if
so from what we
discussed
up to this point
flying for range and flocking for endurance are two
completely separate arguments.
And so we'll be coming back to that. By the
way, you're going to hear it over and over again is the
as the course progresses
It's time down to move on to another concept which
is a lot easier to get your head around.
All over the terminology might be something we need to.
Clear up.
We call it kinetic energy.
now let's start with the
the simple formula
That allows us to calculate.
kinetic energy
but before we do
I just want to put it in the most simple terms because as
we've seen since so far whatever can
be done with formulas and graphs and
things can be said in civil words.
Now if you ask me.
What do you mean by kinetic energy? What what the
hell is it?
It's one very simple answer to that that any school
child knows.
How hard would it be to stop?
full stop
that tells you all you need to know about kinetic energy kinetic
energy if you want to see how much
kinetic energy and object possesses.
Ask yourself how hard it would be to stop
it.
Because kinetic energy is the energy you possess
because of your motion.
And so to find out how much kinetic energy you have
you take the motion away.
You stop it.
And so the formula is
very simple in.
Kinetic energy is one half.
times the mass
by the speed of velocity
But the velocity notices squared.
That that square tells us something.
It means that if you double the speed.
You'll get four times the kinetic energy.
The the relationship is not linear.
It's
it's exponential.
And so by the way, don't let the half bother you
that's put in a math as purely as a mathematical convenience. So
it doesn't concern us right now,
but the formula does say one half times the
mass.
by the speed squared
and when I look at that it means because the
mass
the mass does not have a squared on it.
Say that's a straight direct proportion.
That means double the mass you get double the kinetic
energy.
Double the speed and you get four
times the kinetic energy.
And so that's a very rapid increase.
And the question and the way to think about it is simply.
m stands for the mass of the object
and v stands for the speed that
it's traveling at.
And the speed is squared.
And so that means if you
approach your airplane just a little bit faster.
What you think is only a little bit faster.
You'll be surprised at how much more room you need
to pull up in?
Because for an airplane, that's a perfect example of kinetic energy
how far how much runway do
you need to stop?
How hard would it be to stop that's that's just
the unscientific way of talking about
kinetic energy.
If I travel if I approach a bit faster than I should.
I find that I have a
Very big difference in the distance there to stop by the
way. I'd luckily it works the other way if I can reduce my speed over
the fence.
I have a surprisingly big Improvement in landing
distance. I'll need a lot shorter Landing distance.
And so that's why airplanes and
we'll deal with this later in the course.
Big jet airplanes have got a hell of a lot of mass.
A very very large, Mass.
hundreds of tons
They can't help that because that's where we build them. We build
them to carry weight.
And so the only way to have a sensible Landing distance
is to have less speed over the
fence bit of a dilemma, isn't it for the for the
designer I wanted to go fast, but
I wanted to go slow when I needed to.
And so that's why the Jets have all those lift augmentation
devices on the wings. That's another
day. We'll be discussing that quite simple. We can
we can actually create a whole new wing for landing.
So that I can now fly a jumbo
jet can cross the fence with something like 130 knots.
Which is really slow when you consider its weight.
And so we'll be talking a lot more about that'll still that
when the time comes.
and so
if I double the mass I double the kinetic energy.
If I double the speed I get four times the kinetic
energy.
It's the energy and object has because
it is moving.
So the question to ask is
how hard would it be to stop it?
And the rest of that, of course the relates to motorbikes and semi-trailers and
it's as clear as can be.
and
Landing distance
if I
the distance I need to land.
In depends under the kinetic energy
that I possess when I touch down.
The if I touch down slower.
Then I can pull up shorter.
Almost embarrassing and have to say that I
think I think most people would say. Yeah, that's but the interesting
that there's always a formula that says that in a
way that can't be argued. It's precise.
And the distance required to
stop now. That means two ways
to kinetic energy can be created.
I can have a heavy object traveling
slowly.
It can still have a hell of a lot of kinetic energy a perfect
example would be an ocean liner.
100,000 tons ship
traveling at three knots
Is bloody hard to stop?
It's not going very fast.
But try stopping it.
All right, that's why they have to be so careful when they dock it
now. They got all those propellers that work sideways. But
in the olden days they had to have tug boats that
gently gently nudge it until it's
up against the jetty.
If it's doing one knot and it hits the jetty and it
weighs 100,000 tons good boy, Jenny.
It just continues to travel.
On the other hand, of course a lighter object traveling fast
can end up with a lot of kinetic energy.
a bullet
is a light object.
But it travels at something like 2000 kilometers an
hour when it leaves them a gun.
And so it's it's equally difficult to stop.
Some people have discovered that for themselves. It's hard
to stop a bullet.
and
but this leads us to an interesting discussion.
Because it's one of the most important instruments in our cockpit and
it's vital that we understand it.
And that is a thing we call the indicated airspeed.
airspeed indicator
it's very
it's very poorly understood quite often.
In fact, I find the best way to understand it clearly is
to take a trip down memory lane years
and years ago at the earliest.
ESPN indicators, by the way, did you realize the Wright
brothers didn't have one?
We put so much importance now on AirSpeed your
instructor jumps up and down saying look at what's your SB
does this is as and and I can imagine some students
thinking they must have adverted AirSpeed
indicators first before they had airplanes because no
one could fly without one you'd die for sure.
No, we flew our Appliance without spit
indicators for a long time, but then we discovered you
can't fly it accurately.
You can't get the best out of it. Unless you have
a good Espin indicator, but when it
comes to being safe that must have been the good old days,
you know, you you open the throttle and you sort of feel the wind, you
know, that feels about right. I reckon she'll go now and
so off you go and fly away.
all right, and
yeah, there's been Dakota was what you felt.
But here when they started introducing AirSpeed
indicators, this is one of the earliest and
I love this one because it shows you really clearly.
What it is?
Remember we had that discussion about molecules.
And we said here is that is actually made up of molecules.
And each molecule has got weight a tiny tiny
weight, but each one has weight.
And and the pressure it exerts as due purely to the
impact of those molecules.
And so they invented this gadget which
explains it so clearly
we have a flat plate.
and a spring
All right a flat plate.
down there and a spring
and as I fly the air.
slams into that plate
and molecules slam into that plate.
And that applies a force to that plate?
