The Complex Engine Management Work Group

[216th_Lucas_From_Hell]

Let’s get past the silly name, and establish a few things.

 

1. What is the goal? To help the developers implement engine damage from exceeding operational regimes in a more realistic way, within the scope of this simulator and the time/resource realities of the developers

 

2. How is it achievable? By analysing the behaviour of aero engines operating beyond the manufacturer's specified operational regimes, the type of damage incurred and the timing and consequences of it, using both historical reports for the engines in the game and the principles of physics that apply to piston engines as a whole.

 

3. When is the goal considered achieved? Once the contributors agree on a final report that provides to the developers the following points: What is wrong? What is the ‘right behaviour’? What is the cause of the wrong behaviour, in game terms (both front-end and back-end, if known)? How can the causes of wrong behaviour be altered to achieve the right behaviour (both front-end and back-end)? What implementation of the solution(s) proposed has the best work/improvement ratio? Supporting, easily verifiable sources that help or directly provide these answers.

 

4. Who is involved? Anyone who can provide good information, or good ways to translate this information into an actionable solution, or who can contribute in any way at all. In other words, everyone interested.

 

5. What is the case in focus? To get the best from the knowledge available, I suggest we use the P-40E-1 as the starting point. It uses a motor common to other aircraft in the series, data on it is easily available in English, and it is the engine modelled to the strictest levels in game.

 

Let me know if the format needs changing or not, and if not, I suggest we start. Could the people in the know please (re)post here the concepts and definitions of engine damages from cooling, lubrication, detonation and overspending? Keep it tidy and don't get personal, folks.

 

For the developers: I can translate the final contents of the report or any bits on this thread into Russian, as needed. Let me know if you need that.

[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.

 

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.........

 

 

See attached graphic regarding War Emergency manifold pressure time limits, in Russian manual for P-39L (with similar Allison engine). This airplane and engine did not have factory clearance for War Emergency Rating, however was given such rating by Soviet operators of the aircraft. As the Allison in the P-40E is grossly similar and has design strength appropriate (1500hp, see below graphic), and uses American 100/130 octane fuel (lean/rich ratings) we believe this is also an indication that the P-40E could utilize manifold pressures up to 60" without detonation.

 

See attached letter from the Allison chief of engineering maintaining that they have cleared said F3R Allisons for 60" manifold pressure use by pilots in the field.

 

See attached graphic regarding general RPM / Manifold pressure mismatch detonation range (it is just a general range, but will be similar for ALL super or turbo-charged engines). Note that with American 100/130 fuel, detonation begins at 62 inches Hg.

 

See attached graphic regarding DESIGN weights of P40E (200lbs too heavy, needs fuel and ammo count adjusted).

 

See attached paragraph regarding V-1710-39 design strength (1500hp).

Edited August 19, 2017 by Venturi

[216th_Lucas_From_Hell]

To get this going, here is a nice overview in simple yet accurate terms of the types of damage each piston engine component can sustain without external interference, its causes and immediste consequences.

 

Before starting, keep in mind that in Il-2 random failures and damage carried over from previous misuse are not modelled. For our report, the relevant damage types are those directly incurred by deliberately operating the engine outside of its safe manufacturer parameters (manifold pressure and its time limits, rotations per minute, improper MP/RPM ratio, coolant and oil temperatures). I have highlighted the relevant bits in the article for easier reading.

 

NOTE: This article does not deal with supercharged engines, and only covers the basic principles of engine damage. Damage exclusive to supercharged engine has been covered by Venturi.

Last month, I tried to make the case that piston aircraft engines should be overhauled strictly on-condition, not at some fixed TBO. If we’re going to do that, we need to understand how these engines fail and how we can protect ourselves against such failures. The RCM way of doing that is called Failure Modes and Effects Analysis (FMEA), and involves examining each critical component of these engines and looking at how they fail, what consequences those failures have, and what practical and cost-efficient maintenance actions we can take to prevent or mitigate those failures. Here’s my quick back-of-the-envelope attempt at doing that…

 

CRANKSHAFT

There’s no more serious failure mode than crankshaft failure. If it fails, the engine quits.

 

Yet crankshafts are rarely replaced at overhaul. Lycoming did a study that showed their crankshafts often remain in service for more than 14,000 hours (that’s 7+ TBOs) and 50 years. Continental hasn’t published any data on this, but their crankshafts probably have similar longevity.

 

Crankshafts fail in three ways: (1) infant-mortality failures due to improper materials or manufacture; (2) failures following unreported prop strikes; and (3) failures secondary to oil starvation and/or bearing failure.

 

Over the past 15 years, we’ve seen a rash of infant-mortality failures of crankshafts. Both Cnntinental and Lycoming have had major recalls of crankshafts that were either forged from bad steel or were damaged during manufacture. These failures invariably occurred within the first 200 hours after the new crankshaft entered service. If the crankshaft survived its first 200 hours, we can be confident that it was manufactured correctly and should perform reliably for numerous TBOs.

 

Unreported prop strikes seem to be getting rare because owners and mechanics are becoming smarter about the high risk of operating an engine after a prop strike. There’s now an AD mandating a post-prop-strike engine teardown for Lycoming engines, and a strongly worded service bulletin for Continental engines. Insurance will always pay for the teardown and any necessary repairs, so it’s a no-brainer.

 

That leaves failures due to oil starvation and/or bearing failure. I’ll address that shortly.

 

CRANKCASE

Crankcases are also rarely replaced at major overhaul. They are typically repaired as necessary, align-bored to restore critical fits and limits, and often provide reliable service for many TBOs. If the case remains in service long enough, it will eventually crack. The good news is that case cracks propagate slowly enough that a detailed visual inspection once a year is sufficient to detect such cracks before they pose a threat to safety. Engine failures caused by case cracks are extremely rare—so rare that I don’t think I ever remember hearing or reading about one.

 

CAMSHAFT AND LIFTERS

The cam/lifter interface endures more pressure and friction than any other moving parts n the engine. The cam lobes and lifter faces must be hard and smooth in order to function and survive. Even tiny corrosion pits (caused by disuse or acid buildup in the oil) can lead to rapid destruction (spalling) of the surfaces and dictate the need for a premature engine teardown. Cam and lifter spalling is the number one reason that engines fail to make TBO, and it’s becoming an epidemic in the owner-flown fleet where aircraft tend to fly irregularly and sit unflown for weeks at a time.

