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Students conduct experiments aboard weightless wonder

Students in Weightless Wonder

This summer, a group of UW-Madison students, including engineering mechanics senior James Diebel (right) and engineering mechanics graduate student Jeffrey Johnson, conducted an experiment in NASA's Weightless Wonder. (large image)

Students in Weightless Wonder

The students' experiment examined the efficiency of the fuel injection processes that occur in car engines and rocket motors. With it, they hoped to gain a better understanding of how fuel droplets behave under different conditions to optimize the fuel injection process. (large image)

Adding a new spin to the challenges of engineering, a group of students were literally "in over their heads" this past spring when they took part in the NASA-sponsored Reduced Gravity Student Flight Opportunities Program.

Based at NASA's Johnson Space Center in Texas, the program allows engineering students to conduct zero-gravity experiments aboard the "Weightless Wonder," a modified jet airplane.

Four UW-Madison students flew aboard the KC-135a Reduced Gravity Laboratory, a modified Boeing 707, to perform experiments aimed at examining and improving the efficiency of the fuel injection processes that occur in car engines and rocket motors.

"The first time we went up, we weren't ready, so our feet just flew up behind us and we started floating around," says senior James Diebel, principal investigator for the project, of the initial moments aboard the plane.

To create a sense of weightlessness, the pilot aims the plane at an upward angle of 45 degrees, shooting into the sky like a cannonball. Then, at 34,000 feet, the plane pitches over and falls back toward Earth, simulating weightlessness in the rapid descent. The pilot repeats the flight pattern 29 more times, allowing students to collect data under gravity-free conditions.

The scope of the project stretches well beyond the team's two sessions of two-hour flights from Houston over the Gulf of Mexico. The project began in fall 2000 with an idea to investigate the vaporization of fuel droplets when sprayed into gasoline engines and rocket motors.

Because engines are driven by energy released when fuel droplets evaporate and burn, engine efficiency is determined by how much fuel evaporates in a given amount of time. In a gravity-free environment, convection, the process that makes hot air rise and complicates process of vaporization, would be prevented from occurring.

By comparing the results from fuel vaporization in a reduced-gravity environment with those under normal conditions, the students aim to gain a better understanding of how fuel droplets behave under different conditions to optimize the fuel injection process.

The findings may be used in helping promote changes in engine design while improving efficiency and reducing emissions.

James Diebel, Gabe Hoffmann, Jeff Johnson, Kyle Larson, Katie Plzak, Ryan Curtiss and Keith Tschohl made the trip to Houston. The full team was made up of one graduate student and 19 undergraduates, including students who aided in the engineering, science and business aspects of the project. The group received contributions and funding from several departments, including chemical engineering, mechanical engineering and electrical engineering, as well as the Wisconsin Space Grant Consortium, part of an educational branch of NASA.

Diebel says that while the ideas proposed experiment had been examined before, the NASA program presented the opportunity to perform the experiment under improved conditions that could yield more accurate results. Previously, the experiment had been released from a drop tower, achieving two seconds of weightlessness.

"We were able to achieve [weightlessness] for about 25 seconds, which is very beneficial," Diebel says. "At the beginning of the experiment, there are transient effects, or time-dependent things that go on right at the beginning, and they don't decay into a steady state for about a second. With the drop tower scenario, this would lead to problems with half of the experiment."

The UW team was chosen to join 53 other undergraduate teams from across the country for the two-week program. They transported their experiment by van, driving from Madison to Texas "economy-style," jokes team leader and engineering physics graduate student Gabe Hoffmann, who helped coordinate the project. "Our three-foot tall experiment made the perfect coffee table," he says.

The device's real function was to compress a single droplet fuel in a small gas chamber by using two steel pistons that each moved 10 inches in less than 30 thousandths of a second. The compression heated and pressurized the droplet to create engine-like conditions. This detailed process was the result of efforts that often involved putting in 30-hour work-weeks, often seeming a full-time job, Diebel says.

"It was a lot of work, but it's a good experience," he says. "It makes sense to get some experience actually designing things and putting things together. It's a lot different than the coursework we have, and it's really valuable, so I don�t mind putting the time in. I'm going to school to become an engineer, so I might as well learn how to do this."

Once in Houston, both the students and the experiment were subjected to a series of tests, including daylong training to prepare for the reduced-gravity conditions during flying and disorientation training to reduce the chances of motion sickness.

Safety technicians and NASA experts reviewed the experiment, checking technical details, and students demonstrated the key operations and safety features before loading the device onto the plane.

The team then took part in two days of flying, with two team members flying each day. Hoffmann, who had taken part in the program during previous years and flown before, remained on the ground at the space center with Keith Tschohl, following the flight and helping out with technical details and questions by way of downlink from the plane. The video downlink allowed Tschohl and Hoffmann to see what was happening aboard the plane, with each flyer wearing headphone and microphones to communicate.

Aboard the plane, the experimental device had enough fuel to run for 20 experiments, and the students spent the remaining time exploring the reduced-gravity environment. Though Hoffmann likened his previous first moments in zero gravity to "flopping around like a fish out of water," Diebel described the experience as enjoyable once he became accustomed to the environment. "It's a lot like driving over a hill in a car quickly, and you feel your stomach rise, except with this, that feeling just keeps going and lasts for 25 seconds," he says.

When performing the experiment, students tucked their feet under straps to keep from floating away, but after the data was collected, the students had time for floating and experimenting in other ways. For pure fun, the final stages of the flight simulated Martian gravity, which is 40 percent of earth gravity, and lunar gravity, which is one-fifth of the earth's gravity, and "so light that you can jump up and it takes a couple of seconds to come back down," Diebel says. "People were getting down and doing one-armed pushups with people on their backs."

In addition to time aboard the Weightless Wonder, the program offered students the chance to take a behind-the-scenes tour of NASA, attend lectures and social events, and explore industry-related internship and job opportunities. Reflecting on the experience, Diebel says overall, the educational aspects were the best parts of the program.

"I've learned more about the practical side of engineering that I could in the classroom, and it's given me valuable experience," he says. "It also had more of a guiding influence over other team members, because they weren't really sure what they wanted to do prior to getting involved. This can help guide them toward research as a career path."

Hoffmann says this year's experience with the NASA experiments will be used to achieve better results next year, when the team plans to resubmit their proposal for a second round of experiments.

"We expected the design to work in zero gravity, but it wasn't perfect and our results aren't yet publishable," he says. "We'll be developing a new, improved design and hope to take it down to Houston again next year, and if the results are good, we plan to publish. We learned some good engineering lessons that will hopefully lead to good science data next year."

Sponsoring Organizations

NASA Reduced Gravity Student Flight Opportunities Program
University of Wisconsin
UW College of Engineering
UW Department of Engineering Physics
UW Mechanical Engineering Department
UW Electrical and Computer Engineering Department
UW Chemistry Department
Wisconsin Space Grant Consortium
American Society for Engineering Education

Affiliated Groups

UW Chapter of AIAA
Polygon Engineering Student Council
KC-135 Aircraft Operations

Tracy Hirigoyen