Time Machine Consultant : Maximizing the Bf-109 in January 1943

[Shortround6]

Originally Posted by davebender

Then why didn't the Luftwaffe switch entirely to C3 fuel by 1939?

I don't know but even the Allies Kept much lower grades in production. In fact much of training even with P40s and like in the US was done on 87 octane fuel. Primanry training was done with 73 or 80 octane.

You may get a lower yeild (fewer gallons of gas per barrel of base stock) with the higher octane/performance stuff.
It might require a different cracking or distilation procedure.

The development of "Cat cracking" saved tens of thousands of tons of steel in refinery construction compared to convetional cracking of gasoline for the same yeild.

and you have to get those aromatic compounds from somewhere

[DAVIDICUS]

Off point but related. It appears that in February 1943 Goering may have wanted to produce the Fiat 55 as a replacement for the 109.

G55 - Aircraft History

Transcript from the German official BA-MA archives courtesy of Civettone:

Milch: ... Perhaps Petersen can inform us on this question and also about the comparison flights in Italy.

Petersen: ... There will be a further report about comparison flights with all the Italian types ... Against this, the Italian fighter is equal to the German fighter, especially as regards rate of climb. They are also superior in armament. The Fiat 55 aircraft has four cannon and a performance similar to that of the German aircraft, although powered by an engine that
is a hundred horsepower less.

Peltz: Were they series or experimental aircraft?

Petersen: There is an experimental series of ten aircraft, but these trials concerned new aircraft that had been 'titivated up'.

Goering: I'm glad that the Italians at long last have produced a respectable fighter. And I can only say; let them build them to capacity.

Milch: We also should do something in that sphere. It is indeed a disgrace to our own industry.

Goering: The Italians have never built inferior aircraft and have always been competent in the construction of aircraft and engines. I remember the Fiat and Alfa. They have also held the world speed record. The ability of the Italian aircraft industry has always been of the best. They are unable to mass produce however, and there we must help them. We can consider ourselves lucky, if they have produced a good fighter aircraft. It's one in the eye for our own people anyway.

Petersen: We must attend to this at once. The airframe of the Fiat G 55 can accommodate the DB 603 engine, while the Me 109 is unable to do so any longer. The G 55 with the DB 603 would be an ideal fighter aircraft.

Galland: From our experience the Italians have always forgotten something in their fighter aircraft, either the armour or guns.

Goering: It's to be hoped however that for the purposes of these comparison flights, they've been informed about this, otherwise it's a waste of time.

Petersen: The fighter specialist has flown the aircraft. With the exception of the radio it carried complete equipment, and fuel for one and a half hours, whereas we carried fuel for only one hour. We can't ignore the fact that the Italian aircraft has a performance equal to that of our latest types.

Milch: Then please obtain three Italian aircraft at once, and fly them here, in Rechlin. I would have the DB 603 installed in these aircraft that we have been discussing this morning. It would mean a considerable advance towards the Me 209. I can't imagine the FW 190 with the BMW 801 engine as it is today being sufficient for the next two and half years. [sic!] Especially as we don't know what the English and the Americans are building.

...

Goering: I'm also in favour of the proposal. However I consider it more than likely that the English will effect an improvement with their own types. I would like to ask what is our best means of improving our fighters other than the jet propulsion business?
Milch: The Me 209 and especially its engine. ...

...

Goering: If the Italian aircraft is good, then we won't deny the fact, and we'll mass produce them here. We don't want any false pride.

Milch: Thereby we could advance a year.

Galland: And it would also do our designers good.

Goering: On top of that perhaps we could include the Italian pilots as well, in our complete programme. Anyway I'm very pleased to hear this about the Italians.

[Civettone]

Davidicus, thanks for bringing that up again. It now hits me on how they talk about the DB 603 without even mentioning the Jumo. If the G.55 was licence produced it would have gotten the DB 603. This was still in 1943. Also the Me 209 was designed for both engines. So it seems the DB 603 was considered to be the standard piston engine for fighters of the new generation ...

So could it be that the Fw 190D with Jumo 213 was really meant as a high altitude (45k ft) interceptor and didn't get a DB 603 for that reason? I have never seen anything in that sense before. The performance of the Jumo 213A was well understood. It was not for altitudes over 30k ft...

Kris

[Kurfürst]

Originally Posted by davebender

Then why didn't the Luftwaffe switch entirely to C3 fuel by 1939?

Largely because there was no point - German aero engines had generous displacement - 33 liters and up - and you don't need to use high boosting for such engine to get plenty of power. The limiting factor for German/Russian were thus mechanical factors (ie. the engine bearings and other components had to be able to take that power load), rather than concerns about knocking. Several Allied reports mention that they simply do not understand why the German engines are not taking full advantage of their high octane fuel.

In case of 'small' displacement engines, ie. Allison, Merlin - high boosting was essential if you wanted to get the same powers as the larger displacement engine, and you absolutely needed high octane fuels to get away without knocking. They operated on far greater manifold pressures, to compensate for their much smaller displacement.

As an example, the 35-liter DB 605AM, with a mere 1.7 ata boost, or about +7 lbs/sq. inch, was able to deliver roughly 1800 HP and could do either with water injection and 87 octane, or with 100/130 or 100/150 octane fuel alone. But this boost was used in 1944, and before that, 1.42ata was the max, yet it could still produce 1550 HP, on 87 octane.

