundaries are generated without accounting for aerodynamic and airdata tolerances. Deviation could also occur due to Mach variation in the flight during the maneuver, since the PEBs are generated for a narrow range of Mach values.
A typical error plot between the flight derived pitching moment coefficient and aerodynamic database with predefined tolerance bound is shown in Fig.7.
0.02 Tolerance Bound 0.015 0.01
Cm
0.005 0 -0.005 -0.01 -0.015 -0.02
Fig.6. Screenshot of PEBs page during real-time monitoring
AOA (1unit = 10)
Fig.7. Error in pitching moment coefficient 257
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k 1 k K( yk 1 ˆyk 1 )
3.2 Recursive Parameter Estimation (RPE) An online parameter estimation tool along with the visuals of the maneuvers is developed to help in safe expansion of flight envelope. This tool compares the aerodynamic derivatives estimated from the flight data in real-time with the linear models generated from the apriori flight updated aerodynamic database. The main advantage of the tool is the ready availability of data analysis results, which would otherwise take half a day with post flight data analysis. The tool essentially ensures in providing the following:
Recursive Filters
RLS EKF DFT
-
y(t) ˆ
error
+
u(t) Aircraft System
Cut down the PID test points, if the estimation results from the first few maneuvers are satisfactory. Estimates of the stability and control derivatives are available for debrief immediately after the flight test sortie. Accompanying visuals ensure proper execution of PID flight maneuvers, which can otherwise be repeated if found unsatisfactory. Flight test can be aborted if the identified parameters show significant deviation from linear derivative values obtained from the apriori database.
y( t ) Fig.8. Schematic block diagram of Recursive parameter estimation
In the present case, EKF and DFT are implemented for the online estimation of stability and control derivatives, as these methods are routinely used for parameter estimation. The online parameter estimation tool is implemented using MATLAB® [Khadeeja Nusrath et.al (2015)]. Visualization tools are created wherein online parameter estimation results along with 3-D visualization of the maneuvers and the time history plots of important motion parameters can be displayed. The 3-D animation of the maneuvers is implemented by feeding the positions and attitude of the aircraft online during the flight test. A typical screenshot of the display from visualization tool is given in Fig. 9.
Recursive Parameter Estimation (RPE) methods provide a new parameter estimate at every time step by using the new information available from the current measured data and the previously obtained results. The measured signals are fed sample by sample to recursive algorithms running on the computer to get the estimation results (stability and control derivatives) displayed in real-time. Fig.8 shows the schematic block diagram for recursive approach. Making use of the previous estimate and the information content in the freshly collected input/output data, the updated parameter is given by
k1 k K(y k1 yˆ k1 )
(1)
where k is the previous estimate, K is the gain giving the direction of update, and (y k1 yˆ k1 ) is the residual error. If the data is assumed to be noise free and error free, no preprocessing of data is required. Otherwise, the recursive algorithms can be utilized for one time estimation of bias and scale factors present in the data and the same may be incorporated into estimation algorithm prior to carrying out exhaustive real-time flight data analysis.
Fig.9. Screenshot of the visualization window of online parameter estimation for a longitudinal maneuver
Various RPE schemes are discussed in literature, e.g., the time domain techniques like the Recursive Least Squares (RLS), Extended Kalman Filter (EKF) and Recursive Maximum Likelihood (RML). In frequency domain, Discrete Fourier Transform (DFT) is mostly used [Jategaonkar, R.V. (2006), John Valasek (2003)].