 

The good news is that cam and lifter problems almost never cause catastrophic engine failures. Even with a badly spalled cam lobe (like the one pictured at right), the engine continues to run and make good power. Typically, a problem like this is discovered at a routine oil change when the oil filter is cut open and found to contain a substantial quantity of ferrous metal, or else a cylinder is removed for some reason and the worn cam lobe can be inspected visually.

 

If the engine is flown regularly, the cam and lifters can remain in pristine condition for thousands of hours. At overhaul, the cam and lifters are often replaced with new ones, although a reground cam and reground lifters are sometimes used and can be just as reliable.

 

GEARS

The engine has lots of gears: crankshaft and camshaft gears, oil pump gears, accessory drive gears for fuel pump, magnetos, prop governor, and sometimes alternator. These gears are made of case-hardened steel and typically have a very long useful life. They are not usually replaced at overhaul unless obvious damage is found. Engine gears rarely cause catastrophic engine failures.

 

OIL PUMP

Failure of the oil pump is rarely responsible for catastrophic engine failures. If oil pressure is lost, the engine will seize quickly. But the oil pump is dead-simple, consisting of two steel gears inside a close-tolerance aluminum housing, and usually operates trouble free. The pump housing can get scored if a chunk of metal passes through the oil pump—although the oil pickup tube has a suction screen to make sure that doesn’t happen—but even if the pump housing is damaged, the pump normally has ample output to maintain adequate oil pressure in flight, and the problem is mainly noticeable during idle and taxi. If the pump output seems deficient at idle, the oil pump housing can be removed and replaced without tearing down the engine.

 

BEARINGS

Bearing failure is responsible for a significant number of catastrophic engine failures. Under normal circumstances, bearings have a long useful life. They are always replaced at major overhaul, but it’s not unusual for bearings removed at overhaul to be in pristine condition with little detectable wear.

 

Bearings fail prematurely for three reasons: (1) they become contaminated with metal from some other failure; (2) they become oil-starved when oil pressure is lost; or (3) main bearings become oil-starved because they shift in their crankcase supports to the point where their oil supply holes become misaligned (as with the “spun bearing” pictured at right).

 

Contamination failures can generally be prevented by using a full-flow oil filter and inspecting the filter for metal at every oil change. So long as the filter is changed before its filtering capacity is exceeded, metal particles will be caught by the filter and won’t get into the engine’s oil galleries and contaminate the bearings. If a significant quantity of metal is found in the filter, the aircraft should be grounded until the source of the metal is found and corrected.

 

Oil-starvation failures are fairly rare. Pilots tend to be well-trained to respond to decreasing oil pressure by reducing power and landing at the first opportunity. Bearings will continue to function properly at partial power even with fairly low oil pressure.

 

Spun bearings are usually infant-mortality failures that occur either shortly after an engine is overhauled (due to an assembly error) or shortly after cylinder replacement (due to lack of preload on the through bolts). Failures occasionally occur after a long period of crankcase fretting, but such fretting is usually detectable through oil filter inspection and oil analysis).They can also occur after extreme unpreheated cold starts, but that is quite rare.

 

CONNECTING RODS

Connecting rod failure is responsible for a significant number of catastrophic engine failures. When a rod fails in flight, it often punches a hole in the crankcase (“thrown rod”) and causes loss of engine oil and subsequent oil starvation. Rod failure have also been known to cause camshaft breakage. The result is invariably a rapid and often total loss of engine power.

 

Connecting rods usually have a long useful life and are not normally replaced at overhaul. (Rod bearings, like all bearings, are always replaced at overhaul.) Many rod failures are infant-mortality failures caused by improper tightening of the rod cap bolts during engine assembly. Rod failures can also be caused by the failure of the rod bearings, often due to oil starvation. Such failures are usually random failures unrelated to time since overhaul.

 

PISTONS AND RINGS

Piston and ring failures usually cause only partial power loss, but in rare cases can cause complete power loss. Piston and ring failures are of two types: (1) infant-mortality failures due to improper manufacturer or assembly; and (2) heat-distress failures caused by pre-ignition or destructive detonation events. Heat-distress failures can be caused by contaminated fuel (e.g., 100LL laced with Jet A), or by improper engine operation. They are generally unrelated to hours or years since overhaul. A digital engine monitor can alert the pilot to pre-ignition or destructive detonation events in time for the pilot to take corrective action before heat-distress damage is done.

 

CYLINDERS

Cylinder failures usually cause only partial power loss, but occasionaly can cause complete power loss. A cylinder consists of a forged steel barrel mated to an aluminum alloy head casting. Cylinder barrels typically wear slowly, and excessive wear is detected at annual inspection by means of compression tests and borescope inspections. Cylinder heads can suffer fatigue failures, and occasionally the head can separate from the barrel. As dramatic as it sounds, a head separation causes only a partial loss of power; a six-cylinder engine with a head-to-barrel separation can still make better than 80% power. Cylinder failures can be infant-mortality failures (due to improper manufacture) or age-related failures (especially if the cylinder head remains in service for more than two or three TBOs). Nowadays, most major overhauls include new cylinders, so age-related cylinder failures have become quite rare.

 

VALVES AND VALVE GUIDES

It is quite common for exhaust valves and valve guides to develop problems well short of TBO. Actual valve failures are becoming much less common nowadays because incipient problems can usually be detected by means of borescope inspections and digital engine monitor surveillance. Even if a valve fails completely, the result is usually only partial power loss and an on-airport emergency landing.

 

ROCKER ARMS AND PUSHRODS

Rocker arms and pushrods (which operate the valves) typically have a long useful life and are not normally replaced at overhaul. (Rocker bushings, like all bearings, are always replaced at overhaul.) Rocker arm failure is quite rare. Pushrod failures are caused by stuck valves, and can almost always be avoided through regular borescope inspections. Even when they happen, such failures usually result in only partial power loss.

 

MAGNETOS AND OTHER IGNITION COMPONENTS

Magneto failure is uncomfortably commonplace. Mags are full of plastic components that are less than robust; plastic is used because it’s non-conductive. Fortunately, our aircraft engines are equipped with dual magnetos for redundancy, and the probability of both magnetos failing simultaneously is extremely remote. Mag checks during preflight runup can detect gross ignition system failures, but in-flight mag checks are far better at detecting subtle or incipient failures. Digital engine monitors can reliably detect ignition system malfunctions in real time if the pilot is trained to interpret the data.

