Modelling engine wear and WEP limitations

[ICDP]

Seadog no matter how many charts you produce the fact remains that there WAS a limit imposed on the use of +12lbs boost. Even the charts you produce sate that use of +12lbs boost MAY shorten engine life. The fact that an engineer was to assess for potential damage after +12lbs boost was used is a bloody good indicator that potential damage could occur. Not definately damaged but MAYBE damaged, after eventual inspection it may be found that engine is perfect but it didn't mean the potential for damage wasn't there. It doesn't matter if an inspection was mandatory or recommended or even to be contemplated, the fact remains that use of +12lbs boost EVEN FOR A FEW SECONDS, DID require the pilot to make a note in the flight log. It was then up to the engineer to determine if the engine needed overhauled based on the fact that +12 boost INCREASED THE RISK OF DAMAGE. He would not be under orders to do this if there was not some good bloody reason for it.

Not one single person replying to your posts is saying a Merlin will break as soon as 5 minutes at +12lbs boost has passed. We are saying the potential for damage was increased the longer it was used. If you don't want to damage your Merlin then turn off CEM. The rest of us will keep it as close to real as possible.

[Seadog]

Originally Posted by ICDP

Seadog no matter how many charts you produce the fact remains that there WAS a limit imposed on the use of +12lbs boost.

It doesn't matter if an inspection was mandatory or recommended or even to be contemplated, the fact remains that use of +12lbs boost EVEN FOR A FEW SECONDS, DID require the pilot to make a note in the flight log. It was then up to the engineer to determine if the engine needed overhauled based on the fact that +12 boost INCREASED THE RISK OF DAMAGE. He would not be under orders to do this if there was not some good bloody reason for it.

Not one single person replying to your posts is saying a Merlin will break as soon as 5 minutes at +12lbs boost has passed. We are saying the potential for damage was increased the longer it was used. If you don't want to damage your Merlin then turn off CEM. The rest of us will keep it as close to real as possible.

P/O Dutton chose to ignore the 5 min limit. I doubt he was court martialed or penalized in anyway for doing so and his engine may have been a candidate for inspection (as he combined steep dives with overboost), but I doubt he lost any sleep over that.

There is a poster who is claiming that any use of 12lb/3000rpm will result in grounding till a mandatory inspection is done, and I'm glad to see that you disagree with this.

Again, this is exactly what I've been saying. Keep your gauges in the black and 5min+ at 12lb/3000rpm results in increased but still minimal ("low probability") risk, but it is completely ahistorical to claim that pilots did not use 12lb/3000rpm repeatedly or for more than 5 mins as the situation warranted. We know that in the real battle pilots weighed the risks and then "pulled the plug" and some were willing to keep it pulled for more than 5 mins and the game should allow this even with CEM, because that's the way things were. RAFFC went to 100 octane fuel precisely because it allowed the use of 12lb boost and this gave RAFFC a vital edge in performance when it was needed, and some even state that this was the difference between defeat and victory:

V. A. Kalichevsky, author of the 1943 book The Amazing Petroleum Industry wrote:

It is an established fact that a difference of only 13 points in octane number made possible the defeat of the Luftwaffe by the R.A.F. in the Fall of 1940. This difference, slight as it seems, is sufficient to give a plane the vital "edge" in altitude, rate of climb and maneuverability that spells the difference between defeat and victory.

Why bother with a game that goes to great lengths to accurately model aircraft performance, but then takes away the winning edge that 100 octane fuel (despite all the sweat and cost that RAFFC went to make sure that they could take advantage of it) provided during the battle?

[ICDP]

Originally Posted by Seadog

P/O Dutton chose to ignore the 5 min limit. I doubt he was court martialed or penalized in anyway for doing so and his engine may have been a candidate for inspection (as he combined steep dives with overboost), but I doubt he lost any sleep over that.

What? Who the hell mentioned court martials? Is English not your first language?

Originally Posted by Seadog

There is a poster who is claiming that any use of 12lb/3000rpm will result in grounding till a mandatory inspection is done, and I'm glad to see that you disagree with this.

I don't entirely agree with his stance, nor do I agree with yours that an engineer could just shrug his shoulders and say don't worry about it. ALL engines regardless of what boost was used were inspected at the very least at the end of the days flying and preferably at the end of each flight timing permitted. Using +12lbs boost was by your own admission enough to warrant an inspection at the earliest possible convenience. The earliest possible convenience would be that very evening in the worst case scenario. When doing the routine maintenance at the end of each evening the engineer consults the logbooks of all aircraft flown that day. He sees that this particular aircraft has an entry that the pilot used +12lbs boost. He knows from his orders (Straight from Dowding) that it is SOP to do a more thorough check for wear and tear. Do you now dispute this?