But that Force depends on two things it depends
on how fast each molecule is moving when
it hits.
But don't forget it also depends on how many molecules hit.
How close together are they?
That's what we call a density.
if the air is
it isn't just the speed that matters.
if the molecules hit at a certain speed
They'll apply a certain Force.
But if a lot more molecules hit at the
same speed then they'll apply a bigger Force.
And so what happens now is as the airplane
flies.
it
the molecules hitting that plate move it
across the dial.
And this airplane above the door?
Was built by a very good made of iron laying kidbe.
who is a
most amazing gentleman die
I'll tell you more about him at the bar one day but a
fascinating man, but he built that airplane to
commemorate bertinklers flight from England to
Australia.
And he built it in Australia took it to England.
And then flew it out on the same route
that Burt Heckler took.
as a commemoration of Burt angle's flight
And it was originally built.
With one of these aspid indicators. In fact, he
left it on.
He left it on there, but he still had to have a proper one, of course
for Casa to be registered.
But he still had the old one.
And when he came in from England, he landed at archerfield.
and
the front cockpit was actually all fuel tank. So it's
only had one seat.
And he was doing a channel 9 interview.
I mean said to me.
Plans there they can't have floors. See what you reckon.
That's how I jumped off at all. I want to haven't had burrow
in my log book. So and so I jumped
in it and did a couple of circuits.
and
the interesting thing was
this was mounted on the interplan strut.
It's mounted on those struts between the wings those way
outside the cockpit.
And but you you can compare it with the real airspeed
indicator that was in the cockpit and it was
spot on.
So it was a lot I love the way.
I love the way that shows you so clearly.
Just what's going on? And it's so
obvious now that if if the air
is thin?
Then the speed.
The speed and if the speed stays the
same in the air is thin.
Then the indication will be less.
And so the speed of each molecule is really your
true speed.
But then you've got to consider how many molecules are hitting the
plate and that's that's the
density of the air.
So it's a beautiful.
Way to introduce the argument nowadays, of
course, we use a far more sophisticated idea.
and we use
a
capsule that can expand like the Bellows of
a piano accordion
and I pedo tube.
That that reminds us by the way the French had a
lot to do with early flight.
They still I reckon that they did it first before the Wright
brothers.
and
the pedo
Is an open tube that faces forward?
And so there ear molecules that go
in there are traveling at the speed of the aircraft.
And they go up into the capsule and flood into
the inside.
But the outside of the capsule is connected to
a static vent.
And it's a range so that the air doesn't blow in there. The
air goes straight past it, but it doesn't actually blow
in.
And so it doesn't record the speed of the
year. It just records the pressure of the air if
it wasn't moving.
And we call it the static Source or static
vent.
And so as I as I it does the same job as that
old one. It measures the force of
the wind now, of course that's already got static
pressure in there.
But the extra force is called Dynamic pressure the force
of motion.
And it goes in and builds up what we're called total pressure
inside the capsule.
But the pressure here is just the static pressure of the air.
And so that the capsule starts to expand.
Due to the difference between the total
pressure and the static pressure.
And we call that difference the dynamic pressure
the instrument measures the dynamic
pressure of the air.
And so this is basically what happens as my speed increases
the capsule expands.
And the moving capsule drives the hand drives the
pointer.
It's responding that is not to speed.
It's the responding not to speed at all. It's responding
to pressure.
So I don't know why it's actually.
a bit of a fiber
it's not really a speed indicator.
It's a pressure indicator. It's the dynamic pressure indicator.
the molecules enter at the speed of
the true speed of the airplane
But then the number of molecules matters as
well.
When it comes to the pressure that's built up.
the mass now I hope that might
I hope that might remind you of something we said before we
had that short break.
and that is
it responds to the kinetic energy of the
air because that's the mass and the speed.
half MV squared
right notice what this is really doing. It's catching
some of the air and bringing it to
a stop in a dead end.
Well, isn't that what we just said if you want to know how
much kinetic energy it has then stop it and
see how hard it is to stop.
By catching that air and stopping it. We're
releasing its kinetic energy.
And this instrument is measuring the kinetic energy of the
air.
the mass
And the speed together.
Is what it's reacting to.
Okay, and therefore because it's
a pressure that we're talking about.
Remember when pressures act on surfaces they create forces?
We all know that When Storms hit.
The moving air hitting an object
will apply a force to the object.
And the roof blows off the house.
and so
therefore that's got that's got implications for
aircraft.
Because of that Force gets big enough for women or two
the force increases with the square of the speed. You
don't have to go much faster to get a lot
more force and when we build airplanes we can't
make it out of angle iron.
Our big concern is wait.
And so most airplanes are only just strong enough to do the
job.
And therefore it's up to us to be careful that we don't
apply too much force. That is too much
kinetic energy too much indicated airspeed.
And so the espion indicator has the following.
limiting air speeds
right firstly they have a color the white Arc the
beginning of the white Arc.
Is the stalling speed?
with flaps and undercarriage down
the Air Force call it the dirty.
stalling speed
I mean everything's hanging out of aircraft.
flaps them undercarriage down
if you go, but if you go slower than that, there's not enough
kinetic energy in the air to make the lift you
want.
So flight is impossible.
The green Arc is the stalling speed vsi.
Usually I use the Roman letter i for one.
and
that's the green Arc and that's the stalling speed clean.
That's the stalling speed with the flaps up and the gear up.
And then over here, we have the end of the white Arc called
vfe flap extended speed.
That is the greatest speed I can fly out.
Before I start to damage the flaps if they're
down. So any any speed
above vfe.
Means the flaps must be retracted.
Don't forget by the way, not only may you not only may you
damage the flap?
but clearly
if I've got my flaps down.
It could damage the flap itself, but it's also applying a
strong force on the back of the wing.
And that's trying to twist the wing.
So we can actually distort the whole wing.
If we go fast enough with the flaps down that'll apply
a torsion load on the wing a
twisting word.
And so
vfe
It's all about forces.
As I said, it's not it's not speed at all.
It's pressure.
And and then we have v&o.
Which is where the green arcans?
And that's called normal operating.
speed
and it means if you're above that speed.
Then don't allow any
turbulence.
Turbulence can impose those forces as well.
By changing the angle of attack on the wing when
air hits it from underneath.
and so
you can fly that you can still fly up here.
