See, this is the course outline, tenderly,
I have listed out 12 topics starting from
historical development, then rotor configuration,
elements of hovering and forward flight, sorry,
vertical flight, then forward flight, performance,
rotor blade idealization, flap response, trim
and coupled flap lag torsion dynamics and
then, introduction to certain stability problems.
So, these are vast number of topics are covered,
but we will go slowly because it is a very
ambitious thing to cover everything.
But towards the end, if time permits, I will
just give a brief introduction about some
of the issues, which one has to tackle because
unless you understand this basic stuff, you
cannot directly go on, then solve that. You
can address those problems; they are from
map, practical point of view, what are the
real issues, that is why the topic is given
as helicopter theory dynamics and aeroelasticity.
Please note that dynamics is very, very important
for this course, that is rigid body dynamics
I am talking about, later comes flexibility,
structural dynamics, that is important, but
at this level, rigid body dynamics is essential.
So, you can brush up of a rotating system
that is essential.
And I have given the list of references, about
listed 10 books, I will go through one by
one. The 1st book is Gessow and Myers, aerodynamics
of helicopter, which is a 1952, but it is
available one copy in the library and it is
out of print, but it is a good book; basically,
very, very, in the, for a beginner it is good
to read that.
The 2nd book is Bramwell, which is a 1976,
it was published in London. Of course, another
copy has come, but it is no more it is difficult
to follow that book, but it has lot of information,
lot of information, but difficult. Here, in
the beginning it is ok, towards the end, you
sometime, you will not know how those things
are obtained, how the various expressions
are obtained. Then, there is a Stepniewski,
rotary wing aerodynamics, this is a Dover
publication. This also has a lot of information,
but it is difficult to read that book.
Then, Wien Johnson, this is about 1000 pages,
they are also helicopter theory; this is a
good book. See, all these books, later I would
say, if you know helicopters, you can understand
the book, you cannot say, that I will start
reading the book and then understand. That
is where the problem starts because the dynamics
is really important. Of course, I have my
lecture notes copies, which are there in the
library, I do not know how many copies are
there, there is sufficient number and there
I have given all my derivation, starting from
first principles, starting from basics. And
please note, in this course I cannot derive
the equations in the class because if I derive,
then I will spend enormous time only in deriving
and then, at the end, what I require is the
result, but the most of the time is spent
on just algebra.
So, I will be using power point, but the in
between steps you have to read, understand,
how they are obtained and Padfield, this is
a, Prouty is about performance mainly and
then Padfield is about flight dynamics. So,
you will find, that the focus of each book
is slightly different; you will find certain
book will refer some topics, but some other
book you would not see that.
And you will get to know only at the end of
the course, oh, this is what I have mentioned
in the first lecture, what I have told you.
Then, Leishman, this is about helicopter aerodynamics
and then Seddon, this is, I do not have that
book, but it is a basic helicopter. Then Bielawa,
which is structural, this is from an industry,
but slightly different.
So, you will find, that I follow my notes,
but I have all these books, all the books
I have pretty much, except this because I
find it is a little low level, so I did not
buy. These are kind of books, which you require
for a helicopter theory. There is other class
of books, which are like a pilot flying, how
do you fly, that is from the pilot point of
view. They will also called helicopter aerodynamics,
something like that, but it is like a flight
manual, lot of pictures, but you do not see
any equation and only words, it is very difficult
to follow. But because when a person who is
not flying, he does not know what that means,
but the person who is flying, for him equations
are not important, he is more worried about
how the vehicle behaves or flies or what happens.
So, there is a difference between the kind
of books, which are this and the books, which
are pilot manuals. Then, of course, you can
have the maintenance manual and etcetera,
etcetera. We will not get into the maintenance
part.
And of course, the grading, like I said, you
have a midterm final and the assignment term
paper. Term paper you have to, everyone, I
will give one topic, that depends on your
interest plus it is relevant to helicopters
because I want to know, how many have really
registered, because I find the 15, then 7
added, then 2 deleted. So, I have to fix how
many you want, the list comes, I will list
out the topics, I will say each one is going
to do one topic and that is about 30 percent
weightage. And assignments I will give, but
I do not, I will give the problems, you have
to work it out. If you have doubt you can
ask me, but I am not really asking everyday
you submit this assignments, but certain thing
I will ask you to submit. And that is about
the overall picture of the, I would say, the
course outline. I will try to make it like
a story, the whole course.
Now, we start the course. Let us see what
the, helicopter, this is what 15th January
1909, what Wilbur Wright, Wright brothers,
he said about it.
So, he says, like all novices we began with
the helicopter in childhood, but soon saw
it had no future and dropped it. The helicopter
does, with great labour what the balloon does
without labour, and is no more fitted than
the balloon for rapid horizontal flight. If
its engine stops, it must fall with deathly
violence, for it can neither float like a
balloon nor glide like an airplane the helicopter
is much easier to design than an airplane,
but it is worthless when done. So, this is
what the helicopter.
