Aircraft Wing construction

Wings: The wings of an aircraft are surfaces designed to give lifting force

when moved rapidly through the air. The particular wing design for any given aircraft

depends on a number of factors, such as size, weight, use of the aircraft, desired speed in

flight and at landing, and desired rate of climb. The wings are designated as left and

right, corresponding to the left and right hands of the pilot seated in the cockpit

or the pilot'scompartment. Engines mounted on wings are numbered from the

left wing to the right.

Design: The wings of military or large commercial aircraft are usually of

cantilever design; that is, they are built so that no external bracing is needed. With

few exceptions, wings of this design are of the stressed skin type, which means

that the skin is a load-bearing part of the wing structure.

Wing construction: In general, wing construction is based on one of three

fundamental designs: monospar (one), multispar (two or more), or box beam. Slight

modifications of these basic designs may be adopted by various manufacturers. The monospar wing incorporates only one main longitudinal member (spar) in its

construction. Ribs or bulkheads supply the necessary contour or shape to the airfoil. Although the strict monospar type wing is not common, this type of design, modified

by the addition of false spars or light shear webs along the trailing edge as support for

the control surfaces, is often used.

The multispar wing incorporates more than one main longitudinal member

(spar) in its construction. To give the wing contour, ribs or bulkheads are often

included. This type of construction, or some modification of it, is used in the lighter

types of combat aircraft.

The box-beam typeof wing construction uses two main longitudinal members

with connecting bulkheads to furnish additional strength and to give contour to the

wing. A corrugated sheet may be placed between the bulkheads and the smooth outer

skin so that the wing can better carry tension and compression loads. In some cases,

heavy longitudinal stiffeners are substituted for the corrugated sheets. A combination of

corrugated sheets on the upper surface of the wing and stiffeners on the lower surface is

sometimes used.

Other variations in wing design are necessary because of the angle at which the

wing attaches to the fuselage. As shown in below figure, wings angled upward have

positive dihedral, and wings angled downward have negative dihedral. The wing

tip may be square, rounded or even pointed. Both the leading edge and the

trailing edge of the wing may be straight or curved. In addition, one or both

edges may be tapered so that the wing is narrower at the tip than at the root

where it joins the fuselage. Numerous types of modern aircraft use swept back wings.

Construction Futures: The main structural parts of a wing- the spars, ribs,

stringers or stiffeners, and skin are illustrated in below figure. These structural

parts are riveted or welded together.

Spars: Spars are the principal structural members of the wing. They

correspond to the longerons of the fuselage. They run parallel to the lateral axis,

or toward the tip of the wing, and are usually attached to the fuselage by wing

fittings, plain beams, or part of a truss system.

The I-beam type of construction for a spar consists of a web (the deep wall

plate) and cap strips (which in reality are extrusions or formed angles). These

carry the loads caused by the wing bending, and also provide a foundation for attaching

the skin. Stiffeners give additional strength to the spar structure. Stiffeners may be

beads pressed into the web or extrusions or formed angles riveted to the web,

either vertically or diagonally. Detail of above figure, shows a typical I-beam type

of spar.

Ribs: Ribs are the cross-pieces that make up the framework of the wing.

They run from the leading edge toward the trailing edge (front to rear) of the

wing. The ribs are secured to the spars, and since they are curved. They give the

wing its aerodynamic shape when it is covered with the skin. Ribs transmit the

load from the skin to the spar. There are two general types of ribs construction, as

shown in below figure. The reinforced rib is relatively heavy as compared to the

formed rib, and is located only at points where the greatest stresses are imposed.

Formed ribs are located at frequent intervals through the wing. The reinforced rib is

similar in construction to spars, consisting of upper and lower capstrips joined by a web

plate. The web is reinforced between the capstrips by vertical and diagonal angles.

Formed ribs are made of formed sheet metal and are very light in weight. The

bent-up portions of a formed rib are referred to as the flanges, and the vertical

portion is called the web. The web is constructed with lightening holes, with

beads formed between the holes. The lightening holes lessen the weight of the rib

without decreasing the strength. Flanging the edges of the lightening holes helps

maintain the rigidity of the web. The beads stiffen the web portion of the rib.

