introduction to aircrafts

7/29/2019 Introduction to Aircrafts

1/34

Introduction to Aircrafts

An Aircraft is a device that is used, or intended to be used, for flight. It can also bedefined as any machine capable of atmospheric flight.An aircraft counters the force of gravity by using either Static Lift or by using the

Dynamic Lift of an airfoil, or in a few cases the downward thrust from jet engines.Although rockets and missiles also travel through the atmosphere, most are notconsidered aircraft because they use rocket thrust instead of aerodynamics as theprimary means of lift.

1.0 Categories and Classification:

Aircraft fall into two broad Categories.1. Lighter than Air (Aerostats).2. Heavier than Air (Aerodynes).

1.1 Lighter than Air (Aerostats):

Lighter than air also known as Aerostats uses Archimedes Principle. In this the

envelope of a balloon/ airship displaces the air, and therefore there is an upwardforce on the airship which is equal to the weight of the displaced air. If this upwardforce is equal to the weight of the airship, it will float; if the upward force is greaterthan the weight, the airship will rise; if it is less, it will fall.

In order to keep the weight of the airship itself as small as possible it must

Be made of the lightest materials available.

A very light gas must be used in the envelope.
http://en.wikipedia.org/wiki/Airfoilhttp://en.wikipedia.org/wiki/Jet_engineshttp://en.wikipedia.org/wiki/Rockethttp://en.wikipedia.org/wiki/Missilehttp://en.wikipedia.org/wiki/Airfoilhttp://en.wikipedia.org/wiki/Jet_engineshttp://en.wikipedia.org/wiki/Rockethttp://en.wikipedia.org/wiki/Missile


2/34

Examples of lighter-than-air aircraft include non-steerable balloons, such as hot airballoons and gas balloons, and airships. The distinction between a balloon and anairship is that an airship has some means of controlling forward motion andsteering, while balloons simply drift with the wind.

The lightest gas in commercial use is hydrogen, and, for many years, this gas wasalways used in airships and balloons. Unfortunately, however hydrogen is veryinflammable, and its use added considerably to the dangers of Aerostats. So thehelium came to be used in spite of the fact that it is much more expensive than andtwice as heavy as hydrogen.

1.2 Heavier than Air (Aerodyne):

Heavier-than-air aircraft must find some way to push air or gas downwards, so thata reaction occurs (by Newton's laws of motion) to push the aircraft upwards. Thisdynamic movement through the air is the origin of the term Aerodyne. There aretwo ways to produce dynamic up thrust: aerodynamic lift, and powered lift in theform of engine thrust.

Heavier than air aerodynes, including auto gyros, helicopters and variants, andconventional fixed-wing aircraft: aero planes. Fixed wing aircraft generally usean internal-combustion engine in the form of a piston engine (with a propeller) or aturbine engine (jet or turboprop), to provide thrust that moves the craft forwardthrough the air. The movement of air over the airfoil produces lift that causes theaircraft to fly.
http://en.wikipedia.org/wiki/Aerodynamicshttp://en.wikipedia.org/wiki/Powered_lifthttp://en.wikipedia.org/wiki/Aerodynamicshttp://en.wikipedia.org/wiki/Powered_lift


3/34

Exceptions are gliders which have no engines and gain their thrust, initially, fromwinches or tugs and then from gravity and thermal currents. That is, in order tomaintain their forward speed they must descend in relation to the air (but notnecessarily in relation to the ground). Helicopters and auto gyros use a spinningrotor (a rotary wing) to provide both lift and thrust. The abbreviation VTOL is appliedto aircraft other than helicopters that can take off or land vertically. Likewise, STOL

stands for Short Take Off and Landing.

A pure rocket is not usually regarded as an aerodyne, because it does not dependon the air for its lift (and can even fly into space); however, many aerodynamic liftvehicles have been powered or assisted by rocket motors. Rocket-powered missileswhich obtain aerodynamic lift at very high speed due to airflow over their bodies area marginal case

Aircraft based on Usage:1. Civil Transport Aircraft

2. Military Aircraft3. Space Vehicles

1.3 Civil Transport Aircraft:

Civil aviation includes scheduled airline flights and general aviation, a catch-allcovering other kinds of private and commercial use. The vast majority of flightsflown around the world each day belong to the general aviation category, rangingfrom recreational balloon flying to civilian flight training to business trips tofirefighting to medevac flights to cargo transportation on freight aircraft.

Within general aviation, the major distinction is between private flights (where the

pilot is not paid for time or expenses) and commercial flights (where the pilot is paidby a customer or employer). Private pilots use aircraft primarily for personal travel,business travel, or recreation. Commercial general aviation pilots (when not flyingprivately) use aircraft for a wide range of tasks, such as flight training, pipelinesurveying, passenger and freight transport, policing, crop dusting, and medicaltransport (medevac). Piston-powered propeller airplanes (single-engine or twin-engine) are especially common for both private and commercial general aviation,but even private pilots occasionally own and operate helicopters.
http://en.wikipedia.org/wiki/Rockethttp://en.wikipedia.org/wiki/Rocket


4/34

1.4 Military Aircraft:

Military aircraft and helicopters are purchased by governments to meet nationaldefense needs, such as delivering weapons to military targets and transportingtroops and equipment around the globe. Other aircraft, such as unmanned aerialvehicles, are produced to gather defense intelligence such as radio signals or tomonitor movement on the ground.

1.5 Space Vehicles:

The part of the industry also produces space vehicles and the rockets for launchingthem into space. Consumers of spacecraft include the National Aeronautics andSpace Administration (NASA), the U.S. Department of Defense (DOD), ISRO,telecommunications companies, television networks, and news organizations.

2.0 Stages in the development of an Aircraft:

Conceptual Design

Aeronautical ConfigurationCFD, Wind Tunnel Testing

Systems Design Airframe Detail Design Airframe Analysis Airframe Testing Prototype Building Prototype Testing Flight Testing

A large volume of work is involved in Airframe design and analysis

3.0 Air craft Components


5/34


6/34


7/34

4.0 Axis System

5.0 Basic parts of an Aero plane


8/34

6.0 Aircraft Structure and Systems

6.1 AirCraft Structure

The basic functions of an aircrafts structure are to transmit and resist the applied

loads; to provide an aerodynamic shape and to protect passengers, payload,systems etc. from the environmental conditions encountered in flight.