Now, that is a statement, later you will have
a counter statement that I will give at the
end of course. So, what is a helicopter? We
will go slowly, one by one; very simple. We
will start with the key, key difference between
an aircraft and helicopter. Of course, all
flying vehicles, we need to have to lift to
support the weight and you need propulsion
for moving forward because you need to lift,
you need to have propulsion, but then, once
it is up in the air, you need control. So,
basically, you need to have lift, propulsion,
control. These are the three main things,
or of course, structure comes later, that
is all part of it, I am just saying key.
But in the helicopter, all these three, please
note that all the three lift, propulsion and
control, they are all done by the rotor only.
The rotor system has to do all three functions
and you will find some of the terminologies,
which are used in helicopters, they may contradict
what is used in aircraft. So, that is why,
those things will be introduced as we go along
because what you called thrust in an aircraft,
it is for propulsion, but in the helicopter,
the word thrust is for lifting. So, there
are differences, which we will introduce,
you have to get used to that.
But if you look at an aircraft, you have wing
to take care of the lift; propulsion, you
have separately jet or a propeller or any
of these units; then, control you basically
do with aileron, rudder, elevators, etcetera.
It is a traditional aircraft, but the key
difference after this is, helicopter can land
and take off from any terrain, that is the,
you do not need a runway, you can land in
a roof top, you can land in a, even of course,
you need some clearance, so whereas, aircraft
cannot do that. So, it is like a vertical
take-off and landing, you may call it VTOL,
but this is the advantage of the helicopters.
And another, this you will learn as we go
along because this is you need to calculate,
it can hover with minimum power because you
may say, hovering capability you can have
in different types of vehicles, but the power
required to hover for each class of vehicle
may be different. So, helicopters have the
advantage of having minimum power to hover
for the same weight; you have to take a weight
as the baseline.
Now, let us look at the, I will go for the
historical development knowing the key difference
between the helicopters and the aircraft.
What are the key differences you learned?
Difficulties, when they were building helicopters,
please understand, and then I will go through
historical development, these are very common.
For aircraft, structural weight should be
minimum. That means, you must choose a proper
material to design your structure. Then, for
the rotor you need to have a strong light
structure for blade and hub because the kind
of force, just for idea you know, in typical
blade, which is, the Indian blade, I will
take Indian rotor helicopter, which is the
advance like helicopter, the blade masses
about 64 kg, around 64 and it rotates about
300 plus rpm. Now, this at the, the force
you get, the centrifugal force is of the order
of few 100,000 Newton. So, it is a tremendous
amount of force, it comes at the root where
you attach. So, you need to have strong structure
for blade, hub, everything, otherwise you
will simply.
And of course, control including torque because
you are something rotating. So, if you do
not have a compensating, there is anti-torque
device, it will also start rotating. So, how
do you balance the torque? These are the problems;
these are all there right at the beginning.
So, how different people, different people
in the sense, these are all not government
supported projects or anything like that;
it is like a purely personal enthusiasm, that
is all. They just want to fly, they designed
the different aircraft, different thing, tested
it, but it is because of the development of
all these individuals in various places. Finally,
it came to the today, what we call it is a
helicopter. As a history if you go, suppose
I will give, first is, I have just brought
because this is very interesting thing.
So, I showed Chinese top B.C., which is actually
before 400, this is what the Chinese top,
you all know, that is all. This is a helicopter,
very first, but it is a toy, now no more.
But nature also has certain things, very nice,
because this I have picked up my trip from
somewhere, this is actually two blade. If
you drop it, see, so I do not know, whether
you can see, you can capture this, but may
be from height, maybe I will throw it and
then, so this is a two blade. Another one
is a maple leaf, which is a single blade,
but this I founded very interesting. So, even
if you see, but if you have high speed camera
you can really look at how it really turns,
then it starts descending. This is, I call
it nature, this is man-made, this is nature;
this is one because I found two-bladed it
is nice. So, I picked up couple of them and
brought it. I do not know the name because
if you want to know where I picked up, when
I went to Andaman, I saw in some place in
the Andaman, this one. So, I picked a lot.
So, I went home, I brought all this because
the single one maple, that is there. But this
is a very nice interesting thing and it can
float also, there is a seed like thing, it
floats in water, it can go. So, it is very
nice, I thought this is a nature rotor.
Then, you have 15 century Leonardo da Vinci,
I will show, that, which, that picture, which
is actually, Leonardo da Vinci’s picture
is this, this is the, we called it air screw.
That means, air is a medium, you just screw
through that and you go up, that is all, it
is a nice concept.
And this is a famous picture they always show.
