Intrinsically tuned structural panel

• US 3,976,269 A
• Filed: 12/19/1974
• Issued: 08/24/1976
• Est. Priority Date: 12/19/1974
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Gupta, Gautam Sen
• Primary Examiner(s): Steiner, Arthur J.
• Application Number:
  US05/534,518
• Time in Patent Office: 614 Days
• Field of Search: 29/191, 244/119, 244/120, 244/123, 244/124, 244/126, 244/132, 181/33, 52/144, 52/145, 52/629
• US Class Current: 244/119
• CPC Class Codes: B64C 1/12 Construction or attachment of skin panels
• CPC Class Codes: B64C 1/40 Sound or heat insulation , e.g. using insulation blankets
• CPC Class Codes: Y10T 428/12271 having discrete fastener, marginal fastening, taper, or end structure
• CPC Class Codes: Y10T 428/12347 Plural layers discontinuously bonded [e.g., spot-weld, mechanical fastener, etc.]
• CPC Class Codes: Y10T 428/12354 Nonplanar, uniform-thickness material having symmetrical channel shape or reverse fold [e.g., making acute angle, etc.]
• CPC Class Codes: Y10T 428/12375 having member which crosses the plane of another member [e.g., T or X cross section, etc.]
• CPC Class Codes: Y10T 428/12486 Laterally noncoextensive components [e.g., embedded, etc.]

Abstract

A structural panel of the skin-stiffener type, commonly used in aircraft construction, having significantly reduced vibration response, noise radiation and increased acoustic fatigue life, has a skin supported by uniformly spaced stiffeners which are located such that the fundamental natural frequencies of stiffener segments are equal to the fundamental natural frequency of skin sub-panels between the stiffener segments. The physical and geometric properties of the skin and stringers and the spacing of the stringers in various disclosed embodiments depend upon the trace velocity of the excitation field, loading conditions to which the panel is subjected, and end-conditions of the sub-panels and stiffeners.

Claims

1. A structural panel comprising:

a skin of uniform thickness, and;

an orthogonal network of uniformly spaced stiffeners attached to said skin and dividing said skin into a plurality of sub-panels, the fundamental flexural natural frequency of a sub-panel vibrating as a diaphragm being substantially equal to the fundamental natural frquency of an adjoining stiffener vibrating in bending in a plane normal to the skin.

2. A structural panel comprising:

a skin having

a modulus of elasticity E'"'"',

a Poisson'"'"'s ratio ν

,

a mass density p'"'"', and

a thickness t;

a pair of stiffeners attached to said skin and spaced apart a distance b;

a plurality of stiffeners attached to said skin, spaced apart a distance a, each oriented approximately at right angles to each of said pair of stiffeners, and each having

a cross-sectional area A,

a cross-sectional area moment in bending I_b,

a modulus of elasticity E, and

a mass density p;

wherein ##EQU10## and where R is a constant which ranges in value from 1.000 to 2.268.

3. A structural panel having reduced noise radiation characteristics comprising:

a pair of adjacent stiffeners uniformly spaced apart a distance b;

a plurality of stiffeners, each spaced apart a distance a, each attached to and oriented substantially at right angles to each of said pair of adjacent stiffeners, and each having a segment of length b extending between said pair of adjacent stiffeners and having the same fundamental flexural natural frequency F; and

,

a skin of uniform thickness attached to each of said pair of said plurality of stiffeners to form a plurality of sub-panels, each of width a and length b, and each having a fundamental natural frequency F, when vibrating as a diaphragm, substantially equal to the fundamental flexural natural frequency F of the said segments of said plurality of stiffeners.

4. A structural panel having reduced noise radiation characteristics for use on an aircraft fuselage comprising:

two adjacent frames;

a plurality of equally spaced stringers, each attached to said frames and each having segments of equal length extending between said frames and each segment having the same fundamental flexural natural frequency F; and

,

a skin of uniform thickness attached to said frames and said stringer segments to form a plurality of sub-panels, each bounded by said frames and a pair of adjacent stringers, and each having a fundamental natural frequency F when vibrating as a diaphragm substantially equal to the fundamental flexural natural frequency F of the stringer segments.

5. A structural panel having reduced noise radiation characteristics for use in an aircraft fuselage structure having stringers and frames comprising in combination:

two adjacent frames;

a plurality of equally spaced stringer segments, each extending between said attached to said frames, and each having the same fundamental flexural natural frequency F; and

,

a skin of uniform thickness extending over and attached to said frames and stringer segments to form a plurality of sub-panels, each bounded by said frames and two adjacent stringer segments, and each having a fundamental natural frequency F, when vibrating as a diaphragm, substantially equal to the said fundamental natural frequency F of the stringer segments.

6. A structural panel having reduced noise radiation characteristics for use in an aircraft fuselage structure having stringers and frames comprising in combination:

two adjacent frames;

a plurality of equally spaced stringer segments, each extending between and attached to said frames, and each having the same fundamental flexural natural frequency F; and

,

a skin of uniform thickness extending over and attached to said frames and stiffener segments to form a plurality of sub-panels, each bounded by said frames and two adjacent stiffener segments, and each having a fundamental natural frequency F when vibrating as a diaphragm within 20 percent of the fundamental flexural natural frequency F of the stiffener segments.

7. In combination with an aircraft fuselage of the type having a series of annular-shaped frames spaced lengthwise along the fuselage, stringers attached to the frames and running lengthwise along the fuselage and skin panels covering the frames and stringers to form the outer surface of the fuselage, the improvement which comprises:

two adjacent frames;

a plurality of equally spaced stringers, each attached to said frames, each having a segment extending between said frames, and each of said segments having the same fundamental natural frequency F when vibrating in the bending mode;

a skin of uniform thickness attached to each of said frames and stringers to form a plurality of rectangular sub-panels, each having a fundamental natural frequency F, when vibrating as a diaphragm, substantially equal to the fundamental natural frequency F of the stringer segments.