BF109: 1 ata = 29.9"?

[SolarEagle]

I'm trying to figure out the boost gauge on my BF109, and have not found any info on what an ata is. I've found the measurement atm(atmosphere), where 1 atm = 29.9", so I would have to assume a 1 ata = 1 atm. Is that correct?

I crosschecked some engine charts and that seems like it might be the case, though the BF109 only goes to a max a 1.3 ata, which seems a bit low as I'm assuming that means 30% above 1 ata, which would only be 39" if my numbers are right. Can anybody help me out?

[SolarEagle]

Ok I was able to confirm 1 ata is pressure at sea level, though I'm still surprised the BF109e-4 has a max of 1.3 ata(38"?) as the Merlin during the same time period could do something like 52". I see the 109's engine is nearly as large as a Griffon, so I guess the discplacement is needed to make up for the low boost tolerance.

[oakfloor]

I have a BF-109 and the A2A a ME-109, and I cant figure out what ATA is, but when I hold the mouse pointer over the gauge it will indicate MP, so I just use the flight manual settings. It would be nice to have american style gauges and civilian panels, but everyone wants "authentic" and "original" The reason that you only get about 40" or so of MP, is because the germans never had, or did not have much high octaine avgas, IIRC it was only about 80 or 90 grade fuel. Although they did have water injection on some late model 109's and 190's that allowed more MP. The A2A 190D has a water-menthol switch.

[SolarEagle]

Ok that would explain. Thanks for pointing that out. I'll also trying mousing over the boost gauge to see if it gives me MP as that would be quite helpful.

[deimos256]

well in german atmospheres translates to atmosphaeren, so ata could be an abbreviation of that?

[ICDP]

The reason that you only get about 40" or so of MP, is because the germans never had, or did not have much high octaine avgas, IIRC it was only about 80 or 90 grade fuel. Although they did have water injection on some late model 109's and 190's that allowed more MP. The A2A 190D has a water-menthol switch.

It is a very common mistake to label German fuels as sub-standard (lower octane) in comparison to Allied fuels in WWII. The general 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.

For example the most common allied aviation fuel of the later part of the war was 100/125 octane (lean/rich). 100/150 grade fuel was also very common with allied units.

Standard German high-grade C3 aviation fuel used in the mid/later part of the war had lean/rich octane numbers of 100/130. Lets assume that this same fuel was used by both the Allies and the Germans. Using the naming convention of each air force we know the Allies would list it as 130 octane while the Germans would list this as a 100 octane fuel. Same fuel different naming methods and voila, the allied fuel sounds much higher octane and therefore higher quality. The reality is that while German avgas used more aromatics to make the fuel higher grade the octane rating was about the same or only marginally less than the allied fuels.

The myth that German aviation fuel was somehow vastly inferior to allied fuel is based on a misapprehension.

In reference to the original question.

The Db601A (109E) and Merlin III (Spitfire MkI) both weighed around the same and gave around the same power output. The displacement of the Daimler Benz engine was 33.93 L, the Merlin 27.04 L. The higher displacement helped compensate for the lower manifold pressure in the Daimler engine.

[SolarEagle]

I don't think the C3 was all that common was it? If they were running 100 octane I would think they'd be running higher boost than 1.3 atm since power to weight is so important, though I don't know what compression ratio they were using. What I do know is my car can run 1.7 atm with no intercooler, 8.5:1 compression, and 93 octane.

[ICDP]

C3 fuels took up around 2/3 of fuel production according to postwar allied research. The 1.3 ATM boost was for early DB601 engines. As the war progressed the boost rose to around 1.98 on the DB engines. The boost increase on the DB series (and other German aero engines) were never as dramatic as the boost gains on the Merlin for example.

http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/tech_rpt_145_45/rpt_145_45_conclusions.htm


Example of power increase (1939 - 1945) I am not trying to show one engine as being better than the other. My intention is to show that relative power output of both engines increased by similar amounts throughout the war.

Merlin 1939
1,030 HP (87 Octane)

Merlin 1945
2,000 HP (100/150 Octane) 25lb boost.

DB601Aa 1939
1,050 HP 1.3 ATA

DB605 1945
2,000 HP 1.98 ATA (With MW50 Boost)

I am not trying to enter a debate as to the merits of one type of engine over the other. I am also aware that the 1.98 ATA rating for the DB605 may not have been approved operationally but it did reach these power output levels by the end of the war.

[SolarEagle]

Engine tech and tuning is facinating stuff, so I appreciate the info. I've got a couple engine blueprints which are cutaway drawnings about 3ft in size for the Griffon and Merlin. Here's a cool site to check out:

http://www.aviationshoppe.com/Rolls-Royce-Merlin.html

Scroll down to see the blueprints, which are available for many engines and aircraft. They look really sweet in a silver frame.

[oakfloor]

Here is a great website for aero engines http://www.enginehistory.org/

[huub vink]

Thanks for this clear explanation Martin.

Huub