4. CONCLUSIONS The paper elaborates the use of Parameter Excursion Boundaries and Online Parameter Estimation techniques in the real-time monitoring. During the PID and envelope expansion flight tests, these tools helped saving huge flight 258
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test efforts and also ensure safety of the vehicle and pilot. If significant excursions from predicted values either in the trajectory or in the aerodynamic parameters occur during the tests, the test engineer is able to make an intelligent assessment as to whether to continue with the tests, or to abort and analyze the differences. 5. REFERENCES Christoph Deiler (2012). “An online parameter estimation too”, Deutscher Luft- und Raumfahrtkongress, Document ID: 281206. Dennis. O. Hines (2000). “Simulation in Support of Flight Testing”, RTO AGARDograph 300, Flight Test Techniques Series, Volume 19. Jategaonkar, R.V. (2006). “Flight Vehicle System Identification – A Time Domain Methodology”, AIAA Progress in Astronautics and Aeronautics, Vol. 216, AIAA, Reston, VA. John Valasek and Wei Chen (2003). “Observer/Kalman Filter Identification for Online System Identification of Aircraft”. Journal Of Guidance, Control, And Dynamics, Vol. 26, No. 2. Kaliyari, D., Nusrath TK, K., and Singh, J. (2015). “Validation and Update of Aerodynamic Database at Extreme Flight Regimes”, SAE Technical Paper 201501-2567, DOI: 10.4271/2015-01-2567. Khadeeja Nusrath TK, Basappa (2015). “Online Parameter Estimation with Manoeuvre Visualization”, MATLAB Expo, Bangalore. Klas Andersson, Mats Karlsson and Mårten Staaf (2002). “Aerodynamic and Flight Dynamic Real-Time Analysis During Spin and Carefree Maneuvering Tests of the Saab JAS39 Gripen”, ICAS Congress. Oelker Hans-Christoph and Meyer Thomas (2000). “Online Simulation as a Measure to Increase Safety in Flight Testing of High Performance Aircraft”, ICAS Congress. Tormalm Magnus and Bergström Mattias (2000). “The Use of Desktop Simulations in the Carefree Manoeuvring Flight Test Program of JAS39 Gripen”, ICAS Congress. Timothy J. Spaulding, Cory J. Naddy, Jennifer P. Hines, Garrett W. Knowlan, Danny G. Riley, Zachary T. Schaffer (2011). “Near Real-time Parameter Estimation in the C-12C”, AIAA Atmospheric Flight Mechanics Conference, Portland, Oregon. ACKNOWLEDGMENTS The authors gratefully acknowledge National Flight Test Centre, Aeronautical Development Agency, Bangalore, India, for providing the relevant flight data for carrying out this research work. Authors would also like to acknowledge Mr. Nishat M. Hussain, who contributed in the beginning in developing several programs for generating PEBs and Mr. Gopinath, Hindustan Aeronautics Limited, Bangalore, member of National Control Law (CLAW) team who gave valuable inputs based on real-time monitoring during the conduct of PID flights.
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49-1 (2016) 254–259 Enhancing Real TimeIFAC-PapersOnLine Monitoring Support for Safe Envelope Expansion Enhancing Real Time Monitoring Support for Safe Envelope Expansion Enhancing Time Support for Envelope Expansion Enhancing Real RealKhadeeja Time Monitoring Monitoring Support for Safe Safe Envelope Nusrath TK*, Dushyant Kaliyari*, Jatinder Singh* Expansion
Khadeeja Dushyant Kaliyari*, V Patel** Khadeeja Nusrath Nusrath TK*, TK*,Vijay Dushyant Kaliyari*, Jatinder Jatinder Singh* Singh* Khadeeja Nusrath TK*, Dushyant Kaliyari*, Jatinder Singh* Vijay V Patel** Vijay V Patel** Vijay VBangalore Patel** (e-mail: [email protected]) *National Aerospace Laboratories, *National Aerospace Laboratories, Bangalore (e-mail: [email protected]) **Aeronautical Development Agency, Bangalore *National Aerospace Aerospace Laboratories, Laboratories, Bangalore Bangalore (e-mail: [email protected]) *National (e-mail: [email protected]) **Aeronautical Development Agency, Bangalore **Aeronautical Development Development Agency, Agency, Bangalore Bangalore **Aeronautical Abstract: The paper describes a few simulation techniques implemented to support flight testing Abstract: Thesafe paper describes a few fewof simulation simulation techniques implemented to support support flight testing testing activities and envelope expansion a high performance fighter aircraft. One of the important tasks Abstract: The paper describes techniques implemented to flight Abstract: The paper describes aa few simulation techniques implemented to support flight testing activities and safe envelope expansion of a high performance fighter aircraft. One of the important tasks of flight testing is to safely carry out parameter identification flight tests at the edge of the flight envelope activities and and safe safe envelope envelope expansion expansion of of aa high high performance performance fighter fighter aircraft. aircraft. One One of of the the important important tasks tasks activities of flight testing is to safely carry out parameter identification flight tests at the edge of the flight envelope (maximum angle-of-attack). Wind tunnel data updated on the basis of these flight tests is used to upgrade of flight flight testing testing is is to to safely safely carry carry out out parameter parameter identification identification flight flight tests tests at at the edge edge of of the the flight flight envelope envelope of (maximum angle-of-attack). Wind tunnelfor data updated onclose the basis basis of these thesethe flight tests tests always is used used presents to upgrade upgrade the aircraft flight control design. Flying theupdated first time to envelope boundaries an (maximum angle-of-attack). Wind tunnel data on the of flight is to (maximum angle-of-attack). Wind tunnel data updated on the basis of these flight tests is used to upgrade the aircraft flight control design. Flying for the first time close to envelope boundaries always presents an extra degreeflight of uncertainty due toFlying the nonlinear flight dynamics. This uncertainty needsalways to be removed by the aircraft control design. for the first time close to envelope boundaries presents an the aircraft flight control design. Flying for the first time close toThis envelope boundaries always presents ana extra