The P40 thread

[Venturi]

Like I said, engine failure modeling needs to be looked at.

 

You can't have a one size fits all approach to engine failures.

[216th_Lucas_From_Hell]

That's good information, specially for the P-39L. Do you know from which timeframe are these specs? Everything is in line with the P-39L manual (except the 60" which doesn't figure as clarified in the Russian chart), which you can find as a 1944 revision of the 1942 original. However I have seen 1943 manuals for the P-39N (which has the V-1710-85) allowing 50.5" for 5 minutes.

Having 60" (1580 HP very nice) would turn the P-39L into a pretty powerful plane, having similar speed to the La-5 with boost at the deck and climbrate of that of the Bf 109G, according to some performance test I have seen with the P-39N with it's -85 engine at 57" (developing a similar amount of power, around 1400 HP).

I'm not entirely sure but they were pulled from "Airacobras Over Kuban", I assume the author picked Soviet documents referring to that period. Indeed being able to have the full 1580hp in short bursts will make vertical fighting against 109s a breeze.

[Venturi]

Romanenko's Airacobra book has a table on operating the V-1710-63 with 100 octane fuel. Not the same aircraft or exact engine model as the P-40, but the fuel consumption column might be good for planning a flight.

 

The top row reads regime, Horsepower produced, rotations per minute, altitude (ft, m), fuel consumption (litres per hour). The regimes are take-off (up to 5 minutes), WER (up to 5 minutes), combat (up to 15 minutes), nominal (up to 30 minutes), cruise (0.75 of nominal), cruise (0.6 of nominal). The footnote reads "in the technical manual of the P-39K and L there are no instructions on WER".

 

 

There is no mention of the manifold pressure heading in that very nice graphic...

Edited August 18, 2017 by Venturi

[Venturi]

The P39 airframe was much cleaner than the P40 and smaller as well as lighter - overall better for aerobatics, there is no doubt.

 

But the fact that the P39L was powered by essentially the same engine as the P40E should tell everyone something about the engine. 

 

From Whitney's "Vees for Victory" pg 265:

 

The original source document Whitney used as basis for the 1500hp design spec of the V-1710-39 was "Internal Allison Memo to Chief Designer and Design Project Engineers, dated 11/16/1940".

Edited August 18, 2017 by Venturi

[Venturi]

Like I said, engine failure modeling needs to be looked at.

 

You can't have a one size fits all approach to engine failures.

 

See my post on this topic more than a year ago:

https://forum.il2sturmovik.com/topic/21234-p-40-engine-settings-i-found-them-bit-weird/?p=340873

 

This is old news for the old hands, but for those who aren't in the know, see attached for the letter from 1942, by the Chief Engineer of Allison, describing pilot practices of "going above and beyond official power ratings". It is also mentioned in Whitney's book.

 

The 70" Hg manifold pressures he mentions as "requiring overspeeding" refers to manually running the engine RPM over maximum, to achieve a higher supercharger speed and thus a higher manifold pressure. 

Edited August 18, 2017 by Venturi

[Farky]

That's good information, specially for the P-39L. Do you know from which timeframe are these specs? Everything is in line with the P-39L manual (except the 60" which doesn't figure as clarified in the Russian chart), which you can find as a 1944 revision of the 1942 original. However I have seen 1943 manuals for the P-39N (which has the V-1710-85) allowing 50.5" for 5 minutes.

 

 

With P-39L, situation will be similar to situation with P-40E - engine (V-1710-63) was cleared for WER 60 inHg@3000 rpm. However, 60inHg MAP (i.e. WER) was never officialy allowed to use in P-39L, but only because this airplane do not have automatic MAP regulator. Same engine was cleared in P-40K for 60inHg WER, simply because this airplane got automatic MAP regulator. Note - I know that engine in P-40K was V-1710-73 and engine in P-39L (and D-2/K) was V-1710-63. Those engine are however the same, only difference is in gear box.

 

Manual for P-39N issued February 1943 permits use of 57inHg@3000rpm (1420 BHP at 9000 ft). We have to keep in mind however, that engine in P-39N (V-1710-85) have different supercharger gear ratio than V-1710-63. Therefore limits for V-1710-85 engine were different, lower actually.

[Venturi]

Yes, a faster supercharger gear may mean a higher critical altitude, but it also means that the intake fuel/air charge will have higher temps at altitudes below critical. This means the detonation threshold is lower. As Hazen says.

 

(due to the intake air/fuel mix being compressed more with the faster s/c gear as compared to the slower s/c gear - the extra pressure from the faster s/c gearing is vented but the temperature of the rest of the air/fuel mix remains elevated... ideal gas law... PV=nRT)

 

This is why multi-stage s/c was invented. And not just multi-gears. That and impeller efficiency as the impeller tips reached the speed of sound...