But you must not allow the airplane to be
to encounter turbulence.
And then finally have a red line.
Covey and a which stands for never exceed
and that's the speed.
That even if the air is calm and even
if the flaps are up.
you can still cause damage to the
aircraft structure
We've got a lot more to say about that. Later.
but
every pilot should be aware that they speeds exist.
Some of them are actually color-coded as
you can see.
But there are other speed limits that are not color coded.
But they are still important ones.
for example
There's a speed call maneuvering speed or VA.
maneuvering speed
means
do not apply full control deflection if
you're above that speed.
So mostly it's the elevator we're interested.
In that don't pull the elevator all the way back to the
stopper.
If you're above that speed and that mainly and I think
you'd agree would have to be due to.
Pilots
Doing aerobatics because it's not likely that a
pilot would be flying along and then go
I think I'll pull the elevator all the way back, right? Normally.
We don't do that unless this
something seriously wrong, so
so
that's more mostly an aerobatic issue.
VA don't don't have the
elevator fully extended above that speed.
and
then we have another one called turbulence penetration speed.
and turbulence penetration speed
basically works like this.
if
this represents the wing
and this represents my forward speed.
then if
tabulence is basically vertical movement of
the air.
And so if the air comes up from underneath like that.
That it means the effectively the angle of
attack.
The air is now coming from this direction instead of
that direction.
So effectively the angle of attack has
been increased. So hitting hitting turbulence
as much the same as pulling a stick back.
The airplane can't tell the difference.
The airplane can't tell the difference between you pulling
the stick back.
And you hitting an updraft?
It does has the same effect on the wing.
And so nice many airplanes have
a turbulence penetration speed if you
in Canada severe turbulence.
And slow down below that speed.
by the way
You're more likely to be very concerned about that when
you do your instrument rating.
because an IFR pilot a vfi pilot
can see
it's not often a vfi pilot's going to encounter severe
to turbulence.
But in our five Paul is flying in Cloud.
Now imagine this problem. I'm flying in Cloud. I can't
see so how do I there's not a thunderstorm in the
cloud?
a thunderstorm embedded in the cloud
and so one thing that haunts all of our
Pilots is I'm flying along one day and suddenly found
myself in accumulated numbers, and I couldn't see
it coming.
And so if I
Pilots are much more interested in turbulence penetration speed.
Okay. Now this leads us to a related
argument in fact
the idea
of vectors
So let's look at it. I said we're going to talk about
vectors. They're those arrows that people like to
draw all over the board when they're
giving you a briefing.
Imagine I've got a weight and a rope
attached to the weight that I'm trying to drag it along.
And so the real force is acting on the Rope.
That's what I'm really doing.
But it's possible to break that up into two imaginary
forces. They would have the same effect.
And so what I can do is draw
a line along horizontally and another
one vertically.
and if I drop
a perpendicular down
Under the horizontal line and a cross under
the vertical line.
I could create two separate arrows.
To represent two separate forces which would
have exactly the same effect as this one.
Now, sometimes it's convenient to do that.
Sometimes it's handy.
To take one big force and think
of it as though it was two forces acting separately.
the beauty of a vector is
the direction of the arrow represents the direction of the
force.
And the length of the arrow represents the strength
of the force.
How strong it is?
So those two black forces if they
acted simultaneously.
Would have exactly the same effect.
as the real force that is acting
now this happens on the wing.
because when the wing is
Is flying and the air is flying over it?
What really happens is there's a total reaction.
And the total reaction is the caused by
all of the molecules of air.
flowing over the entire Wing surface
Now, of course that would drive us nuts if we try to imagine that is
separate each separate individual molecule. That's what's
really happening. Each molecule is contributing
but we think of it as though one force acted.
And we represent it as a single Force.
That doesn't only lift up but pulls back as well.
that single Force represents
the total reaction of the wing to the airflow.
Now we can split that up into two separate forces.
And we split it this way. We take
one force.
And right angles to the direction of travel.
This one is always at right angles.
to the direction of travel
and we call that one lift.
And then we take another Force.
Which is parallel to the direction of travel.
And we call that one drag.
Now one point I always like to try to make to people
here is we talk so much about lift and
drag.
But isn't it interesting to know that they don't exist?
All right, you'll never understand lift and
drag.
Unless you realize they don't exist. They're not real.
They're imaginary. They certainly handy Way To
Think.
But and that's this by the way explains a
few other things for example.
If you try to change lift.
It's almost impossible.
to change lift without changing drag
because the two are not really separate they really
sides of the same coin
lift and drag
are inseparable
because they really components what we call components
of the total reaction.
And so there's an airplane is in a climb for example.
Then two forces two types of forces are
trying to pull it down.
the weight
and the drag
erecting together
now we can now use another technique with vectors.
With two separate forces we can caught we can turn
them into one.
That that has the same we call it
a resultant a resultant Force. So those
two forces are really separate drag and wait.
but if we then
Do this.
I move weight down to the end of the drag Arrow.
And then I joined that join them with a line.
from the beginning of drag to the end of weight
and that dotted line is actually called a resultant.
Now then I can now forget about dragon and wait.
I can ignore them and I think of it as one
force.
dragonwade acting together
and therefore lift and lift
and thrust also.
Are acting that way and that way.
And I can do the same with that. I can add thrust
and lift together.
And I get a result now. Here's where
you take some advantage.
And what we said earlier.
We now have equilibrium in a climb.
this resultant of dragon White
is
is also
balanced exactly balanced
by the result of lift and thrust
so that that line is the same length as that line.
And they and together they are one straight line.
So they are exactly balancing out.
and so equilibrium now exists
four forces are acting
lift weight thrust and drag
But they combined effectors balanced.
and so equilibrium exists
and the airplane continues to climb in a
straight line at a constant speed.
Now money using that now we're going to
talk about climbing in a lot more detail. Later.
But only using it now as an example of vectors
how a vector can be used to prove a
point.
I can use vectors to prove a point.
The results are equal and opposite so there's no
net force acting.
on the aircraft
and so it'll keep doing what it's doing.
Now this one I'll just go through quickly because I'm sure you
would have done this in PPL.
But let's say a little bit about motion what types of
motion can the airplane perform?
It can do three types of motion.
