A year of new dynamic tests and facilities
By Cristina Riso and Rafael Palacios|December 2024
The Structural Dynamics Technical Committee focuses on the interactions among a host of forces on aircraft, rocket and spacecraft structures.
In January, NASA rolled out its X-59 demonstrator in a ceremony in Palmdale, California. In the following months, the project achieved several milestones toward initial flight tests, scheduled for early 2025. In March, NASA and prime contractor Lockheed Martin performed a structural coupling test, SCT. The aircraft’s control surfaces were commanded to move by computer to ensure that the aircraft’s servoelastic system operates as expected. Based on SCT results, engineers updated aeroservoelastic models. The X-59 project team also completed a flight readiness review in March to prove the aircraft’s airworthiness. In a May news release, NASA described this review as “the first step in the flight approval process.”
Also in March, a new Mach-scaled rotor whirl tower facility was completed at Seoul National University’s Siheung Campus in South Korea. The first experiment, conducted in the same month, involved a trailing-edge flap rotor with a piezo-stack actuator. The 3-meter-diameter rotor rotated up to 1,100 revolutions per minute.
In May, researchers at Sapienza University of Rome, Zurich University of Applied Sciences in Switzerland and the University of Southampton in the U.K. completed a wind tunnel test campaign to characterize the flutter onsets and limit-cycle oscillations of a wing model exhibiting large aeroelastic deflections. By applying new operational modal analysis methods, they characterized the flutter mechanism at various wind tunnel speeds and wing root angles of attack. These experimental findings confirmed that the flutter speed is strongly affected by static wing deformations. The experiments, carried out at three wind tunnels at the participating universities, emphasized the strong effect that differences between wind tunnels can have on test results.
In July and August, NASA and Boeing tested the model for the Integrated Adaptive Wing Technology Maturation subproject, part of NASA’s Advanced Air Transport Technology project. The model is based on an altered semi-span version of the NASA Common Research Model, with an increased wing aspect ratio and flexibility. Researchers aim to validate models and feedback control law design techniques for real-time drag minimization, maneuver load alleviation, gust load alleviation and active flutter suppression. The first test entry, conducted in the Transonic Dynamics Tunnel at NASA’s Langley Research Center in Virginia, used heavy gas R-134a to test Mach numbers up to 0.80 and dynamic pressures up to about 190 pounds per square foot (over 13 atmospheres). Tests were conducted for envelope clearance, static aerodynamic characterizations and dynamic aeroelastic characterizations.
In August, ATA Engineering Inc. of California concluded numerical simulations of Starshade, a deployable structure being developed by NASA’s Jet Propulsion Laboratory. The work correlated finite- element model deployment simulations to test data to ensure that the deployed shade would meet strict shape-accuracy requirements for this highly precise optical system. Throughout 22 deployment simulations, ATA demonstrated excellent agreement with test data in the random shape repeatability error, with a deviation of less than 5% between numerical and experimental results. This demonstrated that a numerical model can accurately predict deployment behavior and shape errors of an optical system, complementing physical testing throughout the design and verification process.
Building on the success of NASA’s Ingenuity Mars helicopter, thin Martian rotors for aeroelastic testing were developed by the Rotor Optimization for the Advancement of Mars eXploration project, led by NASA’s Ames Research Center in California, with Caltech/JPL, AeroVironment, Tohoku University and the University of Maryland as partners. Tests with the rotors, which have a 1% thickness in their outboard sections, could help engineers design larger, more capable Mars helicopters of the future. The full rotor tests were completed in September.
Contributors: George Antoun, Eric Blades, Caitlin Clifton, Giuliano Coppotelli, Anubhav Datta, Jared Grauer, SangJoon Shin and Walter Silva
