[SEAGULLS SQUAWKING] NARRATOR: FOR ALMOST ALL OF HUMAN HISTORY, THE DREAM OF FLYING REMAINED JUST THAT, A DREAM.

BUT WE ARE A STRANGE, CREATIVE SPECIES.

OVER THE AGES, THE IDEA OF HUMAN FLIGHT PASSED FROM ONE MIND TO ANOTHER, AND EVENTUALLY, IT WOULD CHANGE THE WORLD.

BUT THE STORY OF HOW WE TOOK TO THE SKY IS FULL OF EXTRAORDINARY ACCIDENTS AND BIZARRE CONNECTIONS.

IT INVOLVES THE ILL-FATED PENNY FARTHING BICYCLE AND SEVERAL TRIPS TO THE BEACH, A VISIONARY STUDENT... AND A LEGENDARY GENIUS... A DISASTER AT SEA... AND THE ULTIMATE SACRIFICE.

TOGETHER, THESE EVENTS WOULD GIVE US OUR GREAT SUPERPOWER, THE ABILITY TO FLY.

THESE ARE THE INVENTIONS THAT DEFINE OUR AGE AND HAVE CHANGED OUR WORLD FOREVER.

[TIRES SCREECHING] THEY'VE ALLOWED US TO MOVE IN NEW WAYS, TO CONNECT TO EACH OTHER AND DISCOVER OUR PLACE IN THE UNIVERSE, EACH A STORY OF INGENUITY, OF WONDER... OF BREAKTHROUGH.

NARRATOR: AT THIS VERY MOMENT, AT LEAST HALF A MILLION PEOPLE ARE FLYING, MAKING ENORMOUS JOURNEYS AT INCREDIBLE SPEED.

OUR ANCESTORS WOULD BE AMAZED.

WE'VE BECOME A SPECIES THAT HAS OVERCOME OUR EARTHLY LIMITATIONS.

THE INVENTION OF THE AIRPLANE HAS BEEN A TRUE REVOLUTION.

BUT 11 CENTURIES AGO, THERE WAS NO ONE IN THE AIR EXCEPT FOR ONE INGENIOUS INVENTOR WHO WAS WAY AHEAD OF HIS TIME.

[EAGLE SCREECHING] LEGEND HAS IT, IN ABOUT 860 A.D.

IN MOORISH SPAIN, A MAN NAMED IBN FIRNAS CLIMBED TO THE TOP OF A MOUNTAIN.

HE ATTACHED FEATHERS TO HIS BODY AND ARMS.

HE GAVE HIMSELF WINGS.

MAN: OOH.

A LITTLE SHAKY.

A LITTLE SHAKY.

ALL RIGHT.

ALL RIGHT.

ALL RIGHT.

NARRATOR: THEN...HE DID SOMETHING EXTRAORDINARY.

MAN: 3, 2, 1.

IT MUST HAVE TAKEN INCREDIBLE COURAGE FOR THAT LEAP OF FAITH INTO THE UNKNOWN.

I KNOW WHAT IT'S LIKE BECAUSE I'VE DONE IT.

NARRATOR: BRANDON MIKESELL IS ONE OF THE WORLD'S TOP WING SUIT FLIERS, THE LATEST IN A LONG LINE OF PIONEERS PREPARED TO PUT THEIR LIVES ON THE LINE.

THIS IS A PASSION THAT TAKES OVER MY WHOLE, ENTIRE LIFE.

I'VE ALWAYS WANTED TO FLY SINCE I WAS A LITTLE KID.

FLYING IS ABOUT SPEED, ABOUT CONTROL, AND IT'S ABOUT DEFEATING GRAVITY.

NARRATOR: SO, WHAT HAPPENED TO THAT LEGENDARY PIONEER IBN FIRNAS?

THE STORY GOES THAT, ALTHOUGH HE MANAGED TO FLY MORE THAN 1,000 YEARS AGO, WHEN HE LANDED, HE CAME DOWN MUCH TOO FAST.

HE BROKE HIS BACK AND NEVER FLEW AGAIN.

MIKESELL: LUCKILY, THOUGH, I HAVE MODERN TECHNOLOGY ON MY SIDE.

IF IBN FIRNAS WERE ALIVE TODAY, I THINK HIS MIND WOULD BE BLOWN.

I THINK HE WOULD BE AMAZED AT HOW FAR IT'S COME.

I THINK THAT HE'D BE THRILLED THAT WE CARRIED ON HIS SAME PASSION AND HIS SAME LOVE FOR THIS.

NARRATOR: MODERN-DAY FLYING IN ALL ITS FORMS IS DUE TO A MASTERY OF SOMETHING THAT SURROUNDS US BUT THAT WE CANNOT EVEN SEE, AND EVEN THOUGH IT SEEMS TO HAVE NO STRENGTH, IT CAN HOLD US ALOFT...

THE AIR.

IT MIGHT SEEM ODD, BUT THE STUDY OF AIRFLOW IS ACTUALLY CALLED FLUID DYNAMICS.

AND IF THAT DOESN'T SEEM STRANGE ENOUGH, BEFORE WE HAD WINGS, WE HAD TAILS.

WOMAN: THESE STRUCTURES ARE JUST ABSOLUTELY MAGNIFICENT.

I AM A FLUID DYNAMICIST, SO I HAVE STUDIED HOW AIR FLOWS, AND SO WHEN I COME TO A KITE FESTIVAL LIKE THIS, YOU REALLY SEE HOW SIGNIFICANT AIR IS IN BRINGING THESE STRUCTURES TO LIFE.

DETAILS OF THE FIRST-EVER KITE ARE LOST IN HISTORY, BUT IT'S BELIEVED THAT AROUND 2,500 YEARS AGO, THE CHINESE PUT TOGETHER A SIMPLE STRUCTURE OF BAMBOO AND SILK, AND THAT BECAME THE FIRST KITE, AND THE REASON WHY IT'S SO SIGNIFICANT IS BECAUSE IT'S OUR FIRST-EVER UNDERSTANDING OF HOW A STRUCTURE COULD BECOME AIRBORNE AND DEFY GRAVITY.

ONE OF THE MAJOR PRINCIPLES THAT A KITE USES TO STAY AIRBORNE IS BALANCING THE FORCES THAT ARE PUSHING THE KITE DOWNWARDS AND THE FORCES THAT ARE LIFTING THE KITE UPWARDS.

THE WIND THAT'S BLOWING INTO THE KITE AND ALONG ITS UNDERBELLY IS DEFLECTED DOWNWARDS, AND THAT DEFLECTION OF AIR CREATES AN EQUAL AND UPWARD FORCE CALLED LIFT.

NARRATOR: THE CHINESE PUT THEIR REVOLUTIONARY TECHNOLOGY TO MANY PURPOSES.

KITES WERE USED FOR SIGNALING OVER LONG DISTANCES, DROPPING WEAPONS, AND THERE ARE EVEN LEGENDS OF THEM BEING USED TO LIFT PEOPLE.

BUT, OF COURSE, KITES HAVE THEIR LIMITATIONS.

SOMARA: KITES WERE A GREAT FIRST START IN OUR UNDERSTANDING OF FLIGHT, BUT THEY NEEDED TO BE TETHERED, AND THEY NEEDED THE WIND TO BE ABLE TO GLIDE.

SO IT WAS A GOOD START, BUT WE NEEDED MUCH MORE THAN THAT.

[BELLS TOLLING] NARRATOR: TO FLY SUCCESSFULLY, WE NEEDED TO MASTER THE MYSTERIOUS FORCES OF THE AIR.

IT WOULD TAKE A MAN WITH MANY OBSESSIONS TO BEGIN TO SOLVE THIS PUZZLE, AN ARTIST WHO WOULD GO DOWN IN HISTORY AS ONE OF THE GREATEST MINDS WHO EVER LIVED.

