Design of the Electronic Engine Control Unit Performance Test System of Aircraft

aerospace

Article Design of the Electronic Engine Control Unit Performance Test System of Aircraft

Seonghee Kho 1 and Hyunbum Park 2,*

1 Department of Defense Science & Technology-Aeronautics, Howon University, 64 Howondae 3gil, Impi, Gunsan 54058, Korea; [email protected] 2 School of Mechanical Convergence System Engineering, Kunsan National University, 558 Daehak-ro, Miryong-dong, Gunsan 54150, Korea * Correspondence: [email protected]; Tel.: +82-(0)63-469-4729

Abstract: In this study, a real-time engine model and a test bench were developed to verify the performance of the EECU (electronic engine control unit) of a turbofan engine. The target engine is a DGEN 380 developed by the Price Induction company. The functional verification of the test bench was carried out using the developed test bench. An interface and interworking test between the test bench and the developed EECU was carried out. After establishing the verification test environments, the startup phase control logic of the developed EECU was verified using the real- time engine model which modeled the startup phase test data with SIMULINK. Finally, it was confirmed that the developed EECU can be used as a real-time engine model for the starting section of performance verification.

Keywords: test bench; EECU (electronic engine control unit); turbofan engine

Citation: Kho, S.; Park, H. Design of 1. Introduction the Electronic Engine Control Unit The EECU is a very important component in aircraft engines, and the verification Performance Test System of Aircraft. test for numerous items should be carried out in its development process. Since it takes Aerospace 2021, 8, 158. https:// a lot of time and cost to carry out such verification test using an actual engine, and an doi.org/10.3390/aerospace8060158 expensive engine may be damaged or a safety hazard may occur, the simulator which virtually generates the same signals with the actual engine is essential [1]. The virtual Academic Editor: Erinc Erdem engine simulator which replaces the actual engine should be able to provide the simulation of engine operation in real time at almost the same level as the actual engine operation. Received: 22 March 2021 Therefore, the simulation speed should be as fast as the speed of the actual system to carry Accepted: 21 May 2021 Published: 3 June 2021 out input, calculation and output within the time range specified by the user. The development of a real-time engine model which can carry out calculation at almost real time and appropriate hardware is necessary for real-time simulation. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in Many studies of electronic engine control systems of gas turbine engines have been published maps and institutional affil- conducted. Among the previous studies, W.J. Davies et al. performed F-14 aircraft and iations. propulsion control integration evaluation. Their paper presented the FADEC/F-14 integration evaluation performed by PWA and discussed the benefits of the FADEC/F-14 integrated system [2]. H. Yamane et al. carried out an investigation on aspects of aircraft engine control systems. In their work, various electronic control systems for aircraft engines were proposed [3]. F. Schwamm conducted research on FADEC computer systems Copyright: © 2021 by the authors. for safety-critical applications. In Schwamm’s work, the trends in FADEC development Licensee MDPI, Basel, Switzerland. This article is an open access article were investigated [4]. K. Hjelmgren et al. performed a study on the reliability analysis of distributed under the terms and single-engine aircraft FADEC. Their paper presented a reliability analysis of two options to conditions of the Creative Commons fault-tolerant FADEC intended for control of an aircraft gas turbine engine [5]. K. Ito et al. Attribution (CC BY) license (https:// performed a study on the optimal self-diagnosis policy for FADEC of gas turbine engines. creativecommons.org/licenses/by/ In their paper, FADEC is self-diagnosed at the nth control calculations. Numerical examples 4.0/). were finally provided [6]. Ding Shuiting et al. conducted a study on the FHA (functional

Aerospace 2021, 8, 158. https://doi.org/10.3390/aerospace8060158 https://www.mdpi.com/journal/aerospace Aerospace 2021, 8, 158 2 of 18

hazard assessment) method for the VBV (variable bleed valve) position control function of a FADEC system based on an aero engine dynamic model [7]. G.I. Pogorelov et al. carried out research on application of neural network technology and high-performance computing for identification and real-time hardware-in-the-loop simulation of gas turbine engines [8]. Keeyoung Choi et al. performed a study on the development of an integrated high-fidelity helicopter and engine simulation for control system design [9]. Kang-Yi Lee et al. carried out a study on the certification of electronic engine controls [10]. Joo-Hyun Jung et al. conducted a study on the T-50 engine airstart test. Their paper presented the results of airstart tests performed to verify the T-50 airstart capability for various flight conditions [11]. F. Lu et al. performed research on rotating detonation wave propulsion about experimental challenges, modeling, and engine concepts [12]. S. Jafari et al. conducted a study on meta-heuristic global optimization algorithms for aircraft engine modeling and controller design [13]. S. Jafari et al. conducted a study on modeling and control of the starter motor and startup phase for gas turbines [14]. M. Montazeri-Gh et al. performed research on bond graph modeling of a jet engine with an electric starter [15]. A. Imani et al. studied the research on multi-loop switching controllers for aircraft gas turbine engines with stability proof [16]. Salehi. A. et al. conducted a study on hardware-in-the-loop simulation of a fuel control actuator of a turboshaft gas turbine engine [17]. M. Montazeri-Gh et al. analyzed different numerical linearization methods for the dynamic model of a turbofan engine [18]. M. Song et al. conducted research on optimization for the starting process of a turbofan engine under a high-altitude environment [19]. J. Bai et al. carried out a study on a nonlinear single controller of the DGEN380 aero engine design [20]. Y. Qian et al. conducted a study on LPV/PI control for a nonlinear aero engine system based on guardian maps theory [21]. I. Yazar et al. carried out research on a simulation-based dynamic model and speed controller design of a small-scale turbojet engine [22]. K. Beneda developed modular FADEC for a small-scale turbojet engine [23]. J. Lutambo conducted a study on aircraft turbine engine control system development [24]. Bai Jie carried out research on controller design for a small aero engine [25]. S. Victor et al. performed a study on robust control system design of a turbofan [26]. J. W. Connolly et al. conducted research on propulsion control modeling for a small turbofan engine [27]. Joseph. W. et al. carried out a study on advanced control considerations for turbofan engine design [28]. J. Csank et al. performed a study on a model-based engine control architecture with an extended Kalman filter [29]. R. Andoga conducted a study on intelligent situational control of small turbojet engines [30]. After many years of study, various theories of electronic engine control systems for gas turbine engines have been proposed. Even though various engine control design theories have been proposed, little research work on the development of experimental equipment for electronic engine control systems has been conducted. In this study, our research group developed a real-time engine model which was essential for the development of the EECU, a core device in the aircraft engine, and the test bench which embedded the real-time engine model on the real-time simulator and generated the same physical signal with the sensor signal from the actual engine. The test bench’s function test and the test bench’s interface and interworking test were performed. Additionally, then, the real-time startup phase engine model verification test, real-time normal operation phase engine model verification test and target EECU performance verification test were carried out using the developed test bench. Finally, the test results were analyzed.

