The aircraft fuel system is one of the most critical systems for safe aircraft operation, and ensuring its safe and stable operation is of paramount importance. As a core component of aircraft maintenance personnel training, the design of maintenance training equipment is also crucial. Current training systems are relatively outdated, costly, have limited functionality, and poor scalability. To address the contradiction between the current growth of knowledge and the lag in existing systems, this paper proposes a laboratory teaching system that organically integrates hardware and software, utilizing currently popular new technologies. This system provides a range of functions similar to or exceeding those of a real aircraft fuel system: theoretical training on fuel and electrical systems, including the composition of the fuel system, the installation location and working principle of its components, and its internal structure and components; operational simulation of the fuel and electrical systems, including manual/automatic refueling, manual/automatic fuel transfer, and emergency fuel draining; simulated power-on of the fuel and electrical systems, completing the power-on procedures specified in maintenance regulations, such as power-on checks of the left and right front and rear pumps; training on maintenance procedures for fuel and electrical system components, using virtual reality or video to complete training on components, such as the disassembly, assembly, and cleaning of fuel pumps; fault injection and simulated fault troubleshooting functions, allowing instructors to inject faults using the instructor's machine and trainees to simulate fault procedures using the system; and real-time monitoring and recording of the trainees' training process for subsequent analysis and evaluation.
This laboratory system is primarily used for in-laboratory training, enabling trainees to master and improve their troubleshooting skills. The system is already in use.
1. System Overall Structure
As a simulation training device, this device is designed based on the fuel system of a certain fighter jet. Its control logic fully follows the actual control logic, employing a design philosophy that combines physical operation with software operation. The development process integrates hardware construction and software development. The device uses C# and KingSCADA to build the human-machine interface and demonstration screen, PLC technology to implement the electrical logic control of each component, principle simulation technology to simulate circuit board faults in physical components, a CAN bus to achieve communication between the instructor's control console, PLC, and other components, and a fault tree structure to store the case library in an SQL database.
The CAN bus is a serial fieldbus that supports distributed real-time control. It has significant advantages, making it suitable for laboratory systems. It supports a large number of nodes, with up to 110 nodes per bus interface; it operates in a multi-master mode, allowing any node to function as a master; and it offers high transmission rates over short distances.
The overall system structure is shown in Figure 1. The host computer, PLC, simulation unit, and other devices are all connected to the twisted-pair cable via a CAN bus. For easy CAN bus access, a PCI-CAN board is installed on the instructor control console, and the PLC has a CAN-to-RS-485 converter. Since data transmission via twisted-pair cable is susceptible to external interference, the high common-mode rejection characteristic of the receiver can be utilized to improve anti-interference capabilities during communication. Therefore, matching resistors R are used at both ends of the twisted-pair cable to eliminate interference caused by twisted-pair reflections.
The subsystems that perform interactive operations include: fuel supply subsystem, fuel transfer control subsystem, power fuel subsystem, ventilation and pressurization subsystem, refueling subsystem, cooling subsystem, fuel discharge and emergency fuel discharge subsystem, fuel consumption measurement subsystem, residual fuel collection subsystem, aerial refueling subsystem, and buddy refueling subsystem.
Figure 1 System Overall Structure
The instructor console is the core of the entire experimental system, and its functions include: controlling the entire training process; setting specific faults to occur; canceling faults; monitoring, recording, and evaluating trainees' troubleshooting operations; viewing historical training records; and maintaining the database of fault cases.
The student control console is where students conduct theoretical learning and maintenance operation training. It mainly includes principle demonstration training, virtual disassembly and assembly, troubleshooting training, and personal information management.
In summary, this system can simulate and reproduce fuel system faults. By using this system, the principles behind fuel system failures can be studied, helping maintenance personnel develop diagnostic and repair plans, and enabling the most accurate and timely analysis and diagnosis of fuel system faults.
2 Hardware Components
The hardware system forms the foundation of the experimental system, primarily consisting of a control console (for trainees and instructors), an interactive training panel (simulating cockpit and ground equipment), individual simulation units, and a database server. This system, based on a CAN bus local area network, enables rapid and stable transmission of horizontal and vertical information, possessing sufficient bandwidth and strong scalability.
2.1 Console
The console is divided into two parts according to the user: the student console and the instructor console.
The physical structure includes an industrial computer, data acquisition card, data processing card, signal conditioning card, and peripheral devices. The industrial computer is equipped with a PCI-CAN converter card for easy connection to the CAN bus.
The industrial computer is equipped with a PCI-CAN converter card, which facilitates connection to the CAN bus network. It offers advantages such as openness, real-time performance, a user-friendly interface, and multi-tasking/multi-threading capabilities.
