How Planes Work

What are the physics behind flight? We demystify the concept of lift and explain how many sources get the explanation wrong.

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Episode Transcript

Speaker 1 (00:04):
Welcome to Tech Stuff, a production of I Heart Radios
How Stuff Works. Hey there, and welcome to tech Stuff.
I'm your host, Jonathan Strickland. I'm an executive producer with
How Stuff Works and I Heart Radio and I love
all things tech and um I've been going on a
lot of trips lately, both for work and for my

(00:26):
personal life, you know, going on vacations and stuff, which
means that I tend to get on planes quite a lot.
So I thought today we talked about the history of
airplanes and how airplanes work. I've talked a lot about
different parts of planes in the past, but after doing
a quick search, I realized I never really done a
full episode about how planes themselves work. This is actually

(00:49):
a pretty tricky field, as it is one that has
been the subject of a lot of discussion as well
as misinformation or at least an incomplete explanation of how
things work, or an incorrect explanation of the how. The
why tends to be correct, but the how tends to
be confused, and it has led to jokes and memes
that ultimately, you know, airplanes work on some sort of

(01:12):
magic that depends upon us believing that it will work
sort of like the Peter Pan theory of flight, and
that's definitely taking things to extremes, and no one really
believes that. But when you consider all the various explanations
for what is going on, you can feel like the
joke might be coming from a pretty sincere place. So
let's start before we get into the how, with the

(01:34):
history of flight, because you guys know how much I
enjoy going into history lessons on this show. This is
no exception. So there were a lot of people who
dreamed of mastering flight over the past several hundred years,
thousands of years actually. Many attempted to emulate the way
birds fly, which seems pretty understandable. You see birds soaring

(01:58):
through the sky or darting about, and you think, well,
what's the secret there? How can we do the same thing,
And so lots of people tried to emulate that. They
created various rigs or devices that had moving wings, and
the thought was that if we could just build wings
of the right size that can move at the proper
speed and the proper range of motion similar to that

(02:21):
of a bird's wings, we too could fly through the sky. Now,
the name for this type of machine one that has
movable wings is an ornithopter, and legend has it that
Arcatas of Tarentum made a wooden bird with this type
of wing motion back in four hundred b C. And

(02:44):
you might know from Greek mythology the story of Daedalus
and Icarus, who are able to fly using man made
wings attached to their arms, at least they did until
Icarus flew too close to the sun spoiler alert. Leonardo
dive and she similarly worked on a few theoretical designs
that relied upon moving wings in the late fourteen hundreds. UH.

(03:07):
Some people argue that da Vinci's designs would ultimately lead
toward the development of the helicopter, but generally speaking, the
movable wing design remained impractical. It wasn't providing enough lift
or thrust to actually achieve flight. At best, the machines
would allow for very short, unimpressive hops, like maybe hopping

(03:27):
an inch off the ground, and at worst they didn't
manage to lift up anything at all. However, Leonardo da Vinci,
along with several other egg heads in history like Galileo
and Isaac Newton, among many others, would advance our understanding
of aerodynamics, which is the study of properties of moving air,
particularly as it has to do with interactions with solid objects.

(03:51):
By understanding how moving air affects solid objects and vice versa,
we could start to build working theories on how to
leverage that knowledge and create a working heavier than air
flying machine. Now, this work was expanded upon by mathematicians
and engineers people like John Smeaton, Daniel Bernoulli, and Leonard Euler.

(04:13):
They explored the relationship between air pressure and air velocity.
A hoity toity by the name of George Kyley would
prove to be incredibly important in our understanding. He proposed
that any working aircraft would need separate systems to provide lift, propulsion,
and control, something the famous Right Brothers would repeat in

(04:34):
the early nine hundreds. He also began to move away
from the ornithopter design to a fixed wing approach for aircraft. So,
in other words, the wing itself doesn't move with relation
to the body of the aircraft. It stays fixed in place,
and other elements are what allow the aircraft to fly.

(04:56):
You don't have to worry about having the wings move
in any particular path turn Now, Kayley's work led him
to the conclusion that the way to produce lift was
to design a machine that would create an area of
low pressure above the wing and an area of higher
pressure below the wing. So above the wing you have

(05:16):
very low pressure. Comparatively speaking, below the wing you have
very high pressure. So you've got support under you, right,
You've got air pushing up against the wing from below
and not not as much you know, air pressure above,
So the high pressure beneath would lift the wing up,
acting as a support in a way. Kayley was specifically

(05:39):
exploring wing designs that had an arch to them, and
his ideas were sound and in line with Bernoulli's theorem,
which describes the behavior of moving fluids. And we have
to remember that our atmosphere is a fluid. In this sense,
gases have fluid i movement. Gases are fluids, just as
liquids are fluids. It this is where a lot of

(06:01):
sources get things a little muddled, and it's understandable, but
it ends up being a a fundamental misunderstanding of what
is going on. So the incorrect explanations tend to be
right in describing the fact that the reason fixed wing
flight works is that the movement of the aircraft through

