Spitfires

The Vickers Supermarine Spitfire

Designer : R J Mitchell

Type : Single Seat Fighter
Description : Low Wing Monoplane

Wingspan : 36 feet 10 inches ( 11.23m )
Length : 29 feet 11 inches ( 9.12m )
Height (max): 11 feet 5 inches ( 3.48m )
Wing Area : 242 sq feet ( 22.48m2

Weight empty : 4332 lb ( 1965 kg )
Weight loaded : 5750 ( 2609 kg )

Power Plant : Rolls Royce Merlin II V12 liquid cooled
piston engine
B.H.P. :1030 hp

Armament : 8 fixed wing mounted 0.303 Browning
Machine guns

Performance
Maximum speed : 362 mph

Initial Climb rate : 2,300 ft per min ( 700 m per min )
Ceiling : 31,900 ft
Range : 395 miles

First Flight : 5 March 1936
Service Entry : 4th of August 1938

Deliveries of production Spitfire I’s began in June 1938, two years after the first production contract had been placed . In those two years Supermarine laid out their Woolston factory for large-scale production and organized one of the largest subcontract schemes ever envisaged in Britain. Until that time, as it was becoming increasingly obvious that there was no limit to the likely demand for the Spitfire. It was also obvious that one factory alone was not going to be able to meet the demand even with sub-contracting. Large scale plans were laid during 1937 for the construction by the Nuffield Group of a large new shadow factory at Castle Bromwich near Birmingham for Spitfire production. On April 12,1938 a contract was placed for 1,000 Spitfires to be built at this new factory, of which the actual construction had not then even begun. In the following year, on April 29 further contracts were placed with Supermarine for 200 Spitfires and on August 9 for 450. When Britain went to war on September 3,1939 a total of 2,160 Spitfires were already on order.

Supermarine Spitfire Mk I P9554 SH-K flown by Pilot Officer James Joseph ‘Orange’ O’Meara, No. 64 Squadron, Kenley, August 1940 during the Battle of Britain

Structurally the Spitfire was a straightforward design with a light alloy monocoque fuselage and a single spar wing with stressed skin covering and fabric covered control surfaces. The Spitfire was adapted from Reginald Mitchell’s aesthetically pleasing 1925 F.7/30 design. To preserve the clean nose cowling lines originally conceived by Mitchell, the radiator was located beneath the starboard wing with the smaller oil cooler causing some asymmetry beneath the port wing, and the carburettor air intake under the centre fuselage. A De Havilland wooden fixed pitch propeller was employed by the prototype and the first Spitfire I’s had the Airscrew Company’s wooden fixed pitch. Later a De Havilland three blade, two position propeller was adopted after trials on the first prototype. The new propeller gave a 5 mph increase in speed. In 1940 De Havilland three blade constant speed propeller were substituted. Production Spitfires had a fixed tail wheel and triple ejector exhaust manifolds. The X80 HP Rolls Royce Merlin II and later the Merlin III engine was installed.

The Spitfire I weighed 5,280 lb. had a wing loading of 24 lb.’s. ft. and a fuel capacity of 85 Imperial gallons. Its maximum speed was 362 mph its maximum diving speed was 450 mph its initial climb rate was 2,500 ft./min. and it took 9.4 minutes to climb to 20,000 feet. Its combat range was 395 miles and its roll rate was 140 deg./sec. Standard armament in what was subsequently to become known as the A wing was eight 0.303-in Browning machine-guns with 300 rounds of ammunition. The speed of the Spitfire I was marginally higher than that of its principal opponent the Luftwaffe’s Messerschmitt Bf 109E and it was infinitely more manoeuvrable than the German fighter although the Bf 109E could out climb and out dive the British fighter and its sheltering cannon had a longer range than the Spitfire’s machine-guns. The 1,175 h.p. Merlin XII was adopted as the standard power plant in the Type 329 Spitfire II with a Rotol three blade propeller and 73 lb. of amour protection but this variant was otherwise similar to the Spitfire I. Deliveries commenced in 1940 the Spitfire II having followed the Mark I on the production lines and becoming the first major production variant to be delivered from Castle Bromwich.

Mk II (Type 329)

In the summer of 1939 an early Mk I K9788 was fitted with a new version of the Merlin, the XII. With the success of the trial it was decided to use this version of the Merlin in the Mk II which, it was decided, would be the first version to be produced exclusively by the huge new Lord Nuffield shadow factory at Castle Bromwich.


