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

[Crumpp]

there was never a shortage of 100 octane fuel.

What?? There was a shortage of 100/130 grade on several occasions during the war.

There are several reports on the aviation gasoline situation available at both Maxwell AFB and Dayton OH.

[Osprey]

Redbeard Rum.

[Glider]

Originally Posted by Crumpp

I don't have a link Glider. These are not posted on some website but part of my collection. I scan the pages and post them.

So can you scan and show us the sections I have asked for?

[JG5_Thijs]

Hello all,

With great interested I’ve been following the discussion regarding the use of 100 octane fuel by the RAF in the Battle of Britain. I decided to look up some scientific articles, but could only find the following:

Gavin Bailey, ‘Narrow margin of criticality: The question of the supply of 100-octane fuel in the Battle of Britain’ English Historical Review volume 123 number 501 (200 p 394-411. (This article was quoted earlier by 28_Condor on page 98 of this thread, he, however, did not quote the article fully since there are some interesting points that Bailey brings up regarding the impact of 100 fuel use.)

There are some interesting things in this article regarding the use of 100 octane fuel and the performance of the Spitfire Mk I and II. A short summary. First a quick summary of the availability of 100 octane fuel, then the operational usefulness of 100 octane fuel.

Bailey on the availability of 100 octane fuel

Bailey states that at the time the war broke out there was 153,000 tons of 100 octane fuel in stock, compared to 323, 000 tons of other aviation fuels. In February 1940 the stock of 100 octane fuel had risen to 220,000 tons. In May 1940 fighter units began converting to 100 octane fuel and there was plenty of 100 octane fuel available for the duration of the Battle of Britain.(406)

Note by me about 100 octane being used in the game in this respect: This quote above, and the other information provided by other people on this forum, makes me conclude that use of 100 octane fuel was widespread during the BoB. It would therefore be fine to program RAF planes with 100 octane, or give the option to mission builders to choose between 87 and 100 octane fuel.
This, however, is not say anything on the great improvement of 100 octane fuel gives over 87 octane fuel as claimed by many authors and people on this forum.

Bailey on what other authors write about the use of 100 octane fuel:

He says that other authors argue that the use of 100 octane fuel from America was one of the critical advantages for British fighters during the battle, he does not agree with this vision.(394-395) Bailey argues that it tends to be forgotten that the widespread use of 100 octane fuel is in the same time period as the introduction of the constant-speed, variable pitch propeller which offers a much larger performance increase than the new fuel alone. (395)

To demonstrate this Bailey uses two tables:

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


Spitfire MK I test with a fixed propeller.


Table 1: There is only a marginal improvement in the rate of climb and maximum speed comparing both planes in the first table. There is however, a dramatic increase between a Spitfire with a fixed propeller and the newer variable pitch one. See table 2 (401)

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

[Crumpp]

Originally Posted by Crumpp

Pilots Operating Limitations, June 1940:



All out 5 minute Emergency rating as listed in June 1940:



If by June 1940, 30 squadrons were operating 100 Octane, then almost the entire force would need the +12lbs boost instructions instead of the 87 Octane. The Operating Notes would have reflected this and the 100 Octane limits would have been included.

That is a fact and how it works.

Glider says:
So can you scan and show us the sections I have asked for?

Already done.

[Crumpp]

Originally Posted by Crumpp

I don't have a link Glider. These are not posted on some website but part of my collection. I scan the pages and post them.



Exactly. Quite a large "Fly in the Ointment" for silly claims like:

And depending on the dates you pick for the battle to be over:

You wonder why I question what you claim "is known." Facts are it is not known.

See above, Glider.

[NZtyphoon]

Originally Posted by Crumpp

Baloney.

Total is just that...TOTAL for the year.

In 1938 they had 100 Octane in quantity?? No they did not.

I don't think it has anything to do with the columns above it. Can you prove it does not?

Crumpp, Crumpp Crumpp, kindly explain how it is that 52,000 tons of 100 Octane fuel was consumed between July 1940 and October 1940 if, as you claim, only 16 Squadrons were using 100 Octane - so far you have made a lot of fuss regarding fuel shortages etc but you have not explained where 52,000 tons of it went.

Only 15,000 tons was needed to complete all defensive sorties flown by Merlin engined fighters - so again please explain to everyone what happened to 35,000 tons of 100 octane fuel?

I want documentation from you to prove your case, not conjecture.

Prove that there were frontline Merlin engined squadrons using 87 Octane fuel during the battle - I mean combat reports, squadron ORBs and other such documentation - evidence NOT your conjecture.

Originally Posted by Crumpp

That looks like somebodies photo-shop work.

And so do your "June 1940" pilot's notes which you claim embody A.P. 1590B/J.2-W, but, conveniently, haven't shown. I want to see the front cover, inner cover and the relevant fly leaf which has the date.

Originally Posted by Crumpp

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

Then why haven't you shown the relevant pages in the first place, including A.P. 1590B/J.2-W? - better still show us the relevant pages, listed above, including the date of publication.

[Al Schlageter]

Originally Posted by Crumpp

And depending on the dates you pick for the battle to be over:

Still haven't clued in Eugene have you?

All your talk of 87 octane fuel being the predominant fuel is for the whole of the RAF.

Bomber Command had at least 24 squadrons when war broke out. Each a/c in those squadrons carried enough fuel to fuel a squadron of fighters.

[Al Schlageter]

Originally Posted by Crumpp

What?? There was a shortage of 100/130 grade on several occasions during the war.

What the hell does 100/130 fuel, which wasn't even around during BoB, have to do with 100 octane fuel?

We still haven't seen from you the identity of the 16 squadrons that you say were the only squadrons converted to 12 lb boost.

[kendo65]

Great post JG5_Thijs. Thanks.