Improvements to the Spitfire

[Mike Williams]

Now that we're at faster Spitfires - is there a firm performance data on the Merlin-powered PR variants?

I have these:

Spitfire PR Mk.XI MB.789 (Merlin 63) - Level speed performance

Spitfire PR XI Aircraft Data Card (Merlin 70)

 

[stona]

Think that we can agree that Spitfire's basic design offered far more than sometimes was taken advantage of, whether that are categories of performance, or range/radius.

Definitely. Sometimes war time expediency precipitated decisions which curtailed promising developments, as with the Mk III and sometimes prejudice and bad decisions did the same, the issue of range has already been mentioned. Thankfully the latter was rare. The former was pragmatic and usually justified.

I can't think of any two aircraft apart from the Spitfire and Bf 109 which underwent such substantial development between 1939 and 1945 and remained 'at the sharp end' of air combat for so long. Neither was ever substantially out classed in that time period. It is a testament to the inherent design characteristics of both. Some wrong turns were taken in both cases, but overall a reasonable job was done with both.

Cheers

Steve

 

[tomo pauk]

The demise of Mk.III was a result of a half-harted effort.

 

[pbehn]

Laws of physics were firmly with Spitfire's (Shenstone's actually?) choice of thin wing, that made possible good turn of speed even on moderate power. When Spitfire ended up a bit slower than expected, it was due to small details that added up - like external windscreen instead of internal, draggy type of antenna installed, protruding cannon barrels, not fully covered U/C, use of 6 exhaust stacks vs. 12, obsolete carb, unfaired rear mirror, sometimes sloppy fit finish etc.

All of these things were eventually adressed from late 1942 on, it was too bad that Mk. V was the worst offender in here, just in time the LW upped up the bar with their 400 mph fighters from second half of 1941. The Spitfire V was capable for 400+ mph, the Mk XI for 440+ mph (as fast as Merlin Mustang), as can be seen in the document provided by Aozora.

I was thinking more about power output, if it was known what the Merlin and the later Griffon were to produce then I dont think that 2000BHP 24 cylinder fighters (Typhoon) would have been given the go ahead, the gain in power barely compnsates for the increased weight, frontal area, complexity and cost . Not wishing to derail discussion of the Spitfire on the thread but the Typhoon and its Napier/Vulture engines play a part in it. The Typhoon when eventually introduced was faster than the FW190 but ran into its own problems which werent really sorted until end of 1942, this was behind some of the to and fro decision making on the Spitfire. The introduction of the Bf109F and the FW 190 were one side of the story and the fitful development of the Typhoon was another. In the end the RAF ended up with the Tempest and Spitfire which had complimentary qualities.

 

[stona]

The demise of Mk.III was a result of a half-harted effort.

Things just don't move as quickly as we would always like, particularly when the war is demanding other priorities.

Cheers

Steve

 

[Aozora]

Here is a report from 1940, courtesy of the late Edgar Brooks, describing how to improve the paint finish of the Spitfire; it's often assumed that the RAF fighters all had a matt finish in 1940.In fact the "Type S" finish was adopted quite a lot earlier than many modellers realise. Also attached is another report from 1942, plus some instructions from the RAAF on maintaining the Spitfire's airframe.

 

[stona]

Great stuff, never seen that RAAF stuff before.

As a model builder who has always resisted the tendency in the last twenty years or so to make aircraft models looking like patch work quilts it is always reassuring to know the lengths to which people went to ensure that the originals didn't look like that either.

Cheers

Steve

 

[Aozora]

Great stuff, never seen that RAAF stuff before.

As a model builder who has always resisted the tendency in the last twenty years or so to make aircraft models looking like patch work quilts it is always reassuring to know the lengths to which people went to ensure that the originals didn't look like that either.

Cheers

Steve

Thanks Steve; it looks like Supermarine (along with most other aircraft manufacturers) were constantly having to enforce consistent standards of finish. The RAAF material can be found online at the National Archives of Australia http://recordsearch.naa.gov.au/SearchNRetrieve/Interface/SearchScreens/AdvSearchItems.aspx Unfortunately, because it's part of a much larger collection of Spitfire documents I can't remember exactly where I found them; look under "Spitfire", check "digital copies only" at the bottom of the screen and it will list 250 sets of documents: chances are the papers can be found under A705 9/53/1 PART 1 DTS [Directorate Technical Services] - Spitfire Aircraft - general defect file

or

A705 9/41/74 Spitfire aircraft - general technical file

Note: Rubbing down the Spitfire was hard work - no power buffers here!

