Animated 3D model VB Specifications Supermarine Spitfire Mk VB Except for the first two variants of the Supermarine Spitfire (the Mk I and 2), it is a remarkable fact that the most used and, generally, the most successful variants of this fighter were those originally developed as ‘stop gap’ types. Rolls-Royce engineers were already working on a new version of the Merlin incorporating a two-stage supercharger; the combination of the improved Merlin and the Spitfire Mk VC airframe in a "stop-gap" design allowed the RAF to combat the Fw 190 on equal terms.  Several versions of the Spitfire, including Mk XIV and Mk XVIII had extra 13 gallon integral fuel tanks in the wing leading edges, between the wing-root and the inboard cannon bay. Spitfire Performance Testing, Last Viewed: 16 January 2014. The British Supermarine Spitfire was the only Allied fighter aircraft of the Second World War to fight in front line service from the beginnings of the conflict, in September 1939, through to the end in August 1945. Most of the Mk 22s were built with enlarged tail surfaces, similar to those of the Supermarine Spiteful. Because the Americans measured their boost ratings using inches of Mercury (" Hg), their boost gauges more accurately recorded the absolute pressures being generated by the superchargers at all altitudes.. The British Supermarine Spitfire was one of the most outstanding fighter aircraft of the Second World War. It had a new wing design, to improve its critical Mach number and allow safe operations at higher speeds. It was a further development of Supermarine's famous Spitfire and Spiteful aircraft, which by that point was a 10-year-old design following a rapid period of aviation development in history. The Mk 18 missed the war.  The improved armament was more effective for both air-to-air engagements and air-to-ground attacks. ... Supermarine Spitfire … In 1951, Hainan Island (People's Republic of China) was targeted at the behest of US Naval Intelligence for RAF overflights, using Spitfire PR Mk 19s based at Kai Tak Airport in Hong Kong. Rated at 2,050 hp (1,530 kW), the 12-cylinder Vee liquid-cooled Griffon 61 engine featured a two-stage supercharger, giving the Spitfire the exceptional performance at high altitude that had been sometimes lacking in early marks. The basic airframe proved to be extremely adaptable, capable of taking far more powerful engines and far greater loads than its original role as a short-range interceptorhad called for. A key factor which allowed the continued development of the Spitfire was the development of progressively more powerful and improved engines, starting with the Rolls-Royce Merlin and progressing to the bigger and more powerful Rolls-Royce Griffon. The squadron had little opportunity to engage the Luftwaffe before the war ended but scored a rare success on 26 April 1945, when two Spitfire Mk 21s shot up and claimed to have sunk a German midget submarine which they caught on the surface. The Mk XIV differed from the Mk XII in that the longer, two-stage supercharged Griffon 65, producing 2,050 hp (1,528 kW), was mounted 10 inches (25.4 cm) further forward. The new engine had a lower thrust-line than the Merlin and was set with 2 degrees of downthrust. The Spitfire was also adopted for service on aircraft carriers of the Royal Navy; in this role they were renamed Supermarine Seafire. Don Healy of 17 Squadron, based at Madura recalled that the Mk XIV was; ...a hairy beast to fly and took some getting used to. Fighter/ Fighter reconnaissance/ Photo reconnaissance. Due to the many differences in production Spitfires, performance could vary widely, even between aircraft with the same Mark number. Rolls-Royce Merlin 66: 150 Octane fuel, +25 lb/in² boost. As a result the maximum power generated by the Merlin 61 in F.S. Spitfire XIVs began to arrive in the South-East Asian Theatre in June 1945, too late to operate against the Japanese. A total of 287 Mk 22s were built: 260 at Castle Bromwich and 27 by Supermarine at South Marston. In these engines the carburettor injected fuel at 5 psi through a nozzle direct into the supercharger and the compressed air—fuel mixture was then directed to the cylinders. With the increasing use of hard-surfaced runways in the post-war years, many Spitfires were either manufactured, or retro-fitted with, larger mainwheels which were of a "three spoke" pattern. After intensive test flying, the most serious problems were solved by changing the gearing to the trim tabs and other subtle control modifications, such that the Mk 21 was cleared for instrument flying and low level flight during trials in March 1945. The aircraft was soon renamed Mk XX, to avoid confusion with a