STABILITY ANALYSIS AND CONTROL-SURFACE OPTIMIZATION OF A DELTA-WING FIXED-WING UAV

Delta-wing flying wings are attractive for small UAVs because they are structurally simple and carry no tail, but the same absence of a tail leaves a single pair of elevons responsible for trim, pitch control and roll control, and it ties static stability to the wing planform. This paper studies how far that single control pair can be sized down before the airframe loses either its stability or its controllability. We build a compact, reproducible model of a 4.5 kg, 1.6 m span delta UAV with a 55° leading-edge sweep: a Helmbold lift slope combined with the Polhamus leading-edge-suction analogy for vortex lift, strip-theory elevon effectiveness, a four-state longitudinal model and a four-state lateral–directional model. Static margin, short-period and phugoid behavior are examined as the centre of gravity moves, and the elevon layout (chord fraction, inboard and outboard station) is then optimized with differential evolution against approach-trim, roll-rate, pitch-authority and hinge-moment requirements. For a 4 % MAC static margin the optimized layout needs 0.083 m² of elevon area, 41 % less than an initial full-span layout, and lowers the hinge moment by 49 %. The study also shows that approach-trim authority, not short-period behavior, caps the usable static margin at roughly 5 % MAC for a section pitching moment of +0.03, and that this ceiling moves by about one percentage point for every 0.01 of reflex. All aerodynamic inputs are engineering estimates; the results are a design-level trade study and not a substitute for wind-tunnel or flight data.