 

But... back to the P-40E...

Edited August 18, 2017 by Venturi

[216th_Lucas_From_Hell]

The way I see it the model used now is factually incorrect, but at the same time it can understand it as a logical choice when resources and time are thin since it's a matter of inputting data from manuals they already have into clearly-defined limits bound to a period of time. This saves time and creates a standard that applies to all aircraft, thus also clearing potential bias calls from either side.

 

The problems with this system are obvious, too. Mainly, it's not a real representation of engine operational limits, but having engines entirely unrated wouldn't depict the logistical needs either.

 

These manual limits approach, to me, would be fine IF there was a universal standard used when creating them but a lack of convention combined with different needs in some specific cases (pre-war USAAC wanting to make their aircraft last longer compared to wartime Axis and Allied armies wanting to cut losses first, achieve longevity of the engine second) creates problems like the P-40 model. While this stricter model doesn't entirely kill the aircraft's efficiency, it definitely shaves some of it off but whenever any other aspects of it are off, then you have a huge problem (ie conservative engine limits + excessive energy loss right now).

 

My opinion is that a revision of this model on a case to case basis would be good, but only when the time and resources are free.

[Venturi]

I like your statement, but disagree slightly. A system could be applied universally to the engine limits as they are understood now, and this would allow lesser resource allocation.

 

Such a system would introduce significant (not just a few seconds) randomness to anything beyond the official limits. 

 

The random element in such a system could be tweaked on an aircraft-by-aircraft basis, which would allow for specific situations like the P-40E. It would be important that this be done correctly of course, based on evidence such as that shown above.

 

It would also be important to be transparent about such a system to the user base.

 

Gamers are going to be gamers, simmers will always be simmers. Understand where the product lies on this spectrum... do you want this to be a sim? I think that's where the product wants to go, within reason...

 

Be brave about that choice.

Engine realism is at least 50% of the battle. For a sim.

 

Airframe performance is the other 50%, as you mention.

Edited August 18, 2017 by Venturi

[216th_Lucas_From_Hell]

I think we don't really disagree on it, that's exactly the kind of system I had in mind. Why I think it takes time is because once you start looking into it, each engine has its own quirks regarding limits which will need to be looked at objectively (actual resistance at different regimes first, but a secondary reasonable respect to logistics too).

 

For example, the M-82 (together with its predecessor in the I-16) has a very short-lived boosted mode while the M-82F, a slight modification, can run it all day. You also have the Bf-109G-2/4 engines which were initially very restricted due to some teething problems but later the WEP was cleared for longer use. To keep it short, the engines on all BoX aircraft bar the Yak-1, LaGG-3 and Pe-2 had strict manual limits that are present in game. It's a little hard to figure out the specifics for all of them to set the right timers and margins of error, but I believe it to be possible with some time investment.

 

Other less time consuming solutions would be to update the limits to 1942 or 1943 standards for the same engine (on par with the Airacobra L-1, which is only a year older) or, less elegantly, have engine limits as a modification akin to what they did when the Bf-109G-2 and G-4 were given different limits despite using the same engine. This solves this problem for the P-40 but on a larger scale the same thing could happen again under similar circumstances.

Edited August 18, 2017 by 216th_Lucas_From_Hell

[6./ZG26_Klaus_Mann]

The 109s Restrictions were almost always based on Lubrication. The DB605 especially suffered from the Switchover from Ball to Plain Bearings on the Crankshaft, without adding a more Powerful Oil Pump and Scavenge Pump. This could lead to Oil Fires in the Engine, which may well have caused the Death of Marseille. 

 

The DB605s were  retrofitted with a more Powerful Oil Pump and only this allowed the use of the higher Ratings. 

 

The M-82F was also a fixed Version with imroved Lubrication to prevent actual Fires. 

 

As far as I understand the only Reason to not allow use of high Manifold Pressures on the P-40E was the Lack of the MAP Regulator, which could Lead to Severe Over-Pressure in Aerobatics with large Altitude Losses and Fear of Engine Damage due to this as well as reduced Lifetime. The same Engine when used with the MAP Regulator was allowed to go 56", in the P-51As for example. 

 

In my Experience with Overclocked Engines the Valves and Pistons are the First ones to give, normally in a Random Order, but often the Cylinder to get the Oil from the longest Lines with the lowest  Oil Pressure, normally running the hottest as well, as they are also the last ones in line to get Water. So normally the  Rear or most Forward Cylinders. 

