Take the Proper Steps to Flight-Test-Instrumentation Design
Published in Electronic Design
Flight-test-instrumentation (FTI) equipment acquires flight avionics and aircraft structural and environmental parameter data for real-time monitoring during test flights and for offline analysis. Solutions for FTI include data-acquisition units (DAUs), recorders, switches, gateways, cameras, and RF transmitters and transceivers. FTI encoders and RF transmitters deliver real-time monitoring, while offline analysis involves analyzing data recorded during the test flights.
Designers of FTI equipment must meet unique environmental (physical and electromagnetic-interference, or EMI) and size, weight, and power (SWaP) requirements. In practice, the design of RF equipment for FTI applications is both a science and art, with expertise honed through experience and knowledge of flight test industry needs and practices.
Most FTI equipment installation occurs only during the test phase for airborne platforms; it must function without affecting the test platform dynamics and functional performance. In addition, FTI equipment is often installed in space-constrained locations without adequate airflow or cooling, which makes the operating environment more challenging. This puts a premium on compact equipment that draws very little prime power and operates optimally in both high and low temperatures, as well as under severe shock, vibration, and humidity environments as specified by environmental standards like MIL-STD-810.
What’s more, one must consider EMI, both in how it might impact or be impacted by other aircraft equipment. FTI RF equipment must be designed to meet EMI requirements, as dictated by standards such as MIL-STD-461. The FTI RF equipment should have a long mean time between failure (MTBF) and require very little field adjustment or maintenance. Finally, it’s preferable that FTI equipment be deployed as a line replaceable unit (LRU).
The RF solutions used in FTI telemetry (TM) applications include transmitters, transceivers, transponders, and receivers. In the U.S., the RF frequency bands for FTI transmitters, transceivers, transponders, and FTRs are specified by the Range Commanders Council (RCC).
RF transmitters handle real-time (downlink) transmission of flight test data, as well as mission and safety-critical data, to a ground receiver station. The transceivers fulfill a similar role, except they offer bidirectional links (i.e., uplinks and downlinks) between the airborne test platform and the ground station. The bidirectional links enable the ground station to select or modify the list of test parameters that are transmitted on the downlink, during the test flight. Today, the transmitter RF frequency bands are in the L-, S-, and C-bands, with a planned migration to C-band in the near future for most U.S. test ranges. FTI transceivers operate at S- and C-band, with C-band operation being the most common in the U.S.
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