Originally Posted by Seadog

Again, this is exactly what I've been saying. Keep your gauges in the black and 5min+ at 12lb/3000rpm results in increased but still minimal ("low probability") risk, but it is completely ahistorical to claim that pilots did not use 12lb/3000rpm repeatedly or for more than 5 mins as the situation warranted. We know that in the real battle pilots weighed the risks and then "pulled the plug" and some were willing to keep it pulled for more than 5 mins and the game should allow this even with CEM, because that's the way things were. RAFFC went to 100 octane fuel precisely because it allowed the use of 12lb boost and this gave RAFFC a vital edge in performance when it was needed, and some even state that this was the difference between defeat and victory:

We know it was used, we also know it was used for longer than 5 minutes per flight on occassions. Everyone here actually agrees that it could be used and that there was an increased risk. Why do you keep this up, here it is again in big writing. Sorry for shouting but this point is very important.

WE ALL AGREE THAT USING +12LBS BOOST COULD BE AND WAS USED LONGER THAN 5 MINUTES BUT IT WAS NOT A RISK FREE ACTION.

Originally Posted by Seadog

Why bother with a game that goes to great lengths to accurately model aircraft performance, but then takes away the winning edge that 100 octane fuel (despite all the sweat and cost that RAFFC went to make sure that they could take advantage of it) provided during the battle?

Ah the bias starts to show. What you want is some "click here = win" button for the RAF? +12lbs boost gave a boost in performance, it was not a massive advantage that guaranteed victory. Even with +12lbs boost the difference in performance between a Spitfire, 109E and even a Hurricane were close enough that surprise, tactics and pilot skill was the determining factor in the outcome of any engagement.

[Seadog]

Originally Posted by ICDP

I don't entirely agree with his stance, nor do I agree with yours that an engineer could just shrug his shoulders and say don't worry about it. ALL engines regardless of what boost was used were inspected at the very least at the end of the days flying and preferably at the end of each flight timing permitted. Using +12lbs boost was by your own admission enough to warrant an inspection at the earliest possible convenience. The earliest possible convenience would be that very evening in the worst case scenario. When doing the routine maintenance at the end of each evening the engineer consults the logbooks of all aircraft flown that day. He sees that this particular aircraft has an entry that the pilot used +12lbs boost. He knows from his orders (Straight from Dowding) that it is SOP to do a more thorough check for wear and tear. Do you now dispute this?

First off, Dowding's memo states that oil filter checks were mandatory, "when convenient" for aircraft that exceeded 5mins at 12lb/3000rpm:

Let's be very clear on this point.:

Originally Posted by ICDP

Ah the bias starts to show. What you want is some "click here = win" button for the RAF? +12lbs boost gave a boost in performance, it was not a massive advantage that guaranteed victory. Even with +12lbs boost the difference in performance between a Spitfire, 109E and even a Hurricane were close enough that surprise, tactics and pilot skill was the determining factor in the outcome of any engagement.

No, want I want is historical accuracy. The Luftwaffe and RAF were locked in a constant technology battle that eventually saw the Luftwaffe field the Fw-190 when the RAF still had the Spit V and then the Me-262...but in 1940 the use of 100 octane fuel gave RAFFC greater power output at medium and low altitudes, when needed. This was the historical situation and I want the sim to reflect it.

I have read through every source on the Merlin engine that I have, and all the combat reports at:
http://www.wwiiaircraftperformance.org/
From what I can gather, Merlin engine failures, were primarily random events and the main culprit was manufacturing defects/design faults that eventually break the engine. The 50 hour 12lb/3000rpm test is an example of this, where the engine was cycled 100 times at 5min/20min at 12/4.5lb boost and eventually developed a coolant leak from a defect that plagued service engines that were not being run past 6.25lb.

The Merlin in Perspective states that fighters had a higher propensity for coolant leaks than bombers because fighters were cycling engine power from very low to very high much more frequently, but this was still not a common occurrence.

The next greatest problem was bearing failure from oil starvation, and again 12lb boost had little to do with this except for prolonged steep climbs, as per Dowding's memo, but probably the greatest cause was inverted flying and prolonged dives that caused excessive (~3600) RPM.

1939 Merlin TBO:
Fighters: 240 hrs
Bombers: 300 hrs

repair depots:
1942 onward: 35% of engines were there due to time expiry.

1942 onward: average engine under repair had 60% of nominal life, or 144 hrs for a fighter engine and 180 hrs for a bomber engine.