 

Magnetos should religiously be disassembled, inspected and serviced every 500 hours; doing so drastically reduces the likelihood of an in-flight magneto failure.

 

THE BOTTOM LINE

The bottom-end components of our piston aircraft engines—crankcase, crankshaft, camshaft, bearings, gears, oil pump, etc.—are very robust. They normally exhibit long useful life that are many multiples of published TBOs. Most of these bottom-end components (with the notable exception of bearings) are routinely reused at major overhaul and not replaced on a routine basis. When these items do fail prematurely, the failures are mostly infant-mortality failures that occur shortly after the engine is built, rebuilt or overhauled, or they are random failures unrelated to hours or years in service. The vast majority of random failures can be detected long before they get bad enough to cause an in-flight engine failure simply by means of routine oil-filter inspection and laboratory oil analysis.

 

The top-end components—pistons, cylinders, valves, etc.—are considerably less robust. It is not at all unusual for top-end components to fail prior to TBO. However, most of these failures can be prevented by regular borescope inspections and by use of modern digital engine monitors. Even whey they happen, top-end failures usually result in only partial power loss and a successful on-airport landing, and they usually can be resolved without having to remove the engine from the aircraft and sending it to an engine shop. Most top-end failures are infant-mortality or random failures that do not correlate with time since overhaul.

 

The bottom line is that a detailed FMEA of piston aircraft engines strongly suggests that the traditional practice of fixed-interval engine overhaul or replacement is unwarranted and counterproductive. A conscientiously applied program of condition monitoringthat includes regular oil filter inspection, oil analysis, borescope inspections and digital engine monitor data analysis can yield improved reliability and much reduced expense and downtime.

Source: https://blog.aopa.org/aopa/2014/04/09/how-do-piston-aircraft-engines-fail/

 

Now we need to apply this to the game. Relevant damage types need to be caused by in flight use; and if yes they must be classified by the intensity of the damage (light/medium/severe/total), wherein:

 

Light: no or slight loss of power, progresses into medium damage over a long period of time or if operated at military, take-off or emergency regime after sustaining damage

Medium: moderate loss of power, progresses into severe damage over a long period of time or if operated at military, take-off or emergency regime after sustaining damage

Severe: severe loss of power, progresses into total loss of power over a medium period of time or of operated at military, take-off or emergency regime after sustaining damage

Total: full loss of power

 

Based on the article and the write-up Venturi provided on the second post, we have the following groups of damage, and the causes in parenthesis:

 

Light: Cylinder damage (detonation)

Medium: Oil starvation (prolonged oil overhead, impact damage from overspeeding)

Severe: Bearing failure (oil starvation), thrown rods/parts (oil starvation, overspeeding)

Total: Crankshaft failure (oil starvation/bearing failure)

 

Finally, let´s translate these into the game. An engine which has been operated outside manifold pressure limits, time limits for certain pressure ratings, and recommended MP/RPM ranges (and is immune to random failures) would suffer from cylinder damage initially (thus, light damage). An engine that has overheated its oil too much while operating at demanding regimes will suffer from oil starvation initially (medium damage) which can then progress into severe and total damage. An engine that has been operated outside RPM limits would suffer from impact damage from broken parts, thus leading to severe or total failure.

 

Note that some of these damage types are consequences of others, so for efficiency´s sake we can simplify them to the following action-consequence models for players:

 

MP/RPM mismatch, excessive power -> light damage (cylinder damage)

Prolonged oil overheat -> medium damage (oil starvation)

Overspeeding engine -> severe damage (bearing, thrown parts and crankshaft failure)

 

Any objections up until now on this damage mechanic? If not, we can move onto the next point which concerns light damage the most: what engine limits need to be observed for each aircraft, what constitutes above safe limits and finally, what in game solutions can be implemented for that?

Edited August 19, 2017 by 216th_Lucas_From_Hell

[216th_Lucas_From_Hell]

Edits done.

[Venturi]

I agree in general, however:

 

MAP/RPM mismatch can potentially be very devastating, more so than simply too high of MAP. So it is a spectrum depending on how severe the mismatch is. The more severe the mismatch, the more detonation will progress to pre-ignition (and very quick engine destruction).

 

Prolonged and severe oil overheat can be very devastating. It causes oil lubrication breakdown. This will result in seized parts and immediate engine destruction. However, it is harder to overheat the oil than it is to overheat the water, as oil will absorb heat much more slowly than water (less efficient heat transfer. It also cools more slowly.) Otherwise, minor overheats will not do any damage. Simplistically, we can call it an all or nothing phenomenon of damage.

 

Therefore:

 

1. I would recommend a spectrum of severity between light and severe damage for all forms of detonation, reflecting the progression to pre-ignition (which is severe detonation). The more severe the mismatch, or the higher the MAP is over limits, or the LONGER MAP is over limits, then the more severe the damage. Detonation timers should begin at 60" MAP for 100/130 octane fuel, and RPM / MAP mismatch should follow in general the mismatch curve shown above. Additionally, TOO LEAN a mixture will result in detonation, this worsens with higher RPM and MAP, and leaner air-fuel mixes.

 

2. I would recommend prolonged oil overheat result in immediate severe damage, similar to overspeed. Both reflect critical structural failures of major engine components.

 

3. I would recommend prolonged water overheat to result in progressive minor damage to the engine, reflecting head gasket rupture and loss of combustion pressure in cylinders (pressure lost around cylinder head / block interface), which would be progressive. Additionally, any head gasket rupture would result in additional cooling efficiency loss due to loss of pressurization in the cooling system. Failure of this gasket would result in water coolant hitting the windscreen!!

Edited August 19, 2017 by Venturi

[216th_Lucas_From_Hell]

Great input. So we have our (probably final) damage actions and consequences:

 

Prolonged coolant overheat; exceeding timer for engine regime; minor MP/RPM mismatch = light damage

 

Prolonged or demanding operation under light damage; moderate MP/RPM mismatch = medium damage

 

Prolonged oil overheat; overspending engine; prolonged or demanding operation under medium damage; severe MP/RPM mismatch = severe damage

 

Short operation under severe damage = total damage.

[216th_Lucas_From_Hell]

The next point are engine limits as they are, what would be the correct limits and what would be a realistic interpretation of exceeding engine limits (including possible alternative mechanisms to simulate that) which also considers regards to the engine lifespan, taking the P-40 as an example.