LEONARDO DA VINCI WAS BORN FROM FAIRLY HUMBLE ORIGINS, BUT FROM AN EARLY AGE, HE SHOWED AN EXTRAORDINARY TALENT FOR PAINTING AND DRAWING.

HIS SECRET WAS TO LOOK AT EACH SUBJECT IN MINUTE DETAIL, TO TRY AND SEE THE STRUCTURE BENEATH THE SURFACE.

HE WAS OBSESSED WITH HOW THE BODIES OF ANIMALS AND HUMANS ACTUALLY WORK, WHICH HE DISCOVERED THROUGH THE GRISLY PROCESS OF TAKING THOSE BODIES APART.

HE WAS PARTICULARLY INTERESTED IN ANIMALS THAT FLY.

HE WANTED TO KNOW HOW THE BEATING OF A WING KEPT THEM ALOFT.

IF HE COULD DISCOVER THIS SECRET, HE WAS CONVINCED HE WOULD HAVE THE KEY TO THE AGE-OLD DREAM OF HUMAN FLIGHT.

LOOKING EVER CLOSER AT THE NATURAL WORLD, HE NOTICED THE EXQUISITE EFFICIENCY OF FLYING CREATURES.

HE REALIZED THAT ATTACHING WINGS TO YOUR ARMS WAS UNLIKELY TO WORK.

HUMAN MUSCLES ARE JUST NOT STRONG ENOUGH.

SO, HE CAME UP WITH A REVOLUTIONARY NEW IDEA, AN IDEA HE BELIEVED WOULD CHANGE THE WORLD.

INSTEAD OF ATTACHING THE WINGS TO THE ARMS, THEY WOULD BE PART OF A MACHINE THAT HAD BEATING WINGS LIKE A BIRD.

IN HIS MIND, HE HAD INVENTED THE FIRST FLYING MACHINE.

OVER HIS LIFETIME, HE DESIGNED MORE THAN A DOZEN MACHINES THAT FLAPPED THEIR WINGS, BUT AS FAR AS WE KNOW, NONE OF THEM EVER FLEW.

SO, WHY IS THIS?

WHAT IS IT ABOUT A BIRD'S WING THAT ELUDED EVEN THE GENIUS OF LEONARDO DA VINCI?

TO FIND OUT REQUIRES MODERN TECHNOLOGY.

MAN: HE'S FEEDING.

OK. READY?

WIND TUNNEL IS ON.

NARRATOR: AT STANFORD UNIVERSITY, RESEARCHERS ARE STILL IN THE PROCESS OF UNLOCKING MOTHER NATURE'S SECRETS.

LENTICK: THE WAY DA VINCI INSPIRES ME IS THAT, NOT ONLY IS HE AN ENGINEER, NOT ONLY IS HE A SCIENTIST, HE'S THIS ARTIST WHO COMBINES EVERYTHING IN ONE VISION OF FLIGHT.

LEONARDO IS REALLY THE FIRST PERSON TO UNDERSTAND THAT THE STRUCTURE OF A BIRD WING REALLY MATTERS, THE WAY THE WING IS BUILT AND HOW THAT ENABLES FLIGHT.

BUT THIS KIND OF MODERN STUDY OF BIRDS LEAVES US NO DOUBT THAT HE ACTUALLY REALLY STARTED THE SCIENCE OF FLIGHT.

NARRATOR: BUT ALTHOUGH LEONARDO MADE DRAWINGS AND TOOK DETAILED MEASUREMENTS, HE COULD NOT GET THE DATA HE NEEDED.

LENTICK: IT'S ONLY RECENTLY THAT WE'VE DEVELOPED THE TECHNOLOGY TO UNLOCK THE SECRETS OF HOW BIRDS FLY.

NARRATOR: THE KEY IS HIGH-SPEED PHOTOGRAPHY.

LENTICK: TODAY WE CAN SEE WHAT LEONARDO COULDN'T SEE.

HE WAS THINKING THAT IT WAS ALL IN THE BEATING OF THE WING.

THERE'S MUCH MORE TO IT THAN THAT, AND ACTUALLY, TO REALLY TAKE OFF, WE HAVE TO THINK BEYOND FLAPPING WINGS.

NARRATOR: THE COMPLEXITY OF THIS MOTION MEANT THAT THE SECRET OF FLIGHT WOULD REMAIN HIDDEN FOR ANOTHER 300 YEARS, UNTIL A TRIP TO THE BEACH GAVE AN OBSCURE ENGLISH ARISTOCRAT AN IDEA.

[LIVELY MUSIC PLAYING] THIS IS THE COAST OF THE COUNTY OF YORKSHIRE IN THE NORTHEAST OF ENGLAND, AND IT'S HERE THAT ONE OF THE VERY GREATEST MILESTONES IN THE HISTORY OF FLIGHT WOULD OCCUR.

SOMARA: THIS SEASIDE TOWN OF SCARBOROUGH BECAME A FASHIONABLE DESTINATION AT THE TURN OF THE 19th CENTURY.

WEALTHY LONDONERS WOULD FLOCK HERE TO MAKE USE OF THE SPA WATERS, WHICH APPARENTLY WOULD INCREASE WELL-BEING AND MENTAL CAPACITY.

NARRATOR: LIVING IN A GRAND MANSION JUST OUTSIDE SCARBOROUGH WAS A WEALTHY BARONET, SIR GEORGE CAYLEY.

HIS HOUSE STILL EXISTS TO THIS DAY.

CAYLEY WAS A POLYMATH WITH A MYRIAD OF INTERESTS.

HE'S EVEN BEEN CALLED THE ENGLISH LEONARDO.

SINCE CHILDHOOD, HE'D HAD THE SAME DREAM-- TO BUILD A FLYING MACHINE.

IN A SCHOOLBOOK DATED 1784, HE DREW A PICTURE OF A FLYING TOY, BUT IT WAS IN SCARBOROUGH THAT CAYLEY'S DREAM WOULD TAKE FLIGHT.

SOMARA: ONE DAY, CAYLEY WAS AT THE BEACH, AND HE WAS LOOKING AT A GULL.

IT WAS JUST GLIDING THERE.

AND IT REALLY MADE HIM THINK ABOUT HOW THEY STAY UP THERE IN THE AIR WITHOUT FLAPPING THEIR WINGS.

NARRATOR: CAYLEY WAS INSPIRED TO INVESTIGATE THIS FASCINATING MYSTERY SCIENTIFICALLY.

SO, HE CREATED AN EXPERIMENT TO INVESTIGATE THE PHENOMENON.

IT WAS DESIGNED TO WORK HERE, ON THE GRAND STAIRCASE OF HIS MANSION.

IF HE COULD WORK OUT WHAT KEPT THE BIRD ALOFT WHEN IT'S NOT FLAPPING ITS WINGS, MAYBE HE COULD UNCOVER THE SECRET OF FLIGHT.

SOMARA: AND THIS IS CAYLEY'S EXPERIMENT-- THE WHIRLING ARM.

HOW IT WORKS IS THAT WEIGHTS ARE ATTACHED TO A STRING, AND THEY'D BE DROPPED FROM THE TOP OF THIS STAIRCASE ALL THE WAY DOWN TO THE BOTTOM, AND THE STRING IS WOUND AROUND THIS DOWEL, AND WHEN THE DOWEL SPINS, SO DOES THE WHIRLING ARM.

NARRATOR: AT ONE END OF THE ARM IS A SQUARE PLATE, A SIMPLIFIED WING.

IT'S BALANCED WITH A WEIGHT ON THE OTHER END.

AS THE ARM SPINS, THE PLATE IS DRIVEN THROUGH THE AIR AS IF IT WERE A WING IN FLIGHT.

WITH THE PLATE FLAT, CAYLEY NOTED THAT THE ARM WAS AT THE SAME ANGLE AS WHEN IT WAS STATIONARY, AND THEREFORE, THERE WAS NO LIFT.