2. Engine Model 2.1. Target Engine The target engine for the EECU to be developed is a small turbofan engine which is a two-spool and non-mixing type. The general speciﬁcations of the target engine are as shown in Table1. The target engine is a DGEN 380 turbofan engine. Figure1 shows the Aerospace 2021, 8, 158 3 of 18

conﬁguration of the target engine. Figure2 shows the conﬁguration and station numbers employed for a two-spool turbofan engine.

Table 1. Speciﬁcation of target engine.

AerospaceAerospace 2021 2021, 8,, 8x, FORx FOR PEER PEER REVIEW REVIEW Speciﬁcation Value 3 3of of 18 18

Maximum take-off thrust (TOP, ISA, SL, MN0) 2500 N Speciﬁc fuel consumption (SFC TOP) 0.0438 kg/N/h Maximum cruise thrust (MCR, ISA, SL, MN0.338) 1170 N shownshown in in Table Table 1. 1. The The target target engine engine is is a aDG DGENEN 380 380 turbofan turbofan engine. engine. Figure Figure 1 1shows shows the the Speciﬁc fuel consumption (SFC MCR) 7.58 configurationconfiguration of of the theWeight target target (without engine. engine. nacelle)Figure Figure 2 2shows shows the the configuration configuration and and 80station station kg numbers numbers employedemployed for for a atwo-spool two-spool turbofan turbofan engine. engine.

© © FigureFigureFigure 1. 1. 1. DGENDGEN DGEN 380 380 380 turbofan turbofan turbofan engine engine engine (Price (Price (Price Induction Induction Induction©, ,Anglet,, Anglet,Anglet, France). France).France).

FigureFigure 2. 2. Station Station numbering numbering for for the the target target engine. engine. Figure 2. Station numbering for the target engine.

Table2.2.Table Real-Time 1. 1. Specification Specification Startup of of Phasetarget target Engineengine. engine. Modeling In this study, a real-timeSpecificationSpecification heat ﬂow transient performance modelValueValue was developed. The heatMaximumMaximum ﬂow model take-off take-off is the thrust mostthrust accurate(TOP, (TOP, ISA, ISA, model SL, SL, ofMN0) MN0) the real-time engine models. 2500 2500 N N This method does not require iteration. Therefore, it is a real-time engine model most commonly used SpecificSpecific fuel fuel consumption consumption (SFC (SFC TOP) TOP) 0.0438 0.0438 kg/N/h kg/N/h for engine control system hardware development. In this work, a model was developed by MaximumMaximum cruise cruise thrust thrust (MCR (MCR, ISA,, ISA, SL, SL, MN0.338) MN0.338) 1170 1170 N N applying the following equation [31]: SpecificSpecific fuel fuel consumpt consumptionion (SFC (SFC MCR) MCR) 7.58 7.58 WeightWeight (without (withoutd ρnacelle) nacelle)(W − W + WF) 80 80 kg kg 4 = 3 4 (1) dt v 2.2.2.2. Real-Time Real-Time Startup Startup Phase Phase Engine Engine Modeling Modeling InIn this this study, study, a areal-time real-time heat heat flow flow transient transient performance performance model model was was developed. developed. The The heatheat flow flow model model is is the the most most accurate accurate model model of of the the real-time real-time engine engine models. models. This This method method doesdoes not not require require iteration. iteration. Therefore, Therefore, it itis is a areal-time real-time engine engine model model most most commonly commonly used used forfor engine engine control control system system hardware hardware develop development.ment. In In this this work, work, a amodel model was was developed developed byby applying applying the the following following equation equation [31]: [31]:

(( −− +)+) == (1)(1)

Aerospace 2021, 8, 158 4 of 18

dρ4 where dt is the change rate of the density at the combustor outlet, and v is volume of the combustor. dT CP × T × W − CP × T × W + WF × LHV) 4 = 3 3 3 4 4 4 (2) dt dρ CV × T4 × v × dt where LHV is the fuel caloriﬁc value. Equation (2) is the change rate of the temperature at the combustor outlet.

1 γ − 1 γ−1 (W − W ) P = 1 + × M2 × R × T × in out (3) 4 2 v

√ 2 T31 DPcold = Kcold × P31 × W31 × (4) P31

where DPcold is the cold loss of the combustor, Kcold is the cold loss value and M is the Mach number of the turbine inlet. √ 2 T4 T31 DPhot = Khot × P31 × − 1 × W31 × (5) T31 P31

where DPhot is the heat loss of the combustor, and Khot is the heat loss value. P W = Q × √ (6) T

1 T4 − T5 = T4 × η4 × (1 − γ−1 ) (7) γ PR4.5 P − P P − P 1 0 = 100 × (1 − RRF) × 0 amb (8) P0 P0 where RRF is the ram recovery coefﬁcient.

