Spitfire & Hurricane flight model & engine performance thread. (1.09 patch)

[41Sqn_Banks]

First documented use of emergency boost with a Spitfire II is 21 August: http://www.wwiiaircraftperformance.o...-21aug40-1.jpg

Double standard view on the subject:

The use of +12 in Spifire II is
a) documented in combat reports as "emergency boost" 8 days after the first operational use
b) authorized in a later edition of the manual
c) the cut-out is mentioned in the earliest edition of the manual for emergency use. Without a specific modification to +12 boost the cut-out would enable the pilot to obtain any boost up to +17
Invalid. Not enough proof, even if there is nothing that prevents the pilot from using it. The combat report doesn't mention +12 boost, maybe the pilot used the cut-out to obtain the regular boost +9 manually instead of simply moving the throttle full forward.

On the other hand there is 1.4/1.45 ata for DB601A which
a) is restricted to take-off in any edition of the manual
b) is not mentioned by any pilot report for anything else than take-off
Valid. There is nothing that prevents the pilot from using it in combat.

[Kurfürst]

Originally Posted by 41Sqn_Banks

First documented use of emergency boost with a Spitfire II is 21 August: http://www.wwiiaircraftperformance.o...-21aug40-1.jpg

Double standard view on the subject:

The use of +12 in Spifire II is
a) documented in combat reports as "emergency boost" 8 days after the first operational use

Wishful thinking. It doesn't say +12 lbs boost, it says 'emergency boost', which we all know was +9, as per the manual. Selective and wishful use of evidence...

b) authorized in a later edition of the manual

And as such irrelevant for BoB period. Same site you use as a source claims that the 1-min boost for the DB engine was not cleared until 1942, by when the Emil was withdrawn from service. It also claims a gazillion other BS for LW planes and has achieved an unenviable reputation for bias and manipulation as a result.

c) the cut-out is mentioned in the earliest edition of the manual for emergency use. Without a specific modification to +12 boost the cut-out would enable the pilot to obtain any boost up to +17

So by all means model the boost cutout and enable pilots to obtain +17 lbs boost and blow their engines at free will...

On the other hand there is 1.4/1.45 ata for DB601A which
a) is restricted to take-off in any edition of the manual

In contrast of +12 boost being physically restricted (impossible) on the Spitfire II. Nothing restricts the use of 1.4/1.45ata in the 109/110/111, expect for the 1-min clockword which is already present and modelled.

b) is not mentioned by any pilot report for anything else than take-off

Show me say 10 German pilot reports then which 'does not mention it'. No, you have not seen ANY, you just make up an arguement, neglecting the fact that German pilot reports never seem to mention any boost levels during the whole war, and here's why - unlike the British, they had automated systems since the start of the war, so boost levels were meaningless to their pilots - they did not have to set it separately. Neither they needed to overboost woefully undersized engines to compete and thus it was utterly irrelevant to pilots.

Let me show you a real example of double standard.

RAF fans like yourself wish to have a plane modelled in the sim after a crayon graph they drew up themselves in desperation as there is curiously not a single +12 lbs boost report being made, so they had to make up one and wave it around. Ring a bell?

RAF fans like yourself wish NOT to have a plane modelled in the sim after a doucmented and guaranteed tests just because it shows that their cherished RAF plane with much larger drag and 25% greater wing area is, horriblle say, was slower than the blue plane with more power and less drag at sea level.

Said RAF fans then come to the forums and complain about a German rating that was there, and ask for a RAF boost that wasn't there, and wish to model that boost based on no performance test at all.

[Al Schlageter]

Oh dear, Kurfurst has gone on another one of his rants.

The Merlin in Perspective, no.2 in the R-R Heritage Trust's Historical Series

"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......"

[JtD]

Originally Posted by Kurfürst

So by all means model the boost cutout and enable pilots to obtain +17 lbs boost and blow their engines at free will...

You make it sound as if it was a useless option or a bad idea, but it is not. If it is combined with a decent overheat / engine damage model, it would imho be the best and most useful way of implementation in game. The engine could take 12lbs of boost, as we know from the take off setting, and disabling the automatic boost control would give the player a chance to manually set and maintain it. What it is not is a simple press a button solution. It is the minimum that was available historically, it's useful and interesting.

Thanks 41Sqn_Banks for the 17lb figure, I wasn't sure if other restrictions were in place before the 12lb modification was carried out. So I went with worst case.

[41Sqn_Banks]

Originally Posted by JtD

Thanks 41Sqn_Banks for the 17lb figure, I wasn't sure if other restrictions were in place before the 12lb modification was carried out. So I went with worst case.

