AIRFRAME REVISION
Four Major Parts of An Airframe: Fuselage, Wings, Tailplane & Undercarriage.
Structural Loads: Squashing, Tearing, Pulling, Twisting & Bending.
Ties: Resist tension (pulling)
Struts: Resist compression (squashing)
Beams: Resist bending
Webs: Resist twisting or tearing
Cantilever Structure: Beam supported at one end
Compare different materials: Strength to Weight Ratio- how much apiece of material will support before breaking
Common airframe material: Aluminium/Magnesium Alloys
Advantages:
Good Strength to Weight Ratio
Lightweight
Available in different forms-bar plate tubes
Give reasonable magnetic screening
Disadvantages: Corrodes-needs protective finish
Fatigues
Steel Alloys
Advantages:
Cheap
High tensile steels have High Strength to Wei9ght Ratio
Resistant to wear
Good at high temperatures
Easily joined
Good Magnetic screening
Disadvantages: Poor strength to Weight Ratio
Heavy
Titanium Alloys
Advantages:
Good Strength to Weight Ratio
Maintain strength at high temperatures/High melting point
Can be Super Plastically Formed and Diffusion Bonded
Resistant to fire
Disadvantages: Expensive
Difficult to work
Poor magnetic screening
Carbon Fibre Re-inforced Plastic (CFRP)
Advantages:
Lightweight
Low resistance to Radar and Radio signals
High strength to weight ratio
Resists fatigue
Disadvantages: Only strong in one direction-therefore design is critical
Poor Lightening strike protection
Poor magnetic screening
Poor Damage tolerance
Harder to repair-bolted repair, cold bonded repair & hot bonded repair
Glass Re-inforced Aluminium Laminate (GLARE)
Advantages:
Resistant to corrosion
Resistant to impact damage
Lighter
Material Removal:
Drilling, turning, boring, grinding, milling, cutting & broaching
Material Forming:
Bending, Pressing, Forging, Extrusion & Casting
Additive Processes:
Used to make one off prototypes
Fused Deposition Modelling – Laminated Object Modelling – Selective Laser Sintering – Steriolitheography –
Computer Aided Design – Computers design objects to specifications
Computer Aided Manufacturing – Computers control the machines that make the objects
Computer Integrated Manufacturing – Computers control the whole manufacturing process- production line
Plastics Technology
Blow Moulding: Extrusion, Injection & stretch – plastic parts formed from thermoplastic materials
Plastics Extrusion: Plastic melted and forced through a die to form a continuous profile
Thermomoulding: Plastic sheet heated and formed to make a shape then trimmed
Fuselage:
Parts – nose, centre rear
Why Pressurise?
Keeps cabin at a height that supports life
Tubular?
To allow easy carriage of passengers and freight
Easily Enlarged: Add Sections to stretch length of fuselage
Construction – Welded Steel Truss, Monocoque
Frames & Bulkheads – Give shape to and supports fuselage
Stringers and Longerons – Longitudinal members that give strength between frames and bulkheads
Stressed Skin – Attached to frames, bulkheads, stringers & longerons to give more strength
Pressure Bulkheads – Extra strong bulkheads at the nose and tail to withstand pressurisation forces
Floors – Mounted on strong longerons attached to frames giving space above for passengers and below for bags or
freight
Windows And Doors – Cut outs for these need to be re-inforced to maintain structural integrity
Keel Beam – Usually a very strong beam on a fighter mounted in the middle of the fuselage to take stresses of
mounting engines and undercarriage
Wings:
Give lift to make aircraft fly
Slow speed needs highlift devices to remain safe – Flaps, Slats
Transport Aircraft – Large wing to lift heavy loads
Fighters – Short thin wings to cope with high speed and manoeuvring loads
G Loads – Increase the felt weight of the aircraft – 4G = 4 x Aircraft Weight
Speed Of Sound – Approaching S of S shock waves form at leading edge and destroy lift, above S of S air smooths out
Swept Back Wing – Overcomes these problems
Aspect Ratio – Span of the wing squared divided by the area of the wing
High Aspect Ratio – Used on slow aircraft like gliders 35 -50
Low Aspect Ratio – Used on fighter aircraft 5 – 10
Swing Wing – Wing moves to best position for speed – Tornado
Delta Wings – Allow higher angles of attack & give space for good size flaps for low speed handling
Braced Monoplanes – Struts placed between the wings and undercarriage to take some of the load from the wings
Cantilever Monoplanes – Stronger wing to take full load of aircraft
Wing Functions – Carry fuel, Carry weapons, Mount Undercarriage & house Engines
Methods Of Construction
Parts – Spars (Rear, Front & False) , Stringers, Frames, Stressed Skin, Leading edge, Trailing Edge
Fabric Covered – All strength in framework of wing and fabric gives shape to give lift
Stressed Skin – Takes some of the load and allows space inside the wing to be used for fuel
Leading & Trailing Edges – Used to facilitate electrical cables, hydraulic pipes and controls, flying control cables,
bleed air pipes, fuel pipes
Wing Spars – Dual Spar wing (front & rear) used on larger & fatter wings – Multi Spar Wings used on fighters to allow
thin wings for high speed and also give high strength
Torsion Box – Wing structure bounded by the front spar, rear spar and ribs
Machined Skin – Top and bottom wing surface machined from one billet of material
False Spar – Additional Spar behind rear spar to mount undercarriage
Tailplane
Similar construction to wings
Fin size is dependant on engine asymmetric forces – can either be single or multiple fins
Foreplanes – used instead of elevators
Hydraulics
Pascal’s Law - a change in the pressure of an enclosed incompressible fluid is conveyed undiminished to every part of
the fluid and to the surfaces of its container."
