טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGal-Rom Yaniv
SubjectAero-Structural Investigation of an Inflated Wing
DepartmentDepartment of Aerospace Engineering
Supervisors Professor Emeritus Mordechay Karpel
Professor Daniella Raveh
Full Thesis textFull thesis text - English Version


Abstract

Inflated aircraft structures have been proposed as early as in the 1930s. During the 20th century inflated aerial structures included blimps, parachutes, and later on parafoils, inflated only by dynamic pressure. Although few designs of load-carrying structural members have been proposed, the technology of high internal pressurization for aircraft structures was not commonly used. In recent years, a new thrust is seen in this field and new designs and applications are emerging for aerial vehicles utilizing inflated cantilever wings, supported by internal pressure. However, no general schemes have emerged for the treatment of inflation pressure as a structural load component of the wing.

Design of an inflated wing structure requires an understanding of the properties and limitations of such a structure. This thesis proposes an analytical model for the static-aeroelastic characteristics of a membrane cantilever wing, supported by high internal pressure. Conditions for membrane wrinkling and membrane mechanical failure are suggested. The conditions are used to define typical envelopes of allowed combinations of internal pressure vs. dynamic pressure or wing loading.

Analytical formulation is presented for the case of a rigid wing-structure composed of an inflated beam with a single-cell box section. Numerical analysis scheme is presented for the case of an elastic cantilever inflated wing with a multi-cell box section. The scheme is scalable in terms of model complexity, enabling either a simple or a more comprehensive analysis of a wing design. The model is capable of evaluating the static aeroelastic load an inflated wing can bear, as a function of its material, geometrical properties, and inflation pressure. It utilizes the Strip Theory for elastic wings, enhanced to account for large deflections.

The numerical example is that of a rectangular planar wing with either a single-cell or a multi-cell box section, aspect ratios of 3 to 10, thickness ratios of 12% to 18%, and membrane thickness of 100 to 400 microns. Results show the existence of an envelope of allowed dynamic pressure vs. inflation pressure, as well as an envelope of allowed wing loading vs. inflation pressure. An investigation of the influence of design parameters on the allowed pressures envelopes is performed and explanations for envelope shapes are suggested. The model developed in this thesis enables a preliminary estimate of an inflated membrane wing’s performance, given the geometry and material, and can provide an important tool for wing preliminary design and configuration selection.