degree of uncertainty due to the nonlinear flight dynamics. uncertainty needs to be removed by gradually expanding flight envelope through flight tests. Parameter Excursion Boundaries (PEBs) offer extra degree degree of of uncertainty uncertainty due due to to the the nonlinear nonlinear flight flight dynamics. dynamics. This This uncertainty uncertainty needs needs to to be be removed removed by by extra gradually expanding expanding flight envelope through flight tests. Parameter Parameter Excursion Boundaries (PEBs) offer offer convenient option to flight monitor the critical safety parameters in real-time during envelope expansion. PEBsaa gradually envelope through flight tests. Excursion Boundaries (PEBs) gradually envelope flight tests.for Parameter Excursion Boundaries (PEBs) offer convenient option to flight monitor the critical critical safety parameters inspecified real-time duringcondition envelope expansion. PEBsa decide theexpanding safe limits of excursion ofthrough these parameters ain flight and configuration. convenient option to monitor the safety parameters real-time during envelope expansion. PEBs convenient option to monitor the critical safety parameters in real-time during envelope expansion. PEBs decide the safe safecase, limits of excursion excursion ofprocess these parameters parameters for aa maneuvers specified flight flight condition and configuration. In the present batch simulationof of the relevant to becondition carried out during the flight decide the limits of these for specified and configuration. decide the safecase, limits of excursion ofprocess these parameters for a online specified flight condition and configuration. In the present batch simulation of the relevant maneuvers to be carried out during the flight flight tests was used to generate the PEBs. Apart from this, parameter estimation tool was also In the the present present case, case, batch batch simulation simulation process process of of the the relevant relevant maneuvers maneuvers to to be be carried carried out out during during the the In flight tests was used to generate the PEBs. Apart from this, online parameter estimation tool was also . developed for improving the flight test efficiency and for assuring pilot and vehicle safety tests was was used used to to generate generate the the PEBs. PEBs. Apart Apart from from this, this, online online parameter parameter estimation estimation tool tool was was also also tests . developed for improving the flight test efficiency and for assuring pilot and vehicle safety .. Flight developed for improving theFederation flight test test efficiency and forBoundary, assuring pilot and vehicle safety Keywords: Real-Time Monitoring, Parameter Excursion Parameter Estimation, Test © 2016, IFAC (International of Automatic Control) Hosting by and Elsevier Ltd.safety All rights reserved. developed for improving the flight efficiency and for assuring pilot vehicle Keywords: Real-Time Monitoring, Parameter Excursion Boundary, Parameter Estimation, Flight Test Keywords: Real-Time Monitoring, Parameter Excursion Boundary, Parameter Estimation, Flight Keywords: Real-Time Monitoring, Parameter Excursion Boundary, Parameter Estimation, Flight Test Test using only ground-based simulators to cover the envelope using only ground-based simulators to cover the envelope and select maneuvers for flight tests [Tormalm Magnus et. al using only ground-based simulators to cover the envelope using only ground-based simulators toaerodata cover Magnus the envelope and select maneuvers for flight tests [Tormalm et. al (2000)]. A real-time online model and control tool 1. INTRODUCTION and select for flight tests [Tormalm Magnus et. al and selectAmaneuvers maneuvers for of flight testsand [Tormalm Magnus et. al (2000)]. real-time online model aerodata control tool 1. INTRODUCTION (ROMAC), comprising complete simulation model of (2000)]. A real-time online model and aerodata control tool INTRODUCTION A common practice1. followed by the aircraft industry is to (2000)]. A real-time online model and aerodata control tool 1. INTRODUCTION (ROMAC), comprising of complete simulation model of Gripen aircraft, was run of in complete real-time using telemetry input (ROMAC), comprising simulation model of A common followed by the is to use system practice identification tools to aircraft validateindustry the aircraft (ROMAC), comprising of complete simulation model of A common practice followed by the aircraft industry is to Gripen aircraft, was run in real-time input data from the flying test aircraft using and telemetry the simulation A common practice followed by the aircraft industry is to Gripen aircraft, was run in real-time using telemetry input use system identification tools to validate the aircraft aerodynamic database from flight tests. Parameter Gripen aircraft, was run in real-time using telemetry input use system identification tools to validate the aircraft data from the flying test aircraft and the simulation trajectories compared with the flight test data [Klas use system identification tools toapplied validate theParameter aircraft data from the flying test aircraft and the simulation aerodynamic database from tests. Identification (PID) techniques areflight to data gathered data from et. the test and the data simulation aerodynamic database from flight tests. Parameter trajectories compared with the flight test [Klas Andersson al flying (2002)]. At aircraft Daimler Chrysler Aerospace aerodynamic database from flight tests. Parameter trajectories compared with the flight test data [Klas Identification (PID) techniques are applied to data gathered within the flight envelope and, to a certain level, beyond the trajectories compared with the flight test data [Klas Identification (PID) techniques are applied to data gathered Andersson et. al (2002)]. At Daimler Chrysler Aerospace (DASA), the envelope expansion process was supported by Identification (PID) techniques are applied to data gathered Andersson et. al (2002)]. At Daimler Chrysler Aerospace within the flight envelope and, to a certain level, beyond the full operational clearance envelope boundaries. To extract