Then, of course, this is the 18th century,
you say, George Cayley, he made some and there
are other people also, I would say, he made
some models basically with rubberband and
rotor, just rubberbands, that is, all these
are all toys. You may see one rotor, rotor,
rotor and another one horizontal something,
but all these things and it is a nice concept,
that you can go, you can climb, but it has
no bearing, unreal big helicopters, till the
time people were thinking how to fly, how
to go, that is all. But then, if you really
want to know, the development of helicopters
started with the 19th century, I would say
it was realized first, I will give some details
about that.
We got steam engine, so steam powered models
were made small couple of kgs, that is all,
and they were able to fly. It was demonstrated
to various, what we call, academies, science
academies I would call it, science academies.
I give you the 19th century first half, I
will write the name, that is, because these
are, because if you understand history, you
will appreciate.
This is in England, this is in 19th century
and then, Enrico Forlanini, this is Italian,
they built steam powered engines and about
this was 3.5 kgs, worked with rotor. They
showed models, but then Edison, that is a
very interesting thing, they said lack of
reliable light engine that means, power, if
you want to go up, you need to put some power.
So, the first thing, that came up was power.
Now, that power requirement, Thomas Edison,
you will be surprised he said that thing.
Unless you have an engine weight to power,
this is an engine, do not bother about rest
of the things, that the engine, if it is less
than 1 or 2 kg per hp, unless you achieve
that, you just cannot fly.
Now, I can give relating background story.
Present day turbo shaft, 0.2 kg per hp, that
is, of that order engine because we also did
some… See, in the 1980, in, when I was a
student in IISc Bangalore, there was a project
to design a rotor. So, the engine chosen was
a scooter engine, Bajaj scooter engine, and
of course, we four of us, because that time
we were just beginning in helicopter, 80s,
so we designed a big rotor, rotor diameter
more than, what I think, 13 to 14 feet and
then we put that, we were able to rotate the
rotor, was fine, it was rotating, no problem.
And then, we had a big platform on which the
rotor was mounted, the engine was mounted.
Then, when if wanted to lift, of course, when
he said it was not even lifting because the
power later was removed, the engine keep it
outside. So, the engine was removed from the
structure itself, then from that you give
a shaft with the universal coupling and then
engine was removed. This was able to lift
and with that we closed the project. We said,
I think Professor closed it he said, we demonstrated
lifting. The reason why I am saying is, we
did not know at the time, I did not know honestly,
because I started learning about helicopter
only after my PhD.
Then, today you remember lot of people say,
I want flying car. Please understand, yes
you can make a car fly because we should go
up, but please understand, whether your rotor
and the power and the weight, whether it is
sufficient because I remember few years back,
somebody came, he said, that I will put four
fans and then I lift it. How? You just put
something means, it will not, nothing will
be lift. You have to see whether the engine
has the capability to lift your weight; unless
you have that basic thing you will not be
able to lift a helicopter. So, that, that
is the reason I said, that this is very, very
important. If you are going to design a helicopter
aircraft you have a wing because wing lifts.
Here, actually the rotor has to lift the engine
weight, that is the problem, it is like, lifting
it like this vertically aircraft, you need
to give only propulsive and you need to overcome
only the track and if you see the aerofoil,
lift it to drag. Drag is very, very small,
one-hundredth, but one-hundredth of the power.
You give, you can lift it to weight, whereas
here, you have to use all that; that is the
key difference in helicopters.
Now, how the word helicopter came? Actually,
this was coined by 1963 by French man d'Amecourt,
it is called helix and petron, that is, a
spiral wing. Then, it became the helicopter,
of the general word for this class of rotating
wing. Now, people call it rotary wing vehicles,
you may call it helicopter because sometimes
people use the word rotary wheel and these
two are used, you know, commonly in publications.
Some people use rotary wings, some people
use helicopter, that does not matter. But
the real development of helicopters as a vehicle,
you will see, started in 20th century, 1903,
aircraft flew December, that is, Wright brothers,
but most of the developments in terms of building
a machine.
Now, I will show a few of the samples pictures
of how people built various machines, you
will have a idea how the development was going
on in building this helicopter. This is, I
will show, this is the 20th century.
This is in my notes, it is there, lot of pictures;
I have also CD where I put my notes. 1904,
Renard, France; then Paul Cornu, 1907. Please
have remember, aircraft flew 1903, I will
just give some, this is the one of the interesting
way constructed. The first man carrying helicopter
with 2 contra rotating rotors of 6 meter diameter
in tandem, that is, one behind other, the
total weight of the vehicle was 260 k g and
was powered by 24 hp engine.
This helicopter achieved an altitude of 0.3
meters for about 20 seconds and it had problems
with stability. However, Cornu became the
first person to succeed in actual helicopter
flight, 0.3 meters, 20 seconds. This are the.
Please as you go along you will see really
how people were struggling to build.
