4 seconds per rotation = ~175'/sec.
175 feet/sec. = ~10,500'/minute = ~ 115 mph.
115 mph with an axis w/o horizontal velocity.
With horizontal velocity, add for lead, subtract for lag.
The wing tip or tail could have a velocity through air approaching 200mph.
The airborne Fin detachment argument for sideways tail velocity in a spin is misbegotten and cannot be sustained.
WHY?
The spinning (or flat spinning] aircraft is in a downward helical flight-path, so everything is
relative to that spiral flight-path. The actual sideways velocity relative to the air in that flight-path would be minimal.
The only time that "relative to the world at large" sideways yawing motion would become pertinent to fin detachment would be upon entering the new medium (i.e. the sea).
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