Concluding our review of production changes to the Spitfire Mk. IX/XVI family is the list of main modifications to the wings, undercarriage and tail.

Blisters above wheel wells

With the introduction of the C or “universal” wing on the Mk. V, the “D”-shaped bump above the wheel wells disappeared. This was a consequence of an increased forward rake of the extended undercarriage legs resulting in less space being needed for the wheel when retracted. Thus all Spitfires Mk. Vc and early Mk. IXs had completely flat wheel well roofs.

(This  statement however, may be still open to discussion: At least some early Spitfires Mk. IXc did have bulges over the wheel well, as can be seen on the Mk. IXc preserved at TaQ’ali museum in Malta. It is possible that this modification (No. 529) was introduced already on the Mk. VC, replacing the previous overwing “fences” with thicker-gauge skin, bulges and internal stiffeners in the wheel wells. – Ed. Thanks to Edgar Brooks for information on this item).

Then, at some point, a second type of wheel well roof blisters began to appear, this time of teardrop shape. These are especially frequent among currently airworthy examples.

According to Rolf Meum, who has accumulated 100+ hours of Spitfire flying with the Old Flying Machine Company, Duxford, the teardrop-shaped blisters above the wheel wells correlate to a modified wheel axle geometry adapted to tarmac/concrete runway operation. The original “grassfield” undercarriage had a substantial toe-in. As tarmac, concrete and PSP runways became usual during the course of the war, the toe-in resulted in severe wear on the port main wheel due to the engine torque during take-off. With the modification, the toe-in was decreased, but the wheels could no longer lie flat in the wheel wells and therefore needed more space to fit.

This may explain why the blisters are  frequently seen on surviving warbirds and other post-war Spitfires while being rather rare on pictures taken during the war.

Teardrop-shaped blister over the wheel well roof characteristic of the modified undercarriage.
[Martin Waligorski]

Undercarriage variations

Late Mk. IXs and Mk. XVIs had oleo legs with scissor links, whereas earlier examples didn’t. Please note that a zig-zag pattern of bolt heads seen on the earlier type legs is absent on the link-type, these bolts probably projected into the oleo cylinder and acted as guides for the splined section of the oleos.

A modified contour of wheel well and cover, with a more smooth transition between the leg and wheel portion of the well, probably reflects the addition of the torque link, which needed some extra room. To cover the “cut corners” of the wells, undercarriage covers with a more smooth outline (smooth transition between leg and well portion) were introduced.

Also relatively unknown is the fact that the legs on the “universal” and “e” wings did not retract completely into the wing. This is reflected by slightly bulged undercarriage covers. This change stemmed in part from the introduction of increased forward rake of the main undercarriage and also to allow completely smooth upper wing surfaces in this area.

The changed geometry of the undercarriage pintle axle made the small blister near the wing root disappear, while a new blister under the wing, just aft of the pivoting point, was introduced.

Five-spoke wheels were the rule for all production Mk. IXs well into 1944. On the photographs, the wheels are often hidden behind the undercarriage covers, but the five-spoke wheel type can still be identified by the five bolts surrounding the axle nut.

Four-spoked wheels seem to have appeared in Mk. IX production during 1944, typically on Mk. IXe’s. Three-spoked wheels are mostly seen on late-production Mk. XVIs. The two latter wheel types largely seem to coincide with link-type oleo legs.

This photo of the pilot of No. 403 Squadron RCAF taken during the summer of 1943 shows the initial undercarriage configuration with five-spoke wheels
[Pat Murphy coll.]

The four-spoked wheels (above) appeared in production during 1944, replacing the previous five-spoke type. Also visible in this view are the characteristic features of the modified undercarriage: scissor links and rounded as well as bulged undercarriage covers.
[Martin Waligorski]

Here is the last, three-spoke type of wheel used on the Mk. XVI. This type is probably most commonly known from the post-war Griffon variants of the Spitfire. Compared with the previous two photographs it is apparent that the tyre dimensions are very different, optimized for use on hard runways.
[Martin Waligorski]

Port for “gun-camera”

In the Spitfire Mk. V, the gun camera was placed in the starboard wing root. Early versions of Mk. IX had the camera removed and the larger, framed air intake to the fuel cooler system placed in the same location. Aircraft equipped with this device did not have the gun camera installed.