renamed PR type, then it became the Mk XII. Some 300 F Mk 18s and FR Mk 18s were built, before production ended in early 1946. I realised at once that we should have to correct its directional characteristics and probably its longitudinal stability also, both of which in due time we achieved. It certainly put the cat among the pigeons and among the VIPs. Many variants of the Spitfire were built, using several wing configurations, and it was produced in greater numbers than any other British aircraft. The basic airframe proved to be extremely adaptable, capable of taking far more powerful engines and far greater loads than its original role as a short-range interceptor had allowed for. Merlin 63, 66 or 70 engine with a two-stage, two—speed supercharger. The majority of Spitfires, from the Mk VIII on, used three basic wing types — the C through to the E types.  , The Mk 23 was to be a Mk 22 incorporating a revised wing design which featured an increase in incidence, lifting the leading edge by 2 inches (51 mm). 4 × 0.303 in (7.7 mm) Browning machine guns, 350 rpg. A contemporary of the Supermarine Spitfire and Hawker Hurricane, it was the first single-seat, twin-engined, cannon-armed fighter of the Royal Air Force. As a fighter, the F Mk 24 armament consisted of 4 × short-barrelled Mk.5 20 mm Hispano cannon – operational experience had proved that the hitting power of these larger weapons was necessary to overcome the thicker armour encountered on enemy aircraft as the war progressed. Chief among the changes was the upgraded 1,175 hp (876 kW) Merlin XII engine. "Your exciting Journey into digital world of aviation starts " Because the first XIVs were converted from existing Mk VIII airframes the first true production serial No. According to fighter ace J.E. Chapel, Charles Eward; Bent, Ralph D; McKinley, James L. Lovesey, A C. "Development of the Rolls-Royce Merlin from 1939 to 1945. The first one of these was flown by Jeffrey Quill on 20 January 1943. Some versions were built in Canada by the Canada Car and Foundry Co Ltd. There were 24 marks of Spitfire and many sub-variants. Mk XIIs were manufactured from Mk VC and Mk VIII airframes: early production aircraft had the fixed tail wheels, Dunlop AH2061 pattern "five spoke" mainwheels and small elevator balances. . In the case of the Merlin II/III, XII and 40 series as the air was being compressed it was mixed with fuel which was fed through an SU carburettor before being fed into the engine's cylinders. . Rolls-Royce designed the engine and first ran it in 1933 as a private venture. By contrast the Merlin 70, which was optimised for high altitude flight, had critical altitudes of 14,000 feet (4,300 m) (M.S) and 25,400 feet (7,700 m) (F.S).. Stronger undercarriage legs were raked 2 inches (5.08 cm) forward, making the Spitfire more stable on the ground and reducing the likelihood of the aircraft tipping onto its nose. The Mk XII flew operationally with their rounded wingtips replaced by shorter, squared off fairings; the single-stage supercharger of the Griffon II or IV used in the Mk XIIs meant that it was rated and used as a low altitude fighter, and the LF prefix used by Merlin-powered Spitfires was never applied. , The Mk XIV was used by the 2nd Tactical Air Force as their main high-altitude air superiority fighter in northern Europe with six squadrons operational by December 1944. The next essential ... was an improvement in the directional stability and control and a new fin was drawn out with a substantial increase in area (7.42 sq. The majority of Spitfires, from the Mk VIII on, used C, D and E wing types. This armament later became standard for all Spitfire Mk XIVs used by 2 TAF as fighters. This was the final mark of Spitfire powered by a Griffon 85 driving a five bladed Rotol propeller. The Royal Navy, noting both the success of the Spitfire in land-based service, and also the success of their own Sea Hurricanes, ordered the production of the Seafire, a carrier-based version of the Spitfire.  The first of the Griffon-engined Spitfires flew on 27 November 1941. The British Supermarine Spitfire was facing several challenges by mid-1942. The most reliable performance figures and weight measurements came from the tests carried out throughout the Second World War by the Aeroplane & Armament Experimental Establishment (A&AEE) based at Boscombe Down. 1943–1948 was a transition period during which new aircraft entering service were given Arabic numerals for mark numbers but older aircraft retained their Roman numerals. The Mark numbers used in the aircraft designations did not necessarily indicate a chronological order; for example, the Mk IX was a stopgap measure brought into production before the Mks VII and VIII. As the critical altitude was passed a pressure-operated aneroid capsule operated the gearbox which changed speed to Full Supercharger (F.S.) The first trial installation of the installation (modification 1029) was made in BS118, a Mark XI in November 1943. . I was also easily leaving the Typhoon behind and the eventual finishing order was, first the Spitfire, second the Typhoon, third the Fw 190.  