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

[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)

[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.