Kind: captions
Language: en
this propeller craft was built to settle
a physics debate
because what its creators claim it can
do
is so counter-intuitive that it seems to
violate the law of conservation of
energy
so i've come here to drive it myself and
see if it really works
and is it safe it feels makeshift i'm
not gonna lie i need some wind
give me a gust it's a little unbalanced
isn't it
this video was sponsored by kiwico more
about them at the end of the show
i've come to el mirage a dry lake bed a
couple hours from los
angeles to race a one-of-a-kind
propeller craft
it's called blackbird and i'm here with
its inventor
rick and the current owner neil
it all started with a brain teaser can
any
wind powered vehicle go directly
downwind
faster than the wind itself
if you've got a sailboat and you're
sailing it straight down wind yeah
as soon as that sailboat is going the
same speed as the wind
then there is no more wind that is
correct you can't push the sailboat
so sailboats can't just go downwind
faster than the wind
not straight downwind not straight not
direct downwind
imagine a boat floating in the water as
the wind picks up it pushes the sail
accelerating the boat the boat gets
faster and faster
until its speed exactly matches the wind
but at this point the wind can't push
the sail anymore
i mean if you imagine it from the frame
of reference of the boat there's no
longer
any apparent wind there's no air moving
over the boat because the air and the
boat are moving together
at the same speed so a sailboat going
directly downwind
can only match the speed of the wind
never exceed it even if there's no drag
but the claim is blackbird can do it
it can go straight downwind faster than
the air that is pushing it
well i the weather forecast is still
holding okay good
we can feel it's at like one now yeah
but el mirage has a reputation of like
when it feels
yeah it happens it happens i think we
started somewhere in the middle
all right well let's let's move over
we're moving to a spot that will give us
a long straight path
downwind with no obstacles all we need
now
is for the wind to pick up and maintain
its direction
but we've been out here in the hot
desert
for hours and there is still no wind
[Music]
this is uh gene he runs the youtube
channel potato jet
all the awesome drone shots in this
video are his
so if you like cameras and gear and
amazing drone shots go check out his
channel
this is this is about a typical day how
it goes
derek i think the wind has just chosen
its direction i want to move us to the
other side
we'll set up we'll we'll point downwind
over in this direction
we'll put you in let's make it happen
yes all right i want to do it
so maybe i need to keep going should i
get something behind me well
i'm very reclined yeah let me see what i
can find it's slightly terrifying to uh
not be able to push the brake all the
way so you're kind of
right at the limit of size yeah you
wouldn't want to be any smaller
uh so steering is i push to go left
push to go left pull to go right
while steering with my right hand i have
to control the pitch of the propeller
blades with my left hand
and and then in terms of like when i'm
getting to the end or something or i
really want to slow down
the right move is pull back
you're saying the right move is pushed
forward i'm glad that the two
experts here are disagreeing on what to
do in the emergency case of like i just
want to stop the vehicle
feel which is slowing you down and do
that
it's just terrifying not to have a
blanket rule well
uh this is intense i have never tried to
go
faster than the wind downwind in a
vehicle where i'm just supported by this
mesh hammock under my butt it feels like
being in a
rolling coffin it's just been
shoddily put together but i'm excited to
try it and i'm excited to survive
you can look at that orange string right
there it's showing that
the wind is picking up behind me this is
what i need
on the front of blackbird there's a
telltale a little piece of string
which shows which way the wind is
blowing to drive straight downwind
i just need to follow the telltale so it
should be pointing straight out
in front now if i get up to wind speed
the telltale should drop straight down
because effectively i'll be in still air
i'll be
moving exactly the same speed as the
wind
[Music]
all right good luck derek thank you i
hope i survived this
come on come on i need some wind
give me a gust now if i can actually go
faster than the wind
the telltale should flip around and
point straight at me
indicating that i have an apparent
headwind even though the true wind
standing on the ground is coming from
behind
we're going straight downwind what have
i got six miles an hour
the string is just dangling you see the
string dangling there
oh i just need a gust right here i just
need a bit of wind that's all i need
i will uh hop on the brakes here man we
were so close
i mean i saw that string dangling down
i was like okay this is it let's keep
going and then unfortunate at one point
it was dangling and i asked what speed
are we
and he said we're five or six miles an
hour and i'm like damn because he's
almost exactly wind speed yeah
five or six miles an hour is just not
enough to get you right past there i
needed just
like that extra few miles an hour kind
