The DIY Flier
In July, at the Experimental Aircraft Association's annual Airventure show in Oshkosh, Wisconsin, the Martin Jetpack hovered three feet off the ground for 46 seconds—13 seconds longer than any other pack has flown. It's five feet tall, five and a half feet wide, and weighs 250 pounds. A custom-built four-cylinder engine powers fans that sit inside two garbage-can-size ducts. In design and appearance, it's less James Bond's rocket-belt and more personal airliner. By next year, Martin says, pilots will be soaring several hundred feet in the air, flying for 30 minutes at a time. The machine, he says, will be a Jet Ski for the skies.
Martin recognizes that this kind of talk may sound fanciful, but in his mind, and according to his tests, he's being perfectly realistic. "If I'd got to the point where I'd sat down and my equations told me it wasn't possible, I would've happily walked away. But every time I came across a technical challenge, I sat down and figured out a solution. I haven't managed to get to the point where I've convinced myself that I couldn't do it."
STEP ONE: DITCH THE JET
When Martin started the project in 1981, he was majoring in biochemistry and physiology at the University of Otago. Why not aerodynamics? He decided laboratory science would better teach him how to invent: to be careful and methodical, to study and plan before doing any tests. That's why, instead of reaching for a wrench, he began the jetpack enterprise by reading everything he could on previous efforts. The most famous, the Bell Rocket Belt, built for the U.S. Army in the 1960s, could lift a man into the air, but its hydrogen-peroxide fuel supply ran out in roughly 20 seconds. Martin didn't see a way to improve this approach dramatically (nor has anyone else—today's best rocket-belts have flown for only 33 seconds). What he wanted was time in the sky. He wanted to soar, not hop.
So he looked at the turbofans that run modern airliners, which get most of their thrust from the fan blades spinning inside the ducts below each wing, and some from the turbojets that power those blades. Increase the turbojet's workload, and you get a faster aircraft that guzzles fuel. Boost the fan's share, and you get something slower but far more efficient. One year into the project, while studying a diagram of an airliner's engine in his flat, Martin had an epiphany. If the fans were so efficient, why not turn the entire job over to them and ditch the turbo? Why not take the jet out of the jetpack?
In one sense, this would make the project easier: Any engine could turn the fan. But getting enough thrust out of those fans would be a far grander challenge. If he was going to design a ducted fan that was exponentially more efficient than any before it, he'd need to master the theory first. Martin spent his spare time during the rest of his college years probing aerodynamic equations, learning how to apply them to blades and ducts. In 1984 he dropped out of a biochemistry graduate program, figuring he'd learned what he could from science. But he still needed a job, so he went to work as a pharmaceutical sales rep and spent nights and weekends on "the project."
By 1987, he had saved enough money to devote himself to it full-time. None of his friends understood why he quit his lucrative job; he had told almost no one about the pack. "In New Zealand, we have something called the tall-poppy syndrome," Martin says. "If you stand out in the crowd, you get slammed down pretty quick. I knew that if I told people what I was doing, some men in a white van with nice jackets that wrap around your back would come along and take me away."
Locked inside his shop, Martin found that the mechanical work came easily. He started with kitchen ventilation fans, cobbling together small test rigs, even trying one out on a hang glider. The tests finally gave him a chance to apply all that theoretical homework. For each new rig, he could compare the thrust numbers the equations predicted against actual results and keep tweaking the fans. "Each prototype got a little bit more powerful, a little more reliable, a little more efficient," he says. But they were still too heavy. They wasted too much horsepower lifting themselves, never mind a pilot. Half a decade in, he still hadn't left the ground.
By the late 1980s, Martin was obsessed with the weight problem. He was convinced that his ducted design could fly if only it were light enough. Looking for parts to ditch wholesale, it occurred to him: Lose the three 25-pound gearboxes.
These had been critical components; they allowed the fans to spin in opposite directions. If the fans both spun in the same direction, the torque generated would cause the whole machine to turn. But, Martin realized, there was another way to keep it stable. Designed correctly, the struts that hold the fan in place inside the duct could also straighten the air rushing out. This way, instead of turbulent, swirling air, the ducts would kick out a coherent vertical jet. That could produce just enough counter-torque to cancel out the force of the spinning blades.