I would propose the following:

Any engine has a 65% probability of random major engine failure, during 240 hrs of operation, or about 160 sorties. Another way to express that would be a 6.5% probability of one aircraft out of 16 having major engine failure on a typical mission. I don't know how to model the use of 12lb/3000 rpm for more than 5mins, but a simple way would be be multiply the failure probability by, say 1.15, to simulate the increased RPM and stress on the engine.

[Crumpp]

First off, Dowding's memo states

Who cares? The published Operating Instructions and Technical Orders for the Spitfire are clear. Dowding was not the technical expert on Rolls Royce engines. He had people to fill that role for him and he followed their advice.

It is a fact, ANY use of +12lbs in the Merlin engines requires a log book entry and a mechanics inspection before the engine is returned to service.

You seem to think that having the engine inspected after the extreme stress of over boosting is uncommon.

Almost every fighter aircraft engine in WWII had to have it done.

BMW, Diamler, Rolls Royce, Allison, and just about every else required it. It only makes practical sense.

Even OUR P51D Merlin had the same instructions:



I think you just want a magic win button for your game.

[Seadog]

Originally Posted by Crumpp

Who cares? The published Operating Instructions and Technical Orders for the Spitfire are clear.

They certainly are clear and Dowding's memo leaves no room for doubt.

Originally Posted by Crumpp

Dowding was not the technical expert on Rolls Royce engines. He had people to fill that role for him and he followed their advice.

He certainly did, which is why the memo is worded the way it is.

Originally Posted by Crumpp

It is a fact, ANY use of +12lbs in the Merlin engines requires a log book entry and a mechanics inspection before the engine is returned to service.

You seem to think that having the engine inspected after the extreme stress of over boosting is uncommon.

Almost every fighter aircraft engine in WWII had to have it done.

BMW, Diamler, Rolls Royce, Allison, and just about every else required it. It only makes practical sense.

Even OUR P51D Merlin had the same instructions:



I think you just want a magic win button for your game.

War emergency power on a Mustang!!!? The Mustang/Merlin 60 series was not the same as 12lb boost on a Merlin III:


67 inHg = +18 lbf/in² boost
61 inHg = +15 lbf/in² boost
46 inHg = +8 lbf/in² boost
44.5 inHg = +6 lbf/in² boost

so they are talking about pulling 18lb boost and 1700hp from a Merlin Engine with a two stage SC, or about 30% more power than a Merlin III at 12lb boost.

The Normal full throttle setting on the Mustang is 61" boost or 15lb boost and at that setting no extra inspection is required.

The Merlin XII was cleared for 12lb boost on T/O, so this was simply normal operations for a Spit II

[Blackdog_kt]

All i know is that takeoff power or emergency power is called that way for a reason: it is to be reduced to lower levels under all other regimes of flight.
Otherwise they would just call it full power and be done with it.

The mustang's 67" of MP is equivalent to the Spits +12lbs, the 109's 1.45 Ata and so on and so forth, take your pick, in the sense that they are not meant to be ran for eternity because things will start to break. Maybe not on this sortie or the next, but definitely something will give after a few missions, especially if i push it that way on every single sortie and the mechanics follow your reasoning of not inspecting it afterwords

As another example, for later mark Spitifires like the Mk.IX it was advised to take off with a mere +9lbs no matter if it could do +12, +16 or +25 and that's a pretty critical phase of flight in terms of power reserves in case something goes wrong.

If they didn't slam the throttle to the stops on takeoff that's telling me that full power at low airspeeds was a combination for insufficient cooling, overheat and eventual engine seizure if the oil dissolved. True, this is for later mark Spits with a higher power output, but these also had an extra radiator to help with cooling which our in-game early Spits lack, so it's more or less a trade-off.

All that is enough explanation for me to convince me that operating limits are there for a reason. I want a difficulty setting that imposes penalties if i exceed them, that's all. If you don't like it, feel free not to use it.

However, the majority of people in the community won't stand for implementing changes to the FM/DM that have all other aircraft adhering to some kind of limits while the Spitfires suffer none and it's not even for balancing reasons. It's because it's common sense to assume that emergency and takeoff power are named that way for a reason.

Can we please get back on the topic of how such a game mechanic/feature could be implemented? If you want to continue debating if +12lbs classified as emergency power, feel free to start a different thread about it, you're just being off topic in this one:

The current thread is not about "what can the Merlin run with impunity?". The topic is "how do we punish the player that exceeds what the engine can reasonably run, if he chooses to enable the relevant difficulty/realism settings". It's about ALL engines, not just the Merlin.

