gone under the hood of a solar race car,

２章にわたり バッテリー技術の話もしたね

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

今回は設計を掘り下げる

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

レースカーの話だけじゃない

that's not just important to race cars,

あらゆる乗り物や設計物にとって 重要な要素

but every vehicle, or really anything and everything

それが空気力学

that's designed and engineered.

今回のテーマは これよ

I'm talking about aerodynamics.

“現在のソーラーカーは 空気力学の未来につながるのか？”

In this chapter of our Learning Playlist,

空気力学とは 空気中の物体の動きの研究よ

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

空気力学的な設計とは？

drive us toward a more aerodynamic future?

[番組ホスト　マレン･ハンスバーガー]

Simply put, aerodynamics is the study

飛行機の設計を例にとると...

of how an object moves through the air.

世界一の画家じゃないから許してね

But how do you engineer something to be aerodynamic?

飛行には４つの力が働いてる

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

まとめて説明するね

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

１つ目は重力

But we have four forces of flight,

物体に下向きにかかる力のことよ

say that three times fast, to consider here.

それに対抗する上向きの力が揚力

The first is weight.

物体の下の空気によって生じる

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

それから推力

The opposing force to that to that is lift.

物体を前進させる力よ

That's the upward push,

飛行機の場合はエンジンのこと

typically provided by the air underneath the moving object.

最後が抗力

Then there's thrust.

推力と反対方向に働くの

That's the forward force that moves an object forward

物体の動きに抵抗する力よ

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

飛行機や宇宙船はもちろん ソーラーカーにも

And then finally, there's drag.

同じ４つの力が常に働いてる

and that goes in the opposite direction to thrust.

これはブラックマンバの3Dモデル

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

2019年のソーラーカーレースに参加した スタンフォード大学のレースカー

Now, whether we're talking about planes,

この設計には重力を考慮する必要があったの

spacecraft or solar race cars,

軽量の車を目指していたからよ

the same four forces are always at play.

車が軽くなると

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

より少ない力で動ける

the Stanford Solar Car Project's solar racer

ブラックマンバの重さは 約180キロになった

for the 2019 World Solar Challenge.

車としては 本当に軽量ね

When designing Black Mamba,

トラクションとグリップも 操縦と勝敗の鍵になる

the Stanford team had to account for weight.

揚力を弱めてくれるの

They wanted to keep the car as light as possible.

レースカーは高速で軽量だから 浮き上がる恐れがある

And that's because, the lighter the car,

高さがある幅広のタイヤを使い

the less force it takes to move the car.

特製のスポイラーで車体周りの風向きを変えるの

Now, the real Black Mamba tips the scales

車の接地力を高めるために 考慮された設計よ

at roughly 180 kilograms.

次は真っすぐに進む推力

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

ボンネットの中のエンジンが 車を前進させる力を生むの

And traction and road grip are also crucial

化石燃料を動力源とする車の場合 出力は馬力で表され―

to maneuvering and winning races,

電気または電池式の車は キロワットで表される

because they can counteract lift.

１キロワットは約1.34馬力よ

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

ブラックマンバのエンジンは 48Ahのリチウムイオン電池で

they're at risk of literally taking off.

テスラが使っているものよりも コンパクトでパワーは小さいの

So, using taller, wider tires,

でも車が軽いから

and specially designed spoilers or wings

このバッテリーでも 最高で時速110キロほどは出るのよ

that redirect the air around the vehicle

最後に抗力

often factor into a race car's design

空気による抵抗力のことで 前進する車に対してかかる

to help the vehicle keep in contact with the road.

抗力の計算式は

Then we've got thrust.

まず抗力係数に空気の密度を掛けるのよ

And this one's pretty straightforward.

次に速度の２乗の1/2を掛け―

It's the power pushing the race car forward.

最後に前面投影面積を掛ける

That's typically generated under the hood

でも この計算式を使うのは

by the car's engine.

NASAやカーレースの技師くらいね

Traditionally, with fossil fuel powered vehicles,

この式から分かるのは

this power output is measured in horsepower.

多くの要素が働いているということ

But with electric or battery powered vehicles,

特に重要なのは抗力係数

we can also think of it in terms of kilowatts,

流れの中を動く物体が受ける抵抗を

with one kilowatt equaling roughly 1.34 horsepower.

数値で表したものなの

The real Black Mamba has an engine

ここでは 物体がソーラーカーで 流れは空気のことね

powered by a 45 amp hour lithium-ion battery,

抗力係数に影響する要素には 物体の形と表面粗さがある

which is actually much smaller and less powerful

車と空気の摩擦の減少に関わるわ

than what something like a Tesla uses for its battery.

