BF109 Engine Damage in boost/emergency mode

[Venturi]

Should also be noted that the TBO of the V-1650 engine was a similar 200 hours during WW2.  The V-1710 also featured a similar TBO, but it went as low as 50 hours in Russian service.

Wrong. 700-1000hrs to TBO for the V-1710. 400hrs + for the Merlin. Whereas in the best case scenario, the DB605 had around 200hrs, and often much less in the realm of 50hrs, if you read the above information posted on Kurfurst’s site (indeed am glad for this site to host info like this). I have posted evidence for the Allison TBO elsewhere in the forum previously, and corroborating information to this effect can also be found throughout the internet.

 

Honestly, I do not believe discussing this with you or other gamers is a productive conversation anymore. Multiple very knowledgeable people have contributed much evidence to the contrary of your claims, showing that engine limits are realistic and moreover, necessary to the sim.

 

As I stated previously, the real solution here is modeling of detonation parameters.

 

Twain, that famous American, has a statement on arguing when you shouldn’t, and I’m now going to heed it.

[LColony_Kong]

Wrong. 700-1000hrs to TBO for the V-1710. 400hrs + for the Merlin. Whereas in the best case scenario, the DB605 had around 200hrs, and often much less in the realm of 50hrs, if you read the above information posted on Kurfurst’s site (indeed am glad for this site to host info like this). I have posted evidence for the Allison TBO elsewhere in the forum previously, and corroborating information to this effect can also be found throughout the internet.

 

Honestly, I do not believe discussing this with you or other gamers is a productive conversation anymore. Multiple very knowledgeable people have contributed much evidence to the contrary of your claims, showing that engine limits are realistic and moreover, necessary to the sim.

 

As I stated previously, the real solution here is modeling of detonation parameters.

 

Twain, that famous American, has a statement on arguing when you shouldn’t, and I’m now going to heed it.

Almost every document and cited evidence here, and in the other thread, was posted in support of the engine limits being bogus. 

 

also I love the key word "you and other gamers"

 

your arrogance is incredible. 

 

But your right on one thing, this conversation is completely unproductive when your side wont cede to any evidence at all because you must defend your precious coconut effect. Heaven forbid you not have levers to pull and settings to manage. 

Edited January 23, 2018 by Fumes

[LColony_Kong]

well no, all the so called "evidence" you posted just show you have no understanding how engine limits worked or that engine limits are real.

 

The reason why this "conversation" is unproductive is because everyone here knows the Devs will never do anything as silly as removing all engine limits with no restriction since that would be totally unrealistic.

 

Again I repeat my offer, just show me one account of any German pilot in WW2 who ran a 109F/G at 1.42 ata for a long time. The LW had thousands of fighter pilots in WW2. Hundreds gave interview or wrote biographies after the war. Surely there most be at least one you can find if it was as common as you seem to believe. 

quite the opposite actually. The evidence showed exactly what it was supposed to. And long runs of 1.42 ata were given....

 

But the coconut mindset cannot be overcome because the perception that "harder and more complex" = "more realistic" is a notion that is nearly impossible to disillusion in simulator communities. Your typical sim "expert" loves to argue every single mechanic should be harder and more complex because of that perceived notion. 

 

People think removing the limits is silly has nothing to do with actual engineering. This is why not one person in this thread of that position has actually posited some specific reason why they think that is other than 1 or 2 anecdotes, or accusing the other side of not knowing about engines, or how we cant have a game fix because it might not work on one single plane (p40)

 

 

That is why this entire notion of time limits is bogus. The time limits were NOT written for the purpose of preventing per mission destruction. They were written to stop undue wear on the motor over many missions. That is an absolute fact. Period.

 

There is no evidence for time related engine detonation. None. The entire notion is reliant upon evidence that has nothing to do with the proposition. 

[Sgt_Joch]

quite the opposite actually. The evidence showed exactly what it was supposed to. And long runs of 1.42 ata were given....

 

 

 

where?

[LColony_Kong]

where?

Read both threads. If you are asking where then you havent read them. 

[Panthera]

Wrong. 700-1000hrs to TBO for the V-1710. 400hrs + for the Merlin. Whereas in the best case scenario, the DB605 had around 200hrs, and often much less in the realm of 50hrs, if you read the above information posted on Kurfurst’s site (indeed am glad for this site to host info like this). I have posted evidence for the Allison TBO elsewhere in the forum previously, and corroborating information to this effect can also be found throughout the internet.

