good morning friends we are back here again
after completing three courses namely airplane
performance stability and control and introduction
to experiments in flight now we are here to
start a course on aircraft design primarily
will you focusing on the conceptual design
based on aerodynamic considerations we will
be mostly talking about performance related
issues in designing an aircraft yes we will
be talking more on civil aircrafts civil transport
aircrafts we will be also discussing how to
design the aircrafts so that it is having
right type of handling qualities in turned
we will talk about how to layout wing tail
vertical tail horizontal tail
so that we have right amount of stability
margins its damping ratio its natural frequency
which already we have some exposure this is
the time to synthesize whatever we have learnt
in earlier three courses before i start this
course lets understand our country has produced
space vehicle or launch vehicle satellite
launch vehicle of various capacities we recently
had mangalyaan a wonderful venture we have
deployed hundred and four satellites particular
orbit
all these things talks about the synthesis
of design the same time you could see we have
lot of success in designing missiles including
air difference missile ballistic missiles
we also have tremendous success on fighter
airplane light combat aircraft this is l c
a and country is also moving forward towards
the next version with higher capacities and
capabilities
but you will see that we have not really done
enough as far as designing of civil transport
airplane and that is where this lecture is
dedicated to can we through these courses
make design a popular course so that younger
generation can get inspired and empowered
technically so that they can add values and
convert this understanding do technologies
and maybe in extend twenty years we will have
our own civil transport airplane with that
understanding with that motivation i thought
i will again interact with you and share with
you whatever i understand in terms of aircraft
design please understand that when i say we
havent been able to produce ah really good
civil transport airplane i am not undermining
that we have already developed answer three
at trainee aircraft of course under n a l
national aerospace laboratory
we had some success with airplane but for
an unfortunate incident which is a part of
development and i am sure n a l will come
up with new ventures but a question comes
are you ready are you really creating right
type of manpower we will be able to take these
challenges and this course will help in a
smaller way to fulfil that requirement coming
back to this courses in particular aircraft
design we need to understand ourselves what
are the immediate thing that comes to our
mind when i when we see an aircraft for example
if i am seeing this aircraft which is sinus
nine one two motor glider if i see the as
a typically as a passenger a joy rider my
first focus goes towards this propeller which
is the engine side and the propeller rotates
and creates enough power to take it out give
a [prop/proper] proper speed to the plane
so that it can generate right type of lift
but for a passenger what comes to his mind
the moment it is a single propeller airplane
it is oh my god so only a single propeller
if something happens what will happen so that
is the impression a passenger gets he doesnt
get much bothered about seeing the wing or
the vertical tail for him immediate psychological
focus will be on the engine for example you
will ask what is a single engine what will
happen if the engine starts off but now think
same aircraft when viewed by an maintenance
engineer he starts looking to every component
for him yes he puts enough inspection to ensure
that this engine is air worthy reliable he
also looks for the wing he looks for this
pitot tube because you know this pitot tube
will tell you what is the air relative speed
the airplane is having so we will take extra
care to see that the pitot tube is not blocked
because of some for in particle and that is
why some covering will be there the part of
mandated regulation
so for an engineer he sees from purely from
maintenance angle he is not bothered about
whether this design or this angle of the landing
gear is ok or not for him he believes he starts
from that point that design has been done
properly he looks from the maintenance point
of view he will be checking whether when the
aircraft lands whether the landing was proper
or not there are many occasions were landing
maybe heavy landing so he will immediately
come and check as per the maintenance schedule
what the landing gear is ok or not
he will be also checking if we see here checking
this ailerons this control surfaces similarly
elevators rudder you will see whether when
the pilot moves it with a stick whether these
things are being deflected proportionately
or not as per the manual but the question
comes the basic question which comes to our
mind in this course is how much it should
be deflected for a particular mission and
how much stick force the pilots to apply to
deflect this up and down on elevator up and
down that should be properly designed and
before you design you do a proper evaluation
and once you say ok this much of area i need
of the wing to be aileron
then come that comes the next the design i
will see whether stand alone aileron size
ok but when i fly the machine when this aileron
deflection also gets coupled with yaw in motion
the ailerons are primarily for roll motion
right but as it rolls it yaws also so it will
also create some yaw motion on the airplane
and then you have to correct it through rudder
so designer will see the effect of each individual
not only separately but also as a cumulative
performance and that is a good design when
you take the advantage of each component effectively
and make the whole airplane worthy as per
the handling requirements dictated by design
parameters please do not forget whatever airplane
to design finally the pilot will be flying
so when the pilot flies the machine when he
touched down he should tell oh so wonderful
machine lovely to fly you should not say oh
my god what is this aircraft i am have to
pull do you so many of forces to deflect the
elevator or aileron i am getting tired
so all those inputs are to be taken to finally
design an airplane if it is from that angle
the second angle you understand that ok i
will like to go the particular speed i like
to fly at a particular angle the question
comes whether the structurally it is good
enough to withstand that much of a dynamic
load or not it should not happen that as i
deflect the aileron the aileron starts deforming
right then the aileron will not be effective
so that part is taken care by the structural
designer you could understand this is typically
like a cantilever wing and if there is a load
here and if there will be bending moment at
the root there may be a torque acting on the
ah on the wing so the wing should not deflate
unnecessarily or whatever deflections are
there we should be able to estimate it and
apply appropriate corrections right in the
design
if you further see from a designer point of
view this portion the huge large span you
know its the wing and the question comes to
our mind the wing is primarily to produce
enough lift to balance the weight of the airplane
the moment we think of wing producing lift
first thing comes to our mind what will be
the area of the wing we should be able to
produce the lift at a particular speed