Andersson et. al (2002)]. At Daimler Chrysler Aerospace within the flight envelope and, to a certain level, beyond the (DASA), the envelope expansion process was supported by “Parallel Simulation” comprising of a non-linear simulation within the flight clearance envelope and, to a flight certain level, beyond the (DASA), the envelope expansion process was supported by full operational envelope boundaries. To extract the aerodynamic parameters from data, flight data is (DASA),that the was envelope expansion process waswhile supported by full operational clearance envelope boundaries. To extract “Parallel Simulation” comprising of a non-linear simulation model operated simultaneously the test full operational clearance envelope boundaries. To extract “Parallel Simulation” comprising of a non-linear simulation the aerodynamic parameters from flight data, flight data is gathered from specially designed system identification and “Parallel Simulation” comprising of a non-linear simulation the aerodynamic parameters from flight data, flight data is model that test aircraft was was up inoperated the air simultaneously for flight tests while [Oelkerthe Hansthe aerodynamic parameters from system flight data, flight dataand is model was operated simultaneously while the test gathered from specially designed identification performance maneuvers performed throughout the envelope. model that that was operated simultaneously while theHanstest gathered from specially designed system identification and aircraft was up in the air for flight tests [Oelker Christoph et. al (2000)]. Different real-time parameter gathered from specially designed system identification and aircraft was up in the air for flight tests [Oelker Hansperformance maneuvers performed throughout the envelope. A reliable Decision Support System (DSS) during these aircraft was up in the air for flight tests [Oelker Hansperformance maneuvers performed throughout the envelope. Christoph et. al (2000)]. Different real-time parameter estimation techniques have been used toreal-time speed up parameter the flight performance maneuvers performed throughout the Christoph et. Different A reliable Support System (DSS) during these flight tests isDecision crucial for carefree manoeuvring andenvelope. efficient Christoph et. al al (2000)]. (2000)]. Different real-time parameter A reliable Decision Support System (DSS) during these estimation techniques have been used to speed up theduring flight testing by analysing the aerodynamic characteristics A reliable Decision Support System (DSS) during these estimation techniques have been used to speed up flight tests is crucial for carefree manoeuvring and efficient flight test data gathering. estimation techniques have been used to speed up the theof flight flight tests is crucial for carefree manoeuvring and efficient testing by analysing the aerodynamic characteristics during the conduct of flight tests and making the results data flight tests is crucial for carefree manoeuvring and efficient by analysing the aerodynamic characteristics during testing flight test data gathering. testing by analysing the aerodynamic characteristics during flight test data gathering. the conduct of flight tests and making the results of data analysis available for post flight debrief [Christoph Deiler flight gathering. the conduct of tests and making the results data There test aredata different schemes employed in the telemetry the conduct of flight flight tests and making the results of ofDeiler data analysis available for post flight debrief [Christoph (2012), Timothy J. Spaulding et. al (2011)]. analysis available for post flight debrief [Christoph Deiler There are different schemes employed in the telemetry station to provide support to the pilot for maximum analysis available for post flight debrief [Christoph Deiler There are different schemes employed in the telemetry (2012), Timothy Timothy J. J. Spaulding Spaulding et. There are different schemes employed in for the telemetry (2012), et. al al (2011)]. (2011)]. station to provide the pilot maximum performance without support the risk to of ending up in an out-ofstation to provide support to the pilot for maximum (2012), Timothy J. Spaulding et. al (2011)]. station to provide support to the pilot for maximum performance without the risk of ending up in an out-ofcontrol situation. Flight simulators have been generally used This paper discusses the techniques developed to support performance without the risk ending up in an out-of performance the risk of of and ending up generally in the an present out-ofcontrol situation. Flight simulators have been used flight for flight test without planning, execution safety. In This paper discusses the techniques developed to support data gathering and safe flight envelope expansion of a control situation. Flight simulators have been generally used This paper discusses the techniques developed to control situation. Flight tools simulators have beenspread generally used for flight test planning, execution safety. In the present This paper discusses thesafe techniques developed to support support scenario, simulation haveand wide use in flight data gathering and flight envelope expansion of high performance fly-by-wire aircraft. These algorithms areaa for flight test planning, execution and safety. In the present flight data and flight envelope expansion of for flight test planning, execution andwide safety.spread In during the use present scenario, simulation tools have in flightperformance dataatgathering gathering and safe safe flight envelope expansion ofare supporting carefree manoeuvring, especially the high fly-by-wire aircraft. These algorithms installed the telemetry station for real-time monitoring ofa scenario, simulation tools have wide spread use in high performance fly-by-wire aircraft. These algorithms are scenario, simulation tools Real-time have wide spread use the in supporting carefree manoeuvring, especially during high performance fly-by-wire aircraft. These algorithms are flight envelope expansion. or near real-time installed at the telemetry station for real-time monitoring of the critical flight parameters