(06:21):
the air creates an area of low pressure above the
wing in an area of high pressure below the wing.
But they often mess up the actual explanation of how
this is happening, what is actually going on. So let
me give you the wrong way to describe it first
and we'll get that out of the way. So typically
the description starts with the design of the wing itself,

(06:44):
which is usually described as having a flat bottom and
a curved upper part, in which the front part of
the wing, the leading edge, ends up curving up to
become a bit thicker towards the front of the wing
and then tapers to ord the back of the wing,
where the upper surface you know, slopes back down and
meets the lower surface for the back edge or trailing

(07:07):
edge of the wing. And if you're looking at the
cross section of the wing, then you kind of get
a sideways tear drop shape right the the leading edge
gets thicker and then tapers back down until it meets
again at the trailing edge. Um, by the way, the
technical name for the cross section of a wing is

(07:30):
an airfoil. Air Foils do not necessarily have to follow
that shape, but many do. Many early air foils would
follow that curved design. Now, again, the wrong description for
what is causing lift states that when the wing moves
through a fluid, or conversely, when a fluid moves past

(07:50):
the wing, either way will work. There has to be motion,
but the motion can work in either way. You can
either have the fluid moving at a proper speed against
the solid object. That's the way we test things out
in wind tunnels. We have a stationary object and we
blow wind past it, or the object itself can move

(08:10):
through the fluid, which is the way airplanes work. They
fly through the air either way. According to this incorrect explanation,
the air molecules when they hit that leading edge, that
front edge of the wing, end up splitting into two
different pathways. Some of the air molecules are traveling over
the top surface of the wing and some are traveling

(08:32):
on the bottom surface of the wing. Well, the top
surface of the wing has that curve to it, which
means that the air molecules have to travel further from
the front edge to the back edge right than it
would on the lower side of the wing because the
lower side is straight, and as we know, the shortest
distance between two points is a straight line, So the

(08:53):
bottom edge of a wing is a straight line to
go from the leading edge to the trailing edge straight path.
The if you're going over the top, you have to
follow that curve, which means you're actually traveling more distance,
and so that is a longer way to travel. And
according to this incorrect description of lift, the air molecules

(09:16):
traveling on top of the wing have to go faster
than the molecules traveling below the wing, and then they
meet back up at the trailing edge. So let's say
you've got air molecule one and air molecule to. Molecule
one's traveling over the wing, Molecule two is traveling under
the wing, and they both meet at the far end.
But in order to do that, molecule one has to

(09:38):
travel faster than molecule two. And according to bern Newley's
theorem Daniel Burn Newley, a fast moving fluid is at
a lower press pressure than a slower moving fluid. So
says this description, the air pressure above the wing is
lower than the air pressure below the wing. Now it
is true that the air pressure above the wing is
lower and that the air pressure below the wing is higher.

(10:02):
I keep thinking that I've said this is the wrong way,
because I'm talking about above and below and higher and
lower than you flip them right, because everything above the
wing is a lower pressure, everything below the wing is
a higher pressure. That part is right. So the destination
is correct. It's the journey to get there that we've
got wrong, because, uh, there would need to be some

(10:23):
reason for the upper and lower air molecules to have
to travel to arrive at the same destination at the
same time. But there's no reason for that at all.
There's no reason why air molecule one and air molecule
to have to meet back up again at the trailing edge.
One of them can easily travel faster than the other.
There's no conservation of velocity between the two. Now, if

(10:46):
it were true that the air molecules on the top
and the air molecules on the below had to travel
at a speed where they would meet up again, that
that was absolutely necessary. This description would work if that
were true. If air molecule wanted two had to meet
on the far end again, this would be an accurate theory. However,
the flaw in this description goes by the name the

(11:08):
equal transit theory or sometimes the longer path theory. Now,
before I explain what is really going on with lift.
Let's consider for a moment how we know this common
description is incorrect. First, if this were actually how wings
would generate lift, it would mean that any plane that
did not have this wing design would fail to generate

(11:30):
lift because you wouldn't have that longer path on top. So,
in other words, if you had a straight wing design
for your aircraft, there's no way it would be able
to fly. It could not generate lift if this were
in fact the only way it worked, and we know
that's not the case. There are lots of aircraft out
there to have a flat wing design. A paper airplane
doesn't have a curved wing, and it can generate lift.

(11:53):
You just have to give it enough thrust and it
will fly. It doesn't immediately plummet um. It does lose
speed because of drag. We'll talk about dragon a little bit,
and if it loses speed then it's not generating enough
lift to maintain flight, so it will eventually fall. But
that's a flat wing and it does work. So flat
wings can work as well as curved wings, so that

(12:15):
part is out Further, if that explanation were absolutely true,
planes with curved wings would never be able to fly
upside down, because if they were to roll over, and
the whole reason why lift was generated was because air
was traveling further on one side than the other and
then meeting back up with the air molecules, then the

(12:36):
plane's wings would actually create lower air pressure below the
plane and higher air pressure above the plane that would
drive the plane downward. So instead of having lift holding
the plane up, you would be creating a force that,
combined with gravity, would pull the plane downward or push
the plane downward, and you would end up with a

(12:56):
catastrophic result. But we know that's not the case. Trained
pilots can fly upside down, and properly designed aircraft, you know,
aircraft that can withstand the forces of rolling over on
on to their backs. You can still fly inverted that way.
So clearly there has to be something else going on here.