γ−1 γ PR2.3 − 1 T3 − T2 = T2 × (9) η2

1 dP γ − 1 γ−1 W − W = 1 + × M2 × R × T × in out (10) dt 2 v dP where dt is the pressure change rate of the volume. A real-time transfer function transient performance model was considered by the following equation: ! ! ! TC TC dt NL(t) = WF(t) × 1 − lead + 1 − lead × [NL(t − 1) + (NL(t) − WF(t − 1) × (1 − e TClag ] (11) TClag TClag

where NL(t) is the number of revolutions of the low-pressure turbine at time t. A real- time lumped parameter transient performance model was considered by the following equation. The partial derivative of the state variable is obtained from all other parameters. ∂NL ∂NLdot ∂NLdot ∂NLdot = × (NL − NL ) + × (NH − NH ) + × (WF − WF ) (12) ∂t ∂NL b ∂NH b ∂WF b where b is the operating point. The modeling of the real-time startup phase engine model in the form of a lookup table based on time was carried out through the reconﬁguration of startup phase test data measured from the target engine EECU, as shown in Figure3. The real-time startup phase engine model was composed of a “Master Switch” module which played the role to start Aerospace 2021, 8, 158 5 of 18

the engine, a “Startup Real Test” module which provided startup phase data for 0~109 s Aerospace 2021, 8, x FOR PEER REVIEWin the lookup table and an “Engine Simulator” module which generated a physical5 signal of 18

by converting all output signals into analog and discrete signals. Additionally, a “switch model” was added to simulate the short circuit test by assigning a switch to all signals separatelyseparately and and turning turning on on or or off a certain signal during the simulation.simulation. SIMULINK was used,used, as as shown shown in in Figure 33.. InIn orderorder toto loadload thethe modeledmodeled real-timereal-time startupstartup phasephase engineengine modelmodel on on the the engine engine simulator, SIMULINK was used.

Figure 3. Real-time engine model of startup phase.

3.3. Test Test Bench Development InIn this study,study, the the test test bench bench (TB) (TB) was was configured configured for thefor purposethe purpose of verifying of verifying the target the targetEECU EECU by loading by loading the real-time the real-time engine model.engine Themodel. test benchThe test was bench configured was configured to satisfy theto satisfyrequirements the requirements to enable the to enable integrated the integrat performanceed performance test of the targettest of EECU.the target The EECU. test bench The testprovided bench theprovided interface the for interface installing for andinstalli operatingng and theoperating target EECUthe target as well EECU as theas well virtual as theengine virtual which engine could which simulate could fault simulate signal fault input signal and input the same and input the same and input output and signals output as signalsthe actual as the engine actual through engine the through dual channel. the dual channel. TheThe test test bench bench consists consists of of a a hardware hardware unit unit (HW) (HW) including including a a real-time real-time engine engine simu- simu- lator,lator, a flight flight vehicle/cockpit simulator, simulator, a a so softwareftware simulator, simulator, a a mapping mapping box, box, cables and connectors,connectors, a power power supply supply unit, a a console console and and desk desk and and a a monitor monitor and and operating operating software software unitunit (SW). (SW). The hardware unit in the test bench consists of a “cockpit simulator” which handles the operation and management of the test bench, management of the test database of the test bench and target engine, management of the ARINC429 communication and data and operation and management of the EHD module, a “real-time engine simulator” which is embedded with the real-time engine model simulating the same performance as the actual

Aerospace 2021, 8, x FOR PEER REVIEW 6 of 18

engine and simulates engine and drive system signals in real time, “engine controls” which play the role of the cockpit where hardwire signals are sent to the EECU directly Aerospace 2021, 8, 158 and various switches are operated to control the EECU through mechanical production6 ofof 18 a PLA lever which adjusts the engine thrust and a “software simulator” which carries out the modeling of the real-time engine embedded in the engine simulator or plays the role of the host PC for the engine simulator and uploads software on the target EECU. HW blockThe diagrams hardware of the unit test in be thench test are bench shown consists in Figure of a4. “cockpit simulator” which handles the operationThe test bench and management operation software of the testwas bench, programmed management using NI of theLabVIEW, test database and it ofcon- the Aerospace 2021, 8, x FOR PEER REVIEWtest bench and target engine, management of the ARINC429 communication and data6 of and 18 sists of a “TB Operation” program of the main GUI which operates and controls the whole operationtest bench, and an “EECU management Monitoring” of the EHDprogram module, which a monitors “real-time and engine uses simulator”the target EECU which isand embedded all input and with output the real-time signals through engine modelthe ARINC429 simulating communication, the same performance an “EECU Test” as the actualprogramengine engine and which simulates and can simulates monitor engine engineand and save anddrive data drive systemin th systeme verification signals signals in tests inreal real suchtime, time, as “engine the “engine target controls” controls” EECU whichperformancewhich playplay thethe test, rolerole logic ofof thetestthe cockpit cockpitand startup wherewhere phase hardwirehard testwire and signals an “EHD” are sent program to to the the EECUwhich EECU directlycreates directly andaand database various various of switchesswitches data saved areare after operatedoperated the target toto controlcontro enginel the test EECU offline through and carries mechanical mechanical out state production production diagnosis, of of atrenda PLA PLA monitoringlever lever whichwhich and adjustsadjusts maintenance thethe engineengine phase thrust mana and gement.a “software SW simulator” block diagrams which which ofcarries carries the test out out thebenchthe modeling modeling are shown of of the the in real-time real-timeFigure 5, engine engineand the embedded embedded detailed in inspecifications the the engine engine simulator simulatorof the developed or or plays plays the theTB role roleare of theshownof the host hostin PC Table forPC the2.for The enginethe conceptual engine simulator simulator diagram and uploadsan ofd theuploads developed software software on TB the ison shown target the target EECU.in Figures EECU. HW 6 blockandHW diagrams7.block diagrams of the testof the bench test be arench shown are shown in Figure in Figure4. 4. The test bench operation software was programmed using NI LabVIEW, and it consists of a “TB Operation” program of the main GUI which operates and controls the whole test bench, an “EECU Monitoring” program which monitors and uses the target EECU and all input and output signals through the ARINC429 communication, an “EECU Test” program which can monitor and save data in the verification tests such as the target EECU performance test, logic test and startup phase test and an “EHD” program which creates a database of data saved after the target engine test offline and carries out state diagnosis, trend monitoring and maintenance phase management. SW block diagrams of the test bench are shown in Figure 5, and the detailed specifications of the developed TB are shown in Table 2. The conceptual diagram of the developed TB is shown in Figures 6 and 7.

