airframes chapter 4 fuselage notes

8/13/2019 Airframes Chapter 4 Fuselage Notes

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lift from the wings, transmitted through the centre of the fuselage to carr" theother parts of the airframe.

1. From loo)ing around at the aircraft on displa" at airshows, it is obvious thataircraft fuselage design varies.

1#. Combat aircraft fuselages have man" comple/ shapes and si?es due to thespecial tas)s that the" have to accomplish, whilst transport aircraft on the wholehave a fairl" standard tubular fuselage design.

14. The reason for this is fairl" straightforward, as the tubular section is aconvenient shape for carr"ing bul) cargo or passengers and ma)es it possible tostretch fuselage designs to accommodate more cargo and* or passengers.$tretching is achieved b" inserting e/tra sections, pieces or plugs withoutresulting to a major redesign..

The result is mainl" c"lindrical designs with tapered nose and tail sections. 9ne/ample of the stretch concept is the 9irbus 9# famil". The 9#1: is ashortened version of the 9# -so it has had sections removed, whilst the 9#1has had sections added to ma)e it longer.

@ariations in Crosssection


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ethods of Construction

15. 9 similar method of construction to that used in the wings can be used forfuselages and tail units -or foreplanes

(n general, there are two methods of fuselage construction;

elded $teel Truss

onoco0ue


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hold the stringers in place and all these structural elements join together toprovide a rigid fuselage framewor).

The stressed s)in is then attached to the longerons( bul'%eads and the otherstructural members, such as the $rames, which protrude into the fuselage interior

b" about 1 13 mm, leaving the rest of the fuselage clear for pa"load.

Dltimatel", it is the stressed s)in that carries part of the structural load of theairframe. 9lthough, the designer will tr" to find the best compromise of s)instrength -and weight and frame and stringer strength, it should be noted that thes)in thic)ness will var" with the load being carried and the stresses sustained atan" given location as a result. 9 general design rule is that the s)in will end upta)ing appro/imatel" half of the loads.

9dvantages of Dsing $emionoco0ue Construction

. There are a number of advantages to utilising a semimonoco0ue fuselage in

an airframe design.

#. (t leaves a large proportion of the inside free to accommodate crew,passengers and cargo as the loads that would have normall" been carried b" aWelded Steel Trussin previous designs are carried largel" b" the stressed s)in.

4. The !ul)head, Frames, $tringers and Longerons aid in producing astreamlined fuselage and add to the strength and rigidit" of the structure.

3. 9s a semimonoco0ue design relies on a number of structural members forstrength and rigidit", the fuselage can withstand a reasonable amount of

damage.

5. Loads from pressurisation can be up to 35 )ilogrammes force per s0uaremetre -that is a force e0ual to the weight of si/ cars for ever" s0uare metre offuselage s)in. This is easier to contain in semimonoco0ue construction.

%ressure !ul)heads

7. $o we have established that using a circular or oval cross section allows thefuselage to be pressurised, but how do we ensure that the ends of the tube aresealedE The answer lies in the shell of an egg

6. The nose and tail of the fuselage uses double curvature bul)heads, li)e thesurface of an egg, to ma)e the s)in even stiffer. %ressure bul)heads are fitted inthe nose and close to the tail of most aircraft. The" are flat discs, li)e a drums)in, or curved, li)e a brea)fast bowl -see figure below. Their job is to withstandthe loads imposed b" pressurisation of the fuselage.

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Cabin Floor

:. Dnli)e a combat aircraft, in a civil airliner, the cabin will re0uire a floor. Thisconsists of beams across the inside of the fuselage and covered in sheet allo" orcomposite panels.

#. This ensures a flat surface for wal)ing on and fitting seat and it also allows

the designer to compartmentalise -or divide up the fuselage

This leaves space for luggage and the man" aircraft s"stems in the lowerfuselage space.

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2owever, most modern commercial aircraft have outward opening cabin doors,

so as to ma/imise the amount of internal space available. 9n e/ample of amodern cabin door is given below.

#3. 9irframes must also include other access doors for maintenance and allowstowage of those components not re0uired for flight, such as the undercarriage.(n particular the cargo compartment needs a door, and some aircraft designed fortransporting cargo have larger doors. Li)e cabin doors, these still need to resist

the cabin pressure and maintain the strength of the fuselage, but are often asimpler hinge arrangement with a robust loc)ing mechanism.

Combat 9ircraft Fuselage


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usuall" smaller, containing just the coc)pit and perhaps an electronics ba", andpressures are much lower, because the pilot also uses an o/"gen mas).

9dditionall", the fuselage will probabl" have a strong beam, called the A'eelbeam+, which runs fore and aft, and man" of the major parts, li)e the engines,

cannon and undercarriage are mounted to it.

Conclusions

#7. Far from the fuselage being a simple structural component of the airframe, itis itself a comple/ assembl". The fuselage has to be able to cope with not onl"those loads e/erted on it during flight, but it also must cope with beingpressurised.

#6. (t also needs to be spacious, in order to accommodate passengers andcargo, but "et structurall" strong and rigid to withstand the loads.

#:. Gou should now have an understanding of both the function of the fuselage,the methods of construction and the specific considerations that need to beaddressed during its design.

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airframes chapter 4 fuselage notes

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