Then, of course, this is again 1907, this
has 4 rotor helicopter. So, you see, you have
to have 1st engine, that was the first it
was realized. Steam engine was built, but
then they made only models, then came the
IC engine, internal combustion engine. Now,
with the internal combustion engine only the
development started going on in the helicopter
field. And this is another, Louis Charles
Brequet, he built a machine, which he called
helicoplane. It had four rotors, 8 meter diameter
rotors, gross weight 580, engine 45 hp. This
made a tethered flight at an altitude of 1
meter for about 1 minute; this is in 1907.
Then, I will give some group in US, is a father-son
combination. In 1922 Emile Berliner and Henry
Berliner, the father-son combination, they
built a two engine co-axial vehicle, please
understand. Now, you see, there are two types
of how different, different geometries are
there, that is why, I want to indicate you,
each group was trying different configurations.
This is a one below other, same thing he also
made, another one side by side; the earlier
one is tandem and other group at four in a
crush berth. He built a side by side helicopter
in which forward flight control was achieved
by tilting the rotor shaft, these vehicles
were highly unstable.
So, first you want to lift the vehicle, after
lifting, the problem comes on stability. For
lifting, the engine requirement; when you
go to stability, you have to understand the
vehicle dynamics. So, without that you cannot
achieve stability. You may lift, but you not
have any control for the vehicle. You see,
how the development really went about in building
a vehicle.
And of course, you may know there are lots
of things. Sikorsky, he was in Russia earlier,
he is a Russian, 1910, he built a vehicle
with co-axial rotors. It could lift its own
weight, but not with a pilot, that is all,
nobody concerned.
But later he moved to US, initially he was
in Russia. In Russia he was trying to build
a co-axial, but there is another Russian,
in 1912, he built a, Yuriev, two bladed main
rotor, small anti-torque tail rotor. This
helicopter did not make any successful flight.
Now, I will give, there are lot of pictures,
different groups of people and this is in
Austria. Lieutenant Petroczy and von Karman
constructed a tethered contra rotating co-axial
helicopter with three engines of 60 hp each,
the rotor diameter was 6 meters. Vehicle was
designed as a platform, observation platform.
Even now people talk about observation platforms,
but it made several flights, but had control
problems.
Another, because they were able to lift, this
is an interesting vehicle George de Bothezat,
it is in USA, in 1922 he built a large helicopter
with four six-bladed rotors at the ends of
intersecting beams. Now, you know, everybody
building intersecting beams. Good control
behavior was obtained by utilizing differential
collective; we will learn about collective,
what it means, later. This vehicle made several
flights with passengers up to an altitude
of 4 meters to 6 meters. This was the first
successful rotor craft, which was ordered
by US Army, but later it was abandoned due
to mechanical complexity of the vehicle because
you have 4 rotors, each one has to be controlled
with different rpm, etcetera.
Then, this is another very interesting configuration,
this is in France again. Etienne, I do not
know how do you pronounce, Oehmichen built
a machine with four two-bladed rotors to provide
lift. Five horizontal propellers, horizontal
propeller means propeller like this, plane
of rotation is this for attitude control,
that means, pitch roll, etcetera. Two propellers
for propulsion, one propeller for yaw control.
So, how many rotors have this vehicle? All
powered by 120 hp engine, it had thirteen
separate transmission systems. The vehicle
made several flights and set a distance record
of 360 meters.
Now, why I am bringing this kind of various
configurations is, today there is a lot of
interest among students to build, I do not
know, micro-vehicle, flying vehicle. They
will say, I will put six rotors, I will put
ten rotors, I will put this, I will put one
more for forward flight, I will make this,
it is good. But one should also know if you
try, similar thing long time back and what
are the problems they faced. It is important
one should understand the history because
history teaches a lot of things even in aviation.
It is not, writing equations later is all
fine, but please understand, all these people
built, I do not think the level of mathematical
knowledge, what we have today they had. It
is for sure because I do not think they had,
but they tried, they built, but it is with
conviction, it like discipline, they try to
make, each person tries because let me try
this vehicle, let me try this vehicle and
that is how the development started.
Now, this is another configuration, you look
at it, this look like Wright brothers, now
Biklin, but he has, it is in Spain 20-26,
Raoul Pescara built a helicopter with two
co-axial rotors of four blades having a diameter
6, this was powered by 120 hp engine for forward
flight control. He warped the biplanes to
change their pitch angle; how you warped,
I do not know the technical details, but he
was twisting, you will learn later. So, he
was the first to demonstrate, please note,
cyclic pitch control. Earlier, I used the
word collective, now there is another word,
cyclic.
So, these are key terminologies in the helicopter
flight. This vehicle set a distance of 736
meters, again stability problems.
Now, a little deviation will go and that is
the autogyro. I will give a brief history
on the autogyro; this is Cierva in Spain.
What happened was, see, he wanted to build
an aircraft, he build an aircraft, but then
the low speed the aircraft stopped he said
that I want to fly at very low speed that
was his. So, he was the first one to design
something called autogyro.