During production of the Mk VIII and Mk IX, a new undercarriage leg was introduced which had external v-shaped "scissor-links" fitted to the front of the leg; this also led to small changes in the shape of the undercarriage bay and leg fairings. Depending on the supercharger fitted engines were rated as low altitude (e.g. The British Supermarine Spitfire was one of the most popular fighter aircraft of the Second World War.wikipedia. The new wing of the Spitfire F Mk 21 and its successors was designed to help alleviate this problem; the wing's stiffness was increased by 47%, and a new design of aileron using piano hinges and geared trim tabs meant the theoretical aileron-reversal speed was increased to 825 mph (1,328 km/h). The Hawker Hurricane was a British single-seat fighter aircraft designed and predominantly built by Hawker Aircraft Ltd. (article and images). With the end of the war, most orders for the Mk 21 were cancelled and only 120 were completed. Title: Supermarine Spitfire IX Variants (206) Page 02-960 File name: Supermarine Spitfire IX Variants (206)_Page_02-960.jpg Dimensions: 703 x 960 px The remedy, invented by Beatrice "Tilly" Shilling, was to fit a metal diaphragm with a hole in it, across the float chambers. Media related to Supermarine Spitfire Mark XIX at Wikimedia Commons The Mk XIX was the last and most successful photographic reconnaissance variant of the Spitfire. A similar contra-rotating propeller unit was later used on production Seafire 46 and 47s. The first of 100 Supermarine-built production aircraft started appearing in October 1942; two RAF squadrons in total were equipped with the XII. If this failed the pitch of the rear propeller was no longer under control and might do anything which was potentially dangerous. British Spitfire References. The impellors were driven by a hydraulically operated two-speed gearbox. For example, even relatively minor damage on the wing leading edges could drastically reduce top speed. ft) and a much larger rudder and fitted to the second aircraft JF317. The wings were redesigned with a new structure and thicker-gauge light alloy skinning. To help balance the new engine, the radio equipment was moved further back in the rear fuselage and the access hatch was moved from the left fuselage side to the right. With the increasing use of hard-surfaced runways in the post-war years many Spitfires were either manufactured, or retro-fitted with, larger mainwheels which were of a "three spoke" patt… Concepts for adapting the Spitfire to take the new engine had begun as far back as October 1939; Joseph Smith felt that "The good big 'un will eventually beat the good little 'un." Media related to Supermarine Spitfire Mark XVIII at Wikimedia Commons. The Merlin 66 used in the L.F. Mk IX produced slightly more power but because of the use of slightly different gear ratios driving smaller impellors, the critical altitude ratings of the supercharger stages were lower, 7,000 feet (2,100 m) and 18,000 feet (5,500 m) respectively. Initially known as the PV-12, it was later called Merlin following the company convention of naming its piston aero engines after birds of prey. F Mk IIc its multitude of variants Spitfire VIIIs. These field-converted aircraft were allocated to 430 squadron RCAF. We still had some work to do to improve its longitudinal and directional characteristics, but it was powerful and performed magnificently. As an example, the maximum power generated by the Merlin 61 was 1,565 hp (1,167 kW) at 12,250 feet (3,730 m) (critical altitude) at M.S. Although the first version of the Seafire, the Seafire Ib, was a straight adaptation of the Spitfire Vb, successive variants incorporated much needed strengthening of the basic structure of the airframe and equipment changes in order to survive the demanding maritime environment. Like the Mk XIV there were fighter and fighter reconnaissance variants built. Indeed, DP485 eventually went through many phases of development throughout and I, and others, flew in it a great deal; it became one of our favourite aeroplanes. The many changes were made in order to fulfill Royal Air Force requirements and to successfully engage in combat with ever-improving enemy aircraft. All had the larger "Spiteful" tail units; modifications