Chapter A16 Sample Test

INTERNAL PRESSURE
SAMPLE TEST

1. An idealized monocoque fuselage with cylindrical midsection and spherical caps, is to be fabricated from aluminum alloy 2024-T4 (ult. normal strength of 68,000 psi, and ult. shear strength of 41,000 psi). Knowing that a maximum allowable gauge pressure of 14.7 psi is desired and factor of safety of 1.5 in tension and 2 in shear are required, determine the minimum allowable skinthickness.
The inside diameter of the pressurized fuselage is 72 in. The end caps are spherical, and have the same thickness as the cylindrical section.

Answer:

tmin = .0129 in. (minimum allowable skin thickness)

2. Consider the cylindrical section of a semi-monocoque fuselage. The fuselage is pressurized to 15 psi gauge. The 50-in diameter fuselage shell is stiffened by 10 identical stringers. All memebers are made of the same material having ult. normal strength of 40 ksi, and ult. shear strength of 20 ksi with Poisson's ratio of 0.3. Using the factors of safety of 1.2 in tension and 2 in shear and keeping the ratio of total stringer area to skin area at 15%, determine

(a) the minimum allowable thickness for the fuselage skin,
(b) the cross-sectional area of each stringer.

Answers:

(a)tmin = .0188 in
(b)Ast = .044 sq. in.

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