fixed wing vs rotary wing aircraft

8/16/2019 Fixed wing Vs Rotary Wing Aircraft

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I. ABSTRACT A brief summary of information is presented on

the differences between fixed wing aircraft suchas airplanes and rotary wing aircraft such as

helicopters in this paper. Both the structural and

operational differences of the two types of

aircraft will be explored. Their advantages and

disadvantages based on their versatility and

usage limitations are also highlighted.

Index Terms--- Aerodynamics, airplanes,

aviation, helicopters.

II. INTRODUCTION

For centuries, man has observed the birds

flying, soaring the sky by spreading out their

wings in the air and has dreamed of flying ever

since. As man realized that fastening sheets of

cloth on his back and umping from towers with

his arms spread out and flapping like a bird was

ust not how nature planned for human to go

airborne, he began his struggle to make a

contraption that would take him into the air. After

enormous contributions from men like !ir

"eorge #ayley and $tto %ilienthal &'( and

countless fatalities and failed experiments,history was made as the )right*+ flyer made its

'*second flight over the windswept dunes of

-ill evil /ills, 0orth #arolina. !oon after this

flight, the first successful helicopter flight was

made on '1th 0ovember, '234 by 5aul #ornu

which lasted 3*seconds. Though the flight was

untethered, it was not until +gor !ikorsky6s 7!*

133 that helicopters were put into mass

production.

An airplane is a machine that moves in the air

with the help of its engine and its wings. The

wings are responsible for creating the lift by

overcoming the force of gravity which pulls the

aircraft downwards and the engine is

responsible for its translational motion through

the air.

Figure 1 An Airplane

A helicopter is a machine which moves

through the air with the help of its horizontal

power*driven propellers &( which are rotating

wings, rotated with the help of an engine. +n a

helicopter, the rotors are responsible for overcoming the drag and the force of gravity and

produce the re8uired lift and thrust to move the

aircraft through the air.

Figure 2 A Helicopter

A wing is the basic surface in an aircraft which

provides lift. A wing utilizes the Bernoulli6s

principle which states that a fluid flowing moving

with high speed over a surface creates an area

of low pressure on that surface. The structure of

a wing is designed such that air has to cover a

longer distance over the wing surface. As the air

speeds up over the surface, an area of lowpressure is created over the wing surface. The

pressure under the wing is now greater than the

pressure over the wing. Thus, the air under the

wing pushes the wing upward resulting in lift.

Both the fixed wing and rotary wing aircraft are

used for a wide variety of purposes which differ

from each other. Both have many differences,

Fixed Wing vs. Rotary Wing Aircrat!yeda Faiza !aad


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some very obvious while others not*too*obvious

but all of their differences and advantages and

disadvantages will be explored in detail over the

next few pages.

III DIFF!R!NC!S

A Structural Differences

The first structural difference between the two

types of aircraft is the most obvious one i.e.

airplanes have fixed wings whereas a helicopter

does not. +n a helicopter, the wings are replaced

by a rotor which consists of rotor blades which

move about an axis. The rotors function as

moveable wings as they are responsible for lift.

The rotor assembly consists of the rotor blades

connected to a hub through the blade grips. The

hub is mounted on a shaft via the 9esus 0ut.

The shaft is further connected to the engine

which enables it to move at varying speeds in

order to provide lift.

Figure 3 Rotor Assembly of a Helicopter [3]

Another uni8ue feature of a helicopter is its back

rotor. The idea, first utilized by +gor !ikorsky,

provided a mechanism to counteract the tor8ue

produced by the main rotor of the helicopter thus

effectively earning it the name, anti*tor8ue rotor.

Another one of the most obvious difference

between the two types of aircraft is their cargo*

carrying capacity. An airplane has considerably

more space than a helicopter and can carry

hundreds of passengers at a time. Although,

there are airplanes which carry only two people

at a time but in the broadest terms, an airplane

can carry more people and more cargo.

An airplane has control surfaces such as the

ailerons, elevators and the rudder which control

its motion about the three axes and many other

surfaces which help these three primary control

surfaces. /owever, a helicopter does not have

any of these surfaces and makes use of its main

and back rotors for movement along different

planes.