 

I'm struggling to find them for some reason, could anyone share both the 1941 (in game) and a couple of later operational guidelines for the V-1710-39 for comparison to the -63 and other models?

[Farky]

See attached graphic regarding War Emergency manifold pressure time limits, in Russian manual for P-39L (with similar Allison engine). This airplane and engine did not have factory clearance for War Emergency Rating, however was given such rating by Soviet operators of the aircraft.

 

 

No, VVS never cleared P-39L for War Emergency Rating. Attached picture is actually saying that WER 60 inHg is not cleared in manual for P-39K/L.

 

 

See attached letter from the Allison chief of engineering maintaining that they have cleared said F3R Allisons for 60" manifold pressure use by pilots in the field.

 

 

No, V-1710-F4R (-73) engines were cleared by Allison for 60 InHg MAP, V-1710-F3R (-39) were cleared for 56 inHg.

 

 

I'm struggling to find them for some reason, could anyone share both the 1941 (in game) and a couple of later operational guidelines for the V-1710-39 for comparison to the -63 and other models?

 

I don't understand why do you want compare V-1710-39 with other models. Anyway, V-1710-37, -63 and 73 were very similar (-63 and -73 models were "stronger", therefore higher MAP for WER), other models were different.

 

V-1710-39 limits are here - https://forum.il2sturmovik.com/topic/25323-p-40-turn-rateflight-model-check/?p=456002

[Venturi]

The design limit for the V-1710-39 was 1500hp.

It clearly says in Hazen's letter, that F3R was cleared for 60" MAP.

[216th_Lucas_From_Hell]

Cheers, Farky. You're right, we should try to keep details to the same engine model for good practice's sake.

 

I found these limits from 1942, referring to the P-40E-1 among other aircraft. Are these exclusive to units with the MAP regulator or can they be generally applied to the engine as a whole? If these only apply to MAP regulator units, could you walk me through what happens if a pilot tried to operate in those regimes without the MAP regulator installed?

 

https://m.imgur.com/nFbmOHh

[Farky]

The design limit for the V-1710-39 was 1500hp.

It clearly says in Hazen's letter, that F3R was cleared for 60" MAP.

 

Allison never cleared 60 InHg for F3R. 1500 bhp limit is red line, red arrow is maximum MAP within structural limit of V-1710-39. And it is at 3000 rpm @ 4 300 ft, which is in perfect match with table 5-19 in Vee's for Victory (page 167). So, maximum safe MAP for V-1710-39 (F3R) was 56 inHg @ 3000 rpm.

 

 

 

I found these limits from 1942, referring to the P-40E-1 among other aircraft.

 

Ok, here we go again - this is NOT chart from 1942, but from 1944. 1942 date refers to date of issue of general specification AN-H-8, NOT to date of issue of this specific chart.

 

Are these exclusive to units with the MAP regulator or can they be generally applied to the engine as a whole? If these only apply to MAP regulator units, could you walk me through what happens if a pilot tried to operate in those regimes without the MAP regulator installed?

 

Everything around P-40E engine was discussed to death. I would highly recommend to read this thread first - https://forum.il2sturmovik.com/topic/21234-p-40-engine-settings-i-found-them-bit-weird/ .

[Venturi]

Yes, I'm not saying it was RATED at 1500hp. I'm saying the DESIGN spec was at 1500hp.

 

Understand please:

 

If you want to model "the manual", you are not going to get reality. Manuals have a lot more in mind than just how things work and maximum realistic performance. Like, bearing life. Again:

 

TBO:

700hrs Allison

400hrs Merlin

150hrs DB60x

 

So, do you want "the manual" or do you want a simulation? They are not the same.

 

Engines do not fail at 5min WER +/-30sec. 5min is a NOMINAL value, not a FAILURE value. It is there to ensure safety and reliability over the TBO time of the engine.

 

And if you want to simulate a huge number of engines which are all similar to the Allison V-1710-39 with no pressure regulators, then you better come up with a way to simulate their limits more accurately than "the manual". Or we're back to IL-2 1946.

 

Fuel octane determines detonation limits. That's why the DB60x series had to run 1.4ata. Structural strength determines actual engine failure limits. So I have no problem with anything beyond 1500hp triggering a randomized timer for the V-1710-39's destruction. But I do have a problem with saying 5min at 1470hp causes failure.

 

And that's where you're going. It's the wrong direction.

[Farky]

I don't get it, I never say anything about time limits. So I'm not going anywhere. My reaction was about your statement that Allison cleared F3R for 60 inHg, which they didn't. That's it.

[216th_Lucas_From_Hell]

Lads, we're being pedantic here. We have a decent pool of values to work with (thanks for the link to that thread by the way I'd read it over a year ago so a refresher was nice). There are field reports, anecdotes, official manuals and tests done involving the -39, most of it falls within the same ballpark. The very final interpretation of the details is up to the developers, we need to give them clear ways to choose actionable solutions and provide the data to back these proposals. I'll sleep on it and try to sketch up something on the time limits tomorrow based on the contents of this thread and others, for the more knowledgeable folks to use as a basis to get it just right.

[Venturi]

Yes, Lucas, I agree.

 

I suppose the point here is that detonation needs to be modeled independently of engine structural failures due to too much HP being made. 

 

Thus,

 

1. Detonation, as based on:

 

1. Absolute maximum MAP allowed - based on fuel quality (Germans have 87 octane fuel, Allies have 100/130 octane fuel)

2. mixture (if too lean for given MAP)

3. if too much MAP for the RPM... see graph

 

and 2. engine strength being the other factor, which is variable for each engine's design 

 

So, I suppose the only thing different is that we are adding in engine strength as an additional point at which a timer might be employed.

This would be a bit of a chore to research because it will depend on each engine. For instance, the V-1710-39 was good for 1500hp, but the DB605 had problems with strength until the crank bearing issue had been taken care of.

