One jetpack flies loops, four jets blasting you across the Grand Canyon and through the air at up to 300km/h.
The other mostly hovers. Its appearance, as Time magazine put it, is redolent of giant leaf blowers.
Guess which one is Kiwi-made.
The "Jetman", Yves Rossy, hurtled into world headlines last month clad in blindingly yellow tights, posing mid-air with the Grand Canyon as a backdrop. The Swiss flaunted his daredevilry on his first flight in the United States, strapped into a custom-built contraption of four jets and a small, black wing. He spent 30 years honing his piloting and skydiving skills, and in recent years has been jumping out of planes on a weekly basis to practise his craft.
Glenn Martin, an engineer from Canterbury, spent 20 years perfecting a ducted fan.
He came up with his first design in 1981, spent years tinkering and meticulously testing, and then ditched the fancy outfits, swapped his turbines for jets, and last week sent his invention 1.5km into the sky.
He has now received expressions of interest for 6000 machines - 3500 from governments, militaries, search and rescue organisations, police, fire services and emergency response teams around the world.
He doesn't want to be lumped together with the Jetman.
"I very much admire Yves, but his is not practical, because he's the only one that can do it. He's spent hundreds of thousands of dollars learning to fly this thing," Martin says. "It's very impressive - very stunt-y. But that's not our space. We're here to make a serious business."
Martin prefers to talk about practicalities: the applications, the mechanics, and "the secret". But this is difficult when you're talking about a jetpack which could literally add a new dimension to our lives, finally realising a dream passed down for generations.
Rossy, the Jetman, chases this dream. He has held it since childhood, slowly working his way closer from fighter jets to hang-gliders, skydiving, sky surfing and finally his jetpack.
"It's one of the oldest dreams of mankind: to fly like a bird. When you're looking at a bird on your window and up it goes, away, and a few seconds later lands on a branch on a tree, you think, 'I would like to have that liberty of movement and freedom'," Rossy says.
"I don't know from where it comes, but it comes naturally."
But people aren't made to fly, he says - "or we would have feathers" - so there is always a compromise. The jetpack he has assembled extends his free flights to 10 minutes, and for the first time lets him break his fall and fly upward.
It's the closest you can get, Rossy says. "In the air, it's total freedom. You move your arm and shoulder a little bit and you turn; you arch a little and you climb. You're in the element."
He says he will bring his acrobatics to Hamilton during the Rugby World Cup. But there is a lot more he wants to do: take off from a moving car, train a wingman to fly alongside him, and strap on a bigger engine.
Rossy and Martin have approached the jetpack from opposite ends - Rossy from the air, relying on speed attained by jumping off planes, and Martin from the ground.
The Martin Jetpack has in many ways bucked the trend. It is a business, a machine and a mode of transport - not a superhero.
"I want to take it out of the 'I'm a 5-year-old and I want a new toy' [narrative]. There's another story about a Kiwi company that has developed a unique technology ... and could become the Nokia of the South Pacific, for jetpacks rather than cellphones."
It isn't fantasy, Martin says. His list of potential applications for the Martin Jetpack includes border patrols, tours, airborne missile platforms, medic deliveries and recreation.
"There are serious uses, doing jobs helicopters currently do."
At $35 an hour, with petrol costing about another $90 per hour, the Martin Jetpack will run at a third of the operating cost of the most popular low-cost helicopter. And compared to helicopters currently used for urban surveillance and search and rescue work, the jetpack's hourly operating cost is projected to be a tenth. It could fly rescuers to where helicopters and planes cannot go, while unmanned jetpacks could be used for delivery, observation and extraction in situations
too dangerous for people.
At $100,000, it is also a third of the price of low-cost helicopters, while militaries will pay more for higher specifications and still get 500 jetpacks for the cost of one Blackhawk helicopter.
Martin also says the jetpack takes less training and is theoretically safer for pilots. Its final undercarriage is expected to protect pilots from falls up to 10m, or almost four storeys. And unlike helicopters, it can deploy parachutes, expected to protect pilots down to 10m. This would make it the first aircraft without an avoidance curve - a deadly range of altitudes in which aircrafts have no viable safety mechanisms.
Depending on how much money the company can raise, Martin says the first jetpack could be shipped in about 18 months. The latest test, last week, showed the jetpack can safely fly to high altitudes.
The jetpack was first depicted in 1928 on the cover of a science fiction novel. So why, after 83 years, is the dream suddenly so close to reality? In an age of computers and networks, the riddle of the jetpack remains unusually mechanical.
"The pioneers had to start from the ground," says Rossy.
The Jetman has had the luxury of surviving his failures.
He says he has had to throw away his wings in mid-flight about 20 times, but he could still parachute safely to the ground.
After years of experimenting, he has settled (for now) on a 2m wing with four model jet plane engines. They are powerful enough to let him climb in altitude, but he depends on flying fast for stability, meaning he cannot take off from a standstill. He says new lightweight materials were also crucial to getting a sufficient power-weight balance.
"I just had the right idea at the right time," Rossy says.
Where Rossy took his cue from a model jet plane, the Martin Jetpack is more of a helicopter - it doesn't have jets at all. It relies on two ducted fans rather than helicopter rotors, which improve both efficiency and safety.
Past attempts to create backpack helicopters used a tail rotor, or two rotors rotating in opposite directions. Both options add complexity and weight.
