Armstrong Flight Research Center

Abstract Avenues for disseminating work by applied and collaborative statisticians to statistical audiences are extremely limited. Methodological advances made in the course of effectively executing applied work often fail to reach an audience of other practicing statisticians. We consider questions posed from several viewpoints, including as members of the professional community in academia, government, industry, and independent statistical consulting. We highlight key challenges and opportunities that exist in this space and start the discussion to examine pathways to share this important work. We conclude with recommendations for possible next steps for the dissemination of impactful work by applied, practicing statisticians.

The foundation for a safe and successful flight test of the National Aeronautics and Space Administration (NASA) X-57 Maxwell all-electric experimental airplane, or any X-Plane, is comprehensive system testing on the ground. This test campaign includes verification and validation (V&V) that the integrated system operates as designed and expected, as well as understanding how the system reacts and responds to failures that can occur during flight by performing failure modes and effects testing (FMET). The aircraft should be in the final flight configuration for these test activities because any modifications, even those that appear insignificant, could affect test outcomes. Although the plan was to perform V&V and FMET testing once the airplane was in the flight configuration, due to multiple component redesigns, concurrent software development, and other problems with on-aircraft testing, the X-57 Maxwell never made it into a full-flight configuration. As a result, a build-up approach was followed to test software and hardware as they became ready in order to continue making progress wherever possible. Using this approach revealed problems with the hardware and software faster than waiting for a full-flight configuration, allowing solutions to be found more quickly and in parallel with other project tasks. Other than unloaded motor testing in a lab setting, the only other test setup was on the airplane itself. On-aircraft testing was preferrable in order to test things as close to a flight configuration as possible but was time consuming due to the requirements for testing on the airplane. To overcome some of the on-aircraft barriers, off-aircraft test configurations, such as the Systems Integration Laboratory (SIL) and hardware-in-the-loop (HIL) setups, were used, but each of these setups had limitations to be considered. As a result, solutions found in the SIL or HIL configurations did not always work as expected on the airplane, resulting in an iterative process between on- and off-aircraft testing to find the final solution. Having a dedicated test platform such as an iron bird that closely represents the aircraft - without flight hardware - would have been the most effective off-aircraft test setup, which could have allowed the project to save time and money and potentially reach flight. This paper will highlight the V&V and FMET considerations and testing prerequisites, the build-up approaches to both software and system testing, the benefits and drawbacks to different test configurations, as well as battery testing and operations.

As the advancement of In-Situ Resource Utilization concepts and systems continue to develop, applicable technology development and maturation continues in parallel. While there are many different ways to use the resources found on other bodies, one of the most prevalent suggested applications is the manufacturing of propellants. One of the key technologies for the eventual use of these propellant production based ISRU systems is the liquefaction and storage of the produced propellants. The most mentioned propellant combinations include oxygen-hydrogen and oxygen-methane. The liquefaction of oxygen in these systems will be different than that on Earth, which mainly revolves around the distillation of air. These systems have been developed conceptually and many of the components have been previously tested or are in development. However, the need to demonstrate the system level operations still exists. The demonstration of a prototypical oxygen liquefaction system using tube-on-tank broad area cooling was completed to better understanding system level operations during liquefaction activities. Demonstration testing included system performance determination, constant liquefaction demonstrations, and transient liquefaction demonstrations. The demonstrations showed the operational capabilities of the tube-on-tank system with an integrated cryocooler. Additional testing explored subsurface vs ullage introduction of the gaseous oxygen flow stream as well as demonstrating a novel fiber optic sensor that measured the temperature gradients along the fluid center line within the tank.

Rapid prototyping and testing are key enablers of iterative designs common in early technology research and development. Testing in a dusty environment is critical to prepare the Cryogenic Magnetic Coupler for lunar operations. To enable early and iterative testing of dust mitigation concepts, a low-cost, low-fidelity representative lunar regolith environment was developed at the National Aeronautics and Space Administration (NASA) Armstrong Flight Research Center (Edwards, California). Based on preliminary testing with this test setup, a similar setup may be of interest to universities and other entities looking to develop the capability to safely test relatively small-scale components with lunar regolith simulant. The development of this lunar regolith test chamber and results from preliminary testing are presented in this paper. Also discussed are further development strategies for the potential improvement of this setup.