(13:16):
The explanation does not work as it stands, so to
be clear, the end result of how lift works is
the same in that a plane's wings do create areas
of low pressure above and high pressure below the wing,
but the way they do it is different from the
explanation commonly given. So, in other words, the common explanation
gives us the right end result but uses the wrong

(13:38):
way to get there. So it's sort of like using
the wrong process to solve a math problem but accidentally
getting the right answer anyway. Sure, the answer is technically
what you were looking for. The important part is not
getting the right answer, it's knowing the right way to
get to that answer. So let's talk about what's actually

(13:59):
going on. First. Air does in fact move faster over
the top edge than the lower edge of the wing,
much faster. In fact, air molecules traveling over the top
of the wing will arrive at the trailing edge before
air molecules traveling on the lower side. So that air
molecule one and two example I gave before, air molecule

(14:19):
one is going over the wing, air molecule two is
going under the wing. Air molecule one is actually going
to arrive at the trailing edge first. They don't meet
up again, so there's none of those air molecules splitting
up at the leading edge meeting at the trailing edge.
The air molecules traveling beneath the wing are actually meeting
up with totally new air particles that hit the leading edge.
Later on, more importantly, a wing deflects air and then

(14:43):
the way it does so creates the area of lower
pressure above the wing and the area of higher pressure
below the wing. You can think of the air below
a wing as getting compressed or squished, while the air
immediately above a wing enters into more space than it
had previously occupied. And this is because we're talking about
a solid structure moving through a fluid. The difference in

(15:04):
air pressure is what causes the big change in the
fluids speed. So, in other words, the change in air
pressure is what is effect affecting those air molecules speed
across the wing. It's the opposite of what the equal
transit theory states, which is that the difference in speed
causes the change in pressure. Actually, it's the change in
pressure that causes the difference in speed, and the air

(15:27):
molecules traveling both on the top side of the wing
and the bottom will at the end have a downward
velocity once they leave the trailing edge of the wing.
So why does the air traveling over the wing move
downward at the end. If the air molecules moving over
the top of the wing this curved surface in your
typical airfoil, why would those air molecules be moving downward?

(15:48):
I mean surely they would just continue horizontally in a
straight line right now. It's because in our system we
still have the atmosphere above the plane to consider that.
You know, when we're first talking about air pressure around
the wing, we're looking at the immediate area around the wing,
but you still have all the rest of the atmosphere
above the plane to consider. Now, immediately over the wing,

(16:09):
the air pressure is lower due to the presence of
this physical object moving through a fluid, or the fluid
moving across the object, or both, because it's all a
matter of perspective. But above that you still have all
that atmosphere a normal air pressure depending on that altitude.
So all that air is still pushing down on the

(16:30):
area around the plane, and it starts pushing down on
that lower pressure air, and that forces that lower pressure
air downward at the trailing edge of the wing. And
this brings us to another big important factor and lift
called down wash, that is the amount of air the
wing is forcing downward. Now, according to Isaac Newton's third
law of motion, if you have a mechanical system applying

(16:51):
force in one direction in a system, and equal opposite
force applies to that mechanical system, so an airplane, for
saying air downward, will also experience lift upward. It's equal
to the amount of force of the air going down.
This is easier to imagine if we think about a helicopter, right.
A helicopter has rotors that act similar to the way

(17:14):
and airplanes air foils works. The rotors rotate in a circle,
So instead of a plane moving horizontally through a fluid,
you have this rotor that's rotating around in a circle
and that forces air downwards, and that creates the lift
that allows helicopters to fly. Airplane wings do the same thing,
but it's less obvious to us. Those downward traveling air

(17:35):
molecules at the trailing edge of a wing are the
down wash of a plane, and it's a secondary source
of lift along with that air pressure description I just gave,
So it's not the primary source. It's secondary, but it
does contribute to the lift that the plane experiences. Now,
this is why an airplanes wings aren't perfectly horizontal with
regard to the body of the plane. If you look

(17:56):
at an airplane, you will notice that the wings have
a bit of a to them, so that the leading
edge of the wing is actually pointed up a little bit,
and the trailing edge is pointed down a little bit,
and this creates what we call the angle of attack,
and the angled wings encourage this down wash effect. If

(18:16):
you've ever put your hand out into the wind and
you tilted your hand in different ways and you get
to that sweet spot where you feel like, oh, well,
now my hand is staying up because of the angle
it's at as it's going through the wind, like if
it's out a car window. By the way, don't do that,
it's dangerous. But if you were to do that and
you felt it, you know what I'm talking about the
same thing with airplane wings. That's why they're at that tilt,

(18:39):
all right. So that's the explanation of the lift. And
in a moment I'll talk more about how the right
brothers or I'm creating a working heavier than air flying machine.
But first let's take a quick break. Now, I just