were also made to the trim tab gearings to perfect the F Mk 24's handling. This article adopts the convention of using Roman numerals for the Mks I–XX and Arabic numerals for the Mks 21–24. After the first 25 (type 389s) were produced, later aircraft were also fitted with the pressurised cabin of the Mk X and the fuel capacity was increased to 256 gallons, three-and-a-half times that of the original Spitfire This version was the type 390. II which, it was decided, would be the first version to be produced exclusively by the huge new Nuffield “shadow” factory at Castle Bromwich. Unless otherwise noted all Griffon-engined Spitfire variants used the strengthened DunlopAH10019 "four spoke" pattern mainwheels. The lower thrust line and larger capacity of the new engine meant that the contours of the engine cowling were completely changed, with more prominent blisters over the cylinder heads, plus a third tear-drop shaped blister on the upper forward cowling to clear the magneto, and a deeper curve down to the spinner, which was much longer than previous types. This wing was structurally modified to reduce labour and manufacturing time plus it was designed to allow mixed armament options, A type, B type or four 20 mm Hispano cannon. When the Mk XII was able to engage in combat it was a formidable fighter and several Fw 190s and Bf 109-Gs fell victim to it. The majority of Spitfires, from the Mk VIII on, used C, D and E wing types. However, constant problems with the development of the Griffon meant that the decision to proceed with building a Spitfire with this engine didn't come to fruition until 1942, with the successful flight trials of the Mk IV. On reflection the general scheme became clear. , On 4 December 1939, the Supermarine design staff produced a brochure which mooted the idea of converting the Spitfire to use the Rolls-Royce Griffon engine. Main landing gear was strengthened and moved 2 inches (5 cm) forward to … A total of 957 of all variants were produced. A four blade Rotol propeller of 10 ft 5 in (3.1 m) was used. In December, it was refitted with a Griffon 61 and re-designated as a Mk 21 initial prototype. Protracted development of the Mk 21 meant that this variant did not reach operational service until January 1945. The Spitfire had many variants throughout its service life. The British Supermarine Spitfire was the only Allied fighter aircraft of the Second World War to fight in front line service from the beginnings of the conflict, in September 1939, through to the end in August 1945. The Supermarine Seafire was a naval version of the Supermarine Spitfire adapted for operation from aircraft carriers. The type has the distinction of being the first jet fighter to enter operational service with the FAA. Since it had diverged considerably from the Typhoon, it was renamed Tempest. gear, which drove the impellers faster, thus compressing a greater volume of the air-fuel mixture. Replaced by 2 x .50 in (12.7 mm) M2 Browning machine guns 250 rpg Mk XIVE and FR Mk XIV. This would lead to 19 marks of Spitfire and 52 sub-variants being produced throughout the Second World War, and beyond.  In 1944 100/150 grade fuels enabled the Merlin 66 to produce 1,860 hp (1,387 kW) at low altitudes in F.S gear. The name Seafire was derived from the abbreviation of the longer name Sea Spitfire. A supercharger can be thought of either as artificially increasing the density of the air by compressing it - or as forcing more air than normal into the cylinder every time the piston moves down.. The Mk XIV could climb to 20,000 ft (6,100 m) in just over five minutes and its top speed, which was achieved at 25,400 ft (7,700 m), was 446 mph (718 km/h). The Griffon IIB which powered the Mk IV was a single-stage supercharged engine of 1,735 hp (1,293 kW). K9795, the 9th production Mk I, with 19 Squadron. The proposed new design was called the Mk 21, which at first displayed poor flight qualities that damaged the excellent Spitfire reputation. These were soon removed and a mock up of a proposed six-cannon armament was fitted, three in each wing. "A Case For Standardisation: Puzzle of the Boost Gauge; British Unit an Anachronism: "Centibar" Suggested" (article and images). The new design also had a modern inwards-retracting undercarriage. https://military.wikia.org/wiki/Supermarine_Spitfire_variants:_specifications,_performance_and_armament?oldid=4790233, 1,030 hp (770 kW) at 16,000 ft (4,877 m) 87 Octane fuel, +6 lb/in² boost, 1,135 hp (846 kW) at 12,250 ft (3,734 m) 100 Octane fuel, +9 pounds lb/in² boost, 1,470 hp (1,096 kW) at 11,000 ft (3,353 m), 1,585 hp (1,181 kW) at 3,800 ft (1,158 m), 1,415 hp (1,054 kW) at 14,000 ft (4,267 m), 367 mph (582 km/h) at 18,600 ft (5,669 m), 354 mph (570 km/h) at 17,550 ft (5,349 m), 371 mph (597 km/h) at 20,000 ft (6,096 m), 350.5 mph (564 km/h) at 5,900 ft (6,096 m), 354 mph (570 km/h) at 17,400 ft (5,349 m), 2,175 ft/min (11.0 m/s) at 9,700 ft (2,956 m), 2,995 ft/min (15.3 m/s) at 10,000 ft (3,962 m), 3,250 ft/min (16.5 m/s) at 15,000 ft (4,572 m), 1,350 ft/min (13.5 m/s) at 28,000 ft (4,267 m), 1,530 mi (2,462 km) with 170 Imp gal (204 US gal) drop tank. As a result the prefixes which were used on most later Spitfire variants, L.F. Mark..., F. Mark.. and H.F Mark indicated whether the engines fitted were suited for low, medium or high altitude. 