1. ..........On instructions from Headquarters, Fighter Command, a production Spitfire XII, No. EN.223, was collected from A & A.E.E., on 21st December 1942, for tactical trials.
2........... This aircraft is a standard Spitfire VC airframe modified to take a Griffon III engine in order to produce a high performance low altitude fighter. It differs otherwise from the VC in that the wing tips have been removed to improve manoeuvrability, the bulge over the cannon feed on the mainplane is much smaller, the rudder and trimming tabs are larger, and the engine cowlings and spinner differ considerably. It is fitted with facilities for beam approach and about the first seven, including the aircraft on trial, have the oil tank behind the pilot. This is not acceptable operationally and subsequent aircraft will have the oil tank mounted immediately aft of the fireproof bulkhead. The fuel capacity is retained at 85 gallons, and jettison tanks can be used if required. The first six aircraft, again including EN.223, have dural propellers, the remainder will have wooden ones. The external finish of EN.223 was far better than has been seen on standard production Spitfire Vs and IX's.
3........... The Griffon III engine has two speed manually operated superchargers, giving full throttle heights at about 6,000 feet and 18,000 feet. It is fitted with a standard Claudel Hobsen carburettor and cuts fairly easily under negative acceleration forces. In the early models .45 reduction gear is fitted; later aircraft will have .511 reduction gear which will improve the rate of climb, especially at low altitude. The Coffman method of starting is employed. No automatic radiator shutter is at present fitted.
|Zero to 10,000 feet -||Spitfire XII slower by about 30 seconds.|
|10,000 to 20,000 feet -||Spitfire XII slower by about 45 seconds.|
|..........When compared in the climb below 10,000 feet with the Spitfie V using 16 lb. boost, it was found that there was little to choose between them during a full throttle climb away from take-off.
8........... A steady full throttle climb for the prototype is shown in Appendix 'B', but on the production aircraft with clipped wings the operational ceiling of 1,000 ft/min. is reached at 28,500 feet, and the rate of climb for the earlier aircraft is slightly slower, but when modified as described in paras. 3 and 4, the climb may well equal that of the prototype. The time taken for a section climbing easily to reach 28,500 feet is about 25 minutes.
Cine Camera Gun
17........... The Spitfire XII handles in general better than the previous marks of Spitfire. Its longitudinal stabililty has been improved, but the rudder control is not at present completely satisfactory, as it needs constant re-trimming and is rather heavy.
18........... The aircraft fills the category of a low-altitude fighter extremely well, being capable of speeds of 372 m.p.h. at 5,700 feet, and 397 m.p.h. at 18,000 feet.
19........... The climb is not as good as the rest of the performance in general, being inferior to the Spitfire IX (R.M. 10 SM) and similar to the Spitfire V at 16 lb. boost up to 10,000 feet. The operational ceiling (with clipped wings) is about 28,500 feet. Modifications already in hand should improve the rate of climb, especially at low altitudes.
20........... The aircraft dives well and benefits from having its wing tips clipped.
21........... Manoeuvrability is excellent particularly in its rate of roll.
22........... The sighting view over the nose has been slightly increased to give a total deflection allowance of 120 m.p.h.
23........... The similarity of design to Spitfires V and IX, will make its identification by the enemy difficult.
1. ..........By arrangement with Headquarters, Fighter Command, Spitfire XII, No. EN.222, fitted with a Griffon IV engine, was made available for short trials. The earlier aircraft - EN.223 (Griffon III) - has been used during recent bombing trials and a note is therefore included on its suitability.
2...........The aircraft differed from EN.223 (Griffon III), which was the subject of Report No. 61, in having a lower reduction gear, .511 instead of .45, and a wooden propeller instead of dural. It was otherwise standard. The differences were noticable only in climb performance.
ERRATA.................... A.F.D.U. Report No.61