Due to the Engine Power these Cylinders don't Seize, but get destroyed, Holes in the Top, Cracked Valves etc. normally leading to little more than loss of Power on 1 Cylinder an a lot of Oil Loss, but not immediately Catastophic. 

 

In any Case, Overclocked Engines tend to have rather Localized Rod Bearing/Piston/Valve Damage, Power Loss but Catastrophic Failure as it normally happens ingame is rare. 

[Venturi]

Engine oiling follows a completely different sequence than water coolant flow.

 

Engine oil does not cool cylinders. It cools the valvetrain. Also, the first things to get oil are the crankshaft main bearings (all of them sequentially), then camshafts and valvetrain. Front to back does not play into it.

 

Water coolant flows in between cylinders in the engine block. This is being pumped under pressure and the specific heat of water is so large that it does not matter which cylinder gets the water first.

 

What you describe is accurate for a air-cooled engine, because the cylinders with the least airflow are usually in the back. But we are not discussing radial engine planes.

Maybe you are referring to small modern pancake-4 air-cooled engines as in Cessnas, but inline engines are different.

[216th_Lucas_From_Hell]

In any Case, Overclocked Engines tend to have rather Localized Rod Bearing/Piston/Valve Damage, Power Loss but Catastrophic Failure as it normally happens ingame is rare.

 

So, translating it into the game, an "engine damaged" message with slight reduction of power, worsening progressively the further you go past the limit?

[Gambit21]

So, translating it into the game, an "engine damaged" message with slight reduction of power, worsening progressively the further you go past the limit?

 

Only we'd want more indication that didn't rely on 'techno-chat' as well.

Be that some kind of knocking, or however this damage would manifest from a noise/sound perspective.

[216th_Lucas_From_Hell]

Is that in line with the actual signals an engine gives when it starts wearing out though? Wouldn't want any gamey gimmick to be introduced. The three times I've experienced engine problems in real life were in completely different aircraft with different engines (once in a HS 748 in flight, twice in a C-130H during take-off), but there were no audible clues resembling a knock of anything. In the 748 and the first 130 incident the problems only came up in the engine readings, while the last time you could see one of the engines was not reaching the correct RPM but once again no knocks or such, just a slight change in pitch.

 

Unless I'm wrong (and given these were high-end piston aircraft as opposed to transport turboprop birds I could really be), a more realistic way would be to just let the instrument readings and natural sounds (such as changes in pitch from spikes/drops in manifold pressure or rotations) do the job. Anyone fiddling with the engine beyond its limits probably needs to know how much it can take and when it's taken too much.

[Gambit21]

Is that in line with the actual signals an engine gives when it starts wearing out though? Wouldn't want any gamey gimmick to be introduced. The three times I've experienced engine problems in real life were in completely different aircraft with different engines (once in a HS 748 in flight, twice in a C-130H during take-off), but there were no audible clues resembling a knock of anything. In the 748 and the first 130 incident the problems only came up in the engine readings, while the last time you could see one of the engines was not reaching the correct RPM but once again no knocks or such, just a slight change in pitch.

 

Unless I'm wrong (and given these were high-end piston aircraft as opposed to transport turboprop birds I could really be), a more realistic way would be to just let the instrument readings and natural sounds (such as changes in pitch from spikes/drops in manifold pressure or rotations) do the job. Anyone fiddling with the engine beyond its limits probably needs to know how much it can take and when it's taken too much.

 

I wouldn't know...but techno-chat is a gimmick, and one many would tend to turn off I think.

So given that it would be nice to have some kind of (plausible) indication, even if it ended up being a compromise of sorts.

[6./ZG26_Klaus_Mann]

Engine oiling follows a completely different sequence than water coolant flow.

 

Engine oil does not cool cylinders. It cools the valvetrain. Also, the first things to get oil are the crankshaft main bearings (all of them sequentially), then camshafts and valvetrain. Front to back does not play into it.

 

Water coolant flows in between cylinders in the engine block. This is being pumped under pressure and the specific heat of water is so large that it does not matter which cylinder gets the water first.

 

What you describe is accurate for a air-cooled engine, because the cylinders with the least airflow are usually in the back. But we are not discussing radial engine planes.

Maybe you are referring to small modern pancake-4 air-cooled engines as in Cessnas, but inline engines are different.

Well, most of my Petrol Experience is on old BMW Motorcycles, Vespas and Mopar, Ford or Lexus Small Block V8s.

We use the V8s in our Glider Winches , so they are Specced up to around 300hp and run a quite unhealthy Diet of 1 Minute Sprints close to Overheat, less than 2 Minute Cooldown, Stop, Start and amost immediate 1 Minute Sprint. 