Advantages:
Lightweight
Can develop unlimited force
Reliable
Easy to maintain
Smooth and responsive to inputs
Operate – Undercarriage, Flying Controls, Flaps, Slats, Spoilers, Doors & Shock Absorbsion
Consists Of – Fluid, Resevoir, Pump, Pipes, Valves & Actuators
Pumps
Gear
Low output
Vane
Low output
Piston High output and pressure
Radial Pistons driven from central shaft with pistons radiating outwards - uncommon
Axial
Pistons parallel to drive shaft and driven by swash plate – normal
Pneumatic Systems
Similar to hydraulic but less effective
Consists Of: Storage cylinders, pressure gauges, pressure valves, pipes, actuators & selector valves
Undercarriage
Uses: Absorbs shock Of landing, absorbs side loads, supports aircraft on ground, absorbs braking forces,allows
taxying
Tail Sitter – 2 legs on wings an one small at tail – poor visibility on T/O & Landing, hard to steer
Tricycle – One nose leg and 2 wing legs and on large aircraft fuselage legs – easy to taxy, good visibility, floor level on
ground
Oleo Leg – Absorbs shock of landing – Oil compression (Unusual) – Oleo pneumatic (normal)
Steering – Nose wheel rotates to give directional control
Wheel Units – Single, Double, Tandem, Bogie – more wheels spread the load
Retraction – Mounted on wing by rear or false spar and sings up into fuselage – Uplock, Downlock, Retraction Jack,
Oleo Leg, Axle, Wheels
Falures – Blowdown – Once only use of air bottles to drop the gear
Free Fall – Mechanical levers release the locks to allow the weight to drop the gear
Locks – Up & Down Locks part of system, Ground locks fitted after engine shutdown to stop inadvertent raise
Brakes – Drum – Inefficient and poor heat dissipation – Rarely used
Disc – Efficient , good heat dissipation – Normal
Other Braking Methods – Air Brakes – uses airflow to slow down
Reverse Thrust – Prop – negative blade angle to push air forwards
Jet – Diverts exhaust forward to give braking
Flying Controls
Ailerons, Elevators & Rudder
Control Column – Operates Ailerons and Elevators
Rudder Bar – Operates Rudder
Forces – May be too large for pilot therefore powered flying controls needed – Hydraulic
Manual – Pilot operates the controls directly
Power Assisted – Hydraulics aids the pilot but can revert to manual
Powered - Hydraulics operated and no manual revertion
Fly By Wire – Some aircraft have controls purely operated by computers – reduces weight – no cables
Failures – Powered units with no manual reversion overcome a failure by having the flying control in various sections
so a single failure will still allow flight
Elevons – Usually on delta wing – canoperate together or individually to combine the ailerons and elevators
Canards – Mounted at the front of the fuselage to replace the elevators
All Flying Tailplane or Stabiator – Whole tailplane becomes elevators to overcome huge forces of high G turns
Tailerons - similar to elevons, but in this case the two halves of the tailplane are moved independently to do the job
of the ailerons and together to act as elevators.
Autopilot
Needed – Long flights tiring, lets pilot do other tasks, allows complicated routes to be flown easily, smoother ride
Types – Gyro Stabilised – Mechanical system that takes some of the load from the pilot when airborne only
Computer – Takes more of the load and can fly the aircraft throughout flight including T/O & Landing
Operation – Senses disturbance from present profile and feeds corrections proportional to disturbance to bring the
aircraft back to original profile – uses rate gyros to detect and servo motors on the flying controls to correct