gone under the hood of a solar race car,

and explored battery technology in not one, but two episodes.

So now it's time to dig into an element of design

that's not just important to race cars,

but every vehicle, or really anything and everything

that's designed and engineered.

I'm talking about aerodynamics.

In this chapter of our Learning Playlist,

we're asking, could today's solar race cars

drive us toward a more aerodynamic future?

Simply put, aerodynamics is the study

of how an object moves through the air.

But how do you engineer something to be aerodynamic?

Now if we take a plane design as an example...

Well, forgive me because I'm [CHUCKLES] not the best artist in the world.

But we have four forces of flight,

say that three times fast, to consider here.

The first is weight.

That is the downward force exerted on the object by gravity.

The opposing force to that to that is lift.

That's the upward push,

typically provided by the air underneath the moving object.

Then there's thrust.

That's the forward force that moves an object forward

like, in the plane's case, the plane's engines.

And then finally, there's drag.

and that goes in the opposite direction to thrust.

It's the force that resists an object's motion.

Now, whether we're talking about planes,

spacecraft or solar race cars,

the same four forces are always at play.

This is a 3-D printed model of Black Mamba,

the Stanford Solar Car Project's solar racer

for the 2019 World Solar Challenge.

When designing Black Mamba,

the Stanford team had to account for weight.

They wanted to keep the car as light as possible.

And that's because, the lighter the car,

the less force it takes to move the car.

Now, the real Black Mamba tips the scales

at roughly 180 kilograms.

As far as cars go, that's really light.

And traction and road grip are also crucial

to maneuvering and winning races,

because they can counteract lift.

See, race cars are often so fast and so light,

they're at risk of literally taking off.

So, using taller, wider tires,

and specially designed spoilers or wings

that redirect the air around the vehicle

often factor into a race car's design

to help the vehicle keep in contact with the road.

Then we've got thrust.

And this one's pretty straightforward.

It's the power pushing the race car forward.

That's typically generated under the hood

by the car's engine.

Traditionally, with fossil fuel powered vehicles,

this power output is measured in horsepower.

But with electric or battery powered vehicles,

we can also think of it in terms of kilowatts,

with one kilowatt equaling roughly 1.34 horsepower.

The real Black Mamba has an engine

powered by a 45 amp hour lithium-ion battery,

which is actually much smaller and less powerful

than what something like a Tesla uses for its battery.

But because the car is so light,

Black Mamba can top out at around 110 kilometers per hour.

even with that battery.

And finally, there is drag.

That's the resistance caused by air

pushing against a race car as it drives forward.

Now, in order to calculate drag,

you multiply the drag coefficient

by the density of the air

times half of the velocity squared

times the object's frontal area.

Now, don't worry,

you'll probably never have to use this calculation

unless you're a NASA or NASCAR engineer.

This complex equation does give you a sense

of how many factors are at play

when we talk about drag,

including the all-important drag coefficient.

The drag coefficient is the number we use

to quantify the resistance

that the object encounters when moving through a fluid.

In this case, our object is our solar race car

and our fluid is air.

Some other factors that affect drag coefficient

include the object's shape and surface roughness

to reduce friction between the car and the air.

If you watched our documentary series

on the 2019 World Solar Challenge,

you may recall that teams

like the one from Tokai University

worked really hard

to make their cars seamless and slippery.

In an effort to create a smooth flow of air

across their race car,

some teams even use an innovative film wrap coating

called "shark skin" to better redirect air flow

and improve their car's aerodynamics.

Now, the concept of drag coefficient

can be a little bit abstract.

So it might be useful to think of the drag coefficients

of some everyday objects,

like a brick.

A brick has a drag coefficient of about one.

Not very aerodynamic as you'd guess.

In fact, the most aerodynamic shape that we know

is the teardrop

with a drag coefficient of about 0.05

Think about some other objects, the...

A 1996 Dodge Caravan

has a drag coefficient of about 0.35.

MAREN: A brick with its blocky shape and its rough surface

encounters greater resistance

when it's moving through the air

than, say, a smooth aerodynamic teardrop.

In the same way, a boxy minivan

encounters greater resistance

than a sleek solar racer

with a lower drag coefficient.

Now, the Stanford solar team

wouldn't share Black Mamba's actual drag coefficient.

Yeah, so our team doesn't share some numbers

just in our design.

It's mainly just the drag coefficient.

It's kind of a long-standing thing

within the solar teams.

I get it. I mean, in a race as competitive

as the World Solar Challenge,

letting the competition know

just how aerodynamic your car is

is, you know, probably not a good idea.

But the Stanford team did confirm

that their new racer is sleeker

and more aerodynamic than the past designs.

So the driving design change that we had

was going with a single fairing bullet style aero body.

And that was the first time we ever tried doing

a single fairing aero body.

We've always done, like, a multi-fairing car.

Usually that's a catamaran.

MAREN: The multi-fairing design

has been widely used

by many solar racers throughout the decades,

including all of the winners of the World Solar Challenge

going all the way back to the very first race in 1987.

And, spoiler alert,

the winner of last year's race,

you guessed it, another multi-fairing catamaran design.

So why is a multi-fairing design so successful,

even though it may not be

as aerodynamic as the bullet design?

I think there is two main disadvantages to a bullet car.

In terms of stability, it improves the aerodynamics

if you have the wheels closer together.

but the trade-off to that

is as you move your wheels closer together,

it's a lot easier to tip your car over.

The other problem is with the array size.

MAREN: Compared to a sleeker, single fairing bullet car,

the catamaran is wider

and it has more room to fit a larger solar array.

This ability to generate more energy

combined with greater stability

tends to make for a winning combination.

So while the bullet design does allow

for a smoother air flow and improved drag,

which can translate into greater efficiency

and potentially faster speeds,

it hasn't quite translated into taking home the trophy.

At least not yet.

Fun fact here. Many race cars, not just solar racers,

are actually designed

to have a higher drag coefficient than minivans.

Yeah, that's right. Formula One designers

deliberately increase drag

to help counteract upward lift

and improve traction and maneuverability.

The Stanford Solar Car team plans to stick

with Black Mamba's sleek bullet design

while continuing to improve

their solar racer's aerodynamics.

And their goal is winning the next World Solar Challenge.

But the drive to innovate goes far beyond the next race.

So, in the final chapter of our Learning Playlist,

coming up next...

Will solar cars really be a viable option

for all of us in the future?