 

We are basically killing these Engines by the Book. And their Deaths and Autopsy (and Rebuilds) are among my Favourite Parts apart from flying because it's a Learning Experience every time. 

 

The most Fun and Peculiar was a Case where 1 Piston had huge Hole melted into it, but all the Metal from it was melted onto the Top of the Opposite Side Piston. It got there through the Oil. 

In every case it's pretty much always the #1 and #2 or #7 and #8 Cylinders that Fail, normally with cracked Valves or Melted Pistons. These have the longest Distance to the Oil Pump depending on Manufacturer and where the Pump Sits. 

And since the Water goes in through the Block, but out through the Head, the Cylinders closest to the Water Pump experience the largest difference in Cooland Temperature between Block and Head. 

 

Especially the Mopar Engines suffer from this. The Forward Cylinders have the worst Lubrication and the largest Cooland discrepancy. 

 

The Allison has a somewhat better Coolant Distribution, but still only one Oil Pump, so there will be Temperature Spikes on the Cylinders Furthest away from the Pump I imagine as well. 

 

The Main Problem is Lubrication Piston to Cylinder Wall. When the Engine starts running too hot there is always a Pair of Cylinders where the Lubrication Fails first. The Pistons heat up and Fail the the Weakest Point, normally at thinnest Part of the Top. And when the Spit hot Metal into the Exhaust Valve, get it Stuck, they tend to shatter the Valve as well. 

 

I bet that a long V12 Block isn't immune from Physics. 

Edited August 18, 2017 by 6./ZG26_Klaus_Mann

[Venturi]

Well, most of my Petrol Experience is on old BMW Motorcycles, Vespas and Mopar, Ford or Lexus Small Block V8s. 

We use the V8s in our Glider Winches , so they are Specced up to around 300hp and run a quite unhealthy Diet of 1 Minute Sprints close to Overheat, less than 2 Minute Cooldown, Stop, Start and amost immediate 1 Minute Sprint. In other words, you are using a totally abnormal fuel with completely different detonation characteristics than what we are dealing with here.

 

We are basically killing these Engines by the Book. And their Deaths and Autopsy (and Rebuilds) are among my Favourite Parts apart from flying because it's a Learning Experience every time. I bet...

 

The most Fun and Peculiar was a Case where 1 Piston had huge Hole melted into it, but all the Metal from it was melted onto the Top of the Opposite Side Piston. It got there through the Oil. How, through the cylinder head? Or through the engine block? No way to get there "through the oil"... 

 

In every case it's pretty much always the #1 and #2 or #7 and #8 Cylinders that Fail, normally with cracked Valves or Melted Pistons. These have the longest Distance to the Oil Pump depending on Manufacturer and where the Pump Sits. 

And since the Water goes in through the Block, but out through the Head, the Cylinders closest to the Water Pump experience the largest difference in Cooland Temperature between Block and Head. You do not get enough of a coolant heat difference across a block to cause any sort of detonation. If you got that hot, the cylinder head gasket would rupture.

Again, oil does not cool piston tops. It may cool valve heads. However, what you are describing is DETONATION.

 

Especially the Mopar Engines suffer from this. The Forward Cylinders have the worst Lubrication and the largest Cooland discrepancy. Again, nothing to do with cooling. Your alcohol fuel and whatever else you've done to the fueling / timing is causing this.

 

The Allison has a somewhat better Coolant Distribution, but still only one Oil Pump, so there will be Temperature Spikes on the Cylinders Furthest away from the Pump I imagine as well. You cannot take incorrect theories and apply them to different engine types, with different fuel types completely, and different operating regimes. It's like comparing a top fuel dragster engine to a formula 1 engine to a turboprop engine. NOT the same.

 

The Main Problem is Lubrication Piston to Cylinder Wall. When the Engine starts running too hot there is always a Pair of Cylinders where the Lubrication Fails first. The Pistons heat up and Fail the the Weakest Point, normally at thinnest Part of the Top. And when the Spit hot Metal into the Exhaust Valve, get it Stuck, they tend to shatter the Valve as well. I disagree with you. Lubrication will ALWAYS fail first at the crankshaft, because it has the largest bearing load. This is why there are so many bearing journals and why it gets fed oil FIRST before anything else.

 

Your problem is detonation from improper fuel and improper other unspecified things. The reason you get TWO cylinders always having the same problem, is because the fuel/air mixture is different across the cylinders. You are seeing detonation occur first in the cylinders which have the most improper fuel/air mix, which will always be across from each other - they receive a leaner mix than the rest, because these engines do not have direct fuel injection.

 

I bet that a long V12 Block isn't immune from Physics. I also bet it isn't, and I also bet it isn't immune from detonation or bad theories.