Edited August 20, 2017 by Venturi

[Retnek]

Being far from an engine-specialist, just two notes, even I suspect you already know:

 

1) Luftwaffe used different fuel

• Fliegerbenzin, Mitte der 1930er Jahre (73–77 ROZ)
• Flugzeug-Treibstoff B1 (70–80 ROZ, Bibo (Treibstoff) aus 60–70 % Benzin und 40–30 % Benzol)
• Flugzeug-Treibstoff B2 (87 ROZ, Bibo (Treibstoff) aus 30–40 % Benzin und 70–60 % Benzol)
• Flugzeug-Treibstoff B4 (87 ROZ), siehe Entwicklung der Ottokraftstoffe#Weitere Ottokraftstoffe
• Flugzeug-Treibstoff C3 (100 ROZ), siehe Entwicklung der Ottokraftstoffe#Weitere Ottokraftstoffe

(source: https://de.wikipedia.org/wiki/Flugbenzin)

 

Luftwaffe fuel supply btw is an interesting topic of (war-) economy and the influence of patents, licenses etc. If and how to deal with rogue nations - very much like today. For the Luftwaffe-logistics those different fuels always have been a pain in the a..

 

 

2) a lot of planes used more or less complex systems for engine management automation. One reads about the trouble pilots had with malfunctions of those devices from time to time, so it might be useful to include this topic:

- is there just one system managing all aspects or are there several ("unknown") autonomous subsystems

- in what limits the devices were able to care for a healthy engine (up to the question "did the pilots used it")

- are there different levels of failure or damage effects, failures by attrition, battle damage

- if damaged, what kind of work-around the pilot had (and are those available in the sim)

Edited August 20, 2017 by 216th_Retnek

[JG5_Schuck]

Well, as an engineer of 30 years i can tell you this is all academic if we don't know what actual 

system management is being modeled in game,

What parameters are being used and how they interact with each other.

I have noted from a purely mechanical view (not aerodynamic) a number of issues with the management systems.

But all aircraft engines (prop engines) function in exactly the same way its only the management systems that vary.

I suspect the game doesn't go into so much detail as to model fuel rating/quality and detonation/timing.

By the way detonation is also caused/cured by engine temp, charge intake temp, ignition timing and any kind of cooling ie water injection.

Ive asked the devs in the developers questions section before what parameters are used, but never had an answer. 

[unreasonable]

A simulation is just an illusion: all we are trying to do here is make the illusion more credible, especially for the people (probably a small minority, of which I am not a member) who know anything about the topic beyond broad generalizations.

 

So we do not actually need to know anything at all about the system management in the game, if indeed there is any.  All we need to do is try to match up observed inputs (cockpit dials etc) with outputs (various kinds of engine failure) in a way that is regarded as more plausible by expert opinion than the current match up.

 

The developers can then adjust whatever coding they have to give that match up - or not.

 

The simple way to do that is to come up with an entirely generic list of input - output pairings first in terms of "if X then Y" rather than argue about specific engines.  Once you have a template that apples to every engine, you can then fill in the specific numbers. 

[216th_Lucas_From_Hell]

Unreasonable is being very reasonable here (as he often is, despite the moniker ) If we go into parameters like engine strength for each engine in game and their subvariants not only nothing will ever get done, but there will rarely be actual credible information on the physical resistance of each engine. Hearsay in this case is not the best way to go.

 

Since detonation isn't modelled yet, it's a proposal that needs to be made with supporting evidence of the safe operating MP/RPM ranges for at least, let's say, three engines in game so they can evaluate if they agree with a blanket formula involving a simple RPM/MP ratio that applies to all engines when adjusted to their nominal modes. Do we have that for anything besides the Allison F3R? DB, BMW, Shvetsov, Klimov, etc.

 

On the topic of the limits that constitute safe operations, the 1943 operations manual for the V-1710-F provides some interesting data here. First, it goes into great detail to make clear that only aircraft equipped with the MAP regulator (among other requirements such as specific spark plugs, a throttle detent, stricter maintenance, use of ethylene glycol to AN-2-E specification and more - our P-40 doesn't meet many of these requirements) are cleared to use the 56" boost for five minutes. It can, however, employ a Standard Emergency Power of 52" for 5 minutes. Furthermore, the F3R is the only engine in the F family not officially cleared per this manual for 15 minutes of military power, being restricted instead to 5 minutes operating at "42. Thought I haven't time to go through the full 135 page manual, considering this is from 1943 and specifically singles out the F3R for more conservative regimes, I assume there is some reason for it. This matches the game limits, yes?

 

If these indeed to match the game limits, we have the next problem. We know that these limits are made with a certain margin of safety, we know the type of damage that exceeding them can eventually incur, and we also know that through a combination of experimentation and the installing of MAP regulators the F3R was eventually cleared for 15 minutes of military power in 1944, and the 5 minutes of WEP. Most people, both end users, pilots and seasoned engineers, can agree that the tolerance for going past regulated regimes is extremely low, and its damage is too severe.

 

With this information in mind, and after some consulting with a General who commanded an Air Force material park which worked on similar engines, two variations could work. The most realistic one, using the Allison example, would be to leave the manual limits as the regular time, then introduce a 5 minute timer after the pilot exceeds the time in this regime or goes straight into a disallowed limit (56" to 60") where a formula calculates the minutes spent in emergency power (1-5 depending on regime) multiplied for a random number given at the first minute. Once (x . t) equal a certain y value before the pilot throttles back, the engine receives light damage and the pilot is forced to throttle back to nurse the engine home. If the developers prefer to not use randomness, a 2.5 . t would bring more or less similar results for the player. This logic can be applied to all engines which use strict modes.

 

Another alternative proposed during this discussion is more straightforward but less realistic - once a limit is exceeded, after 30 seconds the throttle is set back into the next operational mode and the pilot loses the ability to enter the next regime until the engine rests from it.

 

Thoughts so far?

[Venturi]

I agree that a universal system needs to be applied, and I also agree the important aspect is the end-result for the pilot.

 

I do disagree when you say fuel/air mix is not important, and I'll tell you why. It is because 1. It is present on all a/c without automatic management, as it is a fundamental control for these engines, 2. Manipulating this incorrectly or correctly should have important implications for the engines :

 

(preignition /detonation /loss of power /optimal mix /loss of power again... in the order from too lean to too rich)

 

It is already modeled as a control and really does very little currently. Note that the fuel we are discussing is 100/130 octane. This means at normal a/f mix ratios, octane is too low to support high boost levels without detonation. Yet, max mix which allows these boost levels, would be too rich for anything other than full-out power. So you see, it is a vital aspect of engine management in the aircraft which do not have automatic management systems.

