DCS Spitfire Mk IX performance

Exactly. And its no small power when it comes to driving that supercharger - the Griffon for example, noted for its very powerful supercharger, used some 600 horsepower (yes, SIX hundred) just to run the supercharger at full speed. Other may have used less, but its still in the hundreds of horsepower digits.

 

Now, quite typically for a WW2 engine, fuel consumption was around 235 grams/HP/h, in other words just to drive the (Griffon) supercharger you are burning 0,235 kg/HP/h, or 140 kg (cc. 185 liter) of fuel every hour. Just for the supercharger, because the driving the prop consumes the rest.

 

You are entirely correct that very high levels of supercharging is a very straightforward way to increase power. But it comes at a cost higher fuel consumption (meaning that you have to carry more fuel) and on the long term because of dimenishing returns and efficency

 

When you are using high boost rates, you would probably want to stick to lower compression ratios (which again are not so good for engine effiency, as for the same amount of fuel burned, there is less useful mechanical work), to avoid extreme end pressures that your fuel cannot take without detonation. After a while you probably want to use higher lead content or aromatic fuel for the same reason, which leads to to deposits and corrosion in the engine.

Sooner or later you will also need some sort of intercooling (and the drag and weight of the intercooler radiators and plumbing associated with it) to deal with the extreme heating up of the charge in supercharger itself (again leading again to fuel detonation).

 

Which is probably the answer why the DB engines are lighter and more fuel efficient BTW - they tended to operate at moderate supercharging (the large volume needed rather less boosting), using rather high compression ratios and did not used intercoolers at all (apart from the similar MW injection on later models). A designer has to weight all that. There is no point in an engine developing twice the horsepower if its increased weight (of the whole powerplant - inlcuidng fuel reserves, radiators, oil tanks, propellor size and weight) and size leads to such an increase in drag that the net gain in thrust is marginal, or not there at all.

 

Designing a new, larger block and making it work reliably is a matter of many years, and in wartime, you do not have the luxury of waiting for a new block. In wartime, you have to make the most out of the existing one and keep it competitive.

I think there's more to the DB's light weight than that, as the similarly sized Jumo 213 (which seems to have been designed using a very similar paradigm) was over 900kg, not far off the weight of a 60 series Griffon. Maybe they were doing some clever things with materials choice and structural design to shave off weight.

On the intercooling- It's worth noting that the 60 series Merlin was originally designed for a high altitude version of the Wellington bomber. Where water/methanol injection is the logical choice for a short range fighter (as you demonstrated, it is easy to carry enough fluid for a 1 hr fighter sweep) the intercooler makes a lot more sense for a high altitude bomber which might need to use high boost for long periods of time. It so happened that this new 'bomber engine' was also the best option for upgrading the Spitfire's altitude performance, so the high altitude Wellington project was shelved and production devoted to the Spit. The Brits would probably have loved to develop a water/methanol system for their engines but never did so until after the war (though I have read something suggesting that they tried Nitrous oxide on one squadron of Photo-recon Mosquitos). Presumably time/resources issues prevented it.

Maybe Wiki has it wrong.

DB 605AM

Dry weight: 756 kg (1,667 lb)

Merlin 61

Dry weight: 744 kg (1,640 lb)

Merlin be lighter than the DB.

The Merlin 66 weighs 748 kg at 27 l displacement,

the Griffon 65 weighs 948 kg at 36.7 l displacement,

The DB 605 D weighs 745 kg at 35.7 l displacement.

I guess thats what they were trying to compare. The DB 605 D really is rather light, but doesnt have a carb nor intercooler for example. Makes perfect sense to me.

The engine card of the DB 605 AM says btw it weighs 730 kg.

This is Kurfurst you are talking to...remember, nothing (not even an F-15) can beat a 109. NOTHING!:thumbup:

I think there's more to the DB's light weight than that, as the similarly sized Jumo 213 (which seems to have been designed using a very similar paradigm) was over 900kg, not far off the weight of a 60 series Griffon. Maybe they were doing some clever things with materials choice and structural design to shave off weight.

The Merlin was a relatively complex engine (eg: about 11,000 parts, cf 7,100 for the Allison V-1710, not sure what the parts count for the DB605 was), mostly built using Rolls-Royce proprietary alloys and steels - like the cars, the quality of design and construction was high, but the trade off was extra weight.

One reason the DB 601 & 605 series were light-weight is that they used magnesium for castings and other parts.

As an interesting aside, this article describes how Merlins that are still in use in racing warbirds can be overhauled and modified to run at up to 150 inches of boost @ 3,800 rpm, generating 3,500 hp.

Exactly what do you do to hop up a Merlin? “Simple,” Thorn says with a grin. “Disconnect the boost [limiting] control. We’ve seen 150 inches of boost, which is where the gauge stops. And which is probably just as well.”

Nixon’s most recent project has been the restoration of a rare Daimler-Benz DB 601 inverted V-12 for a New Zealand collector’s Messerschmitt Bf 109E. “The biggest problem has been all the magnesium parts—intake manifolds, valve covers, accessory cases, things like that,” he says. “Since they’re all down at the bottom of the engine when it’s mounted in the inverted position, moisture gets at them and they corrode away.

The Brits would probably have loved to develop a water/methanol system for their engines but never did so until after the war (though I have read something suggesting that they tried Nitrous oxide on one squadron of Photo-recon Mosquitos). Presumably time/resources issues prevented it.

From Alec Harvey Bailey: The Merlin in Perspective: The combat years:

The Merlin was a relatively complex engine (eg: about 11,000 parts, cf 7,100 for the Allison V-1710, not sure what the parts count for the DB605 was), mostly built using Rolls-Royce proprietary alloys and steels - like the cars, the quality of design and construction was high, but the trade off was extra weight.

 

One reason the DB 601 & 605 series were light-weight is that they used magnesium for castings and other parts.

 

As an interesting aside, this article describes how Merlins that are still in use in racing warbirds can be overhauled and modified to run at up to 150 inches of boost @ 3,800 rpm, generating 3,500 hp.

 

 

 

 

 

 

 

From Alec Harvey Bailey: The Merlin in Perspective: The combat years:

<snip>

So it was night fighters, not photo recon! Thanks for the references, both on Mozzies with NOS and the other stuff.