FigureFigure 4. Structure of test bench hardware. hardware.

The test bench operation software was programmed using NI LabVIEW, and it consists of a “TB Operation” program of the main GUI which operates and controls the whole test bench, an “EECU Monitoring” program which monitors and uses the target EECU and all input and output signals through the ARINC429 communication, an “EECU Test” program which can monitor and save data in the verification tests such as the target EECU performance test, logic test and startup phase test and an “EHD” program which creates a database of data saved after the target engine test offline and carries out state diagnosis, trend monitoring and maintenance phase management. SW block diagrams of the test bench are shown in Figure5, and the detailed specifications of the developed TB are shown inFigure Table 4.2 .Structure The conceptual of test bench diagram hardware. of the developed TB is shown in Figures6 and7.

Figure 5. Structure of test bench operational SW.

FigureFigure 5. 5.Structure Structure ofof testtest benchbench operationaloperational SW.

Aerospace 2021, 8, 158 7 of 18

Table 2. Required speciﬁcation of test bench.

Classify Speciﬁcation Temperature Sensor RTD (8 Ch), Thermocouple (6 Ch), PTC (2 Ch) Pressure Sensor 12 Ch Glowplug Current 2 Ch Output RPM Sensor 4 Ch Engine Simulator PLA Sensor 2 Ch Frequency 6 Ch Discrete 14 Ch Discrete 12 Ch Input PWM 6 Ch Communication ARINC429 (2 Ch), RS232 (2 Ch), Ethernet (2 Ch) PLA Sensor 2 Ch Cockpit Simulator Output Discrete 22 Ch Aerospace 2021, 8, x FOR PEER REVIEW 7 of 18 Aerospace 2021, 8, x FOR PEER REVIEWInput Discrete 22 Ch 7 of 18

FigureFigure 6. 6.Conceptual Conceptual diagram diagram of of developed developed test test bench. bench. Figure 6. Conceptual diagram of developed test bench.

Figure 7. Test bench integration. FigureFigure 7. 7.Test Test bench bench integration. integration. Table 2. Required specification of test bench. Table 2. Required specification of test bench. Classify Specification Classify Specification Temperature Sensor RTD (8 Ch), Thermocouple (6 Ch), PTC (2 Ch) Temperature Sensor RTD (8 Ch), Thermocouple (6 Ch), PTC (2 Ch) Pressure Sensor 12 Ch Pressure Sensor 12 Ch Glowplug Current 2 Ch Glowplug Current 2 Ch Output RPM Sensor 4 Ch Output RPM Sensor 4 Ch Engine Simulator PLA Sensor 2 Ch Engine Simulator PLA Sensor 2 Ch Frequency 6 Ch Frequency 6 Ch Discrete 14 Ch Discrete 14 Ch Discrete 12 Ch Input Discrete 12 Ch Input PWM 6 Ch PWM 6 Ch Communication ARINC429 (2 Ch), RS232 (2 Ch), Ethernet (2 Ch) Communication ARINC429 (2 Ch), RS232 (2 Ch), Ethernet (2 Ch) PLA Sensor 2 Ch Cockpit Simulator Output PLA Sensor 2 Ch Cockpit Simulator Output Discrete 22 Ch Discrete 22 Ch Input Discrete 22 Ch Input Discrete 22 Ch

Aerospace 2021, 8, 158 8 of 18

4. EECU Veriﬁcation Test 4.1. Functional Test of Test Bench The manufactured test bench is shown in Figure7. The state of the test bench was inspected through the functional test after integrating the test bench. For the functional test of the test bench, the inspection cable was connected to each pin at the end of the cable directly connected to the target EECU. The test items, standards and methods for the signals in all items of channels A and B were summarized as shown in Table3. Three measurements were carried out for each test item, and if all measurement values were within the error range, an “OK” judgment was given.

Table 3. Result of test bench functional test (discrete output_CH_A).

Measurement (Case No.) No. Test Items Standard Method Reference Decision X1 X2 X3

Master (0/5 V, 0 V < X < 2.6 V (ON) 0.698 0.699 0.698 1 OK FS ± 10%) 2.6 V < X < 5 V (OFF) 4.05 4.05 4.05 IGN 0V < X < 2.6 V (ON) 0.702 0.703 0.701 2 DCRANK 0 V < X < 2.6 V (ON) 0.684 0.684 0.684 OK WCRANK 0 V < X < 2.6 V (ON) 0.696 0.696 0.696 2.6 V < X < 5 V IGN 4.8 4.8 4.8 (OFF) 2.6 V < X < 5 V 3 CH. Normal DCRANK 4.8 4.8 4.8 OK A Discrete Digital (OFF) Multimeter Output 2.6 V < X < 5 V WCRANK 4.8 4.8 4.8 (OFF)

WOW (0/5 V, 0 V < X < 2.6 V (ON) 0.704 0.704 0.704 4 OK FS ± 10%) 2.6 V < X < 5 V (OFF) 4.8 4.8 4.8 CH_A 0 V < X < 2.6 V (ON) 0.7 0.7 0.7 5 CH_AUTO 0 V < X < 2.6 V (ON) 0.692 0.692 0.692 OK CH_B 0 V < X < 2.6 V (ON) 0.690 0.690 0.690

OFCsts (0/5 V, 0 V < X < 2.6 V (ON) 0.142 0.141 0.141 6 OK FS ± 10%) 2.6 V < X < 5 V (OFF) 4.21 4.22 4.22

The result of the functional test is as shown in Table4, and the measurement values for all test items in channels A and B are within the error range; therefore, it can be regarded that the functional reliability of the test bench for the veriﬁcation test of the target EECU has been secured.

Table 4. Result of test bench functional test.