Now this is going back to baby.
stuff on the beginning of everything the airplane
can pitch
that means it can move and that fashion.
It can roll.
So it can move in this fashion.
and it can your
so it can move in this fashion.
Now we don't need to say that I'm sure to you as you got a private
license, but one thing that is interesting though,
and a lot of people miss this
point.
often cease to say this to instructors that I trained we
tell all the students the airplane can pitch and
role in your
but we often don't say the most important thing.
And that is it can't do anything else.
It can't do anything but pitch role in
you the most complicated aerobatic maneuver.
There was ever devised.
this picture role in your
Okay, they might be all simultaneous but the airplane
can only do three things.
And that's that's reassuring because it means if
I've got three controls.
I can control each of those three motions. There's nothing
the airplane can ever do providing the controls
remain effective.
There's nothing the airplane can ever do that. I can't control.
And so these are important things
but here's another point. I'd just like you to think about
briefly.
when an airplane pictures
then the nose comes up we'll know that the nose
comes up in the tail goes down.
like that
and that means everything neither the nose goes up.
And everything near the tile goes down.
but he's a point that often we don't stop and think
about
if the tail is going downwards and the nose
is going upwards.
What there must be a place somewhere where it swaps
were changes?
There must be a point where everything ahead of
that point.
Is traveling up.
And everything behind that point is traveling down.
That's the axle or axis of
rotation.
right and
That's the point about which the rotation does occur and
for every object in the universe not just airplanes.
That are free and spiced to rotate and
they're not attached to something.
everything that rotates and moves
the point about which it rotates is the
center of gravity.
Of that airplane. That's what Senator gravity is. It's
the point about which the rotation occurs will
be coming back to that. Of course when we do performance.
It's called the center of gravity. It's the
point about which the rotation occurs
and it rotates about an imaginary axis.
which can be thought of as a
as a wire that goes through the airplane from wingtip
to wingtip.
If we held it by that wire the only
motion it could do would be to pitch.
It's called the lateral axis. We'll be
dealing with this and much more detail too. Later.
Now rolling is a similar argument if the
airplane rolls then everything on one side goes up
and everything on the other side goes down.
So there must be a changeover.
There must be a point.
About which it will about which it rolls.
And again, that's the center of gravity.
The center of gravity is again the
Pivot Point.
And we can imagine an axis.
Now that passes through the airplane longitudinally from
the nose to the tail.
And if I held the airplane by that axis.
Then the animation possible.
Will be role.
And finally if they are applying yours.
Same argument part of it goes one way to the
right and part of it goes to the left. There's again,
there's a changeover.
Which is the center of gravity?
Okay.
And the center of gravity in this case when it comes
to your ring. The axis is a vertical axis that
passes through the airplane
from roof to floor.
It's proper name is normal.
It's called the normal axis if I
hold the airplane by that axis the only motion possible.
is your
and the whole three axes
all go through the center of gravity.
So the center of gravity is actually the
center of it all that's the point where all three
axes meet. In fact.
and
pitching about the lateral axis
rolling about the longitudinal axis
and urine about the normal axis.
Now sometimes it is an examiner. I talk
about a plane of motion.
It's really same argument that I'd like to just mention it
in passing.
The plan of motion is an imaginary sheet
of glass.
And this guy says it's the pitching plane.
That passes through the airplane from spinner to tile.
when the airplane pitches
it is moving in the pitching plane. It's
just another way saying the same thing.
Also, we have a plane that moves.
That vertical plane that goes across the wings.
And when it moves in that plane that's rolling the rolling
plan.
And then it has a horizontal plane that passes
that way.
and when it moves in that plant
it's urine.
We call it the urine plan now, they're just
definition so I won't dwell on them.
And of course, we all know this.
We have three controls elevators the control pitch.
They are notice that it control doesn't only prevent doesn't
only cause motion a control
is often used to prevent motion.
If you do if you do a loop in an
airplane, if I fly around a loop,
then the only motion is pitching but that
doesn't mean there's only using the elevator.
Because while you're doing that you don't
want that to happen either.
And so if you do a loop, especially in a high
powered aerobatic airplane, you're going to have to use the rudder.
to prevent motion
Okay, and you'll have to use the Allen's because
you don't want this to happen either.
I want to go around the lip. And so even though you're
only the only emotion is
Is pitch it doesn't mean the only control?
is elevator
Controls are used to prevent as well as to initiate motion.
And so
so we've said all this this morning so I won't I'll just
go through the quick as a quick revision.
State of motion speed and direction is what
motions all about.
A force is a pusher or pull that attempts to change motion.
and forces that act on aircraft lift drag
thrust
and white
Okay and a little bit more to say about
lift and drag.
as the air flows across the wing
we get a total reaction.
Which can be then resolved into two separate forces
or imaginary forces.
called
and right angles to the role of air flow lift parallel
to the relative air flow.
drag
infectious shooting me once
white is lifted right angles to the relative air
flow.
And I said because I said so.
Why why because it
don't lift doesn't exist.
I just decided that that part of it that does
act it right angles.
I will call that lift.
We chose we chose to do that. That's that's not a
law of nature.
And so
we've already once once I've established lift
and drag then I can forget about the total reaction.
So we'll be doing that a lot.
now
for people
watching this video
will now on suggesting that you should stop hit the
pause button.
And try exercise A1 on page 17 of their
Dynamics book, you'll find the answers are fully
explained on page 17.
So now we'll move on to the next part of
what we want to say.
and that is
how does lift get made in the first place?
What what causes lift to be generated?
So there are a number of different ways we
can consider it.
for example
Isaac Newton said
For every action, there's always an opposite reaction Philly
well known statement.
Which originally was Isaac's contribution?
so when the air before the air hits the wing
it's traveling in the direction indicated.
by that Arrow
and the end result
when the air leaves the wing it's been deflected.
And it's now changed its direction
and its speed.
Now that that's the action the action is the air before
the wing was traveling and that direction and after
the wing it's traveling in that direction.
Now Isaac said you can't have an action without a
reaction.
So if you've deflected the air downwards.
Then you'll deflect the wing up and back.
So most of this again has gut feeling it's
like it makes common sense to say that.
There that's called the total reaction. It pulls
the wing both up and back.
But one thing that that Casa say
because you're here to try to pass an
exam.