The PLC used is a Siemens S7 300 CPU 317-2 PN/DP, which has significant advantages: easy programming, short construction cycle for the control system, and easy system maintenance. The use of a PLC in the fuel system fault simulation device enables the simulation of fuel system control relationships and the setting of electrical faults, reducing response time and making the control of switching quantities more accurate.
2.2 Interactive Training Panel
The interactive training panel mainly consists of cockpit and ground equipment simulations. The cockpit operation simulation panel is a replica of all operations related to the aircraft's fuel system within a real aircraft cockpit. The ground monitoring equipment simulation panel only has minor modifications to the external appearance of the equipment. Its function is to control the fuel system's functional commands and display various alarms, fuel levels, and various status parameters.
It includes feature diagrams of all subsystems and their components, and is connected to the instructor's console device, achieving the following functions: acquisition and uploading of various parameter data; simulation of cockpit display and operation; status control of each component; transmission and control of each switch command; displaying corresponding fault phenomena after receiving commands from the instructor's console; and allowing trainees to perform testing and maintenance through manual operation.
2.3 Simulated Unit
The internal hardware simulation architecture is consistent with the real system, and its external interface can connect with real equipment to achieve interoperability. The simulation unit has both software and hardware network functions: on the software side, it implements tasks such as receiving, processing, executing, and sending status information, providing users with a convenient control interface; on the hardware side, the interconnection is consistent with the actual system, realizing fault simulation, interface status setting, information transmission, data processing, signal reception and conversion, providing effective hardware support for operation and maintenance training.
The simulated unit is an important component of the system and also the core of the simulation system. Physically positioned on the student control console according to the actual location of the aircraft, it enables students to develop an effective spatial concept.
Figure 2 Simulation of the single-unit structure
As shown in Figure 2, the hardware circuit of its communication module consists of an AT89C52 microcontroller, an SJA1000 CAN bus controller, and an 82C250 CAN transceiver. The 82C250 CAN bus transceiver can increase the communication distance, improve the instantaneous anti-interference capability, reduce radio frequency interference (RFI), protect the bus, and achieve thermal protection, etc.
The software primarily implements communication between the microcontroller and the CAN bus controller, including initialization, sending, canceling sending, receiving, and testing. To facilitate the use of external measuring devices, a measurement interface is designed, which is identical to a real-world interface, enabling direct measurement of various parameters.
For example, the simulation unit of a three-phase AC oil pump has a 4-pin external interface for measurement. This simulation board can simulate normal motor operation and various fault modes, such as phase loss, open circuit, and short circuit. Measurements taken from the interface show pin-to-pin voltages as zero, pin-to-pin resistance as infinite, and pin-to-pin resistance as zero.
3 Software Design
The system's host computer software mainly consists of three parts: the instructor's end, the student's end, and the database.
As shown in Figure 3, after logging in, instructors gain high privileges. In addition to having all the privileges of students, they can also generate standard fault cases, maintain the database, set various parameters, manage student accounts, and evaluate student performance.
Figure 3 Software Architecture
Students log in with low privileges, enabling them to view demonstration screens, conduct simulated troubleshooting training through the operation panel, and view their own historical performance records.
Figure 4. Main functions of the host computer software
The database primarily stores a standard case library, various historical system parameters, student operations, and scores. It provides an open OPC (OLE for Process Control, an application of object linking and embedding in industrial control) interface.
The functions are shown in Figure 4, and mainly consist of four parts: fault setting and troubleshooting, database management and maintenance, standard troubleshooting process, and system settings.
5. Applications and Conclusions
To clearly and effectively demonstrate the principles of each subsystem and more accurately represent the series of phenomena that occur after a fault, this system uses KingSCADA to create demonstration screens for each subsystem. The configuration demonstration screen for the oil transportation subsystem is shown in the following figure:
Figure 5. Configuration screen of the oil transportation subsystem
The system's design, based on the principles of aircraft fuel systems, fully meets training requirements. Furthermore, many of its functions are impossible to implement in real-world aircraft field training. The system can quickly set up any aircraft state, shortening training time; it allows for in-depth and repeated learning of certain typical faults, enabling trainees to accumulate extensive experience in a short period; it can simulate faults that cannot be simulated in real-world aircraft training, such as fire alarms, power failures, and water ingress; it can allow faults to persist and cause further damage, deepening trainees' understanding of the hazards of these faults; and it can conduct in-depth research on various parameters to improve and optimize existing aircraft fuel systems. In short, the system is low-cost, has a short development time, and significantly improves training quality.
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