SOMARA: FOR THIS EXPERIMENT, WE'VE GONE FROM A HORIZONTAL PLATE TO SIX DEGREES OF INCLINE OR ANGLE.

NARRATOR: CAYLEY OBSERVED THAT, WITH AN INCLINATION OF JUST SIX DEGREES, SOMETHING MAGICAL HAPPENED.

THIS TIME, THE ARM IS AT AN ANGLE.

IT'S BEING RAISED BY THE PLATE MOVING THROUGH THE AIR.

THE PLATE IS PRODUCING LIFT.

SOMARA: IT WAS A REAL LEAP IN OUR UNDERSTANDING OF FLUID DYNAMICS, BECAUSE ESSENTIALLY, SCIENTISTS UP UNTIL THEN ONLY THOUGHT THAT LIFT WAS POSSIBLE THROUGH MECHANICAL ACTION, OR THE FLAPPING OF WINGS.

NARRATOR: WITH THIS DATA, CAYLEY COULD AT LAST SET ABOUT MAKING HIS FLYING MACHINE, BUT IT WOULD TAKE HIM ALMOST 50 YEARS TO PERFECT HIS DESIGN, UNTIL, IN ABOUT 1849, HE WAS READY TO FLY A MAN.

WELL, A 10-YEAR-OLD BOY AT LEAST.

SOMARA: AND LIKE THE MAN WHO FIRST FLEW ANCIENT CHINESE KITES, THAT LITTLE BOY'S NAME WAS LOST IN TIME, BUT ONE DAY, IN THIS VERY FIELD, THAT SMALL BOY BECAME THE FIRST HUMAN BEING TO FLY IN AN UNTETHERED AIRPLANE.

NARRATOR: THIS FLIGHT CHANGED EVERYTHING.

CAYLEY HAD CREATED THE FIRST WORKING GLIDER, AND CAYLEY HIMSELF COULD SEE HOW REVOLUTIONARY THIS TECHNOLOGY WOULD BE.

SOMARA: "I FEEL PARTICULARLY CONFIDENT "THAT THIS NOBLE ART WILL SOON BE BROUGHT HOME "TO MAN'S CONVENIENCE "AND THAT WE SHALL BE ABLE TO TRANSPORT "OURSELVES MORE SECURELY BY AIR THAN BY WATER "AND WITH A VELOCITY BETWEEN 20 AND 100 MILES AN HOUR."

NARRATOR: AT A TIME WHEN MOST PEOPLE TRAVELED BY HORSE AND CART, THE IDEA OF FLYING AROUND AT 100 MILES PER HOUR MUST HAVE SEEMED ABSURD.

YET THERE WAS ALREADY A WAY TO TRAVEL BY AIR USING A RIVAL INVENTION-- THE BALLOON.

ALL THROUGH THE 19th CENTURY, BALLOONS WERE A BIG DEAL.

MANY WERE PRODUCED AND USED FOR TRANSPORTING BOTH PEOPLE AND MAIL.

BUT OTHERS WERE CONVINCED THAT ONLY A HEAVIER-THAN-AIR MACHINE WOULD ALLOW US TO FLY WHEREVER WE WANTED.

MANY SUCH FLYING MACHINES WERE DESIGNED, ALTHOUGH FEW WITH ANY GROUNDING IN SCIENCE.

BUT BY THE MID-1800's, THE IDEA OF COMMERCIAL AVIATION WAS FULLY FORMED, TOO.

EXHIBITIONS WERE HELD, DETAILING FANTASTIC PROPOSALS TO AN ENTHRALLED PUBLIC.

BUT NOW THERE WAS A TWIST IN THE STORY, QUITE LITERALLY, WITH THE INVENTION OF THE RUBBER BAND.

IN 1870, A 20-YEAR-OLD FRENCHMAN, ALPHONSE PENAUD, HAD A BRAINSTORM.

HE DESIGNED A TOY HELICOPTER, DRIVEN BY A TWISTED RUBBER BAND.

A YEAR LATER, HE DESIGNED ANOTHER MODEL, THE PLANOPHORE.

THE TOY FLEW FOR ALMOST 200 FEET.

NEXT, PENAUD DESIGNED A FULL-SIZED AIRPLANE.

IT FEATURED TWIN PROPELLERS, AN AUTOPILOT, AND RETRACTING LANDING GEAR.

IT WAS YEARS AHEAD OF ITS TIME.

YET, WITH THE BIG MONEY IN BALLOONING, PENAUD COULDN'T PERSUADE ANYONE TO INVEST IN HIM.

DEPRESSED, AGE 30, HE TOOK HIS OWN LIFE.

BUT PENAUD'S WORK WOULD NOT BE IN VAIN.

AROUND THE TIME OF HIS DEATH, A MAN WALKED INTO A STORE AND BOUGHT A TOY HELICOPTER, INSPIRED BY PENAUD'S DESIGN, FOR HIS TWO YOUNG SONS, WILBUR AND ORVILLE.

THIS MACHINE WOULD TRIGGER AN OBSESSION WITH MECHANICAL FLIGHT THAT WOULD EVENTUALLY TAKE US TO THE AIR.

BUT BEFORE THAT HAPPENED, A WEALTHY ENTREPRENEUR IN GERMANY WAS READY TO PUT HIS REPUTATION AND HIS LIFE ON THE LINE.

HE CONSTRUCTED A MACHINE THAT WAS BASED ON YEARS OF STUDY, PARTICULARLY ON THE WINGS OF THE STORK.

HE NOTICED HOW THE WINGS ARE CURVED AND HOW IMPORTANT IT IS THAT THEY ARE AT THE CORRECT ANGLE TO THE ONCOMING AIR.

HIS NAME WAS OTTO LILIENTHAL.

HE WAS CONVINCED THAT A FULL-GROWN MAN COULD GLIDE LIKE A BIRD.

LENTICK: WHAT MAKES LILIENTHAL SPECIAL IS THAT HE ACTUALLY COMBINED ALL THE DISCOVERIES AND BUILT A FLYING MACHINE THAT CAN WORK.

AND TO FLY THAT GLIDER, HE BUILT HIS OWN HILL.

[PEOPLE GASPING] NARRATOR: THE DREAM OF A FLYING MAN WAS REAL AT LAST, EVEN THOUGH THE FLIGHT COULD NOT BE SUSTAINED.

[APPLAUSE] IN 2016, THE GERMAN AEROSPACE CENTER BUILT AN ACCURATE REPLICA OF ONE OF LILIENTHAL'S GLIDERS TO SEE HOW STABLE AND AIRWORTHY IT WAS.

THEY PLACED THE GLIDER IN ONE OF THE MOST ADVANCED WIND TUNNELS IN EUROPE.

THE TUNNEL BLASTED AIR OVER THE REPLICA, WHICH WAS HELD STEADY BY AN ARM RIGGED WITH DOZENS OF SENSORS LINKED TO COMPUTERS IN THE CONTROL ROOM.

THE RESULTS SHOWED THAT THE GLIDER'S CURVED WINGS DO INDEED PRODUCE A REMARKABLE AMOUNT OF LIFT.

THE AIRCRAFT WAS CAPABLE OF FLYING NEARLY FOUR TIMES FARTHER THAN IT FALLS.

BUT LILIENTHAL WAS AWARE THERE WAS MUCH MORE WORK TO DO.

HE WROTE THAT, "ONLY WITH MUCH MORE SCIENTIFIC RESEARCH WILL WE EVER MAKE SUSTAINED FLIGHT A REALITY."

BUT LILIENTHAL'S FLIGHTS HAD ALSO HIGHLIGHTED A MAJOR PROBLEM--CONTROL.

