Lockheed Martin Reduces Costs and Time Testing F-35 Joint Strike Fighter with LabVIEW Real-Time

The Portable Digital Data Acquisition System (PDDAS) incorporates both LabVIEW Real-Time and PXI to control wind tunnel tests and acquire and record air pressure data from 128 different channels.
Author(s):
Dave Scheibenhoffer - G Systems
Michael
Fortenberry - G Systems
Industry:
Government/Defense, Aerospace/Avionics
Products:
Dynamic Signal Analyzers, PXI/CompactPCI,
LabVIEW
The Challenge:
Replacing a proprietary VME-based DSP
system owned by Lockheed Martin Aeronautics Co. (Lockheed Martin) with a system
that acquires, analyzes, and stores dynamic pressure data from a next-generation
jet fighter engine design.
The Solution:
Using industry-standard, off-the-shelf
technologies including PXI, MXI, UDP, and RAID with LabVIEW Real-Time to create
a tightly integrated data acquisition and control system that meets stringent
technical demands.
"Lockheed Aeronautics Company (Lockheed Martin) engineers now can configure their PXI-based system 10 times as fast as when using their previous VME equipment while doubling their channel count. Also, the Portable Digital Data Acquisition System (PDDAS) reduces test cycle time from 2 sec to 50 ms all for less than it would have cost to upgrade only a portion of the VME-based test system."
Dramatically Reducing Test Cycle Time
At G Systems Inc.,
we upgraded VME-based equipment with a more robust, compact, and reliable data
acquisition and real-time control system in less than four months. Lockheed
Martin engineers now can configure their PXI-based system 10 times faster than
their previous VME equipment while doubling their channel count. Also, the
Portable Digital Data Acquisition System (PDDAS) reduces test cycle time from 2
sec to 50 ms all for less than it would have cost to upgrade only a portion of
the VME-based test system.
Improvements to jet engine designs require
precise characterization of engine operating parameters. To accomplish this,
design engineers examine the jet engine inlet air pressure profile to observe
the air flow pattern distortions across the engine turbine inlet. To acquire
this data requires an accurately scaled model of the aircraft and a transonic
wind tunnel to simulate actual operating conditions.
Engineers at
Lockheed Martin use scale models of equipment in the testing of the F-35 Joint
Strike Fighter. Because their previous VME-based test
system proved too difficult to configure and upgrade, engineers at Lockheed
Martin commissioned the new PDDAS system that we developed to control and
acquire data fro their wind tunnel tests.
The PDDAS includes 128 channels
of simultaneously sampled dynamic pressure measurements based on two PXI
chassis, equipped with a total of 16 NI PXI-4472 Dynamic Signal Acquisition
boards. At first glance, two chassis may seem to unnecessarily complicate the
system; however, by linking the two chassis using the NI MXI fiber-optic
extension, no additional complexity was introduced. MXIbus basically performs as
a PCI bridge to the second chassis. From a software point of view, the boards in
the second PXI chassis appear as though they reside in the first chassis. Using
PXI also provides high enough data transfer rates (132 Mbytes/sec) at a
competitive price for future expansion.
Also included in the PDDAS is the
NI SCXI-1520, which connects to a full-bridge Kulite pressure transducer for
strain gauge signal conditioning. With LabVIEW Real-Time, we can achieve the
deterministic response time needed to both acquire air pressure data and to
provide control signals back to the wind tunnel to vary operating
conditions.
Reflective Memory
With The PXI architecture, we can
handle the large data sets acquired in the PDDAS system, and LabVIEW Real-Time
handles what is known as the “buzz” calculation (approximately 450,000 floating
point calculations per 50 ms), that looks for a resonance condition in the
engine inlet. At certain operating parameters, the air to the inlets may be in
phase. If allowed to reach full resonance, the resulting forces can damage the
engine. To prevent this, the PDDAS system constantly monitors for approaching
buzz conditions and provides feedback to the wind tunnel control system to
change tunnel operating parameters as required.
With the large data
volume and computationally intensive calculations, the embedded PXI-8176 Pentium
controller does not have enough remaining bandwidth to store all the acquired
data to disk for permanent storage. To resolve this challenge, we used a VMIC
reflective memory card in the PXI chassis. NI provided a LabVIEW Real-Time
driver to support the setup and configuration of the reflective memory board.
With this solution, we can “reflect” the acquired data to a Pentium host
workstation running Windows 2000. This workstation uses an off-the-shelf Fibre
Channel board and driver to write the data to a Redundant Array of Independent
Disks (RAID) as a secondary task. Reflective memory proves a simple, yet elegant
solution to resolve a potential system bottleneck.
System
Communication
Because the PDDAS system is used at a number of wind
tunnels throughout the country, Lockheed Martin engineers need a ubiquitous
mechanism to provide real-time feedback to the individual wind tunnel control
systems. Therefore, we used User Datagram Protocol (UDP) for this application.
Though UDP is not a deterministic protocol, it is a readily available interface
at each wind tunnel facility. By carefully selecting the LabVIEW task
priorities, the PDDAS can send UDP packets at a deterministic rate of 50
ms.
For more information, contact:
Dave
Scheibenhoffer
G Systems, Inc.
Tel: 972-516-2278
Fax:972-424-2286
E-Mail: info@gsystems.com
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