The structure of an aircraft is required to support two distinct classes of load: thefirst, termed ground loads, includes all loads encountered by the aircraft duringmovement or transportation on the ground such as taxiing and landing loads,towing and hoisting loads; while the second, air loads, comprises loads imposed onthe structure during flight by manoeuvres and gusts. The two classes of loads maybe further divided into surface forces which act upon the surface of the structure,e.g. aerodynamic and hydrostatic pressure, and body forces which act over thevolume of the structure and are produced by gravitational and inertial effects.

The structure of an Aircraft includes: Fuselage

Wings

An Empennage

Landing Gear and

Power plant

The Fuselage contains crew and payload, the latter being passengers, cargo,weapons plus fuel, depending on the type of aircraft and its function; the Wingsprovide the lift and the tailplane is the main contributor to directional control. Inaddition, ailerons, elevators and the rudder enable the pilot to manoeuvre the

aircraft and maintain its stability in flight, while wing flaps provide the necessaryincrease of lift for takeoff and landing. The Landing Gear support the aircraft whenparked, taxing, takeoff or when landing.

6.1.1 Fuselage

The fuselage, or body of the airplane, is a long hollow tube which holds all thepieces of an airplane together. The fuselage is hollow to reduce weight. As withmost other parts of the airplane, the shape of the fuselage is normally determinedby the mission of the aircraft. Cylindrical shape for containing pressure Streamlined to reduce Drag

Nose houses Radar Carries a part of the fuel It is the main structure or body of the aircraft. The fuselage must be strong and streamlined, to enable it to withstand the forcesthat are created in

flight. The fuselage serves several functions. It is the attachment point for the othermajor components. It


9/34

provides space for passenger, cargo, power plant, controls, accessories, andother requirements

depending on the purpose viz.. Civil, military, transport.

The Fuselage is divided into three main sections:

The nose section Normally up to the cockpit bulk head includes cockpitavionics bay etc., The center section - includes passenger cabin and the baggage compartments The tail section - including the empennage and tail cones.

The construction of aircraft fuselages evolved from the early wood truss structuralarrangements to monocoque shell structures to the current semimonocoque shellstructures.

6.1.1.1 Truss Structure

It consists of two force members, Tension/Compression and are bolted/ riveted /welded in joints, generally made of steel, aluminum tubes. The main drawback oftruss structure is its lack of a streamlined shape. In this construction method,

lengths of tubing, called longerons, are welded in place to form a well-bracedframework. Vertical and horizontal struts are welded to the longerons and give thestructure a square or rectangular shape when viewed from the end. Additionalstruts are needed to resist stress that can come from any direction. Stringers andbulkheads, or formers, are added to shape the fuselage and support the covering.


10/34

Frames/ Bulkheads:Structural members which transfers concentrated loads to the shell of the aircraft(for wing ribs).

Types: Machined frame / sheet metal built up / truss type. Bulkheads, which resistpressure loads due to fuel and air pressurisation, will have full webs.

SkinIt can resist only air loads. It cannot resist shear / bending loads.

Stringers & LongeronsThese are longitudinal members of the fuselage structure which resist bending andaxial loads. It helps in redistribution of shear flows in skin panel by panel braking.Longerons are located at the edges of opening in the shell, of greater area of crosssection than the stringers.

6.1.1.2 Monocoque

As technology progressed, aircraft designers began to enclose the truss members tostreamline the airplane and improve performance. This was originally accomplishedwith cloth fabric, which eventually gave way to lightweight metals such as

aluminum. It also includes other high technology materials such as titanium,corrosion resistance steel and carbon composites for primary structures, fiberglassand Kevlar for the secondary components. In some cases, the outside skin cansupport all or a major portion of the flight loads. Most modern aircraft use a form ofthis stressed skin structure known as monocoque or semimonocoque construction.

Monocoque construction uses stressed skin to support almost all loads much like analuminum beverage can. Although very strong, monocoque construction is nothighly tolerant to deformation of the surface. For example, an aluminum beveragecan supports considerable forces at the ends of the can, but if the side of the can isdeformed slightly while supporting a load, it collapses easily.

Because most twisting and bending stresses are carried by the external skin ratherthan by an open framework, the need for internal bracing was eliminated orreduced, saving weight and maximizing space. One of the notable and innovativemethods for using monocoque construction was employed by Jack Northrop. In1918, he devised a new way to construct a monocoque fuselage used for theLockheed S-1 Racer. The technique utilized two molded plywood half-shells thatwere glued together around wooden hoops or stringers. To construct the half shells,rather than gluing many strips of plywood over a form, three large sets of sprucestrips were soaked with glue and laid in a semi-circular concrete mold that looked


11/34

like a bathtub. Then, under a tightly clamped lid, a rubber balloon was inflated inthe cavity to press the plywood against the mold. Twenty-four hours later, thesmooth half-shell was ready to be joined to another to create the fuselage. The twohalves were each less than a quarter inch thick. Although employed in the earlyaviation period, monocoque construction would not reemerge for several decadesdue to the complexities involved. Every day examples of monocoque construction

can be found in automobile manufacturing where the unibody is consideredstandard in manufacturing.

6.1.1.3 Semimonocoque

Semimonocoque construction, partial or one-half, uses a substructure to which theairplanes skin is attached. The substructure, which consists of bulkheads and/orformers of various sizes and stringers, reinforces the stressed skin by taking someof the bending stress from the fuselage. The main section of the fuselage alsoincludes wing attachment points and a firewall. On single-engine airplanes, theengine is usually attached to the front of the fuselage. There is a fireproof partitionbetween the rear of the engine and the flight deck or cabin to protect the pilot andpassengers from accidental engine fires. This partition is called a firewall and isusually made of heat-resistant material such as stainless steel. However, a newemerging process of construction is the integration of composites or aircraft madeentirely of composites.

6.1.2. Wings


12/34

The wings are airfoils attached to each side of the fuselage and are the main liftingsurfaces that supportthe airplane in flight. There are numerous wing designs, sizes, and shapes used bythe various manufacturers. Each fulfills a certain need with respect to the expectedperformance for the particular airplane.