THE ONLY WAY LILIENTHAL COULD STEER HIS GLIDER WAS BY SHIFTING HIS WEIGHT FORWARDS AND BACKWARDS AND FROM SIDE TO SIDE.

IN 1896, HIS LUCK RAN OUT.

HIT BY A GUST OF WIND, HE LOST CONTROL AND PLUMMETED TO EARTH, BREAKING HIS NECK.

LEGEND HAS IT THAT HIS FINAL WORDS WERE, "SACRIFICES MUST BE MADE."

LILIENTHAL DIED KNOWING THAT SUSTAINED FLIGHT SHOULD BE POSSIBLE, BUT WHAT HE DIDN'T REALIZE WAS THAT A CRAZE FOR ANOTHER FORM OF TRANSPORTATION HAD ALREADY SET THE WHEELS IN MOTION.

[MUSIC PLAYING AND MAN WHISTLING] BACK IN THE 1880's, WHILE LILIENTHAL WAS SHOWING OFF HIS GLIDERS, OTHER DAREDEVILS WERE RISKING THEIR NECKS ON PENNY FARTHING BICYCLES.

IT WAS A DIFFICULT AND DANGEROUS MACHINE.

BUT THEN A BREAKTHROUGH-- THE SAFETY BICYCLE WAS INVENTED.

IT WAS EASIER TO RIDE AND MUCH MORE COMFORTABLE THAN ANY BICYCLE BEFORE.

CYCLING BECAME A NATIONAL CRAZE.

30,000 CYCLE SHOPS OPENED IN LESS THAN A DECADE...

INCLUDING THIS ONE IN DAYTON, OHIO.

IT WAS OWNED BY THE TWO BROTHERS WHO HAD RECEIVED A TOY HELICOPTER WHEN THEY WERE BOYS.

THEY WERE, OF COURSE, WILBUR AND ORVILLE WRIGHT.

FLETCHER: I'VE BEEN INTERESTED IN AEROSPACE ENGINEERING SINCE THE AGE OF 11.

I'VE ALWAYS BEEN INTERESTED IN DESIGN AND MATHEMATICS AND SCIENCE, SO WHEN I SAW THE WRIGHT BROTHERS' FLIER, I ALWAYS WONDERED, HOW COULD SOMETHING THAT LOOKS SO FRAGILE AND FLIMSY ACTUALLY ACHIEVE CONTROLLED FLIGHT?

NARRATOR: THE WRIGHT BROTHERS STARTED BY READING ALL THEY COULD ABOUT CAYLEY, PENAUD, AND LILIENTHAL.

THEY REALIZED THAT THERE WAS STILL MUCH TO LEARN ABOUT THE SCIENCE OF WINGS.

THEY BUILT A DEVICE USING A WHEEL ATTACHED HORIZONTALLY TO THE FRONT OF A BICYCLE.

ON THIS WHEEL, THEY ATTACHED MODELS OF DIFFERENT KINDS OF WINGS.

BY RIDING ALONG, THEY PRODUCED A STEADY STREAM OF AIR, WHICH GAVE THE BROTHER REAL DATA ON HOW WINGS WORK.

FLETCHER: THEY WERE RIDING THEIR BICYCLE UP AND DOWN THE STREET, TRYING TO DISCOVER THE PERFECT WING FOR THEIR GLIDER.

NARRATOR: THE WRIGHTS FOUND THAT THEY COULD IMPROVE ON LILIENTHAL'S DESIGNS BY CHANGING THE SHAPE OF THE WINGS, BOTH IN THEIR CURVATURE AND BY MAKING THEM LONGER AND NARROWER.

ULTIMATELY, IT WOULD BE SCIENCE THAT WOULD GET US INTO THE AIR AND KEEP US THERE.

FLETCHER: AT THE TIME, PILOTS HAD THE ABILITY TO LEAN IN ORDER TO CONTROL THE GLIDER.

CYCLISTS HAD THAT SAME ABILITY WITH BIKES, BUT THEY ALSO HAD ONE OTHER ADVANTAGE--HANDLEBARS.

THE WRIGHT BROTHERS HAD TO FIGURE OUT HOW TO STEER.

AS THE STORY GOES, IN 1899, WILBUR WRIGHT HAD A BREAKTHROUGH.

HE WAS PLAYING WITH A CARDBOARD BOX OF AN INNER TUBE FOR A BICYCLE, AND HE HAD AN IDEA, AN IDEA THAT WILL TRANSFORM FLIGHT.

NARRATOR: THE IDEA WAS CALLED WIND WARPING.

BY WARPING OR TWISTING THE WING, IT SHOULD BE POSSIBLE TO CHANGE THE AMOUNT OF LIFT EACH SIDE PRODUCES.

THE SIDE THAT TWISTS UP SHOULD PRODUCE MORE LIFT, ROLLING THE PLANE AND STEERING IT A BIT LIKE A BICYCLE.

THE SYSTEM WAS CONTROLLED BY THE PILOT, LYING IN A CRADLE.

AN ARRANGEMENT OF WIRES MEANT THAT, IF HE MOVED HIS HIPS, THE WINGS WOULD TWIST, AND THE GLIDER SHOULD TURN.

A MOVEABLE RUDDER ON THE REAR OF THE MACHINE CONTROLLED THE DIRECTION, AND A HORIZONTAL SURFACE ON THE FRONT CONTROLLED THE PITCH OF THE GLIDER.

FOR THE FIRST TIME, HERE WAS AN AIRCRAFT THAT SHOULD HAVE CONTROL IN ALL DIRECTIONS.

IN 1902, THEY BROUGHT THE NEW MACHINE HERE TO KITTY HAWK IN NORTH CAROLINA.

THEY CHOSE THIS PLACE BECAUSE OF THE COMBINATION OF RELIABLE WINDS AND SAND DUNES, WHICH WOULD SOFTEN ANY LANDINGS.

BRUCE WEAVER IS A LIFELONG FAN OF THE BROTHERS AND ESPECIALLY THEIR 1902 GLIDER.

WEAVER: THE 1902 WRIGHT GLIDER, I THINK, IS ARGUABLY THE MOST IMPORTANT AIRCRAFT EVER BUILT.

THIS IS THE ONE THAT THEY FIGURED OUT HOW TO FLY ON.

NARRATOR: NOW BRUCE IS GOING TO TRY AND FLY IT WHERE THE WRIGHT BROTHERS FLEW THEIRS OVER A CENTURY AGO.

WEAVER: AND THIS ONE IS AN EXACT REPRODUCTION OF THE ORIGINAL.

THE 1902 GLIDER IS WHERE THEY ACTUALLY CREATED THE CONTROL THAT THEY NEEDED TO HAVE SUCCESSFUL MANNED FLIGHT.

WEAVER: ALL RIGHT.

ARE YOU READY?

NARRATOR: HIGH WINDS TODAY MEAN THAT THE MACHINE MUST BE TETHERED FOR SAFETY.

BUT AS FOR LIFT AND CONTROL, BRUCE IS FLYING THE GLIDER ON HIS OWN, JUST AS WILBUR AND ORVILLE WOULD HAVE DONE.

WEAVER: FLYING IT, IT'S AMAZING HOW EFFICIENT THE GLIDER IS WITH ITS CONTROLS.

IT'S AN INCREDIBLE MACHINE.

WHAT I DIDN'T REALLY GRASP UNTIL I ACTUALLY FLEW IT SEVERAL TIMES WAS JUST HOW BRAVE THE WRIGHT BROTHERS WERE.

YOU KNOW, THEY WERE TAKING THIS AIRCRAFT THAT THEY'D INVENTED THEMSELVES-- NO ONE HAD EVER DONE IT SUCCESSFULLY BEFORE-- AND THEY WERE TEST PILOTS.

ACTUALLY BEING ABLE TO FEEL WHAT THE WRIGHT BROTHERS FELT, FLYING THROUGH THE AIR ON THEIR INVENTION, IT'S ABSOLUTELY OVERWHELMING.

