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Why C 3 fuel for the DB 605 AS ?
- Thread starter Achi
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From impression the stocks (fuel stocks in airfields in Northern Italy and Souther Germany it seems that the ratio of stocks was 50-50%, or perhaps 60-40% for C-3, so it appears that the 'roughly 2/3s of late avgas production was C-3' statement is definietely correct.
From early 1945 DB notes of meetings it appears that there was a tendency that fighter units in the East relied on B-4, and fighter units in the West relied on C-3, where possible (basically this means Bf 109G/Ks and the FW 190D, which could use either fuel, while the FW 190A/F types always needed C-3).
Basically by the start of 1944 all Bf 109s with methanol boost would use C-3 grade avgas as a rule. The reason for this was probably that in case of failure in the water injection system, C-3 had high enough octane rating to do without knocking, while B-4 would lead to engine damage in this case (though B-4 with methanol water injection allowed the same boost just as fine, so it was probably a safety measure).
The exception being the Bf 109G-10 and K-4 with the DB 605D engine which would need C-3 if they were to use of higher boost pressures; it would appear that they used both fuels.
From early 1945 DB notes of meetings it appears that there was a tendency that fighter units in the East relied on B-4, and fighter units in the West relied on C-3, where possible (basically this means Bf 109G/Ks and the FW 190D, which could use either fuel, while the FW 190A/F types always needed C-3).
Basically by the start of 1944 all Bf 109s with methanol boost would use C-3 grade avgas as a rule. The reason for this was probably that in case of failure in the water injection system, C-3 had high enough octane rating to do without knocking, while B-4 would lead to engine damage in this case (though B-4 with methanol water injection allowed the same boost just as fine, so it was probably a safety measure).
The exception being the Bf 109G-10 and K-4 with the DB 605D engine which would need C-3 if they were to use of higher boost pressures; it would appear that they used both fuels.
ALL the DB 605's could run on either B4 or C3.
Are you sure? I believe that use of either fuel only became possible with the DB 605 DB/DC and DB 605 ADB/ASC which didn't arrive until November 1944 and January 1945 respectively.
The DB 605 AS engine used the MW50 boost under the designation DB 605 ASM. It could only use C3 grade fuel.The MW50 system was developed in May 1944 and the first DB 605 ASM engines were produced in July of that year so there was a period where only one fuel was useable.
The Bf109G-6 AS/MW used the MW50 boost system in a slightly different way,by modification of the old GM-1 system,and also required C3 grade fuel.
Cheers
Steve
Last edited:
The information in my post comes from Daimler Benz documents.
Also In a meeting held at Rechlin on April 44, it was noted that GM-1 systems were being installed in the Bf109G with DB 605AS currently in production, in order to convert quickly to MW 50 use. In such cases, C3 would be mandatory.
See DB Aktennotiz Nr. 6127 v. 22.4.44
If you would like to tell me where you got the idea that all DB 605 engines could run on both grades I'm all ears.
Steve
Also In a meeting held at Rechlin on April 44, it was noted that GM-1 systems were being installed in the Bf109G with DB 605AS currently in production, in order to convert quickly to MW 50 use. In such cases, C3 would be mandatory.
See DB Aktennotiz Nr. 6127 v. 22.4.44
If you would like to tell me where you got the idea that all DB 605 engines could run on both grades I'm all ears.
Steve
sure. http://kurfurst.org/Engine/Boostclearances/DB_Niederschrift6730_DB605DBDC_20-1-45.pdf. I'm sure you'll agree that any B4 fuel DB 605 can use C3. the link provided will tell you why a C3 fuel DB 605 can run on B4, including circumstances and directions.If you would like to tell me where you got the idea that all DB 605 engines could run on both grades I'm all ears.
Steve
A DB 605 can run on B4 fuel and as those documents (with which I am familiar) show could run at a higher boost with C3 fuel,just as the British could run their Merlins at higher boost when 100 octane fuel arrived from the USA.