Wings may be attached at the top, middle, or lower portion of the fuselage. Thesedesigns are referred to as high (stable), mid (acrobatic), and low-wing (less drag),respectively. The number of wings can also vary. Airplanes with a single set ofwings are referred to as monoplanes, while those with two sets are calledbiplanes.

Many high-wing airplanes have external braces, or wing struts, which transmit theflight and landing loads. The principal structural parts of the wing are spars, ribs,and stringers. These are reinforced by trusses, I-beams, tubing, or other devices,including the skin. The wing ribs determine the shape and thickness of the wing(airfoil). In most modern airplanes, the fuel tanks either are an integral part of thewings structure, or consist of flexible containers mounted inside of the wing.

Attached to the rear, or trailing, edges of the wings are two types of controlsurfaces referred to as ailerons and flaps. Ailerons extend from about the midpointof each wing outward toward the tip and move in opposite directions to createaerodynamic forces that cause the airplane to roll. Flaps extend outward from thefuselage to near the midpoint of each wing. The flaps are normally flush with thewings surface during cruising flight. When extended, the flaps move simultaneouslydownward to increase the lifting force of the wing for takeoffs and landings.


13/34

The wing frame work made up of1. Spar2. Ribs3. Stringers and4. Skin.

Spar: Are the main strength members of the wing and run along the length of the

wing.

There will typically be two spars in the wing structure, or possibly three for

larger aircraft. These form the main span wise beam of the wing and takemost of the span wise bending and torsional loads.

These also form a closed-cell configuration inconjunction with the skin.

Ribs:

Run from the leading edge to the rear of the wing and support the covering

and provide the airfoil shape (camber) that allows the wing to create lift.

Ribs help to maintain the aerodynamic shape of the sections and act with the

skin to resist the distributed aerodynamic pressure loads.

They are often located close to concentrated loads (e.g. pylons, landing gear,

etc) and at discontinuities.

Stringers

The stringers improve the skin buckling resistance by dividing it into smallerpanels.


14/34

Skin

Skin forms an impermeable aerodynamic surface and transmits aerodynamic

forces into the above mentioned structures.

It also helps to resist the shear torsion loads and react against the axial

bending loads.

CONTROL SURFACES

On high-speed airplanes, flight controls are divided into primary flight controls andsecondary or auxiliary flight controls. The primary flight controls maneuver theairplane about the pitch, roll, and yawaxes. They include the ailerons, elevator, and rudder. Secondary or auxiliary flightcontrols include tabs,leading edge flaps, trailing edge flaps, spoilers, and slats.

Movement of any of the three primary flight control surfaces changes the airflowand pressure distribution over and around the airfoil. These changes affect the liftand drag produced by the airfoil/control surface combination, and allow a pilot tocontrol the airplane about its three axes of rotation.

Secondary or auxillary flight control surfaces are the high lifting devices.

A wing has the following control surfaces among the above said.

Ailerons

Flaps

Slats and

Spoilers

Ailerons:

Ailerons control roll about the longitudinal axis. The ailerons are attached to theoutboard trailing edge of each wing and move in the opposite direction from eachother. Ailerons are connected by cables, bellcranks, pulleys or push-pull tubes toeach other and to the control wheel. Moving the control wheel to the right causesthe right aileron to deflect upward and the left aileron to deflect downward. Theupward deflection of the right ailerondecreases the camber resulting in decreasedlift on the right wing. The corresponding downward deflection of the left aileronincreases the camber resulting in increased lift on the left wing. Thus, the increasedlift on the left wing and the decreased lift on the right wing causes the airplane toroll to the right.


15/34

Differential AileronsWith differential ailerons, one aileron is raised a greater distance than the otheraileron is lowered for a given movement of the control wheel. This produces anincrease in drag on the descending wing. The greater drag results from deflectingthe up aileron on the descending wing to a greater angle than the down aileron onthe rising wing. While adverse yaw is reduced, it is not eliminated completely.

Frise-type AileronWith a Frise-type aileron, when pressure is applied to the control wheel, the aileron

that is being raised pivots on an offset hinge. This projects the leading edge of theaileron into the airflow and creates drag. This helps equalize the drag created bythe lowered aileron on the opposite wing and reduces adverse yaw.


16/34

Flaps:Flaps are the most common high-lift devicesused on practically all airplanes. Thesesurfaces, which are attached to the trailingedge of the wing, increase both lift and

induced drag for any given angle of attack.Flaps allow a compromise between highcruising speed and low landing speed,because they may be extended when needed,and retracted into the wings structure whennot needed.

There are four common types of flaps:

Plain,

Split,

Slotted, and

Fowler flaps.

The plain flap is the simplest of the four types.It increases the airfoil camber, resulting in asignificant increase in the coefficient of lift ata given angle of attack. At the same time, itgreatly increases drag and moves the centerof pressure aft on the airfoil, resulting in anose-down pitching moment.

The split flap is deflected from the lowersurface of the airfoil and produces a slightlygreater increase in lift than does the plain

flap. However, more drag is created becauseof the turbulent air pattern produced behindthe airfoil. When fully extended, both plainand split flaps produce high drag with littleadditional lift.

The most popular flap on airplanes today isthe slotted flap. Variations of this design areused for small


17/34

airplanes as well as for large ones. Slottedflaps increase

the lift coefficient significantly more than plain or spilt flaps. On small airplanes, thehinge is located below the lower surface of the flap, and when the flap is lowered, itforms a duct between the flap well in the wing and the leading edge of the flap.When the slotted flap is lowered, high-energy air from the lower surface is ducted to

the flaps upper surface. The high-energy air from the slot accelerates the uppersurface boundary layer and delays airflow separation, providing a higher coefficientof lift. Thus, the slotted flap produces much greater increases in CLmax than theplain or split flap. While there are many types of slotted flaps, large airplanes oftenhave double- and even triple-slotted flaps. These allow the maximum increase indrag without the airflow over the flaps separating and destroying the lift theyproduce.

Fowler flaps are a type of slotted flap. This flap design not only changes the camberof the wing, it also increases the wing area. Instead of rotating down on a hinge, itslides backwards on tracks. In the first portion of its extension, it increases the dragvery little, but increases the lift a great deal as it increases both the area and

camber. As the extension continues, the flap deflects downward, and during the lastportion of its travel, it increases the drag with little additional increase in lift.

