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No limitation on MW-50?


J13 Serenity

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G14 high altitude variants running DB603 compressors had reduced engine life due to excessive cylinder bore wear, like down to 15 hrs or so before replacement - AFAIR. Those were 1.7-8 ATA boost, so its not unreasonable to assume that a DB605D would suffer similar wear as a result of "excessive use of MW50". There was a severe shortage of hard metals at that time, so it can't necessarily be assumed that newer 605s were 'hardened' for higher boost durability. It may have happened, but I doubt it. Engine use limits in operating manuals seem to have been established as a projection / expectation before the actual motors were fully developed.

 

Of course you have inexperienced pilots abusing the motors, or the motors weren't properly broken in, various POL quality problems affecting output and durability etc. I'm SURE that loss of cylinder compression as a result of cylinder bore deterioration was a real problem, and was mentioned in several sources, which I am too lazy to rediscover, lol.

 

You know, that's a good point, about deteriorating metal quality in later years, as that would def have created a gap between 'on paper' and 'reality'.

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G14 high altitude variants running DB603 compressors had reduced engine life due to excessive cylinder bore wear, like down to 15 hrs or so before replacement - AFAIR. Those were 1.7-8 ATA boost, so its not unreasonable to assume that a DB605D would suffer similar wear as a result of "excessive use of MW50". There was a severe shortage of hard metals at that time, so it can't necessarily be assumed that newer 605s were 'hardened' for higher boost durability. It may have happened, but I doubt it. Engine use limits in operating manuals seem to have been established as a projection / expectation before the actual motors were fully developed.

 

Really interested in that book, thanks for the hint! Not only G-14 AS, but also all ASB, ASC, DB and DC variants were running the larger DB603 supercharger. In the September 44 K-4 manual it states normal 50h intervals for engine inspections and with C-3 fuel the engine is not time limited in any way at 1.8 ata.

 

I hear lots of anecdotal claims that MW50 would burn out the engines really fast, but I dont see a scientific reason behind it. The ADI actually causes lower combustion temperatures as I have said several times now. As the water is evaporated during combustion it turns into steam and soaks up tremendous amounts of heat, while the steam causes a good but safe (because late) increase in cylinder pressure. Then it basically steam cleans the cylinder and exits through the exhaust while also having decreased the exhaust temps.

 

In this doc from 20.01.45 (http://www.kurfurst.org/Engine/Boostclearances/DB_Niederschrift6730_DB605DBDC_20-1-45.pdf), Dr. Scherenberg from Daimler Benz explains that "troubles with white flame with subsequent burned cylinder can be mostly attributed to inferior fuel quality". And I think this is really where the crux lies. Basically what happened was that detonation occured due to too low octane and contaminated fuel and completely wrecked the cylinders. But that is no effect that could be attributed to ADI. ADI actually is supposed to prevent exactly this damage from happening. I say it again, I very much doubt that engines were wrecked due to prlonged use of ADI.

 

Btw DB responded to this problem by retarding the ignition point and decrease knocking of the engine which causes a loss of 50 HP at Sondernotleistung. Also of note is, that this document talks about that on the eastern front mainly B-4 fuel was used so to this front it is important to give out the information about ignition retardation as soon as possible. Which implies that on the western front C-3 fuel was in frequent use. Considering the overall number of LW aircraft at that point it probably werent that many. :smilewink:

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Really interested in that book, thanks for the hint! Not only G-14 AS, but also all ASB, ASC, DB and DC variants were running the larger DB603 supercharger. In the September 44 K-4 manual it states normal 50h intervals for engine inspections and with C-3 fuel the engine is not time limited in any way at 1.8 ata.

 

I hear lots of anecdotal claims that MW50 would burn out the engines really fast, but I dont see a scientific reason behind it. The ADI actually causes lower combustion temperatures as I have said several times now. As the water is evaporated during combustion it turns into steam and soaks up tremendous amounts of heat, while the steam causes a good but safe (because late) increase in cylinder pressure. Then it basically steam cleans the cylinder and exits through the exhaust while also having decreased the exhaust temps.

 

In this doc from 20.01.45 (http://www.kurfurst.org/Engine/Boostclearances/DB_Niederschrift6730_DB605DBDC_20-1-45.pdf), Dr. Scherenberg from Daimler Benz explains that "troubles with white flame with subsequent burned cylinder can be mostly attributed to inferior fuel quality". And I think this is really where the crux lies. Basically what happened was that detonation occured due to too low octane and contaminated fuel and completely wrecked the cylinders. But that is no effect that could be attributed to ADI. ADI actually is supposed to prevent exactly this damage from happening. I say it again, I very much doubt that engines were wrecked due to prlonged use of ADI.

 

Btw DB responded to this problem by retarding the ignition point and decrease knocking of the engine which causes a loss of 50 HP at Sondernotleistung. Also of note is, that this document talks about that on the eastern front mainly B-4 fuel was used so to this front it is important to give out the information about ignition retardation as soon as possible. Which implies that on the western front C-3 fuel was in frequent use. Considering the overall number of LW aircraft at that point it probably werent that many. :smilewink:

 

Well there is one area where the engine was sure to be subject to increased strain, and that is simply mechanical effects. More RPM, More power = More mechanical load on internal components. Bearings are a particular concern- overheat them (via friction) and the engine will soon cease to function.

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As rel4y already said the engine was rated to make these exact same revs and the exact same amount of power with C3 fuel without time limitations...

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I agree with Nerd1000.... bearing durability seemed to be on the minds of line pilots, outside of what the factory specified... This probably had something to do with a combination of a move to plain as opposed to roller bearings, again lack of hard alloys, and lower quality oil. The Jumo, which ran at higher rpm at emergency power, didn't seem to have as many problems with this.

 

Has anyone seen any tech data on metal composition of DB or Jumo blocks, heads, bearings, etc? It would be interesting to compare those to what's know about western types. Perhaps Calum's book will shed light on these issues when it comes out.


Edited by Barfly
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mw50

 

bf-109 in dcs runs 1.79(53inHg) ata max boost with mw50 irc. so have to think that bf-109 is running preaty low boost compare to about 67inHg for spit and about 67inHg for p-51 late version of p-51 were running about 75inHg. db605 has 35-36dcm3 of deisplacment merlin has 27dcm3 so about 30% less. Everyone knows that bigger engine handles bigger loads better heat exchange area is much bigger in db605 than in merlin. so bf109 load is equivalent to about maby 53inhg for p-51 and you can run at this setting for a long time in p-51

water methanol injection cools air/fuel mixture so your engine can avoid knock at higher boosts but mw50 is not adding any power by it self.

on other side fw190 runs 1.9ata(57inHg) at low speed of supercharger and something around 2.1ata(63inHg) at high speed of supercharger expect that engine in fw190 will have harder time to cool it self

Bf-109 k-4 was one of very rare plane that could compete with p-51-d most of bf-109 fighting p-51 would fall behind with power and aerodynamics a lot behing p-51


Edited by grafspee

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