Equivalent Axial Load (EAL) Computation for D-shaped Aerospace Vehicle Structures Subjected to Axial Force and Bi-axial Moments

Deepak B.P.; Prashanthan A.; Raju B.S.

CALL FOR PAPERS : Feb-2026

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25-Feb-26

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Equivalent Axial Load (EAL) Computation for D-shaped Aerospace Vehicle Structures Subjected to Axial Force and Bi-axial Moments

Author(s):

Deepak B.P. , Vikram Sarabhai Space Centre, ISRO; Prashanthan A., VSSC, ISRO; Raju B.S., VSSC, ISRO

Keywords:

D-section, EAL, eccentricity, moment ratio, stress

Abstract:

Reusable Launch Vehicle (RLV) structures have non-axisymmetric cross sections and the fuselage is generally D-shaped to dissipate the heat generated due to aero-thermodynamic effects during re-entry. Equivalent axial Load (EAL) computation procedure for D-shaped sections is not available in literature. In this paper, a procedure developed for computation of EAL for D-shaped aerospace vehicle structures subjected to axial force and biaxial moments is described. The theoretical derivation of EAL, the computation procedure and parameters which control the EAL for D-sections are discussed. Interaction diagrams are developed for quick computation of EAL and compared with that of circular sections. The maximum stress occurrence point in a D-section is found out for different bi-axial moment combinations. Verification of the EAL computation procedure using finite element analysis method is also carried out. The concept may be useful for reducing the complexities in the fuselage design process, testing schemes, arriving at flight clearance strategies for Day of Launch (DOL) winds and for flight data analysis.