Personal jetpacks and solar-powered ships
Kiwis demonstrate how to save and waste fuel
In a weekend of contradictions, New Zealanders have demonstrated technologies showing off the best and worst in fuel efficiency: a petrol powered personal jetpack joined the mile-high club, while a solar-powered ship made an unassisted trip from Monaco to Brisbane.
A crash test dummy has returned unharmed after riding a Martin Aircraft Company personal jetpack to a claimed 5,000 feet. At the end of the test flight for the New Zealand-built Jetsons device, a parachute brought the dummy back to the ground without damage.
Martin Aircraft, basking in the turnaround from ridicule and skepticism to more favourable coverage, now says it is seeking investors for further development of the device towards commercialization, which the company optimistically hopes could be within 18 months.
With more than NZ$12 million already spent bringing the device to last weekend’s unmanned flight, as much as NZ$8 million more is needed to bring it to market. It claims an ascent rate of 1,000 feet per minute and carrying capacity of around 120kg.
In case the idea of a petrol-powered personal jetpack with just half-an-hour’s flight time looks like an extravagant way to burn both oil and money (Martin expects the commercial units to cost around NZ$100,000), the company cites search-and-rescue, supply, and border observation applications for the unit.
The New Zealand Herald has an edited video of the ten-minute flight here.
Meanwhile, a Kiwi-designed solar-powered boat, Turanor Planetsolar, made landfall in Queensland eight months after setting out from Monaco. The boat is seeking to complete an east-to-west navigation without calling on any fuel source other than the sun.
Its 500 square metres-plus solar modules supply an engine consuming 20 kW on average. While the boat needs to take it easy in overcast weather, it claims a range of 200 km per day in favourable charging conditions.
Constructed by the Knierim Yacht Club in German city Kiel, the 31-metre vessel is following what’s called the “English conditions” for a circumnavigation, which include two crossings of the equator, and matching its southerly trip to the northern latitude of the starting point.
So far, the Turanor Planetsolar claims to have made the fastest Atlantic crossing by a solar-powered vessel, and the longest trip made under solar power alone.
From Australia, its itinerary includes two China stopovers, Singapore, India, the Emirates, returning to Monaco via the Suez Canal. ®
yes that's right
It is "just" a small personal helicopter, able to operate from a couple of square meters and extremely close to obstacles with no risk of rotor strike. It's the smallest practical man-carrying helicopter the world has seen (let's exclude toy quadrocopters, which this has a lot in common with, but which can't carry people).
Some are complaining about the 30 minute endurance. This turns out to be a legal limit for the class of ultralight aircraft it is being operated as. If you are a customer able to operate it under other rules then they could fit a bigger tank for you.
Of course you'd never get even close to that using a rocket or even a jet turbine. The old peroxide-powered Bell Rocket Belt (it's not a belt, it's a pack!!) has an endurance of 30 seconds.
A fundamental property of a rocket engine is the "Isp" (specific impulse). This has units of "seconds" and can be interpreted as the amount of time that the rocket could hover in 1 gravity, ignoring the weight of the engine itself, the tanks, and anything else on board.
Hydrogen peroxide monopropellant rockets have a theoretical maximum Isp of 160 seconds. The improved RB2000 Rocket Belt produces 145 kgf (enough to lift it's own 60 kg weight plus a human weighing less than 85 kg) for 30 seconds from 32 kg (23 liters) of fuel, implying an Isp of about 135 seconds, so there's not much room for improvement. The 1960's version had an Isp of about 100.
The very best chemical rockets give an Isp of about 450, so you're unlikely to ever get a rocket belt with more than about three times the endurance (90 seconds), and it's certainly impossible to get more than 7.5 minutes even if it's carrying its own fuel and nothing else.
A turbojet can achieve an effective Isp of 2000 - 3000, which is much better, but still would give an endurance of no more than about 10 minutes.
It seems to me Martin is using the right technology for a practical machine, regardless of whether it fit's someone's Buck Rogers definition of what a "Jetpack" should be.
 542 seconds was achieved in a rocket engine using liquid lithium, fluorine, and hydrogen but this is .. er .. expensive, dangerous, highly toxic, and just generally impractical.
Search and rescue is an application...
or a requirement?
"Yes, I've located the shipwreck, the crew are safe. Can you pick me up first, this bloody thing doesn't float!"
It took that boat 8 MONTHS
To get from Monaco to Australia? They're doing it wrong. The old SAILING ships of 100+ years ago did that trip in a couple of months. Obviously the wind power we'd been using for hundred of years is somewhat superior to solar, not to mention a damn sight cheaper. Newer is not always better!