(18:59):
spent a lot of time going over lift. But that's
just one of the forces that are acting on a
plane in flight. And I mentioned one other briefly as well.
There are three other forces that are all acting on
a plane. So for total you've got lift. That's an
upward force on the plane. There's thrust that's the forward

(19:20):
force of a plane then, and you have to have
your thrust to be strong enough to create an airflow
around the wings to generate the lift to keep a
plane in flight. So you need to be moving forward
enough through the fluid, fast enough through the fluid so
that you can generate lift, or the fluid has to
be moving fast enough past you in order to do that. Again,

(19:41):
it's all a matter of perspective. If a plane moves
too slowly through the air, it won't create the difference
in air pressure and down wash sufficient enough to maintain lift,
So thrust is really important. Drag is a force that
opposes the forward motion of the aircraft. So this is
sort of the force that's acting uh in a backward

(20:01):
motion against the aircraft. It's a mechanical force generated by
the interaction of a solid body with a fluid, and
it depends upon the difference in velocity between the solid
object and the fluid. You experienced drag if you've ever
been swimming pool. You're just walking through and you feel
that resistance. That resistance is drag. You're forcing water molecules
to move around you as you walk through. Uh, friction

(20:23):
plays a factor in this. There's also a concept called
induced drag, which involves the way that the air pressure
is is changing and sort of how that is um
reconciling at the trailing edge of a wing. But it
gets really technical, and I figure you guys probably need
a break after I tackled lift. Suffice it to say,

(20:45):
drag opposes forward motion. So through aircraft design and propulsion systems,
we have to overcome drag to maintain a proper forward
velocity to maintain lift. So we do that with making
aircraft more aerodynamic, you know, reducing that resistance, and by
having appropriately powerful engines to propel with enough thrust to

(21:09):
maintain lift. The fourth force in flight is gravity. This
is obviously the force pulling downward on the plane. So
we have thrust that's the forward force, drag which is
the backward force, lift which is the upward force, and
gravity which is the downward force. All of these are
vectors because they all have an amplitude and a direction.

(21:30):
So aircraft design has to take all of those forces
into account. All right, So we got the technical description
of the forces acting on the planes out of the way,
let's get back to the history of stuff. I'll keep
in mind that throughout this history description that I'm doing,
people were still sussing out the nature of lift, as
is obvious by the fact that we still today have

(21:50):
textbooks and articles that give an incorrect explanation of what
is going on, or maybe how I should I should
say how it is going on now. In the eighteen seventies,
a couple of engineers, one named Francis h Winham and
John Browning Is the other built the first wind tunnel
and that would become a critical component for testing wing
designs and learning more about the practical effects of those designs.

(22:14):
More work was done by a dude named Horatio Phillips.
A lot of really great names in this history. By
the way, Horatio Phillips built an improved wind tunnel and
created an airfoil design that would become the basis for
most wing designs in the following decades. Then we have
Auto Lelandhall. He was a or Lilonhall. He was a
German engineer who took Cayley's work and began serious testing

(22:39):
of various wing designs and angles of attack to find
out what would work best, what is the most efficient
way to generate lift? What's the best design and best
angle to get that effect? And he saw that different
angles of attack allowed for different results and lift. Angling
a wing could improve the ability to generate lift up

(23:00):
to a point, and then beyond a certain angle which
is around fifteen degrees uh, the ability to generate lift
would drop off again. So as work became the basis
for many other engineers who followed, including the Right brothers,
and Otto himself was no slouch. He built several gliders,
including biplane gliders, and he began conducting test glide flights,

(23:22):
both manned and unmanned ones, and he probably went on
more than two thousand, maybe as many as twenty hundred
test flights. Tragically, it was during one of those tests
that he met his end in eighteen nineties six after
a fatal crash. Next we have Samuel Langley, who was
an astronomer who seemed to have a pretty promising jump

(23:42):
on creating a working aircraft. He wanted to use a
steam powered engine to create the thrust needed to achieve
the lift necessary for flight, so he built a model
of a plane smaller than a full scale version, and
it was an unmanned aircraft and He called it the
Aerodrome in one so a few years before Auto would

(24:05):
have his his fatal crash. Langley tested this design and
the aerodrome flew for about three quarters of a mile.
At that point the aircraft ran out of fuel steam
powered aircraft. It was enough to get Langley a sizeable
grant to try and build a full scale version, but
unfortunately he discovered his design couldn't scale up because as

(24:29):
you got larger, you're going to need more power to
generate the thrust, and more power meant you needed a
heavier steam engine, and and eventually that that ratio just
wouldn't work out. The steam engine was just too heavy,
and so you would need even more power to generate
enough lift to get the heavier aircraft up, and there

(24:49):
was no way to have the steam engine actually provide
the power needed and he ultimately had to abandon his
design at the plane just needed more lift and it
could generate front thrust, and thus it could not fly.
In Octave, Chanut, another great name, published a collection of
works called Progress in Flying Machines. He collected the wisdom

