CS-9 → CS-9 D — the arrangement that works

No airflow in this figure — just the aircraft and the two pins that decide whether it flies. Flip between A, the aircraft as designed, and D, the buildable canard-less low-wing arrangement: the canard leaves (its 10 kg carved with it), the wing drops 412 mm with its nacelles riding it, the crew rise onto the pack — and the grey centre-of-gravity pin and the blue neutral-point pin trade places. That trade is the whole story: in A the neutral point sits 11 mm ahead of the CG (−1.2% — the margin is not there); in D it stands 122 mm behind it (+13.2% — a stable aircraft). Pin stations are the measured values, drawn to true scale.

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CG neutral point runway — prop disk

The two configurations, measured

Neutral point
Solo-pilot CG
NP − CG
Flare reserve, flaps full, α12
Prop disk above runway
Rotation to prop strike

Static margin

Where the pins actually stand

The lever the planar model gets wrong in sign: the first-order estimate said the wing drop moves the neutral point 9 mm forward. Measured, it moved aft — and re-attaching the nacelles to the dropped wing added +43 mm more the floating study article missed. Two vertical-geometry surprises in two days; the planar family cannot even sign a vertical move.
configuration