 

The problem with people who don't understand how something SHOULD work, is that they always come up with bad theories about what went wrong after the fact.

Edited August 18, 2017 by Venturi

[216th_Lucas_From_Hell]

Let's try to establish a repeatable behaviour that applies to the Allison. Knowing how the engine runs and its idiosyncrasies, in the event of a failure through actual excessive use of available power, which components were most likely to fail, why, and what effect would this have on the engine in flight?

 

If to propose any changes to the developers it would be good if we could at least establish what were the actual consequences of running the engine on emergency, combat or take-off power for too long as opposed to the effects in game.

[Venturi]

There are several effects in play here for emergency power. I've written about them before but I can do some writing again now.

 

The three main effects which are relevant to the sim are:

 

1. Overheat of coolant and of oil (these are different)

2. Detonation

3. Overspeed failure of components

 

I'll deal with these in order.

 

1a. Overheat of coolant

This is due to inadequate thermal dissipation.

Coolant (water) has a very large specific heat, it takes a lot of energy to increase its temperature. It also absorbs thermal energy quickly (unlike oil). It has a high heat transfer efficiency. This is what makes it useful as a coolant. A internal combustion engine at its best is about 30% efficient, if we are talking about power output through the crankshaft (not taking into account efficiency losses from prop, geartrain, etc). That means 60-70% of the energy in the fuel must be dissipated as thermal energy. This is primarily accomplished, in water cooled engines, by the water based coolant. The rate of temperature increase will depend on the mass of the coolant, the energy it is absorbing, and the rate of cooling... but it should not be very quick as long as there is cooling occurring, by design. As far as absolute "overheat" of coolant goes, most airframe and radiator designs have sufficient capacity to cool the engine in most situations. Obviously, if you are climbing at max angle in emergency power with anything less than full radiator open, you deserve to get a overheat. And you may not be able to use your engine very long at high output power levels in that circumstance.

 

1b. Overheat of oil

This is also due to inadequate thermal dissipation. However, oil does not have a high heat transfer efficiency and does not have a high specific heat, unlike water coolants. It has the advantage of being primarily a lubricant, so can be places in the engine (and cool parts in the engine) which are not necessarily going to be close to a water -coolant jacket. So, it absorbs less heat but still has an important role to play. Usually oil temperature increases or decreases track with coolant temperature increases or decreases, but the temperature changes are delayed compared to the water temperature changes. In other words, your oil will continue to get hotter after using emergency power and then going back to regular power. Whereas the direction of rate of change in water temperature will almost immediately track the engine thermal output changes.

 

2. Detonation

This is the trickiest and also the most important aspect. It is what limits manifold pressure and power in aircraft engines of the timeframe we are dealing with. Detonation occurs when the heat from combustion in the cylinders is so high on certain small spots of the cylinder, like valve reliefs in the piston tops (but not in the whole engine, only in small spots that get extremely hot), that it causes the fuel/air mixture to explode in a disorderly extremely violent manner, while the piston is near the top of its stroke. This hammers the piston top and erodes the rings and seal of the piston against the cylinder (AKA, power loss and oil burning in the cylinder). A related and more serious phenomenon is pre-ignition, which is where these same areas ignite the fuel/air mixture even sooner, before the piston comes up. This hammers the piston even harder and will burn through the top of the piston and might even fracture engine parts. Consider it a spectrum of the same problem, with detonation occurring before pre-ignition. 

 

3. Overspeed (RPM) failure of components

Every engine has a max RPM at which its components like connecting rods will fail. The stress on the components is proportional to the square of the RPM. There is usually a fair amount of tolerance in the design of engines, and aero engines like these ran at fairly low RPM. In these circumstances, you will get a connecting rod breakage or valvetrain/piston "kiss" or collision at higher RPMs, which would almost immediately spell out catastrophic failure of the engine. However, it would take a fair bit of time and RPM over the specified "maximum power level RPM". 

 

So, now how these would actually play out:

 

1. Coolant (more than Oil) overheat is a problem which might arise relatively quickly in extreme flight circumstances, or when idling on the ground, or when the pilot has exerted his engine for a very long time at high power levels (causing "heat soak"). Any plane should be subject to such stresses and limits, some more than others. Otherwise it should not be too much of an issue for a properly designed aeroplane in normal flight.

 

Oil/air cooled radial engines work slightly differently. 

 

2. Detonation is the MAJOR problem when using engines at high power levels. It is brought about by two forms of use: Too Much Absolute Pressure for Too Long, OR Too Much Pressure at Too Low an RPM. 

 

When you run an engine at high pressures and low RPMs, you cause detonation. This is a major pet peeve of mine. You should only be able to run maximum pressures at or near the maximum design RPM of the engine.