Leading Edge DevicesHigh-lift devices also can be applied to the leading edge of the airfoil. The mostcommon types are fixed slots, movable slats, and leading edge flaps.

Fixed slots direct airflow to the upper wing surface and delay airflow separation athigher angles of attack. The slot does not increase the wing camber, but allows ahigher maximum coefficient of lift because the stall is delayed until the wingreaches a greater angle of attack.

Movable slats consist of leading edge segments, which move on tracks. At lowangles of attack, each slatis held flush against the wings leading edge by the high pressure that forms at thewings leading edge. As the angle of attack increases, the high-pressure area movesaft below the lower surface of the wing, allowing the slats to move forward. Someslats, however, are pilot operated and can be deployed at any angle of attack.Opening a slat allows the air below the wing to flow over the wings upper surface,delaying airflow separation.


18/34

Leading edge flaps, like trailing edge flaps, are used to increase both CLmax andthe camber of the wings. This type of leading edge device is frequently used inconjunction with trailing edge flaps and can reduce the nose-down pitchingmovement produced by the latter. As is true with trailing edge flaps, a smallincrement of leading edge flaps increases lift to a much greater extent than drag.

As greater amounts of flaps are extended, drag increases at a greater rate than lift.Spoilers:

On some airplanes, high-drag devices called spoilers are deployed from the wings tospoil the smooth airflow, reducing lift and increasing drag. Spoilers are used for rollcontrol on some aircraft, one of the advantages being the elimination of adverseyaw. To turn right, for example, the spoiler on the right wing is raised, destroyingsome of the lift and creating more drag on the right. The right wing drops, and the

airplane banks and yaws to the right. Deploying spoilers on both wings at the sametime allows the aircraft to descend without gaining speed. Spoilers are alsodeployed to help shorten ground roll after landing. By destroying lift, they transferweight to the wheels, improving braking effectiveness.

6.1.3 EmpennageThe correct name for the tail section of an airplane is empennage. The empennageincludes the entire tail group, consisting of fixed surfaces such as the verticalstabilizer and the horizontal stabilizer. The movable surfaces include the rudder, theelevator, and one or more trim tabs.


19/34

A second type of empennage design does not require an elevator. Instead, itincorporates a one-piece horizontal stabilizer that pivots from a central hinge point.

This type of design is called a stabilator, and is moved using the control wheel, justas you would the elevator. For example, when you pull back on the control wheel,the stabilator pivots so the trailing edge moves up. This increases the aerodynamictail load and causes the nose of the airplane to move up. Stabilators have anantiservo tab extending across their trailing edge.

The antiservo tab moves in the same direction as the trailing edge of the stabilator.The antiservo tab also functions as a trim tab to relieve control pressures and helpsmaintain the stabilator in the desired position. The rudder is attached to the back of

the vertical stabilizer. During flight, it is used to move the airplanes nose left andright. The rudder is used in combination with the ailerons for turns during flight. Theelevator, which is attached to the back of the horizontal stabilizer, is used to movethe nose of the airplane up and down during flight.

Trim tabs are small, movable portions of the trailing edge of the control surface.These movable trim tabs, which are controlled from the cockpit, reduce controlpressures. Trim tabs may be installed on the ailerons, the rudder, and/or theelevator.

ElevatorThe elevator controls pitch about the lateral axis. Like the ailerons on small

airplanes, the elevator is connected to the control column in the cockpit by a seriesof mechanical linkages. Aft movement of thecontrol column deflects the trailing edge of the elevatorsurface up. This is usuallyreferred to as up elevator.

The up-elevator position decreases the camber of the elevator and creates adownward aerodynamic force, which is greater than the normal tail-down force thatexists in straight-and-level flight. The overall effect causes the tail of the airplane to


20/34

move down and the nose to pitch up. The pitching moment occurs about the centerof gravity (CG). The strength of the pitching moment is determined by the distancebetween the CG and the horizontal tail surface, as well as by the aerodynamiceffectiveness of the horizontal tail surface. Moving the control column forward hasthe opposite effect. In this case, elevator camber increases, creating more lift (lesstail-down force) on the horizontal stabilizer/elevator. This moves the tail upward and

pitches the nose down. Again, the pitching moment occurs about the CG.

As mentioned earlier in the coverage on stability, power, thrustline, and the positionof the horizontal tail surfaces on the empennage are factors in how effective theelevator is in controlling pitch. For example, the horizontal tail surfaces may beattached near the lower part of the vertical stabilizer, at the midpoint, or at the highpoint, as in the T-tail design.

RudderThe rudder controls movement of the airplane about its vertical axis. This motion iscalled yaw. Like theother primary control surfaces, the rudder is a movable surface hinged to a fixed

surface, in this case, to the vertical stabilizer, or fin. Moving the left or right rudderpedal controls the rudder. When the rudder is deflected into the airflow, a horizontalforce is exerted in the opposite direction.

By pushing the left pedal, the rudder moves left. This alters the airflow around thevertical stabilizer/rudder, and creates a sideward lift that moves the tail to the rightand yaws the nose of the airplane to the left.Rudder effectiveness increases with speed, so large deflections at low speeds andsmall deflections at high speeds may be required to provide the desired reaction. Inpropeller-driven aircraft, any slipstream flowing over the rudder increases itseffectiveness.

6.2 Principles of FlightIn order to understand the operation of the major components and subcomponentsof an aircraft, it is important to understand basic aerodynamic concepts.

The following defines these forces in relation to straight-and-level, unacceleratedflight.Thrust is the forward force produced by the powerplant/ propeller. It opposes orovercomes the force ofdrag. As a general rule, it is said to act parallel to the longitudinal axis. However,this is not always the case as will be explained later.Drag is a rearward, retarding force, and is caused by disruption of airflow by thewing, fuselage, and other protruding objects. Drag opposes thrust, and acts

rearward parallel to the relative wind.Weight is the combined load of the airplane itself, the crew, the fuel, and the cargoor baggage. Weight pulls the airplane downward because of the force of gravity. Itopposes lift, and acts vertically downward through the airplanes center of gravity.Lift opposes the do wnward force of weight, is produced by the dynamic effect ofthe air acting on thewing, and acts perpendicular to the flightpath through the wings center of lift.