2019年のワールドソーラーチャレンジの 動画を見た人は

But because the car is so light,

東海大学のチームを覚えているでしょう

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

滑らかな車体にするため 懸命に取り組んでた

even with that battery.

空気が車体上を滑りやすくするようにね

And finally, there is drag.

シャークスキンという フィルムを使った―

That's the resistance caused by air

チームもあった

pushing against a race car as it drives forward.

空気の流れをよくして 車の空気力学を改善するのよ

Now, in order to calculate drag,

抗力係数の概念は難しい

you multiply the drag coefficient

[デレク･ミューラー]

by the density of the air

身近なもので考えよう

times half of the velocity squared

例えば レンガだね

times the object's frontal area.

抗力係数は約１～1.5

Now, don't worry,

空気抵抗はそれほど小さくない

you'll probably never have to use this calculation

実のところ 空気抵抗が最も小さいのは滴だ

unless you're a NASA or NASCAR engineer.

抗力係数は約0.05

This complex equation does give you a sense

この他には―

of how many factors are at play

1996年のダッジ･キャラバンの 抗力係数は約0.35だ

when we talk about drag,

大きくて表面が粗いレンガは

including the all-important drag coefficient.

空中を動く時 大きな抵抗を受けるの

The drag coefficient is the number we use

滑らかな滴より抵抗は大きくなる

to quantify the resistance

同様に ミニバンが受ける抵抗も

that the object encounters when moving through a fluid.

滑らかなソーラーカーより大きいのよ

In this case, our object is our solar race car

スタンフォード大学のチームは ブラックマンバの抗力係数を公開してない

and our fluid is air.

設計上の数字は公開していない

Some other factors that affect drag coefficient

主に抗力係数だね

include the object's shape and surface roughness

長年 公開は控えている

to reduce friction between the car and the air.

ワールドソーラーチャレンジのような レースでは当然のことね

If you watched our documentary series

チームカーの空気抵抗を 競争相手に教えるのは

on the 2019 World Solar Challenge,

いい考えではないでしょ

you may recall that teams

でもスタンフォード大学は 以前の設計よりも

like the one from Tokai University

空気抵抗が少ないとは答えた

worked really hard

今回初めてシングルフェアリングの―

to make their cars seamless and slippery.

[スタンフォード　コーリ･ブレンデル]

In an effort to create a smooth flow of air

流線形ボディーにした

across their race car,

初めての試みだった

some teams even use an innovative film wrap coating

ずっとマルチフェアリングで カタマラン型だったの

called "shark skin" to better redirect air flow

マルチフェアリングのデザインが 数十年間 主流だった

and improve their car's aerodynamics.

1987年の初開催までさかのぼって

Now, the concept of drag coefficient

全優勝チームが マルチフェアリングだったの

can be a little bit abstract.

ネタバレだけど 去年の優勝も...

So it might be useful to think of the drag coefficients

マルチフェアリングのカタマラン型

of some everyday objects,

[アゴリア]

like a brick.

流線形のデザインより空気抵抗が大きくても

A brick has a drag coefficient of about one.

なぜマルチフェアリングが勝つの？

Not very aerodynamic as you'd guess.

流線形と比べて不利な点は２つ

In fact, the most aerodynamic shape that we know

車輪同士を近づければ 空力性能が向上する代わりに

is the teardrop

ひっくり返りやすくなる

with a drag coefficient of about 0.05

もう１つの問題はソーラーパネルのサイズだ

Think about some other objects, the...

シングルフェアリングの流線形に比べて

A 1996 Dodge Caravan

カタマラン型は幅が広い

has a drag coefficient of about 0.35.

大きなソーラーパネルを置けるでしょ

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

安定性を保ちつつ よりエネルギーを生む能力が

encounters greater resistance

勝利の組み合わせなのね

when it's moving through the air

流線形は空気の流れと抗力を改善し

than, say, a smooth aerodynamic teardrop.

効率性と速度を大きく向上してくれる

In the same way, a boxy minivan

それでも優勝はできないのよ

encounters greater resistance

今のところはね

than a sleek solar racer

ソーラーカーだけでなく 多くのレースカーが

with a lower drag coefficient.

ミニバンより抗力係数が高くなってるの

Now, the Stanford solar team

F1レースでは 故意に抗力係数を増してる

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

揚力を弱め トラクションと操縦性を高めるためよ

Yeah, so our team doesn't share some numbers

スタンフォード大学は 流線形のデザインのままで

just in our design.

空気抵抗の改善に取り組み続けてる

It's mainly just the drag coefficient.

目標は 次の ワールドソーラーチャレンジ優勝よ

It's kind of a long-standing thing

でも革新はレースのためだけじゃない

within the solar teams.

だから最後となる次回のテーマは

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

“ソーラーカーは みんなにとって 将来の実現可能な選択肢か”よ

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?