Back in 2011 I got excited about building a Spitfire F MK III. Why? It’s a unique mark that is as unique as K5054 or the Speed Spitfire (K9834). It also marks the transition from the early Mk I/II series to more significant Spitfires that came later -- The Mk IX/XVI and ultimately the Griffon series. Many improvements developed for the Mk III were implemented on these later variants.
In my first post on the subject, I summarized my understanding (at the time) of these airframes. Attempting to model the radiator as a first step, I stalled when I began to learn more details and ultimately other projects came to the fore. Sounds familiar...
What I think I know today
References: Britmodeller Forum 1, Britmodeller Forum 2, Spitfire the History
Prototype only, 2 examples built.
N3297 was originally to be a Mk I, but the serial number was allocated as a “Superiority Spitfire” and built to the initial Mk III configuration with a Merlin XX engine. It was tested by 11 Group Fighter Command to late June, 1940. From September to February 1941 it was modified and tested in a second configuration based on 11 Group feedback with a standard wing. Then from March to September 1941 it was modified yet again with a Merlin 61 engine and later became the Mk IX prototype.
Configuration 1:
- Merlin XX engine
- Lengthened cowl (4")
- Short span "a" wings (cut to rib 19, not just removal of tip)
- de Havilland prop, 11' diameter
- Retractable tail wheel
- Main landing gear covers (similar to K5054)
- Speed Spitfire (K9834) oil cooler
- Speed Spitfire (K9834) radiator
Some key notes on this initial configuration. While I’m confident of the Speed Spitfire oil cooler, there is only a passing reference to use of the Speed Spitfire radiator in StH, Supermarine noting its use, already, in the Speed Spitfire. In parallel to initial construction of N3297, the Speed Spitfire was flying with a modified Merlin and a cooling system greatly modified (enlarged) from the existing Mk I. Since Supermarine and Rolls-Royce both knew the Merlin XX would need greater cooling it stands to reason they would use their experience with the Speed Spitfire as the starting point. What amplifies this thought (theory really) is their obvious use of the oil cooler developed for the Speed Spitfire.
While the larger radiator on the Speed Spitfire is deeper, and contains an interesting contour, no photo exists of it actually installed on the Mk III. Debate favors a more radical design with boundary layer splitter, however I believe that to be a later development, more probably during her second configuration (if then), and possibly on W3237 only.
Secondly, StH refers to 4 different props considered for the initial configuration, but specifically states the DH prop as configured when tested. Some contend the Rotol prop was used during this testing, but StH clearly states the Rotol was installed when N3297 was rebuilt.
Configuration 2 (as configuration 1 but with):
- Standard "a" wings
- 3 Blade, Rotol constant speed prop, 10' 9" diameter (Mk V standard)
- "New" radiator (not much detail on this)
Of particular note this reconfiguration was in direct response to Fighter Command’s preference for lower wing loading (they did not like the short span wings). StH makes it clear the radiator was also changed, but to what configuration is not clear. In parallel to W3237 (Spring 1941) StH discusses radiator testing, but it is not clear if that is on W3237 alone or additionally on N3297 (which by Spring of 1941 had gone to Rolls-Royce for another rebuild with the Merlin 61).
Configuration 3 (as configuration 2 but with):
- Merlin 61 engine (I believe length now 31' 3.5")
- Individual ejector exhausts (fishtail)
- 4 Blade, Rotol prop, 10' 9" diameter (Mk IX standard)
- Radiator probably of Mk XII type, but may have been one of the designs tested on W3237.
At this point N3297 is beginning to look more like a Mk VIII or IX, and is considered the prototype Mk IX by early 1942. There is never any mention of N3297 getting Mk IX type radiators, so my theory is that while testing of radiators on W3237 was ongoing, eventually something that may have looked like the deeper Mk XII radiator may have been installed. To underscore this theory, the Mk IV (Griffon prototype) had morphed into the Mk XII prototype by this time (via a short stint as a Mk XX) and probably enjoyed the same developments in the radiator.
W3237 was similarly taken from Mk V production and built to take the Merlin XX engine, being delivered in June 1941. Eventually this airframe tested a number of technologies, resulting mainly in radiator configurations, canopy/windscreen configurations and the "c" wing design. Apparently it was delivered with a "c" wing. Essentially it's configuration was basically a Mk Vc but with a longer cowl (4"), and depending on date could have had short, standard, or long span wings, Mk V windscreen or rounded windscreen, early Mk V or later bulged canopy, and most critically various radiator configurations.
Since W3237 was used extensively for testing well into 1944 or even later (like N3297) I believe her radiator probably stabilized on a Mk XII design as well. So that by sometime in 1942 she looked like a short nosed Mk XII with standard rudder and Merlin XX engine.
Paint schemes
For some reason Morgan & Shacklady, in StH, decided to note the color of N3297 in Spring/Summer 1940 as “egg shell”. Additionally, they included a color profile of yellow topsides and black/white wings on the undersides. While an interesting scheme it defies logic. Besides not knowing the shade of “egg shell” (although my wife knows!) it is inconceivable that a Spitfire with 11 Group would be painted yellow on its topsides in 1940 when no other aircraft (besides trainers) would have been painted thusly. “Egg shell” probably refers to the finish (smooth) not the color.
Debate seems to agree the more likely scheme during Spring/Summer 1940 for N3297 was the standard Fighter Command scheme of Dark Earth/Dark Green topsides over Aluminum undersides, but with Night/White wings.
When rebuilt in the Fall 1940, agreement is around a Dark Earth/Dark Green topsides over Yellow undersides. By the end of 1941, N3297 was likely in Dark Green/Ocean Grey over Yellow, with a yellow P in circle behind the roundel.
Thanks for reading...
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