Reg. No. :

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.

Fifth Semester

Aeronautical Engineering

AE 2302 — AIRCRAFT STRUCTURES — II

(Regulation 2008)

Time : Three hours Maximum : 100 marks

Answer ALL questions.

PART A — (10 × 2 = 20 marks)

1. A uniform and homogenous beam subject to its self-weight will always

bend in a symmetrical manner — Is this True or False?

2. Explain why an aircraft wing spar bends in an unsymmetrical manner

during steady level flight.

3. State the criterion used for the lumping of thin webs.

4. Relate shear stress and shear flow in thin-walled beams.

5. Cell twist decreases when a stronger material is used — Is this True or

False?

6. Relate shear flow and cell twist when a thin-walled tube is subject to

torsion.

7. State the formula of Gerard’s method and explain the use of this method.

8. Give two examples of thin-walled columns in an aircraft.

9. Sketch a semi-cantilever aircraft wing and circle the part which acts as a

beam-column.

Question Paper Code : 55117 429 429 429

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10. When is an aircraft fuselage subject to torsion?

PART B — (5 × 16 = 80 marks)

11. (a) Obtain the bending stress at points A and B for the section shown in Fig. 1. The section is subject to a 1600 Nm bending moment in the vertical plane.

Fig. 1

Or

(b) Using the neutral axis method, obtain the bending stress distribution for the section shown in Fig. 1. Determine also the neutral axis orientation.

12. (a) Derive an expression for the shear flow variation in a thin-walled unsymmetrical open section subject to shear. State all the assumptions involved.

Or

(b) The webs of the section shown in Fig. 2 are effective in bending. Section height is ‘h’ while the width of the horizontal webs is ‘b’. All the lumped areas have equal area. Derive an expression for the shear center location of the section. Wall thickness is ‘t’ throughout.

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Fig. 2

13. (a) Obtain the shear flow variation in the walls of the multi-cell tube shown in Fig. 3. The section is subject to a pure torque of 1800 Nm. Wall thickness is 1.7 mm everywhere.

Fig. 3

Or

(b) (i) Derive and obtain an expression for the cell twist when the section given in Fig. 3 is subject to a pure torque T. The shear modulus of the material used is ‘G’ while the wall thickness ‘t’ is the same throughout. (12)

(ii) Why is a thin-walled multi-cell tube subject to pure torque said to be statically indeterminate? (4)

14. (a) The sheet-stringer panel shown in Fig. 4 is loaded in compression. The sheet is assumed to be simply-supported at the loaded ends and along the rivet lines, but free at the sides. Each stringer has an area of 0.7 cm2. E = 70 GPa for the sheet and stringer material while the yield stress is 20 MPa. Determine the total compressive load carried under the following conditions :

(i) when the sheet first buckles

(ii) when the stringer stress is 200 MPa.

How can the ultimate load carrying capability of this sheet-stringer panel be estimated?

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Fig. 4

Or

(b) The cross-section of a thin-walled column of length 1 m is shown in Fig. 5. Material used is aluminium (for which E = 70 GPa). Compare the crippling load for the given column for the following cases: (i) t = 1.8 mm, and (ii) t = 1.6 mm. Consider the column ends as simply supported.

How can the crippling load of a given column be increased without altering its dimensions?

Fig. 5

15. (a) Write notes on the following topics :

(i) Gust loads on an aircraft. (8)

(ii) Features of a V-n diagram. (8)

Or

(b) Refer Fig. 6. The beam shown in the figure is assumed to have a complete tension field web. The cross-sectional area and elastic section modulus of the flanges are 350 mm2 and 750 mm3 respectively. The web thickness is ‘t’ mm. The angle of diagonal tension is 42.6°. Material used for construction is aluminium while web thickness is 1.5 mm. Determine the following quantities :

(i) maximum direct stress in the top flange (6) 429 429 429

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(ii) maximum direct stress in the bottom flange (6)

(iii) compressive load in the vertical stiffeners. (4)

Fig. 6

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