Stability and Control characteristics of the Early Mark Spitfires

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The P-39 has less stick travel and a lighter elevator and was still accepted into service.

Because it did have acceptable characteristics overall.

The P39 exhibited neutral stability at its most rearward CG. The stick travel was 1 inch from cruise to CL max at 1.8 pounds per G.

However, the P39 required 12.5 degrees of elevator travel to reach the stall point AND its acceleration changed in proportion to elevator angle appropriately. There were no wild fluctuations in acceleration and the pilot is able to precisely meet and hold a given acceleration.

If you look at the abrupt pull out curves, the P39 met all the requirements of the NACA standard.

It was not divergent, unlike the Spitfire.