h a l f b a k e r yNo, not that kind of baked.
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One of the problems with making a flying car capable of
VTOL and hovering is that air is pretty low density.
Therefore, in order to produce a reasonable amount of
lift,
you have to have very powerful fans throwing the air
downward. Truly immense volumes of air must be
moved
in this way.
This
need to move large volumes of air causes problems.
For example, a hovercar will inevitably be very noisy. It
will also tend to blow away anything underneath it. It's
all
not terribly good.
Fortunately, the clever people at MaxCo. have a solution.
The MaxCo Bouncing Ball Flying Car (marketing are
working
on the name) has, at each of its four corners, a highly-
modified tennis-ball-firing machine. Each such machine
fires 3-inch silicone-rubber coated steel balls downward,
at a rate of about 20-40 per second, at moderately high
velocities.
These balls, on being fired, act as a dense and efficient
reaction mass, providing lift.
But wait! There's more! You are probably wondering
how
long the MaxCo Bouncing Ball Flying Car can remain
aloft,
before running out of balls. Fear not. The downward
trajectory of each ball is chosen so that its rebound
(hence
the silicone rubber coating) brings it back up into a
catcher
on the underside of the car, whence it is directed back
to
one of the four ball-throwers for reuse.
In early versions, the bounciness of the balls was
adjusted
so that they would rebound with just enough speed to
reach the catcher. However, inadvertent use of some
over-
bouncy balls revealed an unexpected bonus: the balls
deliver extra lift as they slam upward into the catcher.
It turns out the maximum lift is provided if the balls are
as
perfectly elastic as possible, providing both reaction
mass
as they are fired downward, and the greatest possible
force when they rebound to strike the catchers on the
underside of the car.
Noise-wise, the MaxCo Bouncing Ball Flying Car has
proved
considerably quieter than comparable vehicles using fans
or rotors. The only drawbacks are the need for a
reliably
flat road surface, and the greater risk to anyone who is
overflown by one.
Triple-Barreled, Pn...eaction Hovermobile
[xaviergisz, Jul 17 2015]
[link]
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// need for a reliably flat road surface // loses any kudos
that might have come from "flying". |
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// risk to anyone who is overflown by one // no foul.
Anyone loitering in the road has only themselves to blame if
they happen to be mown down by a vehicle of any sort. |
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Horizontal motion is possible by slightly vectoring the
ball-throwers; the throat of the catcher is wide
enough to make this possible. |
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//// need for a reliably flat road surface // loses any
kudos// |
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In practice, we find that many irregular surfaces
become flat after being overflown a few times. |
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For // other than vertical motion // there would need to
be additional catchers outside the notional 'footprint' of
the vehicle, such that balls may be directed at variance
from from purely vertical to provide lateral impetus. The
external catchers would need to be mounted on
extensible booms to adjust to compensate for varying
lateral speeds. |
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If enough such vehicles were deployed, and were
equipped with appropriate on-board communications and
suitable protocols, a sharing system may be possible with
vehicles emitting and collecting balls. Computational
power required to co-ordinate this scheme is unlikely to
be available for some time. |
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// many irregular surfaces become flat after being
overflown a few times // |
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How does that happen? If the surface is irregular the balls
won't return in the required trajectory and will be lost,
resulting in catastrophic failure due to lack of balls. Any
driver (pilot?) would surely avoid any surface which is not
already sufficiently flat. |
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Perhaps there's scope for tethering the balls on elastic
just in case they're deflected and fail to return to the
catcher. This brings further complications though, since
the firing mechanism must then support the passage of
tethered balls. |
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// catastrophic failure due to lack of balls// |
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Being under a catastrophic failure is known to cause
flattening. |
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//tethering the balls on elastic// |
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We did briefly do a trial with loops of very dense
rope. Briefly. |
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(+) The balls can be made to rebound vertically plumb from slightly irregular surfaces if you spin them just right. There would be a maximum kilter you wouldn't be able to fly above but there wouldn't be too many roads, other than in San Francisco, you couldn't hover above. |
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//But this only lasts for time t e.g. 0.02 of a
second.// |
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Ah, but you see, there's the problem. I could e.g. a
different time t and get a very different answer. |
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For horizontal motion one could use boomerangs, generating thrust by hurling the reaction mass of boomerangs rearward, and extra thrust via the impact of returning boomerangs. Perhaps one large boomerang would be best to avoid fouling the outgoing with the incoming. |
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Maybe boomerang propulsion should be its own
separate idea. I was going to say that a standard
propeller would be much better than a boomerang,
but assuming you could get it to work (the
halfbaked part), theoretically you could get some
of the benefits of a very large propeller without
the difficulties of mounting a huge propeller. |
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I think you would need to figure out how to have
many in the air at once though to get any benefit. |
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Those benefits might be tempered by the amount
of mass required in the boomerangs being larger
than the mass of the equivalent large propeller |
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I suspect that a mechanical boomerang thrower could throw in a standardized way such that the path taken of each boomerang is very like the one before and after. One could keep a stream of boomerangs in the air this way. |
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Also boomerangs could be thrown from multiple sites on board as long as the paths do not cross. |
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Don't space-hoppers give kids wonderful dreams to pursue. |
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You could cross the paths as long as the releases were suitably staggered. |
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"There's a ball-thrower to see you, Doctor, who's been slightly vectored, and a catcher with something in his throat. Oh, and this gentleman here has suffered some kind of catastrophic failure that he's too distressed to explain." |
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