 

The more traditionally understood problem, is when you run the engine too long at high pressures, and you cause detonation. For American 100/130 (lean/rich ratings) octane fuel, the limit seems to be around 65" Hg manifold pressure for instantaneous detonation. As you increase the duration of use however, this pressure level may need to be reduced as "hot spots" are created in the engine.

 

3. Overspeed of components. This is a pet peeve of mine in the sim. You can run these engines at high RPM but moderate manifold pressures indefinitely. RPM should not by itself be a timer trigger for "extreme" engine states. ONLY manifold pressure should trigger timers. However, the game does simulate overspeed kills of engines pretty well in my opinion.

 

There you have it. Any honest questions please ask.

[216th_Lucas_From_Hell]

Thanks a lot for taking your time to write this out, Venturi!

 

If I understood it right then, a simple improvement of engine damage simulation (even within the current system) could involve:

 

1) use manifold pressure only to determine timers for excessive use

 

2) start a timer, possibly randomised, once the pilot exceeds the time limit for take-off or combat regimes (or once they go beyond 65") with the chance and scope of damage directly proportional to the time spent over the limit, simulating early and late detonation causes by hot zones within the engine

 

3) keep overspending as a separate damage trigger that is more catastrophic and quicker to come into effect

 

Something like this, yes?

[Venturi]

Yep! I would add in detonation at low RPM and high boost, too. There is a graphic somewhere for the Allison which would be universally applicable I think as a general guideline, since all engines had this limitation.

Edited August 19, 2017 by Venturi

[Venturi]

Here it is in Whitney's "Vees for Victory", on pg 371. The graph is for the F series engine, but this should not matter as it is really more about the RPM v manifold pressure and danger of detonation.

 

ANF-28 fuel was standard American 100/130 octane fuel as sent to the Soviets.

 

I would use 62" Hg as the initiation point for the detonation timer, as specified on the graph.

Edited August 19, 2017 by Venturi

[216th_Lucas_From_Hell]

I'm not entirely sure but I think overboosting through low RPM is simulated for most engines, but it could be a case of bad memory.

 

Graphs like that would be great to have, since they add some practice to the theory here. I assume e they could help determine the time allowed over the limit, or at least like you said provide a general guideline.

[Venturi]

I'm not sure that it is implemented.

 

For instance, I have flown multiple aircraft - like an La-5, which does not have a "overboost" timer - at full boost and at low RPMs, without damage.

 

This should be a limitation of ALL engines in the sim. In general, the automatically managed engines match RPM and Manifold Pressure without the pilot's input. However in manual engines, it should be modeled in such a way that the detonation timers start when the engine is "HIGH BOOST / LOW RPM". As noted on the graphic.

 

But this is an advanced concept that not even DCS has implemented.

[216th_Lucas_From_Hell]

Thanks for the graph, I looked around for supporting documentation and it seems to check out. It would make the P-40 a bit of a hot rod at sea level but at most altitudes it would remain the dog it always was, but the flight model corrections should keep it a dog that can bite on occasion. Since the data refers to the P-38J/L, do you have the specific operational limits per manual for each regime in the P-38, when Allison understood their engines were tougher than initially thought?

Edited August 19, 2017 by 216th_Lucas_From_Hell

[Venturi]

I would have to dig into my sources for info on the P-38 variants of the Allison. I thought we were working on the P-40. This graph is applicable to show the detonation point for the fuel used in the P-40 as well as to show the general RPMs at which various MAPs could be used without detonation... for all aircraft.

 

I look forward to any P-38 however and would be happy to help research that... in its own thread.

Edited August 19, 2017 by Venturi

[216th_Lucas_From_Hell]

I'm just curious about the P-38J/L manual limits because they were penned with the documents you mentioned in mind, despite the differences.

[unreasonable]

Interesting discussion - thank you - and even actionable suggestions!  

 

If, as I understand it,  Lucas is proposing a general overhaul of CEM based on Venturi's analysis of what goes wrong and why, not just a tweak to the P-40, it probably needs it's own thread.  Not only will that make it more natural to include discussion of other engines, and whether the proposed changes capture their characteristics, but it will make it easier to get developer attention.

 

Perhaps someone knowledgeable about engines could start a more general CEM thread with an analysis like Venturi's and proposals similar to Lucas' post and notify someone - perhaps Gavrick, since his English is good and he seems responsive to feedback. 

[216th_Lucas_From_Hell]

I found a general testing chart with a footnote mentioning military power was available for 15 minutes, no specifics though.

