Spit IIa is now so much more inferior to the 109

[41Sqn_Banks]

Originally Posted by Kwiatek

So for Merlin III at 87 octan fuel we have:

max take off - +6 1/4 at 2850 RPM

...

So with Merlin III at 100 Octan we have:

take off - +6 1/4 at 3000 RPM

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

[Kwiatek]

Originally Posted by 41Sqn_Banks

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

Hmm interesting have you some documents with such Merlin power settings? I miss really manual ( pilot notes) for Spitfite MK1 and Hurricane MK1

[Crumpp]

from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III

It also shows maximum boost at emergency power at 12,500ft as +10.55lbs at 3000 rpm for the Merlin III when you use boost override or pull the tit on 87 Octane.

Absolutely NOTHING to do with the use of 100 Octane fuel.

[Kwiatek]

Originally Posted by Crumpp

It also shows maximum boost at emergency power at 12,500ft as +10.55lbs at 3000 rpm for the Merlin III when you use boost override or pull the tit on 87 Octane.

Absolutely NOTHING to do with the use of 100 Octane fuel.

Yep it is also interesting

[Crumpp]

Yep it is also interesting

I thought something like this might be discovered when I saw the 1937 instructions for boost cut out in the RAF Training Manual......

[Ernst]

Originally Posted by Kwiatek

Yep it is also interesting

Are the SPITFIRE FMs at UP 3.0 RC4 yours?

[NZtyphoon]

Originally Posted by Crumpp

It also shows maximum boost at emergency power at 12,500ft as +10.55lbs at 3000 rpm for the Merlin III when you use boost override or pull the tit on 87 Octane.

Absolutely NOTHING to do with the use of 100 Octane fuel.

Actually the modifications to the boost control cut out had not yet been instigated in June 1939; the modifications to the boost control cut-out were needed before the engine could reach +12 lbs boost. This is full power test proving that the engine was strong enough to withstand high boost pressures, and that relatively high pressures could be achieved on 87 Octane fuel. Once again this is a pre-war document which proves nothing germain to Crumpp's "case".

http://www.wwiiaircraftperformance.org/ap1590b.jpg

http://www.wwiiaircraftperformance.o...ol-cut-out.jpg

[Seadog]

RR was using 100 octane fuel for testing and development from 1937 onward:

Appendix IV

The Merlin and 100 Octane Fuel

Questions have been asked on the early use of 100 octane fuel and in particular on its influence during the Battle of Britain. Until 1937 the Merlin had been confined to 87 octane fuel to DTD230, because it was felt that in the event of war 100 octane. which was being developed by the Americans, might not be available to the British. This anxiety arose from the American Neutrality Act. which could prevent supplies being shipped to this country. Probably as the result of a paper by Rod Banks in January 1937, the Air Ministry agreed to proceed with engine development to take advantage of high octane fuel.

At that time the American 100 octane did not suit the Merlin because it lacked a good rich mixture response. Esso undertook the development of a suitable fuel, using 10% aromatics, and the driving force behind this was Dr Bill Sweeney whose fuel mix became known as Sweeney's Blend. Three months before the start of the war an Esso tanker Beaconhill delivered a full cargo of the special 100 octane fuel to Britain and by March 1940 the decision had been taken to switch Fighter Command to this type. Bomber Command changed over early in 1941.

The effect of 100 octane was to allow the Merlin to run at 12lb boost putting up the power of the Merlin III from just over 1000 hp to 1300 hp. However, this high power was obtained at between 8 000 and 9 000 ft and above this altitude, at a max combat power rpm of 3000, the boost and, therefore. power advantage was progressively declining. On 87 octane fuel and 6lb boost, using 3 000 rpm, the maximum power was 1030 hp at 16 000 ft. At this point on either fuel the engine was giving the same power, so above this height 100 octane fuel offered no advantage. The majority of the air fighting in the Battle of Britain was at 18 000 ft and above and the engine in most common use was the Merlin III. The gain in performance from 100 octane was entirely at lower altitudes. Before the end of the Battle Spitfire IIs with Merlin XIIs were in service, with the supercharger gear ratio increased from 8.58 to 9.09:1 giving a better full throttle height at 12lb boost and a small number of Hurricane IIs fitted with two-speed Merlin XXs. with ratios of 8.15 and 9.49:1 for MS and FS gear, these engines could take much greater advantage of 100 octane fuel and in the case of the Merlin XX were capable of maintaining 12lb boost to over 20 000 ft at 3 000 rpm, thanks to the new central entry supercharger.

This set the pattern and without 100 octane fuel the further power development of the Merlin would not have been possible. As an example the two stage blown Merlin 66 was capable of over 1600 hp at 16000 ft using 3000 rpm and 181b boost. The pioneering work of Esso to produce a suitable 100 octane fuel was the key to the high power Merlins in all spheres of operation and it was not until 1944 when 150 grade fuel became available that further advances in boost pressure to 25lb were made, allowing over 2 000 hp to be used in squadron service.

The opening paragraphs of this appendix are the result of information supplied to Michael Evans, Chairman of the Rolls-Royce Heritage Trust by Alexander Ogston, Historian of the Wings Club in New York, who has had a lifetime in fuel technology and a conversation which I had with Rod Banks shortly before his death.

The Merlin in Perspective, p87.

[NZtyphoon]

Originally Posted by 41Sqn_Banks

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

This most likely has a great deal more to do with the adoption of two speed and CS propellers; in 1938 the majority of the Hurricanes and Spitfires were still using the fixed (coarse) pitch two bladed wooden props, so the maximum allowable rpm was fixed at 2,850.

The Merlin III had the universal prop shaft allowing de Havilland or Rotol propellers to be fitted, and the availability of two-pitch and especially CS props would have allowed for higher rev limits with less strain on the engine than a fixed-pitch unit. It also makes sense that in wartime some restrictions are lifted to allow for maximum power. One of the reasons 100 Octane fuel was originally adopted was to allow greater take-off power.

[41Sqn_Banks]

The Hurricane I Pilot's Notes mention that during take-off 2850 RPM will not be achieved with fixed-pitch propeller.
IIRC the Merlin II was only able to take the DH propeller (2-pitch and later converted to CSP) and the Merlin III could take both. Some early Merlin II were not able to take a CSP at all as they didn't have a connection to drive the CSP unit. I can't remember where I've read this ...