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

[Seadog]

Originally Posted by JG5_Thijs

The following table shows a test of a Spitfire Mk Ia and Spitfire Mk II (399)

Table 1: There is only a marginal improvement in the rate of climb and maximum speed comparing both planes in the first table...

Bailey concludes that the main advantage of 100 octane fuel was at lower altitudes, but was marginal at best at higher altitudes.(401) His table demonstrate that there is actually a drop in top speed at higher altitudes.

Bailey on the boost of the Merlin engine

The author gives the following information about the boost increase that was achieved by 100 octane fuel: Normal limitation on the supercharger compression of a Rolls-Royce Merlin III with 87 octane fuel was +6.25 inch above atmospheric pressure. The introduction of 100 octane fuel increased this to +12 for short periods, not exceeding 5 minutes.(39


Take off to 1,000 ft — 3,000 rpm at +7 psi/+12.5 psi;
Maximum climb (1-hr. limit) — 2,850 rpm at +7 psi/+9 psi;
Combat (5 min. maximum) — 3,000 rpm at +7 psi/+12 psi.
(This chart is about Spitfire MK II with 100 octane boost which Baily took from the following source: Air Ministry, Air Publication 1565B, Pilots Notes, Spitfire IIA and IIB Aeroplanes, Merlin XII Engine (anonymous Air Ministry publication, London, 1940, amended 1942).)

Conclusion by Bailey:

He concludes that the dramatic performance increase because of 100 octane is overrated and that other, earlier, authors wrongly claim that there is. These other authors forgot that the variable pitch prop was the real source of the dramatic performance increase of RAF planes which they contribute solely to 100 octane fuel.

Comment by me regarding the information given above: It seems that an increase from 87 to 100 octane fuel (but with a variable pitch for both) only leads to a marginal improvement. Whether the planes in this game are modelled correctly is not within the scope of this argument.

Regards,

Thijs

The performance figures given in your post are for the MkI/IIaircraft using 6.25/8.8lb boost and the actual performance test results verifying this can be seen here:

http://www.spitfireperformance.com/spitfire-II.html

but the data you quote also states the maximum boost as 6.25lb/9lb respectively, which explains the small margin of improvement of the MkII over the MkI, especially as the MkII is somewhat heavier as well.

Thus neither aircraft was using the 5min/12lb boost combat rating of the engine which was only possible when using 100 octane fuel. By way of comparison a Hurricane I could achieve ~323mph at 10,000ft by using 100 octane fuel/12lb boost:



and here's the RAE data for a Spitfire I with various boost levels:


A RAF memo from 1939 confirms all the above:

It will be noted from the service reports that an approximate increase in speed due to the use of emergency 12lb boost of 28/34mph is obtained depending upon the altitude flown up to 10,000ft.
http://www.spitfireperformance.com/spit1-12lbs.jpg.

[28_Condor]

Originally Posted by Crumpp

The answer to the question of the extent of 100 Octane all depends on when you place the dates of the Battle of Britain. September 15th 1940 as an end date is a post war and has nothing to do with Fighter Command's actions in context.

The RAF official history takes the battle out to the end of October 1940 when German Daylight raids ceased. Other histories end the battle in December 1940:

OK, But in which scientific article I can read this information?



Interesting: I read again the CLIFFS OF DOVER AIRCRAFT OPERATIONS checklists by Composite Aviation Regiment 2nd Guards (OP2GvSAPINST 3710.1A 15 July 2011) and there all aircrafts are operating on 100 octane (frist part), and in the second part you can read:

Errata
Additional Aircraft
Known Sim Inaccuracies or Limitations
Operating Limits and Procedures for Non-Standard (87 Octane, Fixed Pitch Props) or Non-Pilotable (Anson) Aircraft

Meanwhile, in the A2A Spits:

Types You Can Fly
We have three Spitfire models available, the Mk Ia, fitted with a Merlin III engine designed for 87 octane fuel, +6 psi max boost, or a Mk II
with a Merlin XII, designed for the higher 100 octane fuel, beefier block, slightly increased supercharger, and capable of a higher +12 psi.

[41Sqn_Banks]

Originally Posted by Crumpp

If the aircraft in service were most commonly using 100 Octane, those limits would be the ones listed under the limiting Operating Conditions of the Pilots Operating Notes.

That is how it works.

The 87 Octane limiting operating conditions are published as the predominate operating limits of the aircraft in June 1940. References to 100 Octane are minor footnotes denoting specialized circumstances that are not the common configuration.

So how do you know it worked that way? Source please.

Here is evidence that it didn't work that way:

Hurricane I "operational limitations" May 1941 (thanks Klem):

http://forum.1cpublishing.eu/attachm...4&d=1334674718
http://forum.1cpublishing.eu/attachm...5&d=1334674727

Spitfire I "operational limitations" January 1942 (I'm sure someone has a better copy of this)

http://forum.1cpublishing.eu/attachm...5&d=1334723739
http://forum.1cpublishing.eu/attachm...6&d=1334723745

Merlin II, II and V "operational limitations" November 1940

http://forum.1cpublishing.eu/attachm...7&d=1334724557
http://forum.1cpublishing.eu/attachm...8&d=1334724563
http://forum.1cpublishing.eu/attachm...9&d=1334724569

In all of these publications 100 octane fuel and +12 is only a "minor footnote" and the "All out" limit is given as +6 1/4.

