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Undergrad Cameron Castleberry holds up the football and baseball used in the wind tunnel.

How Fast is a Mach 4 Field Goal? UTSI Interns Found the Answer

Associate Professor Phillip Kreth loves showing off the large Mach 4 wind tunnel in the lab at the University of Tennessee Space Institute (UTSI) in Tullahoma. Helping visitors conceptualize how fast Mach 4 speeds actually are, however, can be a challenge. 

Since UT resides in SEC country, Kreth has always used a football analogy to give them a better perspective with more relatable terminology. At standard sea level conditions, Mach 4, which is four times the speed of sound, is the equivalent of 15 football fields per second. 

A football makes its way through the wind tunnel at hypersonic speed.

Kreth wanted to take the analogy a step further by placing a football in the wind tunnel and getting pictures and videos to share with the public. He believed it could generate more interest in STEM, hypersonics, and the aerospace engineering field. 

He just needed to find a student intern willing to help. Cameron Castleberry was game. The senior aerospace engineering major tackled the project with as much vigor as a defensive end sacking a quarterback. 

“I’ve always been a Vol fan, so I wanted to take charge on that project because I’ve always been so excited about Tennessee sports,” said Castleberry, who was assisted by graduate student Zane Shoppell. “Once Dr. Kreth said he’s always wanted somebody to put a football in the Mach 4 wind tunnel, that really clicked with me immediately.” 

Measuring the speed of sports

As the project began taking shape last summer, the UT baseball team was in the middle of its national title run at the Men’s College World Series. Castleberry and Shoppell decided to add another sport to the equation to celebrate the Vols historic win. 

Shoppell bought a baseball from Alumni Hall and the two began mapping out the details. 

“The baseball was so much easier than a football. All we really had to do was drill a hole in it, thread a rod into it with some epoxy in the middle, and then we mounted it into the wind tunnel,” Castleberry said. “But the football would explode if we did that, so we had to 3D print a football to use instead. That process worked great.” 

A UT baseball makes its way through the wind tunnel at hypersonic speed.

The group was able to get some “really cool images” of each ball to help visualize the aerodynamic shock structure and flow field around them. 

How fast would a Mach 4 fastball be? 3,091 mph. 

For perspective, former Vol pitcher Ben Joyce threw a pitch 105.5 mph last season for the Los Angeles Angels. It was the second-fastest pitch in Major League Baseball history by 0.3 mph. 

How long it would take to kick a field goal from Tullahoma to Neyland Stadium in Knoxville? Less than 2 ½ minutes. 

“It takes just about 2 1/2 minutes to walk from my office down to the classroom,” Kreth said. “But if I could go from here to Knoxville in that same time, I would really appreciate that.” 

Making hypersonics more accessible

Kreth is assembling the test results to create posters and charts that he can hang in the lab at UTSI for visitors. The group has also considered creating a YouTube video that discusses the sports-related wind tunnel project and the science behind everything. 

“I think it’s important for us to connect with a broader audience and help enlighten them about what happens to aircraft as they approach and travel at hypersonic speeds,” Kreth said. “I have seen some others in my field do similar things by putting Star Wars Lego models and even a toy cow in their hypersonic wind tunnels. It’s good for us to do things like this that are more relatable to help demonstrate these concepts and generate interest in aerospace engineering and hypersonics.” 

Castleberry was thrilled to combine her love of aerospace and sports into one project as part of her experience at UTSI last summer. She gained valuable knowledge about aerodynamics that she plans to share with others as much as possible. 

“I learned a lot about compressible flow and pressure changes in the wind tunnel. Getting to visualize that was a big thing for me,” she said. “Seeing the tunnel’s starting shock waves accelerate the flow to Mach is something you can’t get from being in a classroom or reading a book. It was very rewarding.” 

Contact

Rhiannon Potkey (865-974-0683, rpotkey@utk.edu)