during flight testing. The paper supporting carefree manoeuvring, especially during the installed at the telemetry station for real-time monitoring of supporting carefree manoeuvring, especially during flight envelope expansion. Real-time or near real-time installed at flight the telemetry station for real-time monitoring of parameter estimation techniques have also been used the for the critical parameters during flight testing. The paper is organized as follows: Section 2 of the paper describes the flight envelope expansion. Real-time or near real-time the critical flight parameters during flight testing. The paper flight envelope expansion. Real-time or near real-time parameter estimation techniques have also been used for the critical flight parameters during flight testing. The paper ensuring the safety and efficiency during the flight testing at is organized as follows: Section 2 of the paper describes the batch simulation process used tothegenerate parameter parameter estimation techniques have also been used is organized as Section 2 paper describes the parameter estimation techniques have been testing used for for ensuring the safety and efficiency the flight at is organized as follows: follows: Section 2 of of thethe paper describes the extreme flight regimes [Kaliyari, Dduring et. al also (2014)]. batch simulation process used to generate parameter excursion boundaries (PEBs) for critical safety ensuring the safety and efficiency during the flight testing at batch simulation process used to generate parameter ensuring the safety and efficiency during the flight testing at extreme flight regimes [Kaliyari, D et. al (2014)]. batch simulation process used to generate parameter excursion (PEBs) critical safety parameters. boundaries Section 3 explains thefor use the of online parameter extreme flight regimes [Kaliyari, D al excursion boundaries (PEBs) for the critical safety extreme regimes [Kaliyari, D et. et.literature al (2014)]. (2014)]. excursion boundaries (PEBs) foruse the critical safety There is flight enough information in open to suggest the parameters. Section 3 explains the of online parameter estimation techniques for improving the flight test efficiency parameters. Section 3 explains the use of online parameter There is enough information in open literature to suggest the parameters. Section 3 explains the use of online parameter use of desktop simulators for ensuring safety during flight estimation techniques for improving the flight test efficiency during envelope expansion. Concluding remarks are There is enough information in open to suggest the estimation techniques for improving the efficiency There isdesktop enough information in ensuring open literature literature toduring suggest the use of simulators safety flight estimation techniques forthe improving the flight flight test test efficiency testing. The introduction offor desktop simulations for JAS39 during envelope expansion. Concluding remarks are provided in Section 4 of paper. use of desktop simulators for ensuring safety during flight during envelope expansion. Concluding use of desktop for ensuring safety during flight testing. The of desktop simulations for JAS39 during envelope expansion. Concluding remarks remarks are are Gripen led introduction tosimulators significantly higher coverage of the provided in Section 4 of the paper. testing. The introduction of desktop simulations for JAS39 provided in Section 4 of the paper. testing. The introduction of desktop simulations for of JAS39 Gripen led to significantly higher coverage the provided in Section 4 of the paper. operational flight envelope compared to the approach of Gripen to higher of Gripen led led flight to significantly significantly higher tocoverage coverage of the the operational envelope compared the approach of operational flight envelope compared to the approach operational flight envelope compared to the approach of of Copyright © 2016 IFAC 254 2405-8963 © 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Copyright 2016 responsibility IFAC 254Control. Peer review© of International Federation of Automatic Copyright ©under 2016 IFAC 254 Copyright © 2016 IFAC 254 10.1016/j.ifacol.2016.03.062
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2. PARAMETER EXCURSION BOUNDARIES (PEBs)
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(AOA) and sideslip, at higher AOAs from wind up turns, keeping all other parameters within safe limits. The input type is decided based on the energy spectrum of the input signals [Jategaonkar, R.V. (2006)]. Optimal input design for data gathering from parameter identification (PID) maneuvers is discussed in Section 2.1.
During the critical flight tests at the edges of flight envelope, it is always desirable to have pre-defined excursion boundaries for the critical flight parameters pertaining to each configuration and flight condition to be test flown. These excursion boundaries are used in the telemetry to monitor the exceedence in the critical parameters, if any, during flight tests. Parameter Excursion Boundaries (PEBs) can be thought of as a “set of pre-defined boundaries of some critical flight parameters (such as angle-of-attack, sideslip, etc.), for a given flight test condition and configuration, that assist in deciding the safe limits of excursions for these parameters”. The aim of PEBs is to have a set of boundaries that would allow safe envelope expansion without having to stop the flight envelope expansion process prematurely because of tolerable model inaccuracies. Parameters monitored online through PEBs include control surface deflections, angle-ofattack, angle-of-sideslip, Mach number, roll rate, yaw rate and their steady state (trim) values. Figure 1 gives a schematic of the process of generating PEBs for real-time telemetry monitoring.
2.
Designed inputs are used in Real Time Simulator (RTS) to verify the extent of excursions in important flight parameters. If the excursions are found to be inadequate for parameter estimation studies, the inputs are redesigned using desktop simulator. Step1 is repeated till the magnitude of excursions in flight parameters from RTS is satisfactory.