About +17 is the amount of boost that the supercharger can produce at sea level, it's not restricted.

[JtD]

That I find highly unlikely, if it can produce +9 lb at 17000 feet, it should be able to produce about ((9+14)/527*1013)-14 lb at sea level, which is about +30 lb. The compression ratio should not change much. If it does happen, though, there's some sort of throttle in the way, and be it just too small cross sections somewhere between the intake and the supercharger.

(Note about the calculation: (9+14) - total pressure in the supercharger at full throttle altitude; 527 - outside pressure at full throttle altitude; 1013 - outside pressure at sea level; - 14 - to get from total pressure in the supercharger to overboost as used by the British)

[41Sqn_Banks]

Originally Posted by JtD

That I find highly unlikely, if it can produce +9 lb at 17000 feet, it should be able to produce about ((9+14)/527*1013)-14 lb at sea level, which is about +30 lb. The compression ratio should not change much. If it does happen, though, there's some sort of throttle in the way, and be it just too small cross sections somewhere between the intake and the supercharger.

(Note about the calculation: (9+14) - total pressure in the supercharger at full throttle altitude; 527 - outside pressure at full throttle altitude; 1013 - outside pressure at sea level; - 14 - to get from total pressure in the supercharger to overboost as used by the British)

You are of course correct. +17 boost is for Merlin III, but Merlin XII runs at much higher boost.

However I doubt that any Merlin XII had a unrestricted boost cut-out.

[Robo.]

Originally Posted by Kurfürst

Wishful thinking. It doesn't say +12 lbs boost, it says 'emergency boost', which we all know was +9, as per the manual. Selective and wishful use of evidence...

+9 was also climb boost (at 2850 rpm) and there was also all out setting which was +9. All out suggets just full throttle and full rpm, it is not emergency boost and pilots would not refer to it as emergency boost.

With BCC-O, Merlin XII was technically capable of pressures higher than +9lbs., it was certainly safe to operate it at +12lbs. (for that was the take-off power with the throttle gate system and also supported by simple fact that XII was improved III and III was approved for that MAP). +17lbs. is consistent with R-R raw tests but perhaps JtD is right, I don't know. I agree that as for Pilot's Notes the Merlin XII are set correctly for the sim (at +9lbs max), there is not enought direct evidence and the date of amendment is not clear, unofrtunately. The best authority at early Merlins is the Merlin in perspective publication quoted by Al Schlageter in here but it does not clarify the date of emergency boost amendment. There was no modification necessary to achieve that fore sure, it was physically possible to have boosts higher than +9lbs from day one on Merlins XII.

I agree with you that it would be great and interesting to have the BCC-O (ABC) modelled, I would not mind. It is logical and almost certain that it has been used in combat.

For the operation and technical details of both Take Off power and ABC, there were some interesting scans and description by Banks in some other thread.

[bongodriver]

I'm struggling with some of the logic behind the use of 12lbs here.......for the life of me I can't think of a single circumstance where a pilot would need to break a sealed lever to get an emergency take off boost in a single engine aircraft, take off performance should be accounted for using max available non emergency power...........OR have I got the wrong idea and 12lbs boost was available without breaking the seal but was instead achieved by use of a throttle gate and was automatically reduced above 1000' and if you hadn't climbed above 1000' on departure you were expected to reduce after a max of 3 minutes? thereafter the max boost was 9lbs?........which means that the sealed boost lever has not yet been used.......I wonder what would happen if I used it?

[Robo.]

Originally Posted by Kurfürst

the fact that German pilot reports never seem to mention any boost levels during the whole war, and here's why - unlike the British, they had automated systems since the start of the war, so boost levels were meaningless to their pilots - they did not have to set it separately. Neither they needed to overboost woefully undersized engines to compete and thus it was utterly irrelevant to pilots.

Well to be fair, the automatic boost control was also automated as the name suggests and yet pilots verbally referred to its use in many instances when they decided to override it.

There was actually very specific vocabulary to describe the use of emergency combat boost. The same went for any other conflict where they could use some extra power available (e.g. afterburners in Vietnam war) and often described it in their narrations, written or spoken. I am sure German pilots would be doing the same if that was the case. The only thing that could explain that lack of specific references to Erhoehte Notleistung (and mind you it referred to by the pilots in some late war combat literature as they were flying German aircraft with extra combat power designed by one mean or another) is that in the Emil, for emergency MAP one had to slam the throttle fully forward, there was no switch or knob or any gate to go through to prevent the use of 1,45 ata. So perhaps that is why.