Topic 2

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

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.

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

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