Application of fighter jets based on LabVIEW

Portable Digital Data Acquisition System (PDDAS) uses LabVIEW Real-Time and PXI to control wind tunnel tests and record air pressure data from 128 different channels

"LabVIEW Real-Time provides the deterministic response times required to acquire air pressure data and provide feedback control signals to the wind tunnel under a variety of operating conditions."

– Dave Scheibenhoffer, G Systems

Challenge:

Replace a proprietary VME-based DSP system at Lockheed Martin Aeronautics with a system that acquires, analyzes, and stores dynamic pressure data from a next-generation jet fighter engine design.

Solution:

Leverage industry-standard, off-the-shelf technologies, including PXI, MXI, UDP, and RAID, along with the LabVIEW Real-Time Module to create a tightly integrated data acquisition and control system that meets stringent technical requirements

. At G Systems, we completed the upgrade from a VME-based device to a more robust, compact, and reliable data acquisition and real-time control system in less than four months. Now, Lockheed Martin engineers can configure their PXI-based system 10 times faster than their previous VME device while doubling their channel count. Furthermore, a portable digital data acquisition system (PDDAS) reduces test cycle time from 2 seconds to 50 milliseconds, all for less than the cost of upgrading only a portion of a VME-based test system.

Design improvements to jet engines require accurate characterization of engine operating parameters. To accomplish this, design engineers examine the air pressure distribution of jet engines to observe the distortion of the airflow pattern at the engine turbine inlet. To acquire this data, an accurate scaled-down model of the aircraft and a near-sonic wind tunnel are required to simulate actual operating conditions.

Lockheed Martin engineers use scaled-down models of equipment used in F-35 Joint Strike Fighter testing. Having determined that their previous VME-based test system was difficult to configure and upgrade, Lockheed Martin engineers commissioned us to develop a new PDDAS system to control and acquire data from their wind tunnel tests.

The PDDAS includes 128 channels of simultaneous dynamic pressure measurement sampling based on two PXI chassis with a total of 16 NI PXI-4472 dynamic signal acquisition modules. At first glance, two chassis seemed to overcomplicate the system; however, by connecting the two chassis using NI MXI fiber optic extensions, no additional complexity was introduced. The MXI bus essentially acts as a PCI bridge to the second chassis. From a software perspective, the cards in the second chassis appear to be in the first chassis. The use of PXI also provides a sufficiently high data rate (132MB/s) at a competitive cost to allow for future expansion.

The PDDAS also includes an NI SCXI-1520, which is connected to a full-bridge Kulit pressure sensor for strain measurement signal conditioning. Using the LabVIEW Real-Time Module, we can achieve deterministic response times, which is necessary for both acquiring air pressure data and providing control signals back to the wind tunnel to change operating conditions. Reflective Memory The

PXI

architecture allows us to process the large amount of data acquired in the PDDAS system, while the LabVIEW Real-Time Module handles the so-called "buzz" calculations (nearly 450,000 floating-point calculations every 50 milliseconds) that search for a resonant condition in the engine intake. Under certain operating parameters, the airflow into the inlet may become out of phase. If allowed to reach full resonance, the resulting forces could damage the engine. To prevent this, the PDDAS system continuously monitors near-buzz conditions and provides feedback to the wind tunnel control system to change the wind tunnel operating parameters as needed.

Given the large data volume and high computational intensity, the embedded PXI-8176 Pentium controller did not have enough spare bandwidth to save the acquired data to disk. To address this problem, we installed a VMIC mirrored memory card in the PXI chassis. NI provides LabVIEW Real-Time drivers to support the installation and configuration of the mirrored memory card. In this solution, we mirrored the acquired data to a Pentium host workstation running Windows 2000. The workstation uses a proven commercial Fibre Channel card and driver to write the data to a redundant array of independent disks (RAID) as a secondary task. Mirrored storage provides a simple and elegant solution that eliminates potential bottlenecks in the system.

System Communications

Because the PDDAS system is used in multiple wind tunnels across the country, Lockheed Martin engineers needed to find a universal mechanism that could provide real-time feedback to each wind tunnel control system. Therefore, we use the User Datagram Protocol (UDP) in our application. Although UDP is not a deterministic protocol, it is suitable for every wind tunnel device. By carefully selecting the LabVIEW task properties, PDDAS can send UDP packets at a fixed transmission rate of 50 ms.