This article was taken from the April 2011 issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.
The Mojave Desert's dry Ivanpah lake bed shimmers under a vicious solar glare creating the illusion of water. Piercing the mirage are dozens of sails -- a vast array of colour streaking over a dusty ocean.
It's the last week in March, and Ivanpah is hosting the North American Land Sailing Association's annual dirt-boat championships, the America's Cup. It may seem odd to give this competition the same name as the more famous ocean race, but truth be told, in a strictly technical sense the two America's Cups are quite similar.
Dirt sailing is sailing, after all: the tactics are the same; the manoeuvres are the same. The main difference, as people who race on dirt are keen to point out, is speed. Sailing on a dry lake is about three times faster than sailing on water.
Then there are the competitors themselves. "There's just something about the desert that attracts strange people," says Richard Jenkins. He should know: Jenkins is the current king of the Dirt Cup, as some call it, having set the world speed record at the competition in 2009, when his land yacht, Greenbird, hit 203kph. "Land sailors are a weird bunch. Oddballs. Alternative in every respect," he adds.
No one here is weirder or more alternative than a moustachioed man who has shown up this year with an exceptionally strange-looking dirt boat and an extraordinary claim. The man, fast-talking inventor Rick Cavallaro, says his craft -- Blackbird -- can, if sailing directly downwind, go faster than the wind propelling it.
Jenkins, like other Dirt Cup veterans, thinks this is preposterous. There's no doubt that a boat (dirt or otherwise) can go faster than the wind. By running at an angle to take advantage of crosswind effects, a boat can outpace wind speed. But directly downwind? Impossible, they say. In a best-case scenario, a sailing vessel heading directly downwind will move at the speed of the breeze pushing it.
The problem with downwind sailing is that once the craft reaches
wind speed, there is no more wind. And if there's one thing every sailor knows, it's that "you can't power through zero wind," as Jenkins says. Not only would the craft have to pull ahead of the wind pushing it, but from the perspective of the sailors on board, it would face what feels like a headwind pushing it back. In sailing, zero wind -- real or apparent -- is considered an absolute barrier, like the speed of light in physics. Yet Cavallaro claims
Blackbird can break this barrier. Not only that, he says, it will probably go downwind twice as fast as the wind. The boast is made all the more outlandish by the fact that Blackbird doesn't have anything that looks even remotely like a sail.
The craft is a crude contraption, made of plywood, carbon fibre, bicycle parts and pieces of go-cart. It's low and relatively streamlined, except for the 4.3m-high tower mounted behind the cockpit. Attached to this is what can loosely be described as
Blackbird's sail. Most people would call it a giant propeller, because it has two diametrically opposed 2.4m-long blades that rotate just like, well, a giant propeller. But propellers imply motors. Blackbird's rotating propeller-shaped sail is the motor. Cavallaro has connected the prop to wheels via a drivetrain, so the faster the cart rolls, the faster the sail-prop spins, thereby creating a feedback loop that Cavallaro says will accelerate the cart from a standstill through the zero-wind barrier and beyond.
To most people, Blackbird's engineless drivetrain sounds like a perpetual-motion machine. "Cartoon physics" was typical of the barbs thrown at Cavallaro when he revealed his idea.
But he remained undaunted. Blackbird is the result of a years-long quest to prove something deeply counter-intuitive to the world. A software and hardware developer with a degree in aerospace engineering, Cavallaro has done the maths. He has made small models and run tests. His contraption will work, he insists. But engineers and physicists are not so sure. Since Cavallaro first posted
Blackbird's design on the internet, his concept has been ridiculed in blogs, forums and a magazine. The debate recently reached a fever pitch among a certain type of geek, especially in Silicon Valley, so much so that some notable entrepreneurs, including Google cofounder Larry Page, forked out the cash to let Cavallaro finally build the vehicle. After four years of online arguments, explanations and insults, Cavallaro has brought his vision here -- to the Dirt Cup -- to prove he can beat the wind.
Cavallaro is suited up in a helmet, goggles and motorcycle pads.
All he has to do now is make the damn thing work. He climbs into
Blackbird's coffin-like cockpit. His seat is just a hammock that hangs a few centimetres above the ground. A BMX front wheel rests between his feet. There is a rudder in his right hand and a brake under his left foot. Every instrument -- every GPS device, every anemometer, every radio -- is double-checked to make sure Blackbird's speed is recorded accurately. The ground crew triple-checks that the craft is pointed directly downwind. When Blackbird is finally ready to roll, Cavallaro pops open the brake.
And nothing happens.
Blackbird started with a brain-teaser. Al Alcorn, the Atari engineer famous for giving the world Pong, had a question for his friend Rick Cavallaro -- never one to refuse a logic challenge: could a sailing boat outrun a balloon? The question, an old sailing conundrum, was new to Cavallaro, and it pushed his buttons hard.
