Aeronautical structures & forces 640


stringer – this is a tie that surrounds the airplane. it takes tensile stresses or forces given by the fuselage structure by pressurization.The formers too resist this stresses. the two are shown below :-

landing gear – has oleo pneumatic struts that resist compressive stresses when landing.

Adhesive bonding processes – this resist shear stresses.

bending, torsion & buckling has all three forces shear, compressive and tensile stresses.

    Lift          =   G

weight

2.5 G = public transport aircraft

3.4 – 3.8 G = utility aircraft

6 G = aerobatic aircraft

loads acting on a plane

Ground loads – include all loads encountered by the aircraft during movement or transportation on the ground such as taxiing, landing, or towing.

Air loads – comprise loads imposed on the structure during flight operations.

loads may be further divided into forces :-

  1. surface forces –  this are forces which act upon the surface of the structure e.g aerodynamic forces and hydro-static pressure forces.
  2. body forces – which act over the volume of the structure and are produced by gravitational and inertial effects e.g force due to gravity.

more loads : –

  1. fuselage loads
  2. wing & tail loads
  3. landing gear loads
  4. Engine thrust loads

all these loads are caused by compressive stress, tensile stress or shear stress.

materials used in aircraft structure

The plane is constructed mostly of aluminum and its alloys. Steel and titanium is used for the major structural components.

Dularumin – its a aluminium and copper based alloy. it has good fatigue resistance, good thermal and electrical conductivity but is difficult to weld.

Steel – this is used for undercarriage units because it is structurally sound.

Titanium – used where fire protection is required i.e engine fire walls.

Magnesium alloy – used where strength to weight ratio is good i.e in gearbox composite material made up of layers of fibre, moulded with hot resin.

Epoxy –its made of moulded kevlar, fibre, carbon, glass.

C.F.R.P – carbon fibre reinforced plastic .The two are used in different parts of an aircraft.

Properties of structural materials

  1. Ductility – ability to deform under tensile stress,
    withstanding large strains before fracture occurs
  2. Strength – The strength of a material is its ability to withstand an applied stress without failure
  3. Toughness – is the ability of a material to absorb energy and plastically deform without fracturing.
  4. Brittleness – material exhibits little deformation before fracture
  5. Elasticity – A material is said to be elastic if deformations disappear completely on removal of the load.
  6. Stiffness – Stiffness is the resistance of an elastic body to deformation by an applied force.
  7. Plasticity – A material is perfectly plastic if no strain disappears after the removal of load.
  8. Fatigue – Mechanical fatigue occurs due to the application of a very large number of relatively small cyclic forces
  9. Corrosion – is the gradual destruction of materials i.e usually metals by chemical reaction with its environment

 

 


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