 

Honestly, I do not believe discussing this with you or other gamers is a productive conversation anymore. Multiple very knowledgeable people have contributed much evidence to the contrary of your claims, showing that engine limits are realistic and moreover, necessary to the sim.

 

As I stated previously, the real solution here is modeling of detonation parameters.

 

Twain, that famous American, has a statement on arguing when you shouldn’t, and I’m now going to heed it.

 

Didn't know you saw yourself as such an expert, must be frustrating 

 

Anyway RR themselves recommended a ~240 hour TBO for the Merlin (200 hours being mentioned for the Packard by US pilots), whilst a TBO of 700-1,000 hours for the V-1710 I don't believe was ever achieved at anything outside of civil use. Allison themselves apparently recommended just 120 hours TBO for the V-1710 in Russian service.

 

As for how you can claim that the DB605 only had 200 hours in the best case scenario I really don't know, esp. considering a TBO of even 100 hours was there during the period where there were obvious issues with cooling & piston burn throughs. After these issues were solved the recommended TBO was 200 hours for 1.42ata cleared engines, a run in period with two 5 min intervals @ 1.42ata even being std. practice before delivery, which I'd say rather conclusively proves that the issues with piston burn throughs were at this point solved and a thing of the past.

 

Then there are a couple of pilot accounts of TBO's as low as 30-50 hours, but these are all refering to the very late war period where a general lack of maintenance due critical shortages of spare parts & oil no doubt were  to blame, evidence of this being the plummeting availability rates occuring amongst all German motor vehicles during this time. For comparison the Russians at times also only managed 50 hours with the Allison V-1710, and that probably due to similar issues.

Edited January 24, 2018 by Panthera

[Blutaar]

 

 

After these issues were solved the recommended TBO was 200 hours for 1.42ata cleared engines, a run in period with two 5 min intervals @ 1.42ata even being std. practice before delivery,

 

Maybe all of the Notleistung the engine could handle was used up in the 2x5mins run in periods. lol (just kidding)

 

After all i still think 1min is just rediculous and that nobody would allow 1.42ata if there is a chance that the engine would blowup for using it a few seconds to long. While "experts" talking about low actane fuel and that 1.42 ata is the absolut limit with 87 octane fuel, what was the fuel used in the M-105 PA/PF engines? Must be some high octane stuff!

 

I would like to see a 9 min Notlesitung pool which starts to being used up after 1 min of Notleistung in the 109. So that you can use Notlesitung for 10 minutes total in a 109 while only be able to recover 1 minute. Everything above 1 minute will use up the 9 min pool followed by a blowup. For other planes there should be other limits like for example 7 min in the FW so you also can have 10 mins total Notlesitung. Sure it would be not very realistic but it should be easy to implement and is better then what we have now in my opinion.

[Dakpilot]

Maybe all of the Notleistung the engine could handle was used up in the 2x5mins run in periods. lol (just kidding)

 

After all i still think 1min is just rediculous and that nobody would allow 1.42ata if there is a chance that the engine would blowup for using it a few seconds to long. While "experts" talking about low actane fuel and that 1.42 ata is the absolut limit with 87 octane fuel, what was the fuel used in the M-105 PA/PF engines? Must be some high octane stuff!

 

I would like to see a 9 min Notlesitung pool which starts to being used up after 1 min of Notleistung in the 109. So that you can use Notlesitung for 10 minutes total in a 109 while only be able to recover 1 minute. Everything above 1 minute will use up the 9 min pool followed by a blowup. For other planes there should be other limits like for example 7 min in the FW so you also can have 10 mins total Notlesitung. Sure it would be not very realistic but it should be easy to implement and is better then what we have now in my opinion.

 

Well a M-105PF runs at max 1.38 ATA with a lower compression ratio, heavier engine, less extreme cam timing on 94 octane fuel, minimum grade or 95/100 optimum  

 

Engines have designed limits, when you exceed them, especially temps, rpm's and boost pressures, things change very rapidly on a very non linear scale, and generally when you have a problem when an engine is developing 1500HP or so things go wrong VERY rapidly and usually catastrophically

 

Klimov's, Daimler Benz, BMW, Rolls Royce, Allison, P&W and Shvetsov (and different models of each manufacturer) all have big differences in design, it is just too simplified to just compare with power output or weight or ATA etc.