What it means is, there is a propeller, you
see, is like an aircraft and of course, is
a small wing is there. This rotor is a freewheeling
rotor like a wind mill, what it does is, the
rotor will be kept at this angle, once it
said, like what we showed from the seed, which
when it is coming down, wind is going up,
so it is rotating and then it will slows down.
That means, wind is going through the rotor
and because of that, rotor start rotating
like your wind mill and then, when it rotates
and some angle, it lifts because the cross-section
of every blade is an aerofoil. So, you get
the lift and he does not need any antitank
because it is freewheeling and you can fly
very low speed; that is what he built that
vehicle.
But what happened was, but you need to go
forward speed, you cannot just hover because
you need a forward speed for the vehicle,
like you see kids, when they run with that
small fan type in the paper, they are, when
wind blows it starts rotating, same thing,
you run, instead of that you move aircraft
little slowly, it start spinning and then
it lifts.
But what he found was, the problem he faced,
because why he is listed in, you consider
this as a rotor disk and this is rotating,
this is wind is coming this way.
So, when it is rotating, you will find here,
you will have a, because this is omega times
some smaller velocity, then this is forward
velocity, the relative wind is additive. Then,
you have a large relative wind, but once will
go this side, the relative wind subtracts.
So, he found, on one side I am getting increased
lifts, other side reduced lift. So, as the
result, the moment the vehicle takes up, it
was rolling. So, what he did, that was his
why he regarded is his ingenuity he said,
that because there is a rolling movement that
is generated on the vehicle when it starts.
So, I am going to, if you do not want rolling
movement, I will put a hinge 
like a door because it is rotating, centrifugal
force pull, lift force will go and the movement
transfer to the fuselage is minimized. So,
he was, this is a great engineering solution
and it was successful. He built 500 autogyros,
he formed a company, he sold, it was a very
successful vehicle; this 19, 25, 27, that
is Cierva, this is 28.
Later, this is called way, please note, I
will use the word flap. Flap means, this is
again a new word for rotor blade going up
and down, that is out of plane of rotation,
that is called flap, but it is rotating, but
it is going up and down. Now, he introduced
a flap hinge, the first and that is how he
is successful and he is credited for that
engineering solution.
Then, of course, subsequently there is the
other problems happened. When it was going
up and down, you know, that centrifugal force
is pulling this way, lift force is doing this
way, but you will start getting because one,
it moves your center of gravity of the blade,
is coming, moving back and forth from the
access of rotation, then you will create Coriolis.
The coriolis will be in the plane that means,
if you move your blade like this, you are
going to get a force in this plane, and if
it is not strong enough you will break it,
so there was a crash. Then, he said, oh this
is another problem, go and put one more hinge
in the plane normal to that; that is called
lead-lag, lead-lag hinge, so he put that lead-lag.
So, you see, from dynamics now I can go back,
but there are certain failures happened. I
learned, name anything, see certain interesting
thing you put up there are certain absorbers,
which are put in rotors, not all rotor.
If you want to reduce the vibration, there
is something called a vibration observer system,
pendulum observers. And I am just giving you
story initially, they put a pendulum with
2 kg weight, which was fine, it is reducing
the vibration. But then, they put 4 kg with
the same attachment, but then one wing flied,
it flew off because the attachment, whatever
you have, because if you have 4 kg then plane
coriolis force is tremendous, you are just
increasing it and as a result, that whole
thing broken.
So, you have to see from dynamic points of
view, whenever you have, anything, system,
which is rotating, which is moving, flapping
up and down and which also moves back and
forth. You need to evaluate the dynamic force
precisely, that is why, the dynamics becomes
very important in the rotor bullet. Please
understand this rotor bullet, like I said
6 meters, that is just for sample, the blade
radius normally around 6 meters, you can say,
there are blades, which are 13 meters long,
the diameter is more than 100 feet, there
are helicopters.
So, please imagine, that is a very long blade,
it is highly flexible, that is why, when the
helicopter is parked, we find the blades are
down. So, you are now dealing with a system,
a beam you can say, a very long beam, a beam,
which is like, can do this and you are rotating.
So, you have to be careful about the dynamics
of that. So, that is why, structural dynamics
is very, very important in the rotor.
And he gave an engineering solution, now it
is used I, in this form or in some other form.
So, as we go along in the course, you will
see, oh flap hinges by Cierva. That is why,
he given, even though this is not a real helicopter,
he did not build a helicopter because it cannot
hover.
Then, this is another vehicle, which was Henry
Frock, this is in, I think it is in Germany,
he built a helicopter with two rotors side
by side, but you see, a small propeller like
thing, actually that is not propeller, that
is a cooling. This is a rotor to cool the
engine, just like in your car your radiator,
you have some small fan, it is like that,
it is not propulsive thing and he built this.