3.
The designed FTP inputs are further used to carry out batch simulations at the desired flight conditions and configurations, with varying fuel conditions to study the effect of the movement of center-of-gravity (CG).
4.
For the defined configurations and flight conditions, parameter excursion boundaries are generated from the simulated trajectories in offline mode. The generated PEBs indicate the precincts of the flight parameters, both for the steady state (trim) flight as well as allowable manoeuvring area.
5.
PEBs are put into operation at telemetry station for real-time monitoring and safe envelope expansion during PID data gathering. The excursion boundaries for monitoring the flight test are selected based on the aircraft configuration and the test point trim condition to be executed during the sortie.
2.1 Optimal input design at envelope boundaries To perform Parameter Identification (PID) maneuvers at extreme boundary conditions (at high angles-of-attack, high load factor), the pilot needs to hold the target AOA at constant Mach for a sufficient duration. Generally “wind up turn” maneuver is used to achieve this than the pull-up maneuver. In pull-up maneuver, large speed variation occurs and the pilot is left with very small time window to execute the input. For the test aircraft considered, computer generated flight test inputs through flight test panel (FTP) are executed at the target AOA in windup turn. FTP inputs are designed in such a way that excite the flight parameters of interest within the permissible safe limits and yet provide sufficient information in the data to permit aerodynamic characterization.
Fig.1. Schematic for Parameter Excursion Boundary generation
Since the envelope expansion in the extreme pockets of flight envelope takes place with small increments in angleof-attack, the criterion used for designing FTP input was that the AOA excursion during PID maneuver should be at least 1.0 deg from the trim but should not exceed 1.5 deg to
The following steps are performed to generate the PEBs: 1.
Desktop simulation software is used to design suitable automated Flight Test Panel (FTP) inputs to get the desired excursions in angle-of-attack 255
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maneuvers for the desired range of angles-of-attack for which the envelope expansion is targeted. Fig. 3 gives the typical trajectory plot from the batch simulation process. It shows the magnitude of FTP inputs in pitch, roll and yaw axis and the corresponding excursions in AOA for 6 different cases, corresponding to 6 different trim angles-ofattack. Longitudinal Input Amplitude
Normalized PSD
ensure the safety. The FTP inputs normally selected for data gathering are either doublets or 3-2-1-1, based on the frequency range to be excited. This is determined based on the study of energy spectrum of these inputs [Jategaonkar, R.V. (2006)]. Fig. 2 provides typical energy spectra of different inputs such as pulse, doublet and 3-2-1-1. The FTP inputs are executed to excite the longitudinal, lateral and directional motion and observe the excursion in flight parameters. 1 Pulse Doublet 3211 Modified 3211
0.8 0.6 0.4
5
4
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2 3 4 Normalized Frequency
5
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Fig.3. Batch Simulation
Fig.2. Energy spectra of different inputs
2.3 PEB generation from simulated responses
2.2 Batch simulation For PEBs
The flow chart in Fig. 4 gives the schematic representation of how simulated trajectories are used to generate excursion boundaries for the critical flight parameters. Simulated responses from all the test maneuvers at each Mach number are collated. Angular rates and control input surface deflections are sorted in ascending order of angle-of-attack. Minimum and maximum value of the parameters is picked at each angle-of-attack. Since lateral parameters and control surface deflections are maneuver dependent (clockwise/anticlockwise wind-up turn), larger of the minimum and maximum values are chosen to provide a symmetric excursion boundary.
Simulation tools when used in conjunction with the actual flight testing, greatly improve the efficiency and effectiveness of flight test program [Dennis. O. Hines (2000)]. Simulation permits the flight envelope to be investigated and understood prior to flight testing. Since the number of possible maneuvers and flight conditions to be flown is generally very large, batch simulation eases the process of generating PEBs for various configurations for different prototypes. The desktop simulation model comprises of a 6DOF state-space model and other submodels for airdata, aerodynamics, rigid body and FCS etc. Aero data models are validated and updated in an incremental manner using system identification and parameter estimation techniques. The desktop simulation can be controlled interactively or with the use of scripts.