/elicopter rotors usually have symmetrical

airfoils i.e. the airfoils in which the mean camber

coincides with the chord. These symmetrical

airfoils best suit the rotary wing aircraft because

their centre of pressure does not vary duringflight which provides the best lift*drag ratio for a

large range of velocities. These airfoils provide

less lift and have undesirable stall

characteristics but they have an upper hand

over the asymmetric airfoils because they do not

produce a twisting force on the rotor blades

which would be produced in case of the

symmetric airfoils. Asymmetric airfoils are better

suited for airplanes as airplanes need to fly at

considerably high altitudes. As they need more

lift to accomplish this, the fixed wing aircraft

generally employ asymmetric airfoils. &:(

Figure 4 Asymmetrical and Symmetrical Airfoils

Another structural difference between the two is

the different construction of their tails. An

airplane has a vertical as well as a horizontal tail

on which the rudder and the elevators are

mounted respectively. The horizontal and

vertical tails are collectively termed as the

empennage. The elevators control the pitching


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motion or the motion of the aircraft about the

lateral axis whereas the rudder controls the

sideways motion of the nose of the aircraft which

enables it to change directions &;(. The

helicopter has a longer tail as compared to an

airplane. This tail consists of a tail boom which is

the long, hollow part of the tail. At the end of the

tail boom, the anti*tor8ue rotor is mounted which

moves in a vertical plane and produces

horizontal thrust.

B Controls

An airplane uses numerous control surfaces

which enable it to move along the three axes in

the air by overcoming or utilizing the primary

aerodynamic forces of lift, drag, weight and

thrust. A helicopter on the other hand, makes

use of its moveable parts which control its

movements about the axes.

3 degrees.

This yawing is further controlled by the tail rotor

which, when its pitch angle ?the angle between

the rotor blades and their plane of rotation@ is

changed by pressing the anti*tor8ue pedals,

varies the thrust produced by it causing the

aircraft to yaw in the direction of the pressed

pedal.

%+FT

A fixed wing aircraft uses its wing for producing

lift by creating a pressure difference above and

below the wing. ue to the aerodynamic shape

of the wing airfoil, the air on the top has moredistance to cover, thus it speeds up and causes

a drop in pressure in accordance with Bernoulli6s

principle. The increased pressure at the bottom

of the wing exerts an upward force on the wing

which ultimately overcomes the force of gravity

as the air speed increases.

Figure 5 ernoulli!s "#planation of $ift [%]

The lift can be varied by using the flaps which

when inserted into the airstream produce drag

which can be used to either increase or

decrease the lift. Another method of varying the

lift of an airplane is to change the angle of attackof the wing which is the angle between the chord

and the relative wind or the oncoming wind. The

lift has a direct relation with the angle of attack

and increases up to a certain point with the

increase in the angle of attack after which the lift

decreases because the air can not flow under

the wing.


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Figure % Angle of Attac& 's( $ift )o*efficient [+]

A helicopter utilizes its rotor blades to

produce the lift. The same principle is embeddedin its operation. The air moves downward as the

rotor blades move horizontally and this exerts an

upward directed force on the aircraft according

to 0ewton6s Third %aw. This lift can be

manipulated using the #ollective 5itch #ontrol.

This instrument changes the pitch angle of all

the rotor blades at once by the same amount

thus e8ually affecting the lift produced by each

rotor blade. This helps the aircraft to rise

vertically into the air ?7ertical Take*$ff and

%anding 7T$%@, a feature uni8ue only to rotary

wing aircraft.

T/=!TThrust is produced in an airplane by the power

plant or the engine of the aircraft. The engine

sucks in the oncoming air and spits it out

backwards with a force which propels the aircraft

forward in accordance with 0ewton6s Third %aw.

A helicopter, unlike an airplane, uses its rotors to

produce thrust. The rotor blades are identical to

the wings of an airplane &C(. After rising into the

air vertically, the pilot uses the cyclic controls to

pitch the helicopter nose downwards. This

causes a decrease in altitude and an increase in

airspeed. The air from the back of the helicopter

pushes it forward which implies that some of the

lift of the helicopter has been converted into

thrust. The swash plate is also tilted forward

using the collective pitch control and then the

cyclic control is pushed forwards to move the

helicopter forwards.

