Differences between Spitfire Marks

A Spitfire is instantly recognizable. Despite this, there were enormous changes made to the basic Spitfire design, and very little of the original aircraft other than general outline persisted to the last Marks. Since in practice, Spitfires were continually being upgraded or simply repaired with whatever fitted and was immediately available, many Spitfires never fitted the description of a typical Mark V (or whatever). However, it is possible to outline the major characteristics of any particular Mark, so here goes.......

The basic shape of the Spitfire was developed by this point. The characteristic wing, of NACA 2200 series airfoils, had a 6° dihedral with a 2.5° washout, a 2° incidence,and an area of 242 square feet. The airframe was 30 feet in length, 37 feet wingspan, and 8.2 feet in height. It had a maximum all up weight of 5 359 lb and was powered by a 990 HP Rolls-Royce Merlin C driving a 2-blade, fixed pitch propeller.

This was basically the same airframe as the prototype allowing for changes to facilitate a production line. The all up weight was increased to 5720 lb, and a 998 HP Merlin II (later 953 HP Merlin 3) fitted. The airscrew was initially 2-blade fixed pitch, but was soon changed to a 2-pitch 3-blade design from either De Havilland or Rotol. Armament was eight 0.303 Browning machine guns. Terminology will change frequently through these descriptions, as it did originally, and one of these changes involved the Mk 1b Spitfire. The (b) suffix usually denotes a particular wing variant, but since there was only one wing type in this Mark, it refers to a limited number of airframes armed with 20 mm cannon. These had a tendency to jam and were not popular with aircrews. Altogether 1569 Mk I Spitfires were produced.

The major change from the Mark I was the use of the 1050 HP Merlin XII with higher supercharger gearing and a Coffman cartridge starter. 921 were produced.

A number of changes were introduced here. It was powered by the 1265 HP Merlin XX with a 2-speed supercharger, a constant-speed airscrew, and introduced a number of refinements, including a smoothed windscreen, retractable tailwheel, and clipped wings. The maximum all-up weight had increased to 6350 lb. Only 2 were produced, although many of the new features were introduced into the developing models.

In the second name change, the Mark IV was initially the first Griffon-engined variant. As production continued with Merlin-engined Spitfires, the Griffon-powered Spitfires were introduced later as Mark XII. A Photoreconnaissance aircraft named PRIV was powered by a Merlin 45 or 46, and 229 were produced. Essentially a smoothed Mk V, the torsion box in the wing leading edge was modified to provide extra fuel and oil tanks.

With the arrival of the Me (Bf)109F an interim aircraft was produced by adding the latest Merlin to a strengthened airframe. They were powered by a 1230 HP Merlin 45 or 46, with a maximum all-up weight of 6170 lb. 3 patterns of wing were introduced-

• A- eight 0.303 Browning machine guns
• B- two 20mm cannon, and four Browning machine guns
• C- either four cannon or either of the other combinations.

6478 of the MkV were produced. In a number the wings were adapted for high altitude (extended, pointed tips) or low altitude (clipped wingtips, for faster roll rate), and the supercharger settings adapted for the selected altitude.
Those airframes intended for desert conditions acquired a deep "chin" in the form of an air filter to keep out the desert sand.

This was introduced to combat the threat of high flying German bombers. It was fitted with a Merlin 46 or 47 driving a 4-bladed propeller, and extended (high altitude) wingtips. Some were fitted with injection of liquid oxygen into the air intake. The most notable change was the addition of a partially pressurized cabin, with a canopy that was fixed in place on the ground except for emergency jettisoning. It was not a successful variant, and only 100 were built.

This introduced the 60 series Merlin engines, with 2-speed, 2-stage superchargers. The aircraft consequently had the symmetrical large radiators under each wing, rather than the asymmetric radiator/oil cooler combinations of earlier Marks, and a larger rudder.

This was essentially a low altitude, unpressurized MkVII, with a 1565 HP Merlin 61 or a 1710 HP Merlin 63 driving a 4-bladed airscrew. Changes to the carburetor allowed negative "g" manoeuvering. Although the MkVIII was intended as the major developmental line for the Spitfire, the MkIX was hurried into service, and only 1652 were eventually produced, many modified for tropical climates. A single airframe was converted into the first official 2-seat Spitfire -the Tr8- but no great interest was shown and it was not followed up.

