Why are current design tools falling short?

The aviation industry designs aircraft using computer models backed by wind-tunnel data. Those tools handle typical icing conditions well.

Engineers have lingering questions about how well the same models capture the physics of supercooled large drops. The core uncertainty is whether existing code can predict ice growth on aft surfaces when droplets are 20 times larger than the design envelope assumes.

NASA is upgrading the equipment it uses to generate and measure test clouds inside the Icing Research Tunnel so future models can be checked against better data.

What did the new probes measure?

Researchers deployed new optical probes that detect droplets larger than 45 microns and report sizes in real time. They will compare those readings with the slower post-processing of droplet images captured inside the tunnel — an established calibration technique.

A different probe already handles droplets smaller than 45 microns. Combining both datasets should give a complete size spectrum for the test clouds, from the smallest specks up to the largest freezing-rain-sized drops.

Photographs from the campaign, taken by NASA photographer Quentin Schwinn, show clear ice accumulations on unheated sections of an instrument probe inside the tunnel. The probe body carried no heating, so any ice that formed there came directly from the simulated cloud.

What happens next?

The campaign marks an important milestone for NASA's Subsonic Flight Demonstrator project, part of the agency's Research and Technology Mission Directorate. Detailed data analysis continues.

NASA's project team plans to share the findings with the broader aerospace community once the analysis is complete.