Cavallaro was born in Cuba in 1962, the son of a US Naval flight surgeon. By the time he was 12, the family had moved to Florida, where Rick grew into a thrill-seeking teen. He owned a car before he could legally drive and would later sneak on to a yet-to-be-opened highway to push his Mazda RX-4 up to 217kph. At 16, he got his pilot's licence and started flying Cessnas. He also took to the sky with an assistant to his physics teacher, who owned a stunt plane.
After studying at Georgia Tech and the UCLA, Cavallaro worked in Southern California's defence industry. In 1989, he got a job at high-tech startup Etak in San Francisco. After Etak was bought by News Corp, Cavallaro joined sports-media effects company Sportvision, where he is now chief scientist. Cavallaro's singular obsession, however, has long been the wind. In addition to aircraft, he pilots sail-planes and experimental hang-gliders and has recently taken up powered paragliding. This passion, plus a penchant for brain-teasers, drew Cavallaro to John Borton, Sportvision's director of manufacturing, and a champion glider pilot. Their friendship began as an argument over an aerodynamics riddle that hinged on whether you could tell the direction of the wind while hang-gliding without looking at the ground. (You can, although Cavallaro has never fully conceded the point.)
Alcorn's balloon-versus-sailing-boat poser was exactly the type of thing the two loved to debate. Both knew sailing boats can sail faster than the wind. What's more, they understood the physical principles behind the phenomenon, which boil down to lift.
Aerodynamically speaking, a sail with wind travelling across it acts like a vertical wing. It will pull a boat forward the same way an aeroplane wing will hoist a fuselage into the air. Sails and wings produce lift, as long as there is wind moving across them.
That said, the two men realised that on a direct downwind heading, there is no wind moving across the sail; the sailing speed limit is the speed of the wind.
So, to beat a balloon, a sailor must navigate at an angle to the destination, then turn, or tack, the boat back toward the finish line. This downwind zigzag course -- jibing, in sailing terminology -- is often the fastest way to traverse between points A and B. But given that you have to cover more ground and take the time to turn, is it really fast enough to beat the wind itself (represented by the balloon)?
Answering that question requires factoring in things like drag and angle of attack, and using racing-performance data to figure out wind-speed multiples for every angle of sail. Of course, you could just skip this and turn to Google. A quick search reveals that Steve Fossett's speed-record-smashing yacht,
Cheyenne, has the capability -- the wind-speed multiples and attack angles -- to beat a balloon in a downwind race. So yes, Mr Alcorn, a sailing boat can outrun a balloon.
Cavallaro isn't the kind of man to Google an answer, though -- preferring thought experiments to web searches. And the balloon-versus-sailing boat hypothesis he came up with took him to another planet altogether: a cylindrical planet entirely covered by water, with a constant wind blowing down its length. Call it "Planet Water-Barrel" and visualise a balloon racing a sailing boat from one end to the other.
The advantage of holding a race on this planet is that because the boat can sail completely around the cylinder, it never has to zigzag to end up at the same end point as the balloon. Instead, the craft can stay on one continuous crosswind heading and spiral all the way around the barrel, ending up at the finish line. On Planet Water-Barrel, the maths simplifies. But forget the maths for a moment and concentrate on the visual picture.
What if the balloon-versus-sailing-boat race ran a down cylindrical planet of much a smaller diameter: Planet Steel-Rod? In that case, the boat would essentially be spinning around its own axis and its sail would suddenly look a lot like a turning propeller blade.
This is the point where a little Blackbird-shaped light bulb lit up over Cavallaro's head. With his background in aeronautics, he knew that a sail on a downwind tack and the blade of a spinning propeller are aerodynamically the same.
Blackbird's sail-prop-driven design quickly coalesced in Cavallaro's mind. Imagining it, he realised that the crosswind-only caveat to sailing faster than the wind didn't apply to
Blackbird. The lift the propellers provided would pull the cart forward, with the wind.
That forward motion would feed back into the system through the wheels, which would turn the prop even faster, creating even more lift, or -- as it's usually called with a propeller -- thrust.
The propeller -- on its continuous rotational tack -- would then simply screw itself through the zero wind.
Forget about tacking and sail-efficiency tables and
Cheyenne. Here was a wind-powered vehicle that could outrun a balloon in a drag race from point A to point B.
Cavallaro realised he had stumbled on the perfect setup for a new brain-teaser. And so, in spring 2006, he started a fresh thread on Runryder.com, a forum for model-helicopter enthusiasts. His post, with the subject line "Annoying Brain Teaser #1", went like this: can you make a vehicle that goes directly downwind, powered only by the wind, faster than the wind?