And Casa syllabus is clearly that you
should be able to explain lift production.
By referring to a man called Mr. Benealy.
And talk about his contribution.
So
Mr. Benealy said
that
pressure
The pressure in a gas we've already said this now we can start taking
some advantage of what we said earlier.
The pressure in a gas is due to molecules that hit
the surface.
And so he's one individual molecule it
hits the surface and when it hits
the surface it applies.
a pressure on that surface
But manually also said something else.
He said if the molecule hits the surface and the
air isn't isn't actually traveling anywhere. It's
staying still.
Then the molecules are hitting the surface.
And that way and that fashion.
but if the air starts to move
then the molecule while it's coming down is also going forward.
And so it hits the surface like that.
It comes down hits the surface and goes up now that
means
That if it hits the surface and a glancing Blow instead
of straight down it won't push
so hard.
So what ultimately what he said was if it
starts to move across the surface?
Then the pressure it exerts on that surface will be
reduced.
because the molecules of air are now hitting
at an angle instead of straight down because of
the forward motion.
of the air
and so
an interesting principle is
this
so here it is just as a bit of a
a simple animation
stationary air
means the molecules doing that.
And so they're applying a fairly strong force on the surface.
but moving air
the molecules are doing this.
And so they don't press down so hard.
But it reduces the force pushing downwards.
So it basically said if you travel if you start
to speed the air up.
Then it will have less pressure. It will exert less pressure.
And we can prove that and Engadget called a
Venturi.
A Venturi is nothing more than I Hollow pipe
with a narrow neck in the
middle.
and as the air flows through that Venturi
the air has to speed up to get through that narrow
Gap.
In the same way that a river has to speed up when
the banks come closer together and the Rapids form.
and so
when air flows through the Venturi it flows
in that fashion.
faster in the middle
and this area where the air is traveling faster means it
doesn't have enough time to press sideways. It's
too it's too much
of its energy is going into forward motion.
And I can't press sideways as hard.
so if I turn to this Blackboard
and I say I'm going to push on the Blackboard like that.
Then I can push pretty hard.
But if you change the rules and say I've got to walk past
and push.
Then I can't push this hard anymore because some
of my energy is going into forward motion.
and therefore the pressure
in the narrow part of the Venturi B
drops
and then an increases again as the air comes out the other end.
now if we connect a pipe to that and that
point
That will produce.
a suction
that low pressure will produce a suction exactly
the same effect as if you put a
drinking straw in your milkshake and suck on
it and you suck the the liquid up.
in fact carburetors use this
as a means of sucking the fuel into the engine.
And so that's the Venturi.
if speed increases
then pressure will decrease and I can
use that a little illustration again.
If that string represents the total energy that the
air has.
Then some of it is speed.
And some of it is pressure.
But if you the length of a string
doesn't change the total energy doesn't change. So
if speed increases the pressure has
to decrease.
and speed decreases
The pressure has to increase.
That's what you know, Mr. B nearly was saying
by the way, I might add that must have been nearly.
was
was born and lived and died long before airplanes ever
flew. He wasn't trying to build an airplane.
He was mainly interested in the flow of water.
And he's interested in rivers and dams and
things like that, but his rules
still apply to subsonic air.
And here's an example. Otherwise, this
is a target moth and out
on the side. We see.
a beautiful example
of a Venturi
and through that
through that little pipe coming in from the side to the
narrowest part.
That's causing a suction, which is sucking air.
And that's sucking air out of a gyro.
So what what it does by the by the way is something like this?
Imagine we have a wheel.
And it has a little buckets cut in it.
that
and we put that in our case.
And we put a little jet here.
That's a little nozzle.
And a filter to keep everything clean.
And then we connect this to a Venturi.
And his egg goes through the Venturi.
It creates a low.
pressure
and it sucks air out.
And that means fresh air.
Gets pulled in.
Through the through this.
And it comes out and hits the buckets.
And that makes the jurors spin.
So by the this in in a
tiger moth, which is what that airplane is.
And that I don't have a vacuum pump. We have
a vacuum pump. That's run by the engine.
But eventually works perfectly. Well, it
sucks the air out of that case and makes the door
spin.
And that's the instrument that it runs.
the turn and Bank indicator
okay, and so
what what?
Benue's theorem says is as the
air flows over the top of the wing it travels faster.
And as it flies underneath the wing if anything
it slowed down a little.
And so we get a low pressure area above the wing.
And that means there'll be a force acting up.
The total reaction now. I'm sure in your
life as you progress. You're going to
hear instructors.
Who challenge that and say
that being really fear and can't be
used to explain to fully explain lift.
We're not here to get involved in philosophical arguments. We're
here to pass an exam and so it cast
aside that that's how it works.
So at least we should be able to we should at
least be able to say how the newly's theorem
could be applied.
But there's a strong argument among people
now that
that it isn't really a full explanation.
of lift generation
However, you should know the principle behind.
the newly's lift Theory
So anyway, whatever whatever
the magic is that causes lifts to be
made.
There are some basic things that we need to know.
Anything any shape that's designed to
make lift.
It's called an aerofoil. So you'll hear
that phrase used a lot from now on.
The airfoil has got some names that we need to be sure of.
The front of the era foil is called the Leading Edge.
The back is called the trailing Edge.
The straight line that joins the trailing Edge to the
leading to the center of curvature of the Leading Edge.
It's called the chord line.
But his very interesting point most people know
that already.
The chord line is used by the way to measure the angles.
like angle of attack
because the wing is curved.
generally
And so that we need a straight line to measure an angle.
So the cord line is Handy.
If you want to be accurate and measure angles.
Now if you draw this is interesting, right if
you draw a whole lot of lines across the cord and
they're all at right angles to the cord.
And then I find the midpoint.
of each one of those short lines
each one of those lines going across
I find the exact middle of them.
And so I do that put a little dots there all those dots
are exactly halfway along the line.
and so those dots
is why join them?
I get a line like that. Call the main Campbell line.
and that
that line that line always remains the
same distance.
Between the top and bottom of the wing at any
given point that line is the same distance from
the top and the bottom.
It's called the candle on.
and
when we
talk about a wing having camber.
we talk about
the separation
between the chord line
and the cameline
and we've if we find the point where that separation
is that it's greatest.