NARRATOR: THE 1902 GLIDER SOLVED THE MOST DIFFICULT CHALLENGE, ADDING TRUE CONTROL OF FLIGHT, BUT IT WAS STILL JUST A GLIDER.

IT WASN'T UNTIL THE FOLLOWING YEAR THAT THE WRIGHT BROTHERS MANAGED TO CREATE AN ENGINE THAT WAS LIGHT ENOUGH TO POWER THEIR AIRPLANE.

AND SO, ON DECEMBER 17, 1903, THE WORLD'S FIRST POWERED FLIGHT TOOK PLACE AT KITTY HAWK.

IT HAD TAKEN OVER 1,000 YEARS FROM IBN FIRNAS AND HIS LEAP OF FAITH FOR HUMANS TO BE ABLE TO AT LAST TRULY FLY.

AND NOW AVIATION DEVELOPED RAPIDLY.

THE WRIGHT BROTHERS SOLD THEIR FIRST PRODUCTION AIRCRAFT IN 1908 FOR $25,000 TO THE U.S. DEPARTMENT OF DEFENSE.

THAT'S ALMOST $700,000 TODAY.

OVER THE NEXT DECADE, THE AIRPLANE WAS DEVELOPED AT BREAKNECK SPEED, ACCELERATED BY THE ADVENT OF WORLD WAR I.

AND AS WAR PLANES WENT HIGHER AND FASTER, NEW DANGERS AROSE, BUT IT WILL TAKE ANOTHER CHILDREN'S TOY TO TRIGGER THE NEXT BREAKTHROUGH IN FLIGHT.

MAN: BY THE 1920's, PILOTS WERE RISKING THEIR LIVES FLYING THROUGH THICK FOG, THROUGH COMPLETE DARKNESS.

FOR A PILOT, LOSING SIGHT OF THE HORIZON, EVEN FOR JUST A FEW SECONDS, CAN BE VERY DISORIENTATING.

AT BEST, THEY COULD VEER OFF COURSE, AND THAT COULD BE QUITE SCARY.

AT WORST, IT COULD BE FATAL.

AT THE TIME, THE AVERAGE LIFE EXPECTANCY FOR A PILOT WAS JUST THREE YEARS.

THE PROBLEM OF FLYING IN POOR VISIBILITY WAS ONE OF THE MOST PRESSING CHALLENGES OF THE DAY, AND THE SOLUTION TO THAT PROBLEM WAS FOUND BECAUSE OF THIS SHIP.

AL-KHALILI: THIS REVOLUTION BEGINS NOT ON LAND OR IN THE AIR, BUT AT SEA IN A DIFFERENT TIME WITH AN ATTEMPT TO SOLVE A VERY DIFFERENT PROBLEM.

IN 1838, THE GREAT ENGINEER ISAMBARD KINGDOM BRUNEL DECIDED TO BUILD THIS, HIS NEXT SHIP, THE S.S. GREAT BRITAIN, FROM IRON.

WHEN IT FIRST SAILED IN 1845, IT WAS THE LARGEST SHIP IN THE WORLD, A GRAND STATEMENT, AND, OF COURSE, EVERYTHING CHANGED.

THE AGE OF OAK SHIPS WAS OVER.

BRUNEL HAD KICK-STARTED THE AGE OF THE IRON HULL, BUT HAD ALSO UNWITTINGLY CREATED A PROBLEM.

FOR CENTURIES, SHIPS HAD BEEN FINDING THEIR WAY ACROSS THE HIGH SEAS ASSISTED BY A MAGNETIC COMPASS, ALWAYS POINTING UNFAILINGLY TOWARDS THE NORTH.

SUCH A VAST AMOUNT OF IRON INTERFERED WITH THE SHIP'S COMPASS.

THE DEVICE THAT HAD BECOME AN ESSENTIAL PART OF ANY VOYAGE TO SEA WAS NOW DANGEROUSLY UNRELIABLE.

THE S.S. GREAT BRITAIN HERSELF LOST HER COURSE...

BECAME GROUNDED OFF THE COAST OF NORTHERN IRELAND, AND WAS BEACHED FOR ALMOST A YEAR.

BUT WITH HUNDREDS OF IRON-HULLED SHIPS PUT OUT TO SEA EVERY YEAR, A RADICAL SOLUTION HAD TO BE FOUND, AND FOUND QUICKLY.

ELMER SPERRY WAS A SUCCESSFUL ENGINEER, INVENTOR, AND BUSINESSMAN... AND PROLIFIC PROBLEM-SOLVER.

BY 54, HE'D INVENTED A SEARCHLIGHT SIX TIMES BRIGHTER THAN EVER SEEN BEFORE.

SO, WHEN THE PROBLEM OF COMPASSES AND IRON SHIPS CAME TO HIS ATTENTION, HE WAS DETERMINED TO SOLVE IT.

OF ALL THE IDEAS THAT SURROUNDED AND FILLED THE WORLD OF ELMER SPERRY, THE ONE HE LOVED THE MOST WAS THE GYROSCOPE.

HE LOVED THE CURIOUS FORCES AND THE MECHANICAL PRECISION OF THE DEVICE.

ESSENTIALLY, IT'S A SPINNING WHEEL THAT, IF YOU SPIN IT VERY FAST, IT MAINTAINS THE SAME DIRECTION.

NO MATTER WHAT FORCES ACT ON IT, IT RESISTS THOSE FORCES THAT MIGHT TRY AND CHANGE ITS DIRECTION OF SPIN OR THE SPEED OF ROTATION.

SPERRY REALIZED THAT A SPINNING GYROSCOPE, WHICH IS NORMALLY JUST A CHILD'S TOY, WOULD, IF MOUNTED IN A GIMBALED FRAME AND KEPT SPINNING, MAINTAIN THE DIRECTION IT'S POINTING TO NO MATTER HOW THE FRAME AROUND IT MIGHT MOVE.

IF A MOUNTED GYROSCOPE WAS POINTED NORTH AND THEN SET SPINNING, IT WOULD REMAIN POINTING NORTH THROUGHOUT THE SHIP'S JOURNEY, AND UNLIKE A MAGNETIC COMPASS, IT WAS UNAFFECTED BY THE IRON HULLS OF THE NEW SHIPS.

NARRATOR: A FEW YEARS LATER, SPERRY'S THIRD SON, LAWRENCE, WHO WAS A KEEN AVIATOR, REALIZED THERE WAS A NEW AND PROFITABLE USE FOR THE GYROSCOPE.

WHAT IF IT COULD BE USED NOT JUST AS A COMPASS, BUT ALSO TO TELL A PILOT WHICH WAY WAS UP, EVEN IN A THICK FOG.

WE NOW CALL THE DEVICE AN ARTIFICIAL HORIZON.

AL-KHALILI: SPERRY CLAIMED THAT, WITH HIS NEW GYRO HORIZON, A PILOT COULD FLY WITHOUT BEING ABLE TO SEE THE TRUE HORIZON.

ESSENTIALLY, HE COULD FLY BLIND.

IN 1929, A PILOT NAMED JAMES DOOLITTLE VOLUNTEERED TO PUT THE SYSTEM TO THE ULTIMATE TEST.

HE CLOSED THE COCKPIT OF HIS BIPLANE TO BLOCK OUT ALL LIGHT.

LUCKILY FOR DOOLITTLE, THE SYSTEM WORKED.

WE SEE THIS HAPPENING TIME AND TIME AGAIN IN THE HISTORY OF SCIENCE, WHERE A COMPLETELY CHANCE DISCOVERY LEADS TO AN APPLICATION THAT NO ONE WAS EXPECTING.

NARRATOR: NOW COMMERCIAL AVIATION BEGAN IN EARNEST.

