# 1.98ata boost



## Milosh (Sep 21, 2009)

> Of course all of us can look it at different the evidence posted at angles, but a very definietive claim like this should be backed up by very definietive sources speaking in no uncertain terms. Certainly if 100 octane fuel was used in such an uniform manner as some posters claim, there should be evidence easily found for this.



This can be applied to the 1.98ata boost used on the K-4. Unfortunately there has been no conclusive proof that 1.98ata boost was used by the 4 Gruppen authorized to use the 1.98ata boost, *only speculation*.

The only so called proof is:

*a/* A German document (Lw.-Führüngstab, Nr. 937/45 gKdos.(op) 20.03.45) saying 'boost increase to 1.98 ata'.

The problem here is there is no primary documentation presented for 1.98 ata boost useage.

*b/* a secondary source saying there was 284,000 liters (62417 Imp Gal) of C3 on Bavaria airfields.

The problem here is the airfields where there is C3 fuel are not specified. C3 at airfields where the 4 Gruppen authorized to use 1.98 ata boost are not based is not of much use to those K-4s.

Oliver Lefevre:

_"And even after the clearance only few gruppen got it because of shortages due not only to C3 production but also to C3 delivery to the units." 

"From other documents I know that C3 and B4 had severe quality problems beginning in late 1944."

"At least DB documents underlined the need for cleaner fuels than those in use at that time."_

from Douhet: Still Relevant Today

"It wasn't until 1944, when Major General Ira Eaker, Commander Eighth Air Force, changed target priorities that strategic bombing started to have the desired effect on German war production. General Eaker identified two major target groups: 
(1) The Sources of Energy Group (coal and synthetic oil); 
(2) The Transportation Group (canals and railways). (6:285) 

Once the major emphasis of strategic bombing was moved to these two target groups, measurable
results were seen. The air objective was to disrupt all rail traffic in Germany. By October 1944, rail traffic was nearly paralyzed.

Essen Division car replacement of coal which had been
21,400 daily in January 1944 declined to 12,000 in
September. By November delivers of coal to factories
in Bavaria had been reduced by nearly 50 percent. By
January 1945 coal placements in the Ruhr district were
down to 9,000 cars per day. Finally, in February well
-nigh complete interdiction in the Ruhr district was
obtained. Such coal as was loaded was subject to
confiscation by the railroad to supply locomotive fuel
coal. As mining continued at a higher level than trans
port, coal stock reserves increased from 415,000 tons
to 2,217,000 and coke stocks increased from 630,000
tons to 3,069,000 in the same 6 months (7:63)

In May 1944, preliminary attacks were made on the larger synthetic oil plants. These plants had been producing 316,000 tons a month; in June their output fell to 107,000 tons, and in September to 17,000. Aviation fuel production also dropped from 175,000 tons to 5,000. These attacks dealt a crippling blow to the munitions and explosives industries, and reduced the supply of synthetic rubber to about one-sixth of its war time peak of 12,000 tons a month (6:286)."

Not sure of the source but believe it is Oliver Lefebvre

_A 1944 K-4 should be equipped with a DB605DM at 1.75ata since delivery of DB605DB did not occur until mid january 1945. The DC which were basically the same engine were to be delivered in the DB configuration until the 1.98ata boost was cleared.
By february 1945 orders were issued to begin tests of the DB605DC set to 1.98ata, and plans were made to convert existing squadron with DB605DB engines to DB605DC standard.
What is not known is to what extend it was done before war ended as we do not know whether testing was positive or negative and if the former at what time the DC was considered operational. 
Just to correct some confusion about the C3 issue.
When first issued the DB605DM/ASM/AM were required to use C3 fuel, and it was not until some time that those engine were cleared to use B4 as well. It required some timing adjustement as well as some nerves since a failure of the MW-50 system in such a configuration broke the engine almost immediatly.
So it's quite normal to see C3 markings on a K-4 or G-10 it does not mean by anyway that the a/c is actually using a DB605DC.
for instance almost all K-4 of the 330xxx-333xxx batches wear a C3 triangle while the later 334xxx batch a/c are wearing a B4 triangle.
It flew but to what extend tests made by the II/JG11 with the DB605DC at 1.98ata were positive is not known at this time. Early reports of the 1.90ata test underlined spark plugs troubles as well as mechanical troubles and the insufficient cooling of the 109. Those troubles prompted the decision to deliver all DC engines set to DB standard at 1.8ata.
All those events took place in february, and plans were made to clear it for operational use as underlined by planned unit equipments listing. Now it remains to be seen to what extent it was done before the war ended._

One often sees a photos of K-4s with a C3 fuel decal. This does not mean the K-4 used 1.98 ata boost. Besides, one of these photos is an K-4 from 11./JG3.