So let's say let's say it's about
there.
backs maximum separation occurs
at that point
then that's what we mean by kamba.
Kamba is telling us.
How far what is the greatest distance or separation?
between the Campbell line and the chord line
now another thing that designers do
and have done for many years.
We like to put Wings in Wind tunnels and test
them.
But that's a very expensive business big wind
tunnels. Don't come cheap.
And so
What are we discovered was?
If you make an exact model of your wing.
And keep all those proportions the same.
If you keep all those distances exactly the same
you can build a smaller version of the wing.
And you can put it in the Wind Tunnel.
And you can get valid results about how
it's going to behave have a real Wing will
be Hive in other words what you're
really saying is you can test this shape.
With any size and then you
can scale it up or down and you'll all the data will
be valid.
It'll still be correct.
And so when they build a wing they
made this rule up years ago.
The chord the red line there the chord
line.
becomes
the basic
basic measurement of everything the cord
everything else is expressed.
As a percentage of the chord instead
of a number of millimeters.
Because by expressing it as a percentage of the chord.
Then I can if I keep those percentages the same
I can make the wing bigger and smaller and
be the same shape.
It'll always be the same shape even though it's bigger or smaller.
And so they express everything as a
percentage.
That means that a designer if we
could leave drop on a all the designers
having a coffee break.
That'd be talking about I'm working on a wing
that's 12% thick.
What do I mean by 12% think?
They mean the thickest part of the wing is 12% of the cord.
All right, and I'm working on a wing that's 12% thick
at 30%
if it's 12% thick at 30%
then it's 12%
The maximum thickness is 12% and it
occurs 30% down the cord.
So it's a really cool way to explain everything you want to
say about that wing.
And more importantly, it'll say what's this distance here?
and he might say
This ring has got a 4% camber.
A 4% camber would mean that that distance had separation
is 4% of the total chord.
And it's 4% camber at?
40%
telling you where it is as well.
So it's a really clever way to fully describe
the wing.
And then if someone wants to build it.
All I have to do is get all those percentages.
and I might get any Source they like
And they don't have to go they don't have to put it in the Wind Tunnel
again.
The wind tunnel tests are valid.
and so
we'll hear a lot more about percentages of chord.
as we go into performance ladder
and discuss that
but
so if you wanted to build a wing
they keep all these wind tunnel tests and NASA did
them all they keep all these wind tunnel tests in big
computer.
So I could write a letter and say I guys
I want to Wing that'll do this.
And I'll tell them how I want my wing to behave.
And they gave such the database and they
find the wing that's close. Most closely resembles
the one I want.
And they say railroad we found your
wing.
Do you want it and you say yeah, please
I'll have it and they say enter your bank
card details.
and all I send you
Is all the percentages?
All right, and then you go down the backyard and build that wing.
according to those percentages
and you've got a wing now that you know how
it's going to behave it's been tested.
That particular shape has been tested.
So it's really smart idea.
So don't be frightened. By the way. Those numbers are just gave you
with a fairly typical of most general aviation Wings.
They're mostly about 12% thick and
they mostly about 4% camber. They're very
a bit but
That's pretty close.
Except there are some special.
Wings, for example, I can build a wing
with no camber.
Now a lot of people think camber is
like thickness.
But that's that's not true Fitness isn't
Canberra. I can have a thick wing with no camber.
Because this is how I build a wing without camber.
I simply make.
The top and bottom a mirror image of each other.
and so the now
the chord line is the candle line.
Because the chord line is equal distance from the top and
bottom surface.
as well
so that Wing has zero can but doesn't have zero thickness.
It is there a canva?
We call it a symmetrical airfoil.
It would have some serious disadvantages.
because without camber
the only way it can make lift.
Is by having an angle of attack a fairly big angle of attack?
Whereas a candid Wing can make lift it
no angle of attack because it's got that shape over
the top.
But but some airplanes do use symmetrical aerofoils.
Some aerobatic airplanes. I spent a lot of my time flowing
a pit special and that aerobatics
and things and their foil
is
In the case of the pit special. It's pretty much exactly
symmetrical.
and the idea of a symmetrical aerofoil of
course means
if you want to fly upside down.
Then a cambod Aero foil is a disadvantage because it's
making lift the wrong direction.
You need a very big angle of attack to fly upside down.
And so there are many
aerobatic airplanes have
symmetrical or very nearly symmetrical
wings and of course, don't forget there are
some aerofoils their aerofoils beside Wings. What about
Rutters and elevators?
an irons
well
It would make sense that they should be symmetrical.
Because sometimes I go one way sometimes they
go the other we don't want to have it favoring one myth One
Direction.
and so
symmetricular foils are effective life
and they do exist.
in the case of the symmetrical aerofoil
the cordliners the candle line
a sign
so no angle of attack. It makes no lift.
I was decided aerobatic students.
A symmetrical aerofoil Works equally
badly on the way.
It doesn't allow you to fly upside down.
But you pay the price when you want to fly the right way up.
So it works equally badly.
Okay.
Now another thing we need to say a little bit about
and this is really important area actually.
and that is
as the air flows across the wing
air has another property by the way that we often forget about.
We call it viscosity.
now a lot of people would be surprised if I
had me say
that they're a sticky.
But again, that's because we live here.
And we're used to it. There is sticky stuff.
If you've got a ceiling fan.
the ceiling fan spins around
and it drags here with it.
But pretty soon all the air in the whole room is moving around
and the fans not doing it the fans
Not hitting all the air.
It's stirring it up and the rest and the air is
dragging the rest of it with it. It's sticky like, honey.
On not as bad as that, but it's the concept
it has viscosity.
And so when the air flows across the wing the air
at the very very surface if we
get right down to the scale of a molecule.
The air at the surface of the wing actually sticks
to the wind.
And then the air above that.
if this represents the wing
the air right at the bottom of the wing is actually
stuck to the wind
at the scale of a molecule is actually stationary.
And then the air above that is moving a little bit.
And the air above that a bit faster.
And so that happens until they get
far enough away for the wing to have no effect.
But you have this region in here.
Where the air is?
Actually, it's flowing in layers.
The bottom layer is still the layer above
that is moving slowly the layer above that
a bit faster a bit faster a bit faster. And then finally
it's too far away to be affected.