IN THAT SAME YEAR, THE FIRST COAST-TO-COAST AIRLINE SERVICE WAS LAUNCHED.

[MUSIC PLAYING] THE SERVICE ADVERTISED THE AMAZING JOURNEY TIME OF 48 HOURS FROM NEW YORK TO LOS ANGELES.

THE TRIP WAS THE HEIGHT OF GLAMOUR, COSTING $5,000 ONE WAY IN TODAY'S MONEY.

BUT IT WAS A REAL TEST OF ENDURANCE.

FIRST, PASSENGERS BOARDED AN OVERNIGHT TRAIN FOR A 530-MILE RIDE TO THE AIRPORT IN COLUMBUS, OHIO.

THERE THEY BOARDED A FORD TRIMOTOR AIRLINER FOR THEIR FIRST DAY OF FLYING.

THE PLANE HAD TO STOP FOUR TIMES TO REFUEL BEFORE THEY EVENTUALLY ARRIVED IN OKLAHOMA, WHERE THEY BOARDED ANOTHER SLEEPER TRAIN FOR THE NIGHT TO GET TO THE NEXT AIRPORT.

ON DAY TWO, THE PASSENGERS TOOK A SECOND AIRPLANE...

WHICH HAD TO STOP ANOTHER THREE TIMES.

FINALLY, AFTER TWO STRAIGHT DAYS OF TRAINS AND PLANES, LOS ANGELES CAME INTO VIEW.

WHILE THIS PROMOTIONAL FILM MAKES IT SEEM PIONEERING AND FUN...

THE REALITY WAS OFTEN SOMEWHAT DIFFERENT.

[THUNDER] FLYING AT JUST 5,000 FEET, THE TRIMOTOR WAS VULNERABLE TO BAD WEATHER, MAKING FOR AN UNPLEASANT RIDE.

AND THAT SEPTEMBER, A TRIMOTOR CRASHED ON MOUNT TAYLOR, ARIZONA...

KILLING ALL ON BOARD.

IT WAS THE FIRST COMMERCIAL AIRLINE DISASTER.

TO MAKE AIR TRAVEL BOTH SAFER AND FASTER, ANOTHER BREAKTHROUGH WAS NEEDED, THIS TIME INSPIRED NOT BY SOMETHING IN THE SKY, BUT SOMETHING FAR BENEATH THE WAVES.

THE RADICAL IDEA WAS TO USE DEEP-SEA DIVING TECHNOLOGY TO EXPLORE THE UPPER ATMOSPHERE.

MAYBE A PLANE COULD AVOID BAD WEATHER BY FLYING ABOVE IT AND TRAVEL FASTER THROUGH THINNER AIR.

IT MEANT VISITING A PLACE THAT THIS AIRCRAFT CALLS HOME.

FRANQUEMONT: THE U-2 IS MEANT TO FLY HIGH.

IT IS LIKE WRESTLING A BEAR DOWN LOW.

ONCE WE GET IT UP TO ALTITUDE, IT FLIES LIKE A SPORTS CAR.

SO, TODAY WE'RE GONNA FLY UP TO AROUND 70,000 FEET.

NARRATOR: THE U-2 IS ONE OF THE WORLD'S HIGHEST-FLYING AIRCRAFT, ABLE TO CRUISE AT OVER 13 MILES HIGH.

BUT 90-ODD YEARS AGO, NOBODY KNEW WHAT WAS POSSIBLE.

FRANQUEMONT: TODAY THERE WERE SOME THUNDERSTORMS AROUND, AND WE ACTUALLY CLIMBED HIGHER THAN THE THUNDERSTORMS.

WE'RE GOING TO BE ABOVE ALL THE WEATHER.

IT'S AN INCREDIBLE EXPERIENCE ANY TIME YOU GO UP HIGH LIKE THAT.

NARRATOR: THE DIFFICULTY WAS NOT JUST GETTING UP HERE.

IT WAS STAYING ALIVE ONCE YOU'D ARRIVED.

IN 1929, CAPTAIN HAWTHORNE C. GRAY ASCENDED TO OVER 40,000 FEET BY HELIUM BALLOON.

BUT WHEN THE BALLOON LANDED A DAY LATER, HE WAS FOUND DEAD AT THE CONTROLS.

ENTER AN AVIATOR WITH A NEED FOR SPEED.

[MUSIC PLAYING] WILEY POST HAD LOST AN EYE IN AN ACCIDENT AND USED THE INSURANCE MONEY TO GET INTO AVIATION.

IN 1931, HE AND HIS NAVIGATOR, HAROLD GATTY, CIRCUMNAVIGATED THE WORLD IN JUST EIGHT DAYS, EARNING THEM A WORLD RECORD, INSTANT FAME, AND A TICKERTAPE PARADE.

BUT WILEY POST WANTED MORE SPEED STILL AND BELIEVED THAT FLYING HIGH WAS THE SOLUTION.

TO DO IT, HE WOULD HAVE TO DEFEAT THE HIDDEN KILLER THAT LIES ABOVE THE CLOUDS.

HERE, AT BEALE AIR FORCE BASE, U-2 PILOTS ARE SUBJECTED TO TESTING IN A CHAMBER THAT REPLICATES THE DANGERS OF HIGH-ALTITUDE FLIGHT.

THOMAS: THIS CHAMBER IS PRETTY SIGNIFICANT.

IT'S ABOUT 60 YEARS OLD.

IT IS A GIANT IRON BOX WITH LOTS OF VALVES AND THINGS LIKE THAT, BUT WHAT WE DO IS IT'S CONNECTED TO A VACUUM SYSTEM, AND WE CAN PLACE PILOTS INSIDE, EVACUATE SOME OF THE AIR THAT THEY'RE IN SO THAT WE CAN SIMULATE THE REDUCED PRESSURE THAT THEY WOULD EXPERIENCE IF THEY WERE AT ALTITUDE UNPRESSURIZED.

NARRATOR: EXPERIENCING THE RISKS OF HIGH ALTITUDE IS A VITAL PART OF PILOT TRAINING, THE EXACT SAME DANGERS THAT WILEY POST FACED.

SO, GO AHEAD AND OPEN UP YOUR VISOR.

THOMAS: SO, HE'S AT ROUGHLY 24,000 FEET.

HE'S IN AN ALTITUDE WHERE WE CAN ACTUALLY EXPOSE HIM TO THE AMBIENT PRESSURE.

WOMAN: OK.

SO, FIRST, CHRISTIAN... THOMAS: WE'LL HAVE THEM WORK THROUGH SOME MENTAL SKILLS-- NAME OFF STATE CAPITALS OR DO MATH PROBLEMS.

OK.

SO, WHAT'S THE CAPITAL OF CALIFORNIA?

SACRAMENTO.

THOMAS: FOR FOLKS LIKE WILEY POST, WHO WERE EXPLORING THIS ENVIRONMENT, THEY NOTICED THAT WITH SUSTAINED EXPOSURE TO EVEN THOSE MODERATE ALTITUDES ABOVE 10,000 FEET, THAT IT HAD SERIOUS FATIGUING EFFECTS ON YOUR MENTAL PROCESSES.

WOMAN: WHAT IS 90 MINUS 4?

86.

WOMAN: OK. CAN YOU COUNT BACKWARDS FROM 100 BY 3?

97... HA HA.

UM... 94, 91... WOMAN: OK. YOU'RE AT 87.

OK. 87.

UH...SO, 89.

80...79.

HA.

SUDDENLY A LITTLE CONFUSION.

DEFINITELY STARTING TO FEEL A LITTLE WARM IN MY FACE AREA.

NARRATOR: THIS MENTAL CONFUSION CAN LEAD TO MISTAKES WHICH, IN THE AIR, CAN BE FATAL.

THOMAS: THEN AN EMERGENCY HAPPENS.