C Maneuverability

/$7D

$ne of the most distinguishing features of a

helicopter is its ability to hover i.e. its ability to

remain stationary at a point in the air. A

helicopter pilot performs this complex maneuver

by making the lift force supplied by the rotor

e8ual to the weight of the aircraft which

effectively cancels both the forces and allows

the aircraft to remain still for a considerable

period of time. The e8uality of lift and weight is

achieved by keeping the rotor assembly parallel

to the ground ?no wind condition@. This enablesthe aircraft to neither move sideways nor

backwards or forwards. This difficult maneuver

re8uires constant pilot input and cannot be

performed on airplanes.

BA#-)A F%+"/T

A helicopter can fly backwards, unlike an

airplane which can only move forwards. The

backward movement can be achieved by tilting

the swash plate assembly backwards using the

cyclic control. This causes each rotor blade to

produce maximum lift at a certain point its cyclewhich leads to thrust in the direction the swash

plate assembly is tiltedE in this case, backwards.

The cyclic control changes the angle of attack of

the rotor blades in such a way that the blades

are pitched lower at the back of the rotor

assembly than its front. This creates more lift in

the front and less lift at the back and as a result

of this une8ual lift, the aircraft is pushed

backwards.

D If the Engine Fails+n case the engine fails, an airplane will act like

a glider and with the help of an experienced

pilot, it can land safely in most cases with

minimal damage and loss of life. An airplane that

has lost its engine can keep flying by keeping its

airspeed up &2(. This is done by converting lift

into thrust. The elevators are deflected to pitch


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the nose lower than the wing in order to keep

the aircraft airborne as this results in an increase

of speed.

/owever, a helicopter makes use of the

autorotation phenomenon in order to land safely

in case of engine failure. /e reduces the pitch of

the rotor blades causing the aircraft to lose

altitude. As the aircraft still possesses the ability

to move sideways, therefore the pilot can search

for a good landing spot. $nce over that spot, the

pilot pulls back on the cyclic to decrease the

forward speed while simultaneously increasing

the collective pitch to slow the descent. +f done

properly, the helicopter can land safely. [10]

I". AIR#$AN!S O"!R %!$ICO#T!RS

An airplane is suited to travel long distancesbecause it can fly faster and at higher altitudes

than a rotary wing aircraft which is relatively

slow and flies at low altitudes. /elicopters

cannot carry much fuel therefore they are suited

for short term flights.

Airplanes, in most cases, are more comfortable

than helicopters because they have more space.

Dspecially the airliners are very comfortable and

provide many facilities to the passengers to

make their flight as comfortable as possible. As

helicopters are not meant for long term travel,

they are not very comfortable.

/elicopters have tons of moving parts which

results in vibrations which lead to noise. This

noise also makes a helicopter ride extremely

uncomfortable. The most significant noise is

because of the rotor movement. Airplanes,

though they do make a lot of noise because of

their engines, this noise is damped out because

of the glass windows and one doesn6t notice it

much during flight.

Also, unlike the airplanes, helicopters cannot fly

at very high altitudes because their cabins arenot pressurized. The pressurized cabins in the

airplanes enable them to fly at very high

altitudes without causing any inconvenience to

the pilots or the passengers.

Another advantage that the airplanes hold over

the rotary wing aircraft is their fuel efficiency.

Airplanes have separate parts to generate lift

and thrust. The lift is generated through the

wings whereas the thrust is produced by the

power plant or the engine. Thus, the fuel is used

only by the engine. $n the other hand, in a

helicopter, the engine drives the rotors, both the

main rotor and the tail rotor, to produce thrust as

well as lift. Thus, a helicopter engine has to do

more work as it has to overcome two

aerodynamic forces, drag and weight, so it

consumes more fuel than an airplane and also

at a higher rate. This is also one of the reasons

why a helicopter is not suited for long distance

travel as it runs out of fuel before it has flown

very far. &''(

Although both the airplanes and the

helicopters have evolved with the passage of

time but it6s only the airplanes which have

stepped into the supersonic and evenhypersonic regimes. /elicopters are still

considerably slower than airplanes.

