Take off with a conventional jetpack strapped to your back and you'll have about 60 seconds
of airtime. The short duration is due to the low
specific impulse
of rockets and jets. Alternatively, electrodynamic propulsion delivers a higher specific
impulse, but at significantly lower thrust. However, a new device called the Lifter,
may offer higher efficiencies than rockets or fans.
The Lifter (right) is a modern
recreation of De Seversky's ionocraft which has gained considerable popularity among
experimenters in recent years. The lifter's appeal can be traced to three factors:
they can be built from common materials like balsa wood and aluminum foil, results are
easily reproduced, and they represent the first heavier-than-air craft to fly without
moving parts. This last fact led some experimenters to believe they had demonstrated
anti-gravity. Vacuum tests by
NASA and the
Mythbusters, however, concluded that the only phenomenon at work is
ion wind. To back up this claim,
researchers measured the downward blast of air from the lifter with an
anemometer and
found that it accounted for 100% of the thrust needed to levitate the device.
Sorry folks, but no antigravity here.
So even though the lifter is not anti-gravity, it continues to fascinate
hobbyists and scientists alike. The lifter works by creating a high electric
field between the emitter wire and a collector (made from aluminum foil). When
powered by a source of high-voltage DC (typically 15-30kv), the emitter wire
produces an ion cloud which draws the collector upwards towards it by the force
of electrostatic attraction. When the ions collide with the collector, there is
a transfer of charge leaving a neutral downward flow of air.
The lifter has an average thrust loading of
.29g/watt.
In comparison, a helicopter has an efficiency of about 8.5g/watt or
14lbs/hp. But by using
a more effective ionization process, HoverTech believes the lifter's thrust can be
increased by as much as 30 times given the same amount of power. This would put the
lifter on par with helicopters and ducted fans, but without the noise.
Progress with lifters has been steady. For example, a craft built by Jean-Louis
Naudin of JLN Labs was able to
levitate a
mouse.
So are ion-propelled jetpacks next? We'll have a better idea after conducting
experiments, but a jetpack that doesn't require flame-resistant underwear could
certainly be useful.
More about HoverTech's Theories >