 

even something as seemingly clear cut as Allied fuel octane rating is not so simple, with US and British octane rating being quite a bit different

 

am sure some of the figures are not exact but I hope you get the gist

 

But I am sure some people will just continue to say it is unfair/bias that VVS run at 100% and Luftwaffe cant run at 100%, not understanding what max CONTINUOUS power rating entails, or base things on  the simple assumption that it is 2018 Mercedes/BMW vs Lada with a closed mind

 

It is interesting that VVS pilots do not campaign to be able to overboost their Klimov engines beyond approved limits (apparently common Allison mod in the west) for a short period because it would not do any damage (if kept in temps) in the short term   (sort of joking)

 

Cheers, Dakpilot

Edited January 24, 2018 by Dakpilot

[=EXPEND=13SchwarzeHand]

 

 

Klimov's, Daimler Benz, BMW, Rolls Royce, Allison, P&W and Shvetsov (and different models of each manufacturer) all have big differences in design, it is just too simplified to just compare with power output or weight or ATA etc.

 

I do agree with you on this. I think you are very knowledgeable on this subject. IMO You do seem to miss a very simple and basic thing though. In your opinion there is one standard in definition on continuous power, combat power and wep, which is standardized across all manufacturers and nations. While this may be the case today. I am sure it wasn´t back then. Do you know if "Notleistung" is comparable at all to what the allies defined as WEP? Do you know what other instructions were given in Russian manuals, that do not necessarily fall into this categorization, but might hint at not using 100% all the time?

 

 

 

ut I am sure some people will just continue to say it is unfair/bias that VVS run at 100% and Luftwaffe cant run at 100%, not understanding what max CONTINUOUS power rating entails, or base things on the simple assumption that it is 2018 Mercedes/BMW vs Lada with a closed mind

 

Has it ever occurred to you that 1) soviets might have just used a different categorization or used different standards 2) That the German category of Notleistung might have been much broader than what one would understand as WEP today or as what the allies considered it to be? I am really actually asking and I would be glad to learn more!

[JtD]

Yes, you're right. There are major differences between the nations in terms of definitions and requirements. Not going there right now, just as food for though one major point to consider:

 

The Germans designed their aircraft to 'peace time' standards, meaning their aircraft were designed to last hundreds of hours of service. The aircraft were fairly complex, over-engineered and resource hungry. On the other hand, they were relatively comfortable and durable.

The Soviets did not design that way, they designed to 'war time' standards, meaning their aircraft were designed to last less than a hundred hours of service. The aircraft were simple, functional and required few resources. On the other hand, they were harder to operate and less durable.

 

In the end, hardly any aircraft was retired due to old age, but with an average of maybe 50 operational hours, the Germans lost 90% of the designed life span, the Soviets 50%. That pretty much confirms the Soviet approach as the proper one, and the German industry after 1942 put a large emphasis on making their design simpler, cheaper and less durable (see for instance use of wooden components or welded steel instead of cast aluminium).

 

This difference in philosophy shows in various places, and makes a direct comparison of the materials inappropriate. Dakpilot keeps bringing up the 'continuous' rating of the Klimov. This is, however, from the very basic principle, not comparable to the 'continuous' power of a DB or Jumo (or Allison for that matter). The Soviets simply didn't care about getting 500+ hours out of their engines, they knew not even half of them would get to 50.

 

While I do 'understand' what continuous means, I just don't put the same faith into a word on a piece of paper and therefore have a different opinion.

[Dakpilot]

Without going into semantics, continuous would mean safe to operate at that limit for the designed life, without expecting it to blow up if kept within temp and RPM limits in any language

 

manufacturing defects are another matter, and VVS and Luftwaffe both suffered at stages during the war

 

there were 129,000 or so M-105's built so there was not much shortage of supply, pretty much all pilot reports talk of using "full throttle" with no issues, it was designed to be simple to operate with little training

 

they were surprised when early P-40 Allisons and Spits fell apart when treated the same way, this is also well documented and with proper operating limits/procedures they got reliability to a greater extent

 

Cheers Dakpilot

[Sgt_Joch]

It is not really true that you can run a M105 engine at 100% continuously since, in many situations, it will eventually overheat and blow up. In effect, the damage model for the Russian engines is better since it is directly linked to excess heat.

