JNTU
JNTU B.Tech III AEROSPACE VEHICLE STRUCTURES II Previous Question Paper (November/December - 2018 - R13)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
What is a diagonal tension field beam?
Answer
A diagonal tension field beam is a thin-webbed beam designed to carry shear loads primarily through diagonal tension in the web after the web has buckled under shear stress. The flanges and stiffeners remain to carry the resulting compressive loads and maintain the beam's overall geometry.
Distinguish between primary and secondary (local) instability in aircraft structures with examples.
Answer
Primary instability refers to the global buckling of an entire structural member, such as a wing spar or a fuselage longeron, under compressive or bending loads. Secondary (local) instability refers to the buckling of individual components or elements of a section, such as the skin panels between stiffeners or the flanges of a channel section, before the entire member fails.
Define shear centre and indicate its location for some typical beam sections.
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State Bredt-Batho formula for the torsion of closed section beams and list the assumptions involved.
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What do you understand by idealization in structural analysis?
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What are the implications of structural idealization on the analysis of open and closed section beams?
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Explain the reasons for structural constraint stresses in either closed section or open section beams.
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What are the assumptions in Wagner torsion bending theory?
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Distinguish between monocoque and semi-monocoque structures
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What are different structural elements used in aircraft wings?
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Part B
Explain pure bending of thin plates and show that the deformed shape of the plate is spherical and of curvature
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Derive the governing differential equation for combined bending and in-plane loading of a thin rectangular plate.
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Calculate the shear centre for the thin-walled channel section shown in the following figure 1 assuming the thickness t of the walls to be constant.
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Determine the shear flow distribution in the beam section shown in the following figure 2, when it is subjected to a shear load in its vertical plane of symmetry. The thickness of the walls of the section is 2 mm throughout.
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The beam section shown in the following figure 3 has been idealized into an arrangement of direct stress carrying booms and shear stress only carrying panels. If the beam section is subjected to a vertical shear load of 1495 N through its shear centre, booms 1, 4, 5 and 8 each have an area of 200 mm2 and boxes 2, 3, 6 and 7 each have an area of 250 mm2. Determine the shear flow distribution and the position of the shear centre.
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Calculate the shear flow distribution in the channel section shown in the following figure 4 produced by a vertical shear load of 4.8 kN acting through its shear centre. Assume that the walls of the section are only effective in resisting shear stresses while the booms, each of area 300 mm2, carry all the direct stresses.
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Determine the shear flow distribution at the built-in-end of a beam whose cross-section is as shown in the following figure 5. All the walls have the same thickness t and shear modulus G; R=200 mm
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Derive the expression for the total torque of ‘I’ section beam subjected to torsion using diagrams.
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An axially symmetric beam has the thin-walled cross-section shown in the following figure 6. If the thickness t is constant throughout and making the usual assumptions for a thin-walled cross-section, show that the torsion bending constant ΓR calculated about the shear centre S is ΓR =(13/12)d5t.
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What are the various forms of fuselage structures? Explain the procedure for shear and bending moment distribution in a fuselage structure.
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Write short notes on fuselage frames and wing ribs.
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