Modelling engine wear and WEP limitations

[VO101_Tom]

Originally Posted by Seadog

Crumpp says it. The Merlin engine service manual doesn't. The service manual says check the oil filter after emergency boost, so does Dowding. The rest of what Crump writes is his own fantasy based upon the idea that RAFFC operated on the same lines as civil aviation. The reality is that most combat aircraft were destroyed before their hundred hour checks, and 25-40% of RAFFC pilots died before they achieved 100 hours of combat flying. The Merlin engine could be flown continuously at 12lb boost with a low probability of failure and this engine was cycled 100 times from 4.5 to 12lb/3000rpm and the bearings held up just fine:
http://www.wwiiaircraftperformance.o...bs-14nov39.jpg
without the need for repeated engine checks, since by definition the engine was being cycled multiple times per sortie.

I agree, huge difference is between 5 min and 8 hour, but the engine failure IS exists. If 20% of flight time using 12lbs boost, the engine gets damege certainly. After 50 hour test, this Hurri have cylinder head cooling leak. But you don't know, after how much time got damage. Maybe after 5 minutes, maybe one hour, maybe eight. Maybe its far from 5 min, but also far from "continously without damage". We do not say that the engine has to explode after 5:01 minute. But the problem exists, and it is not possible to leave it out of consideration.

I believe it if you say that a limitation was official onto the machine, but nobody took it seriously. Okay. But this does not mean that it did not have consequences. If you don't want to, you do not deal with it in the game. But let it have consequences. As it is for the other side.

[VO101_Tom]

Yeah I forgot this According to you, what was the purpose that the oil filter was taken out (without an oil change)? What did they make with it? It was thrown in into a big green box, on which was a huge "not interest " stencil?

[Seadog]

Originally Posted by VO101_Tom

I After 50 hour test, this Hurri have cylinder head cooling leak. But you don't know, after how much time got damage. .

The early Merlin engines were prone to cylinder head leaks, as per the memo, and this had little or nothing to do with 12lb boost. WW2 combat engines had a short service life, by civil aviation standards, and, as I have pointed out most aircraft and engines never survived past 100 hours.

Originally Posted by VO101_Tom

Yeah I forgot this According to you, what was the purpose that the oil filter was taken out (without an oil change)? What did they make with it? It was thrown in into a big green box, on which was a huge "not interest " stencil?

They would examine the filter for evidence of metal filings which typically indicated bearing damage. No metal = no need for further investigation. Obviuosly the engine flown for 49.5 hours with repeated cycling of 12 and 4.5lb boost never showed evidence of bearing damage, or they would have stopped the trial.

[TomcatViP]

Originally Posted by Seadog

The early Merlin engines were prone to cylinder head leaks, as per the memo, and this had little or nothing to do with 12lb boost. WW2 combat engines had a short service life, by civil aviation standards, and, as I have pointed out most aircraft and engines never survived past 100 hours.




They would examine the filter for evidence of metal filings which typically indicated bearing damage. No metal = no need for further investigation. Obviuosly the engine flown for 49.5 hours with repeated cycling of 12 and 4.5lb boost never showed evidence of bearing damage, or they would have stopped the trial.

Man engine and airplane are strategical assets in a war. Not so much men This why you've got disciplinary council and your superior makes good or bad report on your behavior. This was not paparazzi on look. Think that the logistical bckgrd to sustain a full air-force at war was simply enormous. You don't want to change an eng because some fighter jock only wanted to buzz Lili's home.

May I remind you the late war LW with thousands of a/c build each month but with only hundreds on the fronts?

Even in the late war Tempy the Emergency power had a restricting safety link.

The Spitfire during BoB was a wonderful aircraft, potent, powerful and survivable. That's it.

[Blackdog_kt]

Originally Posted by Seadog

Crumpp says it. The Merlin engine service manual doesn't. The service manual says check the oil filter after emergency boost, so does Dowding. The rest of what Crump writes is his own fantasy based upon the idea that RAFFC operated on the same lines as civil aviation. The reality is that most combat aircraft were destroyed before their hundred hour checks, and 25-40% of RAFFC pilots died before they achieved 100 hours of combat flying. The Merlin engine could be flown continuously at 12lb boost with a low probability of failure and this engine was cycled 100 times from 4.5 to 12lb/3000rpm and the bearings held up just fine:
http://www.wwiiaircraftperformance.o...bs-14nov39.jpg
without the need for repeated engine checks, since by definition the engine was being cycled multiple times per sortie.

Sorry, but the fact that you claim continuous running on what's called emergency power and then try to support it with the argument that most planes would be destroyed pretty fast anyway, makes it all sound like an effort to disguise the fact that if the aircraft survived long enough they would get a higher proportion of engine failures.

It would be more accurate to phrase this a bit differently: engine failures were rare not because WEP was free of charge, but because the aircraft rarely survived long enough for the engine abuse to take effect.

Like i said before, they wouldn't call it emergency power if it was fine to use it all day long and fuel burn was the only real drawback. They would just call it full power and insert a footnote "warning, it burns fuel really fast".