Club simulated responses of all the test cases at each Mach number (𝛼𝛼, 𝛽𝛽, 𝑀𝑀𝑎𝑎𝑐𝑐ℎ, 𝑝𝑝, 𝑞𝑞, 𝑟𝑟, 𝛿𝛿𝑎𝑎, 𝛿𝛿𝑒𝑒, 𝛿𝛿𝑟𝑟)
Sort the motion parameters w.r.t. 𝛼𝛼 ®
A Graphical User Interface developed in MATLAB is used to access the input file, which contains the state parameters, events and other configuration settings for running the desktop simulation. Provision is made to select the aerodynamic database corresponding to the configuration being test flown. Envelope points and parameters are specified and the maneuvers to be performed are selected. The model is trimmed, and the actual maneuver is simulated. The simulated time trajectories of all the parameters required for PEB creation are stored in an output file. Simulation using the same maneuver, flight condition and configuration is repeated for different fuel conditions to capture the effect of variation in center-of-gravity. The entire process is automated to simulate all the test
Obtain the minimum and maximum excursion of the parameters at each 𝛼𝛼
Adjust the min & max values to generate symmetric excursion of the parameters
Parameter Excursion Boundaries (𝛼𝛼 𝑣𝑣𝑠𝑠. 𝛽𝛽, 𝛼𝛼 𝑣𝑣𝑠𝑠. 𝛿𝛿𝑒𝑒, 𝛼𝛼 𝑣𝑣𝑠𝑠. 𝑝𝑝, 𝛽𝛽 𝑣𝑣𝑠𝑠. 𝛿𝛿𝑟𝑟, 𝑒𝑒𝑡𝑡𝑐𝑐.)
Fig.4. Generation of PEBs from simulated data 256
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This leads to a set of closed boundaries of flow angles v/s control surface deflection as well as angular rates. Similarly, trim boundaries are generated to verify the trim state of each test point during its execution in real-time.
3. ONLINE PARAMETER ESTIMATION TOOL Online estimation tools can provide an effective means of ensuring safety during flight testing and PID data gathering near envelope boundaries. Two approaches have been developed.
Fig. 5 provides the PEBs plotted in red along with the flight data plotted in green from the test maneuvers during a flight test sortie. These kinds of plots are used for data debrief and post flight data analysis.
a)
A direct comparison of the flight derived aerodynamic coefficients with those obtained from updated simulation tool (Coefficient Matching Approach) b) Real-time estimation of aircraft stability and control derivatives and their comparison with the linear models generated from apriori aerodynamic database using Recursive Parameter Estimation techniques.
0
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3.1 Coefficient Matching Approach
0
e (1unit = 2 )
The simulation tool is continuously updated as the flight testing progresses. Close to the edge of the flight envelope, flight testing is carried out in small steps of AOA due to high degree of uncertainty in aerodynamic database at higher AOAs.
r (1unit = 20)
Aerodynamic force and moment coefficients are computed from flight measured angular rates and linear accelerations, and compared with the simulation output in real-time to check for the discrepancies in the coefficients. If the error is small and lies within the pre-defined tolerance bounds, the flight testing can proceed unhindered. Else, the aerodynamic database needs to be updated to account for the newly found trends in the error plots of the aerodynamic coefficients. It is desirable to do a timely update to the aerodynamic database so that the simulation matches the flight measured responses, particularly as the aircraft is flight tested close to the edge of the flight envelope.
Fig.5. PEBs with flight test data gathered for all the test points Fig.6 shows the screenshot of PEBs used for real-time monitoring while an FTP pitch doublet input is executed during wind up turn manuever. The PEBs page includes plots for elevator (DE) v/s AOA, roll rate (P) v/s AOA, yaw rate (R) v/s AOA. During the execution of the test, it can be noticed that the flight data plotted in green lie within the boundary and it helps in safe envelope expansion. If the flight parameters during the execution of maneuver deviate considerablly from the boundaries, the flight test can be aborted and the flight data is analysed to find out the cause of descripencies in the postulated model. Slight deviation from the PEBs are acceptable since the boundaries are generated without accounting for aerodynamic and airdata tolerances. Deviation could also occur due to Mach variation in the flight during the maneuver, since the PEBs are generated for a narrow range of Mach values.
A typical error plot between the flight derived pitching moment coefficient and aerodynamic database with predefined tolerance bound is shown in Fig.7.
0.02 Tolerance Bound 0.015 0.01
Cm
0.005 0 -0.005 -0.01 -0.015 -0.02
Fig.6. Screenshot of PEBs page during real-time monitoring
AOA (1unit = 10)
Fig.7. Error in pitching moment coefficient 257
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k 1 k K( yk 1 ˆyk 1 )
3.2 Recursive Parameter Estimation (RPE) An online parameter estimation tool along with the visuals of the maneuvers is developed to help in safe expansion of flight envelope. This tool compares the aerodynamic derivatives estimated from the flight data in real-time with the linear models generated from the apriori flight updated aerodynamic database. The main advantage of the tool is the ready availability of data analysis results, which would otherwise take half a day with post flight data analysis. The tool essentially ensures in providing the following:
Recursive Filters
RLS EKF DFT
-
y(t) ˆ
error
+
u(t) Aircraft System
Cut down the PID test points, if the estimation results from the first few maneuvers are satisfactory. Estimates of the stability and control derivatives are available for debrief immediately after the flight test sortie. Accompanying visuals ensure proper execution of PID flight maneuvers, which can otherwise be repeated if found unsatisfactory. Flight test can be aborted if the identified parameters show significant deviation from linear derivative values obtained from the apriori database.
y( t ) Fig.8. Schematic block diagram of Recursive parameter estimation
In the present case, EKF and DFT are implemented for the online estimation of stability and control derivatives, as these methods are routinely used for parameter estimation. The online parameter estimation tool is implemented using MATLAB® [Khadeeja Nusrath et.al (2015)]. Visualization tools are created wherein online parameter estimation results along with 3-D visualization of the maneuvers and the time history plots of important motion parameters can be displayed. The 3-D animation of the maneuvers is implemented by feeding the positions and attitude of the aircraft online during the flight test. A typical screenshot of the display from visualization tool is given in Fig. 9.
