Spitfire III - questions

[Dominik]

Hello!

Reading a few books on Spitfire I have met different informations about Spitfire Mk III.
First of all, wing span and surface. According to Caygill's book (Combat Legends) it's 9.93m. Matusiak in his book on Spitfire Mk V writes that the span was 9.30 m. Same information I found in Price's Spitfire monography (published by AJ Press in 1997). I also have Shaklady and Morgan's 'Spitfire - The History', yet there's no information about it...or maybe I have overlooked it.
Now the surface problem. What was it?
Second problem. What version of Merlin powered Spitfire Mk III during its maiden flight - Merlin X or Merlin XX?
And the last, I think, problem. What was the original painting scheme?

Thank you for every hint.

[Andy Fletcher]

Spitfire The History - Chap 12, Aerial Spies, page 241

Spitfire I (PR) Type A, later re-designated PR.III
Spitfire I (PR) Type B, later re-designated PR.III
Spitfire I (PR) Type C, later re-designated PR.III
Spitfire I (PR) Type D, initially re-designated PR.III but later re-designated PR.IV

Best Regards

Andy Fletcher

[Revi16]

This may help,
http://www.spitfires.ukf.net/index.htm

http://www.spitfiresociety.demon.co....mark.htm#MkIII

Regards,
Mike

[Graham Boak]

The Spitfire Mk.III was designed to take the Merlin XX, as this was expected to be the standard next-generation Merlin. I know of no reference suggesting the prototype first flew with any other engine, although the Merlin X was discussed for early production aircraft in the case of delayed production of the Merlin XX.

The wings were clipped by 3.5 feet of each tip, giving a quoted span of 33ft 8in. Following disappointing flight trials, the aircraft was refitted with a standard wing, but by then the decision had been made to cancel production. This was partially due to the number of changes required to fit the longer engine into the Spitfire, including changes in the undercarriage geometry, which would lead to lower production numbers. (The Mushroom Monthly book is wrong is suggesting the Mk.III was the same length as standard Spitfire.) Many of the lesser improvements suggested for the Mk.III found their way into later production Mk.Vs.

Look in Spitfire The History for a fuller history of the Mk.III.

[Dominik]

Originally Posted by Graham Boak

Look in Spitfire The History for a fuller history of the Mk.III.

I did. And there is information according to which there were production problems with Merlin XX so they decided to use Merlin X for first batch. There is no information about the engine when Spitfire Mk III was weighted for the first time. The engine is mentioned when talking about second weighing. Another information suggesting that Merlin X was installed in Spitfire Mk III is performance data at the end of the chapter which states Merlin X as the engine.

The span you sugested is ca. 10.3 metres (sorry that I use metric system) while LF versions had less than 10 meters, Spitfire is suggested to have even less than LF versions.

@Andy. Thanks for the hints but I've meant Spitfire Mk III, not PRs.

@Revi16 I know those sites. Interesting but not very helpful.

[Graham Boak]

The prefix LF applies to the engine fit, not to the clipped wings. The dimensions quoted are those in STH. They are contradictory, as 3.5 feet off each tip would give a span just under 31ft. Perhaps it should say 30 ft 8in? This is close to Wojtek's 30ft 6in. 30ft 6in is also quoted in the Harleyford Spitfire book, and in Price's Spitfire Story. Given that the Spitfire was built in Imperial units, conversion to metric simply introduces an additional source of error. Perhaps the answer is to draw out the wings and determine which span gives the correct wing area, which appears to be consistently 220 sq ft.

STH does not specifically say what engine was installed for the first flight, but does say that it was delayed because supply of a new DH propellor was delayed. A new propellor suggests a new engine. The reweighing was with a Rotol propellor, which may (or may not) have been sufficent reason. However, the Merlin X is not a standard Spitfire engine anyway. The text here is again contradictory. It talks of the desired engine being the RS 2M (P.127) Merlin XX. P.132 describes the RS 2M as the X, and the RS 3M as the XX.

Perhaps we need a definition of just what a Merlin X was before attempting to judge which of the contradictory statements is an error. The Merlin X was the 2-geared engine in the Halifax Mk.1, rated at only 1130hp for take-off compared with 1175 for the Merlin XII in the Spitfire Mk.II. If so, the performance of any interim Mk.III could only be disappointing, and it is not clear how the figures quoted on P.132 can apply to the aircraft fitted with a Merlin X. Or barely to the Mk.III at all.

A delay for production engines may not imply a delay in delivery of a prototype, but it is an interesting idea.

[Dominik]

Originally Posted by Graham Boak

The prefix LF applies to the engine fit, not to the clipped wings.

I now that, but I used it as a mental shortcut.

Originally Posted by Graham Boak

Given that the Spitfire was built in Imperial units, conversion to metric simply introduces an additional source of error.

I try to be as precise as possible, althoug it won't be 100% accurate.

Originally Posted by Graham Boak

It talks of the desired engine being the RS 2M (P.127) Merlin XX. P.132 describes the RS 2M as the X, and the RS 3M as the XX.

And I still don't know which is which. Unfortunately I don't have any books on the British piston engines.

[Graham Boak]

You can be equally precise in Imperial or metric, and having used both professionally I prefer SI, but once you start converting from one to another you are losing precision not gaining it, plus running the risk of introducing error. For aircraft designed in Imperial it is more precise to use the Imperial. And vice versa, of course.

I have a small number of such books, but I don't think any of them extend to this detail. The RR Heritage Trust would be the best place to ask for help. I have their initial book on the wartime Merlin: I tried looking for it before answering last night but it seems to have gone into hiding.

I have come across a reference to the Hurricane being tested with an RS3M or Merlin VIII. Ho hum.

[Kutscha]

In the list of engines used in the Spitfire, S:TH has:

Merlin X - RM1SM (2 speed)
Merlin XII - RM3S (1 speed)
Merlin XX - RM3SM (2 speed)

Is that a typo error for the Merlin X?