本論文研究之目的為開發一款具有折收柔性之無人飛行器機翼主樑。此機翼主樑在飛行器飛行過程中必須提供足夠的剛性，以承受氣動力負載；於飛行前置作業過程中，該主樑則具有類似機構的功能，可使機翼沿預設軌跡進行折收動作。以上所提及主樑的兩狀態分別稱為：展開飛行狀態與折收狀態。
此款機翼主樑發想於高海拔長滯空無人飛行器之需求。由於高空飛行環境與較低飛行速度，此類型的無人機通常使用高展弦比機翼。因為細長結構加上輕量化的嚴苛要求，可折收的機翼主樑必須避免傳統機構的設計，免於額外的重量。為求示範具有折收柔性機翼主樑之概念的可行性，本研究選擇SC&I Lab所研發一款無人飛行器-Hawk作為一設計案例。在Hawk的任務需求中，對機翼主樑最具挑戰的要求為將翼展2公尺的Hawk收納至直徑40公分、長100公分的圓柱型酬載艙。
為使機翼主樑的設計滿足兩者看似衝突的狀態，本研究選用具有超彈性特性的形狀記憶合金之複連通 (multiply connected) 薄殼作為主要結構部件。此部件以同心方式與折收時可免於塑性變形的高分子圓管組合，可使主樑保有圓柱外型的連續性以維持結構在展開狀態下的穩定性。根據力學觀念，以翼樑帽抗彎曲力矩、螺旋線抗扭矩與抗剪力；此兩者結合所形成複連通面，狀似曲面上的桁架。這樣的結構可以承受飛行負載，同時可避免主樑在折收時產生永久塑性應變。形狀記憶合金結構的外型係以Abaqus有限分析軟體輔助設計。此設計過程為一迭代程序；由不同的設計構形分析所獲得的經驗進行演進改良。在演進過程中發現：1) 為降低應變值，折收處應避免幾何性的高拘束，。2) 頂樑與底樑的寬度足夠時，兩側面的桁架近似平面結構，因此可被簡化以更利於折收，而仍具抗剪力之剛性。
本研究所開發具有折收柔性之機翼主樑展現出應用於特殊無人飛行器之潛力。其在展開飛行狀態時，可提供剛性承受氣動力負載，另一方面，在折收狀態時可利用結構柔性變形的特性達到機翼折收的目的。

High-Altitude Long-Endurance (HALE) vehicles, which usually have high aspect-ratio wings, have the potential to evolve into cost-effective communication and reconnaissance platforms. The SC&I Lab proposed a concept of aircraft with foldable wings in order to overcome challenges in designing with high aspect-ratio wings.
The objective of this study is to develop a structural concept for wing spars with folding compliance and demonstrate its feasibility. For the demonstration, the spar of an unmanned aerial vehicle (Hawk) proposed by the SC&I Lab, which could be pre-stowed in a cylindrical payload container, was designed to exemplify the concept.
The spar is expected to withstand flight loads, while permanent plastic deformation should be prevented during folding. To enable the spar to have the two seemingly conflicting states, the spar is constructed by sandwiching a multiply connected Shape Memory Alloy (SMA) shell structure with two concentric thin polymeric tubes. An iterative design process using the Abaqus nonlinear finite element code was performed to determine the geometry of the SMA shell. The spar was designed to meet foldability, strength, and stiffness requirements for the folding state (defined by the dimensions of the container) and extending states (defined by a 3-G maneuver loading). Among the various requirements, foldability represents the most demanding one.
The accomplishment of the example suggests the potential of lightweight foldable wing spars for enabling UAVs to carry out special missions that are virtually impossible without a compliant structural design.

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