In contrast, the 27 liter Merlin III at +6.25 sq./inch produced 1030 HP on 87 octane; the Merlin 66, to produce 1700 HP, it required +18 lbs/sq. inch or 2.22 atm, and to produce 2000 HP, a boost as high as +25 lbs/sq. inch or 2.7 ata was required.

In constrast to the 35 liter DB 605 and the 27 liter Merlin, the 44.5 liter DB 603A on the other hand, could produce 1750 HP at 1.42ata, and did not required more than 87 octane. Of course you could boost it further with high octane fuels, and the last ones of the 603s developed as much as 2800 HP, but plenty of work had to be done until the engine was not falling apart under such loads... take a look at say the racing engines in the 1930s... the DB 601 racers produced as much as 2600 HP or so, but could not last more than a couple of hours under such load.. obviously this isn't practical for military applications.

As the Americans say, there is no replacement for displacement. You can get the same results by superchargering, intercooling et all, but its much more complicated to do so.

[Milosh]

The German engines had much higher compression ratios, Merlins stayed at 6:1. Increased CRs require an in increase in octane for proper operation.

[Kurfürst]

Appearantly even DB 605D with its 8.5:1 CR could operate at 87 octane fuel and produce up to 1550 PS at 1.5 ata, so I don't think increased CR had that high 'octane requirements'. It did enchance fuel economy and especially altitude output though.

[davebender]

The DB605 may be limited to 1.42ata for normal operations but it would be nice to have 1,800 to 2,000 hp availble for emergency use. You don't worry about damage to engine bearings when bounced by enemy fighter aircraft. If you survive to return home then the engine will be replaced.

[Shortround6]

Actually it is the combination of compression ratio AND boost that requires high octane.

Think of 2 engines, one with a 7.5 compression ratio and using 1.5 ata of boost and the other 6.0 compresion ratio and 2.0 ata of boost.
Combining the two factors together gives 11.25 for the first engine and 12.0 for the second. if every thing else is the same they are going to need similar fuel.
I know it doesn't work exactly like this but I am trying to keep it simple.

Factors that do affect this are many, fuel injection, shape of combustion chamber, cylinder cooling and a whole lot more inculding "TEMPERATURE OF THE INTAKE CHARGE/AIR" Since what we are trying to prevent is the auto-igniton of the fuel it is actualy the heat of compresion that is causing a large part of the problem.
Our second engine is heating the air more before it even gets to the cylinder. The first engine is heating in more in the cylinder.

THe two engines are going to behave differently IF the cylinders are the same size. The first engine will use it's fuel more efficently, more power per pound of fuel burned going to the crankshaft but the second engine will actually make more power.

Why?

Because at 2.0 ata of intake pressure it is putting 33% more fuel air into the cylinder than the engine using 1.5 ata of pressure. this is more than enough to compensate for the lower compression ratio.

Of course the second engine will have to be built heavier to stand up to the extra pressure/power and cooling.

Here is something that we tend to forget looking back at some of these engines. While the engine designers may have used power per unit of displacement as a measure of how good an engine was ( and we still do) the AIRFRAME designer could care less. The airframe guys only cared about THREE things.
1.Power per unit of weight. how heavy the engine was for the power it gave.

2.THE bulk per HP. how big the engine was, frontal area or length, what was it going to take to house the engine.

3. The fuel efficency of the engine/s. how many pounds of fuel was it going to take to fly a certain mission. Intercepter mission of 1 hour or flying the mail across the atlantic.

THe airframe guys could care less about how many liters of displacement it took or how many rpm.

as a concrete example it was estimated that the 6.67 compression ratio of the Allison cost it about 10% in max power compared to the Merlin's 6.0 on the same fuel. of course the Allisons extra displacement got back almost 5% of of that and the Allison did get slightly better fuel economy.

[Shortround6]

Originally Posted by davebender

The DB605 may be limited to 1.42ata for normal operations but it would be nice to have 1,800 to 2,000 hp availble for emergency use. You don't worry about damage to engine bearings when bounced by enemy fighter aircraft. If you survive to return home then the engine will be replaced.

Returning home with a rod sticking through the side of the block isn't all that easy. Main bearing failures could result in the engine seizing completely and rod bearing failures usually ment throwing a rod.

[proton45]

Originally Posted by Civettone

Sorry for the long read.
Kris

Golly, no reason to apologizes Kris, that was interesting reading.

[davebender]

If a Spitfire is pumping lead into your aircraft then throwing a rod is not your most immediate concern.

[Shortround6]

Originally Posted by davebender

If a Spitfire is pumping lead into your aircraft then throwing a rod is not your most immediate concern.

No but if you throw a rod in the next two minutes the Spitfire will be back to pumping shells into your aircraft.

Or into your wingman as your 109 turns into a glider

[Civettone]

Originally Posted by davebender

If a Spitfire is pumping lead into your aircraft then throwing a rod is not your most immediate concern.

If you are you going to tell the German pilot to only use it when bounced or only in extreme danger I wonder how that is going to work out. He'll probably use it whenever he judges it to be beneficial.

Kris

[davebender]

He'll probably use it whenever he judges it to be beneficial.

How did they enforce power restrictions on early model DB605s (before the oil foaming problem was fixed)?

[Civettone]

By saying they will be shot if they use it. In fact I don't know, did this problem allow them to use full power at times or not at all ?


Kris