 

Unreasonable, it would be a decent idea to have a separate thread to flesh out the ideas and work them over time into an actionable proposal/suggestion. That being said thanks to Klaus' additions on some of the engine examples mentioned it looks like the Allison is a very specific case where the manufacturers/operators lowballed the limits lower than Sunderland last season. If the folks in the know could contribute with details to every engine to see if they need a closer look or not - that would also depend if we're after a short term fix to one/a few engines (more actionable, short term solution) or a complete comprehensive overhaul (harder to implement, long term solution).

Edited August 19, 2017 by 216th_Lucas_From_Hell

[Venturi]

The Allisons in the P38 were very similar, only differing in that they used turbosuperchargers (which is a big difference). But the basic engine was the same as the V-1710-39.

 

Understand please: maximum manifold pressures closely tracked the development of better fuels. Obviously much research was being done on this during the war.

 

It is why the Germans with their lower quality fuel, could not provide the same level of maximum manifold pressure in their engines as the Allies could (except with water or methanol injection, both of which are ways of retarding detonation).

 

1.4ata = 1.4bar = 41 inches Hg

 

This is why the Db601 or Db605 needed to have more displacement than the Merlin or Allison to provide the same power output. They have significantly more swept volume (they are less efficient in terms of HP / Liter displacement). They are impressive engines given the fuel restraints the Germans were under.

 

The Allison and Merlin both displaced 27L. The DB601 displaced 33.9L. The DB605 displaced 35.7L.

 

So, as long as an engine was strong enough, it could take manifold pressures up to the point at which the octane rating of the fuel was no longer sufficient to prevent detonation. For this reason, all aircraft using American 100/130 fuels will have approximately the same detonation point.........

Edited August 19, 2017 by Venturi

[unreasonable]

I found a general testing chart with a footnote mentioning military power was available for 15 minutes, no specifics though.

 

Unreasonable, it would be a decent idea to have a separate thread to flesh out the ideas and work them over time into an actionable proposal/suggestion. That being said thanks to Klaus' additions on some of the engine examples mentioned it looks like the Allison is a very specific case where the manufacturers/operators lowballed the limits lower than Sunderland last season. If the folks in the know could contribute with details to every engine to see if they need a closer look or not - that would also depend if we're after a short term fix to one/a few engines (more actionable, short term solution) or a complete comprehensive overhaul (harder to implement, long term solution).

 

I would have thought that comprehensive is better: just like the FM revisions that are coming. Then the special cases can get worked on in a context of the wider system.  Part of the problem with the CEM is that it is - or seems to be - a bit of a succession of ad hoc decisions so we get oddities like the ratio of allowable time limits to cool down limits being seemingly arbitrary, or at least unexplained.  Additionally, as I understand it, the question of how to model engines without automatic regulators will become more pressing with the BoP, if the series makes it that far.  Venturi's point that it should be manifold pressure that is the key determinant of damage (especially combined with low rpm) seems an entirely general one. 

 

Anyway, I am certainly not qualified to take the initiative on this, as all I know about engines is that which I have read in threads like these! But a general CEM thread might attract more input and attention, in which case a change to the P-40 might be easier to get as part of a comprehensive review.

 

As to how difficult it is to implement, obviously I do not know for sure, but I suspect that it is rather easy. I doubt that the internal workings of the CEM model are an especially complex simulations of the physical processes of an engine, unlike the FM. I would guess that they are mostly a series of "if-then" conditions with the "ifs" being things like "if rpm greater than X for Y seconds" and so on.  These would be easy to change. 

Edited August 19, 2017 by unreasonable

[Venturi]

I mean it could be overreach.

 

The primary thing is to fix the P40. I am hopeful this will be done.

 

But the rest of it is true.

...

[ZachariasX]

Interesting discussion. Thnx Venturi for you summing up the key factors on internal engine loads and also Klaus for his experiences with "overclocked" engines.

 

I think it is a good idea to make a dedicated CEM thread to come up with a generic suggestion of how to implement that in a more consistent way. The devs then can take from that what they see fit. But at least there is (hopefully) a base of common understanding.

[6./ZG26_Klaus_Mann]

I wasn't talking Detonation, but the Structural/Metallurgical/Lubrication Failure of Overclocked Engines. Lubrication always fails at the hottest Part of the Engine. Above 150°C Engine Oil becomes useless, breaks up and is destroyed and depending on Quality will even start to Granulate. 

 

And one of the First Points on an Engine where this happens is on the Cylinder Walls as they are the Thermally most stressed Part of any Engine at Full Power and quite far up. I haven't seen any Rod or Crankshaft Bearings die without the Pistons giving in first. The Oil Pressure down at the Crank is much higher than at the Pistons, and since the Oil Lines running through the Engine distribute the Oil unevenly the Pistons are on a Spectrum from the best to the Worst Lubricated/Cooled Cylinders. 

