Bricks
Teslas
Splitters
Wings
- Spoiler alert, we're talking about aerodynamics
(electronic music)
There are sleek cars
and boxy cars
There's weird things sticking out of race cars
and rice cars
and they're all trying to take advantage of aerodynamics
Aerodynamics is the study
of how gases interact with moving objects.
The two basic aerodynamics forces are drag
and lift
Drag is the force air exerts against a car as it moves,
while lift is the perpendicular force
exerted by the air on the car.
Lift includes both positive lift
that's the flying kind
and negative lift
and that's down force.
Air moves in a very similar way to liquid,
you just can't see it.
If you think about it, every time you drive,
you're practically swimming through an endless air ocean
Air obviously isn't as dense
as liquid, but it's still touching stuff.
So there's friction
when something moves through it and that makes drag
probably the most important aerodynamic factor
that we have to consider.
And drag is basically a things velocity squared
multiplied by it's drag coefficient and it's frontal area.
Drag coefficient depends on a lot of factors
some of which are an objects overall shape, surface roughness
and speed
A brick has an awful drag coefficient of one,
while a teardrop, the most aerodynamic shape there is,
has a drag coefficient of about .05.
When you're loafing around at low speed,
the air's not much to be worried about
so there's not much drag
and cars have plenty of power to push the air out of the way
even if it's shaped like a brick.
In the very early days of automobiles,
manufacturers really didn't have to car about shape
because cruising speeds barely got up to 45,
but I don't know, maybe if Model T was more aerodynamic,
it could've gone 50.
- 50.
- The earliest land speed record racers
quickly realized streamlining their cars
are gonna make it way better for going fast.
Because of that velocity squared part of the equation,
drag increases significantly the faster you go.
Some might call it exponentially.
At 70 miles an hour there's four times more drag
than there is at 35 miles an hour.
That means it takes a lot more work
to push something through the air.
Looking at a fast-moving, non-aerodynamic brick,
air's gonna pile up in front of it
and create an area of high pressure there.
At the back a low pressure air pocket forms
and creates a pressure differential.
So not only is there frictional drag simply from the motion,
now there's another force
trying to drag the brick backwards.
All this makes drag a really big factor
in determining fuel efficiencies and top speeds.
A reduction in drag coefficient
from point three to point .25
would increase fuel economy by about a mile a gallon.
By the same reasoning,
an electric car can go further on a charge
the more aerodynamic it is.
That's why they look so weird.
Now that we're regularly cruising at speeds
over 70 miles an hour,
we got a new focus on fuel efficiency
or battery range
Production car designers
try to get the lowest drag coefficients possible.
Most modern cars have a drag coefficient
somewhere between point .25 and point .35.
With SUVs
and trucks
somewhere around point three and point four.
The electric Tesla Model X
is a super sleek crossover with one of the
lowest drag coefficients of any production car, .24.
But if two different cars are going the same speed,
there can still be more overall drag
on the really aerodynamic bigger car
than on a less aerodynamic smaller car
You can calculate how draggy a particular thing is
by multiplying it's drag coefficient by it's frontal area,
which is called drag area
Let's compare the slippery Model X to the Nissan 350z
which has a mediocre CD of .31
with a frontal area of 20.88 square feet,
it's got a drag area of six .47.
The Model X has a larger frontal area, 27.88 square feet
and with it's low .24 drag coefficient,
it has a bigger drag area of 6.69,
and therefore it's got a bit more drag.
More drag.
So maybe now you're thinking, 'Hey, F1 cars
'are really fast, I bet they're' crazy aerodynamic
Well, you'd be wrong
They got a drag coefficient of about point seven,
that's more than a minivan, what?
F1 cars and most race cars
are designed mostly with lift in mind.
Traction and grip are just as important to fast lap times
as speed and power.
Turns out keeping a car from flying off of the ground
helps improve grip.
(revving)
(audience cheering)
And pressing down on the tires with negative lift; downforce
improves grip even more.
Down force also creates a ton of drag
but the trade-off is worth it
because without all that down force,
F1 cars would still be spinning their tires
at 100 miles an hour
and with extra force pressing towards the tires,
they get increased lateral grip
for better cornering speed
A heavy car could achieve the same result
but it wouldn't be able to accelerate
or corner
as well as the light ones
So, what's creating that lift or down force?
- [Crowd] Yeah.
- Like our super draggy fast brick with high pressure in front
and low pressure in the back
it's created by having a difference in air pressure
between the top
and the bottom
of a car.
Let's use the 350Z again and say there's a hypothetical
one PSI, less pressure on top than underneath,
with a surface area of about 12,240 square inches,
there'd be about 12,240 pounds of air pressure
lifting the car up.
That would suck.
To get the desired down force,
we tapped into a phenomenon called Bernoulli's Principle
and that says that a fast moving fluid
will have lower pressure than a slower moving fluid.
A wing mounted on a car generates down force
when air moves more quickly across the bottom of the wing
than it does across the top.
In this case, the fluid's the air.
So the slower moving air across the top of the wing
exerts more pressure than the faster moving air underneath
resulting in
Downforce
But how do we get the air to do that?
Make the wing an air foil shape.
When air runs into a curved surface,
it'll try to follow that surface and that's called a Coanda Effect
- [Men] Words, words, words-
- [Woman] Coanda.
- [Men] Words, words, words.
- And the direction you mount the wing
determines whether or not
positive or negative lift is generated.
The air that has to travel farther speeds up
and that creates a pressure imbalance that produces lift
or negative lift
which is downforce
But what if your car's just got a little trunk spoiler tacked on the back?
Well, it actually does something.
Since the air follows a car's curved roof line down a bit
and creates a fast and smooth flow,
a lower pressure area of lift gets created
around the rear end. - [Children] Ew.
- The spoiler interferes with the air flow just a bit,
helping to cancel out some of the lift.
It spoils the air flow
It's a spoiler. (laughs)
Anyway, they don't generate their own down force,
but that's why spoilers
give you a little more high speed stability,
and if you look at the Audi TT,
which is kind of like a jellybean cut in half,
it was getting in accidents anything over 110 miles an hour.
All they had to do was add a little baby spoiler,
problem solved.
Say you got yourself a big wing,
now there's down force pressing on your rear tires.
What about the front?
A lot of rear down force itself can cause
- [Man] Boo, you suck.
- And no one wants that.
It'd help to balance things out
to add down force to the front tires using a splitter
Like our brick, air stacks up against the car's front end
and creates a high pressure area
before moving either over or under the body.
When more air goes into that tight space under the car
than the amount of air that goes over it,
well, you're gonna have lift-off.
(revving)
(thud)
Most production in street cars
generate positive lift at high speeds and like the wing,
you'd really rather have low pressure air go under the car
whilst high pressure air goes over the top.
When a splitter is added, it
the amount of
air can stack up against
while helping more of it move over the car
Now with more pressure on top
and lower pressure underneath
you've got a net down force on those front tires.
We mentioned earlier
that there's not much aerodynamic drag at low speed
and that means there's hardly any down force either
so as much as I wanna believe it,
those splitters and shopping cart wings
really aren't doing much for the average daily drive.
- [Crowd] Aw.
- But the good news is that
downforce increases exponentially
with speed, just like that annoying drag does.
- [Man] You suck.
- So, what do air dams, canards, under trays, side skirts, vortex generators
and diffusers
do, what?
No, the people need to know this, Eddie.
(light music)
Well, it looks like we're out of time.
Look, there's so many aero accessories
that we can't explain them all in one video.
So, guess what?
We're gonna do more videos on aerodynamics
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