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.
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 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.)
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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.