This rotor had articulated hub, articulated
means, you put a hinge, later I will explain
what is articulated, and he has directional
control and vertical. Of course, he had to
put a tail, it also has a shape of an aircraft,
but wings are not there, the rotors are the
wings. This vehicle set records for speed
122 kilometers per hour, altitude more than
2 kilometers and endurance 1 hour 20 minutes
and set a distance record of 224 kilometers.
This was one of the successful vehicles.
But then, you go to Igor Sikorsky in US in
1939-41, first he built because he moved from
Russia to US, VS, it called VS-300, 1941,
which had a single three-bladed main rotor,
a tail rotor.
See, here in this picture you will see, there
is one rotor here, one rotor here, there is
one rotor here and then one main. These are
two horizontal thing, initially this model
had this, later he removed these two horizontal
rotors, put them in the middle as one rotor,
later that also he removed.
That one was R-4, a derivative of VS there
was constructed, that is why it was reduced
to two and finally to one vertical tail rotor,
1942, R-4, a derivative of VS-300 was contracted.
This helicopter had single main rotor and
one tail rotor; main rotor diameter 11.6 meters.
So, you see what, and then, weight 1100 kg
185 hp engine. This model went into production
and several hundred were built during World
War 2, basically for medical evolution. So,
the helicopters first used in military was
for evacuation and please note, Sikorsky vehicle
is considered to be the first practical, truly
operational, mechanically simple and controllable,
that is all.
So, till this, it was all helicopter development,
development, development. Once you have a
successful vehicle, successful in the sense,
a vehicle, which can fly. Of course, it has
problem, problems will always there, even
today problems are there, but this is a successful
vehicle, practically operational.
Now, after you build the helicopter, then
you will say, now I have built a helicopter,
now what is going on, what is that I have
to do because helicopters are built, they
are flying. So, you start thinking about what
next is actually improving in the, like you
said performance, which goes the technology
because the developments, now mainly in the
field of improving the capability of the vehicle
with increased, with further technology improvement.
You will also have improvement in the vehicle.
So, today, now you would say, you are going
to build a helicopter, you can build a helicopter,
it is, everybody knows what you are going
to do because already people have build it.
Then, you say what technology you are going
to use and what is the configuration you are
going to choose? How? So, the focus, that
is, 1942 please remember. Now, I think I will
show you, of course, I will give some pictures
here, the type of configurations.
You all know what are the various configurations
of helicopter, you have a single main rotor,
one tail rotor. Of course, this tail rotor
here, it is a fan-in-fin, it is called fenestron
because open tail you can have; another one,
the same tail rotor put inside a shrouder.
This is few companies make, only recently.
Then, there is another scheme, which was start,
you do not need a tail rotor, but you have
a jet rotor, of course it was abandoned, it
is just for picture I am showing. So, you
have a jet at the two ends and it keeps spinning.
So, you have a jet rotor that means, it can
lift, no problem. Well, of course dynamic,
various other, other issues will come, but
you do not need a tail because this, if torque
transfer is not, there is a freewheeling.
Then, you have another configuration, which
is the co-axial on below the other, but today,
this type of configuration is built only by
Russians, that is a Cornu helicopter because
they have specialized, they make these helicopters.
Then, what is the use? One of the uses is
because it is a compact you do not know the
tail, which is long hanging there.
There are advantages, disadvantages. The disadvantage
is, tail requires power, that means, you actually
spend power not for lifting, but for just
having control. That is, here, both the rotors
here I am using, one is in one direction,
another one another direction and the vehicle
is compact, but then controls more complex.
Then, you have the configuration of this side-by-side,
of course this is, I showed the picture, this
was a project, V-22 Chprey. See, it went on
for more than 50 years, 40, 50 years; US navy
was pumping money to build this side-by-side
rotor. You, it is the tilt rotor configuration,
others are only, of course, pure helicopter
more, this is the tandem.
Advantage in tandem, please understand, you
can shift your CG to a large, the CG travel
is more, whereas in conventional helicopter,
the CG travel is highly limited. Please understand,
it may be less than, may be 20, 30 centimeters
in the longitudinal direction, you cannot
put wherever you want. So, there are restrictions
where the CG should be because otherwise,
you just cannot fly the vehicle.
So, but this is for heavy lift, you cannot
do the same kind of a very highly memorable
things. So, every vehicle has its pluses and
minuses. Of course, the transmission system
is complex and you see, the tail rotor, this
rotor is slightly above this rotor because
the wake or whatever disturbance from this,
should not hit it. If it hits, then it have
its own problem. So, you have, these are the
basic configurations.
And of course, there is another configuration,
which is called the notar, that is, no tail
rotor; that is, no tail rotor. This is the
name they gave, but it does not mean, that
there is no tail rotor. What they do? They
have a jet and they have coanda effect, gives
the side force. It is like, I will draw the
picture, it will come and then the flow comes
out like this and the rotor downwards comes.
So, one side you get a side, this is the rotor
and this is the tail cross section.