Stringers: Stringers or stiffeners are attached to the skin where high

compressive loads arc encountered, or where a shape must be held. These are usually

found closely spaced on the underside of the upper wing skin, where stiffening

demands become extreme, the skin is usually reinforced by a corrugated panel or

honeycomb sandwich instead of individual stringers. Cross sections of typical

stiffened panels are shown in below figure.

Skin: The skin used as wing covering is quite strong in tension and shear. The

skin is employed as a primary load-carrying member in wing construction. The

thickness of wing skin varies widely, depending upon the stresses encountered.

Thicknesses vary from as low as inch in small aircraft to as much as

. inch in the wings of heavy bombers. If weigh reduction is of prime

importance, the skin is tapered so that the proper amount of strength is provided. In the last few years, machine milled skins (below figure) have become

routine in the aircraft industry. Many parts on high performance aircraft have been

redesigned for machine milling. This process results in fewer parts, fewer fasteners,

decrease in weight, easier assembly, greater load carrying capacity, and easier field

repairs. Many different machines are required to machine mill skins. They

include vertical milling machines, horizontal milling machines, detail milling

machines, drilling machines, and routing machines.

Chem-milling is a process used to shape metals to an exacting tolerance by

chemical removal, or deep etching, rather than by conventional mechanical

milling or machining operations. Originally developed as a means of providing

increased metal thickness, at the edges to be butt-welded, the chem-mill process

has mushroomed into a full-scale production tool. Designs which were once

avoided as impossible to produce, or prohibitive in cost are being achieved daily

in chem-milling facilities.

Chem-milling or etching, is the immersion of a part in an etching solution

to remove metal and leave a predetermined design. The etching solution

dissolves the metal not only in a direction perpendicular to the exposed surface,

but also undercuts the mask. That is, the solution cuts underneath the mask

approximately as far as it cuts into the metal. A series of tanks filled with

special solutions are arranged to allow a rapid transfer of parts from one to

another as etching and rinsing proceeds. The depth of metal removed depends

on the time of immersion in the etching solution. Honeycomb panels are also used as skin coveringon certain sections of the wing.

The type of honeycomb assemblies most commonly used consists of a

honeycomb core of aluminum foil and then aluminum facing material bonded

together with an adhesive. You can recognize honeycomb assemblies by their thin

outer skin, the absence of fasteners and the light weight of the complete assembly. Below figure shows one type of honeycomb skin panel assembly.

Wing sections: The leading edge, center section and trailing edge section are

the three sections that make up an aircraft wing (front to rear). The leading edge is

the front section of the wing. The purpose of the leading edge is to streamline the

forward section of the wing. The space within the leading edge is sometimes used

to house extra equipment such as landing lights, plumbing lines or thermal anti-

icing systems. Leading edges constructed with thermal anti-icing systems consist of

two layers of skin separated by a thin airspace. The center section of the wing is from

the front spar to the rear spar. This is the main structural section of the wing. All

external structures are attached to this section. The space within this section is

sometimes used to store fuel, and on fighter type aircraft this space serves as housing for

the landing gear. The center section is where the wing walkway areas are located.

The trailing edge section is the rear most part of the wing. Attachments for

the control surfaces are located within this section.

External structures: On multiengine type aircraft, the streamlined structural

units placed around the aircraft engines to provide a smooth surface for airflow are

called nacelles. The nacelles on jet aircraft are attached to a strut which in turn is

attached to the center section of the wing. Below figure depicts this type of

design.

On propeller driven aircraft, the nacelle is built as the part of the wing itself.

Below figure illustrates the internal structural units for a built-in type nacelle. The

construction features are similar to that of the fuselage. On twin-engine aircraft, the

nacelles also house the wing landing gears and related equipment. On a four engine

aircraft, the landing gear is enclosed in the inboard nacelles. An engine cowling with

quick release type fasteners and latches provides access to the engine within the nacelle.

Fairings: Fairings are auxiliary members that streamline various parts and

locations on the aircraft to reduce drag. They cover the joints formed where wing

sections meet the fuselage and where the vertical and horizontal stabilizers mount on

the main structure.

