Spitfire III - questions

[Graham Boak]

The prefix LF applies to the engine fit, not to the clipped wings. The dimensions quoted are those in STH. They are contradictory, as 3.5 feet off each tip would give a span just under 31ft. Perhaps it should say 30 ft 8in? This is close to Wojtek's 30ft 6in. 30ft 6in is also quoted in the Harleyford Spitfire book, and in Price's Spitfire Story. Given that the Spitfire was built in Imperial units, conversion to metric simply introduces an additional source of error. Perhaps the answer is to draw out the wings and determine which span gives the correct wing area, which appears to be consistently 220 sq ft.

STH does not specifically say what engine was installed for the first flight, but does say that it was delayed because supply of a new DH propellor was delayed. A new propellor suggests a new engine. The reweighing was with a Rotol propellor, which may (or may not) have been sufficent reason. However, the Merlin X is not a standard Spitfire engine anyway. The text here is again contradictory. It talks of the desired engine being the RS 2M (P.127) Merlin XX. P.132 describes the RS 2M as the X, and the RS 3M as the XX.

Perhaps we need a definition of just what a Merlin X was before attempting to judge which of the contradictory statements is an error. The Merlin X was the 2-geared engine in the Halifax Mk.1, rated at only 1130hp for take-off compared with 1175 for the Merlin XII in the Spitfire Mk.II. If so, the performance of any interim Mk.III could only be disappointing, and it is not clear how the figures quoted on P.132 can apply to the aircraft fitted with a Merlin X. Or barely to the Mk.III at all.

A delay for production engines may not imply a delay in delivery of a prototype, but it is an interesting idea.