(25:12):
and experimental results of numerous efforts throughout the aeronautic societies
out there and and essentially wrote down everything that had
been done up to that point in the efforts to
achieve powered flight. Then we get to Orville and Wilbur
right the right brothers. They recognized Cayley's wisdom and the

(25:33):
need for separate systems to provide the lift, thrust, and
control of the aircraft. They also relied upon Chanut's book
to help guide their own efforts. They came up with
their own experiment with regard to controlling a flying body's
motion through flight, the whole steering part of the equation.
They believe that by controlling the shape of the wing
they can control the flight itself, including stuff like roll

(25:56):
and pitch. So the three types of movement you need
to know about with aircraft once they're flying in three
dimensional space are roll, pitch, and yaw. Roll is sort
of the the tilt, the side to side tilt of
an aircraft, so whether it's tilting to the left or
tilting to the right. Um as I'll talk about later,

(26:19):
this tilting becomes a very important part of steering. Pitch
is the uh the angle of the nose and the
tail right. So if if you are um pitching up,
then the aircraft's nose is at a higher altitude than
the tail, and the aircraft is climbing pitched down, and

(26:40):
the nose is at a lower altitude than the tail,
and the aircraft is descending. And then yaw involves turning
to the left or to the right, although yaw and
roll are very very important components for steering. Anyway, those
are the three ways of thinking about the three different

(27:00):
axes of flight controls in three dimensional space. So we'll
come back to that in a little bit. So anyway,
the Right brothers said, all right, well, by manipulating the
shape of the wing, we can add steering to an aircraft. Um.
They built several gliders, both unmanned and manned gliders, and

(27:20):
tested different wing shapes and designs, including in wind tunnels,
and they worked on perfecting that. And this brings us
to another important component of the design. Getting up in
the air is one thing, but from that point on,
how do you control where you're going? Right? How do
you actually maneuver a solid object through the air that
three dimensional space there's no ground to brace against, and

(27:42):
how do you steer the darn thing? And that was
what the Right brothers were really working on. In those
early tests trying to determine the most effective way to
control the flight of an aircraft once it's airborne. So
we'll talk about that for a second. Steering something means
you have to be able to control the direction in
which that something is traveling. It's very basic and obvious observation,
but I feel like we have to start somewhere. So

(28:04):
you need to be able to change the object's velocity
because velocity is a vector. Again, a vector is something
that has both an amplitude and a direction, has an
amount and a direction associated with it. So even if
the speed of the moving object doesn't change, it's moving
at the same rate of travel even as you change

(28:24):
its direction. If you change the direction, you've also changed
the velocity because the direction part of a vector has changed. So, uh,
that's an important thing to remember that a velocity can
change even if the speed stays the same because you've
changed the direction of travel. Tilting the plane having one
wing dip lower than the other side means that some

(28:46):
of the lift acting on the plane is now actually
pushing the plane in a sideways motion. So when you
roll the plane a little bit, you are actually changing
the lift dynamics, and some of that lift that otherwise
would be holding the plane up is pushing the plane
to UH to a side. It creates centripetal force, and
it eventually will make the plane move in a circular path.

(29:08):
You know, the more the dramatic the roll up to
a point, the more tight that circle is going to be. However,
this is, by the way, as known as banking. When
you talk about airplanes banking, it's because they're they're tilting
this way and the rolling and UH starting to turn.
But another thing you have to remember is this reduces

(29:29):
the amount of lift actually holding the aircraft up. So
you know, you're dedicating some of the lift to turning
the aircraft, not just holding it up. So if you
don't do anything, if you're maintaining the same speed, you're
changing the velocity by changing the direction. That reduction in
lift means that your aircraft is going to start to
lose altitude, So you've got to do something to counteract that.

(29:53):
Typically you do something like increase the angle of attack
of the wings or using the tail u to compensate
for this loss of lift of upward lift so that
you don't lose altitude. Modern aircraft do this with a
flight control surface called an elevator, often on the tail,
and the elevator can adjust its angle to change the

(30:15):
angle of attack with the fluid that the aircraft is
moving through the air itself and provide more upward lift.
Other movable control surfaces can affect the plane's pitch, um
and the yaw. The yaws typically a it's a rudder
that's attached to the tail of a plane, and steering
actually involves controlling the roll and yaw of the aircraft.

(30:37):
So you have both the yaw and the tilt of
the plane that allows you to make more controlled turns
with the aircraft. Each of these systems has its own controls,
and in modern aircraft uh the ailerons controlled the role.
These are on the outer rear edge of the wings
and they can move in opposite directions. So if you

(30:58):
ever sat on window seat that's right next to a
wing and you see this little thing at the very
end of the planes wing and it's either tilting down
or it's tilting up, that's part of this system that's
meant to control the role of the plane and allow
for turns. Um. The yaw, like I said, comes from

(31:19):
the plane's rudder. It's typically a vertical tail fin that
can swivel left or right, and the pitch comes from
the elevators like I mentioned earlier, those are typically on
the aircraft's tail as well, on a horizontal plane, not
a vertical plane, like the rudder is, and the elevators
can also tilt up or down, decreasing or increasing lift
on the tail, which makes the airplane behave a little