They are often used to streamline around fittings, navigation lights,

landing gear struts, wheels, and the like. Fairings are not strength members and are

not intended to carry any of the principal loads placed on the aircraft structures.

نکات مهم در طراحی بال هواپیماهای مسافربری:

در طزاحی تال اپیوا یاسد پاراهتز اصلی جد دارد و ػثارتذ اس:

(؛Sتال)هساحت هزجغ .1

( در Mean Aerodynamic Chord( تزهتسط آیزدیاهیىی)Spanتؼییي د هتغییز د تال)

ایي لسوت اس اویت سیادی تزخردار است.

هحل ػودی صة تال؛ .2

تطرولی چار هحل صة تال ت تذ جد دارد و ػثارتست اس:

( تال تاالHigh Wing؛)

( تال سطMid Wing؛)

تال( پاییيLow Wing؛)

( تال تاالتزParasol Wing؛)

(؛Airfoilهمطغ تال) .3

تایستی وذ یؼی در حالت تؼادل یزیی ایفا هی Cruiseایزفیل مش اصلی خد را در حالت

تاشذ ایي هالن اتخاب یا طزاحی ایزفیل است. Dragتیشتز اس ضزیة Liftضزیة

طزاحی همطغ ایزفیل؛

طزاحی ایزفیل پزشی یاسهذ اهىاات گستزد هتخصصیي ستذ دارد.

اتخاب اس هماطغ استاذارد؛

هؼزفیت تیشتزی NASA( یا NACAای ساسهاى افضای هلی آهزیىا )ایزفیل

دارذ.

:هشخصات ػوهی ایزفیل

شد تا ( تیشتز هیCl) Liftضزیة تیشتز شد ایزفیل ای اجام شذ، زچ سای حول تا تج ت تزرسی

تا 11 تیي" ( گیذ. ایي سای تمزیثاStallوذ و ت ایي مط، مط اهاذگی )آجا و شزع ت افت هی

درج )تست ت ع ایزفیل تزای اپیواای هسافزتزی( دارد. 15

(؛Aspect Ratioسثت هظزی) .4

ت تز هتسط آیزدیاهیىی تال است .سثت دا تال

( 2

(Rectangula ), (Trapze)b

AR r ARc S

b )

:اثزات سثت هظزی

.زچ تال درتز اس ریش تاشذ اثز گزداب تال ووتز است

زچ سثت هظزی افشایش یاتذ، سای اهاذگی واش خاذ یافت چى سای

یاتذ.حول هثز ن تال افشایش هی

افشایش یاتذ، سى افشایش خاذ یافت.زچ سثت هظزی

زچAR افشایش یاتذ ، max

LD

-تزای اپیواای هادى صت واش هی

یاتذ.

یاتذ.زچ سثت هظزی واش یاتذ، پسا افشایش هی

(؛Taper Ratio / سثت هخزطی) .5

ریش تال است.سثت تیي تز ن تال ت تز

طرولی سثت تاریه شذگی تیي یه)تال هستطیلی( صفز)تال هثلثی( است.ت

تزیي هؼیار تؼییي سثت هخزطی، رساذى تسیغ تزآ ری تال ت شىل تیضی است.اصلی

:اثزات ایي سثت ػثارتذ اس

دذ.تسیغ تزآ ری تال را تغییز هی

تزد.تز وزد شی ساخت را تاال هیواش ایي پاراهتز ساخت را هشىل

دذ.واش ایي سثت، سى را واش هی

(؛ Twist / tپیچش) .6

در صرتی و سای حول ن تال تا سای حول ریش تال تفات داشت تاشذ، تال دارای پیچش

و ( در صرتیWash-inاست. در صرتی و سای حول ن تال تیشتز تاشذ، پیچش هثثت)

-3در اپیواا پیچش هفی تد تیي صفز تا "( است. ػوهاWash-outووتز تاشذ هفی)

درج است.

:د دلیل اصلی پیچش تال ػثارتست اس

جلگیزی اس اهاذگی ن تال لثل اس ریش تال؛

تغییز تسیغ تزآ ت یه تسیغ تیضی؛

اس ظز ایوی هشىل اهاذگی شد لی در ػض جد پیچش هفی تاػث واش تزآ هی

حل شذ است.