 

But I see that we are shooting for something a bit less complex. So I will only say this is the ideal simulation setting and how the mix lever ought to work.

 

I am happy that the devs are consulting ex professionals regarding this important issue. I would suggest that they consider either one of your two above proposals as a good "simplistic fix" which does improve on the current problems. Obviously I prefer the first as it is slightly more realistic. Especially on aircraft without automatic systems...

 

Or if they really want to take the simulation a step further, they should apply some of the basic ideas which are being set forth in this thread, about the different ways engines are actually restricted and operate.

 

Regarding the MAP/RPM mismatch, there are to my knowledge no graphs for every engine. That does not mean they don't exist, I just am not aware of them. This does not mean that this is not a general principle in effect for EVERY supercharged engine. It is. However, this effect does not need to be exact. It is not a maximum performance situation, which would vary for every a/c and be divisive. Rather, this is a general issue and the graph I provided should be a general guide which could be interpreted loosely for every aircraft.

Edited August 20, 2017 by Venturi

[Venturi]

Keep in mind this generic range should be viewed as a ratio between MAX rpm and MAX MP. Since different fuels allowed different max MP levels, this does need to be a ratio. Obviously the automatic systems maintained the correct MP/RPM ratios so these could be taken as the optimum ratio for the German a/c.

 

I believe this is not an exact effect, as mentioned engine temp and ambient temp all modify it. (Warmer engine temps induce detonation more quickly, warmer ambient temps result in richer a/f mixes for a given mix setting - air is less dense).

 

It is an important effect to model in some basic way. Precision might be nice but it is also relatively low yield.

 

(Germans did not use C3/100 oct except for very late Me's and DB601N models - they used 87 oct for all the a/c we are dealing with here)

[Farky]

If we go into parameters like engine strength for each engine in game and their subvariants not only nothing will ever get done, but there will rarely be actual credible information on the physical resistance of each engine.

 

 

But in case of V-1710-39, you must go with engine strenght, because that was THE limiting factor of this engine.

 

 

On the topic of the limits that constitute safe operations, the 1943 operations manual for the V-1710-F provides some interesting data here. First, it goes into great detail to make clear that only aircraft equipped with the MAP regulator (among other requirements such as specific spark plugs, a throttle detent, stricter maintenance, use of ethylene glycol to AN-2-E specification and more - our P-40 doesn't meet many of these requirements) are cleared to use the 56" boost for five minutes. It can, however, employ a Standard Emergency Power of 52" for 5 minutes. Furthermore, the F3R is the only engine in the F family not officially cleared per this manual for 15 minutes of military power, being restricted instead to 5 minutes operating at "42. Thought I haven't time to go through the full 135 page manual, considering this is from 1943 and specifically singles out the F3R for more conservative regimes, I assume there is some reason for it. This matches the game limits, yes?

 

 

Well, not exactly. V-1710-39 was cleared for 56 inHg for 5 minutes, so we know that engine was capable running on it without issues. It doesn't matter if automatic MAP regulator was required for WER or not, because it doesn't matter if throttle is moved by regulator or directly by pilot via throttle lever in cocpit, if you stay in limits of course. 

Standard Emergency Power - nobody was using this rating, nobody knows what it actually means, what is purpose and what are requirements for this rating. As far as I know, operators of Allison engines never use this term.

 

 

Rather, this is a general issue and the graph I provided should be a general guide which could be interpreted loosely for every aircraft.

 

 

Do you mean for every aircraft with Allison V-1710 engine right ? Not for every aircraft.

[Venturi]

We have a saying in this country, I'm not sure if it is used in others (I would be curious though).

 

"The enemy of good, is perfect."

 

I doubt that anything will be implemented at all if we insist on absolute perfection. Also, due to the nature of detonation, there are a host of factors which will be almost impossible to model perfectly.

 

I think it is good enough to model RPM/MAP mismatch the way I have described, above. This is already a quantum leap forward from where we are now.

 

Can you say my RPM/MAP mismatch proposal is incorrect... in a general sense?

 

And can you say if precision in this is absolutely required?

 

Because what we are really modeling with this is the general relationship between piston speed, fuel/air mix, octane rating, and manifold pressure. Among other things. And again, "generally correct" is a good step in the right direction, and sufficient, as this is not really a max performance phenomenon, but a realism one.

Edited August 20, 2017 by Venturi

[Venturi]

I recommend everyone read this article I've attached, which is about the Merlin engine. 

 

ESPECIALLY page 222, which is the 5th page in the document. I have attached a picture if you are interested in the key parts.

 

It explains in excellent detail why detonation was the limiting factor for absolute power output, and why fuel quality was the primary driver of how high MP / power could be due to detonation:

 

You will see that about 1500 hp was the maximum power that could be obtained in the Merlin (and by extension - Allison, which had exact same displacement... 27L) with 100/130 octane fuel (from graph...)

 

Obviously, as I posted earlier, the way the Germans got around this was by increasing the actual swept volume (engine displacement) in the DB601 and 605, while maintaining a lower manifold pressure to prevent detonation with their lower octane rating fuels. This is how they were able to obtain 1400hp or so at 1.4bar MAP. However, if you look at the specific output (HP / L displacement), the DB605 had 41hp / L at 1.42ata ... while the Allison at 56" Hg had 55hp / L....

merlin-lovesey.pdf

Edited August 20, 2017 by Venturi

[Farky]

Can you say my RPM/MAP mismatch proposal is incorrect... in a general sense?

 

Yes I can, it doesn't work for US radial engines for example. Even incoming A-20B (on Military power) will be according this chart in detonation range.

 

And can you say if precision in this is absolutely required?

 

No, absolute precision is not required of course. On the other hand, it can not be too simple, because it can cause lot of issues in future.

 

It explains in excellent detail why detonation was the limiting factor for absolute power output, and why fuel quality was the primary driver of how high MP / power could be due to detonation: You will see that about 1500 hp was the maximum power that could be obtained in the Merlin (and by extension - Allison, which had similar displacement) with 100/130 octane fuel (from graph...)

 

And yet they get on 100/130 Grade fuel 1720 bhp from Packard Merlin V-1650-7 (P-51D engine) at 67 inHg @ 3000 rpm (which is btw also in detonation range according "P-38 chart").

[Venturi]

It gets more complex. You want a more complete reasoning...

 

Well, detonation is also a factor derived on piston compression ratio, that is, how "squished" the air fuel is by the piston.

