Spit1a > SpitII

[Kurfürst]

Originally Posted by winny

Thanks for the link, I'll get in touch with Kew and see what the score is..

I get to the UK regularly and visit the archives and photograph AVIA files. I will visit the archives in a week or so and look up these files.

Thank you for that, both of you. I guess most of us would be greatly interested in your findings, as you seem to be honestly curious about the truth behind the matter, just like I am. Frankly people so far only seem to have been interested in putting forward snippets, and curiously their story just 'cuts' after May 1940, which I find somewhat suspicious because of the findings of that Australian reasearcher I already quoted, and the tanker situation that appears to be recorded by most authors (Blair, Morgand and Shacklady etc.).

I'm starting to think this 100 octane issue is just one factor in the speed issues.

I suppose we'd need to know what the serial of the Rechlin MK1 was, when it was captured and what condition it was in and it's age. It could have been knackered!

One can try his luck with Morgan and Shacklady's serial number listings, perhaps somthing turns up. However I was checking into my files, and found a German document of a captured Spitfire II and tests done with it - albeit with a Merlin III which would pretty much make it a Spit I.. though I'd believe that they coulnd't capture this example earlier than 1941. What is interesting though that they make a comparison between the Spit I and II, and list the Spit I with 87 octane and 2 bladed wooden (fixed) propeller, which is indeed true for the initial few dozen, and the Spit II with CSP and 100 octane. I don't think much should be read into it though, given the uncertainities. Whatever its worth, they measured the Spit II/Merlin II to be good for 547 km/h, and then 557 km/h in a later test run, at 5km. Speed at 0 m alt. was 460, which would indicate +6 1/4 lbs.sq.inch boost.

I was reading an account yesterday by Pete Brothers (It might have been Tom Neil!) and he took the mirror off his Spit and fitted a car mirror inside the cockpit, he reckoned he gained 4mph, he also spent his time when on standby filing down rivet heads which he reckoned gave him another 4 or 5 mph.
I also read a guide to the groundcrew reminding them that battered bodywork and poorly fitted fairings could cost as much as 10mph.

Indeed its true, I have a UK report of Spitfire drag changes during the war, and the effect of serial production on performance. The mirror looks just about right, and its often the most unlikely items that cause the most surprising amunt of drag - cannon stubs, external arm. windcreen and even the internal one for example.

It's a minefield really, the Brits, French, Russians and Germans all tested Mk1 spits and none of them came back with the same top speed..

Yes, that's why I don't like to draw guesswork form relative test reports. For example Kwiateks observation about the relative speed difference of 109 and Spit are entirely reasonable, and I tend to believe myself that they probably captured and tested the said Spit with 87 octane in Rechlin. It probably neither had the fuel nor the mods at that time when captured yet.. also when you consider differences in invidual airframes, engines, day temperatures.. the margin of error just becomes too great. For example, manufacturers gave some + or - 5% tolerance on speed. That means we already have an anout 50 km/h margin of error. You can never know if it was a poorly made Spit (109) compared to a exceptionally well made 109 (Spit), how many hours were logged into the motor and so on..

BTW I did a bit of a comparison table of FC's sorties vs. the amount of 100 octane and 'other' (ie. 87 octane) aviation fuel issued during the month. Its interesting.



A few of my own observations:

a, It seems clear that 100 octane has begun replacing 87 octane towards the end of September / start of October. Until then, 87 octane is by far the major fuel consumed.
b, This corresponds with what the Lord Beaverbook memo noted about re-starting the conversion
c, Its also very appearant that issues have a bit of 'delay' built into them. Obviously supply's nature is that they re-supply after the fuel at the airfields has been used and there's reported need for new issues. This takes time.
d, 100 octane issue curves are clearly responding to FC sorties number increase/decrease. Though that's not news, FC used that fuel. But it should be kept in mind that number of Blenheim Sqns also used and were issued 100 octane fuel, and a Blenheim sortie would consume 4-6 times the fuel a fighter sortie would.
e, On the other hand, 87 octane issues ALSO clearly reacts to FC sorties number increase/decrease. It shouldn't, if all frontline Sqns would be using only 100 octane.
f, Obviously the 87 octane curve reaction is less pronounced, as
fa, A good percentage of FC used 100 octane, so they don't their needs 'do not exists' from the 87 octane issues POV
fb, A large number of other aircraft also uses 87 octane, and many of them - bombers, patrol craft etc. - consume much more fuel than small fighters.

In my opinion, the most conclusive evidence that even towards the end of October a number of fighter squadrons were flying on 87 octane is evident by the sudden and perfectly parallel rise of both 87 octane issues and FC sorties curves at the time.