Question for Daimler-Benz experten...

[Rami]

To all,

Tweaking airfiles for the Bf-109g, I am looking at engine data for the Daimler-Benz DB-605A. I've noticed that at 87 octane, the compression ratio was about 7.4:1, whereas with 100 octane fuel, the compression ratio was about 8.4:1. Which octane fuel was the Luftwaffe more opt to use?

Depending on which one I choose, it has a significant impact on the airfile.

 

[Wulf190]

I'd say supplies of 87 octane were used most. It really depends though on what version of the Gustav we are talking about and the engine used. If the engine is an AS or ASM (which was used on higher performance G-6, early G-10, and G-14 types) or the DB605D (Used on later G-10 builds and K-4) then I'd say 100 octane.

 

[Rami]

Wulf190,

In this case it's a Bf-109g-6 equipped with the Daimler-Benz DB-605A.

One of the ideas PSULLYKEYS and I were kicking around last night was for future German campaigns, having some missions where you use an alternate set of airfiles, perhaps in this case where your plane has been equipped with 100-octane fuel for a particular mission.

Other scenarios would include the inclusion of paddle-bladed props on the P-47 Thunderbolt that would give a significant boost to performance.

What do y'all think of that?

 

[Wulf190]

Sounds great to me.

Wulf190,

In this case it's a Bf-109g-6 equipped with the Daimler-Benz DB-605A.

One of the ideas PSULLYKEYS and I were kicking around last night was for future German campaigns, having some missions where you use an alternate set of airfiles, perhaps in this case where your plane has been equipped with 100-octane fuel for a particular mission.

Other scenarios would include the inclusion of paddle-bladed props on the P-47 Thunderbolt that would give a significant boost to performance.

What do y'all think of that?

 

[erufle]

What they used and what they wanted to use may have been two different issues. 87 octane may not have been optimal for the higher compression engine. It probably would have worked in an 8.4 to 1 engine but if we assume 1940s cylinder head designs had a ways to go they would have tried to get higher octane.

Modern engines can run up to 10 to 1 on 87 octane but that is because manufacturers have eliminated sharp spots inside the combustion chamber that get red-hot and cause detonation (an over-simplification).

Another way to look at it is engine tuning. You could have advanced the timing on the 8.4 to 1 motor if you used 100 octane. Thus, more horsepower. If you put 87 octane in it you have to retard the timing to prevent detonation. Thus, horsepower loss.

The bottom line. If you want to fly a souped-up bf109 they had 100 octane. If you have to fly against the 109 they only had 87 octane. Your call if you ask me.

 

[PSULLYKEYS]

Erufle is correct.....mislead you yesterday Rami.:redf:

A little research produced this:

109E1-4 - DB601A - 1175HP - TO - 88 octane
E4N -7 - DB601N - 1200HP -TO - 96 or 100 octane
Feb 1941 - introduction of N20 injection/powerboost on all subsequent engines
F2-4 - DB601E - 1350HP - TO -87 octane to the end of the war - late 1940
G1-4 - DB605A - 1475HP - TO
G5-6 - DB605AS - (starting 1/44)
G10 - DB605D -2000HP - TO
later models used whatever engine they could get.
K - DB605DB and some without power boost with DB605DB or very few (K14) with the DB605L - 730KPH @ 11500 m!

So 100 octane used spring through late fall 1940 = BOB. However ground attack units and notably JG5 in the far north (& training units) received the E castoffs as F's and later Gs were available.

Trained crew could change a DB engine in a 109 in 20 minutes, I wonder if some of the old E's had whatever engine available installed later in the war?