 

[stona]

I hope your National Archives are better organised than ours! It can be fun finding odd stuff in odd files, but I'm still waiting for hard copies of some stuff I ordered a week before Xmas.
Cheers
Steve

 

[tomo pauk]

Not really on how to improve, but this might cover 'whys' and 'hows' regarding the choice of planform profile of Spitfire's wing: link.

Also gives a probable clue on why Hawker's design team chose thick wing for Hurricane and Typhoon/Tornado.

 

[stona]

I'd recommend 'Secrets of the Spitfire- the story of Beverley Shenstone the man who perfected the elliptical wing' by Lance Cole, the book referred to in Ackroyd's piece. It devotes much time to Shenstone's time at Supermarine but also his time before at Junkers and working with Lippisch as well as his later illustrious career.

Also consider 'Spitfire's Forgotten Designer- the career of Supermarine's Joe Smith' by Mike Roussel. Less detail about the Spitfire but a better overview of the men and organisation that built it.

I've just dug them both out of my library and shall be giving them a look over, particularly the Joe Smith volume.

Cheers

Steve

 

[stona]

I just came across this from the late Edgar Brooks regarding the Spitfire III. It may cast a little light on what was needed to change production to it rather than the V.

"The XX-powered Spitfire III needed a redesigned engine compartment, strengthened fuselage, extended engine bearers, strengthened and extended (forwards) u/c, and, after all that, its top speed still didn't reach 400 mph."

He doesn't even mention the new radiators.

Cheers

Steve

 

[tomo pauk]

Thank you.
Do we know what modifications were involved when Mk.II become Mk.IIc once the Merlin XX was fitted, the Mk.IIc used by Coastal Command?

 

[stona]

I thought the IIC was an air sea rescue conversion of a standard Spitfire II (A or B).
Cheers
Steve

 

[tomo pauk]

Yes indeed, powered by Meflin XX.

 

[stona]

Yes indeed, powered by Meflin XX.

Really? I've never read that. The conversion was usually done at a maintenance unit, not by Supermarine or Rolls Royce, so I very much doubt it involved a change of engine. 39 Maintenance Unit converted several Spitfire IAs to my knowledge. Were the Merlin XII and XX easily interchangeable? I doubt it! Someone who knows more about the engines might know.

Cheers

Steve

Okay, Alfred Price writes "...in 1943 some 50 Mark IIs were fitted with the more powerful Merlin XX engine and operated in the air sea rescue role as the IIC." I don't know what his evidence is, I've never seen a change of engine in the IIC specification, but I'll take his word for it. I don't think an MU changed the engine, probably just fitted the ASR equiment, modified the flare chute etc.
As it is only 50 aircraft and in 1943 I don't suppose whatever work was involved had any effect on overall production. The Spitfire II wasn't exactly a front line aircraft in 1943.

 

[tomo pauk]

Such Mk.II is also mentioned by Morgan Shacklady.

 

[stona]

Such Mk.II is also mentioned by Morgan Shacklady.

With the Merlin XX? I never noticed

Cheers

Steve

 

[LisaM]

With the Merlin XX? I never noticed

Cheers

Steve

Yes it was aimed at 400mph and reached, with an early Merlin XX (and low boost), about 380MPH (roughly a MK V but with better mid/low altitude performance) . 400 would have been reached with the later 20 series Merlins and the higher boost levels..

The key thing was tidying the parasitic drag, windscreen about 5mph, radiators at least another 5-10mph and so on. Little bits all adding up.

Check Mike Williams site about the Crossbow efforts, even just cleaning up the leading edge paintwork and filling in gaps added 10mph to just about every plane they worked on (Spit, Mustang, Tempest, etc)..

The Mustang's better speed on the same engine power was 66%-75% radiator and 25%-33% better detail efforts and quality control.
The Mustang needed 300bhp for the same speed, NA's own figures showed they radiator gave them, at least,. 200bhp of that.

The Spit III's better radiator was mostly a better position, further forward into less turbulent air and hence more efficient, the photos show that very clearly, bit deeper too.

 

[stona]

The British were worrying about the finish on their high speed aircraft from the earliest days of the war. I have copies of various circulars to the Resident Technical Officers in early 1940 impressing on them the need for a smooth finish, particularly when the 'Type S' paints were introduced.
What does seem amazing is that the filling of butt joint and rivets that run along the leading edge of a Spitfire wing (as well as paying particular attention to smoothness back to 20% of the chord of the wing and rubbing down of the undercoat) were not introduced until 1942. The meeting here was in August '42.

Cheers

Steve