Test Result No. Test Items Ch. A Ch. B 1 MASTER OK OK 2 IGN OK OK 3 DCRANK OK OK 4 WCRANK OK OK 5 NORMAL OK OK 6 WOW OK OK 7 CH_A OK OK 8Discrete Output CH_AUTO OK OK Aerospace 2021, 8, 158 9 of 18

Table 4. Cont.

Test Result No. Test Items Ch. A Ch. B 9 CH_B OK OK 10 OFCsts OK OK 11 FFCsts OK OK 12 OLLsts OK OK 13 FMVsts OK OK 14 FSVsts OK OK 15 OSOVsts OK OK 16 GPcmd OK OK 17 FMVcmd OK OK 18 FSVcmd OK OK Discrete Input 19 OSOVcmd OK OK 20 SGstart OK OK 21 SGmode OK OK 22 PS3 OK OK 23 P0 OK OK 24 PFuel OK OK 25 POil OK OK 26 T6 OK OK 27 T0 OK OK 28 TFuel OK OK 29 TOil OK OK Analog Output 30 TSG OK OK 31 GPcur OK OK 32 PLA OK OK 33 NH OK OK 34 NL OK OK 35 FPMspd OK OK 36 OPMspd OK OK 37 SGspd OK OK 38 FPMcmd OK OK 39Analog Input OPMcmd OK OK 40 SGcmd OK OK

4.2. EECU Interface and Interworking Test The interface and interworking test between the test bench and target EECU is the test to check if the data transmission and reception between the test bench and target EECU through the ARINC429 communication are carried out smoothly after connecting the test bench and EECU with a cable and operating the test bench operating program. The interface and interworking test was carried out in the process as shown in Figure8. At this time, a separate interface test engine model was embedded in the engine simulator, and the test items, standards and methods for the signals in all items of channels A and B were summarized as shown in Table5 in a similar way to the functional test. Three measurements were carried out for each test item, and if all measurement values were within the error range, an “OK” judgment was given. The result of the interface and interworking test between the test bench and target EECU is as shown in Table6, where it is conﬁrmed that all test items in channels A and B were within the error range. Therefore, it can be regarded that the functional reliability for data signals through the communication between the test bench and target EECU has been secured for the following veriﬁcation test of the target EECU. Aerospace 2021, 8, x FOR PEER REVIEW 9 of 18

15 OSOVsts OK OK 16 GPcmd OK OK 17 FMVcmd OK OK 18 FSVcmd OK OK Discrete Input 19 OSOVcmd OK OK 20 SGstart OK OK 21 SGmode OK OK 22 PS3 OK OK 23 P0 OK OK 24 PFuel OK OK 25 POil OK OK 26 T6 OK OK 27 T0 OK OK 28 TFuel OK OK 29 TOil OK OK Analog Output 30 TSG OK OK 31 GPcur OK OK 32 PLA OK OK 33 NH OK OK 34 NL OK OK 35 FPMspd OK OK 36 OPMspd OK OK 37 SGspd OK OK 38 FPMcmd OK OK 39 Analog Input OPMcmd OK OK 40 SGcmd OK OK

Figure 8. Process of interface test.

Table 5. Result of interface and interworking test (discrete output_CH_A).

No. Test Items Standard Method Reference Measurement (Case No.) Decision

Master MASTER ON ON ON ON 1 OK (ON/OFF) Switch OFF OFF OFF OFF IGN (ON) IGN IGN IGN IGN DCRANK MODE DCRANK DCRANK DCRANK DCRANK 2 (ON) OK Switch WCRANK WCRANK WCRANK WCRANK WCRANK (ON) 3 NOMAL (ON) NOMAL NOMAL NOMAL NOMAL OK

WOW WOW Ground Ground Ground Ground 4 OK (ON/OFF) Switch Flight Flight Flight Flight CH_A CH_A CH_A CH_A CH_A Channel 5 CH_AUTO CH_AUTO CH_AUTO CH_AUTO CH_AUTO OK CH. Switch A Discrete CH_B CH_B CH_B CH_B CH_B Output Engine Discrete, 0 Clogged Clogged Clogged 6 OFCsts (0/5 V) OK Simulator Discrete, 1 Not Clogged Not Clogged Not Clogged

Engine Discrete, 0 Clogged Clogged Clogged 7 FFCsts (0/5 V) OK Simulator Discrete, 1 Not Clogged Not Clogged Not Clogged

Engine Discrete, 0 Low Oil Low Oil Low Oil 8 OLLsts (0/5 V) OK Simulator Discrete, 1 Enough Oil Enough Oil Enough Oil

FMVsts Engine Discrete, 0 Open Open Open 9 OK (0/5 V) Simulator Discrete, 1 Closed Closed Closed

Engine Discrete, 0 Open Open Open 10 FSVsts (0/5 V) OK Simulator Discrete, 1 Closed Closed Closed

OSOVsts Engine Discrete, 0 Open Open Open 11 Simulator OK (0/5 V) Discrete, 1 Closed Closed Closed Aerospace 2021, 8, 158 11 of 18

Table 6. Result of EECU test bench interface test.

Test Result No. Test Items Ch. A Ch. B 1 MASTER OK OK 2 IGN OK OK 3 DCRANK OK OK 4 WCRANK OK OK 5 NORMAL OK OK 6 WOW OK OK 7 CH_A OK OK 8Discrete Output CH_AUTO OK OK 9 CH_B OK OK 10 OFCsts OK OK 11 FFCsts OK OK 12 OLLsts OK OK 13 FMVsts OK OK 14 FSVsts OK OK 15 OSOVsts OK OK 16 GPcmd OK OK 17 FMVcmd OK OK 18 FSVcmd OK OK Discrete Input 19 OSOVcmd OK OK 20 SGstart OK OK 21 SGmode OK OK 22 PS3 OK OK 23 P0 OK OK 24 PFuel OK OK 25 POil OK OK 26 T6 OK OK 27 T0 OK OK 28 TFuel OK OK 29 TOil OK OK Analog Output 30 TSG OK OK 31 GPcur OK OK 32 PLA OK OK 33 NH OK OK 34 NL OK OK 35 FPMspd OK OK 36 OPMspd OK OK 37 SGspd OK OK 38 FPMcmd OK OK 39Analog Input OPMcmd OK OK 40 SGcmd OK OK Aerospace 2021, 8, x FOR PEER REVIEW 12 of 18 Aerospace 2021, 8, x FOR PEER REVIEW 12 of 18