Introduced as another temporary measure, the Mk IX started life as a strengthened MkV airframe with the latest, 60 series, Merlin engines driving a 4-bladed airscrew. It proved so successful that all in total around 7180 were produced. Trainer variants were produced by the USSR (no details known) and UK (after the war, Tr9).

After the end of the War, with widespread sales of Spitfires, a limited number of Mark IX Spitfires were bought back by Vickers Armstrongs and converted to the Trainer (Tr) Mk IX. The front cockpit was moved forwards, and a second cockpit with raised seat and high domed canopy was added behind it. 26 were produced. During the War there were an unknown number of local conversions to a 2-seat configuration, mostly in the Soviet Union. These did not conform to Type 509 standard. Any information will be gratefully accepted.

This photoreconnaissance aircraft was a converted Mk VII airframe, with PRXI wings, although many had the MkVII pressurization removed in service. 16 were produced. Photoreconaissance Spitfires could be easily recognised by the absence of armament in the wings, a low visibility paint scheme (later PRU blue, earlier a sort of blue-green called Camotint the precise shade of which is still the subject of much debate, or even pink! Although it sounds bizarre, and there is no doubt that pilots felt rather vulnerable over Occupied Europe in an unarmed pink aircraft, against an overcast sky a pink colour scheme provided very good camouflage) and a deeper chin under the nose to allow a larger oil tank. The oil consumption of a Merlin could be measured in gallons per hour!

The photoreconnaissance variant of the successful Mk IX was similar in many ways, but with cleaned up wings carrying no armament and integral fuel tanks. In total 471 were produced.

The first major change to the Spitfire was the introduction of the Griffon engine. Like the Merlin it was a V12 supercharged engine, of 36 litres swept volume rather than the 27 liters of the Merlin. The 4-bladed airscrew also turned the opposite way. The Griffon III or IV fitted to the Mk XII generated around 1720 HP. 100 were produced. A retractable tailwheel appeared early in the production run, and most were clipped-wing, low altitude variants.

In classic Spitfire tradition, the new engine, a Griffon 61 (and later Griffon 65), was mated to an available airframe- in this case a Mk VIII. To absorb the power generated, a 5-bladed airscrew was introduced. Some of the Mk XIV were produced with a cut-down rear fuselage and "teardrop" canopy for increased visibility. 957 were produced.

A large number of Mk IX Spitfires (1054) were produced with Packard built 1372 HP Merlin 266 engines and designated Mk XVI. Many were built alongside Mk IX variants and sequential production numbers may have different mark designations.

Mk T16

I am at something of a quandry over this designation. The difference between the Mk IX and XVI was largely the engine installation. Drawings were made of a conversion of the Mk XVI to trainer configuration, but no airframes were available for the conversion. With the current restorations, it is likely that some of the T9 aircraft currently flying already have a Packard Merlin installed, or may be re-engined as such in the future. If this occurs, should they be redesignated T16? Comments would be valued.

The basic Mk VIII airframe was fitted with 2-stage, 2-speed 2035 HP Griffon 65 or 2375 HP Griffon 67 engines. 300 were produced.

This aircraft was the photoreconnaissance derivative of the Mk XIV, and was pressurized. 225 were built.

Along with a new way of writing the Mark numbers, the 20 series Spitfires were a major rebuild of the design. Although superficially similar, there was very little structurally in common with the earlier Marks. The long nose of the Griffon engine was prominent, along with a wider (>3 feet) stiffer wing of similar aerofoil. 120 were produced.

This was essentially a Mk 21 with a cut-down fuselage and a teardrop canopy. 287 were built.

Although introducing short-barrelled Hispano cannon, it was essentially the same as the Mk 22. Only 54 were built. The engines powering the 20-series Spitfires were the 2050 HP Griffon 61, 2120 HP Griffon 85, and 2340 HP Griffon 64.

These aircraft were converted Mark VB airframes with a universal wing and an "A" frame hook attached to fuselage frame 15. In all 340 were built.

The first true Seafire, it was built on the Mk VC production line, but with strengthening for catapult launching, lengthened undercarriage with forward raking (to reduce the risk of tipping over on full power), and a strengthened wing to allow external stores to be carried. 372 were built.

Fitted with a Merlin 55 and a 4-bladed propeller, this differed from the IIC in having a wing that could be manually folded to increase storage space on the aircraft carriers. Production Spitfires with 4-bladed propellers almost all had an enlarged radiator under the left wing due to the 2-stage supercharger, but this was not true of the Seafire Mk III. 1218 were produced in total.

