Supermarine Spitfire Mk. IX in Detail
Wing & Undercarriage details

n by Martin Waligorski
n photos by Martin Waligorski, Mattias Linde and Phillip Treweek

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The wing root fillet with solid leading edge visible here was not common for all Mk. IXs. Early production batches powered by Merlin 61 and 63 series engines had a relatively large circular air intake there serving the fuel cooler, a device used to prevent the fuel from boiling at the relatively high climbing speeds of the new fighter. The fuel cooler installation was identical as on the previous Mk. VII high-altitude version. It is not a widely-known feature as it was later removed and none of the surviving Mk. IXs seems to have it retained. 

In the same spot, earlier Spitfire marks had a smaller opening for a  gun camera.  Because of the fuel cooler installation, it was initially omitted altogether on Mk. IXs, and later on moved to the starboard wing fillet.
  

Close-up on the rear part of the wing fillet. Note the different style of riveting compared to that on the fuselage.
 

The streamlined fairing of the wing-mounted Hispano cannon.

In the initial production, all Mk. IXs were equipped with the "C"-type wing. This wing could carry both cannon and machine gun armament, and is often associated with four protruding cannon barrels often seen on the Mk. VC. However, because of the weight restrictions caused by the use of the more powerful - and heavier - engine, the Mk. IX could not carry the full complement of four cannon, and all production machines were equipped with two cannon (located in the inboard bays) and four machine guns.

The abandonment of four-cannon option on the Mk. IX had two consequences. First, the "leftover" wing cannon mount resulted in the short stub outboard of the cannon barrel, plugged with a solid rounded tip.  Later on, as it has been realized that the the second cannon bay will never be used, the stub was removed altogether, as seen on this photograph.

The second consequence was the shape of the upper wing blisters. These blisters were introduced to provide sufficient room for the ammunition drums of the Hispano cannon. Initially the "C" wing used a single wide blister covering the twin cannon bay. As it was realized that only one cannon was necessary, a new blister was introduced to the Mk. IX production line. This blister was narrow and elongated, and can be seen on the wing photograph in  The Airframe section of this essay.

Still later, the wing was modified to the "E" type. Structurally, this was identical to the "C" wing, but adopted to carry two 0,50" machine guns in place of the four 0.303" Brownings.
 

The Pitot tube was mounted under the port wing tip.

The initial production Mk. IX had the same undercarriage as the Mk. V and earlier marks. This early type is recognizable by five-spoke wheels and perfectly flat undercarriage covers.

The above photograph  shows the mid-production type of undercarriage, which was an entirely new construction. The main legs were not only strengthened, but also raked forward at a steeper angle to counter the increased nose weight.  The new four-spoked wheel featured a larger tyre. 

Towards the end of the war,  production shifted to three-spoke wheel which can bee seen on many late marks of the Spitfire.

Another new detail of the updated undercarriage leg was a forward-facing scissor link over its oleo part -  barely visible here behind the wheel cover. Also the covers differed from the earlier marks, having a distinctly bulged appearance, necessary as the thicker tyre could no longer fit into the thin wing when retracted.
 

A peek into the starboard wheel well, showing the compact undercarriage retraction mechanism.
 

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