Now I'm gracefully exaggerating that.
The thickness of that we're talking about is like a
couple of millimeters.
It's not nothing like what I've drawn.
And we call that laminar flow.
So it's very orderly.
There's no mixing.
the air at the bottom
So if you are a molecule.
And you were down on the bottom.
There'd be no wind.
They could have a barbecue.
All right, the wind is all happening above your head.
And so
However, the laminar flow doesn't persist.
for the whole length of the journey
the laminar flow tends to stay laminar
while the wing is getting thicker.
In other words well over the air is going uphill.
Here it's there's going uphill.
Whether it's going uphill the rest of the air is trying to push
down on it.
So it stays lamina.
But as soon as the air tries to go downhill.
Then it doesn't stay laminar. It starts
to Tumble.
Now don't confuse that with stalling.
It doesn't leave the wing.
It just rolls the rest of the way Lord ball
bearings.
If you want to see laminar Flow, by the way.
Don't get in the kitchen and turn the tap on
if you turn the tap on just a tiny bit. The water
comes out is a beautiful clean strain.
If you keep turning it suddenly it'll
break up into rum into rumbling water.
into sort of frothy water
if the first little bit of turning on
a tap the water comes out as laminar flow and
when you turn it a bit further, it becomes turbulent changes
this whole appearance.
and
this becomes
turbulent flow
and this point here where the changes it changes
quite suddenly usually
from laminar to turbulent
That point is called transition point.
Now turns out.
As you can see from this drawing.
that the lamina flow
the flow stays laminar
Whatever the airfoil is getting thicker.
While over the air is going uphill.
As soon as the air starts to go downhill.
it tumbles and
it stays on the wing so it's not stalling. This is
only happening in a couple of millimeters.
And it becomes turbulent for the rest of the journey.
Ultimately, of course to the whole airflow will separate
completely off the wing. That's a stall
that's the turbulent flow isn't
a still it's just a different way of
moving across the wing
Okay, don't confuse it.
with stalling
now
there are some Advantage for high-speed flight.
There are some advantage.
in
Keeping the airflow laminar.
for a longer time
because that actually creates less drag.
You can probably but you can see that if there's
turbulence there's got to be more energy being used up and so
drag if you could keep the airflow laminar.
Then it will.
It will reduce the total drag and we already
saw that that's pretty important.
If you can reduce drag.
and so
we can build a wing that is designed to
keep the airflow laminar.
And we do it like this.
We the flow will stay laminar
while over the aerofoil is getting thicker.
So why don't we put the thickest part further back?
Why don't we have the point of Maximum camber at
about 50% of the cord?
And so that means it'll stay on
her longer.
And so that's called a laminar air flow
aerofoil.
A normal cambered aerofoil looks like that.
That's the typical general purpose thereofoil.
A laminate floor will look like that.
And also it makes some sense.
To keep this part of where wallet is going uphill.
That means more of the wing will have lamina flow.
And it makes some sense to keep that really smooth and clean.
Because that'll help it style lamina.
So usually the wing will be flush riveted.
For that part of the Winking will be flush riveted and
the nice smooth polished surface.
And then down the back here. They often go back to roundhead rivets
because they don't care anymore.
And of course the symmetrical airflow we know
about now, here's a case of a lamina error foil.
And this is Papa. I'm sorry. This is a Mooney.
And if you look at that airport, you see
where's the thickest part?
Well, it is it's probably half. It's probably halfway down.
And and also when you look up close.
The all the front part of smooth and the
back part has got the roundhead rivets.
But the front part is kept very smooth and Polished.
Here's a Cherokee 140.
notices laminar flow
You can see that really clearly. The thickest part
of the wing is at least halfway down.
That's a fairly unusual Wing show.
and
Interesting, by the way that Piper ended up
going back to normal aerofoles.
So he tried he tried lemon a flow.
as a sort of fashion statement
and then he found that it doesn't
make that much difference. You know, why because lemon flow
doesn't really have any big effect until you
start talking about 300 knots or faster.
You can bet every year or every airliner will have
lemon flow.
but Lord aircraft
blood aircraft that is more of a fashion statement. Oh look
at me. I've got a lemon flow wing.
But so what it's probably
not much better than any other wing.
So there's the thickest part of the chord.
halfway down the wing
so you can tell you can pick a line on the floorboard looking at it. You
can tell what sort of wing it is.
Okay. Now a few other little things I hear about angle
of attack.
You know this from PPL.
the angle of attack is defined as
the angle between the chord
line
and the direction of the role of airflow
most light aircraft when they're in Cruise
would have an angle of attack of something like two degrees.
Not much.
Just a little tiny angle of attack.
Because the speed is making the lift. You don't
need a lot of angle of attack.
if I
if I present the wing at a bigger angle to the
airflow.
Then the angle of attack.
has increased
and if I presented an even bigger
angle of attack.
So the that's what we mean by angle of attack.
the angle of attack
Is the angle between the direction and by
the way, the direction of the role of airflow is really the direction you're
flying.
It's the direction you're flying compared to.
the code line of the wing
sometimes if you want to sound really cool.
And impress the girls.
Then scientists talk about Alpha.
All right. So that's a always make sure
I say that if I'm at a conference or
I had a pretty high alpha.
today
All right, and I increased Alpha is
just a flash drive saying angle of attack.
People like to say it if they want to impress everybody is to
how clever they are.
Okay.
Now the next thing we want to look at.
Is again very simple.
It's angle of attack and inertia.
for example
Here is a way now. What's this carefully? It's and
it's an animation.
But you need to look carefully to notice.
If the wing is moving through the
air and the pilot now pulls back
on the elevator.
And that makes their airplane pitch nose up, but
here's the important thing even though the airplane
pitched nose up.
For a little while. It keeps flying.
down the same path
that's called inertia.
every object in the universe
takes a while before it changes.
And so if I'm flying like that might be better
than you put it on this side.
If I'm flying like that, and I suddenly
pull the nose up.
I'm exaggerating it. Now then for a
few seconds, you're a plane keeps going on that same path.
And therefore you get a big increase in angle of attack, especially
if you do it suddenly if the airplanes
flying like this and I pull back on the controls the
nose comes up, but initially it
keeps going but then of course it'll get more lift.
And So eventually it'll start to
climb.