The documents for the Martin Jetpack's four patents don't give away too many secrets, but they are remarkable for the seeming simplicity of the design.
The machine eschews gearboxes by spinning both fans in the same direction. The latest addition to its propulsion system patents is a bit of a cup over the turbines, which draws air through the engine for cooling.
The jetpack uses a petrol-fuelled internal combustion engine (first built in 1876) and a lightweight carbon fibre-based composite shell (available in some form for decades). Far from relying on sci-fi quantum physics, it seems the perfect example of Kiwi ingenuity, built on good old mechanics and practical sense.
But the secret to the Martin Jetpack also lies elsewhere. "I've spent 20 years of my life developing a torque neutral, high-efficiency fan," Martin says.
Helicopter rotors are about 70 per cent efficient, and much of the remainder threatens to spin the machines out of control.
His torque neutral fan is 92 per cent efficient and relieves the need to counteract spin.
It is the key ingredient that allows the company to say it has developed the world's first practical jetpack, bringing the concept that has been entrenched in imaginations for so long within our sense of reality.
It also permits a mention of the United States Federal Aviation Administration's "Highways in the Sky" project.
"It is not inconceivable that at some stage in the future commuting via jetpack may become a reality," says the Martin Jetpack website.
Can you envision walking out the door in the morning and strapping in to your jetpack, as you would hop on your bicycle or in your car?
Rossy says that for 200,000 years of human life we've been grounded as we walked and ran, or later cycled, skated and drove, always depressed by gravity. Sure, we've had flying vehicles for a century - notably helicopters, which can suspend us in the third dimension.
"But when you dream of flying, you don't have a big machine around you. It's just you, free - or you're in your pyjamas if you're dreaming at night," Rossy says.
The Jetman is keen to try out the Martin Jetpack himself. "Individual air transportation for human beings, I think, is the future."
Arguably - depending on your views on evolution - we've been stranded for 150 million years ever since those damn birds took flight.
Designed by: Swiss adventurer Yves Rossy as a jetpack with wings
Max speed: 300km/h
Flight time: 10 minutes
Applications: Acrobatic stunts
Similar to: A model jet plane
Takeoff and landing: Jump out of an aeroplane and parachute to the ground
Propulsion: Four jet engines
Fuel capacity: 30 litres
Price: Not for sale
Disadvantages: Can't take off vertically
The Martin Jetpack
Designed by: Glenn Martin of New Zealand
Max speed: 100km/h
Flight time: 30 minutes
Applications: Defence, search and rescue, recreation
Similar to: A small helicopter
Takeoff and landing: Hover up off the ground and hover back down
Propulsion: Two fans
Fuel capacity: 20 litres
Price: US$100,000 ($122,521)
1993: Begins skysurfing and diving with wingsuits.
1999: Experiments with inflatable wings.
2003: Straps jet engines on to wings - but fails to fly.
2005: First (underpowered) flight with two engines on fixed wings.
Nov 2006: First successful flight - six minutes with four engines.
Nov 2010: Performs aerial loops on a newly-developed model.
May 2011: Flies across the Grand Canyon.
1981: Concept first developed.
1998: Theoretical design verified by an independent expert.
Late 2005: "Prototype 9" achieves "sustained controlled flight".
July 2008: Global launch at a United States airshow.
August 2009: First five-minute manned flight at low altitudes.
May 2010: First demonstration of the unmanned Martin "Skyhook".
May 2011: Unmanned jetpack flies 1.5km high.
Fantasies of untethered flight
In his daring ways, the Jetman embodies the ideal passed down through generations.
"Petrified with astonishment, Richard Seaton stared after the copper steam-bath upon which he had been electrolysing his solution of 'X', the unknown metal."
So begins The Skylark of Space, from 1928. It was with those humble words that the first imagining of the jetpack arrived on the scene. The heavy bath soon jumps "endwise" and is gone - "like a shot, with nothing to make it go". Seaton, for the first time in history, has untapped the infinite possibilities of intra-atomic energy, and his bath flies away on it.
The indomitable jetpack arose out of this attempt, by a food chemist, at novel writing - which in some ways proves just how unshakable the fantasy is. The mere suggestion has propelled the concept through a century, no matter how clumsily depicted. In fact, there aren't even any jetpacks in the text - they exist only on the cover illustration. The Skylark of Space features nuclear-powered spaceships, though another story in the magazine, Armageddon 2419 A.D., envisions an anti-gravity belt for hopping soldiers of the future. It later becomes the foundation for the first jetpack-wearing hero, Buck Rogers.
The jetpack's wonder has endured riding a timeless, comic-book fantasy - a man clutching a stick, donning a single-colour, skin-tight suit, and soaring with a rocket on his back.
It was channelled through James Bond in Thunderball, in The Rocketeer, and, more recently, by Buzz Lightyear in Toy Story. For 83 years, the jetpack has sunk deeper into the realms of sci-fi gimmick. As late as the 1990s, the best real humans could do was a 30-second flight.
The concept remained a mere dream until two men broke free. In 2005, a jet-strapped daredevil fell through the skies, his propulsion too weak to lift him - a fledgling attempt at free flight, in the same year a Kiwi inventor achieved his own tenuous lift-off from the other side of the globe.By Michael Dickison Email Michael