Inaccurate performance data for BOB fighters in COD comparing to RL data

[lane]

When using emergency boost pressures in excess of 6.25 lbs/sq.in. 100 octane was required, therefore if a pilot recorded use of emergency power it necessarily follows that the aircraft was fueled with 100 octane fuel.

Operational Notes for Pilots on Merlin II and III, January 1939 (thanks 41Sqn_Banks)


Pilot's Notes, Merlin II, III and IV, 4th Edition, April 1940, page 6.


Spitfires were cleared for use of 100 octane fuel for improved take-off in September 1938 just a month after the introduction of the type into service.



By 12 December 1939 100 octane fuel was approved for Spitfires, Hurricanes and Defiants.
100 Octane Fuel - Issue of.

[pstyle]

seems like all you needed was a new set of plugs and a ground test to check smooth running when using the 100 too...

Sounds contradictory to the more doom-and-gloom scenarios presented by some thread participants...

[Crumpp]

The RAF training manual quote only mentions the use of boost control cut-out to obtain maximum permissible take-off boost.

That is true.

What does it have to do with the fact the system was used before 100 Octane was an issue?

If this is true, this renders the whole 100 octane debate obsolete as pilots would simply use the increased power if necessary independent of the used fuel.

Right. From the certificate we see that a higher boost above +6 1/2lbs was available using the system on 87 Octane.

We also have Operating Note instructions in the General Operating Notes that allow for its use.

I bet Dowding did see a large increase in motor failures.

[Crumpp]

seems like all you needed was a new set of plugs and a ground test to check smooth running when using the 100 too...

You really don't need to do anything to the engine to run 100 Octane fuel. The engine was made for 87 Octane and can run a higher knock limited performance fuel without penalty.

100 Octane has a higher lead content so changing plugs to one that are more resistant to fouling is not a bad idea.

The engine will not see any performance gains of the additional knock limited performance without modification as instructed by RAF. Those instructions to gain that performance benefit represent major modifications and inform when those major modifications where done. Those instructions have been posted ad-nauseum in this thread.

[bongodriver]

Just out of interest...did anyone realise the use of 'boost cut out' is only authorised for use in combat 'if' 100 octane fuel is used?, this shows that 'any' combat report showing the use of boost in combat confirms the use of 100 octane.

[JtD]

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.

[bongodriver]

Originally Posted by JtD

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.

[Crumpp]

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 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.

[JtD]

Originally Posted by bongodriver

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.