36 OPMspd OK OK 36 OPMspd OK OK 37 SGspd OK OK 37 SGspd OK OK 38 FPMcmd OK OK 38 FPMcmd OK OK Aerospace 202139, 8 , 158 Analog Input OPMcmd OK OK 12 of 18 39 Analog Input OPMcmd OK OK 40 SGcmd OK OK 40 SGcmd OK OK 4.3. Real-Time Engine Model Verification Test 4.3.4.3. Real-TimeReal-Time Engine Engine Model Model Verification Verification Test Test The interworking test with the target EECU was carried out by loading the startup TheThe interworkinginterworking test test with with the the target target EECU EECU was was carried carried out out by by loading loading the the startup startup phase real-time engine model established from data obtained through trial operation of phasephase real-time real-time engine engine model model established established from from data data obtained obtained through through trial operation trial operation of the of the target engine on the engine simulator. targetthe target engine engine on the on engine the engine simulator. simulator. ItIt waswas confirmed confirmed from from the the NH, NH, NL, NL, T6 T6 and and FMVsts FMVsts result result on on the the startup startup phase phase that that It was confirmed from the NH, NL, T6 and FMVsts result on the startup phase that thethe testtest data data matched matched well well within within 1% 1% in thein the whole whole startup startup phase, phase, as shown as shown in Figures in Figures9–11, 9– the test data matched well within 1% in the whole startup phase, as shown in Figures 9– and11, and data data were were saved saved in a fixed in a time fixed interval time interv (0.02 s).al Therefore,(0.02s). Therefore, it was confirmed it was confirmed that analog that 11, and data were saved in a fixed time interval (0.02s). Therefore, it was confirmed that sensoranalog outputsensor signalsoutput andsignals discrete and discrete output signalsoutput ofsignals the actual of the engine actual wereengine monitored were moni- analog sensor output signals and discrete output signals of the actual engine were moni- intored the enginein the simulatorengine simulator embedded embedded in the real-time in the engine real-time model engine through model the ARINC429 through the tored in the engine simulator embedded in the real-time engine model through the communication,ARINC429 communication, and the signals and were the within signals the were permissible within the error permissible range of the error target range EECU. of the ARINC429 communication, and the signals were within the permissible error range of the Ittarget was verifiedEECU. It that was this verified model that could this be model used as could the startup be used phase as the real-time startup engine phase modelreal-time target EECU. It was verified that this model could be used as the startup phase real-time forengine the startup model phasefor the performance startup phase verification performance of the verification target EECU. of the target EECU. engine model for the startup phase performance verification of the target EECU.

Figure 9. Result of startup phase performance test (NH). FigureFigure 9.9.Result Result of of startup startup phase phase performance performance test test (NH). (NH).

Figure 10. Result of startup phase performance test (NL). FigureFigure 10.10.Result Result of of startup startup phase phase performance performance test test (NL). (NL).

Aerospace 2021, 8, 158 13 of 18 Aerospace 2021, 8, x FOR PEER REVIEW 13 of 18

FigureFigure 11. 11.Result Result of of startup startup phase phase performance performance test test (T6). (T6).

4.4.4.4. Startup Startup Phase Phase Control Control Logic Logic Verification Verification Test Test EECUEECU software software consists consists of of a a control control logic, logic, application application software software and and a a real-time real-time oper- oper- atingating system. system. Here, Here, the the control control logic logic handles handles the the engine engine speed speed control, control, sequence sequence control, control, engineengine state state monitoring monitoring and and engine engine protection protection functions. functions. It is It the is mostthe most important important part inpart the in developmentthe development of EECU of EECU software. software. The applicationThe application software software handles handles the system the system communica- commu- tionnication interface interface and dual and channel dual channel management, management, and the real-timeand the real-time operating operating system manages system themanages tasks of the the tasks application of the application program to beprogram carried to out be in carried a consistent out in and a consistent appointed and time. ap- pointedThe verificationtime. test of the control logic which performed the most important role in theThe EECU verification software test was of carried the control out using logic the which test benchperformed developed the most through important this study.role in Currently,the EECU thesoftware target was EECU carried is being out developedusing the test in thebench country. developed Therefore, through the this test study. was carriedCurrently, out the for target the control EECU logic is being of the developed startup phasein the country. which was Therefore, developed the test up towas date. car- Whenried out the for target the EECUcontrol is logic developed of the startup completely phase in which the future, was thedeveloped control logicup to testdate. will When be carriedthe target out EECU for the is whole developed operation completely phase in of the the future, target engine.the control The logic startup testphase will be control carried logicout for test the was whole carried operation out in the phase process of the as target shown engine. in Figure The 12startup. phase control logic test wasThe carried EECU out delivers in the process FPMcmd, as shown FMVcmd in Figure and FSVcmd 12. output values according to the controlThe logic EECU calculation delivers result FPMcmd, to the engineFMVcmd in the and startup FSVcmd phase, output as shown values in accordingFigures 13 to–15 the, andcontrol the enginelogic calculation receives the result input to of the this engine command. in the Thestartup result phase, shows as thatshown the in control Figures logic 13– in15, the and early the stageengine of receives development the input shows of this a significant command. difference The result from shows the referencethat the control data. Therefore, the reasons for the error occurrence from the control log were analyzed, and the logic in the early stage of development shows a significant difference from the reference control logic was modified accordingly. The test was carried out again until the final control data. Therefore, the reasons for the error occurrence from the control log were analyzed, logic test result almost matched with the target data. and the control logic was modified accordingly. The test was carried out again until the final control logic test result almost matched with the target data.

