Designing Rugged Flight Test Solutions for Aircraft with Limited Space
Aerospace and defense data acquisition systems are used for such applications as flight test, operational monitoring, and collecting data from onboard systems and experiments. They typically consist of multiple elements, such as data acquisition units (DAU), recorders, and transmitters. Some types of aircraft have very limited available space to install any hardware. This is particularly true for platforms such as missiles and smaller UAVs, but it is also the case for post-production aircraft, especially military jets and smaller rotorcraft.
One solution is to create a dedicated line replaceable unit (LRU) with all the elements optimally integrated into a single package. Unfortunately, such solutions are rarely flexible, which can lead to increased time and cost in a program. Using modern technologies and combining them into functional systems can save space and weight in SWaP-constrained applications. Solutions can be designed to meet the needs of platforms without compromising on performance and environmental requirements. Established modular and programmable systems free users from becoming stuck with a set configuration and long lead times for even minor configuration changes. This can be highly advantageous for applications where configurations change throughout a platform’s development and operational life, such as in missile and lot sample testing.
Limited Space for System Installation
Examples of aircraft types with particularly limited available space are missiles, pods, sounding rockets, small and medium UAVs, space vehicles, rotorcraft, and fast jets.
For these vehicles, installing traditional data acquisition systems (DAS), which typically consist of DAUs, a recorder, and a telemetry system (transmitter, associated amplifiers, and antenna), can be a challenge. The DAU is usually required to gather data from multiple input sources and encode them for telemetry and/or recording. The type of data generally gathered includes analog, digital, and bus data, as well as possibly video and seeker information. A PCM transmitter is generally necessary for a flight test program or any other application where recovering a recording will be challenging (e.g., a missile or sounding rocket application).
Missiles typically utilize a dual-band wrap-around antenna mated with PCM transmitters and flight termination receivers (FTR). Larger aircraft will tend to have multiple externally mounted antennae with separate transmitters. FTR systems are generally kept separate for safety of flight considerations, although FTR systems are usually monitored for some key parameters from the DAU and the battery system onboard.
Military jets can also have minimal space to install equipment, especially post-production where any available space is generally already occupied. It is sometimes possible to use an external pod to house equipment and often an aircraft may have a weapon, such as a Gatling gun, that can be removed and replaced with a “pallet” of equipment.
The Importance of Installation Flexibility
It is not uncommon for system configurations to change during test and data-gathering programs. For example, sounding rockets may need a different configuration for each launch, depending on the needs of the payload.
It’s unlikely that the validated configuration on a missile program stage would change once it has been established, due to safety issues and the fact that the platform will be destroyed. However, missiles typically do go through various stages of test flights, where the data gathering requirements vary depending on the tests being performed.
During the initial unguided test shots, for example, data from vibration, accelerometers, temperature, strain, pressure, voltages, calorimeter, and radiometer inputs are required. As the test program progresses, these requirements decrease and more guidance and video data is required. Once a missile has been developed, it will also be used in training exercises, where lot-sample tests are performed to ensure the missile platform’s proper continued operation.
A system that can be easily modified to capture different data sets at different program stages will be a huge asset. Elements can be swapped and, following reprogramming, the system’s capabilities will have changed. This can eliminate the need to buy an entirely new system for each phase and keeps spares and logistics costs down as well.
Ideal Systems
The ideal system combines the required functionality with low SWaP and a high level of flexibility. A custom-designed PCB in a custom enclosure should offer lower SWaP than a modular system but will be incapable of being altered beyond some firmware/FPGA changes. DAUs are typically available in different chassis sizes, depending on the solid chassis chosen or how many modules are stacked in a “slice of bread” design. Flexible DAU architecture can be highly beneficial since specific hardware can be made to fit into certain locations while maintaining compatibility with an existing library of off-the-shelf modules. This flexibility can also be beneficial in programs with different phases, such as ordnance testing, where a slightly modified system can be used for engine-test, flight-test, and, later, lot-sample testing.
Having a set of interchangeable components that all work seamlessly allows for custom systems to be built quickly using off-the-shelf parts and reduces integration risk. This can be taken a step further by using standardized systems packaged in a particular form factor. For example, a tray or pallet can be loaded with instrumentation to fit into the space available after a Gatling gun is removed.
Placing the data acquisition system in a pallet can save space, compared to mounting each separate piece individually. What’s more, the user doesn’t have to figure out how pieces connect, and the system can be already set up in software (and thus tweaked quickly). As a result, there can be high confidence that one can modify the system without much risk of integration problems.
Modular systems tend to have a “Goldilocks” size: not too big to be impractical, but big enough to meet performance requirements. That being said, more modern hardware tends to be more compact and capable, and it may also use newer technologies that can result in more flexibility and time savings.
Curtiss-Wright is a leading supplier of data acquisition, recording, and telemetry solutions to test and operational aerospace vehicles for decades. We design DAU, transponder, transmitter, flight termination receiver, and telemetry instrumentation kit (TIK) solutions. In practice, we find that the need for flexibility and performance is usually more important than SWaP-optimization. To this end, we balance reducing the footprint of our data acquisition, recording, and RF systems, without compromising on functionality, flexibility or reliable performance in harsh environments.