21/34

In steady flight, the sum of theseopposing forces is equal to zero.

There can be no unbalanced forces insteady, straight flight (Newtons ThirdLaw). This is true whether flying levelor when climbing or escending. This

is not the same thing as saying thatthe four forces are all equal. It simplymeans that the opposing forces areequal to, and thereby cancel theeffects of, each other. Often therelationship between the four forceshas been erroneously explained orillustrated in such a way that thispoint is obscured. Consider figureshown, for example. In the upperillustration the force vectors of thrust,drag, lift, and weight appear to be

equal in value. The usual explanationstates (without stipulating that thrustand drag do not equal weight and lift)that thrust equals drag and lift equalsweight as shown in the lowerillustration. This basically truestatement must be understood or itcan be misleading. It should beunderstood that in straight, level,unaccelerated flight, it is true thatthe opposing lift/weight forces areequal, but they

are also greater than the opposing forces of thrust/drag that are equal only to eachother; not to lift/weight. To be correct about it, it must be said that in steady flight: The sum of all upward forces (not just lift) equals the sum of all downward forces(not just weight). The sum of all forward forces (not just thrust) equals the sum of all backwardforces (not just drag).

Pitch-Roll-Yaw


22/34

Pitch:Is rotation around the lateral or transverse axisan axis running from the pilot's leftto right in piloted aircraft, and parallel to the wings of a winged aircraft; thus thenose pitches up and the tail down, or vice-versa.Longitudinal control of an aeroplane is nearly always provided by ELEVATORS

attached to the rear of the tail plane. the principle is best illustrated by the oldfashioned system in which the elevators were connected by control wires and leversto the control column in the pilot's cockpit. The control is instinctive i.e. when thecolumn is pushed forward, the elevators are lowered and the upward force on thetail is increased, thus causing the nose of the aeroplane to drop.

Roll:Is rotation around the longitudinal axisan axis drawn through the body of thevehicle from tail to nose in the normal direction of flight, or the direction the pilotfaces.

The roll angle is also known as bank angle on a fixed wing aircraft, which "banks" tochange the horizontal direction of flight.

The usual method of obtaining lateral control is by means of AILERONS hinged atthe rear of each main plane near the wing tips. the ailerons are connected to thecontrol column by a complete system of control wires, by a rigid system of rods, bytorque tubes inside the wings, or again by some power operated system. This timeit is a sideways movement of the control column which moves the ailerons and doesso in such a way that once again the control is instinctive, i.e, if the control columnis moved to the left the right hand ailerons will go down, increasing the lift on theright hand wings, thus banking the aeroplane to the left; at the same time the leftailerons will have been raised, decreasing the lift on the left wing and thus addingto the effect. Some- times the control column has no sideways movement, andlateral control is effected by a type of handlebars, or by a wheel very similar tosteering wheel on a car.

Yaw:Is rotation about the vertical axisan axis drawn from top to bottom, andperpendicular to the other two axes.Directional control is by RUDDER, which has very much the same effect as on ship.

The rudder is connected by wires or rods or by a power operated system to a rudderbar or rudder pedals on the floor of the cockpit. In this instance it is not wise tostress the point that the control movement is instinctive, because some peopleclaim that it works the wrong way and should be altered to make it instinctive. if theleft foot is pushed forward, the rudder moves to the left and the aeroplane turns tothe left. it all sounds instinctive enough, but it is exactly the opposite to whathappens on a bicycle when the hadlebars are move in the same way as the rudderbar.


23/34

6.1.4Landing GearThe landing gear is the principle support of the airplane when parked, taxiing,taking off, or when landing. The most common type of landing gear consists ofwheels, but airplanes can also be equipped with floats for water operations, or skisfor landing on snow.

The landing gear consists of three wheelstwo main wheels and a third wheelpositioned either at the front or rear of the airplane. Landing gear employing a

rearmounted wheel is called conventional landing gear. Airplanes with conventionallanding gear are sometimes referred to as tailwheel airplanes. When the third wheelis located on the nose, it is called a nosewheel, and the design is referred to as atricycle gear. A steerable nosewheel or tailwheel permits the airplane to becontrolled throughout all operations while on the ground.

6.1.5 Power PlantThe powerplant usually includes both the engine and the propeller. The primaryfunction of the engine is to provide the power to turn the propeller. It also generateselectrical power, provides a vacuum source for some flight instruments, and in mostsingle-engine airplanes, provides a source of heat for the pilot and passengers. Theengine is covered by a cowling, or in the case of some airplanes, surrounded by a

nacelle.The purpose of the cowling or nacelle is to streamline the flow of air around theengine and to help coolthe engine by ducting air around the cylinders. The propeller, mounted on the frontof the engine, translates the rotating force of the engine into a forward acting forcecalled thrust that helps move the airplane through the air.


24/34

6.2 Design Configuration

6.2.1 Conventional Configurations:These can be classified as Cantilevered monoplane wing. Separate horizontal and vertical tail surfaces. Control via ailerons, elevators and rudder.

Discrete fuselage to provide volume and continuity to airframe. Retractable tricycle landing gear. Minimum number of power plants needed to meet power and operationalrequirements.

Within the category of conventional aircraft there are many variations from thestandard to be considered: Power Plant Location nose, wing podded, rear fuselage podded, internal. Intake Location nose, side, ventral, dorsal.Wing Vertical Location high, low, mid. Tail Unit Arrangements variable incidence, allmoving, T-tail, multi-finned,butterfly.

Tricycle Landing Gear Configuration numbers of legs, bogeys and wheels.

a. Power Plant LocationNose-MountedMost logical position for any single tractor propeller engine aircraft.Advantages include symmetry of layout, good propeller clearance, access andmaintainability.Wing-Mounted (Outer Wing)


25/34

Many uses: Large aircraft with propellers, turbojets or turbofans. For jets/fans, these will be podded and mounted onto under-wing pylons. For props, these will be mounted directly onto the wing structure. Advantages include: Versatility use of alternative engines.

Compact overall layout. Inertial relief reducing required wing structural mass. Ease of access for maintenance.

