No. 61


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.


4........... The aircraft was flown throughout the trials with wings clipped and full armament, i.e., 2 x 20 mm. cannon and 4 x .303 Browning guns. All guns were loaded with full ammunition. I.F.F. was carried and one oxygen bottle. The all-up weight for the trials was about 7,400 lbs. With wooden propeller and certain other equipment such as I.F.F. removed, the rate of climb and handling can be further improved.

Flying Characteristics
5........... This aircraft has the normal Spitfire feel about it, but the take-off needs care, as the large amount of torque causes it to swing away to the right, not to the left as usual, and if the pilot is slow in reacting the swing is so strong that he will not be able to correct even with full left rudder. This is being considerably improved by fining off the fine pitch stop on the propeller and so enabling full r.p.m. to be obtained at lower boost values. In the air the handling of both EN.223, and another production Spitfire XII which was made available by Supermarine for one day, were felt to be far superior to the normal Spitfire IX or VB, being exceptionally good in the lateral control which is crisper and lighter due to the clipped wings. The longitudinal stability is much better than that of the Spitfire V, and in the dive it was particularly noticed that when trimmed for cruising flight, it stays in easily at 400 m.p.h. I.A.S., and does not recover fiercely. In turns the stick load is always positive and the control very comfortable. The rudder, however, is most sensitive to changes in engine settings and needs re-trimming for most alterations of flight, as it is too heavy to be held by the feet for long periods. The Spitfire XII has the usual Spitfire stall characteristics. The engine runs noticeably more roughly than a Merlin.

6........... The Spitfire XII is capable of high speed at low altitude and is considerably faster than the Spitfire V. It is faster than the Spitfire IX with the dropped blower peak (R.M.10 SM engine) by about 14 m.p.h. at sea level, and 8 m.p.h. at 10,000 feet; above 20,000 feet it is slower than the Spitfire IX. The figures produced by A & A.E.E. for the prototype XII with the special finish including high polish, flush rivetting and with wing tips on at a weight of 7,415 lbs., are reproduced in Appendix 'A' and contrasted with their fiqures for the Spitfire IX mentioned above and Spitfire VC. The maximum speeds are 372 m.p.h. at 5,700 feet, and 397 m.p.h. at 18,000 feet. Checks were made with EN.223 and the speeds were found to be almost identical with those quoted, the absence of wing tips probably making up for the special finish of the prototype.

7........... The climb at full combat rating is not as good as that of the Spitfire IX with the dropped blower peak. Comparitive zoom climbs were carried out with a Spitfire IX of this type which had the standard wing tips, with the following results:-

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.

9........... In comparitive dives with the Spitfire IX when both aircraft maintained the engine settings they had had in formation, the XII pulled away slightly as being the cleaner design, but at full throttle there was little to choose between the two aircraft.

10........... The manoeuvrability of the Spitifre XII is considered to be excellent. It was compared with the Spitfire IX (R.M. 10 SM engine), also designed as a high performance low-altitude fighter, over which it has an advantage in speed but not in climb, and found to be much better in rate of roll. Above 20,000 feet however, the Spitfire IX with standard wing tips has a better all-round performance and was able to out-manoeurvre the XII. It was unfortunate that in the trials the Spitfire IX was only an average aircraft on controls and was inferior to both of the Mk. XIIs flown. It is considered that when used below 20,000 feet it will be able to out-pace, out-turn and roll as well as the FW.190. The general manoeuvrability for dog-fighting is slightly limited by the fact that the engine cuts under negative acceleration forces.

11........... Accurate consumption figures are not yet available. One practice operation carried out in company with a VB. gave a consumption 5 galls. higher for 1 hr. 30 mins. Further consumption tests are being carried out.

Sighting View
12........... Owing to the engine having been set lower than the Merlin in the V. or IX, the sighting view over the centre of the cowling is increased from 100 mph standard to 120 mph., which gives a total of four degrees downward view.

Low Flying
13........... Owing to the slightly improved forward view and to the benefit obtained when looking sideways over the clipped wing tips, pilots have felt very confident in low flying in the Spitfire XII. The aircraft handles very well in all turns but when throttle alterations are made during turns close to the ground, pilots must be careful to guard against the alterations in trim, particularly in a right-hand turn when the nose is pulled down.

Night Flying
14........... No night flying was carried out as the exhausts fitted to the engine at present are the open type without flame dampers, but it is thought that the aircraft will have no different characteristics from ther Spitfires once the take-off has been accomplished.


Cine Camera Gun
15........... No cine camera gun can be carried in the aircraft at present as the oil pressure filter and air changing valve are in the wing root at the normal place for the G.45 camera.

16........... Throughout the trial the standard of maintenance of aircraft and engine was high, except for one or two accessories which were not peculiar to the aircraft. In particular, the crews commented upon the accessibility of the engine especially for the scavange filters and ignition. Oil and coolant consumptions appear normal and the propeller gave no trouble throughout the trial. The priming pump is much larger than usual and starting needs a maximm or 6 dopes in cold weather.


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.

6th February, 1943

[Appendix A] [Appendix B]

No. 61


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.


3........... The rate of climb of the Spitfire XII with Griffon IV is very much better than with the Griffon III. The improvement amounts to about 600 ft/min which reduces the time to climb to 10,000 feet by about 30 seconds. During comparitive zoom climbs, the Griffon III appeared very slightly the faster in the climb for the first 1,000 feet, but after climbing 3,000-4,000 feet, the Griffon IV was pulling away from the other easily, and through 10,000 feet had as much as 25 seconds in hand on the Griffon III. As a result the climb is about the same as that of the standard Spitfire IX (Merlin 66) up to 4,000 feet, after which it is still noticeably inferior.

4........... No direct comparison could be made of the exact loss of speed with the new reduction gear. It appears to be very slightly slower than with the original gear, but no marked sacrifice in speed has been made to achieve the increase in climb.

5........... The Spitfire XII has been used for part of Trial "Marenth" under instructions from Headquarters, Figter Command. This trial was a bombimg exercise of all forms of attack. A single bomb is carried under the fuselage on a rack fitted to the pick up points of the jettison tank. In comparison with Spitfires V and IX, all pilots found the Spitfire XII to be more suitable, as it has a better view over the nose cowlings, and their results in the main were more accurate, especially in low level bombing when the target can be kept in sight almost to the point of release. During medium glide bombing at 45 degrees approach, the increased view also helped, but the need for correct trimming of the rudder made the aircraft slightly less easy to control accurately in the dive than the other Marks of Spitfire.

ERRATA.................... A.F.D.U. Report No.61
.......Para.6, Lines 2 to 5. DELETE from "It is IX."
.......SUBSTITUTE:- "It is faster than the Spitfire IX (Merlin 66) by about 10 mph at sea level and slower by 9 mph at 10,000 feet. It is slower up to 15,000 feet, where it becomes slightly the faster until 19,000 feet.

5th June, 1943

[WWII Aircraft Performance] [Spitfire Performance Testing] [Spitfire XII Performance]