Shape-memory alloys to quiet landings

Adobe Stock | Steve Mann

Texas A&M University researchers developed a computational study that validates using shape-memory alloys to reduce airplane noise during landing.

“When landing, aircraft engines are throttled way back, and so they’re very quiet. Any other source of noise, like that from the wings, becomes quite noticeable to the people on the ground,” says Dr. Darren Hartl, assistant professor in the Department of Aerospace Engineering. “We want to create structures that won’t change anything about the flight characteristics of the plane and yet dramatically reduce the noise problem.”

During takeoff, engines are the primary source of noise; when landing, airplane engines are mostly idling. The wings are reconfigured to slow the airplane and prepare for touchdown.

The front edge of the wing (the leading-edge slat) moves forward from the main structure, creating a gap where air rushes in, circulates violently, and produces noise. A filler that snaps out autonomously as the slat deploys would provide a smoother aerodynamic profile that reduces flow unsteadiness and resultant airframe noise.

Earlier work from Hartl’s collaborators at NASA showed that fillers used as a membrane in an elongated S-shape within the slat-wing space could circumvent the air circulation and lessen the jarring sound. However, the research lacked a systematic analysis of candidate materials that can spring back after landing.

Hartl’s researchers performed comprehensive simulations to investigate if a membrane made of a shape-memory alloy could assume the desired S-shaped geometry during descent and then recess into the front edge of the wing for landing. Their analysis considered geometry, elastic properties of the shape-memory alloy, and aerodynamic flow of air around the material during descent. As a comparison, researchers also modeled the motion of a membrane made of a carbon-fiber-reinforced polymer composite under the same airflow conditions.

Hartl’s team had to perform calculations hundreds to thousands of times before the motion of the materials was simulated correctly, proving that the shape-memory alloy and the composite could change their shape to reduce air circulation and thereby reduce noise. However, they also found the composite had a narrower range of designs that would cancel noise.

Hartl and his team plan to validate the results of their simulations with experiments.

“We might be able to create smaller structures that can reduce noise and don’t require the S-shape, which are actually quite large and potentially heavy,” Hartl says.

Texas A&M University College of Engineering

This research is funded by the Engineering and Physical Sciences Research Council, the Royal Academy of Engineering [UK], and the NASA Langley Research Center.

Read the research paper in the Journal of Aircraft: https://arc.aiaa.org/doi/full/10.2514/1.C036070.