Also several drawbacks and necessary considerations: Ground clearance may be a problem in which case high wings may be used (withtall landing gear) or possibly top-wing mounting (e.g. BAe 748) with aerodynamicpenalty. Spanwise location should depend on prop diameter or statistical analysis of fanburst trajectory and impact on neighbour. Typical values are 30% and 55% semi-span for a 4-engine design; large valuesgive big engine-out yaw problems and larger rudder sizes.

Over Wing-MountedPodded engines Placed above the wings Coanda effect allowing a lower minimum flight speed and decreasing the amountof runway needed for takeoff BAe 748 Shorts SD360 and landing.Wing-Mounted (Inner Wing) Some aircraft have housed the powerplants in the wing root area with significantstructural disadvantages.Rear Fuselage-Podded Used on many moderate sized transport aircraft of the past and also manymodern small business jet aircraft. Advantages

Reduced engine-out yaw smaller rudder size.

Disadvantages

Rearwards movement of CG stability problems.

Structural acoustic fatigue.Wing Podded Vs Fuselage Podded

Wing Podded Fuselage PoddedGround clearance Possible problem GoodInternal Noise Fair GoodAcoustic fatigue Possible problem for wings

& FlapsPossible problem for Fuselage

Crash safety Good Possible problem

PropulsiveEfficiency

Good OK if well positioned

Longitudinalstability

Good Problems due aft CG & Short tailarm

Tip Stall Good Possible problemAsymmetric

ThrustPoor Good

Weight Good Poor


26/34

Enginemaintenance

Good High off Ground

Wingaerodynamicefficiency

Problems form Cut outs Very Good

Fuel feeds to

engine & winganti icing

Good Ducts and Lines through cabin

Internally Housed Used on many single and twin turbojet/turbofan engine aircraft such as militarytrainers and fighters. Advantages Compact layout. Reduced drag. Disadvantages Engine removal and maintenance problems. Structural acoustic fatigue due to jet efflux. Jet pipe length minimized by moving engine rearwards but this affects CG,stability and control.

b. Intake LocationNose Intake Used on many early jet fighters with mid-fuselage mounted engines. Requires use of long inlet ducts and jet pipes gives low flow distortion but hightotal pressure losses. No need for boundary layer diverters. Occupies large amount of internal volume. Only small radome may be housed in shock cone centre-body.

Side Intake (Below Wing) Used on the majority of modern high-wing strike and combat aircraft designs. Leaves the nose area free for radar equipment installation.

The wing is often extended above the intakes to improve highperformance.

Flow diverters are needed to accommodate fuselage boundary layer growth.

Side Intake (Above Wing) Used on many low-wing design trainer and combat aircraft. Wings may be used to shield the intakes and reduce the manoeuvring a. Any sharps bends have to be avoided to prevent flow distortions. Short intake lengths are possible with low overall volume requirements.

Ventral IntakeSituated on underside of fuselage - an increasingly common position for highperformance combat aircraft. Gives very good high-a manoeuvrability. Prone to FOD and debris ingestion. Complicates nose wheel positioning/stowage. Restricts carriage of under-fuselage stores. Low flow distortion and pressure losses into intake.


27/34

Dorsal IntakeSituated on top-side of fuselage. Only tends to be used on 3-engine airliners with 3rd engine buried in the rearfuselage/fin area with a few exceptions. Gives poor performance at high-a due to separated flow ahead of intake.

c. Vertical Wing LocationHigh Wing

The easiest planes to fly are typically ones that have a high wing, or a wing that ison top or above the plane's fuselage. Wing dihedrals (bend or change of angle inwing relative to fuselage) or polyhedrals are also common. Most trainers and parkflyers have this configuration.

These planes hold most of their weight under the canopy of the wing structure andtend to react more like a glider. For this reason, they are very stable and easy to fly.If a high wing plane is out of control, stability can often be regained by returning the

controls to a neutral position, allowing the plane to naturally fall back into a glidingposition.High wings are typical of many vintage private planes, such as the Piper Cub andthe Cessna 170.

Gives an efficient spanwise lift distribution leading to low lift-induced drag.

Improves lateral static stability.

Preferred for most freight and military transport aircraft:

Low floor line for easy loading & unloading.

Good all-round vehicular access when on ground. Wing fuel load away from ground when landing with failed landing gear.

Good ground clearance for powerplants, especially props.Low Wing

This .60 cubic inch/10cc glow-powered Vinh Quang Model Mudry CAP 10 is a fullyaerobatic, low-wing, "sport scale" model plane with slight dihedralLow wing planes offer a higher level of flying difficulty because the weight of theplane sits on top of the wing structure, making the balance a bit top heavy. Mostwing configurations provide a slight dihedral to provide a bit more balance duringflight.

The weight distribution and wing position of a low wing plane provides a goodbalance of stability and maneuverability. The plane's moment of inertia about therotation axis is lower because it is closer to the wing, therefore rolls require muchless torque and are more rapid than a high wing plane.

Low wings are typical ofWorld War II war planes and many newer passenger planesand commercial jets. Improves lateral manoeuvrability. Preferred for most passenger transport aircraft: Wing structure conveniently passes below floor. Volume free fore and aft of wing structure for cargo holds luggage and landinggear stowage. Minimizes landing gear length and mass.
http://en.wikipedia.org/wiki/Dihedral_(aircraft)http://en.wikipedia.org/wiki/Polyhedralhttp://en.wikipedia.org/wiki/Piper_Cubhttp://en.wikipedia.org/wiki/Cessna_170http://en.wikipedia.org/wiki/Mudry_CAP_10http://en.wikipedia.org/wiki/Dihedral_(aircraft)http://en.wikipedia.org/wiki/World_War_IIhttp://en.wikipedia.org/wiki/Dihedral_(aircraft)http://en.wikipedia.org/wiki/Polyhedralhttp://en.wikipedia.org/wiki/Piper_Cubhttp://en.wikipedia.org/wiki/Cessna_170http://en.wikipedia.org/wiki/Mudry_CAP_10http://en.wikipedia.org/wiki/Dihedral_(aircraft)http://en.wikipedia.org/wiki/World_War_II


28/34

Wing provides buoyancy when ditching into water and also a platform foremergency evacuation.