 

That does not mean there is nothing to tweak. As others have pointed out, we have a very simplified heating/cooling model where you can run engines in all sorts of conditions without really worrying about overheating. Any future modification to the engine damage model will have to address that.

[Venturi]

It is interesting that VVS pilots do not campaign to be able to overboost their Klimov engines beyond approved limits (apparently common Allison mod in the west) for a short period because it would not do any damage (if kept in temps) in the short term 

 

It is not about simulating what is desired, it is about simulating what was / is possible, as you know 130oct fuel permits much more than 5min at 45" MP on the V1710-39

 

 (sort of joking)

 

I know

 

 

It is not really true that you can run a M105 engine at 100% continuously since, in many situations, it will eventually overheat and blow up. In effect, the damage model for the Russian engines is better since it is directly linked to excess heat.

 

That does not mean there is nothing to tweak. As others have pointed out, we have a very simplified heating/cooling model where you can run engines in all sorts of conditions without really worrying about overheating. Any future modification to the engine damage model will have to address that.

 

Not totally true, heat does become a larger issue as the Russian engines increase their RPMs. However, the main problem here is that you can run full boost at say 80% RPM, (and for that matter, 50% mixture) without detonation. If detonation parameters were correctly modelled, then max design RPM would be necessary, at full boost levels, to prevent detonation - and this would also incur the proper heat penalty.

 

But overall, I agree the cooling effect on some aircraft is overdone, and some have strange results from cooling flaps settings.

[Barnacles]

 

 

That does not mean there is nothing to tweak. As others have pointed out, we have a very simplified heating/cooling model where you can run engines in all sorts of conditions without really worrying about overheating. Any future modification to the engine damage model will have to address that.

 

Is that because you think more difficult = more realistic or do temperatures in flight regimes (I realise that on the ground behaviour seems wrong in BoS) in this game diverge significantly from historical tests?

 

Please don't think I'm trying to criticize you, I am just genuinely curious as to why a lot of people think that engines should be overheating a lot more. I know a lot of you have grown up on 1946 where full power=eventual overheat so I'm thinking that has possibly prejudiced us against thinking that generally cooling systems in WW2 aircraft were fit for purpose.

 

Edit I'll add that I have no massive insight into this question either way, I do know that there are historical accounts of specific aircraft with heat managment issues (YAK, Spitfire with landing gear and flaps down) But the Dev's have done a large amount of research to develop this game so I'd err on the side of assuming their values are not massively far from reality.

Edited January 24, 2018 by 71st_AH_Barnacles

[=362nd_FS=RoflSeal]

Is that because you think more difficult = more realistic or do temperatures in flight regimes (I realise that on the ground behaviour seems wrong in BoS) in this game diverge significantly from historical tests?

 

Please don't think I'm trying to criticize you, I am just genuinely curious as to why a lot of people think that engines should be overheating a lot more. I know a lot of you have grown up on 1946 where full power=eventual overheat so I'm thinking that has possibly prejudiced us against thinking that generally cooling systems in WW2 aircraft were fit for purpose.

 

Edit I'll add that I have no massive insight into this question either way, I do know that there are historical accounts of specific aircraft with heat managment issues (YAK, Spitfire with landing gear and flaps down) But the Dev's have done a large amount of research to develop this game so I'd err on the side of assuming their values are not massively far from reality.

There is definately something wrong with the heating model of the engines considering aircraft like the P-40 and Spitfire were known to overheat if they were idling on the ground in minutes, requiring the pilot to shut it down immediately, ingame however the P-40 when idling on the ground, runs cool, and overcools in winter weather.

Edited January 24, 2018 by RoflSeal

[Barnacles]

Yes, it's almost certainly wrong on the ground but is it wrong in flight?

[Blutaar]

Well a M-105PF runs at max 1.38 ATA with a lower compression ratio, heavier engine, less extreme cam timing on 94 octane fuel, minimum grade or 95/100 optimum

 

1040 mm Hg is equal to 1.41 ata and not 1.38 ata according to http://www.sengpielaudio.com/Rechner-druckeinheiten.htm. Seems you confused ata with bar.

 

I had not much luck finding out which fuel was used for the M-105PF. Only a qoute without any further info because the site didnt open so i had to copy the sentence from google. "The 2B-78 and 3B-78 gasoline grades were used for the M-105 series engines and the 4B-78 for the M-82.". After further searching i found out that 2B-78 has 92 octane and 3B-78 has 93 octane. It slightly differs from what you postet and it would be nice if you can show me your sources for the 95/100 optimum, thank you.

