Supermarine Spitfire (Griffon-powered variants)
The Rolls-Royce Griffon engine was designed in answer to Royal Navy specifications for an engine capable of generating good power at low altitudes. 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." and Ernest Hives of Rolls-Royce thought that the Griffon would be "a second power string for the Spitfire". The first of the Griffon-engined Spitfires flew on 27 November 1941.
Although the Griffon-engined Spitfires were never produced in the large numbers of the Merlin-engined variants they were an important part of the Spitfire family, and in their later versions kept the Spitfire at the forefront of piston-engined fighter development. This article describes the Griffon-powered Spitfire variants.
Wing types
The majority of Spitfires from the Mk VIII used C, D and E wing types. Unless otherwise noted, all Griffon-engined Spitfire variants used the strengthened Dunlop AH10019 "four spoke" pattern mainwheels. With the increasing use of hard-surfaced runways in the post-war years, many Spitfires were either manufactured or re-fitted with, larger mainwheels which were of a "three spoke" pattern. These were used on modified undercarriage legs which had reduced "toe-in" for the axles, which reduced tyre scrub.C type
Also known as the "Universal wing" the new design was standard on the majority of Spitfires built from mid-1942. This wing was structurally modified to reduce labour and manufacturing time, and was designed to allow mixed armament options: A type, B type, or four 20 mm Hispano cannon.The undercarriage mountings were redesigned and the undercarriage doors were bowed in cross section allowing the legs to sit lower in the wells, eliminating the upper-wing blisters over the wheel wells and landing gear pivot points. Stronger undercarriage legs were raked 2 inches forward, making the Spitfire more stable on the ground and reducing the likelihood of the aircraft tipping onto its nose. 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. 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.
The Hispano Mk.II cannons were now belt fed from box magazines allowing for 120 rpg. The fairings over the Hispano barrels were shorter and there was usually a short rubber stub covering the outer cannon port. 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. To provide room for the belt feed system of the cannon, the inner machine gun bays were moved outboard between ribs 13 and 14. As the Spitfire was no longer to be used as a night fighter, the retractable landing lights were no longer fitted.
D Type
These were specifically made for the Photo-Reconnaissance Spitfires, including the PR XIX; no armament was fitted and the D-shaped leading edges of the wings ahead of the main spar, were converted into integral fuel tanks, each carrying 66 gallons. To avoid the expansion of fuel in hot weather damaging the wing, pressure relief valves, incorporating small external vent pipes, were fitted near the wing tips.E type
Structurally unchanged from the C wing, the outer machine gun ports were eliminated, although the outer machine gun bays were retained and their access doors were devoid of empty cartridge case ports and cartridge case deflectors. The inner gun bays allowed for two weapon fits;or
The 20 mm Hispano cannon were moved outboard and a more effective.50-inch Browning.50 cal M2/AN heavy machine gun with 250 rpg was added to the inner gun-bay replacing the outer Browning.303s. The first trial installation of the installation was made in BS118, a Mark XI in November 1943. This armament later became standard for all Spitfire Mk XIVs used by RAF 2nd Tactical Air Force as fighters. The improved armament was more effective for both air-to-air engagements and air-to-ground attacks.
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.
Starting in early 1945 most Spitfire Mk XIVs also used clipped wing tips, mainly to reduce wrinkling of the wing's skin; again the LF prefix was not applied to these aircraft.
Redesigned late wing
As the Spitfire gained more power and was able to fly at greater speeds the risk of aileron reversal was increasing so the Supermarine design team set about redesigning the wings to counter this possibility. The original wing design had a theoretical aileron-reversal speed of, which was somewhat lower than that of some contemporary fighters. 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 percent and a new design of aileron using piano hinges and geared trim tabs meant the theoretical aileron-reversal speed was increased to. This wing entered service on the Spitfire XXI. The standard armament was now four 20mm Hispano IIs or the shorter, lighter Hispano V cannons, each with 150 rounds per gun.Variants
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. 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.Up until the end of 1942, the RAF always used Roman numerals for mark numbers. From 1943–1948, new aircraft entering service were given Arabic numerals for mark numbers but older aircraft retained their Roman numerals. From 1948, Arabic numerals were used exclusively. Thus, the Spitfire PR Mk XIX became the PR 19 after 1948. This article adopts the convention of using Roman numerals for the Mks I–XX and Arabic numerals for the Mks 21–24. Type numbers are the drawing board design numbers allocated by Supermarine.
