AGK Systems - Aircraft Construction

Question 1

Material Attachment Methods…

Answer 1

Riveting

Welding

Bolting

Pinning

Adhesives

Question 2

Riverting

Answer 2

Used extensively in conventional aluminium alloy structures

Question 3

Bolting

Answer 3

If sections are joined together by Bolts this permits structural parts to be disassembled

Almost invariably the nuts used will have a small drilling through them to allow them to be ‘wire locked’

Question 4

Pinning

Answer 4

Involves straight or tapered fasteners to attach and/or locate one structure to another

Question 5

Welding

Answer 5

Process whereby two or more parts are fused together by means of heat

Question 6

Adhesives

Answer 6

Can be used to join structures

Pressure and heat is applied to the adhesive to ensure completely firm and stable bond

Normally in conjunction with attachment methods such as rivets

Question 7

Bonding

Answer 7

Sections of composites bonded together by fusing the matrix element of two components
~First: requires sections to be tightly mated
~Second: assembly is ‘cured’ in a autoclave(process of combing heat and pressure)

Question 8

Monocoque Structure

Answer 8

E.g. Egg structure

Question 9

Semi Monocoque Structure characteristics

Answer 9

Question 10

Semi Monocoque diagram

Answer 10

Question 11

Machined Structure

Answer 11

Single piece of aluminium forms a skin like stringer structure

No need for rivets and other attachment methods

Saves a lot of weight

Question 12

Airbus Fuselage Construction Method

Answer 12

Fuselage defined by series of alluvium frames

Frames are the covered by 4 shells why form the skin

~Crown
~2 side shells
~Bottom shell
This methods allows skins of different thicknesses to be manufactured

Question 13

Boeing Fuselage Construction Method

Answer 13

Fuselage barel is craeted in once piece on a rotating mandrel

Mandrel contains channels into which the stingers have been laid

During curing process the skin and stingers are bonded together

Once barrel has been cured the frames are then slotted into the structure

The barrels are connected to form the full length of the fuselage

Question 14

Fuselage shape

Answer 14

Fuselage cross section is circular because:

Emirates corners, helps ensure airflow will not superstate at moderate AoA

Much more easily withstand the loads imposed by pressurisation

Question 15

Unpressurised Aircraft

Answer 15

If a/c is unpressurised, fuselage shape can vary more

Some unpressurised a/c incorporate:
Non circular or rectangular cabins

Question 16

What is the Pressure Hull?

Answer 16

The section of fuselage between forward and rear pressure bulkheads

Normally pressurised up to 8-9psi MAX

Question 17

What does the Pressure Hull experience?

Answer 17

Axial Stress - acts along longitudinal axis

Hoop Stress - Acts across fuselage cross section

Both a cyclic stresses

Experienced every time cabin is pressurised

Question 18

How is Axial/Hoop Stress measured?

Answer 18

Pressure Hull has a fatigue life, measured in flight cycles

Question 19

Low mounted wing characteristics

(light a/c)

Answer 19

Easier access to cockpit

Easier to incorporate lightweight retractable landing gear

Good visibility into the turn

Question 20

Light a/c wing construction

Answer 20

Question 21

Wing Spar construction (light a/c)

Answer 21

A. Simple plate, web and extruded beams

B. Fail safe spar in which no crack can propagate across the structure

C. Spar machined from heavy forging

Question 22

Wing Ribs (light a/c)

Stingers (light a/c)

Answer 22

Wing Ribs

Provide aerodynamic shape
Allow the stressed skin to be attacked to the wing structure and transfer the loads into the spar

Stingers

Combine with ribs to share loads and transfer loaf to spars

Question 23

Large a/c wing constrcution

Answer 23

Centre Box

Wing Box

Wing Covers

moveable leading edges

Question 24

Centre Wing Box

Answer 24

Forms part of fuselage

Provides the attachment point for the wing

Question 25

Centre Wing Box location

Answer 25

Question 26

Wing Box

Answer 26

Main structural component of the wing

Also provides mounting points to support various brackets for Hinge points and Actuators

Question 27

Wing Cover

Answer 27

Form the upper and lower aerodynamic surfaces of the wing boxes

Question 28

Winglets

Answer 28

Reduce lift dependant drag

Internal structure of aluminium or composite ribs and mini spars

Assembly fixed to end of wing box

Question 29

Empennage construction

Answer 29

Vertical Stabiliser is attached to fuselage by 3-4 lugs and pins

These are a relatively weak point

Excessive application/deflection of rudder can cause structural catastrophic failure…

Question 30

Engine Pylon

Answer 30

(Fuse Pins)

Strut Braces connected using a special bolt known as a Fuse Pin

These are designed to break at a given load

This potential allows an engine to separate from wing without excess damage to the wing

Question 31

Asymmetric Flight Forces

Answer 31

A flight with on for more engine on one wing not operating

Results in unbalanced thrust forces

Question 32

Thrust Forces

Answer 32

When the engines are mounted on the wing their thrust line tends to cause twisting forces on thew wing structure

A/C wants to pitch up

Question 33

Aileron Forces

Answer 33

On larger a/c the forces created my ailerons can apply unacceptably large twisting moments to the wing

These are locked during high speed flight and roll spiders are used instead

Question 34

What is Flutter?

Answer 34

lack of torsional stiffness in a wing structure can cause flutter

Flutter is an undamped oscillation through the structure due to an aerodynamic balance

Produces a rapid periodic motion (fluttering)

Flutter increases with aerodynamic force

Can lead to rapid structural failure

Question 35

Two design countermeasures to torsional stress and flutter are?

Answer 35

Forward mounted engines to reduce CG/CP

Inboard Ailerons to reduce the Arm/Movement