 

edit:

 

am sure some of the figures are not exact but I hope you get the gist

 

Sorry, just forget what i wrote, my fault for not reading.

Edited January 24, 2018 by Ishtaru

[JtD]

The M105 manual states 'not less than 94.5 octane'.

[SCG_OpticFlow]

The M105 manual states 'not less than 94.5 octane'.

bla001.jpg

 

Octane number is not the same thing in USA and Russia and Germany.

 

There are 3 different methods in use: RON, MON, and AKI.

 

 

For example, the common in EU 95 "super" gasoline has octane rating of 95 in RON, 85 in MON and 90 in AKI. Now remains to find out which scale was used during the WW2 in Germany and USSR.

[unreasonable]

1040 mm Hg is equal to 1.41 ata and not 1.38 ata according to http://www.sengpielaudio.com/Rechner-druckeinheiten.htm. Seems you confused ata with bar.

 

I had not much luck finding out which fuel was used for the M-105PF. Only a qoute without any further info because the site didnt open so i had to copy the sentence from google. "The 2B-78 and 3B-78 gasoline grades were used for the M-105 series engines and the 4B-78 for the M-82.". After further searching i found out that 2B-78 has 92 octane and 3B-78 has 93 octane. It slightly differs from what you postet and it would be nice if you can show me your sources for the 95/100 optimum, thank you.

 

edit:

 

 

Sorry, just forget what i wrote, my fault for not reading.

 

Standard atmosphere = 760 mmHg

 

1040/760 = 1.368

 

Calculator not needed - but it is there on your link on  the second line if you type 104 into the cmHG line.

 

As an interested but mechanically disadvantaged reader of this conversation, I suppose the optimum solution would be to model detonation, as Venturi states. Hope the developers can get round to that.

[JtD]

ata is technical atmosphere absolute, equivalent to 10m of water. 736mm of Hg. It's not identical to the standard atmosphere (atm in German). 1050mm is 1.42 ata.

---

German data on the Klimov also says 94-95 octance, same German source says the V-1710 in the US used 100 octane fuel. Maybe it helps with octane number comparisons.

[Blutaar]

Standard atmosphere = 760 mmHg

 

1040/760 = 1.368

 

Calculator not needed - but it is there on your link on  the second line if you type 104 into the cmHG line.

 

As an interested but mechanically disadvantaged reader of this conversation, I suppose the optimum solution would be to model detonation, as Venturi states. Hope the developers can get round to that.

 

If i write 104 into the cm Hg line i still get 1.41 ata. Atmosphäre (at) techn. is ata as far as i know, i might be wrong about it

[Venturi]

100 octane fuel as used in the v1710 and other aero engines has two ratings - 100 for “lean” mixture and 130 for “rich” mixture. This reflects the retardation of detonation at stoichiometric ratios with higher fuel content for a given O2 content, and is primarily determined by “anti detonation” additives to the fuel.

 

(Here, tetraethyl lead - discovered by General Motors in the USA. Ultimately rich mixture octane ratings would increase to 150 for Allied aviation fuel by the end of the war.)

I’m sure JtD already knows this, but for the casual reader who may not I’m simply repeating a well known fact.

[unreasonable]

Great - learn something every day on this forum. (And I did say that we all experience the Dunning-Kruger on occasion....) 

[Venturi]

The octane rating itself actually maxes at a theoretical "100" - that is, 100% "octane" which as anyone who has taken ochem can tell you, is simply a fully-hydratd, eight-carbon carbon molecule with no branches or double bonds.

 

It is distillation refinement of the fuel which gives a higher octane rating, by fractionating the hydrocarbon mix of the fuel. There are several methods of achieving this, but the point remains the same - achieving a higher concentration of octane in the fuel by separating out the other types of hydrocarbons. Obviously a 100 octane IE pure octane fuel, is nearly impossible to achieve by this method but close approximations can occur.

 

So, any rating at or above 100 tells you an additive was at work to increase even further the detonation point, as compared to a fuel made of 100% octane.

 

Additionally, less well-refined fuel's octane rating can be brought "up to standard" by adding in tetraethyl lead or other "anti detonation" agent at differing amounts. Obviously, too much of this additive can have bad effects, like spark plug (or intake screen fouling)... so best is to start with a high-octane fuel, and add as little as necessary to achieve the desired octane rating.

