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I am confused a bit here, Merlin XX or just X ?
Main differences are the XX and the Hooker designed inlet elbow on the supercharger, different carburetor, and different gear ratios.
Main difference between the X and III is more power down low just as the main difference between an XX and 45 is more power down low.
Did this graph up a while ago, Spitfire curves are from (what I believe to be) an RAE document, and the Hurricane curves are from A&AEE flight tests. Climb data was also given and the Merlin 45 climbs were better for both aircraft. Hurricane '45' was a converted Mk.I airframe.
What was different about the Spitfire II that gave such great difficulties in production vs a Spitfire I?
A number of Spitfire Vs were re-engined Spitfire Is and IIs and a few Spitfire IXs were modified Spitfire Vs, A least one Spitfire MK IX may have started life as a Spitfire I?
Or was it a case of the Factory assigned to build the Spitfire II was having troubles producing anything and would have produced NO MORE Spitfire Is in the same time period?
Did this graph up a while ago, Spitfire curves are from (what I believe to be) an RAE document, and the Hurricane curves are from A&AEE flight tests. Climb data was also given and the Merlin 45 climbs were better for both aircraft. Hurricane '45' was a converted Mk.I airframe.
There were problems getting the Nuffield (Castle Bromwich) Spitfire II into production but the Spitfire I was no great shakes for production either. In July (June 22 to July 27)1940 166 Spitfires were produced of which 143 were Mk Is. In the same time frame 322 Hurricanes were produced.
The Hurricane/45 data seems to indicate that the engine was being run at 2850rpm, hence the low FTH. Hawker data (via Mason) shows that the initial performance data for the HHIIA was also at 2850rpm as speed was 342 at 17,400ft while the prototype managed 348 at 17,500ft.
It doesn't really answer the question. Castle Bromwich may have had trouble getting ANY version of Spitfire into production ( or even the Hurricane) until management was changed.
What were the differences between the MK I and MK II Spitfire that make the MK II harder to build?
Here's the Hurricane IIa inserted into Greyman's chart:
The Hurricane/45 data seems to indicate that the engine was being run at 2850rpm, hence the low FTH.
The problem seems to have stemmed from the complex nature of the Spitfire airframe and the resulting difficulties in placing it into mass production.
The RAE Hurricane IIa/IIb data you referenced is from the A&AEE flight test I have in the chart - but with a new, updated position error correction figure. While the updated RAE figures may be closer to to the aircraft's actual speed in reality and a better indication of its performance compared to other aircraft - it doesn't invite a direct comparison to the Hurricane '45' figures, which still use the old PEC figure.
Since the RAE never calculated the A&AEE Hurricane '45' figures with the updated PEC, I charted both original tests with the old PEC for a direct comparison.
Whoops, good eye. I accidentally put three plot points 2000 feet too low and it messed with the Hurricane '45' curve. Image updated.