Official Fulqrum Publishing forum - Inaccurate performance data for BOB fighters in COD comparing to RL data

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Quote:

Originally Posted by JtD (Post 426499)

The automatic boost control cut out was intended as a emergency measure in case of automatic boost control failure, as 41Sqn_Banks post already indicated. This would be valid independent of fuel used. The procedure would be to cut the throttle, activate the cut out, and reopen throttle until the desired boost is reached. From then on, changes in speed and altitude would cause a change in boost, which could be controlled by change of throttle or engine rpm (supercharger rpm).

The use of as an emergency boost increase was a later practice. However, unless a report makes specific mention of abc failure, there's absolutely no reason to believe it was activated for anything but a 12lbs emergency boost any time 1940 or later.

This exctract of pilots notes from NZTyphoons post seems explicit on fuel type.

Quote:

The can of worms was openend by the RAF General Pilot's notes authorizing the pilot to have the option to balance his risk.

It's use would also have to be recorded as it would be obvious to anyone who examined the aircraft controls.

There is no way to tell if a pilot using it was linked to fuel.

Quote:

Originally Posted by bongodriver (Post 426512)

This exctract of pilots notes from NZTyphoons post seems explicit on fuel type.

I think this is purpose related - boost control cut out in order to increase performance. The boost control cut out as an emergency item has always been available, at least I haven't seen anything indicating Hurricanes did not have the cut out even when 100 octane fuel wasn't around. The March 39 pilot notes say that "it is intended for use should the automatic boost control fail in flight or should it be necessary in an emergency to override the automatic control for an increase of boost". First purpose would be there even if 87 octane fuel was used. I haven't seen earlier pilot notes.

So how exactly does it function? if it's a boost cut out control override how does it help if the boost cut out control has failed, surely a failed ABC is kinda overriden anyway?

Quote:

Originally Posted by bongodriver (Post 426541)

So how exactly does it function? if it's a boost cut out control override how does it help if the boost cut out control has failed, surely a failed ABC is kinda overriden anyway?

A failure of the the boost control influences the opening of the throttle valve. Thus the boost can get dangerously low or way to high. The boost control cut-out gives the pilot direct control over the throttle valve.

Quote:

Originally Posted by Crumpp (Post 426535)

So tell us all Crumpp, how did the RAF manage to consume 52,000 gallons of 100 Octane fuel if only a select few frontline fighter units were supposed to use it? Are you going to tell us it wasn't actually consumed but went into and administrative black hole because it wasn't actually 100 octane fuel (recognised because it was green and smelled funny) but converted back to something else and poured back into reserves was it?

What exactly was your explanation and please don't tell me to go back in the thread and look because I know you have never explained this properly.

Considering those test certificate shown earlier (one issues back in '37) clearly stating that the test engines, even using 87 octane fuel was capable of over 10 1/2 lbs boost at 3000rpm and would give about 200 extra horsepower (at the expence of engine wear and possible failure at some point) at those settings, is there any wonder that in combat situations some of the pilots would try to use it?

Even going so far (before the official modification and the introduction of 100 octane fuel) as modifying their boost cutout controls with match sticks to obtain that extra performance.

I'm sure it was the same for pilots on both sides of the Channel.

Quote:

Originally Posted by Skoshi Tiger (Post 426711)

No, the engine couldn't run at 10.5lb boost with 87 octane fuel. The story about the pilot modding his engine with a match stick pertained to a Merlin III using 100 octane fuel and an unauthorised mod to obtain 16lb boost at low altitude Here's the some info on the use of 100 octane for development at RR:

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

Quote:

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.

as has been pointed out the boost over-ride needed to be modded to allow for greater than 6.25lb boost, and this was only done when 100 octane fuel was used.

Quote:

Originally Posted by Seadog (Post 426769)

as has been pointed out the boost over-ride needed to be modded to allow for greater than 6.25lb boost, and this was only done when 100 octane fuel was used.

This is not correct. In the unmodified condition there was no restriction of the maximum boost when the boost control cut-out was used, thus the boost could be increased to about +17 lbs at full throttle at sea level.

See:
http://forum.1cpublishing.eu/attachm...1&d=1337242614
http://www.spitfireperformance.com/spit1-12lbs.jpg