In this paper a quasi maximum likelihood method for estimating a low order model of a flexible vehicle has been developed and demonstrated. The quasi maximum likelihood method uses a large number of sensors to estimate the parameters and covariance in a method consistent with the maximum likelihood filter-error method. The cost function has been defined in a frequency domain to improve computational efficiency and to enable estimation of an unstable plant. The method has been demonstrated using flight data from the National Aeronautics and Space Administration X-56A Multi-Utility Technology Testbed flex wing tests, which include unstable flutter modes. The method was able to effectively estimate the frequency and damping of the dynamics of the aircraft and generate a transfer function that is useful for control system evaluations.

In modal testing and finite element model correlation, analysts desire modal results using free-free or rigid boundary conditions to ease comparisons of test versus analytical data. It is often expensive both in cost and schedule to build and test with boundary conditions that replicate the free-free or rigid boundaries. Static test fixtures for load testing are often large, heavy, and unyielding, but do not provide adequate boundaries for modal tests because they are dynamically too flexible and often contain natural frequencies within the frequency range of interest of the test article. Dynamic coupling between the test article and test fixture complicates the model updating process because significant effort is required to model the test fixture and boundary conditions in addition to the test article. If there were a way to correct the modal results for fixture coupling, then setups used for other structural testing could be adequate for modal testing. In the case described in this paper, a partial static loads testing setup was used, which allowed significant schedule and cost savings by eliminating a unique setup for a modal test. A fixed base correction technique was investigated during modal testing of a flexible wing cantilevered from part of a static test fixture.The technique was successfully used to measure the wing modes de-coupled from the dynamically active test fixture. The technique is promising for future aircraft applications, but more research is needed.

Electrified aircraft propulsion concepts show potential in using propulsion airframe integration to decrease fuel burn and emissions. Even though electrification offers component efficiency values greater than 90 percent, at high power levels this results in the generation of significant amounts low grade waste heat. A major challenge of electrified aircraft propulsion is managing that heat while minimizing any penalties associated with a thermal management system. This paper explores the potential benefit of power distribution and thermal management innovations at the aircraft system level demonstrated on a turboelectric single-aisle concept. The first innovation is high-efficiency components that eliminate over half of the waste heat. The second takes advantage of the outer mold line of the aircraft to reject heat directly to the environment passively, instead of adding active cooling loops that negatively impact the weight, power, and drag of the aircraft. In order to fully grasp the impact of the advanced power system, we develop methods of modeling the power and thermal management systems to be integrated in the full aircraft conceptual model. In our first model, which acts as a baseline for our study, the aircraft is designed with a state of the art DC power system and active cooling loops. Our second model includes an advanced power system with active cooling, which results in a fuel burn reduction of 2.5 percent. Finally, in our third model, we assess the benefit of an outer mold line cooling scheme with the advanced power system. The outer mold line cooling scheme with an advanced power system yields an additional 0.8 percent reduction in fuel burn, for an overall fuel burn reduction potential of 3.3 percent in addition to aerodynamic benefits from propulsion airframe integration enabled by electrified aircraft propulsion.

This paper will highlight the results of a recent flight test to validate the use of a carbon-based resistive heating layer for visualizing flow transition. This study builds upon recent work that successfully demonstrated the technology on both small, regular shaped airfoils (at the 0.3-m Transonic Cryogenic Tunnel) as well as larger more complex wing shapes at full-flight Reynolds numbers (in the National Transonic Facility). For flight testing, a laminar flow model was attached to an F-15 aircraft with temperature images collected using a commercially available infrared camera adapted for airborne use. This technology was specifically aimed at enhancing visualization of transition at subsonic speeds without the requirements for using solar heating and other modifications of the flight envelope. Successful implementation of this technology in flight will provide a means to greatly enhance transition visualization at subsonic speeds for future flight tests of laminar flow concepts.