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Bogdan Iwiński – Veritech Sp. z oo
Rafał Kajka – Instytut Lotnictwa, Pracownia Podwozi Lotniczych
The goal of the Distributed and Redundant Electromechanical Front Wheel Steering System (DRESS) international project is to create a prototype of an Electronic nose landing gear steering system for passenger aircraft. Scientists in the Landing Gear Department of the Institute of Aeronautics (IoA) designed and built a prototype electronic steering system test rig to simulate real-world conditions. They designed the test rig to withstand quick and easy configuration changes due to the nature of the prototype test project. This flexibility to change configurations almost always results in changes to control and test setup hardware testing.
DRESS test device control system
IoA engineers design, develop, and manufacture the DRESS test system. They completed the mechanical design and fabrication, as well as other requirements for the pilot plant control system. Veritech, a consortium partner of National Instruments, developed the test rig control software. The adoption of the DRESS test procedure facilitates the flexibility of the test rig, such as quasi-static and dynamic loading of the nose landing gear wheels. The pilot rig needs to perform a wide range of tests. Two main test configurations are defined: a dynamic mode that simulates high-frequency oscillations, and a low-frequency, high-torque mode that mainly simulates ground maneuvers. The first is defined as the Dynamic Control Subsystem (DCSS) and the second is defined as the Anti-Torque Control Subsystem (ATCSS). Based on two different load requirements, the system was designed to be created using alternative hardware and software configurations (Figure 1).
To simulate the low speed taxi conditions of the aircraft, a module powered by a hydraulic engine (ATCSS) was created. In this case, low frequencies (to 4 Hz), large angles (to 90 degrees), large torques appear. To simulate the high frequency oscillations that often occur in the nose landing gear, a set of electric drive modules (DCSS) was created. This module can unbalance the nose wheel of the aircraft with two discs fixed to the original wheels. In dynamic tests, the wheels can reach speeds of up to 4,000 rpm to simulate high torques at higher frequencies, where the twist angle is limited (to 5 degrees).
With this approach, a test rig is created that meets the testing needs and is compact enough to easily fit in the intended test chamber. Features of the PXI measurement platform are maximized (eg, tight synchronization between measurement modules within the PXI chassis) for high quality and consistency of test data.
The new version of LabVIEW was used to create a suite of applications that split threads between two cores in a multi-core CPU so that all tasks could be performed within a specified time. The application software can also use an appropriate identification scheme to detect the mechanical configuration of the current test rig. Controlling the main part of the test application maximizes the capabilities of the RTOS. The use of a real-time operating system makes the designed application more stable, which is critical from a security and reliability perspective.
In addition to the stability of the application, which enhances the safety of the test setup, another challenge is the transmission of high-quality signals with correct timing to external test systems created by other project participants. Application software multithreading and synchronization of the PXI platform enable signal transmission with delays as small as milliseconds. A scalable signal is generated, which is measured directly by the experimental setup. Signals can also be derived from the analysis of multiple measurement inputs, which requires proper signal processing optimization and synchronization to achieve proper signal consistency under time constraints.
Using the PXI platform and the NI LabVIEW programming environment, we efficiently developed the test rig control and measurement system. The configuration of the hardware system leaves a lot of room for connecting more input signals and expanding the system with new measurement modules. Thanks to its modular design, we can extend our application by implementing more functions. In addition, ready-to-use signal analysis capabilities in LabVIEW make these implementations as easy as possible.
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