Recursive Parameter Estimation (RPE) methods provide a new parameter estimate at every time step by using the new information available from the current measured data and the previously obtained results. The measured signals are fed sample by sample to recursive algorithms running on the computer to get the estimation results (stability and control derivatives) displayed in real-time. Fig.8 shows the schematic block diagram for recursive approach. Making use of the previous estimate and the information content in the freshly collected input/output data, the updated parameter is given by
k1 k K(y k1 yˆ k1 )
(1)
where k is the previous estimate, K is the gain giving the direction of update, and (y k1 yˆ k1 ) is the residual error. If the data is assumed to be noise free and error free, no preprocessing of data is required. Otherwise, the recursive algorithms can be utilized for one time estimation of bias and scale factors present in the data and the same may be incorporated into estimation algorithm prior to carrying out exhaustive real-time flight data analysis.
Fig.9. Screenshot of the visualization window of online parameter estimation for a longitudinal maneuver
Various RPE schemes are discussed in literature, e.g., the time domain techniques like the Recursive Least Squares (RLS), Extended Kalman Filter (EKF) and Recursive Maximum Likelihood (RML). In frequency domain, Discrete Fourier Transform (DFT) is mostly used [Jategaonkar, R.V. (2006), John Valasek (2003)].
4. CONCLUSIONS The paper elaborates the use of Parameter Excursion Boundaries and Online Parameter Estimation techniques in the real-time monitoring. During the PID and envelope expansion flight tests, these tools helped saving huge flight 258
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test efforts and also ensure safety of the vehicle and pilot. If significant excursions from predicted values either in the trajectory or in the aerodynamic parameters occur during the tests, the test engineer is able to make an intelligent assessment as to whether to continue with the tests, or to abort and analyze the differences. 5. REFERENCES Christoph Deiler (2012). “An online parameter estimation too”, Deutscher Luft- und Raumfahrtkongress, Document ID: 281206. Dennis. O. Hines (2000). “Simulation in Support of Flight Testing”, RTO AGARDograph 300, Flight Test Techniques Series, Volume 19. Jategaonkar, R.V. (2006). “Flight Vehicle System Identification – A Time Domain Methodology”, AIAA Progress in Astronautics and Aeronautics, Vol. 216, AIAA, Reston, VA. John Valasek and Wei Chen (2003). “Observer/Kalman Filter Identification for Online System Identification of Aircraft”. Journal Of Guidance, Control, And Dynamics, Vol. 26, No. 2. Kaliyari, D., Nusrath TK, K., and Singh, J. (2015). “Validation and Update of Aerodynamic Database at Extreme Flight Regimes”, SAE Technical Paper 201501-2567, DOI: 10.4271/2015-01-2567. Khadeeja Nusrath TK, Basappa (2015). “Online Parameter Estimation with Manoeuvre Visualization”, MATLAB Expo, Bangalore. Klas Andersson, Mats Karlsson and Mårten Staaf (2002). “Aerodynamic and Flight Dynamic Real-Time Analysis During Spin and Carefree Maneuvering Tests of the Saab JAS39 Gripen”, ICAS Congress. Oelker Hans-Christoph and Meyer Thomas (2000). “Online Simulation as a Measure to Increase Safety in Flight Testing of High Performance Aircraft”, ICAS Congress. Tormalm Magnus and Bergström Mattias (2000). “The Use of Desktop Simulations in the Carefree Manoeuvring Flight Test Program of JAS39 Gripen”, ICAS Congress. Timothy J. Spaulding, Cory J. Naddy, Jennifer P. Hines, Garrett W. Knowlan, Danny G. Riley, Zachary T. Schaffer (2011). “Near Real-time Parameter Estimation in the C-12C”, AIAA Atmospheric Flight Mechanics Conference, Portland, Oregon. ACKNOWLEDGMENTS The authors gratefully acknowledge National Flight Test Centre, Aeronautical Development Agency, Bangalore, India, for providing the relevant flight data for carrying out this research work. Authors would also like to acknowledge Mr. Nishat M. Hussain, who contributed in the beginning in developing several programs for generating PEBs and Mr. Gopinath, Hindustan Aeronautics Limited, Bangalore, member of National Control Law (CLAW) team who gave valuable inputs based on real-time monitoring during the conduct of PID flights.
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