of the absolute minimum
10 is pretty healthy yeah yeah well i
can't wait
now you might be wondering how it's even
theoretically possible for this vehicle
to go
faster than the wind well sailboats can
do it
as long as they're traveling at some
angle to the wind
in this case the sail acts like a wing
air flows faster
over the outer curved surface than the
inner side which generates
lift a force perpendicular to the
apparent wind
a component of this lift force is in the
forward direction
so maximum speed is reached when this
forward force is equal to
all the drag forces on the boat pushing
it backwards
some boats can go three or four times
wind speed
somebody had asked the question if a
sailboat is tacking downwind
can it do a vmg velocity may good
directly downward can it beat if i if i
release a balloon in the air
can the showboat tack its way down and
beat the balloon to its destination and
i didn't know the answer
it turns out that sailing at some angle
to the wind
a sailboat can go enough faster that its
resulting velocity directly downwind
is faster than the wind itself in other
words
it can beat a balloon that is just
drifting on the wind
i love brain teasers i just love doing
brain tumors so i thought this is
really close to a good brain teaser but
it's right now it's just a question
that if we make it go straight downwind
then people are definitely going to say
no
if the earth were a cylinder instead of
a sphere
i could have a sailboat on a continuous
downwind tack
the wind's going along the earth this
cylindrical earth
and the sailboat is just spiraling its
way down
if i put two sailboats one on either
side they can both do this
[Applause]
well that's a prop
effectively their sails make a propeller
a propeller that is traveling down this
earth faster than the wind itself
it was i posted on two forms that i was
on right and i thought people are
initially gonna go no never work and
then i say okay here's how it works and
they go oh
you got us boy i couldn't have possibly
been more wrong
this is obviously stupid wind power
isn't some kind of magic we all want to
believe in perpetual motion but
i just don't see the logic of this
argument as yet
okay this is clearly fake anyone with a
clue should see the problem here
once you reach wind speed what powers it
past that
i am not a stupid person but i cannot
understand
ultimately we said okay if we build a
little model of one
and put it on a treadmill that just puts
it to bed right
and it worked really well now you you're
holding it back with this fork
mississippi yeah i'm keeping it from
coming forward otherwise it'll climb
right up the top of the treadmill
but people on the internet just wouldn't
believe him they thought it was fake
and even physics professors were arguing
that the treadmill wasn't a good analog
of the real world
i'm like literally day one physics is
inertial frames right it doesn't matter
if you're moving or the air is moving
others were saying there's magnets
there's wires you go there's fans out of
you so then we do one showing
you know the curtains aren't moving and
stuff and finally he says
we got to build the real thing
okay we are cooking i see we're going
seven seven miles an hour eight miles an
hour
come on you got it come on
uh oh
[Music]
i'm very sad about this propeller so i'm
guessing this means the chains come off
how did it feel it was a lot of fun i i
could feel us picking up speed i could
see it spinning i could
see that we got up to like eight miles
an hour and nine miles an hour and i was
like oh we're just gonna do it you know
and then all of a sudden i still felt
like i was going but i noticed that the
prop wasn't spinning
and i thought oh that's a terrible sign
so uh
yeah then we have to stop and and fix
the fix the chain
when in doubt use it yeah you do that
so here's the thing about this vehicle
it's not what it looks like
what you imagine i bet is that when the
wind blows
on that propeller it spins the way the
wind is pushing it and that drives the
wheels
but that's actually not how this works
the way it works is the wind pushes it
from behind
and just because it's a bluff body it's
just
an object sitting out in the desert it
starts to roll forwards a little bit
now that causes the wheels to turn
and they are geared to the propeller in
such a way that they turn it
opposite the direction the wind is
pushing it so
rather than this propeller operating
like a windmill
it spins like a fan pushing air
backwards
and that's what drives the craft
forwards
it's like one of those crazy things you
never think you're gonna do be out in a
dry lake bed with some crazy propeller
vehicle that some physics professors
believe break the laws of science
yeah that's cool
[Music]
really ready if you think so i'm ready
all right we're hoping we can catch one
of these puffs
the wind is strong and the prop is
turning
but something is definitely wrong just
look at that propeller it's a little
unbalanced isn't it
so what's the game plan if you feel
excessive vibration i think we gotta
pull the trigger on it
yeah like and i want to go right out and
say i don't think i would drive
in this window i will
if you would like me to i mean i will
i will given the opportunity but um more
than i i didn't come here to drive