 

You can consider Manifold Pressure as "pre - squish" before it gets to the combustion chamber. Then, on top of this, is the compression ratio inside the cylinder. The sum total of these is what actually gives TOTAL compression ratio, in a supercharged / turbocharged engine.

 

This also explains why some engines can use slightly higher boosts with the same 100/130 fuels... such as the V-1650-7... and still not detonate... it is because they have lower compression ratios than the V-1710-39...

 

The V-1650-7 used 6:1 cylinder compression ratio.

The V-1710-39 used a 6.65:1 cylinder compression ratio....

 

TOTAL compression ratio is about the same... with MAP of 60-62" for the Allison, 67" for the Packard-Merlin...

 

So you see, it all comes down to FUEL OCTANE! 

 

Conversely, engines using 100/130 octane fuel with HIGHER piston compression ratios will only be able to use LOWER manifold pressures than the Allison V-1710, before detonating.

 

AGAIN - this variable does not need to be precise. The graph gives a general idea of what is correct, ONLY. It is more important that the VERY IMPORTANT modelling of detonation takes place, both with lean air/fuel mixes, and high MAPs, and with low RPM / high MAP mismatches...

Edited August 20, 2017 by Venturi

[Farky]

It gets more complex. You want a more complete reasoning...

 

 

Not at all, I just want you to abandon the idea to use that chart for all engines. Every engine (at least every type, not variant) need different "detonation chart", that is my point.

 

-------------------------

 

If you guys need to clear this thread, feel free to delete my responses. They doesn't matter, this is your show and I don't wanna derail this thread.

[216th_Lucas_From_Hell]

Farky, I'm trying to work out a table here to account for that, using the P-38 chart as a reference but definitely not a bible and adding a margin of error there. It's an oversimplification, but an attempt at simulation of real results. RPM/inHg for given regime, detonation parameters for damage trigger in parenthesis.

 

<2300/<38" (n/a)

2600/44" (<2300/44")

3000/54" (<2800/54")

3000/60" (<2900/60")

 

Get a set of regulated operational regimes for an engine, get the RPM variation between cruise and emergency (or whichever has highest MP) modes as 100%. Finally, the tolerance until detonation occurs is different per mode: operating below continuous, nothing happens; at continuous mode, 75% tolerance; at combat mode, 50% tolerance; at emergency mode, 25% tolerance. Past thst limit, then medium damage is triggered. I believe this would port over well to most engines since it accounts for their own variations, no? Thoughts?

 

Also, by all means keep your replies Farky - they've been nothing but constructive and informative criticism so far, which is exactly what's needed to refine this.

Edited August 20, 2017 by 216th_Lucas_From_Hell

[Venturi]

I'm still waiting to be employed for my advice... lol

 

Unfortunately I care more about improving WW2 aircraft simulators than in being paid.

 

I think you need to add in two regimes for detonation:

 

(in addition to absolute MAX MP... which is specific on engine - by - engine basis, but should be around 60" Hg for 100/130 fuel, and around 1.45bar for German fuel, but depending on each engine... as above lays out...)

 

1. RPM / MP mis-match

 

2. Air / Fuel mixture mis-match (to MP and RPM)

 

They are more or less independent to each other.

 

Lucas,

 

For #1, your suggestion above is good.

 

For #2, it is easy, lean mixture settings are less and less tolerated as MP and RPM rises,

 

again... use the spectrum of mismatch results I gave earlier:

 

(preignition /detonation /loss of power /optimal mix /loss of power again... in the order from too lean to too rich... at high RPM and MP, no such thing as too rich) 

 

ALSO

 

(if you want to be really precise, additionally, cooler ambient temperatures will also require richer mix - more air density - and warmer engine temperatures will also require richer mix to prevent detonation)

 

Farky,

 

I agree, but as I said, by using ratios, you can generalize to every engine without knowing specifics.

Edited August 20, 2017 by Venturi

[216th_Lucas_From_Hell]

Venturi, the problem is this isn't exactly standard in some Soviet aircraft. While the M-105 and M-62/82 families operate in the usual linear fashion, the AM-35 and AM-38 families don't - engines are run with the mixture on the middle at most altitudes, gradually brought back after 5000m, and pushed to the maximum only to engage the boosted mode. The specifics of the mechanism aren't well known, as is most of the engine's works, to the extent that only one or two AM-38/38 have been successfully rebuilt since the war and the Russian aviation authority hasn't cleared it even in an experimental capacity. Without knowing exactly what settings lead to what, I feel this would create a poor implementation that leaves us at a different point but the same situation - unrealistic simulation of real situations.

[Venturi]

Thank you for that clarification.

I would think that these controls were similar to the P-40's "auto rich" setting - this mixture control could be forced into "super rich" mode if I recall correctly, when necessary (to prevent detonation).

 

The reason such mixture control would be brought back after 5000m is that it is now above the critical altitude of the engine (if I recall correctly), and the density of the intake air charge is now declining - due to the air now being thin beyond supercharger's ability to give optimal intake pressurization - which would need to be compensated for by a leaner mixture.

 

You would need to advance beyond the "auto rich" setting to "max rich", when using very high manifold pressures, to prevent detonation. Like many other manual mixture set-ups, it is just that this one has a center mode, which is quasi automatic.

 

In other words, it sounds a lot like a P-40's mixture setup. IE: there is a quasi-automatic mode, "auto-rich".

 

I would suggest in this case, that we adhere to the saying,

 

"the enemy of good, is perfect", and go ahead with some sort of "auto rich" interpretation similar to the P-40 for this specific situation.

Edited August 20, 2017 by Venturi

[DD_Arthur]

 Aren't you also going to have to add an effect to simulate plug fouling with high octane fuels and introduce an engine handling regime to combat this?

[Venturi]

In reality yes, however I think this is going too far in realism.

 

If the above suggestions regarding mixtures are implemented, it will advance the engine realism in some way beyond even what DCS is offering. And actually, it is pretty easy to implement from a developer's perspective, as Lucas' examples point out.

 

And it sounds much more complex in explaining it, than it would be to pilots actually in the sim. The advantage of all this is that is helps unify engine ratings and how to use engines across the board.

 

It also emphasizes why automatic engine controls are so useful.

 

One of the best interpretations of fuel/air mix being wrong, is on the DVII "altitude engine" in ROF. 