So, you somehow have to generate a side force
to balance. So, they call it the coanda effect,
you blow the air through a small slit and
then there is also a jet at the end. That
means, there is fan inside the tail, that
blows the air through the tail and the air
comes out and that gives the reaction force
and then balance, this is called a notar configuration.
But it is only for one arc, one helicopter,
that was built actually, that is here. This
picture, there is no tail rotor here, but
there is a fan inside, so and that is blowing
air through this. Now, these are the configurations,
these are the last statement.
What are helicopter? We started with Wilber
Wright, now you say, if you are in trouble
anywhere in the world, an airplane can fly
over and drop flowers, but a helicopter can
land and save you; that is it. So, this was
by Igor Sikorsky in 47.
Now, with this, pretty much the history is
over. So, this is all the history, wherein
of course, more information, colorful pictures,
they all there in my other notes, but this
is the key why I gave this, spent an hour.
And giving a history is to know, that lot
of people have struggled to build a vehicle,
to be a successful vehicle has come out today,
it may be Sikorsky built, but then several
people have contributed towards, that is why
it is with a day. It is not that they were
doing it for name or fame or anything like
that, it is just interest to build that, that
is, it to fly.
Some preliminaries, today with that we will
close today’s lecture, control requirements
for a helicopter because any vehicle we said,
that for lifting we need power, engine selection
is a must. So, you should have a sufficient
power to lift, number one. Once you have lifted,
then comes control. Now, basically you need
to control what position and orientation,
so it is a six degree of rigid body, three
positions, three orientations.
Now, that means, you can have six inputs,
I will say, I will give this input it will
control that. If I gave another input I will
control that. Unfortunately, human beings,
we are restricted with two hands, two legs.
So, what happened is, we can give, only move
these two and both legs, so the controls are
also reduced, but how do you reduce? Mean,
you reduce the number of controls by coupling
that means, if you give one input, it will
not do only one function, it will do something
else, which may be undesirable, but it will
do it.
So, in the helicopter what are the controls?
I have used four main, lists down, one is
the vertical that means, you want to go up
and down, simple. That means, the helicopter's
altitude is changed only by one control, that
control is collective pitch. I have used the
word collective pitch, you will slowly understand
what is the meaning of collective pitch as
we go along you will learn, but from pilot’s
operation point of view, he will have a lever
on his left hand. Please understand, that
lever will, you will pull it up, pull it down,
that is all. If you pull it up, is going up;
if you push it down, is coming down. So, that
is the collective lever; I will show a schematic.
Then, for directional control, because you
need to know, which direction you are pointing,
that is called the yaw, we know because we
are all aerospace engineers. So, yaw control,
that is, by tail rotor pitch angle because
the tail rotor is there, you adjust the side
push. So, if you increase, you will turn,
you will go this way. So, the tail rotor,
which angle he controls by pedal. So, his
two legs are engaged in controlling only the
tail rotor. So, either you will move this
way or you will move this way. So, now, we
have basically kind of split the two functions,
even the later you will understand all of
them are coupled.
Then, comes longitudinal lateral, that means,
you want to move forward or you want to move
sidewards, but then, here when you want to
move forward what happens is the vehicle also
pitches, there is a nose down.
How you move a vehicle forward? See, how you
move a vehicle go up is, you increase the
lifting capability, that is, you increase
the pitch angle of the blade, that is basically
the angle of. You all know the basic aerodynamics
of an aerofoil, I change the angle of attack
of the blade, I get increased lift, so I am
going up. But here, I want to go forward,
forward means, how do I, I do not have a propeller
to push me forward. So, what is done is, this
is the difference between the aircraft and
helicopter, the rotor disc, you say, you call
it the disc, the vector, the force vector,
we call it thrust vector, just for sample,
thrust vector is perpendicular to the rotor.
Now, I tilt the rotor disc forward. When I
tilt the rotor disc forward, my thrust vector
is also tilted forward, as a result I get
a forward component of the force and a vertical
component; vertical component will support
the weight, forward component will push me
forward.
But the problem is when you tilt the rotor,
this is the horizontal thing, I tilt it, so
my thrust is here. Initially, the CG is right
here, is coming down and holding it. Now,
what happen because of the tilt? It has gone;
I am going to get a moment about the CG. Now,
the moment also it will come. Now, if you
do not balance the moment properly, then you
will have, you cannot control the rhythm.
But how the moment is balanced in the helicopter?
You will see as we go long, we will see, this
is a great design, yeah, that is why helicopters
there are, you cannot fly it a very high speed.
There are various reasons for you cannot fly,
sometime you cannot trim the vehicle, that
means, you cannot get an equilibrium, equilibrium
of forces and moments you cannot achieve,
that means, you cannot fly assuming everything
is wonderful.
So, this is what you, when you want to go
forward, you get a coupling of the pitching.