THE MOST FAMOUS BRAIN-TEASER is perhaps the Monty Hall problem (named after the original host of Let's Make a Deal, a popular American TV game-show): suppose you're on a game show and you're given the choice of three doors. Behind one is a car; behind the others, goats. You pick a door, say Number 1. The host, who knows what's behind all the doors, opens another, say Number 3, which he knows is hiding a goat. He then asks, "Do you want to pick door Number 2?" Is it to your advantage to switch your choice?
Yes. Switching your choice always raises your odds (1).
The brain-teaser doing the rounds when Cavallaro had his sail-prop epiphany is known as the Aeroplane on a Treadmill. It goes like this: an aeroplane taxis in one direction on a moving conveyor belt going the opposite direction at the same speed as the wheels. Can the plane take off?
Yes. The plane will take off normally. (2).
In Cavallaro's mind, his brain-teaser -- which soon became known on the internet as Directly Downwind Faster Than the Wind, or DDWFTTW for short -- was no exception. The answer, as he saw it, was yes here, too. You can go DDWFTTW -- if you build a
Blackbird. Considered as a brain-teaser, however, DDWFTTW has a serious flaw: almost no one gets it right. And the braintease has not truly succeeded until its victims acknowledge that, yes, they were wrong and understand the counter-intuitive truth. So far, no one had actually done that.
When Cavallaro made his big reveal on Runryder and six other websites, he didn't yet have Blackbird, or even a working model. Instead, he opted to show everybody how wrong they were with a theoretical vehicle and a planet shaped like a cylinder. At which point the ridiculing began in earnest. "It was a brain-teaser," Cavallaro says, shaking his head. "Of course I had the right answer!" As it happens, others had previously considered making a vehicle with a propeller sail.
Photos show, for example, that a man named Andrew Bauer created a
Blackbird-like craft in 1969. And the idea has resurfaced occasionally in sailing circles ever since. But it wasn't until Cavallaro's brain-teaser that the debate roared to life across the broader internet, with Cavallaro and his few supporters enduring a sustained onslaught by those who said the idea was utter nonsense.
Chief among the DDWFTTW debunkers was Make magazine writer (and former contributor to US wired) Charles Platt. Responding to the online debates, Platt wrote a story for Make in summer 2007 entitled "The Little Cart That Couldn't". It detailed his experience making a table-top model of a DDWFTTW-type car for less than $30. Platt shaped his own wooden propeller with a belt sander.
A rubber belt joined the prop-shaft to the wheels. When he was finished, he sprayed copious amounts of WD-40 on all the moving parts and turned on a powerful fan.
Nothing happened.
Well, almost nothing. After some tweaks, Platt got his cart to move downwind -- at about 5cm per second in a 9m-per-second tailwind. "Hopeless," he concluded in Make's August 2007 issue, in which he branded the DDWFTTW idea "delusionary".
After reading this, an incensed Cavallaro, with the help of Borton, decided to build a model cart of his own. Unlike Platt, Borton and Cavallaro opted to splurge. They used bearings to reduce friction on the moving parts and fabricated the rest from lightweight carbon fibre and aluminium. Their propeller was nylon, sourced from a website specialising in remote-control-aircraft parts. And instead of a belt-drive system, they opted for a long driveshaft to connect the wheels at the front end of the cart with the propeller, mounted at the back. When the prop cranked, the wheels spun, and vice versa. In total, they spent about $40.
Despite the superior construction, come test time even Borton had his doubts. "I was sceptical we could get it to work. Friction is usually what kills stuff like this," he says. But work it did, and rather nicely. They ran their baby Blackbird on a treadmill to simulate the crucial zero-wind moment, as well as in real-world wind on the street. In both cases, they boasted, the cart broke through zero wind and kept accelerating. They uploaded the videos to YouTube in November. "I was happy to stop right there," Cavallaro says. "We had proven it."
Most people who commented on the videos, however, disagreed.
Many criticised the treadmill test, insisting it was propelling the cart. Others faulted the real-world wind tests, saying gusts and turbulence meant the cart wasn't going directly downwind. Rhett Allain, a physicist at Southeastern Louisiana University and a blogger for ScienceBlogs, diagnosed what he called DDWFTTW's "free energy" problem. "You can't get something for nothing," he insisted.
The internet consensus remained that DDWFTTW was not possible. "It wouldn't have bothered me if five per cent of the people didn't accept our results," Borton says. "But it was more like 99 per cent."
Borton finally cracked. A few months later, after stewing over the Platt-inspired mockery he and Cavallaro were getting online, he marched into Cavallaro's office and said, "All right, screw it.
