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

[Crumpp]

I doubt it would be just as likely.

Ok, your opinion is noted. What do you want me to do? Agree with you when I know it is not the case?

Overstress an engine and it might fail then and might fail later. The point being, it will fail and its life is significantly shortenend.

That memo is telling the pilots of the RAF that reality. Overstress the motor and it will fail. There is a good reason why it was a requirement to log the use and have the motor inspected to ensure some reasonable life was left in it.

[Crumpp]

I hope you guys are aware that the line "Emergency 5 mins.max." is related to "95°C" oil inlet temperature?

I know that banks.

The 1937 RAF training manual amends the RAF old definitions for engine ratings.

The only difference is the 1937 RAF Training Manual list's the system for take off purposes.

Chap II
75. Supercharged engines fitted with automatic boost control embodying an override for the take-off at maximum permissible boost, may have a separate control for for the override, or use the mixture control with a gate, or have a gate on the throttle for the same purpose. This override is invariably inter-connected with a mixture enrichening device on the carburetor, to suppress detonation.

[Crumpp]

One can see that the power figures were not pulled from a chart given the differing powers obtained:

There you go, they are testing the engines on a bench at boost over-ride on 87 Octane.

Everything in aviation related to the airworthiness is tightly controlled and must be specified. The Air Ministry documents the standards and conditions they expect their pilots to use down to the point of defining the standards they expect if a pilot violates the airworthiness standards in an life threatening emergency.

The RAF instructs its pilots to balance and evaluate risk before taking the risk of moving outside of the airworthiness instructions. From 1937 on, they are able to use boost override.

Without the specific mention of using +12, an anecdote that makes any reference to boost override, pulling the tit, boost cut out, or anything other term related to the system is irrelevant to the use of 100 Octane.

[lane]

This is what Dowding said about pulling the plug, boost cut out and +12 lb boost:



This is what the pilots were doing when Dowding wrote the memo.

P/O Bob Doe, 234 Squadron


Geoffrey Wellum, 92 Squadron


P/O David Crook, 609 Squadron, 30 September 1940


P/O K. W. MacKenzie, 501 Squadron, 5 October 1940



In many cases pilots would note use of 12 lbs boost or emergency power in conjuction with pulling the plug/tit, thereby establishing a direct connection between the various expressions related to emergency power.

P/O John Bushell, 151 Squadron, 18 May 1940


F/Lt. I. R. Gleed, 87 Squadron, 18 May 1940


F/Lt. I. R. Gleed, 87 Squadron, 19 May 1940


P/O R. P. Beamont, 87 Squadron, 15 May 1940


P/O F. B. Sutton, 56 Squadron, 18 May 1940


P/O Roger Hall, 152 Squadron, 4 September 1940


P/O G. Page, 56 Squadron, July 1940


In some cases, in different recounting of the same event, the pilots mentioned +12 lb. boost and boost cut-out/emergency interchangeably:

P/O Colin Gray (NZ), No. 54 Squadron, 25 May 1940


P/O Colin Gray (NZ), No. 54 Squadron, 25 May 1940



F/LT Brian Lane, 19 Squadron, 26 May 1940


F/LT Brian Lane, 19 Squadron, 26 May 1940

[Glider]

Originally Posted by Crumpp

Without the specific mention of using +12, an anecdote that makes any reference to boost override, pulling the tit, boost cut out, or anything other term related to the system is irrelevant to the use of 100 Octane.

Unless they are one of your 16 squadrons, after all, how can you prove they weren't. As I mentioned before following your logic they probably were.

[41Sqn_Banks]

Originally Posted by Crumpp

Without the specific mention of using +12, an anecdote that makes any reference to boost override, pulling the tit, boost cut out, or anything other term related to the system is irrelevant to the use of 100 Octane.

The RAF training manual quote only mentions the use of boost control cut-out to obtain maximum permissible take-off boost. In case of the Merlin II/III this boost is +6.25 which is obtainable without cut-out.
The maximum permissible boost with 87 octane is documented since 1938 to be +6.25 and since January 1939 it is documented that in excess of this boost 100 octane must be used. The later documents are perfectly in line with the regulations.

This leaves the following explanations for the mentioning of use of boost control cut-out:
a) there was a failure in boost control and the cut-out is used to maintain a boost below +6.25, this doesn't provide any information about the fuel used as it could happen with 87 octane or 100 octane.
b) a boost in excess of +6.25 was used, either for take-off or combat/emergency, this is a proof for the use of 100 octane fuel or the proof for violating the maximum permissible boost.
c) a boost below +6.25 was used and the boost control was disabled without any logical reason and this boost was kept manually by the pilot below +6.25. Again no indicator for the fuel used.

Reason c) is highly unlikely as this would be a violation of the handling guidelines outlined in RAF Flying Training Manual ("This must only be used in emergency and not, in any circumstances, for ordinary flying, ... even if the correct boost is not exceeded") without any benefit.
In most cases reason a) can be ruled out by the context, in case of engine control failure the pilot would try to return to the airfield and avoid any combat and most certainly mention the engine troubles in the report.

So in the remaining cases the reported use of the cut-out is:
- proof for use of 100 octane fuel
- in the other case where 87 octane fuel was used the proof for overstepping of the regular maximum permissible boost. It shows that this was physically possible (or a breakdown of the engine or evidences for detonation would be reported in context) and in addition it was either permitted or tolerated by authority (or it would be reported as a violation in the context, e.g. I'd expect this to be mentioned as one possible reason here http://www.spitfireperformance.com/dowding.pdf).

In both cases it is a proof that the performance of the engine was increase. 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.

My understanding is that this is not true.

[pstyle]

Originally Posted by Crumpp

Without the specific mention of using +12, an anecdote that makes any reference to boost override, pulling the tit, boost cut out, or anything other term related to the system is irrelevant to the use of 100 Octane.

wrong
It's not irrelevant. What you're claiming here is that every reference to those things, where there is no explicit mention of 12lb, means that we can be 100% certain that they were not referring to 12lb. This is illogical.

It's not proof of 12lb boost, but it is entirely relevant and should be investigated to determine if it is, or is not, a reference to 12lb boost, in each case.

[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.