Mid-wingMid-wing planes are usually considered the most difficult to fly. The wings areusually located right in the vertical middle of the fuselage, near the bulk mass of the

aircraft. Very little leverage is needed to turn and rotate the plane's weight.Mid-wings are often straight without any dihedral providing an almost symmetricalaerodynamic structure. This allows the plane to be relatively balanced whetherright-side-up, upside-down, or any other position. This is great for military jets, sportplanes and aerobatic planes, but less advantageous for the learning pilot. Becauseof this symmetry, the plane does not really have any natural or stable flyingposition, like the high wing planes, and will not automatically return to a stablegliding position.

d. Tail Unit (Emphennage)

Conventional Layout Approximately 70% of aircraft in service have a conventionalarrangement comprising separate fixed horizontal stabiliser and vertical finsurfaces for stability and moving elevator and rudder sections attached tofixed surfaces for control. This is the simplest solution & provides optimum overall performance in themajority of cases

Variable Incidence Tailplane Here the forward (main) section of the horizontal surface is not fixed but iscapable of rotation through a small range of angles of attack. As such, it is generally used to adjust pitch trim rather than using the conventionalelevators.

It is especially useful for countering the effects of significant pitching momentincrements caused by deployment of powerful high lift devices. Elevators are still used for pitch control.

All-Moving (Slab) Tailplane Whole of the horizontal tailplane surface is used for both pitch control and trim(with no separate hinged elevator). This offers significant advantages at transonic and supersonic speeds wheneffectiveness of conventional trailing edge surfaces is dramatically reduced. Universally adopted for supersonic fighter designs. Most also use differential movement of opposite sides to improve roll rate (thenknown as tailerons). Powered controls are necessary due to the large control force requirements.

T-Tail Horizontal tailplane mounted on top of fin. Often used on large high-mounted swept-wing designs and also smaller low-wingaircraft.Advantages


29/34

Provides substantial end-plating effect to fin, improving its effectiveness andreducing the fin size requirement. Lifts the horizontal tail clear of any propwash & the wing wake during cruise flight,therefore reducing buffet and fatigue. Allows engines to be mounted on the aft-fuselage, if required.

Disadvantages Gives a large mass penalty to the empennage due to the higher loading andaeroelastic effects. Increased likelihood of deep stall puts tail in wake of stalled wing, makingrecovery difficult or even impossible..

Multi-Finned If fin-sizing exercise results in large single fin dimensions then sometimespreferable to use two (or more) smaller fins instead. Allowed Constellation to operate from existing hangars. Also produces desirable end-plating effect to horizontal tailplane, reducing itssize requirements. Fins have to be positioned far enough apart so that undesirable mutualaerodynamic interference effects are not too severe. If fins are positioned in slipstream of propellers rudder performance is improved atlow speeds. Difficult to avoid fin stall at high sideslip angles. Not generally used nowadays for single-boom layout transport aircraft.

Twin Fin Fighter Aircraft Twin fins nowadays more associated with supersonic fighters. More compatible with twin-engine aircraft (F14/F15/F18) than single (F16) due toengine-out sizing considerations. Special benefit of supersonic application is that interference effect disappearsproviding fin Mach lines do not intersect. Can also provide infrared shielding of engine exhaust to improve stealth,especially if canted (F22). Resultant reduced fin height improves aeroelastic behaviour.

Butterfly Tail In this case the conventional tail surfaces are combined into a pair of inclinedsurfaces. The separate roles of the tailplane/elevator and fin/rudder are combined. Advantages include: Less interference drag; smaller total surface area; improved stealthcharacteristics. Disadvantages include: Cross-coupling of stability/control characteristics; handling difficulties; need forfully automatic flight control system.

Horizontal Positioning Surfaces should generally be positioned as far aft as possible to maximize the tailmoment arm. Restrictions on this may be caused by engine-induced structural fatigue (e.g. F-5).


30/34

e. Landing Gear layout

Tricycle Gear Configuration The most conventional, comprising: Pair of main legs behind aircraft CG. Single nose leg ahead of CG.

Each leg incorporates: Shock absorber to dissipate vertical landing energy. Single or two side-by-side wheels or multiple bogie arrangement. Only main wheels are generally fitted with brakes. Only the nose wheel is usually steered for ground manoeuvring. For effective steering, nose leg should support between 6 and 10% of the aircraftmass. Provision must be made for attachment and stowage of landing gear units. Lateral positioning (track) dictated by need to prevent overturning during groundmanoeuvring

mainly a function of height of CG, track distance & shock absorber characteristics.

Tricycle Gear Configuration Number of Wheels As the aircraft mass increases, operations from runways of given strength dictateneed for more wheels to spread the load many possible variants: Two-axle bogie Three-axle bogie Three or four main legs Multiple legs on single axes

Two-Axle Bogie The main legs are split into two-axle bogies, with usually two wheels per axle. Such as arrangement is generally necessary if the aircraft mass is between about90 and 200 tonnes.

It is common to many civil and military transport aircraft types.

Three-Axle Bogie For very large aircraft (e.g. > 210 tonnes), the load has to be spread even further one option is to use a 3-axle bogie arrangement.

Three Main Legs Some large aircraft use an additional main leg to spread the load, e.g. Airbus A-340:

2-wheel nose gear and 3 main gear, each of double-wheel 2-bogie 14 wheels intotal.

Four Main Legs This will generally be the case for very large civil transports (> 300 tonnes) withlow wing designs (e.g. Boeing 747). It poses significant problems for airframe attachment & stowage.

Multiple Main Legs with Single Axles Good option for heavy high wing military transports with retraction into fuselageblisters.


31/34

Tail Wheel Configuration Here the two main wheels are located forward of the CG and a tail wheel or skidprovides the third support point. This is a simpler, lighter and cheaper design than a tricycle layout but hassignificant disadvantages:

Difficult ground manoeuvring and take-off/landing due to inhibited visibility. This was the norm for many early aircraft but its application is nowadays limitedto simple light aircraft where emphasis is on simplicity and low cost often withfixed (rather than retractable) legs.

f. UnConventional ConfigurationBiplane The norm for the first 30 years of aviation. Early aerofoils were very thin requiring external bracing so that biplanes gavebest structural efficiency. Many penalties of use, especially at higher speeds increased total mass, dragand aerodynamic interference.