*c/* 116000 litres (25494 Imp gal)) of C3 fuel in Italy as of April 23 1945 and only 7000 litres (1538 Imp Gal) on May 1 1945.

This is stock available to the Kommandierender General der Deutschen Luftwaffe in Italien for all his units, German and Italian. The Germans decided who got the fuel, the Italians had no control over this.


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## Milosh (Sep 21, 2009)

Of further interest is this extract from Lorant/Goyat "Bataille dans le ciel d'Allemagne" ...(a translation):

_At Kleinkarolinenfeld, around ten pilots who no longer had aircraft piled into a truck at dawn on 27 April 1945 in order to drive to the airfield at Bad Wörishofen and take delivery of Messerschmitt 109s fresh out of the factories. Fw. Arnulf Meyer (9. Staffel) never forgot the scenes they witnessed that day:

Rows of Messerschmitt 109s and Focke-Wulf 190s lined up around the airfield perimeter, others out in the open (!) under the odd camouflage net. Teams of oxen in yokes in the midst of all this enabled the aircraft to be moved around without utilizing any manpower or fuel… At least one hundred fighters from the assembly lines were dispersed around the field. The Officer that met us showed us the latest sub-types to be delivered: Focke-Wulfs with in-line engines and in particular the Messerschmitt Bf 109 K, an improved sub-type of our “Gustav” model. There was bustling activity on the field. Aircraft were landing and taking off constantly. There was no airfield protection Rotte in the air. Our surprise was even greater when we were told that thirty brand new aircraft were due to arrive at the depot that day if the necessary pilots to ferry them in could be found. We were presented to the airfield commander who had set up his office in a comfortably appointed wooden shack: a fatherly Major who gave us a pleasant welcome. Of course we wanted to take the Bf 109 Ks… He asked us for our papers indicating our various type ratings but after scrutinizing them, he handed them back with a shake of the head and simply said: “sorry, I can’t give you any K-4s. You’ve only flown the G-10, so take the G-10s!”

We tried to explain to him that whether they were the G or K variant, they were still Messerschmitt 109s and any mods were almost certainly to be of a minor nature, unlikely to impact on the handling qualities of the aircraft. He did not appear particularly convinced by our arguments, but I noted how keenly he eyed us smoking our American cigarettes. These were retrieved from US prisoners and our Spieß always had them in his stocks. As naturally as possible, I offered the Major one of these cigarettes. His face lit up. Just for good measure, I left a barely started packet on his desk. He thanked me and told us that he was going to see what he ‘‘could do”. In the minute that followed, more packets of cigarettes changed hands and in this way we soon had authorization to take the Messerschmitt Bf 109 K-4s!

We went to select our Messerschmitts in the company of the line chief, who asked us what our destination airfield was. *The fuel crisis had also reached this field. Our aircraft were fueled with enough for thirty minutes flying time, which was largely sufficient to get back to Kleinkarolinenfeld.* On the other hand the armament magazines were empty. We were given parachutes and life jackets. Suddenly we saw a car drawing up and out climbed the depot commander. He told us in a voice bereft of emotion that he was not sorry that we were taking the 109 Ks. Then he read the text of a teleprinter message he had just received. The presence of American troops and tanks was reported ten kilometers from Bad Wörishofen and he was ordered to immediately destroy all the aircraft housed on the airfield. The Major explained to us that the 109s were easier to blow up than the 190s, as they carried as standard a delayed-action 3 kg explosive charge in the fuselage housed next to the fuselage fuel tank. We smoked a last cigarette together with the officer. The imminent debacle seemed more of a relief to him than anything else. He had fought during the First World War and had been wounded but was of the opinion that the disaster befalling our country was of a much more serious nature on this occasion. He hoped that we would soon be back among our families and that we would not risk our lives pointlessly. He started up his car and drove off.

