If you didn’t know you were looking at a hovercraft, someone would have to tell you. The contraption has a broad, flat base and a big fan in the back; it looks like an antique flying machine come to life. Movement of any sort seems dubious. But that does not deter the student pilot, who jumps in, starts the engine (which sounds like a lawnmower on steroids) and easily pilots the hovercraft forward, letting everyone see the optimistic license-plate-like logo painted on its back: “C.U. LATER.” A cheer rises from its creators, the 10 members of Catholic University’s mechanical engineering senior design class. After all, the hovercraft is their baby. And it’s taking its first baby, er… steps.
A hovercraft doesn’t step, of course, and it doesn’t fly, either. It has no wheels so it doesn’t roll. What it does is glide. Hovering on a pillow of air, this amphibious vehicle cruises easily across water, sand, ice or, in this case, the lawn in front of CUA’s Columbus School of Law.
As the hovercraft slows to a stop, class members breathe a collective sigh of relief. They have completed phase one of an arduous (but fun) yearlong project: They’ve built a hovercraft from a kit and proved they can make it move, turn and stop. Now they will use what they’ve learned to design and build their own hovercraft from scratch.
“The students bring everything they’ve learned to this project — stress analysis, thermal analysis, failure theories,” says Assistant Professor Tung-Huei Chen, who teaches Engineering 441 and 442, the two-semester senior mechanical design course. “This class takes them beyond the textbook, too. Students learn how to present their work, make a cost report and fundraise.” Bringing in a project on budget is also a skill much appreciated by future employers, Chen says. In a word, the students get a taste of what it’s like to be working engineers.
NUTS AND BOLDS
While mechanical engineering seniors build something every year, this is the first time since 1960 that they have constructed a hovercraft. The vehicle may seem unusual, but hovercraft have been used for transportation, rescue, exploration and recreation for more than 40 years. While some hovercraft are used like boats (for instance, they have been ferrying passengers across the English Channel since 1968), their low “footprint pressure” (the pressure they exert on the operating surface) means they can explore swamps and other environmentally sensitive areas where boats or other vehicles can’t go.
The class decided to build a hovercraft last spring when they were juniors; it was a compromise pick between the model aircraft favored by some students and the dune-buggy-like vehicle preferred by others. It’s a good tiebreaker because the hovercraft can travel over land like the dune buggy and it operates on the principles of lift and thrust like the airplane.
The lift comes from a fan forcing air underneath the craft where it’s trapped by a skirt to create a pillow upon which the hovercraft glides. The thrust comes from a fan moving air forward through specially shaped ducts. Powering this is an engine (or two) that must be powerful and light.
The 10 students are divided into three groups. The lift group makes decisions about the fan, air ducts and skirt design. The structure group is in charge of the craft’s frame, buoyancy and safety, among other things. Finally, the propulsion/control group must decide what kind of engine (or engines) to buy, plus design a throttle and rudders to control and steer the machine — so difficult a task that even the original inventor of the hovercraft, Sir Christopher Cockerell, likened it to “driving a car with four flat tires on ice!”
Every week, Chen lectures students on basic design topics and those specific to hovercraft construction. The class meets six hours a week, which gives students time to discuss their designs and to train in the campus machine shop, learning to weld and to use the drill press, lathe and band saw. These are good skills to have — not only now, but also later on, says Kenneth Romney, a retired mechanical engineer and adjunct professor who provides technical know-how to the design class. “It’s good to understand what a carpenter or welder has to do and to be sensitive to that when you design.”
PAYLOADS, DUCT TAPE AND A RAFFLE
In the classroom, students provide regular progress reports to Chen, Romney and Jeffrey Didion, a part-time adjunct professor who also works at NASA. The ratio of three teachers to 10 students allows for the kind of personal attention students at other schools can only dream of. In fact, the senior design seminar is often cited by prospective students as a reason they decide to attend CUA, says Dean of Engineering Charles Nguyen.
During one spirited discussion last fall, students shared their design triumphs and frustrations: “We had problems with the skirt not attaching,” reported Kerri Allen, from Elkhart, Ind., a member of the “lift” team. The problems were resolved later with good, old-fashioned duct tape. “Don’t worry about that,” Didion says to the students. “You’d be surprised how low-tech most things are.”
“We think the key here is weight,” says Erica Dietrich, from Bel Air, Md., of the “structure” team, discussing the important question of payload. The hovercraft handles differently depending upon the weight of the person who’s driving it.
Chen, Didion and Romney urge students to consider price in their decisions, too. Engineering student Melissa Schneider, of Blackwood, N.J., is the project leader and responsible for balancing the budget. While the CUA School of Engineering contributes some money and materials to the project, students must raise several thousand dollars more by finding sponsors and selling T-shirts. This year’s class has come up with a novel way to raise funds — a “Discover the Hover Day” with a name-the-hovercraft raffle, hot chocolate, balloons and a hovercraft gliding demo.
Chen says this year’s class is a good group and, though he doesn’t advertise the fact, they’re actually on time so far. “I never tell students they’re on schedule, I always say they’re behind,” Chen says. “They aren’t doing this project alone. They have many other courses and activities and are looking for jobs, too, so I need to push them.”
Dan McDonald, of Alexandria, Va., doesn’t feel pushed. He says the class has been “a blast” so far. Dietrich says the main challenge of the class is finding the time for everyone to meet and work on the project. “But it’s worth it being able to say, ‘We made a hovercraft!’” she says.
As the first semester winds down, students put the finishing touches on their final design. Their hovercraft will have two engines, and paying for them will be their largest expense. To save money they’ll sew the skirt themselves. The spring semester will be filled with building and testing their hovercraft and preparing to enter it into a national competition.
What’s important in the long run, says Chen, is not so much the students’ particular hovercraft design or construction techniques but how they justify them. “They need to tell me why they decided on a metal frame instead of a plastic one, say, or why they welded instead of bolted something,” he explains. “I need to have calculations and data to support the design. I want to see presentation skills and supporting documents.”
Chen knows that the experiences the students are having will stay with them forever. “Many students write me later,” he says, “and they tell me that this is the high point of their time at CUA.”
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