A newbies impression of the 109 and spit

[JtD]

Stick fixed is just one version of static stability, you're keeping the elevator angle constant over a speed range and check how the aircraft responds. In case of the Spitfire, no trim change occurred, so the plane would keep the same AoA over the entire speed range at the same elevator deflection. That's neutral stability.

The other version NACA was looking at is stick force stability, if you want to call it that, where you are keeping the stick force constant through the speed range and check how the aircraft responds. In case of the Spitfire, stick force increased with the speed, which in turn leads to smaller elevator deflections which means some sort of positive stability.

The Spitfire was dynamically stable.

All for longitudinal stability.