1,720 hp (1,283 kW) at 11,000 ft (3,353 m), 2,050 hp (1,530 kW) at 9,800 ft (2,987 m), 2,120 hp (1,771 kW) at 12,250 ft (3,734 m), 404 mph (650 km/h) at 21,000 ft (6,400 m), 397 mph (639 km/h) at 17,800 ft (5,425 m), 448 mph (717 km/h) at 25,900 ft (7,894 m), 454 mph (731 km/h) at 26,000 ft (7,802 m), 4,745 ft/min (24.1 m/s) at 10,000 ft (3,048 m), 3,760 ft/min (19.1 m/s) at 2,600 ft (792 m), 4,580 ft/min (25.2 m/s) at sea level (0 m), 4,100 ft/min (21.0 m/s) at 17,000 ft (5,182 m), 1,415 hp (1,055 kW) at 14,000 ft (4,267 m), 342 mph (297 knots), (550 km/h) at 20,700 ft (6,309 m), 359 mph (312 knots), (578 km/h) at 5,100 ft (1,514 m), 392 mph (341 knots), (631 km/h) at 12,800 ft (3,901 m), 452 mph (393 knots), (727 km/h) at 20,500 ft (6,250 m), 2,380 ft/min (12.0 m/s) at 16,000 ft (4,876 m), 3,460 ft/min (17.5 m/s) at 4,000 ft (1,219 m), 4,600 ft/min (23.4 m/s) at 4,000 ft (1,219 m), 4,800 ft/min (24.4 m/s) at sea level (0 m), 1,475 mi (2,374 km) with 90 gal drop tank, 8 × 0.303" Browning machine guns; 350 rpg, 4 × 0.303" Browning machine guns; 350 rpg, 2 × 250 lb (113 kg) or 1 × 500 lb (227 kg) bombs, 2 × 20 mm (0.79 in) Hispano II cannon; 60 round drum, 2 × 0.50 cal Browning M2 machine guns; 250 rpg. The full remedy was to use the Bendix-Stromberg pressure carburettor, which allowed more precise metering of the amount of fuel used by the engine and prevented the problem of fuel starvation. 4 × 20 mm Hispano V cannon; 175 rpg inboard, 150 rpg outboard, 2 × 250 lb (110 kg) with 1 × 500 lb (230 kg) bomb, 2 × 20 mm Hispano II: late Seafire IIIs Hispano V cannon; 120 rpg. For example, the Merlin II and III which powered the Spitfire I produced a maximu… Although initially based on the Mk VIII airframe, common improvements made in aircraft produced later included the cut-back fuselage and tear-drop canopies, and the E-Type wing with improved armament. The Supermarine Attacker is a British single-seat naval jet fighter designed and produced by aircraft manufacturer Supermarine for the Royal Navy's Fleet Air Arm (FAA). Neither the German leader Adolf Hitler nor his High Command of the Armed Forces believed it was possible to carry out a successful amphibious assault on Britain until the RAF had been neutralised. The Griffon IIs or VIs used a single-stage supercharger generating maximum power at low altitudes. Spitfire IX: Temporary stop gap marriage of uprated two stage engine, Merlin 61, 63, 66 or 70 with the Mk V airframe. Bromley, Kent UK. 57 Related Articles [filter] Supermarine Spitfire. Although the first version of the Seafire, the Seafire Ib, was a straight adaptation of the Spitfire Vb, successive variants incorporated much needed strengthening of the basic structure of the airframe and equipment changes in order to survive the demanding maritime … The basic airframe proved to be extremely adaptable, capable of taking far more powerful engines and far greater loads than its original role as a short-range interceptor had called for. The most common variant of the Supermarine Spitfire is the Supermarine Spitfire Mk VB. The original production variants of the Merlin used an SU manufactured carburettor in which the fuel flow was metered through a float. Its handling qualities have benefitted (sic) to a corresponding extent and it is now considered suitable both for instrument flying and low flying. , One problem which did arise in service was localised skin wrinkling on the wings and fuselage at load attachment points; although Supermarine advised that the Mk XIVs had not been seriously weakened, nor were they on the point of failure, the RAF issued instructions in early 1945 that all F and FR Mk XIVs were to be refitted with clipped wings.  