NOW YOU'RE TRYING TO COMBAT THAT EMERGENCY WITH LESS THAN ALL CYLINDERS FIRING IN YOUR BRAIN, SO, LESS THAN YOUR FULL MENTAL CAPACITY.

NARRATOR: WILEY POST NEEDED A WAY TO PROTECT HIS BRAIN FROM A LACK OF OXYGEN.

HE BUILT AN OUTFIT INSPIRED BY A DEEP-SEA DIVER'S SUIT, ONLY INSTEAD OF KEEPING WATER OUT, IT WOULD KEEP AIR IN.

THOMAS: WILEY POST, REALIZING THAT WE NEED SOME SORT OF SOLUTION TO KEEP THE AVIATOR SAFE AT THE ALTITUDES THAT THEY WERE EXPLORING, DESIGNED AND BUILT A PRESSURE SUIT.

THAT SUIT CAN CREATE A NEW LIVABLE ATMOSPHERE AROUND THE AVIATOR.

NARRATOR: TODAY'S SUITS WORK ON THE SAME PRINCIPLE.

AND TO SHOW JUST HOW EFFECTIVE THEY ARE, THE TRAINEE IS GOING TO CONTINUE HIS ASCENT.

THOMAS: LOOKING AT THE ALTIMETER, THIS GENTLEMAN IS NOW PASSING THROUGH A FLIGHT LEVEL OF 36,000 FEET PRESSURE ALTITUDE EQUIVALENT.

HE'S NOW GETTING INTO A POINT WHERE HIS SUIT IS GONNA START DOING ITS JOB AND KEEPING HIM SAFE.

OK. WE'RE HEADED INTO FLIGHT LEVEL 6-0-0.

GETTING READY TO SEE... NARRATOR: AS THE PRESSURE FALLS EVEN FURTHER, NEW DANGERS COME INTO PLAY.

AT THIS POINT, ONLY THE SUIT IS KEEPING OUR MODERN PILOT ALIVE, JUST AS WILEY HOPED IT WOULD.

WOMAN: HERE WE GO.

THOMAS: HE'S ABOVE ARMSTRONG'S LINE RIGHT NOW.

ARMSTRONG'S LINE IS 63,000 FEET, WHERE WATER BOILS AT 98.6 DEGREES, YOU KNOW, YOUR BODY BEING ROUGHLY 2/3 WATER, AND SO THE BLOOD IN HIS VEINS WOULD LITERALLY START TO BUBBLE.

NARRATOR: ON A TEST FLIGHT IN 1934, WILEY POST LAID HIS LIFE ON THE LINE.

UNFORTUNATELY, THE INSTRUMENTS MEASURING HIS ALTITUDE FAILED, BUT HE EXCEEDED 30,000 FEET AND REACHED 340 MILES AN HOUR, NEARLY DOUBLE WHAT THE PLANE COULD DO AT SEA LEVEL.

FRANQUEMONT: IT'S REALLY INCREDIBLE TO THINK THAT SOMEBODY WOULD HAVE THE FORESIGHT AND THE COURAGE TO GO UP THERE AND TEST THE LIMITS OF THE HUMAN BODY, TO THINK THAT SOMEBODY WAS DOING THAT ALMOST 100 YEARS AGO, WHEN WE KNEW HARDLY ANYTHING ABOUT THAT PART OF THE ATMOSPHERE.

NARRATOR: WILEY'S PIONEERING FLIGHTS COMPLETELY CHANGED THE FACE OF AVIATION.

AIRCRAFT WERE ABLE TO FLY MUCH HIGHER AND THEREFORE MUCH FASTER.

BY 1938, WE HAD AIRLINERS IN WHICH THE ENTIRE CABIN WAS PRESSURIZED.

NOW PILOTS AND PASSENGERS COULD TRAVEL IN COMFORT, WITHOUT THE NEED FOR BULKY PRESSURE SUITS LIKE THE ONE DEVELOPED BY WILEY POST.

BUT MODERN-DAY AIR TRAVEL REQUIRED ANOTHER BREAKTHROUGH, BECAUSE PROPELLER-DRIVEN PLANES DON'T WORK VERY WELL AT HIGH ALTITUDE.

THIS REVOLUTION STARTED WITH YET ANOTHER BOY WITH YET ANOTHER TOY.

BROWNING: FRANK WHITTLE WAS THE SON OF A MECHANIC, BORN IN ENGLAND IN 1907.

AGE FOUR, HE WAS GIVEN A TOY AIRPLANE WITH A WIND-UP PROPELLER.

JUST LIKE THE WRIGHT BROTHERS, THE TOY INSPIRED A LIFELONG LOVE OF AVIATION.

AND SO, WHEN HE WAS 16 YEARS OLD, HE JOINED THE ROYAL AIR FORCE AND LEARNED TO FLY.

THEN, AS A STUDENT, HE WROTE AN EXTRAORDINARY ESSAY OUTLINING HIS VISION OF THE FUTURE OF FLIGHT, WITH AIRCRAFT ABLE TO FLY MUCH HIGHER AND MUCH FASTER.

I THINK THAT, AT THE AGE OF 21, TO MAKE THESE OBSERVATIONS AND TO NOT ONLY THINK THROUGH WHAT MIGHT BE POSSIBLE IN TERMS OF OVERCOMING THEM, BUT ACTUALLY TO PUT IT DOWN IN WRITING AND TO PUBLISH SUCH A COMPREHENSIVE ALMOST PREDICTION OF WHERE THE FUTURE SHOULD GO, I THINK THAT'S QUITE A REMARKABLE STEP.

EVEN AS HE WAS LEARNING TO FLY PROPELLER PLANES, HE WAS DEVELOPING HIS IDEAS, A COMPLETELY NEW KIND OF ENGINE.

PISTON ENGINES AND PROPELLERS ARE INHERENTLY LIMITED WHEN IT COMES TO PROPELLING AIRCRAFT HIGH AND FAST.

FRANK WHITTLE WAS DETERMINED TO DEVELOP SOMETHING BETTER, AND HE CAME UP WITH THIS, THE JET ENGINE.

NEWSREEL ANNOUNCER: HERE IT IS.

IN THE PRECISE LANGUAGE OF THE ENGINEER, IT'S CALLED A JET PROPULSION GAS TURBINE.

TO YOU AND ME, IT'S THE JET ENGINE.

BROWNING: A CAR ENGINE WORKS BY TAKING FUEL AND AIR INTO A CYLINDER, INTO A SERIES OF CYLINDERS, AND COMPRESSING THAT MIXTURE UNTIL YOU THEN IGNITE IT, AND THE EXPLOSION DRIVES THE CYLINDER BACK.

FRANK WHITTLE REALIZED THAT IF YOU COULD MAKE THAT PROCESS CONTINUOUS, IT WOULD BE FAR MORE EFFICIENT.

[JET ENGINE ROARING] WHITTLE'S DESIGN WORKS LIKE THIS.

AT THE FRONT, AIR ENTERS A COMPRESSOR, WHICH, AS THE NAME SUGGESTS, COMPRESSES THE AIR.

THIS IS MIXED WITH FUEL AND SET ALIGHT, WHICH CREATES A JET OF HOT EXHAUST WHICH CREATES THE THRUST.

THAT EXHAUST ALSO SPINS A TURBINE, LIKE A SMALL WINDMILL, WHICH IS ATTACHED TO THE COMPRESSOR AT THE FRONT, MAKING THE WHOLE PROCESS SELF-SUSTAINING.

IT'S A VERY NEAT PACKAGE WITH A LOT OF THRUST.

WHITTLE BELIEVED THAT A JET ENGINE WOULD HAVE MORE POWER THAN A PROPELLER ENGINE OF THE SAME WEIGHT, SO A JET PLANE SHOULD BE FASTER.

MAN: I'M SORRY TO SAY WE'VE HAD ANOTHER BLADE FAILURE.