Emergency has a pretty strong connotation to it, it means "don't use unless you're about to die" in simple terms.

And finally, this is not a thread about what the Merlin could or couldn't do. This is a thread about modeling engine limitations on ANY kind of engine in the sim if it also had them in reality. If the Merlin did or didn't have such restrictions is a completely different matter and totally out of the scope of this thread. What are doing here is this:
"Supposing engine X has limitation Y, what's the best way to have this reflected in the sim?"

Why do you feel the need to constantly hijack this thread in the direction of the Merlin specifically is completely beyond me, especially when you can just as easily start your own thread and argue your point there without dragging this one completely off-topic.

We are not discussing the capabilities of a specific engine here, we are discussing a proposed idea for a game feature. If you want the Merlin to be exempt from it, feel free to start a separate thread about it or use one of the many already provided. We don't need every single thread around here to revolve around the Merlin and the use of 100 octane fuel, there's several of them already

Excuse me the bolded text, i mean no hostility and it's purely for emphasis. It's just getting mighty tiresome trying to discuss an interesting idea with some like-minded fellows in the pub and having someone from across the bar constantly jump in the middle of your group shouting "AHA" as he dumps a load of old musty dossiers and charts on the table before he starts on something that has almost nothing to do with the discussion at hand. Don't drive us out of the pub man, especially when there are people having the kind of discussion you prefer just two tables over

[Seadog]

Originally Posted by Blackdog_kt

And finally, this is not a thread about what the Merlin could or couldn't do. This is a thread about modeling engine limitations on ANY kind of engine in the sim if it also had them in reality. If the Merlin did or didn't have such restrictions is a completely different matter and totally out of the scope of this thread. What are doing here is this:
"Supposing engine X has limitation Y, what's the best way to have this reflected in the sim?"

Why do you feel the need...

[b2]We are not discussing the capabilities of a specific engine here, [/b]

Excuse me the bolded text,

b) establishing an engine's limitations is a prior requirement before you can sim it. There must be others who can comment on the DB engine's reliability and reliability with WEP. Until these limits are discussed, how can you create a sim based upon RL?

I am not hijacking the thread, when I discuss engine limitations, or the mathematics and probabilities of engine failure versus average service life: These are the essential factors that have to be modelled but if engine life with repeated overboost works out to be greater than the average life of an aircraft, then the use of overboost is probably extending the average life, rather than shortening it.

b2: Indeed not, but no one is presenting info on Luftwaffe engines. I wish they would.

I suspect that those familiar with the Me109 for example, are well aware that the use of a properly modelled WEP while flying over London, will probably mean a long swim somewhere in the English Channel, and thus fuel considerations are probably a primary factor in limiting the use of 1.3/1.4 ATA in the 109, while flying over Britain, and while this is less a worry for RAF pilots it is still very much a factor when fuel consumption rises to ~105gph for the Merlin III at 12lb/3000rpm.

Originally Posted by Blackdog_kt

It would be more accurate to phrase this a bit differently: engine failures were rare not because WEP was free of charge, but because the aircraft rarely survived long enough for the engine abuse to take effect.

OK. Now how to sim that?

[Seadog]

http://i38.photobucket.com/albums/e1...00octane_2.jpg

OK so here we have the engine life of a Merlin III at 12lb boost and in 1938 it was 10 hours and later engines it was 20 hours at 12lb boost.

20 hrs = 30 sorties flown exclusively at 12lb/3000rpm, or 80 sorties at 15min/sortie, which is already exceeding average aircraft life during the BofB.

[Crumpp]

OK so here we have the engine life of a Merlin III at 12lb boost and in 1938 it was 10 hours and later engines it was 20 hours at 12lb boost.

Geez....

Nowhere except in your mind can you run a Merlin at 12lb for 10 hours.

That is the total time the engine ran during endurance trials of 5 minute intervals with a 20 minute rest period between each interval.

It could be used for 5 minutes at a time. That use had to be logged and the engine inspected for serviceability, and the reduction in life assessed before it could flown again.

[Seadog]

"I had to return from Nuremburg in a Wellington II on one engine and used maximum boost and revs on a Merlin X for five hours with no sign of distress..."

= +10lbs at 3000rpm.
The Merlin in Perspective,p25.

[Blackdog_kt]

Originally Posted by Seadog

OK. Now how to sim that?

A few people already gave pretty good ideas on that, but it's currently buried under the Merlin debates

As a short recap:

a) accelerated engine wear model if spawning with a brand new airframe on each sortie, selectable by the player from the difficulty options

b) realistic engine wear model if spawning with the same airframe (relevant aircraft parameters carry over from one sortie to the next in the context of a dynamic campaign), along with a penalty for deliberately "recycling" airframes with abused engines, both for single and multiplayer...once again, selectable from the difficulty options

c) the two above models are mutually exclusive...we shouldn't be able to enable both an accelerated engine wear model and a "carry over" model, clicking one on the difficulty options would deselect the other, but it would still be possible to disable both

This makes sure that if the player is so inclined, he can fly with the uncertainty and chance of mechanical failure that engine abuse would pose.

Simple, clean, optional