Science of Boomerangs: How to Make and Throw the Aussie Magic
Throwing a boomerang is part science, part magic — and, as Eric Darnell knows, so is making one.By Dan Drollette
At the preseason tryouts for the U.S. Boomerang Team in Greenfield, Mass., one figure stands out among the hacky sack players and pizza delivery guys gathering in the soccer fields, limbering up their throwing arms.
Eric Darnell, a soft-spoken 62-year-old Quaker and backyard inventor from South Stafford, Vt., has brought 60 of his latest handmade boomerang prototypes, along with several notebooks, two windsocks and printouts of weather forecasts. While others just hurl their rangs — as aficionados call them — Darnell tries to be as meticulous and scientific as possible about the objects he refers to as "my kinetic sculptures."
When a boomerang won't soar, he adds extra weight here, shaves a wing there or drills a hole somewhere else to improve flight characteristics. When asked what he's doing, Darnell — who has coached three U.S. teams — explains with a blizzard of information about airfoil shapes, Reynolds numbers, local atmospheric conditions, wind shear and the effects of drag.
But he also acknowledges the role of art and intuition: "One of the things that is near and dear to my heart about boomerangs is that there's still some magic involved. You can't completely computerize them. I've seen computer-designed boomerangs, and they’re junk. Sometimes, to fly well, a rang needs to be asymmetrical or unbalanced or off-center. It's counterintuitive; it's not in textbooks about airfoils." Plus, imperfections make a boomerang more fun. "When you see a rang made for maximum time aloft vibrating in the air, it just seems alive."
Though Darnell's degree is in regional planning, he is a self-taught engineer and avid consumer of trade magazines on materials science. He is also a tool-and-die designer, and his list of inventions includes chest protectors for sports, helmets for lacrosse and ice hockey, and a wood-burning stove that is sold all over the world.
But his first love is boomerangs, which he began to make as a child after losing one too many gliders. ("For a 12-year-old, that's devastating," he says.) Today, his boomerangs are used by more competitive throwers than those from any other single boomerang designer. To create a boomerang, Darnell relies on a little theory and a lot of experimentation, often with previous designs. "I have about a thousand rangs in my barn that I use for inspiration," he says. Some of them came from well-wishers and some from obscure shops — several are even made from the same exotic carbon fibers used in submarines.
But the boomerangs he most treasures, Darnell says, are the ancient wooden ones. Aborigines made rangs for hunting, fishing and imitating the flight of hawks; they made boomerangs to catch on the edge of an enemy's shield and hit him from behind. Some have two wings; others, four. Nearly all have some unique feature that Darnell tries to incorporate into one of his own designs.
It must be a sound strategy: Twenty-five world records have been set using Darnell boomerangs or rangs inspired by his models. At last year's world championship in Japan, 127 of 130 competitors used Darnell rangs.
And, yes, there is such a thing as a world boomerang championship. (Next year it will be held in Seattle.) National clubs thrive in the United States, Germany, France, Japan and England. There are rules, regulation fields, exhibition games and individual and team events. There are even pro tours, which date back to 1985, when 10,000 screaming Parisian fans watched U.S. Boomerang Team members Chet Snouffer, Barnaby Ruhe, Peter Ruhf and Darnell set records. "It was like we were the Beatles," Ruhf says.
Darnell has himself set world records for endurance (43 catches in 5 minutes) and maximum time aloft (1 minute and 44 seconds). He has also sold millions of boomerangs. He says he isn't into the sport for the money, although he admits, "I make many happy returns."
Eric Darnell turns native oak into boomerangs that return with eerie precision. Few experts agree on exactly why boomerangs fly the way they do, but a few basic principles apply: lift, spin and an effect called precession.
How It Works
Air passing over the curved top of a boomerang’s airfoil — at the leading edge of the wing — is forced to go faster than air passing over the relatively flat underside. As described by Bernoulli's principle, this generates less pressure above the wing, creating upward lift.
The rate of a boomerang's spin is determined by the length of the wings, the angle at which they're joined, the distribution of material and the amount of force applied by the thrower. Like a gyroscope, a boomerang has greater stability the faster it spins.
A boomerang is thrown at a slight outward tilt from vertical. The top wing rotates with the object's forward motion, so it moves faster than the bottom wing, generating more lift. Because the boomerang is spinning, the lift exerts a steady force that is felt 90 degrees later, at the point in each rotation farthest from the thrower. This force nudges the wing laterally and the spin axis shifts. The boomerang turns — eventually curving all the way back to its starting point.
Four Boomerang Designs
Roughly 30 in. long, this 19th-century rang from Western Australia is made from mulga — a wood so dense "it sinks like a stone in water," Darnell says. It weighs nearly 2 pounds, so, "You definitely want to stay out of the way when it comes back."
The unknown maker carved grooves into the top and bottom, shaving off a tiny bit of weight (crucial in a sport where the mass of a paper clip can clinch a record throw). The grooves also form hollows that — like the dimples on a golfball — create a blunt airfoil, which increases lift.
"This boomerang inspired me to put a shallow hollow, or undercamber, on the bottom of my boomerangs," Darnell says.
More wings mean more lift, which makes the boomerang turn in an extremely tight circle. Unfortunately, early prototypes circled too tightly — traveling only 16 yards before returning. Darnell corrected this problem by putting a single hole near the end of each wing. This spoiled just enough lift to allow the rang to sail out farther — to 27 yards."In addition, the holes slowed the rate of spin, making this boomerang easier to catch," Darnell says. "They showed me that drag is not a four-letter word."
The classic V shape, with a twist. The wings' positive angle of attack allows the boomerang to climb farther and faster. It's made from a type of polypropylene plastic soft enough for the user to bend the wings further, yet resistant enough to hold the resulting shape — making this the first "tuneable" boomerang.
At about 2 ounces and 14 in. across, the Pro-Fly can travel out as far as 40 yards. Even so, Darnell was unsure how the plastic model would be received in Australia, the home of the wood boomerang: "Then I met Bluey Roberts [a well-known Aboriginal artist] — and he was throwing a Pro-Fly. He goes, 'Oh yeah, bloody good rang.'"
Made for the Maximum Time Aloft event at competitions, the MTA has asymmetrical wings that present more surface area to the wind, maximizing lift. And at a mere half-ounce, the 13-in.-wide MTA floats on the slightest updraft.
"It's a crazy shape compared to most other designs," Darnell says. Its airfoil, however, is extremely efficient. It loses little energy to the formation of noise, for example.
A few years ago, officials informally timed the silent rang at 17 minutes aloft. "Sometimes, an MTA just disappears," says Ted Bailey, a former president of the U.S. Boomerang Association. "We call that 'losing it to the jet-stream god.'"