[41Sqn_Banks]

And the explanation for this is given in Pilot's Notes General (1st Edition 1941, not the 2nd Edition).

http://forum.1cpublishing.eu/attachm...0&d=1334727256
http://forum.1cpublishing.eu/attachm...1&d=1334727263

We know that the Merlin II and III was designed for 87 octane and therefore the operational limits are always given for 87 octane.

[lane]

Originally Posted by 41Sqn_Banks

So how do you know it worked that way? Source please.

Here is evidence that it didn't work that way:

Hurricane I "operational limitations" May 1941 (thanks Klem):

http://forum.1cpublishing.eu/attachm...4&d=1334674718
http://forum.1cpublishing.eu/attachm...5&d=1334674727

Spitfire I "operational limitations" January 1942 (I'm sure someone has a better copy of this)

http://forum.1cpublishing.eu/attachm...5&d=1334723739
http://forum.1cpublishing.eu/attachm...6&d=1334723745

Merlin II, II and V "operational limitations" November 1940

http://forum.1cpublishing.eu/attachm...7&d=1334724557
http://forum.1cpublishing.eu/attachm...8&d=1334724563
http://forum.1cpublishing.eu/attachm...9&d=1334724569

In all of these publications 100 octane fuel and +12 is only a "minor footnote" and the "All out" limit is given as +6 1/4.

Nice 41Sqn_Banks, thanks for sharing

[NZtyphoon]

Originally Posted by Crumpp

I have read those Banks. You misunderstand what I wrote. A.P. 1590B/J.2-W is incorporated into the June 1940 Pilots Operating Notes.

Okay, so how about showing the pages incorporating A.P. 1590B/J.2-W, plus the front cover, inner cover and fly leaves confirming the date of publication?

[Crumpp]

Spitfire I "operational limitations" January 1942

The change jumps right out at you. Go compare the operating limits page I posted from June 1940 with the page from January 1942.

You should see it plain as day. If you don't I will point it out to you later.

Why do you think they republished the Operating notes in January 1942? The Spitfire Mk I was not the latest Spitfire Mark at that time. However, 100 Octane was common by that date and required a republication of the notes.

[Osprey]

Face it Crump, even Kurfurst has realised that 100 was in full use - he lost the argument and disappeared. You remind me of one of those Japanese soldiers still fighting the war on some island right up to the 1970's.



Chaps, there's a bug raised about the boost on the bugtracker that I need to update so I will grab this latest stuff for it so it can finally be implemented into the sim.

[41Sqn_Banks]

Originally Posted by Crumpp

The change jumps right out at you. Go compare the operating limits page I posted from June 1940 with the page from January 1942.

You should see it plain as day. If you don't I will point it out to you later.

Why do you think they republished the Operating notes in January 1942? The Spitfire Mk I was not the latest Spitfire Mark at that time. However, 100 Octane was common by that date and required a republication of the notes.

So even with 100 octane fuel being the common fuel in January 1942, the "All out" limit remained +6 1/4. So obviously there is no relation between introduction of 100 octane fuel and the fact that the "All out" limit remained +6 1/4.

Fact is that the June 1940 manual already included all information needed by the pilot for the use of 100 octane and +12 boost:
- The use of 87 octane and 100 octane fuel is allowed (see Section 1 "Fuel", I will provide the page later)
- The boost-control cut-out allows to obtain +12 boost
- The use of the boost-control cut-out is allowed in emergency cases for short periods and when 100 octane is used

The fact that the January 1942 manual introduces an additional limitation of the fuel for operational and training units doesn't outweigh the fact that there not a single line in the June 1940 manual that would prevent the use of 100 octane fuel of whole Fighter Command in June 1940.
It doesn't proof that they did, but it doesn't proof that they didn't - which is your claim.

[Glider]

Originally Posted by Crumpp

See above, Glider.

All I see is someone who will not scan and post the sections that I am now asking for, a third time, as I am confident that those sections on the Propeller and the pilot protection would give us a good idea as to which version of the Spitfire your pilots notes refer to.

Can you even tell us where you got them so I can obtain a copy?

I should remind you that you accused me of posting selective and misleading papers. My reply was to ask which paper you are talking about and I would give you everything I have on those papers or get a full copy for you when I am next at the NA which will be next week. You have not yet told me which paper of mine you were referring to and the offer is still open until next week. I have made this offer twice.

Some people who would think that this insistance on two sets of rules, one for when you post papers, and one where others post papers as a little dodgy?

Kurfurst, if you are reading this the offer is open to both of you. I am going for other purposes so will not spend a lot of time on this topic, but if you can agree one paper I will supply it.