Twenty-First Century Flight Test Engineering Education Using NI LabVIEW Software and PXI Hardware
"We are now in our third term of teaching with flight test data systems based on LabVIEW and the students have embraced it enthusiastically."
- John F. Muratore,
University of Tennessee Space Institute
Developing a system to train flight test engineers because flight testing is critical to the quality and operability of new aerospace systems, but can be hazardous and often requires high-volume data systems.
Upgrading our aircraft at the University of Tennessee Space Institute (UTSI) with an NI PXI-based data acquisition system to measure aircraft parameters, and using NI LabVIEW to provide high-quality data processing.
John F. Muratore - University of Tennessee Space Institute
The Need for an Upgraded Flight Test Environment
At UTSI, we have been training flight test engineers for the last two decades by demonstrating flight test techniques on instrumented low-cost general aviation aircraft with known characteristics. This provides students with the opportunity to plan tests, gather flight data, and process the data to form conclusions while operating in a relatively safe environment. In this process, we used a general aviation aircrafts with very limited data acquisition systems. A student’s primary display console consisted of several gauges on which they could simultaneously monitor eight parameters and they recorded data with a pencil and kneeboard. However, modern flight test engineering is based on gathering large amounts of data with a variety of sensors and then using specialized data acquisition systems and postflight data processing methods such as parameter identification.
Comparing measured flight performance with preflight simulation is also a critical part of 21st century flight testing. Our challenge at UTSI was to provide an equivalent capability in the small general aviation aircraft that we use to teach flight test engineering so that we could instruct students using modern flight test engineering techniques. To provide this flight test environment at UTSI, we upgraded our education and research aircraft with a PXI-based data acquisition system to measure more than 100 parameters on each of our research/educational aircrafts.
Using NI Software to Program Our PXI-Based System
The PXI system, which we programmed in LabVIEW, acquires data from sensors as well as serial instruments, calibrates the data, logs it, and then repackages it for distribution in user datagram protocol (UDP) packets over a local area network (LAN) in the aircraft. We hardwired the LAN to outlets at each crew station in the aircraft. Traditionally, a student would carry a headset and a kneeboard into the aircraft. The kneeboard would contain flight cards that describe the test procedure and had spaces on the cards to record a small number of observed data values. Postflight, the students would then attempt to determine the aircraft’s performance from these hand-recorded observations. With the new system, a student walks onto the aircraft carrying a headset and a Samsung Ultra Mobile PC (UMPC) that has a 7 in. touch screen, battery power, and a connection to the LAN to receive flight test data in real time.
Using the LabVIEW run-time environment, the student can select displays that acquire the data off the network to plot, visualize, and record the data locally on the UMPC. The small, compact size of the UMPC is critical for this task because students have very little space inside the aircraft – there is usually not enough room for each student to operate even a full-sized laptop computer. The UMPC is small enough so that the students can strap the computer to the kneeboards, creating an “electronic kneeboard.”
The LabVIEW displays emulate traditional aircraft instruments using standard LabVIEW controls, indicators, and custom displays built with the LabVIEW Picture Control Toolkit to represent more complex indicators such as an attitude direction indicator (ADI), altimeter, flight control surface displays, and control yoke/pedals position displays. Students can access six baseline displays and configure any of the parameters on the aircraft using pull-down menus to tabular or plot displays. In addition, they can plot and crossplot parameters to dynamically execute flight performance analysis while the test is being performed in the aircraft. For example, the students can observe the second order damped response of the aircraft during a longitudinal stability and control maneuver. By observing plots of altitude and airspeed, the student can immediately visualize how potential energy and kinetic energy are exchanged during this maneuver and estimate damping ratios and natural frequency.
The UMPCs also digitize and record all of the audio on the aircraft using LabVIEW. A typical 90-minute flight test sortie will generate 30 MB of recorded aircraft data in a tab-delimited text file and 105 MB of recorded voice data in a WAV format. After the flight, the student copies the data from the UMPC to a solid state drive “data stick” and leaves the aircraft with a complete record of the flight. Back at the student’s home or office, the student can play back the flight and voice data to observe the flight performance using LabVIEW applications. Playback is controlled using a display with controls modeled after a VCR or DVD player. Students can also read in the file, build plots, and perform computations on system parameters from the entire flight or selected segments.
Comparing In-Flight and Simulation Results
To provide the capability to compare in-flight results to preflight simulation, we use a commercial off-the-shelf (COTS) PC-based flight simulator, X-Plane by Laminar Research. This program outputs data in UDP packets and a LabVIEW application translates the X-Plane packets into data packets of the same format that we use in the aircraft. This allows the students to use their UMPC hardware and software to monitor simulated flights just as they would during a flight, and process their data after a simulation session just as they would after a flight.
We modeled the UTSI fleet aircraft in X-Plane so that the student can fly the simulator with the procedures planned to be used in the aircraft and monitor and record the simulation data before the actual flight. The student then processes the simulation data to predict the in-flight performance. Next, the student can go to the aircraft with the instructor and the other students to monitor the flight and compare results to the simulation predictions.
Successful Upgrades to Our Flight Test System
We are now in our third term of teaching with flight test data systems based on LabVIEW and the students have embraced it enthusiastically. In addition, the tools we developed for the classes have been generalized into a “Flight Test Toolkit” that we now use for all of our flight test and airborne science research. LabVIEW and PXI-based instrumentation have “earned their wings” at UTSI.
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