Aerodynamics and materials advances have led to increased wing loadings (W/S)so that biplanes are mostly redundant nowadays main exception is aerobaticsaircraft where low W/S is an advantage andspecialized aircraft such as crop-sprayers.

Variable Sweep (Swing-Wing) Design Problem: High sweep usually needed for transonic/supersonic speed designs but this affectslow speed performance. Possible solution is to use variable sweep wings. This gives a better matched performance over a wide speed range and offers anaircraft multi-role capabilities over subsonic and supersonic speed ranges.

Variable Sweep - Disadvantages Increased mass over conventional design due to heavy actuation system. Increased system complexity and costs. Increased drag due to interaction between fixed and moving parts of the wing. Trim and stability/control problems due to movements of aerodynamic centre andCG.

Canard Layout The conventional aft horizontal tailplane is replaced by a foreplane (or canard)while the main wing is then moved rearwards for stability purposes. Two main categories: Lifting canard canard provides substantial lift as well as longitudinal trim andcontrol. Control canard - longitudinal trim and control only. This is not a new idea the original Wright Flyer was a control canardconfiguration.

Canard Layout Configurational Advantages Negligible trim drag penalty, usually a download on the rear tail surface on aconventional layout.


32/34

More rapid pitching manoeuvre response as initial change is in required direction.Possible layout advantage (e.g. aft-located wing passes behind thecabin). Better provision for escape from pitch-up (associated with tipstall on highlyswept wings).

Canard Layout Configurational Disadvantages

Airflow interference from the canard over the main wing surface. Increased pitching moment effect with wing flap deployment due to large momentarm sosophisticated high lift devices may not be used with consequent low-speedperformance penalty.

Canard with Forward Sweep Rearward sweep usually preferable as it gives better compromise of aerodynamiccharacteristics especially stability/control. Forward swept wings also more prone to aeroleastic divergence overcome withassociated mass penalty. Torsionally very stiff wing would be required to resist twisting

Method could give overall layout advantages, e.g. by allowing wing carry-throughstructure to pass through rear of aircraft and avoid main section.

Twin-Boom Layout Aircraft Several possible reasons for being adopted: Allows engine to be mounted close to CG particularly pusherprop types & early

jets. Over-riding requirement for aircraft to have unrestricted access to rear of freighthold. Visibility for rear gunner/bomber crew. Results in use of twin fins. Disadvantages include: increased wing mass, increased interference drag and less

usable volume.

Span-Loaders Closely related to flying wing designs whereby the payload held in main wing boxstructure. Small central fuselage pod sometimes used to house flight deck and centralservices.Advantages Spreads the payload across the wing, rather than the fuselage. This gives inertial relief to the wing structure. Most of aircraft then comprises wing (with higher lift/drag than conventionalfuselage). Gives typical 10% reduction in take-off mass.Disadvantages Difficult emergency passenger evacuation procedures. Structural layout problems. Fuel location. Pressurization of wing section. Increased moments of inertia leading to poor roll rates. Complicated flight control system.


33/34

Flying Wing (Blended Wing-Body BWB) Layout Similar to spanloaders optimum aerodynamic solution sought - wing is mostefficient means of lift generation so fuselage is dispensed with altogether.Advantages As for spanloader inertial relief of wing gives lower wing structure mass and

lower costs. Potential for increased passenger cabin volume and improved comfort levels. Major opportunity for using laminar flow technology easier to apply to wing thana fuselage.BWB Aircraft - Disadvantages Passenger wariness of unconventional (more feasible to military & cargotransports). Unfamiliar structural layout & design. Complex aerodynamic interference effects.

g. Special Configurational Issues An aircrafts specifications and requirements may include some special provision

which could then have a dominant influence over the resultant configuration. These include: Short Take-Off & Vertical Landing (STOVL). Stealth. Waterborne Operations.

STOL & STOVL Aircraft Short Take-Off (& Vertical) Landing Aircraft. Two classes of military aircraft sometimes have a need for STOL or STOVLcapabilities. Freight. Combat

Military Freight STOL Airlifters Often required to operate to and from airstrips of short length and poor surfacestrength. No major effect upon configuration selection (unless tilt-rotor/wing technologyadopted) but increased emphasis on: High installed thrust. Complex high lift devices and wing technology. Low tyre pressures. Several civil variants also developed with perceived need.

STOVL Combat Aircraft For vertical landing the available vertical thrust component must exceed thelanding weight. Logical to also use this component for short take-off. STOVL thrust component provided by downward deflection of exhaust gases offorward flight propulsion unit(s). Impractical to locate this thrust component immediately below CG at all times soadditional thrust provision needed for balance. Three standard methods available for providing vertical thrust component: Vectored bypass flow.


34/34

Separate vertical lift engine. Remotely driven lift engines (using main powerplant as energy source). All methods require separate low-speed control capability, usually using reaction

jets supplied with bleed air from main engine compressor.

Stealth Increasingly important for modern combat aircraft designs. Final configuration depends heavily on overall priority of stealth againstperformance.

Stealth General Observations Foreplanes best avoided. Internal powerplants & weapons. Intakes with long curved ducts. Exhausts must be shielded. Avoid surfaces positioned at right angles to each other (e.g. use inclined fins). Minimize discontinuities in shape/surface. Surface edges parallel to each other.

Difficulties with cockpit transparencies use of unmanned vehicles advantageous.

Waterborne Aircraft Very common in the early days of aviation. Can operate from anywhere with a large stretch of reasonably calm water. Became less popular due to: More airfields available after WW2. Trend for using higher wing loadings - Results in higher take-off & landing speeds and high water resistance forces. Use nowadays restricted to small aircraft operating in coastal regions or in remotelocations with many lakes & rivers. Two basic categories float planes & flying boats.

Float Planes Conventional landing gear replaced by large floats. Invariably propeller-driven. Usually direct conversions from landbased types. Usually only applicable to small aircraft (12 tonnes max). Air drag of floats is high and gives large tail download trim requirement.

Flying Boats Usually larger than float planes. Fuselage used as a hull for waterborne operations. Wing tip floats or fuselage sponsons used to provide waterborne roll stability. Some types also have conventional retractable landing gear and are thenamphibious.

introduction to aircrafts

Documents