But this little period is what we're interested in this period
where I pull the nose up.
And for a little while, it doesn't do anything except keep going.
That's a natural consequence because of
the problem of inertia.
And so
That's got some interesting effects. There's with we'll talk
more about later.
So this happens the airplane is going to fly.
along that direction of flight
and if you looked at that carefully, I'll just do it again.
You'll notice that even though the nose even though
the airplane pitched those up.
It still kept going on the same path.
And so it ends up.
That's an important point.
It keeps going on the same path briefly.
angle of attack
increases
so the angle of attack gets greater.
because of inertia
now important another important point
don't confuse angle of attack with nose attitude.
The nose attitude of an airplane is the
relationship between the nose and the Horizon outside.
So the angle of attack
is the angle between the chord line and the
relative air flow so in level float, of
course.
The Horizon would give you a pretty good idea of the angle of
attack because you're going level anyway
however, if I'm climbing
it's possible to have a high nose attitude.
and a small angle of attack
pretty obvious, right? Just because the noses High
doesn't mean you've got a high angle of
attack.
Of course.
If you're flying level in the nose is high then you
have a high angle of attack.
But it's possible to have.
a high nose attitude and a low
angle of attack
because the angle of attack is not interested in the horizon.
It's just it's working on which way you're flying.
and the same thing for a descent
If I'm descending, I have a low nose attitude.
But that doesn't always mean I've got a low angle
of attack.
In fact, we could talk about this briefly in a minute.
It's possible for that to be a dangerous thing.
because if I
just because the noses below the Horizon doesn't mean you don't have
a high angle of attack.
And we all know that an angle of attack is what causes the stall we
certainly got a lot more to say about that as we
progress.
But you should know that from people.
And so therefore don't confuse
those attitude.
with angle of attack
Now there's a very interesting way that we can study this
in great detail.
And we do it by creating a thing called a
wind tunnel.
A wind tunnel allows you as we said
earlier.
It allows them to test the model of the airplane.
And therefore predict exactly how the real airplane will
behave.
And so we put the airplane in the wind tunnel and we
blow the air on it.
And then we change the angle of attack notice by
the way.
This is going to become important.
That can only be done in the Wind Tunnel.
The only way I can I can check the angle of
attack alone.
Just the angle of attack changing.
because if I try to change the angle of attack in Flight, I'll
change the flight path and everything goes
ape s*** as they say right if I
try to change the angle attack in level flight everything go
everything else changes the only one way
for a designer.
to study angle of attack alone
And that's put it in the Wind Tunnel turn the wind on at a
certain speed and then rotate the airplane in that
wind.
You can't do that in a rural airplane the moment you try.
You're going to change the speed and direction and
so it's very hard to know what the hell's going
on.
So that's the beauty of a wind
tunnel. It allows me to do what I can't do in a
real airplane.
It allows me to watch how the angle of attack is behaving
and what effect it's having alone with
everything else constant.
and
that's a smaller cheaper version.
For testing notice, by the
way, they actually in the Wind Tunnel actually suck the air out
of the tunnel.
And the ear that comes in and is nice and smooth.
If you have the propeller up the front the air
coming in would be spiraling and that it
spoil it all.
So they actually suck the air out of the back and then
pull nice smooth there.
to pass over the wing
Now here are some actual wind tunnel tests.
And the beauty of it is we can now see
very clearly What's Happening by introducing
smoke?
With little nozzles in the Wind Tunnel they can
introduce smoke into the wind.
And then we then it all becomes visible. These are
actual movies of actual wind tunnels.
And so we see this happening.
We rotate the wing.
Only the angle of attack is changing.
You see how the air now is separating?
The stall is occurring.
That's not laminar and turbulent flow. That's there is
actually completely breaking away from the wind.
Now here's a big danger.
And this is where it becomes a safety issue.
I'm diving down on the ground at the ground.
And then I pull the nose up.
Now I'll do that again so you can watch it again slot carefully.
What happens to this guy? He's diving at the ground. Now, this
is something that's really important. We call it
ground Rush.
and for many years I was the
test officer for low level aerobatic training
and so when people wanted low level
aerobatic approval to do air shows and
things
On tests are appointed me as the guy who does
the test and but one of the things you check is.
This idea of grand now doesn't happen up high if
you're at 3,000 feet and you're diving
at the ground.
you can't even see the grounds too far away to take
much notice of
but if you're at 300 feet and you're
diving at the ground all of a sudden the
ground starts to expand in the windscreen.
now if you haven't had that experience that can
be really bad news because people
People overreact they see the ground
expanding.
The ground expands in all directions are
about the point where you're going to hit.
So you're looking through the windscreen and everything looks good
for a while and then all of a sudden the ground goes.
And and what and someone who hasn't
been trained says oh s***, and he pulls like
mad on the control column. That's exactly what it's just
talking about the airplane pictures up, but it keeps
going
and all he's done is increase the angle of attack and if
he happens to go through the stalling angle.
Then he's going to end up with less lift.
Instead of more and he's made it
worse not better.
They call it ground Rush. It's a psychological effect.
It's an optical illusion really but it's
a very powerful one if you haven't experienced it.
It'll only happen if you diving deeply at the
ground and also very low, so hopefully you won't be
doing it for a little while. But if you do yeah a low
level neurobatic rating one day.
It's a real thing. I've got some movies later. I'll show you of doing
a loop at 300 feet instead of
at 3,000 feet.
And so this is what happens. I pulled back why it gets
the angle of attack increase now if that
angle of attack goes beyond the stalling angle.
Then he goes.
He's got a problem.
And so we can now check this.
And I'll just finish we'll just get this in before we
have a short break.
as a result of the Wind
Tunnel tests
I can draw a graph.
And in this exam by the
way, the examiner is going to give you graphs.
And he's going to ask you to interpret the graph very simply.
But for example along here
we put angle of attack.
increasing
and up here. We put lift increasing.
Right and then in the wind tile now, this is important. We
keep the speed the same now, you
can't do this in a real airplane.
We have the speed on the same speed and we
just rotate the wing.
and say the lift does this
It goes up and as angle of attack increases.
the lifting creases
and then it reaches a peak.
And that Peak is called seal Max the maximum
lift coefficient. The wing
is now making the greatest possible amount of
lifted leather make
at that speed