 

This is the most important Aspect of designing any Engine Lubrication System. You always have to find a Balance between running well and longevity but you also know which Cylinders are likely to fail first on most Engines. 

 

On the American V8 the Coldest Coolant cools the Cylinder furthest away from the Pump the most, as it sits directly at the Water Pump. This is in an attempt to decrease Oil Temp and insure better Heat Distribution. 

However, if you Kick the Engine right into the Teeth that doesn't help a lot. The Cylinder will get a Localized Overheat, pair to that  a Granule of Dust or a Metal Flake on the Piston Side, gets lodged and creates a Hot Spot on the Piston where it basically breaks the Oil Film and voi'la, the Piston goes glowing hot and when it is soft enough, breaks a hole, either on the Top or at the Cylinder Wall, sometimes both. 

 

And we still have no Clue how the Metal Flakes from #7 Cylinder went onto #8 Piston Top. It's quite mysterious. 

The Allisons in the P38 were very similar, only differing in that they used turbosuperchargers (which is a big difference). But the basic engine was the same as the V-1710-39.

 

Understand please: maximum manifold pressures closely tracked the development of better fuels. Obviously much research was being done on this during the war.

 

It is why the Germans with their lower quality fuel, could not provide the same level of maximum manifold pressure in their engines as the Allies could (except with water or methanol injection, both of which are ways of retarding detonation).

 

1.4ata = 1.4bar = 41 inches Hg

 

This is why the Db601 or Db605 needed to have more displacement than the Merlin or Allison to provide the same power output. They have significantly more swept volume (they are less efficient in terms of HP / Liter displacement). They are impressive engines given the fuel restraints the Germans were under.

 

The Allison and Merlin both displaced 27L. The DB601 displaced 33.9L. The DB605 displaced 35.7L.

 

So, as long as an engine was strong enough, it could take manifold pressures up to the point at which the octane rating of the fuel was no longer sufficient to prevent detonation. For this reason, all aircraft using American 100/130 fuels will have approximately the same detonation point.........

This my Favourite Point to make about the German and Allied Engines. 

Had the Brits had the 109s and run them on 100+ Octane and the Germans the Spits on B3 or B4, there would have been no Contest. 

 

In a defensive War with dwindling Fuel Supplies and Quality, is my Argument, you would have been better of with the German Planes.

[216th_Lucas_From_Hell]

Zach is right, we can supply them the information and a model, it's up to them to take what they see fit from it. That being said since the P-40 is both the most pressing case and the most well-researched subject it's fine to use it as a the main example to begin with. I'll try to sketch out a thread format for the suggestions section so that when the deliberating is over we can submit a clear proposal to the bosses.

[wtornado]

One factor I find that is important is that the engines are running under extreme conditions.

 

I like going to the 1/4 mile race track close to here and you will have 6 bikes racing

in the same category same make with the same size cylinders and  the same turbo' s more or less.

 

I think part of what determined the winner was the mechanics and the drivers that make the difference on the track but it

is the motor that is going to let the driver finish the race or not and drive off the track or get pushed off..

 

Not one single motor is the same.

 

Like the old saying''you did not want a car built on a Monday or a Friday.

 

If they make the game real you could get the surprise of your life or death like Marseille did

on his last flight.

Edited August 19, 2017 by 5./ZG1_WTornado

[216th_Lucas_From_Hell]

Thread is up under the suggestions section.

[Farky]

Slightly OT :

 

The Allisons in the P38 were very similar, only differing in that they used turbosuperchargers (which is a big difference). But the basic engine was the same as the V-1710-39.

 

P-38J/L engines have blower gear ratio 8.10:1, V-1710-39 blower gear ratio was 8.8:1. We can not use same "detonation range chart" for both engines.

 

 

Since the data refers to the P-38J/L, do you have the specific operational limits per manual for each regime in the P-38, when Allison understood their engines were tougher than initially thought?

 

 

Data are from P-38J manual issued September 1943. In Operating instructions for V-1710-89/-91 (August 1943) are slightly diferent limits.

MAXIMUM CRUISE - 35 inHg @ 2300 rpm - maximum AUTO LEAN (YELLOW)

MAXIMUM CONTINUOUS - 44 inHg @ 2600 rpm - AUTO RICH (GREEN)

WAR EMERGENCY - 60 inHg @ 3000 rpm - AUTO RICH (RED)

 

 

[216th_Lucas_From_Hell]

Thanks, Farky Were there time limits specified in the manual for the ranges between maximum continuous up until war emergency?