[ZachariasX]

Obviously, too much of this additive can have bad effects, like spark plug (or intake screen fouling)...

You might want to add that TEL (for which there is no real alternative for high performance engines, even today) is ONLY harmful at low power settings, either at idle (anything below 1200 rpm, depending on the engine) where it is not efficiently cleared from the burning chamber. For this to happen, apart from TEL, you add Ethylene Dibromide, a scavenger compound that is brown in color and is interacting with the lead oxide to clear it from the engine.

 

There is a certain temperature required for the scavenger to be efficient. When starting an engine, temperatures are low and you might have noticed the first cloud coming from the engine (depending on priming and oil residues) is sometimes brownish in color. This is the bromide present in TEL Avagas.

 

Another sitiation, where engine and burn temperatures are low is idle setting. As ethylene dibromide cannot react properly with the lead oxides, these oxides start to build up by the spark plug and the valves. You notice that when you check your magnetos. A significant drop in rpm means you have that sort of dirt there. Running the engine at high rpm again will enable the scavenger to work and the lead deposits are progressively cleared.

 

This is somerthing you have to be aware of with real aircraft that use 100LL Avgas. Especially low compression engines, such that you have in Cessnas or good old Cubs, they don't require the octane rating required for turbocharged engines at all. They also will operate often at lower power settings, where lead buildup can be an issue. Make no mistake, 100LL Avgas contains way more TEL that would be required to keep the valve seats from being worn out on older engines. Newer engines have hardened valve seats and are not prone to excessive wear without the protective layer administred by TEL. The ideal 80 octane Avgas is to be banned soon however. 100LL you can expect to be banned as well at some point in the future wth all consequences to Merlin (and other such) engines.

 

One can say, the more TEL put in your fuel, the shorter the maximum permissible time for flying at low power setting, before it becomes questinable that you'll reach sufficient power output again when you need it. This means, if you were flying the pattern for extensive time or come in from a long descend, you were compelled for a high power run for some minutes to be hopeful you'll be able to make a go around if necessary. People just love high power runs near airfields... not to mention the pilot who often finds himself back at 3000 m AGL...

 

Other than that, even today, there is no alternative to TEL that gives you ~15 octane grades for free.

 

Mogas (for road vehicles) is usually rated with the rich mixture rating, whereas (today) Avgas is measured in lean mixture rating (MON). This is why today, 100LL is great for your P-51. It is not just "100" octane, but much rather 100/130.

 

100/130 Avgas has about 1.12 g/L TEL

100LL Avgas: 0.56 g/L TEL to get the same octane rating (100/130). As pointed out above, fuel composition has been alterd to achieve that.

 

You can see, that fuels got much much better today, requiring less adiititives.

[Panthera]

I remember reading that later during the war German synthetic C3 had additives added which made it the equivalent to Allied 100/150 fuel. Does anyone know what these additives were?

[MiloMorai]

P-51s on there long range escort missions deep into German territory were required to open the throttle every once and awhile to clear the spark plugs. Not doing so could have dire consequences when full throttle was required.

[Sgt_Joch]

I remember reading that later during the war German synthetic C3 had additives added which made it the equivalent to Allied 100/150 fuel. Does anyone know what these additives were?

 

that is another whole can of worms. 

 

The chemical properties of German and Allied fuels were radically different, allied avgas was petroleum based, while German avgas was Synthetic, so it is difficult to directly compare the two.

 

As to the effective octane rating of c3 fuel, I have seen some documentation that it was only around 91-92, as I recall, others have argued it was actually around 100. No one knows for sure.

 

As I said, another whole can of worms.

[Blutaar]

This historical "issue" is based on a very common misapprehension about wartime fuel octane numbers. There are two octane numbers for each fuel, one for lean mix and one for rich mix, rich being always greater. So, for example, a common British aviation fuel of the later part of the war was 100/125. The misapprehension that German fuels have a lower octane number (and thus a poorer quality) arises because the Germans quoted the lean mix octane number for their fuels while the Allies quoted the rich mix number for their fuels. Standard German high-grade aviation fuel used in the later part of the war (given the designation C3) had lean/rich octane numbers of 100/130. The Germans would list this as a 100 octane fuel while the Allies would list it as 130 octane.