The gap in the Mark numbering is the result of an attempt to rationalise the Spitfire/Seafire serial numbers, which was far from successful. This aircraft, the seagoing equivalent of the Spitfire XII, had the two large wing radiators, a Griffon VI of 1750HP driving a 4-bladed propeller, a broad chord rudder and a retractable tail wheel. 450 were produced.

This Mark continued the similarities between the developments in the Spitfire and those in the Seafire. The last 30 airframes from the Mk XV run were modified to XVII standard, implying substantial similarities. A cut-down rear fuselage was introduced, along with a curved windscreen, rear fuselage and wing fuel tanks, a strengthened undercarriage, and an enlarged fin and rudder. Some confusion has been caused by the fact that while the Seafire XVII was in service the numbering was reorganised, allowing the Spitfire Marks to continue as planned, and moving the Seafire series to 40. The Seafire XVII therefore is also accurately referred to as the Seafire 41. 233 were produced.

This was the navalised equivalent of the Spitfire Mk 21, and featured the new wing, and the Griffon 61 engine. It had a short life and 50 were produced.

This Mark introduced the contra-rotating propeller as standard, and the new "Spiteful"-type empennage. Unfortunately, the new wing did not fold, and only 24 were built. As an illustration of the lag times to production, all these were originally ordered as Mk V Spitfires; the order was re-established as Mk 21, before redesignation as Seafire 46.

A good aircraft, too late. 2200HP of Griffon 87 drove a contra-rotating propeller, which virtually eliminated the torque reaction from the power available. It had the huge Spiteful tail section, and a folding wing. Unfortunately it was overtaken by technology (mostly the jet) and only 90 were built.

The early Spiteful was developed with a Spitfire fuselage, a Griffon engine, and a Mustang-like laminar flow wing, which was believed to have better performance characteristics at high speeds. It never lived up too the promise, and was overtaken by the development of the jet engine.

Comparing Spitfire performance is extremely difficult, and very like stating the weather for Europe. You can say that in the middle of Manchester, on Monday at 10.21 it was sunny, with winds of 5 knots from 030 degrees, with temperature, humidity, and pressures of whatever, but generalisations are difficult. So it is with the Spitfire. A given machine might be faster, climb better, turn more readily, and roll more quickly than another at 5 000 feet, but be greatly inferior to that other at 35 000 feet. Below is a collation of official performance figures on specific aircraft, to give a bit of a feel for general progress of the Spitfire over time. As an example of the variation, the notches in the speed curves for each aircraft are largely due to the altitude settings on the supercharger gear changers (which differed between variants- the Mark V had a number of engines, optimised for performance at different heights)

The effect of altitude on rate of climb

The effect of altitude on maximum air speed

Summed Up

While not externally appearing to change substantially, the Spitfire was massively developed. The Mark 24 was one-third faster than the Mk I in level flight. It had a rate of climb 80% faster, despite a maximum all-up weight over 6 790 lb heavier, and had 5 times the firepower. Despite the early origins of the design, and major theoretical criticisms, the performance of the wing near to the speed of sound was not bettered until well into the jet era.

Interlude

There were huge numbers of variations that were tried with varying degrees of success. One of the more interesting was the result of a perception that aluminium would be in short supply. As a consequence 2 fuselages were commissioned in what would today be called "composite materials". The mixture was called "Aerolite", and although they were never flown, and the dire shortage of aluminium did not appear, there are reflections today in a number of designs for Spitfire copies in modern composite materials. Although there are often few parallels in these copies other than in the reproduction of the evocative appearance, perhaps that is the direction that the design team might have taken under different circumstances.

Mark designation

In the course of describing the features of the various Spitfire Marks, I have alluded to the problems of designation where the only difference between Marks is something small and easily changed. The best example is that of the MkIX/XVI, where the difference is essentially an engine change. If a MkIX is reengined with a Packard Merlin, should we call it a MkXVI instead? Or T9 becoming T16? As for modifications that never were part of the original descriptions, such as the PRXIX currently being rebuilt with a contrarotating airscrew on an engine off a Shackleton, I confess to being perplexed. Purists will always be upset, but should we just ignore these features, and call the airframe by its last "official" designation? Answers, please, on a stamped addressed e-mail to the referee of this debate.

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