(31:40):
bit like a lever. Right. If you increase the lift
on a tail, then the tail gets lifted up and
the nose the airplane gets tilted downward, and vice versa.
But that's just one part of the equation, or really,
I guess you could say two parts of the equation,
because wing design contributes to both flight control and lift.
But they also needed to work on thrust. They needed

(32:02):
a propulsion system that we get their aircraft up to
a sufficient speed to generate the lift needed to sustain flight.
They had bill gliders and done manned and unmanned tests
at Kitty Hawk, North Carolina. They chose Kittie Hawk, by
the way, they were not natives to North Carolina, but
they chose kitty Hawk because it was pretty dependable for
some good winds due to being on the Atlantic coast,

(32:25):
so um you get a good stiff breeze over at
Kittie Hawk. I've been there, and one of the most
popular activities over at Kittie Hawk is kite flying. A
lot of people flying kites, big elaborate ones way up
in the sky because they get these nice strong winds.
By the way, if you get a chance to visit
Kitty Hawk and to go visit the site of the

(32:46):
first flight from the right Brothers, I highly recommend it.
It is a very interesting location, a lot of cool
information there, and you can actually walk the pathway of
those test flights. It's pretty neat any way. As part
of this work, the brothers had designed a movable tail
component that would help with the flight stability, particularly when

(33:07):
the pilot of the glider wanted to steer. And now
it was time to work on an aircraft capable of
generating its own thrust to maintain flight, not just to
be able to glide, and this required a lot more research,
as the brothers had to not only design a motor
that could turn a propeller fast enough to generate enough thrust,
but also an airplane frame capable of both supporting the

(33:28):
motor's weight and to withstand the vibrations the motor created
during operation. The result of all their research was the
design of an aircraft they simply called the Flyer, and
some people refer to it as the Right Flyer. A
bicycle mechanic named Charles Taylor would build the motor for
the Brothers. It was a custom built motor, a gasolene

(33:49):
fueled twelve horsepower motor, and the motor was used to
drive a chain that in turn would link to gears
that would turn the two propellers, So it's like a bicycle,
you know, a bicycles wheels. The propellers were changed driven
this motor. Through powering the propellers would provide the needed thrust.
The Right Flyer had a wingspan of twelve point two

(34:11):
meters or forty point three feet, and the right wing
was four inches longer than the left wing. So why
is that? Why was the right wing longer? Well, that
was because the Right Brothers design meant that the engine
for the plane would sit a little to the right
of the center line. It was not centered along the

(34:31):
axis of the airplane. It actually went a little to
the right side that meant the pilot would actually laid
down on the left side of the center line. But
the engine weighed seventy seven point one ms or a
hundred seventy pounds, the pilot weighed only sixty five point
eight kilograms or one five pounds, So the brothers needed

(34:53):
some way to balance the scales as it were, so
that the plane would fly properly without the constant need
for adjustment. Since had a heavier engine on one side
and a lighter pilot on the other, and so they
made the right wing a little longer than the left
in order to generate a bit more lift than the
left side and thus compensate for the added weight on
the right side of the plane. The Right brothers held

(35:15):
the first test flight on December seventeenth three. Orville Right
was the pilot, and the plane lifted off the ground
and traveled about one twenty feet or thirty five meters.
It flew just twelve seconds, but it was enough to
secure the Right brothers the acknowledgement that they had created
the first heavier than air manned, steerable flying machine. They

(35:37):
would build other aircraft based off that design, but the
only one they ever attempted to preserve was the original
Right Flyer, and for a short while that airplane called
the Kensington Science Museum in London home. But in nineteen
the Flyer returned to the United States to become part
of the Smithsonian's exhibits, and it is now in the

(35:57):
National Air and Space Museum in Washington, d C. When
we come back, I'll talk about some other elements of
aircraft and how those contribute to flight. Okay, so the
Right Brothers were two of the many pioneers of piloted

(36:18):
heavier than air aircraft. There were lots of other people,
and I hope I've made it clear that the success
of the Right Brothers depended heavily on the research and
work of numerous people before them. Also, they weren't the
only ones working on the problem when they achieved their
success in North Carolina. It's why I define their successes
being the first to pilot a heavier than air aircraft

(36:39):
that had at least some rudimentary flight controls, because otherwise
you have to talk about a whole bunch of people
who did lighter than air aircraft and and some other stuff,
and many people would quickly follow in the footsteps or
flight steps of the right brothers building better aircraft with
more sophisticated control mechanisms and development and innovation were in
the fast lane. So just going to cover a few

(37:01):
more basics, and I might have to do a future
episode to talk about some of the more modern systems
aboard aircraft, because that would make this show run way
too long if I were to keep up with that.
So let's talk about propellers. The propellers on a prop
plane are effectively doing the same thing that the wings
do on a plane by creating lift, only in this case,