 

Of course this engine is not supercharged, so it is simpler than what we are discussing, but it has many of the features I am referring to here (improper mix causing detonation, etc) ... and you don't hear pilots not understanding it in ROF... 

Edited August 20, 2017 by Venturi

[216th_Lucas_From_Hell]

If they have it implemented, and well, wouldn't it be better to (at this stage anyway) give the Rise of Flight example as a proposal itself? It's already done using their own terms and parameters which they know, which spares us some effort to work out and guess the specifics of each plane.

[Venturi]

Yes, it is a well-done effect. I have not seen it implemented on any other engine in ROF or here.

 

So, to sum up?

 

1. Overheat

   a. coolant (water-cooled inlines)

   b. oil

   c. engine block / head (radials)

 

2. Overspeed

 

3. Engine strength failure

 

4. Detonation 

   a. air / fuel mixture too lean (like D.VII altitude engine)

   b. RPM / MP mismatch

   c. absolute MP limits

Edited August 20, 2017 by Venturi

[216th_Lucas_From_Hell]

Let´s condense that into the actionable format and translating all those things into in-game triggers. Points marked with asterisk involve the addition of new features to complement existing ones; items marked in italics indicate the feature is already present in the game with the appropriate reaction.

 

Engine strength failures fall under the engine limits and their appropriate randomised damage extensions since the strength is one of the many aspects that plays a part into determining these limits in the first place, and information on many engines here is sketchy at best. Also, after a revision of developer diaries, the scope of detonation issues they are looking for is much deeper, complex and ultimately realistic than the proposals we´ve made.

 

The run-down:

 

 

1. Light Damage

a) Prolonged coolant or cilinder overheat

b) Exceeding take-off/climb/combat/emergency time limits*

c) Exceeding maximum boost**

 

2. Medium Damage
a) Prolonged or demanding operation under light damage

b) MP/RPM mismatch***

 

3. Severe Damage
a) Prolonged oil overheat

b) Overspeeding engine

c) Air/fuel mix too lean****

d) Prolonged or demanding operation under medium damage;

 

4. Total Damage
a) Short operation under severe damage

 

In the end we only have three final points requiring a revision or implementation.

 

* 1b. Exceeding time/absolute MP limit for engine regime.

While behaviour within engine limits appears correct, the simulation of moments immediately after does not reflect actual operation above time limits, taking in account the error margins set by manufacturers, and the nature of damage immediately sustained by such handling of the engine. A proposal discussed here by community members with experience working with engines, consulted and approved by a military source directly involved in the maintenance of piston engines, involves setting an additional 5 minute timer where failure can happen as a consequence of overusing non-continuous engine modes. To calculate this, a (t . x) formula can be used where t is minutes spent over the manual limit (maximum 5), and x is the chance of failure, a number between 1 and 5 choosen randomly every time the pilot goes into overtime. If (t . x) reaches 5, the engine sustains light damage which can progress into more severe forms depending on time and engine management by the pilot.

 

x = 5, damage in 1 minute

x = 4, damage in 2 minutes

x = 3, damage in 2 minutes

x = 2, damage in 3 minutes

x = 1, damage in 5 minutes

 

Does anyone have objections, alternatives or corrections to this model, or can we call it the final proposal?

 

Supporting documents must include descriptions of the type of possible damage sustained by going over authorised engine time limits, and operational materials for V-1710-F3R/39 without MAP regulator specifying operational limits (since the P-40E-1 is the example agreed upon when setting out to do this).

 

** 1c, *** 2b, **** 3c, varieties of detonation damage

In the list of plans listed in Developer Diary 120, item 17: "Add engine detonation affect caused by a variety of causes (wron mixture, high miture temperature, engine overboost, etc. );"

 

Consequences of detonation are thus already in the plans, but community research could speed up its implementation. The wording in the DD however leaves it clear they want to implement an almost full fidelity version of this behaviour, in line with the opinion of some engineers who have contributed thus far.

 

If to go on into full detail, this would need to be an independent report of deeper scope to cover it, but to warrant the effort I suggest we contact the developers in the first place to see if they would welcome this research to be made within the community but following their standards to prevent days or weeks of work going down the drain.

 

A simpler model can still be proposed as an alternative however, even if at placeholder capacity. The alternative loosely based on the P-38 chart, to be proposed, would require a table or graph applying the overall formula to all engines in game to prove it does not provide erroneous behaviour.

 

Does anyone have objections, alternatives or corrections to this point?

[Venturi]

We didn't talk much about cylinder head overhead (radials), I would put that under medium damage. It is basically where you can start to get burning of valves, detonation, etc... problems that arise because air / oil cooled radials do not have coolant and the metal itself must deal with cooling... thus overheat directly causes hot spots and metal wear from differential thermal expansion.

 

Otherwise, it looks good to me!

 

I agree, put it forth and see if they want really detailed, super professional interpretation of these limits. It doesn't make sense to put much more work into this if they already have decided on what to do...

[216th_Lucas_From_Hell]

Ah, my bad! Either way the cylinder overhead damage is already implemented (take an La-5 for a spin and play with the shutters to cook them, the reaction is to within the medium damage definition we set).

 

I'll put everything together tomorrow in its final form and share it here for anyone interested to go over again before passing it forth to the developer team.

 

Once more, huge thanks to everyone who collaborated so far

[216th_Lucas_From_Hell]

All right folks, here are the hopefully final files.

 

The report itself: https://drive.google.com/open?id=0B9I9A7xIeg4VMGs0V1E3cWRyb28

 

Supporting material: https://drive.google.com/open?id=0B9I9A7xIeg4VSFJFcl8wb1VOd2M

[Venturi]

I think 52" is the wrong limit Lucas. It needs to be 56", which is 1470hp. This is based on a design for the Allison V-1710-39 of strength sufficient for 1500hp, and is in line with later revisions of the manual. Everyone agrees on this point. Your document lists 52" as the MAP everyone agrees on, this is incorrect.

V-1710-39 was cleared for 56 inHg for 5 minutes, so we know that engine was capable running on it without issues. 

 

All right folks, here are the hopefully final files.

 

The report itself: https://drive.google.com/open?id=0B9I9A7xIeg4VMGs0V1E3cWRyb28

 

Supporting material: https://drive.google.com/open?id=0B9I9A7xIeg4VSFJFcl8wb1VOd2M

Edited August 21, 2017 by Venturi