so when you see the wing yes it first impression
how much will be the area of the wing but
then we also know that its just not the area
we have to also see what is the aspect ratio
of the wing because we know that as i increase
the aspect ratio they induce the component
reduces right
so that impression comes from the area part
ok but same time you know that i want to ensure
that the lift to drag ratio for the wing is
comfortable the way we want it and there we
go for aerofoil right if i take a cross section
like this there are we will discuss and you
know that the whole art of selecting aerofoil
becomes very very important in designing the
wing and when you try to see an aerofoil or
selected aerofoil we primarily see how effective
it is in terms of lifting and what are the
penalties you have if you want to increasing
is lifting characteristics
what sort of c l by c d the wing is supposed
to give another important thing is what is
the stall angle right there at what angle
the wing is supposed to stall and how do i
design or customize the aerofoil so that either
few of this parameters are optimized or or
some time will give more weightage to the
stall angle so all these combinations will
decide what sort of aerofoil you will be using
will be talking in detail in our design ah
exercise in the classroom but before you design
is important that you try to appreciate things
without using a formula right it should come
from your heart yes i want this and looking
for this right
now from wing if i come here this is the horizontal
tail and you know this is elevator and this
is a vertical tail and this is rudder ok so
it is also important to find out what should
be the horizontal tail area how much of this
horizontal tail should i use the area as an
elevator or should i use complete horizontal
tail as an elevator you know when i complete
horizontal tail is use we call it a all movable
tail right same as similar thing is here for
rudder this vertical tail the forty percent
of vertical tail will be rudder fifty percent
sixty percent or all of this area these are
the primary decision you take before you start
conceptualizing a design of an aircraft
now this whatever i have told you is from
the configuration point of view but what is
the role of the wing is it only to give lift
and drag ratio the way you want it the way
we want it is only the role to give enough
area to get enough lift
let us understand this we will go to another
aircraft and try to address this question
so you are discussing about wing and primarily
we are talking about the area required to
the aspect ratio of the aerofoil from aerodynamic
consideration but you see that if this is
a engine which is driven by fuel combustion
engine then i need to have fuel carried in
this airplane so i need to have a fuel tank
please see here this is one of the combination
so design combinational refine people are
putting fuel tank inside the wing right that
means it is just not selecting an aerofoil
we need to see that when i translate that
into a wing i should have enough volume to
accommodate this tank
so that also decides what will be the thickness
of the wing and what sort of a aerofoil i
will be taking all right because each aerofoil
has got thickness to called distribution specified
distribution and we talk about the fuel tank
you will understand i cannot locate this fuel
tank anywhere randomly because this has a
weight almost thirty percent of the weight
of the airplane is the fuel
so if location will determine the location
of centre of gravity of the airplane and more
importantly as we fly the fuel get consumed
so if you are if we are not clever enough
then what will happen as the fuel consumed
there will large variation in the center of
gravity of the airplane and which will directly
affect the stability of the airplane you know
that stability and center of gravity locations
are related
so lot of effort will go in designing and
wing aerofoil combination keeping the housing
of fuel tank so what by this i am trying to
stress is this is real synthesis what is important
you should know each alone stand alone characteristics
but is also should know there are to do multiple
things and study try to satisfy everybody
which generally is not possible so there is
a something called we try to optimize some
time we call ok optimization in truces may
not be feasible but we say ok it is adequate
adequately optimized right
now beyond aerofoil and fuel tank if we said
these are one this ribs they actually maintain
the contour of the wing and the question comes
how many of such ribs should be there how
many of load bearing member longer on will
be there we after all it will always having
a bending load or torsional load how do i
distribute those load across the member through
this sort of a structure and ensure that the
airplane is safe structurally
thats why its extremely important that i not
only designed a wing through aerofoil and
aspect ratio i need to go inside the wing
and see the volume available for accommodating
fuel tank i need to know how do i place the
stiffener inside the wing how do i put the
longerons inside the wing so that it is structurally
enough strengthened right and again you could
see aerodynamic structure and fuel tank all
these three things have to be integrated synthesized
keeping a one mission that my airplane should
have particular mission requirement what are
the mission requirements how do you decide
will be discussing inside a classroom
this is important thing as far as a wing is
concerned but if i ask you a question if this
is an airplane out of this airplane you will
see the engine part engine part we do not
make any engine right so in fact not very
large number of company produces engine so
engine will be use as a standalone as if it
is available in the shelf and what are the
power required what are the trust required
you will pick up the engine and fit in the
aeroplane if you see other sensors which are
there in this aircraft most of them are not
produced here of course of fleet things are
changing but since you are not making your
own such subsystems some time optimization
becomes a constrained situation you wanted
something but you are getting little different
than that but you have no option so you have
to integrate them and compromise accept the
compromise on your mission requirement i am
sure our country also will produce senses
sooner or later lot of efforts are being made
so from wing to engine and if you see this
part this is another type of landing here
which you know we have to also see what should
be the width of this base of this landing
here how much their separation is required
all this thing will come into the conceptual
design right you could have imagine if the
base length is shortened then it will be underground
it will be it will not be stable it will just
topple right all those minor minor things
will take into consideration but we we will
not overload ourselves because finally it
has to be something which we should enjoy
right and relaxed manner we should be able
to do synthesis and that will be the u s p
of this course the pace of this course will
be very very optimally slow to ensure that
you enjoy every moment of it we will go back
and forth check with existing design the concept
validate it so there after the end of this
course you are confidently yes i at least
i know this much ok so we will be having next
class in the classroom wish you all the best
and again welcome to this course on aircraft
design
thank you very much
