Possible discrepancy Spitfire engine limits

[Kurfurst]

The pilot notes are clear, so I do not see that they need to be interpreted.  No interpretation is needed, since the 5 minute limit is clearly stated at 3,000 rpm and +16lbs boost within the stated engine temperature range.

 

Therefore, anything less than the max rpm available (3,000 rpm) is not subject to a time limit. 

 

​Happy landings,

 

​56RAF_Talisman

 

 

First, the limits imposed I depends on the date of the manual you are using as reference. For example, tests were performed in Boscombe Down on Spitfire Mk. VC AA.878 (M45) for climb, speed, and cooling tests at combat rating and a report was prepared on 25 November 1942.

 

It states:

 

"The operational limitations of the Merlin 45 have been increased, the use of 3000 R.P.M. and +16 lb/sq.in. boost being now permitted for periods not exceeding 3 minutes during combat. Tests have been made to determine the performance of the aeroplane at this new rating, and also whether the oil and radiator cooling are adequate."

 

It is quite clear that the +16 rating was introduced sometime in the 2nd half of 1942, and initially the rating was limited to 3 minutes only, presumably because cooling issues. 

 

The second arguement is just plain silly. Suppose the engine limits are 3 (or 5) minutes at +16/3000 rpm. For obvious reasons, this just doesn't become an infinite time when you start to use +16/2999 rpm.

 

Now of course the engine-damage-after-the-time-limit-artificially-set-in-the-manual way of engine modelling is questionable (though simple to do) approach, but it is what it is, and it is used for all planes or not used at all for any plane.

[unreasonable]

@Kurfurst

 

I am fairly sure that both Talisman and I are discussing Air Publication 156E, May 1941 (Reprinted January 1943) titled Spitfire Mk V Pilots' Notes. (Which you can buy from Bloomsbury publications as part of their "The Spitfire Pocket Manual" along with a lot of other interesting stuff).

 

Since it was reprinted Jan 1943 you can be fairly sure that this is the current version of the limits in the Kuban time scale, in which the +16 limit is 5 minutes, as I pointed out to Gavrick and was incorporated into the game.

 

Apart from that I agree.

[Kurfurst]

Hence I said 'initial'. For BoK, the January 1943 manual limits could apply of course. The cooling tests did not go all well iirc so it seems logical that the cooling system would have been revised and once that was done with, a new manual was printed with new limitations.

 

Albeit I am in a bit of an uncertain about the dates of the RAF manuals, since AFAIK several were reprinted after the war for commercial purposes (often based on post war manuals), and I am never quite sure of the scan that appears on the internet is a genuine WW2 manual or maybe some reprint based on a post war manual or offset... with the the data randomly put together from various original issues. 

[Talisman]

There are three issues here:

 

1) The general modelling of engine limitations in BoX vs the nature of the guidance in RL PNs, flying guides etc.

2) The specific difference between the 30 minutes and one hour "limit" for the Spitfire V

3) Whether 16+ is limited to 5 minutes at 2850.

 

On (1) I think we all agree that it is an unrealistic simplification that has unfortunate consequences in the game. Sadly, having no engine limits arguably has worse consequences.  There might be a better system, but so far most people seem unable to agree what it is. The developers are gradually making the system more complex, so maybe this will get better - or not.

 

On (2) you would have to search Gavrick's posts around the time of the Spitfire release DD's to see if he mentions why 30 minutes was chosen. The fact that the in-game notes mention "international power" suggest that they have a document with this limit in it from somewhere, but this is just my speculation based on the assumption that they tend not to just make stuff up without sources, although they do of course make mistakes from time to time.

 

On (3) we have a real disagreement. My bottom line on this is that when I read the PN it is crystal clear to me that what is being limited by the table is the use of "combat boost".  Not "combat boost at 3000rpm only".  "Combat boost" obtains at anytime that you have engaged the boost over-ride and have boost above the next lowest limit, which is +12 for max take-off, which is limited not by time but up to 1,000 feet (ie a very short time).   2850 is explicitly mentioned as being the lowest permissible rpm at which combat boost may be used. Therefore +16 at 2850 is time limited.

 

"and there is no 5 minute combat limit for engine output in terms of rpm and boost under 3,000 rpm and +16 boost."   Wrong. Every boost setting in that table is limited except for those marked as "continuous".  The highest boost level on that table that is not limited is +7

 

If your reading of the table as a limit for "+16 at 3000rpm only" was correct, then +16 at 2999 would also be time unlimited, as would +15 at 3000. Your interpretation of the table defies common sense.

 

If you really think that the devs have made this mistake, and that I - and the other contributors to the thread who have made the same point - are all wrong, go ahead and PM Han pointing out the error. 

 

I believe what you say to be fair comment, but I think what this discussion has highlighted is that the engine limits for the Merlin in the real life Spitfire Pilot notes are something of an artificial construct.  An artificial construct put in place with the best of intentions and arguably necessary, but artificial nonetheless.  

This is also born out by the fact that the real life Pilot Notes General give the pilot discretion to disregard such limits and explain that the engine limits in British aircraft pilot notes are a general guide to the reasonable use of the engine.

For the IL-2 flight simulation developers to then artificially construct catastrophic engine failure for engine limits that were an artificial construct in the first place, is a matter of concern to me and perhaps others.

Have the IL-2 flight simulation developers read Pilot Notes General I wonder?  I do think the devs have made a mistake, but I think they have made a mistake that is far more fundamental than the specific 5 minute combat limit.

 

P.S.  Just as a side note.  I don't know if you have ever read the book by Geoffrey Wellum https://en.wikipedia.org/wiki/Geoffrey_Wellum with the title 'First Light'.

 

https://www.goodreads.com/book/show/518136.First_Light

 

It is a smashing read and includes his self-imposed drill for going into battle in his Battle of Britain Mk1 Spitfire.  His example in the book is when attacking bombers with Bf 109's overhead. 

 

"Thing are starting to get rough.  Automatically I have followed my self-imposed drill that I always do at times like this.  Reflector sight on; gun button to fire; airscrew pitch to 2,650 revs; better response.  Press the emergency boost over-ride, lower my seat a notch and straps tight.  OK, men, I'm all set.  Let battle commence."

 

I recommend 'First Light' to anyone interested in WWII aviation.  It is very atmospheric and is humanely written.

 

Hope to meet up with you in MP some time.

 

Happy landings,

 

56RAF_Talisman

Edited February 6, 2018 by 56RAF_Talisman

[Guest deleted@50488]

This all being very informative, one thing I really find weird, not only on the Spitfire, but also on other models ( 109 included ) is how can hang on the prop, for quite a while, until I am tired of doing vertical aerobatics, and yet nothing / no damage happens to their engines, provided I respect their limits...

 

The Spit being so sensible to cooling, for instance, makes me think if OTOH engine limits are actually very permissive in IL-2 ?

[ZachariasX]

 

 

The Spit being so sensible to cooling, for instance, makes me think if OTOH engine limits are actually very permissive in IL-2 ?

 

I would also say that especially in slow flight regimes, the cooler is too efficient. This is seen in ground handling, where it won't overheat just like that, and this cooling ability also is present when flying slower, especially during steeper climbs.

 

Then again, it makes the game a bit more playable if a simplified way to determine cooling is off a bit in that "easy" direction. 100% accurate would be better, but since it would make some planes more tedious to handle, you better be 1000% sure that what you simulate is actually 100% correct, else people would scream about "broken planes".