Let's build a big one." This time it wasn't going to be a model. "It needed to be huge," Borton says. This was because it had to be big enough to carry Cavallaro through the zero-wind barrier.
The pair contacted local universities and sailing clubs, looking for free labour and sponsorship. Their increasing notoriety meant Boing Boing covered the controversy, as did ScienceBlogs'
.dotphysics. Then a pair of Silicon Valley bigwigs decided they weren't going to let two of their own be derided online without a fight. GorillaPod inventor Joe Ben Bevirt donated $5,000 and Larry Page stumped up $10,000. Everyone wanted to see what Cavallaro and Borton could do. Construction took six months. Cavallaro cobbled together a frame from modified wooden joists, and Borton re-worked an odd assortment of mountain bike and go-cart parts into a drivetrain. The hardest part was shaping the sail-prop out of fibreglass cloth, foam, epoxy, two carbon-fibre windsurfing masts, and a pair of ski poles.
Blackbird's first run, they decided, would take place at the 2010 Dirt Cup. Despite the excitement, Borton was preparing for disappointment. "If it doesn't work," he told himself, "at least we're showing up with something that makes it look like we're serious."
Back in the Mojave, it seems Borton's nightmare has come true.
Cavallaro is sitting in the cockpit, suited up. And nothing is happening. Well, almost nothing. After ten excruciatingly long seconds, Blackbird begins to creak and trundle forward, its huge propeller sweeping a languorous arc, like the second hand of a clock.
Cavallaro's voice crackles over the radio: "Two miles per hour... three miles per hour... four..."
Thirty seconds into the speed trial and the handful of onlookers can walk faster than Blackbird is "sailing". "Six... seven... eight..." Cavallaro continues. A minute in and
Blackbird is moving at a jogger's pace. "Ten... 12 miles per hour." Cavallaro now has to yell to be heard over the
thwomp-thwomp of the propeller.
At 90 seconds, he has accelerated -- very slowly -- to 15mph.
That's sprinting speed, but more important, it's the velocity of the wind today. Blackbird's telltales -- little pieces of orange flag tied to the vehicle's various struts and antennas -- go limp. The craft has reached the zero-wind barrier.
For a moment, everyone holds their breath. Then
Blackbird accelerates. Hard. The telltales reverse direction, blowing back toward the rear of the cart.
Blackbird has pushed itself past the wind. On the far side of the mythical barrier, things get weird. Cavallaro feels wind blowing in his face -- yet the wind is also propelling him forward at... Cavallaro glances at the GPS-enabled speedometer mounted in the cockpit. The numbers tick up faster than he can report them. "Twenty, no, 22!" He's shouting into the transceiver: "30!" Running out of lake bed, Cavallaro hits the brakes.
The team backs up Blackbird for another run. It's on the third run that things go wrong. Blackbird once again powers past the zero-wind point and reaches its highest speed yet.
But the view from the chase car reveals a problem: the dust
Blackbird is raising is only coming off its right rear wheel. Blackbird is starting to tilt and the sail-prop is spinning so fast that it's inflicting roughly 637Nm of torque -- more than in a BMW 750i -- on a drivetrain made of bicycle parts.
Everything is shaking. Cavallaro feels his starboard wheel lift with every turn of the prop and realises he never fully considered the effects of torque at these higher-than-expected speeds. That's a problem, because if Blackbird flips, decapitation is a real possibility.
Crack!
Cavallaro, head still attached, leans on the brake. The chain has ripped the sprocket out of the drive train. "Too much horsepower," he laughs. Slowly he rolls to a stop from a top speed of 46mph.
The sprocket is ruined, but there is no doubt about what
Blackbird has achieved.
The Land Sailing Association refuses to verify the run -- largely as it has no official DDWFTTW race category. But after repairing Blackbird, Cavallaro and Borton return to log their feat in a newly created land-sailing category. Four months later, on July 2, 2010, the association clocks Blackbird's performance at 27.7mph in a 10mph wind. Not as quick as those first runs, but conclusively faster than the wind.
Cavallaro and Borton did the "impossible" with
Blackbird. Since their record-breaking run, the pair have spoken with Larry Page about other potential uses for the technology, including using traction kites on cargo ships. But perhaps most satisfyingly, they have converted the sceptics. The first was land-sailor Richard Jenkins, who, after watching the record-setting runs, felt compelled to blog about Blackbird. "It works," he wrote. Even Make admitted it got it wrong, inviting Cavallaro to write a piece entitled "The Little Cart That Did". And with that, the tide of internet opinion turned.
But Cavallaro and Borton have moved on -- they've found a new brain-teaser: can a vehicle moving directly upwind, powered only by the wind, go faster than the wind? The race is on to solve it.
Adam Fisher is a former senior editor at US Wired.
This article was originally published by WIRED UK