BROWNING: UNFORTUNATELY, WHITTLE HAD GREAT DIFFICULTY GETTING ANYONE INTERESTED IN HIS IDEA.

THE R.A.F.

THOUGHT IT WOULD NEVER WORK, AND INDEED, SOME OF HIS EARLY TESTS ENDED IN DISASTER.

IN A FILM MADE IN 1950, WHITTLE HIMSELF REENACTED THE STORY OF THE JET.

[JET ENGINE ROARING] COME BACK!

COME BACK!

[EXPLOSION] BROWNING: BUT EVENTUALLY, AFTER NINE YEARS OF DEVELOPMENT, HE SUCCEEDED IN MAKING THE WORLD'S FIRST WORKING JET ENGINE.

[DRAMATIC MUSIC PLAYING] WHITTLE'S FIRST JET-POWERED FLIGHT WAS ON THE 15th OF MAY, 1941.

THE JET AGE HAD BEGUN.

FRANK WHITTLE WAS A PIONEER OF HIS AGE.

THE FACT THAT A HUGE PROPORTION OF THE WORLD'S POPULATION GET CAN ON A PLANE FOR RELATIVELY LITTLE MONEY AND TRAVEL ANYWHERE IN A MATTER OF HOURS IS ALMOST ENTIRELY DOWN TO HIS BREAKTHROUGHS.

WHITTLE'S JET ENGINE, OFTEN CALLED THE GAS TURBINE, DOMINATES MODERN AIRCRAFT DESIGN.

NOT ONLY BECAUSE IT CAN OPERATE AT HIGH ALTITUDES, BUT ALSO BECAUSE OF A PROPERTY THAT IS HARDER TO APPRECIATE.

JET ENGINES, EVEN MINIATURE ONES, PACK AN ENORMOUS AMOUNT OF POWER FOR THEIR WEIGHT.

HERE WE HAVE A REAL-LIFE JET ENGINE.

IT'S A MINIATURE VERSION OF WHAT YOU GET ON A... A PLANE THAT YOU GO ON HOLIDAY ON OR EVEN A JET FIGHTER.

AND WHAT WE'RE GONNA DO IS FIRE THEM UP.

THERE'S A LITTLE CONTROL IN HERE.

YOU CAN HEAR THE ELECTRIC MOTORS WHINING AND STARTING UP NOW.

AS THAT STARTS TO FLOOD THE COMBUSTION CHAMBER WITH AIR, AND YOU CAN HEAR NOW, FUEL STARTS GOING IN THE COMBUSTION CHAMBERS.

AND IF YOU LOOK CAREFULLY DOWN THERE, YOU CAN SEE THAT FUEL STARTING TO BURN.

[JET ENGINES ROARING] NARRATOR: IN RICHARD BROWNING'S HANDS, WHITTLE'S INVENTION ALLOWS A MAN TO FLY IN A WAY THAT NOT EVEN IBN FIRNAS, LEONARDO DA VINCI, OR OTTO LILIENTHAL COULD HAVE IMAGINED.

[JET ENGINES ROARING] BROWNING: WHEN YOU SQUEEZE THAT TRIGGER, THOSE ENGINES WILL BE PUTTING OUT A THOUSAND HORSEPOWER, AND AS YOU START VECTORING THAT DOWNWARDS, THE WEIGHT JUST COMES OFF YOUR FEET, AND YOU'RE AIRBORNE.

AS SOON AS YOU LIFT OFF, IT DOES FEEL LIKE IT'S YOU FLYING.

IT DOESN'T FEEL LIKE YOU'RE IN A FLIGHT VEHICLE.

IT'S A REAL COLLABORATION BETWEEN MAN AND MACHINE.

[THEME MUSIC PLAYING] NARRATOR: TODAY, A NEW BREAKTHROUGH IN AVIATION IS UNDERWAY.

ALL OVER THE WORLD, COMPANIES ARE DEVELOPING DIFFERENT CONCEPTS OF THE FLYING MACHINE.

CALIFORNIA STARTUP KITTY HAWK, NAMED FOR THE PLACE WHERE THE WRIGHT BROTHERS LEARNED TO FLY, IS TESTING SMALL SELF-FLYING MACHINES THAT THEY HOPE WILL REPLACE THE AUTOMOBILE AS THE MOST COMMON WAY TO TRAVEL.

OTHERS SEE THE FUTURE AS A DEVELOPMENT OF WHITTLE'S JET ENGINE, ONLY POWERED BY ELECTRICITY.

THIS CONCEPT AIRCRAFT USES A JET THAT HAS AN ELECTRIC MOTOR AT ITS CORE.

IF BATTERY TECHNOLOGY CAN BE IMPROVED TO THE POINT WHERE THEY ARE LIGHT AND POWERFUL ENOUGH, THE ELECTRIC AIRLINER COULD BE THE NEXT STEP IN OUR JOURNEY TO THE SKY.

BUT IF THE AIM IS TO GO HIGHER AND FASTER THAN BEFORE, AS IT ALWAYS HAS BEEN, THEN HYPERSONIC HIGH-ALTITUDE FLIGHT WILL REVOLUTIONIZE MASS TRANSPORT ALL OVER AGAIN.

BRITISH COMPANY REACTION ENGINES IS TESTING AN ENGINE THAT COULD WORK ALL THE WAY FROM THE GROUND UP TO THE EDGE OF SPACE.

IT USES A VERSION OF THE JET WHICH TURNS INTO A ROCKET AT ABOUT THE ALTITUDE OF THE U-2 SPY PLANE.

IF IT WORKS, THE PLANE COULD CRUISE AT SEVERAL TIMES THE SPEED OF SOUND, ALLOWING US TO TRAVEL AROUND THE WORLD IN A FRACTION OF CURRENT FLIGHT TIMES.

WHATEVER THE FUTURE HOLDS, WE, AS A SPECIES, OWE OUR ABILITY TO FLY TO THE PIONEERS OF THE PAST, FROM WHITTLE'S DETERMINATION TO MAKE THE JET WORK TO WILEY POST'S WILLINGNESS TO RISK HIS OWN LIFE EXPLORING THE UPPER ATMOSPHERE, FROM SPERRY'S GROUNDBREAKING IDEA TO USE A CHILD'S TOY TO CONQUER THE PROBLEM OF REDUCED VISIBILITY, RIGHT BACK THROUGH THE WRIGHT BROTHERS' EXTRAORDINARY MACHINES, LILIENTHAL'S SELFLESS SACRIFICE, GEORGE CAYLEY'S DETERMINATION TO UNDERSTAND LIFT, AND DA VINCI'S CONCEPT OF A MACHINE THAT DOES THE FLYING, ALL THE WAY BACK TO IBN FIRNAS, THE MAN WHO JUMPED INTO THE VOID.

WITHOUT THEM, WE WOULD NEVER HAVE LEARNED TO FLY.

[DRAMATIC MUSIC PLAYING] NEXT TIME ON "BREAKTHROUGH," MECHANICAL BEINGS HAVE THE POTENTIAL TO CHANGE EVERYTHING.

HOW WE GOT THEM IS A STORY OF ASTONISHING TWISTS AND AMAZING TURNS.

IT WOULD TAKE AN ANCIENT GREEK LEGEND AND A CHANCE CONVERSATION IN THE PSYCHIATRIC HOSPITAL, A CHILD SHELTERED FROM THE EXCESSES OF HER FAMOUS FATHER, AND THE MISSION TO MARS TO GIVE US THE ROBOT.

[THEME MUSIC PLAYING] TO ORDER "BREAKTHROUGH: THE IDEAS THAT CHANGED THE WORLD" ON DVD, VISIT shopPBS OR CALL 1-800-PLAY-PBS.

THIS PROGRAM IS ALSO AVAILABLE ON AMAZON PRIME VIDEO.