Birds and aircraft don’t make good friends in the air. A flock of geese, through severe misfortune or self-sacrifice, can take down an entire airliner if they’re ingested into the engines. The famous “Miracle on the Hudson,” where Captain Sully Sullenberger (MS LA’73, HDR ’11) ditched United Airlines Flight 1549 into the Hudson River, is an example where all humans on board survived such an event. 

Humans have not always been so fortunate.

That’s why the FAA requires that new engine designspass a bird ingestion test. There’s even a document with guidelines on how to fire birds — already dead ones, from a grocery store — into the throat of a full-scale prototype at “no less than 100 percent takeoff power or thrust.” This being a destructive test, simulating it in a computer first can reduce costs in addition to preventing surprises when it’s time for the real deal.

But meat is notoriously difficult to simulate.

AAE student Tyler Dillard reviews an oscilloscope plot from a Kolsky bar in Purdue's Impact Science Lab. [Alan Cesar/Purdue University]

“Computer models tend to treat things as solids or liquids,” says Tyler Dillard, a Ph.D. student in aeronautics and astronautics at Purdue. “Biological material doesn’t behave that way. It’s very anisotropic. It responds very differently to loading in different directions and at different loading rates.” 

Dillard knows this firsthand. Using the Kolsky bars, hydraulic presses and other equipment in Purdue’s Impact Science Lab, he’s collecting data for an ongoing Rolls-Royce-funded project to provide fundamental-level mechanical responses of biological materials.

He's using duck meat, specifically. It’s USDA approved, for consistency. [Update, June 2025: Dillard's research has since been published in the Journal of the Mechanical Behavior of Biomedical Materials.]

Dillard's faculty advisor, Research Assistant Professor Zherui Martinez-Guo, runs the Impact Science Lab.

“We need to understand all parts of the material. We’re in the third year of the Rolls-Royce project and moving into higher velocity impact scenarios. We’re getting into real interesting territory,” Martinez-Guo says. 

This dimensionless chart, drawn from Tyler Dillard’s experimental research data, shows the differences in observed mechanical properties of biological materials based on the direction of the load relative to the orientation of the fibers in the meat. The anisotropic nature of biological materials has made them historically difficult to simulate in computer models. “Few labs and test setups are able to induce strain rates this high. That’s one of the things that makes our lab special,” Dillard says.

Matthew Kappes, senior technical specialist Rolls-Royce, explains that this fundamental understanding is a boon for their engineers as well as their bottom line:

“With improved material understanding, we can leverage advancements in computer-aided simulation to generate an improved analytical understanding of the bird threat. Improved fidelity analyses reduce the number of costly and destructive engine hardware tests. This reduces the time to evaluation, enables more designs to be evaluated with confidence, and reduces the cost to deliver bird-resistant engine solutions.” 

Martinez-Guo cheekily adds one more line item to the cost of the bird ingestion test: “Besides destroying an engine, you lose an entire turkey as well, and we all know how expensive those are during Thanksgiving.”

This high-speed image sequence shows a projectile impacting a fabric target at Purdue’s Impact Science Lab. This image was published in “Effect of replacement strike-face material on the ballistic performance of multi-ply soft armor targets,” coauthored by Zherui Martinez-Guo, in the “Textile Research Journal” in 2019.

Impact Science Lab accepted into exclusive technical society on aeroballistics

Purdue’s Impact Science Lab, and Purdue University by association, have been accepted into the Aeroballistics Range Association. The ARA is an exclusive technical society of organizations involved in experimental study served by guns and related mechanical launchers.

Purdue, like all members, was voted in based on its unique capabilities. Other ARA member organizations include national labs and defense agencies from around the world, including NASA, the Japan Aerospace Exploration Agency (JAXA), Air Force Research Laboratories (AFRL), and Sandia National Labs.

“We're very specialized. We have hydraulic presses, Kolsky bars, different gun sizes from small particles to large plates, high speed cameras, and various optical, laser, and X-ray diagnostics. We can get snapshots of how materials transform in time and test materials up to very high loading rates. It's a tricky regime, but it’s something our lab is good at.” says Zherui Martinez-Guo (BSAAE ’11, MSAAE ’14, Ph.D. AAE ’20), the lab’s lead professor and Purdue liaison to the ARA.

Martinez-Guo took over the Impact Science Lab from former AAE professor Weinong Chen, who is now chair of aerospace engineering at Iowa State University. Martinez-Guo conducted his PhD research in the Impact Sciences Lab, studying the ballistic impact resistance of high-performance composite fibers. He served as a distinguished postdoctoral associate at Idaho National Laboratory before returning to Purdue as a research assistant professor in 2024.