Modelling engine wear and WEP limitations

[VO101_Tom]

Originally Posted by Seadog

...
Pilots could and did run engines at 12lb/3000rpm for a long as they needed to, and in the final analysis, no one really cared, as long as it gave them the edge in combat, which was why the RAF changed over to 100 octane fuel...

What does this mean according to you then (copy from other topic)?

*Buzzsaw* linked several links in 109 e3b against spitfire II topic, i noticed one thing:

http://www.ww2aircraft.net/forum/avi...2-a-20108.html

"The discussion was led by 'Glider' Gavin Bailey, who is a well respected historical journal whose material is subject to critical scrutiny by the best of English historians."

He wrote this:
1st August 1940 Memo from Downing re the Handling of the Merlin Engine
This note is advising the pilots that there is an increase in engine failures in the overuse of the emergency 12lb boost.
The interesting thing is that this memo was sent to ALL fighter groups. Had we been talking about the 16 squadrons or less this would not have been the case. It would have been sent to the squadrons involved.

I think, this unambiguous warning. If was used continuously the 12lbs boost, and the engine was ruined continuously, it does not interest, if COD makes the same one.

[Seadog]

Originally Posted by VO101_Tom

What does this mean according to you then (copy from other topic)?

He wrote this:
1st August 1940 Memo from Downing re the Handling of the Merlin Engine
This note is advising the pilots that there is an increase in engine failures in the overuse of the emergency 12lb boost.
The interesting thing is that this memo was sent to ALL fighter groups. Had we been talking about the 16 squadrons or less this would not have been the case. It would have been sent to the squadrons involved.

I think, this unambiguous warning. If was used continuously the 12lbs boost, and the engine was ruined continuously, it does not interest, if COD makes the same one.

If you read Dowding's memo carefully:
http://www.spitfireperformance.com/dowding.pdf
he discusses a number of scenarios that result in engine oil starvation and/or overheating. The engines were failing, not just from overuse of 12lb/3000rpm but from overheating and lack of oil pressure. Steep climbs damage the engine from overheating, not overboosting. Inverted flying damages the engine from lack of lubrication not overboosting. Dowding memo is pretty clear: keep your gauges in the black! Yes, Dowding states not to use 12lb boost for more than 5 minutes, but the real culprit is overheating and lack of oil pressure. No sane pilot, in a combat situation, say with a 109 on his tail is going to worry about using 12lb/3000rpm for more than 5 minutes, and Dowding's memo is nothing more than a reminder to not use overboost except when really needed.

[VO101_Tom]

Originally Posted by Seadog

If you read Dowding's memo carefully:
http://www.spitfireperformance.com/dowding.pdf
he discusses a number of scenarios that result in engine oil starvation and/or overheating. The engines were failing, not just from overuse of 12lb/3000rpm but from overheating and lack of oil pressure. Steep climbs damage the engine from overheating, not overboosting. Inverted flying damages the engine from lack of lubrication not overboosting. Dowding memo is pretty clear: keep your gauges in the black! Yes, Dowding states not to use 12lb boost for more than 5 minutes, but the real culprit is overheating and lack of oil pressure. No sane pilot, in a combat situation, say with a 109 on his tail is going to worry about using 12lb/3000rpm for more than 5 minutes, and Dowding's memo is nothing more than a reminder to not use overboost except when really needed.

I read it, thanks. Sry, this did not convinced me
They would write it if the injury of the bearing would depend on the temperature only. "Be watching the thermometer, and untill not in red, u can make what you want". Unnecessarily would limit their pilots (5 min limit) without reason?

"but the real culprit is overheating and lack of oil pressure." - and the strain of the drive. I believe it you recognise it you too, it takes advantage of everything if you squeeze more strength from the drive. Winch, crank, bearing, axis, gaskets, cooling, lubrication. They call it emergency power (notleistung in 109) because of this.

"No sane pilot, in a combat situation, say with a 109 on his tail is going to worry about using 12lb/3000rpm for more than 5 minutes" - totally agree I would not care about it. But the engine from this probably gets ruined yet. U reach home, or dont, it depends of luck. If u lucky enough, u can show the oil filter to maintenance team, if not... with an airplane less.

The same one is true for the Bf 109 anyway. Invert flying prohibited its oil system, and the increase manifold pressure until time only it may be used (start und notleistung). It is not linked to the temperature there actually, but this unambiguous. Temperature OR the time a limit defines it, till when it may have been used.

What is interesting yet, and I did not know about the fact that the system of the hydraulic propeller is bound to the engine, not separate system: "loss of engine oil pressure (inverted flight, slow rolls) has an effect on the Rotol aircrew in that baldes return to a fine pitch position". This means that he should lose very much from the performance at this time right?

[Crumpp]

At least you've given up on this fantasy notion of a strip inspection after every use.

A complete fiction that only exists in your mind. Feel free to quote me on the requirement for an overhaul.

You don't read what anyone else writes.

Crumpp says:
Change the oil, oil analysis, filter changes, compression check, and over all inspection for cracks/leaks/function would be in order to ensure engine health.

That is about 3 hours worth of work on a Merlin engine. If they check crank bearing tolerances then you can add about an hour to it. If they find something then of course, it will get fixed or replaced.

Once that is done, the mechanic would enter into the logbook the work performed and return the aircraft to service. A few hours in the shop is certainly worth the pilots peace of mind.

http://forum.1cpublishing.eu/showpos...0&postcount=27

[Seadog]

Originally Posted by Crumpp

Quote:
Crumpp says:
Change the oil, oil analysis, filter changes, compression check, and over all inspection for cracks/leaks/function would be in order to ensure engine health.

That is about 3 hours worth of work on a Merlin engine. If they check crank bearing tolerances then you can add about an hour to it. If they find something then of course, it will get fixed or replaced.

Once that is done, the mechanic would enter into the logbook the work performed and return the aircraft to service. A few hours in the shop is certainly worth the pilots peace of mind. [/url]

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.

[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.