Four University of California, Davis, students were walking on air recently -- literally. They got a taste of weightlessness when they took their experiments aboard a NASA aircraft that simulates zero-gravity conditions for 25 seconds at a time.

"It's indescribable," said Daniela Fredrick. "Weird, but pleasant, and fun."

"It's very addictive. You immediately want to do it again," said Cosan Unuvar.

The experiments took place aboard NASA's "Weightless Wonder," less politely known as the "Vomit Comet." Fredrick and Unuvar, both graduate students in the UC Davis Department of Chemical Engineering and Materials Science, with undergraduate Jennifer Sween, were joined by UC Davis alumna Laurie Harvey and Anthony Manerbino from Canadian engineering company Guigne International.

NASA's converted KC-135 is used for astronaut training and to carry out experiments with short periods of reduced gravity. To achieve that, the plane flies a series of roller-coaster climbs and dips. As the plane goes over the top of the climb, the apparent gravity on board drops to about one percent of normal. As it pulls out of its dive, the force rises to 2 G, or double normal. The plane makes 40 such maneuvers per flight.

The UC Davis team is studying formation of new materials by combustion in an electric field. A mixture of metal powders is ignited at one end, causing a wave of combustion to pass through it at temperatures up to 1500 degrees Celsius. New materials form behind the wave front. Passing an electrical current through the mixture makes the process more efficient and can create new materials with unique properties, especially nanomaterials made up of extremely small crystals.

Because molten material flows under gravity, the results are different depending on whether the sample is ignited from the top or the bottom. Doing the experiments in a low-gravity environment should sharpen the effect of the electric field, said Zuhair Munir, professor of chemical engineering and materials science at UC Davis and principal investigator on the project.

The work could lead to new ways to manufacture new types of materials, Munir said.

The work is funded by a grant from NASA to Munir and Ben Shaw, professor of mechanical and aeronautical engineering. The apparatus to carry out the experiments was built by Guigne International of Newfoundland, Canada, with combustion chambers and other equipment built at UC Davis.

The students have spent much of the past few months carrying out experiments on the ground and preparing technical and safety documentation for NASA, and there was no let-up when they arrived at the Johnson Space Center in Houston, Texas, in early November. Two thousand pounds of equipment needed to be unpacked, prepared and installed on the aircraft.

"You can't check things enough," Unuvar said.

Once in the air, the team prepared for the first experiment, got into position -- and found weight dropping away, somewhere over the Gulf of Mexico.

"Your first reaction is that you're trying to swim in the air and nothing happens -- your legs are spinning like a cartoon character," Unuvar said.

"You're just smiling the whole time," said Fredrick. "It's totally different from a roller coaster or anything else."

The nearest equivalent, in terms of the uniqueness of the experience, was scuba-diving, Fredrick said. Despite the plane's nickname, none of the group got sick.

"It's too much fun to get sick," Unuvar said.

As weight returned, then doubled, the team had to remove the spent combustion chamber and attach a new one. At the bottom of the dip the nine-pound chambers weighed nearly 20 pounds and it was impossible to stand up. But the changeovers went better than expected and the students were able to complete their experiments with time to spare to enjoy the experience.

Altogether, they completed four flights, including two on the same day, and 158 parabolic maneuvers. Sharing the flights were other researchers and astronauts testing equipment for use in spaceflight.

The students praised the NASA staff running the flights for their hard work and professionalism.

"They were wonderful. They worked 14-hour days and they were always there for us," Fredrick said.

The students will now repeat the experiments on the ground and hope to go on more flights next year.

"If we can go again, definitely!" Fredrick said.