 

After the war the US Navy sent a Technical Mission to Germany to interview German petrochemists and examine German fuel quality, their report entitled "Technical Report 145-45 Manufacture of Aviation Gasoline in Germany" chemically analysed the different fuels and concluded "Toward the end of the war the quality of fuel being used by the German fighter planes was quite similar to that being used by the Allies".

 

Copied from: http://www.madabout-.../kb.php?aid=124

 

Dont know how accurate this is but i leave it to the experts to figure out. 

 

There is also an interesting PDF on Kurfürsts page: http://www.kurfurst....h_Archieves.pdf

 

[Sgt_Joch]

on the other hand...

 

british report of testing of C3 fuel of a FW190 which crashed in July 1944 shows an octane rating of 96 (see post 3).

 

https://ww2aircraft.net/forum/threads/the-lean-and-rich-ratings-for-the-c3-fuel.40709/

 

As I said, it is a whole can of worms with competing and contradictory info, (much like this thread actually  ). I tried to get to the bottom of it some times back, but there is no clear answer.

 

FYI, the british had a program of collecting and testing the fuel from every crashed German planes in WW2 to find out what the Germans were up to in terms of fuel. I remember reading a very interesting article/report on it a few years back which had a lot of interesting info, but now do not recall how I found it. 

Edited January 26, 2018 by Sgt_Joch

[ZachariasX]

I remember reading that later during the war German synthetic C3 had additives added which made it the equivalent to Allied 100/150 fuel. Does anyone know what these additives were?

They had an ever changing formula of octane (as the allies had), iso octane and aromatic compounds to get their base fuel. To this they also added lead, in a same way as the allied. Both B4 and C3 are leaded fuels.

 

The allied benefited from having a higher grade base fuel, meaning they started out with something 80ish octane, whereas the Germans had to make all from coal and had a bit more work to get to a same fuel grade. In principle, you can get any fuel you like in a synthetic way, it just more tedious and they had to learn how to make it. The Germans also reached up to 150 grade octane, coming from synthesized isooctane and large fraction of aromatic molecules. But is a matter of how much you can make of it.

 

The allies on the other hand had could start from well known higher grade unleaded refined fossil fuel (up to WWII, most engines were made for unleaded fuels, given their low compression), and just throwing in lead gave them just about 100 octane grade fuel. Going higher than that meant increasing aromatic fraction as well, and the fuel stank horribly. Aromatic molecules are called aromatic for good reason.

 

Rule of the thumb is, take the octane grade of your base fuel, when adding about 3 g/L TEL, add 20 grade octane.

[Panthera]

Well it could've been some of the older C3 still in circulation before the switch over was complete.

Edited January 26, 2018 by Panthera

[Blutaar]

Would be interesting to find out more about that "Technical Report 145-45 Manufacture of Aviation Gasoline in Germany".

[Sgt_Joch]

Would be interesting to find out more about that "Technical Report 145-45 Manufacture of Aviation Gasoline in Germany".

 

its on Kurfurst's site:

 

http://kurfurst.org/Engine/Fuel/German_fuel_specifications_and_production.html

 

although you will notice it lists the octane rating of C3 fuel as 95.

 

again, since the chemical composition of German and allied fuel is so different, it is hard to make a direct comparaison. 

[SCG_OpticFlow]

its on Kurfurst's site:

 

http://kurfurst.org/Engine/Fuel/German_fuel_specifications_and_production.html

 

although you will notice it lists the octane rating of C3 fuel as 95.

 

again, since the chemical composition of German and allied fuel is so different, it is hard to make a direct comparaison. 

 

But in the scanned page from this link, 95 ON (CFR-Motor Method) is given for C2... http://kurfurst.org/Engine/Fuel/improved150grade_C-3.jpg

[Panthera]

its on Kurfurst's site:

 

http://kurfurst.org/Engine/Fuel/German_fuel_specifications_and_production.html

 

although you will notice it lists the octane rating of C3 fuel as 95.

 

again, since the chemical composition of German and allied fuel is so different, it is hard to make a direct comparaison.

C2 was 95 octane, C3 was 100 octane.

 

The interesting bit is that C3 went from 130 RON to 150 RON later in the war. That the Germans managed this with synthetic fuels during WW2 is very impressive.

[Sgt_Joch]

C2 was 95 octane, C3 was 100 octane.