My first takeoff in the Bf 109 K held no surprises. The aircraft was poorly trimmed and the compass was not functioning, which meant that I had to follow my comrades blindly. A typical product of our war industry in 1945: the instruments were incorrectly calibrated and there was nothing coming through the oxygen mask. Fortunately our flight level did not exceed 1,000 meters. We all landed without incident at Kleinkarolinenfeld. Happily enough the brakes worked…_

The airfields mentioned are in Bavaria and there was a lack of fuel.


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## vanir (Sep 25, 2009)

I believe it is noteworthy that contending no DC was calibrated for 1.98ata in the field is also speculation.


Another point could be that any mechanic with a spanner can recalibrate the boost regulator. If I'm a Luftwaffe jagdflieger and I've got a DC/K-4 and my airfield has any C3 I'm picking up a spanner myself...and that's that. No arguments, damn I'd probably shoot anyone who tried to stand in my way with my sidearm.
War is pretty emotional you know.

Just some viable considerations.


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## Juha (Sep 26, 2009)

Hello Vanir
Quote:” Another point could be that any mechanic with a spanner can recalibrate the boost regulator”
Quote:” my airfield has any C3 I'm picking up a spanner myself...and that's that.”

Not so, it depended did you have right kind of sparks plugs installed; otherwise your flying career might have ended sooner than you could guess. So IMHO a normal engine mechanic with a spanner and a set of spark plugs, just in case, could do the thing but a hot-headed pilot might got himself killed or at least ended front of a military tribunal for sabotage, ie for destroying a combat-plane.

Quote:” No arguments, damn I'd probably shoot anyone who tried to stand in my way with my sidearm.”

Frankly, air forces usually got very dim view on persons shooting their fellow soldiers, who had tried do hinder some unauthorised act of the shooter.

Juha


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## vanir (Sep 29, 2009)

You'll get away with the same heat range as plugs used for 1.8atü (DB motor mit MW50/B4) but indeed a DB motor using C3 without MW50 (1.75atü calibration) will need colder plugs so the cores don't cause ping (glow effect, but only where the heat range of the plug is too high for the new boost calibration). Probably the DB/MW50 motor uses the same plug heat range as the DC/MW50 motor, at worst one heat range lower, which is no prob if you know what you're doing.

Here's how: you need to retard the timing curve at 2600-2800rpm just a shade, again a spanner can be used for this (loosen the right magneto bracket and move it anticlockwise about 5mm then tighten should do the trick but really it's best to change the magneto for a recurved one). Doing it this way you lose a couple of horsepower in engine efficiency for a net gain due to increased boost pressure. It's a trick you use on twin curve auto race engines, again any mechanic can do this with little more than a spanner at a field hangar. In fact when recalibrating boost pressure it is more important to recurve your spark timing than it is to change the plugs, unless the change is dramatic.

As for the plug fouling that is caused by C3 fuel regardless of the heat range of the plug, they must be changed more frequently than for engines using B4 and are more prone to burning out the valves or holing the pistons with overuse. One of the reasons higher than 1.75atü took quite some development time was new piston crowns to help prevent ping even with C3.

My field recalibration of the DB/MW50 motor to use C3 fuel and 1.98 boost might return 1780PS at 5km instead of the MAG figures of 1800PS by fitting properly recurved right magnetos on DC motors for the blower recalibration used. But again probably the very same plugs are used between this engine and 1.8 calibration for B4 fuel or at worst one heat range lower which isn't actually a big difference, the real difference is the spark curve at maximum output to give high perf without ping. Essentially you always want the highest heat plug and lowest octane fuel possible to get the most horsepower, which is almost counter-intuitive because when increasing boost pressure you often have to lower plug heat range and raise octane, but what that actually does is reduce engine efficiency for a net power gain due to other modifications (bigger injectors, higher boost calibration, more efficient head porting, valve timing, etc).