Similarly, you can do the lateral that is
why, the helicopter has an ability to go in
because this is a disc, I can tilt it this
way, I can tilt it this way, any orientation.
That means, I can fly in any direction facing
in one direction, it is not that I have to
turn to the other direction and then fly,
that is the advantage of helicopter, that
is, I do not have to turn and then fly, I
can just go back. Of course, these are requirements,
which the user will demand.
I want to fly this much forward speed, this
much sidewards, all these things I will give
just a brief, why this is. See, this is I
learnt when I was discussing with some defense
people. See, today helicopters, I said that
earlier, it was used for evacuation basically.
Nowadays, they take the role of attack; they
have become a force, earlier it was only for
injured people, emergency evacuation in the
military. The reason was first, you know,
it is a very interesting political thing,
Russians are very good because they have land.
The US thought, initially the whole theater
of war will be only in Europe and Russia is
a land where I can come through with tanks.
But US, if they have to come, they have to
fly because they cannot bring all the tanks.
So, they said we will have a flying tank.
What is the flying tank, is an attack helicopter.
So, now, that is all the concept of attack
helicopter themselves have come about because
they say, that you can hide, you can be below
the tree tower, they suddenly go up, fire
and again you go down or you can go back.
Now, the role of the helicopter is completely,
know the demands are met more and more because
the services say, ok, this is good, we will
use it for some other reason. And of course,
today in India you find, that any floods,
anything will only with helicopter going around
and then picking people, coming because that
is one of the major usage you, because they
can go, hover and you saw even in the, what
is, that terrorist attack in Bombay, how they
landed on the roof top. Again, the helicopter,
because you cannot take aircraft and then
parachute down, so you do not know where they
will go and sit, that slithering. So, the
demands, you see, they are all different types,
so they meet. That is why today helicopters
have become an important flying vehicle. It
is like aircraft, it has its own utility,
which cannot be met by an aircraft, conventional
aircraft. So, you can see, that development
of helicopters and the demand for helicopters
are started increasing tremendously.
Now, if you see, in the defense side army
wants the helicopter. You will say army wants
tanks and other things, why do they want to
fly because now the majority of the helicopters
are operated by army, because they want to
use it as a flying tank type of thing. Of
course, air force has its own utility. Then,
navy, because they want ship based operation.
Now, when I said contra rotating rotor, usually
navy operates. The reason is it is compact,
so they can keep it and store on a ship. So,
the size is small, so demand for helicopter
has gone. Of course, the defense has a tremendous
demand.
In the civilian side, yes, the demand is there
because if you, future, that is what. Now,
air transportation, US normally says where
the city traffic has gone too much, if you
take two hours to reach your airport, means
you fly five minutes, you go there, you land.
But of course, you pay normal money because
helicopter flying is not cheap. Commercial
helicopter, if you say one hour of flight
will cost fifty thousand rupees, of that order,
but still lot of business. People use the
helicopter because if they want to go, instead
of going from Bombay, lots of people have
because they do not want to go from Bombay
to Pune or wherever their factory is. They
hire a helicopter, morning they go, maybe
couple of lacs, and they come back. So, utility
is growing, of course, there are problem.
Now, off shore, which is a civilian operation,
you need to go and then put the personal only
with helicopters or you have to send them
by ship. So, that is why, the helicopter utility
is growing, but it is a very complex vehicle.
At the end of the course today, you may not
know what is the complexity, this is a, this
is what one, one complexity is basic thing.
You have a disc, you want to tilt it because
I said with words, hey this is the thrust,
you just tilt the thrust, good how do you
do it that is the next question?
Because you modify, tilt it, I will fly forward.
Of course, it gives me a coupling of pitch
and coupling of role also, but how do I tilt
it, I cannot take the whole shaft. Please
understand, there is, one way is propellers
rotating, tilt the shaft, that is one way,
this is what the tilt rotor, which use, I
showed the tilt rotor, that means, you have
a rotor, you shift, you actually rotate the
shaft, this is one way. Another way is, I
do not want to rotate the shaft, but the disc
must do this in conventional helicopter that
is what is done. The shaft is not rotated,
please understand, shaft is kept in its orientation,
but you tilt the plane of rotation of the
rotor disc.
How it is achieved, that we will learn as
we go along because these are all there dynamics,
how it is. So, now, you know. Then, you have
longitudinal lateral motion, the 
input that is called the cyclic pitch. So,
we had a collective, collective pitch, tail
rotor pitch, cyclic pitch. We will explain
what cyclic everything is, but how cyclic
pitch is given?
The pilot has a stick in front; he will move
the stick forward. That means, if he moves
forward you will go forward; if we moves lateral,
he will go lateral; if he go this way, it
will go this way; he will go this way, he
will go back.
So, this stick he can move in any direction,
360 he can actually churn. So, left hand right
hand leg all are engaged for the pilot to
fly I think I will leave you now.