so you drive it if you want to do it
i mean if you were gonna decide about
getting in like sarah is there a point
where you say
that's too much um for today and the way
things are 15-ish
okay so 15-inch is what we were
measuring like earlier
what are you seeing now that feels like
15 to me
yeah i've been out there for several
hours
and first it was just waiting to go and
now it's like it's broken
and now it's like we can go but it might
shake itself apart
and the wind is on the high end this is
sketchy for sure
oh god
we get that on camera did you oh
no
[Music]
what's happening is they're getting
pretty uncomfortable with
what they saw in terms of the shake the
wobble and they're worried that it's
going to like
break in half the whole structural
component and the whole propeller is
going to come down on whoever's driving
so they're a little bit reticent to let
me keep driving
so the guy who basically built it he's
gonna risk
himself in the driver's seat and then if
it's not shaking itself apart then maybe
i get another shot after
so that's uh that's the word right now
in rick's run it didn't seem to shake
very much so
they think it's safe for me to jump in
you don't think this wind is much more
than i do i really do
but it means that you will have nearly a
guaranteed success
but you just got to manage your limit
like how much faster than the wind do
you think you need to go
yeah you're doing it man it feels like
just the stakes keep getting higher
like they didn't want me to run it
before because it was too windy
but like now it's windier but they're
comfortable with me
piloting it so
i i don't know what to say this is
frightening but also
i came here for this i want to do it put
me in coach
if this thing doesn't fall apart maybe
i'll be able
to go faster than the wind this time
i'm getting in that vehicle and i'm
headed that way
as fast as i can
the sun is setting and we're going for
it
this is the last chance for me to go
faster than the wind
downwind
this is the one guys
back a little left so that i can make a
straight shot down at the windsock
looks like we're coming up on wind speed
here blackbird is getting faster
and faster i'm just willing it to
go past the wind speed come on
come on come on get up
speed up speed up with me
come on yeah
[Music]
and there you have it the telltale is
pointing straight back
at me showing an apparent headwind while
the windsock
shows the true wind is in the opposite
direction
i'm going faster than the wind
slow down derek
a little attack
oh that was god damn that got my heart
rate up
i thought it was derek did that look
scary because it didn't feel too bad
so how does it actually work well
i worked on this video for weeks without
really understanding
how it works so i want to share with you
the way that i understand it
so if this vehicle is moving at the
speed of the wind
well then there's no relative air motion
over the cart so how can it keep
accelerating
if this were like a windmill that
required air to flow over it in order to
turn
well then it wouldn't accelerate anymore
but that's not how this operates
this propeller operates as a fan which
means if you imagine this still
air the propeller can come down and hit
some of these air molecules pushing them
backwards and therefore get
thrust it's like having a fan on your
cart so of course even in still air
having a fan on the cart will blow you
forwards
but that brings up this idea of it feels
like we're getting
energy from nowhere where's the energy
to power the fan coming from
if it's coming from the wheels why
doesn't that slow us down
more than the fan manages to blow us
back
and the answer to that is that you're
moving at a different speed over the
ground
then you're moving through the air
because you have that tailwind
so the way i like to imagine it is like
this there's
air everywhere going 10 kilometers per
hour
down that way now even if we're going 10
kilometers per hour
we can still push air backwards and so
if you were to look
at a profile of the air in a stationary
reference point you would see that the
wind
behind the propeller would be moving
more slowly
downwind than all the other wind that's
because
this propeller has taken some of the
energy out of that wind
and converted it into the kinetic energy
of this cart
so behind the propeller there would be
say eight kilometer per hour
wind and everywhere else there would be
10 kilometer per hour wind
so the energy from this wind behind the
propeller
has gone into the cart into accelerating
it forwards
so it is moving forwards faster than the
wind
even when this is moving forward faster
than wind speed the propeller can still
push the air
backwards slowing down that tailwind
and taking some of that winds energy
converting it into the kinetic energy
of this vehicle now the people who made
blackbird managed to get a record they
got up to
2.8 times the wind speed
so it is obvious to me from all of the
demonstrations and from
riding in the vehicle myself that this
is physically possible
there is a way to drive a vehicle that
goes downwind
faster than the wind but i know it is so
counterintuitive
that i expect a lot of pushback in the
comments my only request is
please be civil
war
hey this video is sponsored by kiwico a
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