Mk IV / XX (type 337)
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. A top speed of 423 mph at 18,500 ft was predicted. 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.The Griffon IIB which powered the Mk IV was a single-stage supercharged engine of 1,735 hp. Stronger main longerons were needed to cope with the weight of the Griffon and it required a bigger radiator and oil cooler, although it kept the asymmetric under-wing radiator layout of the single stage Merlin marks. The new engine had a lower thrust-line than the Merlin and was set with 2 degrees of downthrust. 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. The lower cowling lost its "pigeon-chested" appearance, with a shallower curve up to the spinner. A four blade Rotol propeller of 10 ft 5 in was used. Apart from these differences the Mk IV airframe was closely related to that of the Merlin-powered Mk III. One feature of the Griffon engine which was to catch a lot of pilots out was that the propeller rotated in the opposite direction to that of the Merlin; i.e.,: to the left, from the pilot's perspective, rather than to the right. This meant that the powerful slipstream swung the Spitfire to the right on the ground, requiring the rudder to be deflected to the left during takeoff.
The Mark IV DP845 first flew on 27 November 1941. It had the full-span C wing combined with a small tail unit and retractable tailwheel, and also had external bracket hinges under the wings, denoting the installation of braking flaps. These were soon removed and a mock-up of a proposed six-cannon armament was fitted, three in each wing. The aircraft was soon renamed Mk XX, to avoid confusion with a renamed PR type, then it became the Mk XII.
Jeffrey Quill, Supermarine's chief test pilot, was the first to fly the Mk IV/Mk XII prototype DP845,
Mk XII (type 366)
The Mk XII was the first Spitfire powered by a Griffon engine to go into service. The first of 100 Supermarine-built production aircraft started appearing in October 1942; two RAF squadrons in total were equipped with the XII. 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. They had a single 85 gal main fuel tank, giving a short range of little over on internal fuel. All were fitted with the larger, pointed tip rudder. The last 45 or so Mk XIIs, were based on Mk VIIIs with two wing fuel tanks, each containing a maximum fuel load of 14 gal, and featured the larger horn balances, retractable tailwheel and undercarriage legs with torque-links, "dished" leg fairings and the stronger Dunlop AH10019 four spoke wheels. The wheels were occasionally fitted with disc-style covers. A later model IFF was fitted, replacing the aerials from the tailplane tip to fuselage with a rod aerial under the starboard wing. Another important feature of the Griffon-engine Spitfires was the entirely flush-riveted finish which was progressively introduced on all Spitfires.The single-stage Griffon engine gave the aircraft superb low and medium level performance, although the Mk XII's performance declined at higher altitudes: because of this all production aircraft had "clipped" wings. In comparative tests with a Mk IX it was faster at sea level, but above it had become slower. Handling, however, was considered to be better than previous Spitfire marks, and the clipped wings conferred excellent manoeuvrability through enhanced aileron response.
At low altitude it was one of the fastest aircraft in the world; in one speed trial, held at Farnborough in July 1942 DP485 piloted by Jeffrey Quill raced ahead of a Hawker Typhoon and a captured Focke-Wulf Fw 190, contrary to expectations.
However pilots found it difficult to exploit this advantage in combat as German pilots were reluctant to be drawn into dogfights with Spitfires of any type below. When the Mk XII was able to engage in combat it was a formidable fighter and several Fw 190s and Messerschmitt Bf 109Gs fell victim to it.
The Mk XII's speed advantage at lower altitudes again became useful near the end of its front line service in summer 1944, when its pilots were credited with 82.5 V-1 Flying Bomb kills. The Mk XII variant was retired in September 1944.