AGK Systems - Aircraft Construction Flashcards
Material Attachment Methods…
Riveting
Welding
Bolting
Pinning
Adhesives
Riverting
Used extensively in conventional aluminium alloy structures
Bolting
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’
Pinning
Involves straight or tapered fasteners to attach and/or locate one structure to another
Welding
Process whereby two or more parts are fused together by means of heat
Adhesives
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
Bonding
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)
Monocoque Structure
E.g. Egg structure
Semi Monocoque Structure characteristics
Semi Monocoque diagram
Machined Structure
Single piece of aluminium forms a skin like stringer structure
No need for rivets and other attachment methods
Saves a lot of weight
Airbus Fuselage Construction Method
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
Boeing Fuselage Construction Method
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
Fuselage shape
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
Unpressurised Aircraft
If a/c is unpressurised, fuselage shape can vary more
Some unpressurised a/c incorporate:
Non circular or rectangular cabins
What is the Pressure Hull?
The section of fuselage between forward and rear pressure bulkheads
Normally pressurised up to 8-9psi MAX
What does the Pressure Hull experience?
Axial Stress - acts along longitudinal axis
Hoop Stress - Acts across fuselage cross section
Both a cyclic stresses
Experienced every time cabin is pressurised
How is Axial/Hoop Stress measured?
Pressure Hull has a fatigue life, measured in flight cycles
Low mounted wing characteristics
(light a/c)
Easier access to cockpit
Easier to incorporate lightweight retractable landing gear
Good visibility into the turn
Light a/c wing construction
Wing Spar construction (light a/c)
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
Wing Ribs (light a/c)
Stingers (light a/c)
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
Large a/c wing constrcution
Centre Box
Wing Box
Wing Covers
moveable leading edges
Centre Wing Box
Forms part of fuselage
Provides the attachment point for the wing
Centre Wing Box location
Wing Box
Main structural component of the wing
Also provides mounting points to support various brackets for Hinge points and Actuators
Wing Cover
Form the upper and lower aerodynamic surfaces of the wing boxes
Winglets
Reduce lift dependant drag
Internal structure of aluminium or composite ribs and mini spars
Assembly fixed to end of wing box
Empennage construction
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…
Engine Pylon
(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
Asymmetric Flight Forces
A flight with on for more engine on one wing not operating
Results in unbalanced thrust forces
Thrust Forces
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
Aileron Forces
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
What is Flutter?
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
Two design countermeasures to torsional stress and flutter are?
Forward mounted engines to reduce CG/CP
Inboard Ailerons to reduce the Arm/Movement