Supermarine Spitfire IIA, P8084 S-SH, flown by Flt Lt James Joseph ‘Orange’ O’Meara, No. 64 Squadron, May – September 1941,
Victory: 11+2 – 4 – 11+1

Chief among the changes was the upgraded 1,175 horsepower (876 kW) Merlin XII engine. This engine included a Coffman engine starter, instead of the electric system of earlier and some later versions of the Merlin, and it required a small “teardrop” blister on the forward starboard cowling.[68] The Merlin XII was cooled by a 70% to 30% water glycol mix, rather than pure glycol used for earlier Merlin versions.

In early 1940 Spitfire Is of 54 and 66 Squadrons were fitted with Rotol manufactured wide-bladed propellers of 10 ft 9 in (3.27 m) diameter, which were recognisable by a bigger, more rounded spinner: the decision was made that the new propeller would also be used exclusively by the Mk II. This engine/propeller combination increased top speed over the late Mk I by about 6–7 mph below 17,000 feet (5,200 m), and improved climb rate. Due to all of the weight increases maximum speed performance was still lower than that of early Mk Is, but combat capability was far better. The Mk II was produced in IIA eight-gun and IIB cannon armed versions. Deliveries were very rapid, and they quickly replaced all remaining Mk Is in service, which were then sent to Operational Training Units. The RAF had re-equipped with the new version by April 1941. The Rotol propeller units were later supplemented by de Havilland constant-speed units similar to those fitted to Mk Is.

A small number of Mk IIs were converted to “Long Range” Spitfires in early 1941. These could be recognised by the fixed 40 gal (182 l) fuel tank which was fitted under the port wing. With a full tank manoeuvrability was reduced, maximum speed was 26 mph (42 km/h) lower and the climb rate and service ceiling were also reduced. Several squadrons used this version to provide long-range bomber escort. Once the Mk II was taken out of front line service, 50 of them were converted for air-sea rescue work, at first under the designation Mk IIC (type 375) but later referred to as the A.S.R Mk II. The Merlin XII was replaced by the Mark XX, a “rescue pack” was fitted in the flare chute and smoke marker bombs were carried under the port wing.

A total of 921 Mk IIs were built, all by Castle Bromwich. A small number of Mk IIs were converted to Mk Vs.

Mk VII (type 351)

The Mk VII was a high altitude pressurised variant, this time powered by the Merlin 64 (F. Mk. VII) or 71 (H.F. Mk. VII) series engine with two-stage, two-speed superchargers. The Mk VII used a Marshall manufactured compressor for pressurising the cockpit; this was mounted on the right of the engine and drew its air through a long intake under the starboard exhaust stubs. An automatic valve allowed a maximum pressure differential of +2 lb./sq.in. This was built up during the climb and was maintained at heights of 28,000 ft and above.

Supermarine Spitfire F Vll MD120 NX-O ‘Spirit of Kent’ flown by Sqn Ldr James Joseph ‘Orange’ O’Meara D.S.O., D.F.C., Officer Commanding No. 131 Squadron, March 1944

Extended, “pointed” wingtips were fitted to the Type C wings, increasing the wingspan to 40 ft 2 in (12.2 m) but because the threat from high altitude bombers never materialised many Mk VIIs later reverted to the normal, rounded wingtip.

While early Mk VIIs were fitted with a detachable canopy, secured by four pilot operated catches, later Mk VIIs were fitted with a “Lobelle” type hood which opened by sliding backwards, as on non-pressurised versions of the Spitfire. This was a big improvement on the clamp down cockpit of the Mk VI. The canopy was double-glazed and used rubber tubing to create a proper pressure seal against the fuselage. The canopy rails were bulkier than the standard Spitfire type.

In total, 140 Mk VIIs were built by Supermarine. Most of them were powered by the Merlin 64 (F. Mk. VII) or Merlin 71 (H.F Mk. VII), the latter fitted with a Bendix-Stromberg “anti-g” carburettor. The HF Mk had superb high-altitude performance, with a service ceiling of 45,100 feet (13,700 m); French ace Pierre Clostermann recalls in his book, The Big Show, the successful interception of a long-range reconnaissance Messerschmitt Bf 109G-6/R3 by a Mk VII ‘Strato Spitfire’ of 602 Squadron at 40,000 feet (12,000 m) over the British Home Fleet‘s base at Scapa Flow in early 1944.

(images courtesy of Mark Styling)