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STATICS - CASE STUDY

    Introduction


Problem Graphic
 

The wing of a P-38 is designed to withstand a 5g maneuver without damage. In order to design the structure, engineers needed to know the internal loads generated by the aerodynamic lift, and the mass and torque of the engine.

What is known:

  • The total airplane mass mt is 9,050 kg.
  • The engine mass me is 735 kg.
  • The engine torque Te is 3,000 Nm.
  • The distance d from the centerline to the engine is 2.4 m.
  • The span b of one wing is 7.92 m.
  • The dynamic load factor G is 5.
  • The acceleration due to gravity is 9.8 m/s2.
  • The lift distribution is given by:
        L(x) = (mt gG/b)(x/b+1) N/m

 

   

Force Diagram
  Question

 

What are the internal loads in the wing structure of the airplane during a 5g maneuver? Due to symmetry, only one wing needs to be calculated.

   
  Approach

 
  • Develop shear and moment diagrams for the aerodynamic lift, engine mass, and engine torque separately using the relationships between load, shear, and moment.
  • Using the principle of superposition, combine the three diagrams to get the shear and moment diagrams for the complete structure.