 

The interesting bit is that C3 went from 130 RON to 150 RON later in the war. That the Germans managed this with synthetic fuels during WW2 is very impressive.

 

no C3 fuel was 95, according to the USSBS july 1945 report:

 

 

(b) Composition and Specifications

There were two (2) grades of aviation gasoline produced in volume in Germany one the B-4 or blue grade and the other the C-3 or green grade. Both grades were loaded with the equivalent of 4.35 cubic centimeters tetraethyl lead per gallon. The B-4 grade was simply a fraction of the gasoline product from coal and coal tar hydrogenation. It contained normally 10 to 15 percent volume aromatics, 45 percent volume naphthenes, and the remainder paraffins. The octane number was 89 by a measurement corresponding to the C.F.R. motor method. The C-3 grade was a mixture of 10 to 15 percent volume of synthetic isoparaffins (alkylates and isooctanes) and 85 percent of an aromatized base stock produced by hydroforming types of operation on coal and coal tar hydrogenation gasolines. The C-3 grade was permitted to contain not more than 45 percent volume aromatics. This aromatic limitation sometimes required that the base stock component include some diluents other than the aromatic fraction, which could then be balanced if necessary by the inclusion of slightly more isoparaffin. (The C-3 grade corresponded roughly to the U. S. grade 130 gasoline, although the octane number of C-3 was specified to be only 95 and its lean mixture performance was somewhat poorer.)

 

and this:

 

 

 

The composition of C-3 with a high aromatic content, resulted in that gasoline having a good rich mixture (less than 1.0) performance. It’s performance of allowable power output at lean mixture was not entirely satisfactory, however. If more isoparaffin had been included, the lean mixture performance would have been improved. This was recognized as the outstanding shortcoming in the German aviation fuel quality position. Had raw materials and equipment been available, more isoparaffins would have been included in the C-3 blend. As isoparaffin content increased the aromatic content could simultaneously have been decreased (by use of base stocks with octane numbers equal to those of the aromatic base stocks) and a gasoline with increased heat content would have resulted. However, because of the relatively greater was of manufacturing aromatics, they were used in large quantity to help gain a satisfactory lean mixture performance, with the result that rich mixture performance was no limiting.

[Sgt_Joch]

by the end of the war, C3 fuel was either the rough equivalent of 95/130 or 97/130. Allied 100/150 was actually closer to 110/150, so the octane rating of U.S./U.K. Avgas was always higher.

 

its not hard to figure out why, German fuel was made from coal which had a lower natural octane rating than petroleum as well as other performance issues. If the Germans had unlimited time and unlimited access to strategic raw materials, they might have been able to produce an equivalent fuel, but they didn't so had to make to with what they had.

 

it's no hard to see that German coal based synthetic fuels did not perform as well.

 

The Germans were running the FW190 A8 with a maximum boost of 1.65 ata in 44-45. 1.65 ata is the equivalent of +49" hg.

 

so you have an engine (BMW 801) with a base compression ratio of 6.5:1 with a max. boost of +49" hg. giving you a max compression ratio of roughly 10.7:1.

 

late war P51s were running with a boost of +75" hg.

 

so you have an engine (Merlin) with a base compression ratio of 6:1 with a max. boost of +75" hg. giving you a max compression ratio of roughly 15:1.

 

of course, octane rating is just one parameter, there were many other design differences as well between the two engine setup.

Edited January 27, 2018 by Sgt_Joch

[JtD]

The BMW is using a single stage supercharger, whereas the Merlin66/V-1650 used a two stage supercharger with an intercooler. This makes total compression rates completely incomparable. Not to mention that one is using fuel injection, the other a carburettor.

 

The BMW801D had a compression of 7.2. 1.65ata are 48" Hg. So it's 11.5:1. If the air was taken from sea level standard atmosphere, which it is not.

 

Comparable might be a

MerlinXXsome series, two speed single stage supercharging, which operated at +25lbs. FTH ~8000feet. Total compression 21.8.

BMW801D, two speed single stage supercharging, which operated at 1.65ata. FTH ~5000m. Total compression 21.6.

(Throttles which reduce total compression at lower altitudes don't reduce charge temperature.)

 

Total compression is relevant for charge temperature, and therefore very roughly comparable. Because of the carburettor/injection thing and several other factors, it is still apples and oranges, and but at least no longer apples and goats.