This "aha" moment spawned a serious to-do list. Martin needed to refine more equations to design the perfect struts, build machines that could accurately measure the thrust and airflow emerging from the ducts—oh, and there was still that super-efficient, lightweight engine to make. The project timeline suddenly stretched beyond a decade.
When he thought about giving up, his wife, Vanessa, would talk him out of it. (Mounting bills forced him to return to work in the early 1990s, but she made him drop out again a few years later.) He even broke the silence a little, looping in select experts. Engineers from the nearby University of Canterbury would stop by, pledge secrecy, offer advice.
By 2003, Martin had rebuilt the engine, using carbon fiber where he could to save another five pounds. Prototype 9 made short hops across the backyard. That was enough to secure several hundred thousand dollars in venture capital, move out of his shed, and hire skilled help. He filed patents, word of the project started to leak, and his investors got itchy to see if there really was a market for the machine.
Martin was ready to tell people, too. Late last year, he contacted the EAA, told them what he'd built—how it could hover, turn, complete figure-8s—and asked whether they thought he should wait until 2009 to unveil it. No, they said. You're ready now.
THE PACK'S OUT OF THE BAG
Today, the heart of the machine is a 130-pound, two-liter, composite-based engine. "There's very little metal left," says Milton Bloomfield, the technical director of New Zealand–based company Dynamic Composites. Bloomfield has been working with Martin since 2004, trying to make every component lighter and optimized for its task. The machine's main beam, for example, is its spine, so it needs to be strong and perfectly straight—even a slight bend could throw off the delicate balance of the fans' rotation. Standard carbon fiber had too much give, so Bloomfield chose a rarely used, extremely stiff form instead. Stiffness comes at the expense of strength, but Bloomfield's math showed that the spine would hold up. He also added a type of fiber typically used in body armor to the ducts, to ensure that no debris could damage them in flight.
But these details weren't what drew the crowd of hundreds to the Oshkosh debut flight on July 29. They came to see someone fly in a jetpack. After a quick talk, Martin pulled white sheets off two prototypes. His 16-year-old son, Harrison, strapped into one and cranked the throttle, revving up what sounded like the world's largest leaf blower. With his dad and an engineer loosely holding on for extra caution, he calmly hovered three feet above the pavement for 46 seconds.
Most of the crowd at Oshkosh were giddy at the maiden flight. But the pack's unique design has also drawn skepticism. Juan Manuel Lozano, president of TAM, one of a handful of companies developing rocket-fuel jetpacks [see "Ready for Takeoff?" March 2006], says Martin's choice of a two-stroke engine is unsafe, since those are known to be unreliable. But Martin is fully aware of those limitations. He spent most of the 1990s designing solutions to them. Among other things, his engine puts out just 200 horsepower, small given its capacity. "You could say, OK, that's a very poorly designed engine," Martin says. "No. It's a very reliably designed engine. It's a low-stressed engine."
More widely noted is that the pack has flown only a few feet off the ground. But Martin refuses to go higher until he's done 100 hours of flight-testing at under six feet. "The Wright brothers in all their early flights never got above about 10, 15 feet," says NASA senior research scientist Thomas Benson. "That's only being safe." Martin knows the only thing that could derail the project now is a catastrophic accident. After 27 years, why rush?
And anyway, he says, the real proof is just a year away: pilots flying at 500 feet. Since the debut, Martin has had a number of unexpected inquiries (an energy-drink company, for instance, wants to buy a fleet of packs for promotions), but individual buyers will be the focus for now. These first customers will come to New Zealand, take a two-week training course and, for $100,000, return home with their very own jetpacks.
But what excites Martin most is simply knowing that the project is nearly complete. "It wasn't done for money and it wasn't done for ego and it wasn't done for fame," he says. "I just wanted to build a jetpack."
Contributing editor Gregory Mone wrote about the Terrafugia flying car in October.
LWS. This is an exciting project! This will fly given the research and dedication of the inventor!
Wasn't one of these already built and TOTALLY proven by somebody else? Or is this guy the original. I even remember watching the video here on popsci where the guy was tethered to a pole in his back yard for safety and took off and maneuvered.
Never mind my first comment. But this guy has already been featured. Here's the video on the popsci website.