Aerospace 2021, 8, 158 14 of 18 Aerospace 2021, 8, x FOR PEER REVIEW 14 of 18 Aerospace 2021, 8, x FOR PEER REVIEW 14 of 18

Figure 12. Process of control logic performance test. FigureFigure 12.12.Process Process ofof controlcontrol logiclogic performanceperformance test.test.

Figure 13. Result of EECU control logic verification test (FPMcmd). FigureFigure 13.13.Result Result ofof EECUEECU controlcontrol logiclogic veriﬁcationverification test test (FPMcmd). (FPMcmd).

Aerospace 2021, 8, 158 15 of 18 AerospaceAerospace 2021 2021, ,8 8, ,x x FOR FOR PEER PEER REVIEW REVIEW 1515 ofof 1818

Figure 14. Result of EECU control logic veriﬁcation test (FMVcmd). FigureFigure 14. 14. Result Result of of EECU EECU control control logic logic verification verification test test (FMVcmd). (FMVcmd).

FigureFigureFigure 15. 15. Result Result of of EECU EECU control control logic logiclogic verification verificationverification test test (FSVcmd). (FSVcmd). 5. Conclusions 5.5. Conclusions Conclusions A test bench for the performance test of an EECU was developed, and the test was A test bench for the performance test of an EECU was developed, and the test was carriedA test out. bench The for test the bench’s performance functional test of test, an testEECU bench’s was developed, interface andand interworkingthe test was carried out. The test bench’s functional test, test bench’s interface and interworking test, test,carried real-time out. The startup test bench’s phase enginefunctional model test, verification test bench’s test interface and target and EECUinterworking performance test, real-time startup phase engine model verification test and target EECU performance ver- verificationreal-time startup test werephase carried engine outmodel using verifica thetion configured test and testtarget bench, EECU and performance the test results verification test were carried out using the configured test bench, and the test results were wereification analyzed. test were carried out using the configured test bench, and the test results were analyzed. analyzed.As the result of the TB functional test, the measurement values for all test items in As the result of the TB functional test, the measurement values for all test items in channelsAs the A andresult B were of the within TB functional the error range;test, the therefore, measurement the functional values for reliability all test ofitems the testin channels A and B were within the error range; therefore, the functional reliability of the benchchannels for A the and verification B were within test of the the error target range; EECU therefore, was secured. the functional As a result reliability of the interface of the and interworking test between the test bench and target EECU, it was confirmed that all test items in channels A and B were within the error range. Therefore, the functional

Aerospace 2021, 8, 158 16 of 18

reliability for data signals through the communication between the test bench and target EECU was secured for the verification test of the target EECU. As a result of the startup phase verification test after the verification of the test bench, it was confirmed that analog sensor output signals and discrete output signals of the actual engine were monitored and saved accurately in a 0.02 s interval in the engine simulator embedded in the real-time engine model through the ARINC communication, and the signals were within the permissible error range of the target EECU. Therefore, it was confirmed that this model could be used as the startup phase real-time engine model for the startup phase performance verification of the target EECU. Additionally, as a result of the control logic test, the control logic in the early stage of development showed a significant difference from the reference data. Therefore, the reasons for the error occurrence from the control log were analyzed, and the control logic was modified accordingly. The test was carried out again until the final control logic test result almost matched with the target data. Currently, the target EECU is being developed in the country. Therefore, the test was carried out for the control logic of the startup phase which was developed up to date. When the target EECU is developed completely in the future, the control logic test will be carried out for the whole operation phase of the target engine.

Author Contributions: S.K., conceptualization, software, validation, writing—original draft prepara- tion; H.P., writing—review and editing, work guidance. Both authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Korea Aerospace Technology Research Association (Project No. 10043602, Development of the EECU platform aircraft for gas turbine engine FADEC) as part of the aerospace parts & technology development project supported by the Ministry of Trade, Industry and Energy, which is graciously acknowledged. This research was funded by the Howon University research fund. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2018R1D1A1B07043553). This research was supported by the Korea Institute for Advancement of Technology (KIAT) grant funded by the Korean government (MOTIE) (P0012769, The Competency Development Program for Industry Specialist). Data Availability Statement: The data presented in this study are available on reasonable request from the corresponding author. Acknowledgments: The authors would like to thank Changduk Kong. Conﬂicts of Interest: The authors declare no conﬂict of interest.

Abbreviations

EECU electronic engine control unit ρ density t time ν volume LHV fuel calorific value DPcold cold loss of combustor DPhot heat loss of combustor Kcold cold loss value Khot heat loss value RRF ram recovery coefficient RTD resistance temperature diode PTC positive temperature coefficient thermistor EHD engine health diagnostic GUI graphical user interface EECU electronic engine control units P pressure NL (t) the number of revolutions of low pressure at time t B operating point Aerospace 2021, 8, 158 17 of 18

