aircraft structures - fuselage

Question 1

What is Fuselage

Answer 1

Main structure of the aircraft that carries the aircraft payload: passengers, frieght, crew, instruments, accessories, controls, equipment

It transfers loads to the wings, tailplanes, landing gears, fin and powerplants

Question 2

Pressurized aircraft - has Axial and Hoop stress

Answer 2

when an aircraft is pressurized, the structure goes through:

Axial Stress: Longitudinal stress that puts tension/elongates the fuselage

Hoop stress: it’s a radial stresses that ‘expands’ the fuselage cross section area

Question 3

Fuselage can be designed / built in a number of cross sections:

Answer 3

In order from less stable to stable:

Rectangular
* Usually for non pressurized ACs
* Cheaper to build
* High weight to strength ratio

Oval:
Less efficient than Circular
Frequently used to complete pressure hull construction in read bulkhead

Double Bubble
* Figure of eight
* Good use of space forpassenger/cargo configuration
* Does not have increased drag
* cost effective

Side by Side bubble
* Even chearper to build
* allows for larger # of passengers/cargo
* further reduced drag
* Engine are rear mounted

Circular
* For pressurized ACs - pressure distributed evenly
* Hoop stresses are spread out
* Can produce high drag
* Some space wasted due to passenger/cargo configuration
* Easy to build
* cheaper tooling

Question 4

Fuselage Construction

Answer 4

For non pressurized aircrafts: TRUSS / FRAMEWORK

For Light Aircraft: Monocoque

For widely used ones: STRESSED SKIN / SEMI MONOCOQUE

Question 5

Framework

Answer 5

light gauge steel tubes welded together to form traingular shapes for rigidness

each tube carries load, its magnitutude depends on whether the aircraft is airborn or on ground

basic, strong, light weight (aluminium) or fabric skin

aerodynamic

Question 6

Monocoque construction

Answer 6

for smaller aircraft/light weight

The outside skin takes the load

Inside is the ‘Formers’ which give the shape

**damage to the ski weaks the structure **, therefore extra strength is required for windowns, doors and undercarriages as these weak the structure.

Question 7

Semi monocoque

Answer 7

handle load much better than monocoque

Additional structures (STRINGERS/STIFFNERS AND LONGERONS) are added lengthwise along the fuselage - joining frames together

the skin is then attached to the frames and stringers by riveting or adhesive bonding

**Skin is stiffened and and load carried length wise **

Note:
Longerons: beems along the length of fuselage, put below the floor which takes the bending loads of the aircraft

Question 8

What’s a FrAME

Answer 8

vertical structures that are open in the centre

take the amjor load of teh aircraft

gives aircraft the shape

Question 9

Bulkheads

Answer 9

like Frames but solid

take some of the main loads

may have access doors

give shape to the AC

Front and back bulkheads which split the pressurized from non pressurized areas

Question 10

Firewalls

Answer 10

separates the flight deck/cabins from the engine

made in titanium alloy or stainless steel

withstand moderate temps for pronlonged period

withstand high temp (ie 3000 degrees) for short period

Question 11

cross beams

Answer 11

beams that add strength to the cargo/passenger floors

Question 12

floor venting

Answer 12

blow out panels

opens authomatically to equalize pressure across the floor structure

help avoid distortion of floor during decompression