Later modifications to the fuel system rendered the fuel cooler unnecessary, but in the meantime the camera was moved to port wing root, then once again moved back to starboard. Occasionally this opening seemed to have been taped over with the same stuff as that used for sealing the gun ports.

These two photos provide useful reference over another elusive detail of Spitfire Mk. IX construction – the gun camera and fuel cooler openings. The photo above shows the gun camera opening in the starboard wing root, taped over indicating than no camera was in use. Originally in the Mk. V production the camera was placed in the port wing, but in the early Spitfires Mk. IX its place was occupied by a large circular air intake for the fuel cooler (below). Thus the camera was first altogether removed, and only eventually replaced in the starboard wing. At the same time, the fuel cooler installation was rather rapidly removed from production. Later machines could therefore have their cameras – if carried – mounted in either port or starboard wing roots.
[Pat Murphy coll.]

Cannon bay cover blisters

As the “universal” wing was designed to accommodate two cannon in each wing, the panel covering the cannon bay initially had a single wide and deep blister. This gun configuration did not prove popular on the Mk. V, and I’m not aware that it was ever used operationally on the Mk. IX. The wide blister remained, however, for some time.

Eventually, the lack of interest for this armament option was reflected in the introduction of a new panel with a more streamlined, narrow fairing over the cannon position in use (inboard). I believe that the new panels began to appear some time in early 1943.

Variations of c-type wing cannon blisters. (1) The initial wide blister intended for four-cannon armament. (2) This has been reduced in size when an armament of two cannon and four rifle-calibre guns was standardised for Mk. IXc.
[Martin Waligorski]

The panels over “e”-type cannon bays had the blister moved outwards and rearwards, it was also a little taller as the cannon breech was moved to a thinner section of the wing.

The layout of e-wing cannon blister is visible in this view of a Danish Spitfire Mk. IXe after a landing accident.
 

Armament variants

The original armament consisted of one belt-fed 20mm Hispano cannon in the inner position of each wing, and two .303cal machine guns in the machine gun bays. The unused outboard cannon stub was closed off with a rounded wooden plug. There is some confusion regarding the proper name for this option; many people feel that the term “c” should be reserved for the four-cannon option, and that the 2x 20mm + 4x .303 option in the universal wing should be termed something like “improved B” – the improvement referring to the more reliable Chatterault belt feed system, which also doubled the ammunition capacity for the cannon.

The later “e” type armament disposed of the outer small-calibre guns, instead having one .5cal machine gun in the inner cannon position, the Hispano cannon being moved to the outer position. The muzzle of the .5cal MG was buried within the large-diameter blast tube, which used to be sealed off either by tape/doped fabric or by a small (wooden?) blanking plate.

Early Spitfires Mk. IXe had cannon barrel fairings with straight taper, some later machines used a more cigar-shaped variety.

The e-type armament is easily distinguishable by the cigar-shaped rather than tapered fairing of the cannon barrel. The cannon in the e-wing was invariably positioned outboard.
[Martin Waligorski]

Bomb racks

Bomb racks were fitted to the centreline and wings. Whereas the centreline rack was a seemingly makeshift contraption made up of “L” section steel bars, the underwing racks, positioned under the middle of the cannon bay, were of a more conventional, streamlined appearance. The centreline rack could carry a 500lbs. bomb, the underwing racks one 250lbs. bomb each.

At least some of the machines with wing racks had deflection plates fitted to the cartridge ejection chutes.

Wing tips

“Clipped” wings were seen on many aircraft, mainly of the LF Mk. IX and Mk. XVI varieties.

Rudder

Late production series airframes, typically Mk. IXe and Mk. XVI, were often fitted with the larger, pointed Mk. VIII-type rudder.

Elevators

All except the initial production Mk. IXs had elevators with extended mass balance horns. Whereas the early Spitfires had a 45-degree break in the hinge line, this new pattern had an additional 45-degree break, resulting in the tip of the elevator pointing straight forward.

As a rule of thumb the early pattern is seen on Mk. IXs converted from Mk. Vs, and early original Mk. IXs. I’ve seen both patterns on aircraft in the MA serial range (Castle Bromwich – mid-1943 vintage).

(1) Early and (2) late type elevators.
[Martin Waligorski]

Late type elevators. The straight-angled mass balance horns are evident in this view.
[Martin Waligorski]