pathology_doc
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My understanding is this:
Spitfire Mk IV (Griffon) = Mark III airframe (which did not see series production) adapted to Single-stage Two-speed Griffon. Single prototype, DP845.
Spitfire Mk XX - DP845 re-labelled to free up the Mark number for PR variants descended from Mk I/II/V lineage.
Spitfire Mk XII - Mark V airframe adapted to basically the same engine as the IV. Production variant.
However, somewhere I vaguely remember - or perhaps misremember - reading something about the Mk XX being intended as a single-stage, two-speed variant of the Mk21, i.e. with the newer wing having the higher aileron-reversal speed. However, the Griffon 60-series was maturing at a sufficient rate that there was felt to be no sense in putting single-stage Griffons into airframes containing the new wing.
IIRC the Mk 23 was supposed to be a Mk 21 with the wing section altered to a non-laminar-flow (non-Spiteful) wing intended to give better high speed/high Mach number performance. IIRC the wing design was test flown but never proceeded with as a production variant, but I cannot find performance data.
Spitfire Mk IV (Griffon) = Mark III airframe (which did not see series production) adapted to Single-stage Two-speed Griffon. Single prototype, DP845.
Spitfire Mk XX - DP845 re-labelled to free up the Mark number for PR variants descended from Mk I/II/V lineage.
Spitfire Mk XII - Mark V airframe adapted to basically the same engine as the IV. Production variant.
However, somewhere I vaguely remember - or perhaps misremember - reading something about the Mk XX being intended as a single-stage, two-speed variant of the Mk21, i.e. with the newer wing having the higher aileron-reversal speed. However, the Griffon 60-series was maturing at a sufficient rate that there was felt to be no sense in putting single-stage Griffons into airframes containing the new wing.
IIRC the Mk 23 was supposed to be a Mk 21 with the wing section altered to a non-laminar-flow (non-Spiteful) wing intended to give better high speed/high Mach number performance. IIRC the wing design was test flown but never proceeded with as a production variant, but I cannot find performance data.