What a DB 605 engine could NOT do was run with the MW 50 system and B4 fuel. C3 fuel was MANDATORY on an engine with the MW 50 system fitted until the introduction of the versions introduced in late '44 and early '45. Remember that the MW 50 system was standard on the G-14AS.
It is probable that the red undercarriage legs seen on some G-5AS/MW was to indicate clearly,at least more obviously than the fuel triangle and from a distance,that these aircraft were to have C3 fuel only.
I refer you back to my posts above.
Cheers
Steve
What a DB 605 engine could NOT do was run with the MW 50 system and B4 fuel. C3 fuel was MANDATORY on an engine with the MW 50 system fitted until the introduction of the versions introduced in late '44 and early '45. Remember that the MW 50 system was standard on the G-14AS.
It is probable that the red undercarriage legs seen on some G-5AS/MW was to indicate clearly,at least more obviously than the fuel triangle and from a distance,that these aircraft were to have C3 fuel only.
I refer you back to my posts above.
Cheers
Steve
You could increase the manifold pressure (boost from the supercharger) when using higher octane fuels in many engines. The documents you posted give the various limits for this in the DB 605 with different fuel types.
This is entirely different from the MW 50 system which injected essentially a water/methanol mixture into the supercharger. For this C3 fuel was mandatory.
That's me done. We'll let people reading the posts draw their own conclusions.
Cheers
Steve
This is entirely different from the MW 50 system which injected essentially a water/methanol mixture into the supercharger. For this C3 fuel was mandatory.
That's me done. We'll let people reading the posts draw their own conclusions.
Cheers
Steve
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- #14
Hello Steve,
Chris Starr writes :"...the first breed of methanol 605s used precious 96 -octane C3.However,the realities of fuel supplie in Germany meant that extreme pressure was applied to DB to develop further engines capable of using regular 87-oktane B4 and,when the firm introduced a final 605 family in late 1944 some were able to use B4 in conjunction with MW 50.Through further refinements of pistons design and the use of Bosch ...sparkplug,the DB 605DB was able to use B4 fuel at the 1850 PS/1.8 ata rating with MW 50." For the parallel DB 605A the same.
Hello Ratsel,
the C3 was in short supplie.The production of this in 1943 was less than 1/4 of the normal "Fliegerbenzin".
Regards,Achi
Chris Starr writes :"...the first breed of methanol 605s used precious 96 -octane C3.However,the realities of fuel supplie in Germany meant that extreme pressure was applied to DB to develop further engines capable of using regular 87-oktane B4 and,when the firm introduced a final 605 family in late 1944 some were able to use B4 in conjunction with MW 50.Through further refinements of pistons design and the use of Bosch ...sparkplug,the DB 605DB was able to use B4 fuel at the 1850 PS/1.8 ata rating with MW 50." For the parallel DB 605A the same.
Hello Ratsel,
the C3 was in short supplie.The production of this in 1943 was less than 1/4 of the normal "Fliegerbenzin".
Regards,Achi
the realities of fuel supplie in Germany meant that extreme pressure was applied to DB to develop further engines capable of using regular 87-oktane B4 and,when the firm introduced a final 605 family in late 1944 some were able to use B4 in conjunction with MW 50.
Regards,Achi
Hi Achi,he is correct. The DB 605 ADB/ASC arrived in January 1945 but that is splitting hairs as he refers to the DB 605 DB/DC series of engines which did indeed arrive in late 1944. As I originally wrote.
"use of either fuel only became possible with the DB 605 DB/DC and DB 605 ADB/ASC which didn't arrive until November 1944 and January 1945 respectively"
Until then the use of the MW 50 system mandated the use of C3 fuel in the DB 605 series engines.
Messerschmitt AG even devised a new stencil,a triangle divided vertically in red/yellow, applied near the MW 50 tank filler to denote the requirement of C3 fuel.
Cheers
Steve
C3 fuel was rare
Hi again Achi,this is a common misconception and there is some evidence to suggest that it might not be the case,in the context that all grades of fuel were becoming scarce.
