Supermarine Spitfire Mk. IX in Detail
The Powerplant

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

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Close-up of the nose housing the Merlin 60-series engine. The double-stage supercharger placed behind the engine necessitated a much longer nose as compared to the earlier single-stage versions such as the Mk. V. 

Many modellers and historians alike refer to the top the Mk. IX cowling not only being longer but featuring a raised hump on its upper side. This photo shows the very feature, but as can be seen, it is not very prominent, indeed from some angles it disappears almost entirely (compare with the previous photograph).

The origin of the hump is as follows. When the new Merlin 60 engine was mated to Spitfire Mk. V airframe, it was not only longer, but its thrust line had to be angled down a little. With the propeller axle retained at the same level as before, the rear part of the top engine block had to be tilted up and came up higher than in the Mk. V. This in turn required more space under the rear top cowling, just in line and behind the last exhaust stack. 

Actually, the author of these words believes that there were at least two different shapes of the production Merlin 60 cowling, perhaps a result of manufacturing differences between  Supermarine and Castle Bromwich factories, the two major producers of the type.
 

The enlarged carburettor intake with built-in compact Vokes Aero-Vee universal dust filter was another feature introduced on the Mk. IX. It became standard only later during Mk. IX production, but was also retrofitted to many earlier machines.

As the picture shows, the intake was equipped with a closing shutter which prevented dust ingestion when taxiiing in dusty field conditions. It often remained closed on even on parked aircraft. 
  

Front view of the port underwing radiator. The Mk. IX radiators had enlarged frontal area as compared to the earlier Spitfire marks. Both radiators were identical rather than being mirror images of each other, divided into two sections - the starboard being an oil cooler, port side being occupied by the intercooler.
 

Close-up of the four-bladed Rotol propeller. 
 

Profile view of the propeller spinner.

View of the propeller blade. The decal is a modern one of Breitling Fighters and does not come from the original manufacturer.

The division of upper cowling panel barely visible in line with the first exhaust pipe indicates that this aircraft has been originally produced at the Castle Bromwich Aircraft Factory. The Supermarine-produced machines had a one-piece upper cowling cover.
 

The Mk. IX and later Merlin-powered Spitfire versions standardised on six individual exhaust stacks shown here, but their presence alone cannot be used as a definitive recognition feature of the Mk. IX. Some late-production Mk. V also had six exhausts.

This view also shows the shape of Dzus cowling fasteners.

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