:ااع پیچش

و اس ظز پیچش آیزدیاهیىی: لتی ایزفیل ریش ن تال هتفات تاشذ

.تز استساخت هشىل

.پیچش ذسی: لتی و ایزفیل ریش ن یىساى تاشذ

(؛Sweepگزد)سای ػمة .7

خاصی اس تز هحلی تا هحر ػزضی اپیوا سای و لث حول تال یا خط گذرذ اس درصذ گاهی

گزد ت ػمة گزد دارد. اگز ن تال ت سوت دم هتوایل تاشذ، ػمةگیذ تال ػمةداشت تاشذ هی

-شاى هی گزد ت جل یا جلگزد گیذ. ایي سای را تا اگز ت سوت دهاغ هتوایل تاشذ، ػمة

دذ.

است:گزد ت دالیل سیز السم ػمة

ای تاالی حذد صت یا هافق صت تا تاخیز اذاختي تثد شزایط در سزػت

پذیزی.اثزات تزاون

تز و ت ن شدیهتظین هزوش ثمل اپیوا هزوش آیزدیاهیه تال ت طری

شذ.

.تثد پایذاری طلی سوتی تزای اپیواای تذى دم

اای ظاهی.افشایش دیذ خلثاى ت خصص در اپیو

(؛Dihedral / )یا فتی تال سزاشیثی .8

.در وای جلی اپیوا، سای تال تا افك است

مش اصلی آى، تاهیي پایذاری ػزضی است (Rolling Stability) یؼی تا چزخش حل

گزداذ. تال تاال، تاثیز فتی تال را تمیت ا، فتی آى را ت حالت افمی تاس هیXهحر

وذ.تال پاییي، فتی را تضؼیف هیوزد

گزدد.تاتزایي سزاشیثی تال، تاػث افشایش پایذاری هی

(؛Incidence Angle / setسای صة تال) .9

.سای تیي تز ریش تال خط هزوشی تذ را گیذ

سى تاذ ثاتت یا هتغییز تاشذ و هتغییز تدى آى اس ظز ایوی افشایش ایي سای هی

یاس ت تویذات تیشتزی دارد.

ایي سای تایذ آى لذر تاشذ تا ضزیةLift Drag .السم را در طل پزاس ایجاد وذ

درج؛ در اپیواای 3تا1ساس ػوهی حذد طر ولی در اپیواای دستایي سای ت

درج 1تا درج در اپیواای جگذ حذد صفز 5تا3حول مل هسافزی حذد

است.

( اتؼاد سای چزخش آى؛Flapع تزآ افشا ) .11

تزآ افشا جشء سطح وتزل ثای تد و ت ػاى اتشار افشایشLift خصص در شست ت

دذ:شد. ایي اتشار چار ػول تز ری تال اجام هی تزخاست، استفاد هی

دذ.ضزیة تزآی تال را افشایش هی

وذ.تز هیتزآی صفز را هفیسای حول

شد.سای اهاذگی تال را واش داد تال سدتز اهاذ هی

دذ.سزػت اهاذگی را واش هی

ای صة تزآ افشا:هحل

(لث حول تالLeading Edge Flap.)

(لث فزار تالTrailing Edge Flap.)

:ااع هختلف تزآ افشا

ن:ه تاى

تزآ "هؼوال( افشا در لسوت داخلی تالInboard شدیه تذ لی شپزا در لسوت خارجی )

گیزذ. ػلت آى واش گشتار تزآ افشای تال افشایش راحتی وتزل )افشایش گشتار تال لزار هی

تاشذ.شپزا( هی

تز تاشذ.زچ هساحت تال تیشتز تاشذ، تایستی تزآ افشا ضؼیف

تز تاشذ.ستی تزآ افشا، لیزچ سى تیشتز تاشذ تای

(؛Aileronشپز ) .11

(شپز در ایجاد گشتار چزخشیRoll.وتزل در سدى دخالت دارد )

تا حزوت هؼىس ری د تال، تیي د تال اختالف تزآ ایجاد وزد تاػث چزخش هی-

گزدد.

2تتزیي هحل آى لث فزار تال تیي3

3تا 4

د است.