A DC motor is definitely not a DB motor with just a recalibration and colder plugs from the factory, it will have probably the same plugs and new right magneto, possibly even different piston crowns.
The confusion I think is that DB motors were also used with C3 fuel but not fitted with MW50 in this configuration, boost recalibrated to 1.75 atm and no other modifications made (source Mercedes Benz AG archives). This is also probably the reason for C3 fuel cards on so many G-10 and K-4 airframes where these are not 1.98atm calibrated motors. They would be 1.75atm DB motors using C3 fuel and no MW50, and much cooler plugs than either version with MW50.

But you could field mod a DB/MW50 for C3/1.98atm if you change the spark curve at high output with a spanner, though it probably won't be quite as efficient as a DC from the factory and if there was a change in piston crowns between the two motors you'd have a 1-2min sondernotleistung instead of the rated 5min use (like the AM and ASM motor at 1.75atm/MW50).
Interesting thing, the DB/C3 without MW50 has roughly the same performance as the ASM motor using C3/MW50 at a much higher fuel consumption rate and much lower engine life (often single use if sondernotleistung was sustained for more than a minute).


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## Milosh (Oct 2, 2009)

Do you have any data on the availability of C3 fuel vanir?

I./JG27 was based at 8 airfields in the time period 19.3.45 > 8.5.45.
III./JG27 was based at 7 airfield in the time period 18.3.45 > 8.5.45.
III./JG53 was based at 6 airfield in the time period 17.12.44 > 8.5.45.
IV./JG53 was based at 4 airfield in the time period 3.12.44 > 8.5.45.

Non of the 4 Gruppen spent very much time at each airfield. Sometimes only a day or two.

Fw. Arnulf Meyer was with III./JG53.


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## Juha (Oct 2, 2009)

Hello Vanir
Very thorough explanation. I have read an article on DB60x engine series which gave rather exact info on different spark plugs needed in different DB605s with different atas but I haven’t had time to dig it out from my piles in my attic. That’s why I wrote that “So IMHO a normal engine mechanic with a spanner and a set of spark plugs, just in case, could do the thing…” And I still think that an average LW pilot in ‘45 would have been incapable to make the engine adjustments needed by himself.

Juha


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## vanir (Oct 2, 2009)

Both good and valid points Milosh and Juha, and probably quite correct.

I offer only an alternative consideration, since the beginning premise is also speculative. And with a Messer pilot in the family who gave me some interesting perspective on the pilot's field environment, plus some research of RAAF units stationed in New Guinea I find the actual field conditions are a lot less politically correct and by the book as the impressions we have in retrospect. Very frequently the field mechanics redecided policy based on what was necessary in that posting, at that time. Fuels qualities in the field and parts availability varied, improvisation was often key, as true for Allied forces in NA and SEA as much as German in NA or the EF, or Japanese in SEA and Burma.

It appears for example operators of the P-40E and K in the Middle East recalibrated the 52" WEP rating offered by Allison to as much as 66" Hg in the field for more than 1730hp WEP under 1000ft (higher if cold ram is used). Allison Division was deeply concerned about this practise, but apparently pilots in the field just didn't care and wanted whatever performance their mechanics could squeeze out of those planes whatever the cost. In Australian postings the same engines were recalibrated for as much as 70"Hg in the field, this is on 100/130 fuel by the way, Allison said the motors must be overspeeding to achieve these ratings and thus wanted the practise stopped, the most they were prepared to adjust their own WEP ratings was for 60"Hg in the F3R/F4R engines.

Similarly when family friend Gunther talked about the Me-109G in Africa he commented on the amazing improvisational abilities of the German field mechanics, whom were superbly skilled and as responsible for the periods of Luftwaffe success there as the pilots.

In other examples of pilot outlook, one Luftwaffe ace talks about how the only thing he could think about flying intercept missions was the fact that his family lived in the city below, where the bombs were dropping. Others cannot remember which variant of Focke Wulf they were flying on a particular mission without looking it up in their log books, one cited a Ta-152H then later it turned out it was a D-12 when he checked. This isn't so much technical ignorance as a completely different set of priorities at the time. And it's not just the late war environment behind this, Gunther didn't differentiate between G-10 and K-4, he made greater differentiation between the G-2 and G-4 because of their different radio fits.