(37:21):
the direction of the lift is forward with respect to
the plane. It's like a helicopter's rotors. Moving the blades
of a propeller in a circular path at a fast
enough rotational speed creates the force and drives the aircraft forward.
But unlike a wing, which tends to have a fixed
angle of attack across the entire length of the wings surface,

(37:42):
a propeller blade has a twist in it so that
the pitch angle varies along the length of the blade.
Some modern planes have a controllable pitch propeller, which allows
the pilot to change this rotation in order to have
the plane perform at optimal efficiencies at different air speed
eads now Jet engines are different, and I've covered them

(38:03):
in past episodes, but here's a quick rundown. From the outside,
a jet engine looks like a tube. If you look
at one head on, you'll see a big fan thing
in the front of that tube. Then at first you
might think that a jet is similar to a propeller plane,
that it's generating forward thrust by just rotating that fan
super fast. But that's not quite right. The purpose of

(38:27):
the fan is to suck air into the jet engine.
The fan attaches to a shaft and it spinds rapidly
and it pulls air into the engine. Behind the fan
on that same shaft, or on a shaft around the
fans shaft, there are a bunch of other blades attached,
and these blades are compressors. They compress the air. They

(38:49):
squeeze that air down into a smaller and smaller space.
That also increases the pressure obviously of the air, and
also the temperature of the air and gets it to
the right temperature for the next stage, which involves combustion.
So behind the compressor is a combustion chamber or series
of combustion chambers, and the compressed air enters into the chambers,

(39:11):
and nozzles that also enter the chambers spray a fine
mist of fuel there, and an ignition component creates an
electric spark that lights the mixture of compressed air and fuel,
and you get burning gases inside the chamber. Those burning
gases expand as the heat up. The only exit out

(39:32):
of this engine is a nozzle at the back, So
the expanding gases escape out the nozzle at a tremendous
amount of force. And because we know every action has
an equal but opposite reaction, we know that this backward
pushing force of escaping gas creates a forward pushing force
on the aircraft itself. So if you can generate enough

(39:53):
force to overcome the weight of the jet and get
it up to speed, you can use it to provide
the thrust needed to get lift and take off. Oh
and that escaping gas also turns a turbine at the end,
So you've got the combustion chamber, you've got an exit
out the back of the combustion chamber where the gas
is passing through a nozzle. It also ends up turning

(40:15):
a turbine, and that turbine provides the rotational force for
the UH, the compression blades on that rotating shaft, and
also the fan. You know I mentioned those earlier. That's
what's actually causing the rotational force. So not only does
the jet engine provide thrust for the aircraft, it also
harnesses some of that energy to operate the components of

(40:36):
the engine itself. There are variations on this design. There
are two or three spool jet engines, for example, but
they all work on the same basic principle. UM. One variation,
the one we see in commercial jets. A very popular
one is the turbo fan jet. In this version, the
engine casing is much larger than the combustion section, so

(40:57):
you can think of it as a big tube around
a much smaller tube. The smaller tube is the combustion part.
So you've got the fan that's pulling air in, You've
got the compressor blades that are compressing the air down,
but there's also space for the for some of that
air to pass along the outside of the combustion chamber,
so some air is kind of going in between the

(41:19):
combustion chamber and the casing for the jet engine itself,
and the air coming in is compressed and most of
that air is passing along the outside of the engine
that provides the majority of the thrust. It's not the
superheated stuff. It's this compressed air that's passing through this
bleed bypass UH section. And it also not just provides thrust,

(41:44):
but it also is able to cool the engine so
that remains in operating operating temperatures. It it avoids overheating,
so the air that passes through the engine still goes
through the same combustion process I mentioned earlier and provides
additional thrust as it escapes, plus provides the UH the
force necessary to rotate that turbine and keep everything in motion.

(42:06):
By the way, jet engines can also be used to
power stuff other than aircraft, or rather, I should say
turbine engines like this can be used to power stuff
like tanks, or they can help power helicopters. They don't
do it the exact same way as a jet plane,
which has this exhaust be part of the thrust mechanism.
Instead the tail end of that engine, there's another turbine

(42:28):
that connects to some sort of drive mechanism, such as
the tank's treads or helicopters rotors. So the the turbine
engine pulls air in, you've got the combustion. All of
this is used to create the energy needed to rotate
a different turbine that then sends that power onto the
propulsion system of the tank or the helicopter. Uh. These

(42:52):
engines also have to have an exhaust port for all
that hot air to escape, but it's not used like
a thruster on a jet plane. But hey, for these
engines to work, you still got to get that turbine
spinning right. And that presents a challenge because these are
engines that work fine while the jet is in operation,
while it's actually moving through the air, because the process

(43:16):
of the jet engine working provides the energy needed to
turn the turbine that pulls more air in through the system.
By the way, you're not generating more energy than you're
expending here, I want to make that clear. Just rather
that the process is not just providing thrust, but providing
the force needed to turn those turbines and those fan
blades and compressor blades. But in order to do that,

(43:38):
you have to get up to speed in the first place.
How do you get it started? Well, the turbines are
too heavy and need to turn too quickly to rely
upon an electric motor to do it. So you can't
just have an electric motor attached to this thing to
jump start the turbine engine. That's not going to work.
They're far too large and heavy. So to do it,