Airplanes are inherently stable. They can

continue to cruise once the adustments have

been made to the control surfaces without

re8uiring any further input from the pilot. 5ilot

input is mostly re8uired during take*off and

landing. An airplane pilot can therefore perform

other tasks during flight. $n the other hand, a

helicopter pilot needs to be attentive throughout

the entire flight because a helicopter is generally

not very stable. The main rotor of the helicopter while rotating induces a tor8ue in the main body

of the helicopter which rotates the fuselage of

the helicopter in the direction opposite to the

direction of rotation of the main rotors. This

tor8ue is counteracted by the tail rotor which

produces a horizontally directed thrust or tor8ue

in the direction opposite to the one in which the

fuselage would move. This can happen at every

point during flight thus the pilot needs to provide

constant anti*tor8ue pedal input to counteract

the tor8ue. The cyclic and collective controlsalso need to be monitored by the pilot at all

times therefore the pilot has to be extremely

attentive over the entire course of the flight and

adust the controls according to his or her needs.


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I %!$ICO#T!RS O"!RAIR#$AN!S

/elicopters are more versatile than fixed wing

aircraft because of their ability to take off and

land vertically. They can be used to performtasks that mere fixed wing aircraft cannot

perform. They can be used to perform

emergency rescue operations to extract people

from places which are unapproachable for a

fixed wing aircraft such as mountains, mines or

ungles. As the helicopters do not need a runway

because of their ability to take off and land

vertically, therefore they can easily access

isolated or congested areas like buildings where

the fixed wing aircraft are unable to land due to

the absence of a runway. &'(

Because of their 7T$% ability and their abilityto hover and their handling properties under low

speed air conditions, helicopters are best used

for traffic monitoring, firefighting and

transportation purposes. /owever, as an

airplane can neither perform hovering nor the

vertical take*off and landing maneuvers, it is

deemed useless in such cases.

The re8uirement of a runway for take*off and

landing limits the usage of aircraft for emergency

purposes. $n the other hand, helicopters can

serve as ambulances for carrying the inured to

the hospitals in time of crisis.

II CONC$USION

+n the light of above discussion, it can be

concluded that both the fixed and rotary wing

aircraft are different from each other and both

have a wide variety of applications. Dach

contraption has its own advantages and

disadvantages which were explored at length. +t

depends solely on human beings on how they

utilize both the machines. )ith the continuedadvancement in technology, both airplanes and

helicopters will surely evolve into more efficient

and even more versatile machines which will

continue to help mankind in its endeavors.

II R!F!R!NC!S

[1] J. G. Leishman, "A HIstory of Helicopter Flight,"

[nline]. A!ailale#

http#$$terpconnect.%m&.e&%$'leishman$Aero$history.html. [Accesse& 1 Fe%rary (01)].

[(] *. J. +oyne, "Helicopter," 1( ecemer (01-.

[nline]. A!ailale#

http#$$.ritannica.com$/+chece&$topic$()

($helicopter. [Accesse& 1 Fe%rary (01)].

[2] 3. +. a. *. Harris, "Ho Helicopters *or," 1

April (000. [nline]. A!ailale#

http#$$science.host%ffors.com$transport$flight

$mo&ern$helicopter).htm. [Accesse& 1 Fe%rary(01)].

[-] 4. 5antrell, "Helicopter A!iation," [nline].

A!ailale#

http#$$.copters.com$aero$airfoils.html.[Accesse& 1 Fe%rary (01)].

[)] H. G. 6. a. J. J. Haggerty, "7he /ssentials of

Flight," in Flight , 7ime Inc., 188, pp. 2-928.

[8] "Lift," [nline]. A!ailale#http#$$.allstar.fi%.e&%$aero$lift2.htm.

[Accesse& 1 Fe%rary (01)].

[:] "Lift 5oefficient," [nline]. A!ailale#

http#$$en.iipe&ia.org$ii$Lift;coefficient.

[Accesse& 1 Fe%rary (01)].

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