Pilots and field mechanics were I think very pragmatic in action. The reports and OP are of course word perfect and by the book, they had to look like that to get filed without somebody losing their job. But in the field it seems to me that commanders gave tremendous latitude and personnel used this in any pragmatic way to get the job done. If it meant contradicting OP and recalibrating the boost regulator in the field, then fine, just don't put it in a report.
In Germany especially by late 44 things were very slap dash and haphazard. Pilots turned up at factory aircraft parks and were sometimes told, "Just take what you want and go away." That's a quote.


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## Shortround6 (Oct 2, 2009)

I am sure that many mechanics/crew operated their aircraft outside of official guidelines.
THe question is how long they could get away with it. 
American engines were supposed to pass a 150 hr test. Other nations used different test to quilify theri engines. Some engines would tolerate more abuse than others, at least short term. 

An Allison might very well survive a 30-60 second excursion at 3200rpm vrs the "official" 3000rpm max and get the pilot back home on THAT flight. But it might mean a breakdown on a later flight that wouldn't have happened for many more hours if the engine hadn't been abused. 

While pilots and maybe even squadron commanders wanted performance RIGHT NOW some of the higher ranking officers were concerned with having operating aircraft several weeks from RIGHT NOW. If you had a fair supply of spare engines and or parts and a good repair/overhaul operation close by maybe you could abuse the engines on a fairly regular basis. if engines and spares were scarce you might be trading some extra performance now for now operable aircaft later. Of course getting shot down means no operable aircraft later either

However the idea that large numbers of squadron mechanics knew more about the operating limits of the engines (or were smarter) than the engineers who designed/developed the engines at the factory takes a bit of swallowing


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## Juha (Oct 3, 2009)

Hello Vanir
From the beginning I have no problem with your point that on the field mechanics did unauthorised things to get more out of planes. LW was sometimes more strict than some others air forces, IIRC in some units at least junior pilots were not allowed to remove the outer 20mm canon from their Fw 190As but as I say engine manipulation is a different thing.

Hello Shortround
IIRC USAAF and Allison were rather conservative when they decided the max boost and rpm allowed, so Allisons had rather large “safety margin”, on the contrary, IIRC DB605A could tolerate only up to 2% overspeeding, Merlin 20% and later Allisons 30%, so one could abuse Allisons more than the other two. One point was the official tests US types vs Zero, P-39D began with clearly higher manifold pressure than was officially allowed, ran into engine troubles, manifold pressure was lowered but test was flown with manifold pressure still higher than which was officially allowed.

Juha


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## Milosh (Oct 3, 2009)

vanir, are you saying that the DB 605 was operated at 1.98ata *without* C3 fuel?


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## vanir (Oct 3, 2009)

Agreed Shortround and Juha, the logic is sound.


> vanir, are you saying that the DB 605 was operated at 1.98ata without C3 fuel?


No, the DB was operated on B4 at 1.8atm using MW50 or C3 at 1.75atm without MW50, whilst the DC was supposed to be operated at 1.98atm using C3 with MW50, although as you mention there is no evidence to support that this configuration was used in service and I personally believe the DC motor described a change of magnetos as well as fuel and boost regulator recalibration hence the designation change...but that a DB motor could be field modified by a regular mechanic to use C3/MW50 and 1.98atm but performance would not be quite as good as a DC motor due to spark timing (rather than plug heat range which are probably the same).

The reason the 605D-series could function at 1.75atm on C3 without MW50 where the 605A-series required MW50 for 1.75atm is the change in the piston crown/combustion chamber between the motors, which had been developed specifically to reduce predetonation at higher boost ratings for existing fuel qualities (although the quality of C3 was markedly improved by 1944 according to Crumpp of "White 8" fame).

As for the availability of C3 fuel, one should remember that all Fw190A/F/G series motors needed C3 to function, so tracing its availability should be as easy as locating all airfields out of which any Fw-190A/F/G series were operating. If there was a BMW engine FW flying sorties out of an airfield, that airfield had C3.


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