References 1. Lobo, L.M.; Dufour, C.; Mahseredjian, J. Real-time simulation of more-electric aircraft power sytems. In Proceedings of the EPE’13 ECCE Europe Conference, Lille, France, 3–5 September 2013; pp. 1–10. 2. Davies, W.J.; Hoelzer, C.A.; Vizzini, R.W. F-14 aircraft and propulsion control integration evaluation. J. Eng. Power 1983, 105, 663–668. [CrossRef] 3. Yamane, H.; Takahara, Y.; Oyobe, T. Aspects of aircraft engine control systems R&D. Control Eng. Pract. 1997, 5, 595–602. 4. Schwamm, F. FADEC computer systems for safety critical application. In Proceedings of the ASME the 1998 International Gas Turbine & Aeroengine Congress & Exhibition, Stockholm, Sweden, 2–5 June 1998; pp. 1–8. 5. Hjelmgren, K.; Svensson, S.; Hannius, O. Reliability analysis of a single-engine aircraft FADEC. In Proceedings of the IEEE Reliability and Maintainability Symposium, Anaheim, CA, USA, 19–22 January 1998; pp. 401–407. 6. Ito, K.; Nakagawa, T. Optimal self-diagnosis policy for FADEC of gas turbine engines. Math. Comput. Model. 2003, 38, 1243–1248. [CrossRef] 7. Ding, S.; Qiu, T.; Liu, X.; Zhang, S. FHA method for VBV position control function of FADEC system based on aero-engine dynamic model. Procedia Eng. 2011, 17, 567–579. 8. Pogorelov, G.I.; Kulikov, G.G.; Abdulnagimov, A.I.; Badamshin, B.I. Application of neural network technology and high- performance computing for identification and real-time hardware-in-the-loop simulation of gas turbine engines. Procedia Eng. 2017, 176, 402–408. [CrossRef] 9. Choi, K.; Jang, S.-A.; Choi, K.; Eom, J.S.; Lee, B.S.; Son, Y.C.; Ryu, H. Development of an integrated high fidelity helicopter and engine simulation for control system design. J. Korean Soc. Aeronaut. Space Sci. 2010, 38, 249–257. 10. Lee, K.-Y.; Han, S.-H.; Jin, Y.-K.; Lee, S.-J.; Kim, K.-S. A study on certification of electronic engine controls. J. Korean Soc. Aeronaut. Space Sci. 2005, 33, 104–109. 11. Jung, J.-H.; Lee, S.-H.; Park, S.-W.; Jeong, I.-M.; Lee, S.-B. T-50 engine airstart test. J. Korean Soc. Aeronaut. Space Sci. 2006, 34, 90–95. 12. Lu, F.; Braun, E. Rotating detonation wave propulsion: Experimental challenges, modeling, and engine concepts. J. Propuls. Power 2014, 30, 1125–1142. [CrossRef] 13. Jafari, S.; Nikolaidis, T. Meta-heuristic global optimization algorithms for aircraft engines modelling and controller design; a review, research challenges, and exploring the future. Prog. Aerosp. Sci. 2019, 104, 40–53. [CrossRef] 14. Jafari, S.; Fashandi, S.A.M.; Nikolaidis, T. Modeling and control of the starter motor and start-up phase for gas turbines. Electronics 2019, 8, 363. [CrossRef] 15. Montazeri-Gh, M.; Fashandi, S.A.M. Bond graph modeling of a jet engine with electric starter. Proc. Inst. Mech. Eng. G J. Aerosp. Eng. 2019, 233, 3193–3210. [CrossRef] 16. Imani, A.; Montazeri-Gh, M. A multi-loop switching controller for aircraft gas turbine engine with stability proof. Int. J. Control Autom. Syst. 2019, 17, 1359–1368. [CrossRef] 17. Salehi, A.; Montazeri-Gh, M. Hardware-in-the-loop simulation of fuel control actuator of a turboshaft gas turbine engine. Proc. Inst. Mech. Eng. M 2019, 233, 969–977. [CrossRef] 18. Montazeri-Gh, M.; Rasti, A. Analyzing different numerical linearization methods for the dynamic model of a turbofan engine. Mech. Ind. 2019, 20, 303. [CrossRef] 19. Song, M.; Jianguo, T.; Sanmai, S. Optimization for the starting process of turbofan engine under high-altitude environment. IEEE Access 2018, 6, 55797–55806. [CrossRef] 20. Bai, J.; Liu, S.; Wei, W. The nonlinear single controller of DGEN380 aero engine design. Int. J. Aerosp. Eng. 2019, 7209428, 1–12. [CrossRef] 21. Qian, Y.; Ye, Z.; Zhang, H. LPV/PI control for nonlinear aeroengine system based on guardian maps theory. IEEE Access 2019, 7, 125854–125867. [CrossRef] 22. Yazar, I.; Kiyak, E.; Caliskan, F. Simulation-based dynamic model and speed controller design of a small-scale turbojet engine. Aircr. Eng. Aerosp. Technol. 2018, 90, 351–358. [CrossRef] 23. Beneda, K. Development of a modular FADEC for small scale turbojet engine. In Proceedings of the 2016 IEEE 14th International Symposium on Applied Machine Intelligence and Informatics (SAMI), Herlany, Slovakia, 21–23 January 2016. 24. Lutambo, J.; Wang, J.; Yue, H. Aircraft turbine engine control systems development: Historical perspective. In Proceedings of the 2015 34th Chinese Control Conference (CCC), Hangzhou, China, 28–30 July 2015. 25. Jie, B.; Shuai, L.; Wang, W. An integrated controller design for a small aero-engine. In Proceedings of the 2019 Chinese Control and Decision Conference (CCDC), Nanchang, China, 3–5 June 2019. 26. Victor, S.; Taymans, A.; Melchior, P. Robust control system design of a turbofan. In Proceedings of the International Conference on Fractional Differentiation and Its Applications, Novi Sad, Republic of Serbia, 18–20 July 2016. 27. Connolly, J.W.; Csank, J.; Chicatelli, A.; Franco, K. Propulsion controls modeling for a small turbofan engine. In Proceedings of the 53rd AIAA/SAE/ASEE Joint Propulsion Conference, Atlanta, GA, USA, 10–12 July 2017. 28. Connolly, J.W.; Csank, J.; Chicatelli, A. Advanced control considerations for turbofan engine design. In Proceedings of the 52nd AIAA/SAE/ASEE Joint Propulsion Conference, Salt Lake City, UT, USA, 25–27 July 2016. 29. Csank, J.; Connolly, J.W. Model-based engine control architecture with an extended Kalman Filter. In Proceedings of AIAA Guidance, Navigation, and Control Conference, San Diego, CA, USA, 4–8 January 2016. Aerospace 2021, 8, 158 18 of 18

30. Andoga, R.; Fozo, L.; Judicak, J.; Breda, R.; Szabo, S.; Rozenberg, R.; Dzunda, M. Intelligent situational control of small turbojet engines. Int. J. Aerosp. Eng. 2018, 8328762, 1–16. [CrossRef] 31. Walsh, P.P.; Fletcher, P. Gas. Turbine Performance, 2nd ed.; Blackwell Science: Oxford, UK, 2004; pp. 444–476.