When you post video of your new jet powered hoverboard, and
half the world thinks it has to be fake, you know you've got something
good. But Frank Zapata's Flyboard Air is no hoax, it's the real deal.
How does one know? All you gotta do is ask him.
These days, with millions of astute viewers scrutizing
every physical detail, the easiest way to make a convincing video that
gets all the physics of something like a jetpack flight right, is to
first make the jetpack. What's the hardest part of making a magic flying
carpet you might ask? "The power is there", says Frank, "and has been
for some time, the trick is controlling it." In other words, the
technical challenge is building a responsive interface that integrates
the control capabilities of the human nervous system and musculature
with that of your machine.
Where the response time of a man-sized electric fan propulsion system may be around a second, a turbine
of a similar power output would have a minimum lag of about three
seconds. That's one of the reasons, if not the main reason that turbine
powered cars never really took off. But the ear doesn't lie. If your
craft sounds more like a hummingbird than a fighter jet, you can expect
it to behave more like one in a strong headwind.
So how do you tame four microturbines putting out a total
160 kg of thrust? Controlling the power output of each turbine
separately, like a quadrotor does, would be a difficult prospect. Even
with thrust vectoring, which adds a whole extra layer of complexity,
there are still basic stability issues. The Flyboard Air design sports
two electric fans which control the yaw. Command the yaw, and bodyweight
can get you a good bit further. It is probably worth pointing out at
this point that if each turbine has its own electric starter motor,
already we are up to six auxiliary motors on one craft. In theory, one
could bleed off some bypass air from the turbines to power the control
fans, but again, the power available from bypass would depend on turbine
RPM.
With the current design, Frank says that he can take off and
land on three turbines. However, if one turbine experiences an
unplanned power loss in mid-flight, he notes that landing becomes
rather tricky. One way to add symmetry and simplify the control of the
machine would be to spin half of the turbines in the opposite direction.
For anyone who might casually underestimate the stability issues
involved in changing the direction of any rotating body with significant
moment of ineritia there is a handy fix:
Grab an angle grinder that has a decent sized grinding wheel on it
and turn it on. Now quickly rotate it upside down. The strong reaction
force you feel compelling your arm to move in a totally unexpected
direction can be quite surprising. If Frank switched to counter rotating
turbines he estimates that he could see at least an additional 5-6%
gain in performance.
Landings present unique challenges to many jetpack designs. In a
platform style machine there is a significant ground effect that would
blow hot exhaust gas back up to the inlets of the turbines. Despite
their power turbines are fickle when it comes to thermodynamics
conditions. Variables like inlet gas pressure, temperature, and humidity
all critically effect performance. That's probably why the video shows
landings taking place on metal grates that don't block the exhaust. For
other kinds of designs, like the quad-turbine wing pack of famed jetman
Yves Rossy, there simply is no landing—flight ends when the parachute is
deployed.
But there is no reason why a VTOL style landing could not be acheived
with a winged design, especially now that the power is there. Adding
aerodynamic flight surfaces to platform designs like the Flyboard Air is
also a possibility which remains to be explored. As described
elsewhere, turbojet packs seem to have the advantage over bulky turbofan or even reciprocating engine powered ducted fan designs like the Martin jetpack.
Although Glen Martin's design has been spun off into a chinese owned
corporate venture, Glen has more recently resigned himself from the
effort altogether. His fellow Aussies, who dramatically buzzed the
statue of Liberty last year with a turbine jetpack dubbed the JB-9 may
still be in the game, although we haven't heard much from them.
The Flyboard Air, on the other hand, has the backing of Frank's own successful business Zapata Racing,
based in Marseille, France. Having birthed an entire industry of
successful water jet powered boards and skies which fly above the
surface of the water, we can look forward to a new line of innovative
products from them.
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