Nothing useless can be truly beautiful, 19th-century textile designer William Morris once said.
Now, a team of engineers at Polytechnique Montréal have demonstrated the inverse of Morris’s famous quote: They started with something truly beautiful and discovered it has an unexpected use – as a new type of parachute.
In a study published Wednesday in the journal Nature, the research shows that a parachute inspired by kirigami – the Japanese art of paper cutting – is ideal for dropping small objects from the air, particularly in places where pinpoint accuracy is required. Versions of the parachute could be used to deliver medicine or other supplies in emergency situations.
“When you use a conventional parachute, it’s quite random where it’s going to fall,” said David Mélançon, an assistant professor in the school’s department of mechanical engineering.
“What is nice about these parachutes is that no matter how you toss them, they will readjust in the air and fall straight down.”
The parachutes do not require careful folding. At rest, they are simply disks of a thin, flexible material measuring several centimetres across. Once airborne, a strategic and mathematically optimized series of cuts in the material causes the chute to open up into a three-dimensional lattice that creates enough drag to slow the fall of the object attached to it.
When it lands, the material collapses back into a disk, ready to be tossed again.
Frédérick Gosselin demonstrates what the parachute looks like once extended.
Dr. Mélançon said he has long been fascinated by such shapes, dating back to his PhD days at Harvard University, where he worked on compact deployable structures that utilize principles of kirigami as well as origami, the art of paper folding without cutting.
The inspiration to apply those principles to parachute design did not arise until he was at Polytechnique Montréal, where he teamed up with fellow professor Frédérick Gosselin, who was interested in airflow around the intricate shapes. They enlisted a graduate student, Daniel Lamoureux, to explore the concept.
At first, Dr. Mélançon said, the team was imagining a configuration where a mass was hung from the kirigami structure on strings, creating an umbrella shape much like a traditional parachute. But while discussing the project with Mr. Lamoureux and tossing samples around in his office, they noticed the tendency of the lattice to open up into the reverse orientation – more like a cup than an umbrella – before unfailingly falling straight down. It was at this point, Dr. Mélançon said, that they hit upon the idea of attaching the mass directly to the centre of the parachute.
Prof. Gosselin speaks with two students, Saeideh Kazembeigi and Pegah Mehrabian, in a laboratory where the parachutes are made with a laser cutting machine.
Wind-tunnel experiments and drop tests, first indoors and then outside, from drones, soon showed how well the design worked. Dr. Mélançon said that by adjusting the length and arrangement of the cuts, the descent and trajectory of the chute can be precisely tuned. In theory, it could work for any mass, but scaling up to the size needed for a human skydiver would be impractical – at least with the designs that the team has explored so far.
When it comes to delivering small payloads, however, the innovative “kiri-chutes” are full of promise. “Because they are so simple to make, they could be produced cheaply in large numbers,” Pierre-Thomas Brun, a Belgian research engineer, wrote in a commentary accompanying the new report. “Imagine fleets of kiri-chutes carrying essential supplies into disaster-stricken or remote regions – places where minimizing costs is key, and where landing might be a challenge, even for a drone.”
Dr. Mélançon said that nature has long been exploring such patterns, from the feathery structures on which dandelion seeds drift to the elaborate cuts in tree leaves that allow wind to flow past without ripping them from their branches.
The team is now exploring various materials for creating the parachutes and new designs, including some that induce rotation, similar to maple keys.
Usefulness aside, Dr. Mélançon said that the designs also serve as an effective teaching tool for students because they are easy to make and delightful to watch in action. “The application is a strong motivator,” he said, “but physics wins over functionality.”