After the war, second hand Mk XIVs were exported to a number of foreign air forces; 132 went to the Royal Belgian Air Force, 70 went to the Royal Indian Air Force and 30 of its reconnaissance variant went to the Royal Thai Air Force. The F Mk 24 achieved a maximum speed of 454 mph (731 km/h) and could reach an altitude of 30,000 ft (9,100 m) in eight minutes, putting it on a par with the most advanced piston-engined fighters of the era. It was also the only British fighter produced continuously throughout the war. Supermarine were seriously concerned because Castle Bromwich had been converted to produce Mk 21s and more were coming off the production lines daily. At low altitude it was one of the fastest aircraft in the world; in one speed trial, held at Farnborough in July 1942 DP485 (now referred to as the Mk XII) piloted by Jeffrey Quill raced ahead of a Hawker Typhoon and a captured Focke-Wulf Fw 190, to the amazement of the dignitaries present. For engines equipped with a single-stage supercharger the air being forced through the supercharger air intake was compressed by the supercharger's impeller. Many variants of the Spitfire were… By 1943, Rolls-Royce engineers had developed a new Griffon engine, the 61 series, with a two-stage supercharger. Also known as the "Universal wing" the new design was standard on the majority of Spitfires built from mid-1942. The Supermarine Spitfire, the only British fighter to be manufactured before, during and after the Second World War, was designed as a short-range fighter capable of defending Britain from bomber attack and achieved legendary status fulfilling this role during the Battle of Britain. The ailerons were 5 per cent larger and the Frise balanced type were dispensed with, the ailerons being attached by continuous piano-hinges. Redesigned upper wing gun bay doors incorporated "teardrop" shaped blisters to clear the cannon feed motors and the lower wings no longer had the gun bay heating vents outboard of the gunbays. Another important feature of the Griffon-engine Spitfires was the entirely flush-riveted finish which was progressively introduced on all Spitfires. Some Spitfires of one mark or variant may have been modified to another; for example, several of the first Mk VBs were converted from Mk IBs; the first Mk IXs were originally Mk VCs. It was analogous in concept to the Hawker Sea Hurricane, a navalised version of the Spitfire's stablemate, the Hawker Hurricane. Supermarine Spitfire – History of a legend (RAF Museum), last viewed: 17 January 2014. It was a splendid aeroplane in every respect. Handling, however, was considered to be better than previous Spitfire marks, and the clipped wings conferred excellent manoeuvrability through enhanced aileron response. This was precisely the opposite result to that expected, or indeed intended. . Post-war, the Spitfire's service career continued into the 1950s. One prototype, JF321, was fitted and tested with a Rotol six-bladed contra-rotating propeller unit; although this promised to eliminate the characteristic swing on take-off (caused by the propeller slipstream) the propeller unit was prone to failure. It was outmoded by jet aircraft, and only 18 were built. This engine included a Coffman cart… In most circumstances this proved to be sufficient but during the air battles over Dunkirk and during the Battle of Britain it was found that whenever the Merlin was subjected to negative "g" forces, such as a quick "bunt" into a dive, the engine would briefly lose power through petrol starvation. As a result the later Seafire variants were usually heavier and, in the case of the Seafire XV/XVII and F. 47 series, they were very different aircraft to their land-based counterparts. When retracted the wheels were fully enclosed by triangular doors which were hinged to the outer edge of the wheel wells. The original Merlin and Griffon engine designs used single-stage superchargers. Post-war, the Spitfire's service career continued into the 1950s. A total of 81 Mk 24s were completed, 27 of which were conversions from Mk 22s. The Merlin III produced 1,030 hp (770 kW) at +6¼lb/in² (43 kPa) of "boost" (the "boost" is the pressure to which the air/fuel mixture is compressed before being fed to the cylinders). It is considered that the modifications to the Spitfire 21 make it a satisfactory combat aircraft for the average pilot. [nb 3], An intercooler, was required to stop the compressed mixture from becoming too hot and either igniting before reaching the cylinders (pre-ignition knocking) or creating a condition known as knocking or detonation. This Spitfire has the "cropped" Merlin 45 series engine and the "clipped" wings. The undercarriage legs also had a 7.75 in (19.7 cm) wider track to help improve ground handling. These figures were only true to the first prototypes, as serial production examples were fitted with a Griffon 65 with different supercharger gearing. , The Hispano Mk.II cannons were now belt fed from box magazines allowing for 120 rpg (the "Chattellerault" system). Spitfire F.24 of 80 Squadron.