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Ñ êíèãè «The Spitfire Story»
Àâòîð: Alfred Price
Appendix B
TACTICAL TRIAL: SPITFIRE XII EN 223
The account below is taken from the report of the tactical trial of the third production Spitfire XII, EN 223, flown by the Air Fighting Development Unit at Duxford in December 1942.
Description
This aircraft is a standard Spitfire VC airfrarne modified to take a Griffon III engine in order to produce a high perfor¬mance low altitude fighter, it differs otherwise from the VC in that the wing tips have been removed to improve manoeuv¬rability, 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 operationallyand subsequent aircraft will have the oil tank mounted immediately aft of the fireproof bulkhead. The fue! capacity is retained at 85 gallons, and jettisonable tanks can be used if required. The first six aircraft, again including EN 223, have dura! propellers, the remainder will have wooden ones. The external finish of EN 223 was far better than has been seen on standard produc¬tion Spitfire Vs and IXs.
The Griffon III engine has a two speed manually operated supercharger, giving full throttle heights at 6,000 feet and 18,000 feet. It is fitted with a standard Claude Hobson car¬burettor 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 [car¬tridge] method of starting is employed. No automatic radiator shutter is at present fitted.
Tactical General
The aircraft was flown throughout the trials with wings clipped and full armament, ie2 x 20 mm cannon and 4 x .303 in Browning guns. All guns were loaded with full ammunition. IFF was carried and one oxygen bottle. The all-up weight for the triafs was about 7,400 Ibs. With wooden propeller and certain other equipment such as IFF removed, the rate of climb and handling can be further improved. Flying Characteristics
This aircraft has the normal Spitfire fee! 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 consid¬erably improved by fining off the fine pitch slop on the propel¬ler and so enabling full rpm 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 Super-marine for one day, were felt to be far superior to the normal Spitfire IX or VB, being exceptionally good in the lateral con¬trol which is crisperand 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 mph IAS 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.
Performance
The Spitfire XII is capable of highspeed at low altitude and is considerably faster than the Spitfire V. It is faster than the Spitfire IX with the dropped blower peak [Merlin 65, 66] by about 14 mph at sea level, and 8 mph at 10,000 feet; above 20.000 feet it is slower than the Spitfire IX. The figures produced by A & AEE [Armament and Aircraft Experimental Establishment—Boscombe Down] for the prototype XII with special finish including high polish, flush rivetting and wing tips on at a weight of 7,415 Ibs [given at Appendix A] show maximum speeds are 372 mph at 5.700 feet and 397 mph 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.
Climb
The climb at full combat rating is not as good as that of the Spitfire IX with the dropped blower peak. Comparative 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 sec¬onds
10,000 to 20,000 feet—Spitfire XII slower by about 45 seconds
When compared in the climb beiow 10,000 feet with the Spitfire V using +16 pounds boost, it was found there was little to choose between them during a full throttle climb away from take-off.
On the production aircraft with clipped wings the opera¬tional ceiling of 1,000 ft/min is reached at 28,500 feet, and the rate of climb for the earlier aircraft is slightly slower. The time taken for a section climbing easily to reach 28,500 feet is about 25 minutes.
Dive
In comparative 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 nothing to choose between the two air¬craft.
Manoeuvrability
The manoeuvrability of the Spitfire XII is considered to be excellent. It was compared with the Spitfire IX [Merlin 65 or 66], 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-manoeuvre the XII. It was unfortunate that in the trials the Spitfire IX was only an average aircraft on controls and was inferior to both Mk XI Is flown. It is considered that when used below 20,000 feet it will be able to out-pace, out-turn the FW 190 and roll as well. The general manoeuvrability for dogfighting is slightly limited by the fact that the engine cuts under negative accel¬eration forces.
Endurance
Accurate consumption figures are not yet available. One practice operation carried out in company with a VB gave a consumption 5 gallons higher for 1 hr 30 mins. Further con¬sumption tests are being carried out.
Sighting View
Owing to the engine having been set lower than the Merlin in the V or IX, the sighting view over the centre of the cowlings is increased from TOO mph standard to 120 mph [equivalent deflection angle of an aircraft in the gunsight], which gives a total of four degrees downward view.
Low Flying
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 XI I. 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 againstthe alterations in trim, particularly in a right-hand turn when the nose is pulled down.
Night Flying
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 charac¬teristics from other Spitfires once the take-off has been accomplished.
Other Points Cine
Camera Gun
No cine camera gun can be carried in the aircraft at present as the oil pressure filter and air charging valve are in the wing root at the normal place for mounting the G 45 camera. Maintenance
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 scavenge filters and ignition. Oil and cool¬ant consumptions appear normal and the propeller gave no trouble throughout the trial. The priming pump is much larger than usual and starting needs a maximum of 6 dopes in cold weather.
Conclusions
The Spitfire XII handles in general better than the previous marks of Spitfire. Its longitudinal stability has been improved, but the rudder control is not at present completely satisfac¬tory as it needs constant re-trimming and is rather heavy.
The aircraft fills the category of a low-altitude fighter extremely well, being capable of speeds of 372 mph at 5,700 feet, and 397 mph at 18,000 feet.
The climb is not as good as the restof the performance in general, being inferior to that of the Spitfire !X [Merlin 65 or 66] and similar to the Spitfire V at 16 Ib 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.
The aircraft dives well and benefits from having its wing tips clipped.
Manoeuvrability is excellent, particularly the rate of roll.
The sighting view over the nose has been slightly increased to give a total deflection allowance of 120 mph.
The similarity of design to the Spitfires V and IX will make its identification by the enemy difficult.