A Combined Ashby, AHP, and TOPSIS Framework for Wing Spar Material Selection in Hybrid Electric STOL Aircraft.

Wing spars carry the primary bending, shear, and torsional loads an aircraft experiences during flight and landing. In hybrid electric STOL aircraft under 2000 kg MTOW, added loads from battery systems, electric propulsion, and short unimproved runways make material selection more demanding. Battery packs near the wing also introduce a thermal exposure risk that conventional spar studies rarely consider, since existing designs predate onboard batteries. AHP and TOPSIS are widely used in aerospace material selection, yet few studies combine Ashby screening with these methods for hybrid electric STOL wing spars, and fewer weigh thermal and fire performance alongside structural factors. This study proposes an integrated Ashby, AHP and TOPSIS framework to close that gap.

Ashby charts based on modulus versus density and strength versus density relationships screened candidate materials, narrowing the field to Aluminum 2024 T3, Aluminum 7075 T6, Ti 6Al 4V, Carbon Fiber Reinforced Polymer (CFRP), and 4130 chromoly steel. Each material was evaluated against seven criteria: mechanical performance, density, manufacturability, corrosion resistance, thermal and fire performance, cost, and availability. AHP determined criterion weights, TOPSIS ranked the candidates, and sensitivity analysis tested ranking stability.

All five materials passed screening as viable lightweight candidates. AHP gave the greatest weight to mechanical performance and density, and TOPSIS ranked CFRP and Ti 6Al 4V highest for their strength and stiffness. Aluminum 7075 T6 offered a balance of performance and manufacturability, while Aluminum 2024 T3 and 4130 steel ranked lowest due to higher density. The top ranking stayed stable across most scenarios, though cost and thermal weighting shifted the standing of CFRP and Ti 6Al 4V.

This framework offers a transparent way to select wing spar materials for hybrid electric STOL aircraft, weighing battery thermal risks alongside structural and economic factors.