Sizing ASTRO-2's fins: flutter, wind and the tip-to-tip layup

The current design

ASTRO-2 uses 4.8 mm G10 fins: root 350 mm, tip 120 mm, span 150 mm and sweep 200 mm. The carbon tip-to-tip layup is a structural element that carries the flutter margin.

Flutter and the layup

The NACA TN-4197 check shows why the bare plate is not the final structural case. The measured layup thickness is rechecked at PDR.

Wind sensitivity

The rail-exit margin is 2.35 cal in still air, about 1.0 cal at 5.7 m/s wind and about 0.5 cal at 12.4 m/s wind.

PDR alternative

A larger fin set, 170 mm span and 6.35 mm plate, is kept as the PDR alternative.