[Kurfürst]

Originally Posted by Seadog

Why bother with a game that goes to great lengths to accurately model aircraft performance, but then takes away the winning edge that 100 octane fuel (despite all the sweat and cost that RAFFC went to make sure that they could take advantage of it) provided during the battle?

I have a funny picture for Mr. Kacys-whatever, who seems to think 100 octane was only on the British side. Note the funny triangle behind the cocpit, and the numbers written on that. It shows what kind of fuel the plane is to be filled up with.

[Crumpp]

[Crumpp]

It's the prop that might fail, not the engine.

The way i presented the example caused your confusion. It is not one thing but two seperate issues. The Hartzell bulletin has nothing to do with take off rating of the engine. It just illustrates how seemly minor changes can have catastrophic effects.

A Lycoming O-360 is take off rated and you don't use it except for take off. That is an engine limitation.

The Hartzell bulletin is talking about specific O-360A1A's equipped with a specific hub/blade combination AND using Lightspeed's Engineering electronic ignition.

Your next point, of course I meant inches of mercury. It does not matter though...you don't exceed the 28 on the EFIS!!

So I would modify your first statement to say that

have to ask who cares and what is point of this portion of your reply? Are you trying to educate me on TBO determination? It is a fact that sometimes TBO are very arbitrary and not based on any real engineering at all. Why? The company does not spend the money or the time or have enough data.

Many times manufacturer's set them very low at first and then raise them as field experience is gained. Rotax 912 is a modern example.

Everyone is expecting the Centurion Diesels to see a TBO raise too. They did the same thing.

http://www.centurion-engines.com/typ...x.php?id=2&L=1

What is important and seems to get covered up in your reply Viper is the following:

Pilot's fly airplanes IAW the Operating Instructions published by the manufacturer.

End of message.

Anything else is baloney and thinking like a gamer, not a pilot.

Engineers do this because it is generally assumed that pilots can't be trusted to obey the limits in the Pilot's Notes. Sad but true.

I would say this baloney in all my real world experience both in college, PIC, and in maintenance of aircraft. I don't know of any RL pilots who condone exceeding published limits at all. It is not the engineers life on the line.

I certainly don't know any licensed A&P's who think that way or do not follow publications. That is good way to kill somebody, lose your rating, and even go to prison. There are shady folks in aviation. One owner and he FBO are in the process of suing one such individual right now. That is if the sheriff does not get to him first.

In reality, not following published procedures can and will kill you. The FAA statistics show this quite nicely.

The reality is only a tiny fraction of the community knowingly violate procedures. Most understand the importance and the consequences of not following it.

I knew this pilot. He was VERY professional and flew his aircraft by the numbers. Nothing he did in an airplane was unplanned or "seat of your pants".

He died because he did not change his altimeter setting. He made a simple mistake and did not follow procedure to monitor ATIS and adjust the altimeter accordingly. He entered a loop and end up with CFIT.

http://www.youtube.com/watch?v=rLDiPEgysYI

You should know the old axiom, "There are Old Pilots and there are Bold Pilots but there are not any Old and Bold Pilots!"

It got to be a axiom because it spells out the truth.

None of this is good, but it is reality.

Your reality is far different from my experiences. I have to take your comments about the 152's and flying outside of CG and everything else with a grain of salt or at least it does not apply to General Aviation in the United States.

Of course there are almost 20,000 airports to land at in the United States. I can find a convenient airport at almost any destination I choose. In the EU, you have just over 2500 airports to land at.....

It is impossible to compare the General Aviation community as GA is a completely different animal in the EU.

Perhaps when the EU GA community matures, it can begin to keep statistics to help make the pilot community safer. Maybe then your civil pilot population will become more educated and not act so recklessly.

As regards to safety, the partial data available gives only some indication as to the main causes of fatal accidents. There are no European wide comprehensive statistics on safety of General Aviation Aircraft

http://www.epats.eu/Files/Deliverabl...PADBase-V1.pdf

Continental did that because they did not test or design the engine for any higher rating. When the O-520 first came out, the crankcase was too light even at maximum continuous and there were many failures as a result. Subsequently Conti went to steel on steel for their rings and now very few of them make it to TBO without a top end.

In short, the engine has had too troubles at it's current rating to even think about a manifold pressure increase.

It is also not tolerant at all of improper procedures. Feel free to invest your money in an O-520 and then not follow the book. :p

If the installation has plenty of power, there is no need for a Take Off rating. The Lycoming O-360 has been adopted to so many installation that including many heavy twins. That little 180 hp engine pulls some weighty airplanes around now. The O-360 series is a close to bullet proof as you can get in a light aircraft engine. I wouldn't trade mine for all the tea in china.