(43:59):
you have to feed compressed air into a stopped jet
engine to get things started, to start turning those fan blades,
and to get enough air pressure in there for you
to ignite the combustion chambers. Now, if everything is working
properly on the aircraft, you can use a system called
the auxiliary power unit or APU to do this. Um

(44:22):
it supplies the jet engine with compressed air, and you
can start with just one engine. I'll explain how in
a minute. So the APU is typically at the far
end of a jet, on the main body of the jet,
the fuselage. It's at the very end, and it has
three main functions. One of those is the main engine
start sequence, but the other two big functions are to
supply electrical power to the jet. There's a turbine in

(44:45):
this jet engine that is connected to a generator, and
thus you can use that to help supply electrical power
to the jet, and also it can provide bleed air
pressure for the air conditioning system bleed air pressure. Think
of the bleed air system as kind of plumbing. It's
a series of conduits or pipes in a jet that
allow compressed air to pass through. So the APU itself

(45:08):
is a small turbine engine similar to a jet engine.
There's an intake panel it slides open. It allows air
to come into the system. And the APU, unlike the
main engines, is small, so you can actually start it
under battery power. You can have an electric motor attached
to the APU. You turn it on. This starts the
fan in the APU spinning, which then draws air in.

(45:32):
And like turbofan engines, the APU has bleed air, so
air that goes around the engine itself and it enters
into this bleed air pathway system that connects to other
components of the jet. So you divert some of the
air going through the APU to enter the jet itself
through this bleed system, and the pressurized air goes to
a component called the air turbine starter, and this connects

(45:55):
to the engine's shaft through a clutch mechanism um and
that allows the APU to provide compressed air to start
turning the fan and turbine in a jet engine. And
this reminds us about fluid dynamics. You can either have
a solid object moving very quickly through relatively still fluid,

(46:18):
or fast moving fluid moving past a relatively still solid object,
and you'll get the same results. So pushing compressed air
through the main engine creates a situation similar to the
engine operating at flight speed. So once the engine reaches
a certain percentage of its top revolutions per minute, somewhere
around twenty eight, the air inside is compressed enough to

(46:39):
sustain combustion, and the engine will ignite fuel in the
combustion chambers and that will provide the energy necessary to
take over from there, and the engine will perpetuate its
own rotation and you can stop pumping compressed air into
the system. From that point. You can use the APU
to power up the second engine, or you could even

(47:01):
use the first engine to do it, because the engine
system feeds into this bleed air system. So again it's
like you know plumbing. You've got all these conduits, you
also have all these valves in that system that either
allow air to pass through or prevent air from going there.
So when you're starting up engine one, you would have
all the other valves closed so that the compressed air
can only follow one pathway to get to that engine. Now,

(47:23):
sometimes the APU isn't you know, totally working and can't
supply enough compressed air to do the job. In those cases,
the ground crew will connect a land based air compressor
that's technically known as an air start unit, but most
folks refer to it by a more informal name, the
huffer cart, And the hover cart sends huffer is h

(47:44):
U F F E R. It sends compressed air into
the bleed system of a jet. So you just plug
it into that bleed system and it provides the compressed air.
And again the valves leaning to one engine are all
open and the other valves are all closed. And once
that first engine has started up and reaches the proper
rotational speed, which is somewhere around the mark, that engine

(48:05):
can provide the compressed air to start the other engine
or engine two. There might be multiple engines on the jet,
like four engines or something. You can keep doing this
process over and over. Now, I honestly didn't know any
of that stuff about how jet engines start from from
a stopped position. Before I researched this episode, I understood
how jet engines worked, but I didn't know how they

(48:27):
got them started. So I always wondered how that happened,
since it seemed like the kind of system that only
works once it's already working, which seems like a catch
twenty two, Like a building that issues permits, but the
only way to get inside the building is to already
have a permit. So how can you start the jet
engine in the first place? And now I know, so,
now you know too. So those are the basics of flight, thrust, lift,

(48:51):
and flight controls. And granted I spent the least amount
of time on flight controls, I may need to do
a future episode to talk more about that in radar detail,
to describe the physics behind them and how modern flight
control systems work. In the meantime, I do have a
lot of older episodes that go into things like jet engines, scramjets,
autopilot systems, and more. It's actually kind of silly that

(49:14):
took me this long just to cover the basics of flight.
That one's on me. If you guys have suggestions for
future episodes of tech Stuff. You can get in touch
with me s me An email the addresses tech Stuff
at how stuff works dot com. Pop on over to
our website that's tech stuff podcast dot com. There you're
going to find an archive of all of our older episodes,

(49:35):
plus links to our social media presence, and a link
to our online store where you can buy tech stuff
merch and every purchase you go and make ends up
helping our show. We greatly appreciate it. I hope you
like the designs. Trying to get some new ones in
there soon and I will talk to you again really soon.

(49:59):
Text Stuff is a for auction of I Heart Radio's
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