Reducing F-35 Fighter Jet Testing Costs and Time with LabVIEW Real-Time Module

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

"The LabVIEW Real-Time Module 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:

Replaced 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 upgraded from VME-based equipment 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 equipment while doubling their channel count. And the Portable Digital Data Acquisition System (PDDAS) reduces test cycle times from 2 seconds to 50 milliseconds, all for less than the cost of upgrading just a portion of the VME-based test system.

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

Lockheed Martin engineers use an expanded model of equipment in testing the F-35 Joint Strike Fighter. 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 consists of 128 channels of simultaneous dynamic pressure measurement sampling based on two PXI chassis, equipped with 16 NI PXI-4472 dynamic signal acquisition modules. At first glance, two chassis seem to make the system too complex and redundant; however, by connecting the two chassis with NI MXI fiber optic extensions, no additional complexity is introduced. The MXI bus basically acts as a PCI bridge to the second chassis. From a software point of view, the cards in the second chassis appear to be in the first chassis. The use of PXI also provides a sufficiently high data transfer rate (132MB/s) at a competitive cost to allow for subsequent expansion.

The PDDAS also includes an NI SCXI-1520 connected to a full-bridge Kullit pressure sensor for strain measurement signal conditioning. Using the LabVIEW Real-Time Module, we can achieve the deterministic response time necessary to acquire air pressure data and provide control signals back to the wind tunnel to change operating conditions.

Reflective Memory

The PXI architecture allows us to process the large amounts of data collected 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), which search for a resonant condition in the engine inlet. Under certain operating parameters, the airflow into the inlet may become in phase. If allowed to reach full resonance, the resulting forces could damage the engine. To prevent this, the PDDAS system continuously monitors for near-buzz conditions and provides feedback to the wind tunnel control system to change the wind tunnel’s operating parameters as needed.

Considering the large amount of data and high computational intensity, the embedded PXI-8176 Pentium controller does not have enough spare bandwidth to save the acquired data to disk. To solve this problem, we installed a VMIC mapped memory card in the PXI chassis. NI provides LabVIEW Real-Time drivers to support the installation and configuration of the mapped memory card. In this solution, we mapped the acquired data to a Pentium host workstation running Windows 2000. The workstation uses a mature commercial Fibre Channel card and driver to write data to a redundant array of independent disks (RAID) as a secondary task. Mapped storage provides a simple and superior solution, eliminating potential system bottlenecks.

System Communication

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 used the User Datagram Protocol (UDP) in our application. Although the UDP protocol is not a deterministic protocol, it is suitable for each wind tunnel equipment. By carefully selecting the LabVIEW task properties, PDDAS can send UDP packets at a fixed transmission rate of 50 ms.