C3 grade was needed to achieve higher boosts in various engines. "Reparatur-Anweisung 2. Nachtrag Nr. 191/345" is essentially a technical bulletin issued 14 March 1945 which explains the conversion of the 1.8ata capable DB 605 DB into the 1.98ata capable DC version. It says that C3 grade fuel was available "for use in unreduced quantity" (my translation).
"TECHNICAL REPORT NO. 145-45, MANUFACTURE OF AVIATION GASOLINE IN GERMANY, 2. Supply and Composition of Aviation Gasolines" was compiled by the allies after the German surrender. It has this to say about production of the two grades of fuel (B4 and C3)
"The relative volumes of production of the two grades cannot be accurately given, but in the last war years the major volume, perhaps two-thirds (2/3) of this total has the C-3 grade. Every effort was being made toward the end of the war to increase isoparaffin production so that C-3 volume could be increased for fighter plane use. The isoparaffin usage in that grade had already been cut to a minimum."
You are correct that the Bf109K could run on B4 fuel but by using C3 the boost could be increased to 1.98 ata and an extra 150 HP attained. In March 1945 I./JG 27, III./JG 27, III./JG 53, IV./JG 53 were ordered to keep their Bf109s but to increase the maximum boost pressure to 1,98 ata manifold pressure (OKL, Lw.-Führüngstab, Nr. 937/45 gKdos.(op) 20.03.45). It is not known how many units had converted to 1,98ata before that order came,if any. Importantly III./JG 27, III./JG 53 and IV./JG 53 were the major users of the Bf 109 K-4 in the Luftwaffe.
Cheers
Steve
- Thread starter
- #18
Hi!
DB 605AS (engine type without MW50) would run on B-4 fuel specification by datasheet of 605AS. This is really logical - AS types is same engine, ratings as A type, but rating altitude greater because of only different kompressor.
MW types (ASM, AM engines) to run on on C-3 because greater pressure (and MW50). But Butch2k 109 expert says later it was sanctioned that it could also run B4 + MW 50. If you read G-14 Karte on LEMB forum, it says: B-4 use is tolerated (late 44 card) Not ideal, but tolerated in need.
DB 605AS (engine type without MW50) would run on B-4 fuel specification by datasheet of 605AS. This is really logical - AS types is same engine, ratings as A type, but rating altitude greater because of only different kompressor.
MW types (ASM, AM engines) to run on on C-3 because greater pressure (and MW50). But Butch2k 109 expert says later it was sanctioned that it could also run B4 + MW 50. If you read G-14 Karte on LEMB forum, it says: B-4 use is tolerated (late 44 card) Not ideal, but tolerated in need.
I'm familiar with that document. It is hard to understand with my limited German so I sought a translation from a native German speaker. Here's what he said. We obviously already know what the document pertains to.
"The document is mostly about the MV booster fuel (methanol/water) that can be used to provide short term boost. It cuts in automatically if you move the throttle beyond a "stop". If you are running on the C3 fuel the MV boost is safe (so long as you keep within set limits). If running on the lesser B4 fuel it's not recommended. This is because if you are running on B4+MV (i.e. with the throttle beyond the stop) and you run out of MV then you''ll wreck your engine. In one place in the document it says you must trottle back but in another is says the damage will be immediate."
So B4 was,as you say,not ideal.
Cheers
Steve
"The document is mostly about the MV booster fuel (methanol/water) that can be used to provide short term boost. It cuts in automatically if you move the throttle beyond a "stop". If you are running on the C3 fuel the MV boost is safe (so long as you keep within set limits). If running on the lesser B4 fuel it's not recommended. This is because if you are running on B4+MV (i.e. with the throttle beyond the stop) and you run out of MV then you''ll wreck your engine. In one place in the document it says you must trottle back but in another is says the damage will be immediate."
So B4 was,as you say,not ideal.
Cheers
Steve
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