
Leonardo da Vinci was, by any metric, a genius – but he was still limited by his time. The man may have been a secret authority on anatomy, music, art, engineering, and even frickin’ paleogeography, but we wouldn’t expect him to understand the best way to, say, design an Unmanned Aerial Vehicle – that is, a drone. He was born more than 500 years ago – surely, he’d barely be able to comprehend the question, let alone answer it.
Except, according to a new study from researchers at Johns Hopkins University – as yet not peer-reviewed, but available to read on the ArXiv preprint server – he totally could. In fact, not only would his design of the “aerial screw” flying machine actually work, but it turns out it even has a few advantages over our current drone designs.
A modern problem
It’s fair to say that drones are… having a moment, right now. They’re up on Everest, saving mountaineers; they’re over in Fiji, air-dropping special anti-dengue mosquitoes; occasionally, they’re in Langley, pissing off the Air Force for unknown, but presumably slightly less noble, reasons. They can be used to corral and conserve wildlife; sometimes, they are the wildlife. Sometimes they’re domesticated. Sometimes, they’re a testament to humanity itself, creating art and challenging almighty Zeus like some tiny technological Typhon.
It’s all very impressive. It’s just a shame it’s so annoying.
“Drones are becoming a growing new source of environmental noise pollution,” points out one 2021 review of the effects of increased drone prevalence on society, “and annoyance reactions to drone noise are likely to occur in an increasing share of the population.”
It’s not simply a question of decibels. Drones are seemingly specially designed to produce as irritating a noise as possible: they produce high-frequency, pure sinusoidal tones – long known as more annoying to human ears than other kinds of noise – and those tones have a tendency to bounce back up off the ground, too, making them even louder and longer-lasting. Altogether, the review concludes, “drone noise is substantially more annoying than road traffic or aircraft noise at the same level.”
So, here’s the question: what can we do about it? One solution is to use novel construction materials: “The culprit is the upward-moving fan motion,” explained Reza Ghaffarivardavagh, then a doctoral student in Boston University’s Department of Mechanical Engineering, in 2019. Along with professor Xin Zhang, he had just designed a new “acoustic metamaterial” that could dampen sound by 94 percent – and, he said, “if we can put sound-silencing open structures beneath the drone fans, we can cancel out the sound radiating toward the ground.”
An alternative, however, would be to adapt the design of the drone itself – and that’s where the new study comes in.
I am not sure about the exact reason da Vinci designed it as a screw, but we should note that no flying machine existed during his time.
Suryansh Prakhar
“We were looking at different propeller shapes with the aim of reducing aeroacoustic noise,” says Suryansh Prakhar, a PhD student at the Johns Hopkins University Flow Physics and Computation Lab, and lead author of the new paper.
“While food and parcel delivery using drones is growing, the aeroacoustic noise remains one of the issues preventing their wide scale use in densely populated areas,” he tells IFLScience.
An ancient solution
It may seem odd to turn to the 15th century for drone designs – but if there’s anyone who could have done it, it’s Leonardo da Vinci. And okay, admittedly the polymath genius didn’t get the idea completely right – but his sketches of an “aerial screw”, bizarre though they may look to modern eyes, genuinely do constitute “one of the very early sketches of a propeller,” Prakhar explains.
The aerial screw is – well, it’s pretty much what it sounds like: a giant screw designed to generate lift and, ideally, flight. “I am not sure about the exact reason da Vinci designed it as a screw,” Prakhar tells IFLScience, “but we should note that no flying machine existed during his time.”
“His aerial screw has features similar to the Archimedes’ screw, but I don’t know the historical context to say if da Vinci knew about or was inspired by the Archimedes’ screw,” he adds.
It looks weird, but technically, it could have worked: “the rotary motion of the aerial screw should and does generate lift, thereby validating the overall concept behind da Vinci’s design,” the paper points out. There’s just one problem: “da Vinci’s original idea […] required people running around a pole to rotate the screw,” Prakhar explains. “[It] would not have worked” in real life.
Still, there might yet be advantages to Leonardo’s strange design. “We were interested in the mechanical power and the aeroacoustic noise characteristics of da Vinci’s screw,” Prakhar says. “We were interested to see how it would compare against traditional propellers.”
And the really surprising part? In a showdown between “decades of military and consumer-driven R&D” and “one lone crank with a 15th-century education who never in his life saw a flying machine” … it seems Leonardo got the win.
Learning from the past
Like all good math – but not, admittedly, the most convincing engineering – the investigation of Leonardo’s screw took place in the abstract. The team modeled the rotor in 3D using CAD [computer aided design] – “Our aerial screw design is based on Elico,” Prakhar says, referring to the Leonardo-inspired helical propellors created by University of Maryland students back in 2020 – and computed the resulting flow and aeroacoustics mathematically, rather than through experimentation.
It’s not ideal if the goal is to build and create the perfect aerial screw drone – but it’s good enough to figure out which design has more mechanical power and lower noise. “For a given load, the aerial screw shows better performance on both these metrics,” Prakhar tells IFLScience.
The reason is simple physics. Since the aerial screw has a larger surface area, it moves slower to create the same lift and, therefore, requires less power. It’s also quieter in every direction; the noise it does make is lower-pitched, and thanks to a bunch of vortices spinning out of its helical shape, it also dissipates quicker.
It is, in total, something of a vindication for the Vincian. So what’s next for the team?
“I am graduating very soon,” Prakhar tells IFLScience, “but FPCL lab will continue to study both traditional and unconventional propellers as well as bio-inspired flight.”
The plan, he says, is “to gain aerodynamic and aeroacoustics insights that could help improve current propeller design.”
The paper can be read on the ArXiv preprint server.
Source Link: Leonardo Da Vinci's Flying Machine Is Better Than Modern Drones For Noise And Power