109 e3b against spitfire II

[robtek]

you actually implement that in a comparision wep is set against full mil.????
You are talking about the N, not the A.

[Crumpp]

Merlin XX would be 1485hp at 14lb/3000rpm @ 6000ft and 1490hp at 16lb/3000rpm @ 12500 ft and 1280hp at 3000rpm/12lb @ TO

The document compares the operational engines at the time it was prepared. At 17500 feet, the document is correct in the power output of a Merlin XX at it's approved Emergency Power rating of +9lbs at the time the engine were compared. It is also correct in its assessment of the DB601N series.

It is not correct in its math of the power to weight ratio of the engines. The Merlin XX is the same as the DB601N.

You need to look at the DB605 series to compare those other ratings. Also ensure you are looking at the correct power, ie...indicated, static or RAM, Brake or Thrust, and if it takes into account exhaust thrust...

[Seadog]

Originally Posted by Crumpp

The document compares the operational engines at the time it was prepared. At 17500 feet, the document is correct in the power output of a Merlin XX at it's approved Emergency Power rating of +9lbs at the time the engine were compared. It is also correct in its assessment of the DB601N series.

It is not correct in its math of the power to weight ratio of the engines. The Merlin XX is the same as the DB601N.

In Nov 1940 the operational limits of the Merlin XX were 12lb/3000rpm TO = 1280hp, and 12lb/3000rpm @8500ft = ~1360hp in MS gear. Operation of the boost cutout would give ~14lb in FS gear, but I don't know exactly when official approval was given, however this capability was present in all Merlin XX engines.

At 1280hp and 1450lb weight gives lbs/hp = 1.13 but I agree that the values given in the chart were confusing.

[TomcatViP]

So I understand now what's all abt lol; You hve been so scared abt the dynamic capacities of the Spit ? The guys that did mod the FM in IL2 did used badly wrong assumptions.

Stay at high speed . Don't over G. Don't put yourself where you'll need AoA and I swear you'll knock down any 109 even at full mil power. Big wings are made for that !

Damn Seadog Is that really a "Cat" tht hve to ensure you on this point ?!!

[Viper2000]

Originally Posted by Kurfürst

Compared to that theory, German DB 601 was same size as weight as single stage Merlin, 605 actually lighter then two staged Merlin, while the French 35-liter class Hispano Suize V12s were considerably lighter than both.

The only practical way a smaller displacement engine can keep up with larger ones is by heavy supercharging, but that does not comes free, superchargers and their systems add weight, and so does decreasing fuel effiency: more fuel need to be carried for same range.

Actually, if you do the thermodynamic analysis, you'll tend to find that supercharging doesn't particularly damage fuel efficiency, provided that you have reasonable component efficiencies and make a fair comparison (which is the difficult bit).

Power:weight at sea level will tend to be fairly insensitive to supercharge because the supercharged engine sees higher pressures and therefore has to be heavier, whilst OTOH the unsupercharged engine is bigger. So you end up with a small area of thick metal vs a large area of thick metal.

The supercharged engine has a higher power density, and this will tend to make life harder for the cooling system.

If you compare at fixed cruising speed, there will be an optimum degree of supercharge, beyond which you'll lose more from the increased cooling problems than you've gained from the smaller engine. OTOH, because the supercharged engine is smaller, it has less non-cooling drag, and so you'd expect to cruise faster, which helps to make the radiator smaller.

In the end, the trade space is complex, and it isn't especially easy to make a general case that one approach to engine design is better than another. Hence the diversity of engine designs; if there was a trivial optimum then engine designers would have swiftly converged upon it, and the world would be a much less interesting place.

[Viper2000]

Originally Posted by Crumpp

Just the fact the Germans had direct fuel injection technology and the allies never did balances any fuel differences. One can make considerable power gains without changing fuel type just by changing the fuel metering system from a carburetor or Throttle Body Injection to Direct Injection. In a 1000 hp engine, you can expect to gain 80-150 hp just by changing the fuel metering method.

The whole debate ends up being a wash.

Direct injection isn't necessarily the best approach.

If you're supercharging then putting fuel into the flow upstream of the supercharger will cool the flow by about 25 K due to the latent heat of evaporation of the fuel.

This considerably reduces the compression work required from the supercharger, which is equivalent to an increase in its polytropic efficiency.

I would suggest that the mixture distribution is likely to be pretty good downstream of the supercharger under design conditions, because the fuel is completely evaporated.

Direct injection will obviously achieve better mixture distribution at low rpm where the supercharger delta H isn't sufficient to guarantee that all of the fuel is evaporated. So DI will give you better performance close to idle. This is very important for car engines, but not so much for aeroplanes.

Furthermore, as you develop your engine and increase the amount of supercharge, you'll tend to cruise higher. Even at constant boost, you'll see a higher supercharger delta H and higher charge temperature, which makes the advantage of adding fuel upstream of the supercharger more important.

It's also much easier and cheaper to make and maintain a single point fuel injection system (be it via a pump or a carb) than it is to make individual injectors for each cylinder.

http://www.flightglobal.com/pdfarchi...0-%200562.html
http://www.flightglobal.com/pdfarchi...0-%200563.html
http://www.flightglobal.com/pdfarchi...0-%200569.html

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking. The fact that they didn't do so speaks volumes.

See also:
http://www.wwiiaircraftperformance.o...in-lovesey.pdf
(The chronology of engine ratings and outputs may also be of general interest; presumably Mr. Lovesey counts as a primary source...)

[CaptainDoggles]

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking. The fact that they didn't do so speaks volumes.

But engine design was heading towards turboprops in those years (and obviously turbojets), what with the "trent-meteor" hybrid that was instrumental in the development of Rolls-Royce's Dart engines.

[Crumpp]

2009 Technology of the Year: Direct Fuel Injection

Direct injection-squirting pressurized fuel straight into each cylinder-is the key to keeping internal-combustion engines relevant in the future. For enabling a major step forward in gas and diesel engine power, efficiency, and cleanliness, direct fuel injection is AUTOMOBILE MAGAZINE's 2009 Technology of the Year.

While injecting fuel into the combustion chamber requires approximately fifty times the pressure used with port injection and additional electronic control sophistication, significant benefits are delivered. Since no fuel is deposited on intake-port walls, the air/fuel mixture can be more precisely maintained, benefitting both mileage and emissions. In addition, the cooling effect of gasoline droplets changing to vapor inside the combustion chamber facilitates a higher compression ratio without incurring detonation. Squeezing the mixture harder during compression and allowing it to expand longer on the power stroke wrings additional power out of every ounce of gasoline.

http://www.automobilemag.com/feature...ion/index.html

Single point injection has no advantages over direct fuel injection at all. The Supercharger is on a completely separate circuit and the engine still receives all the benefits of supercharging with the additional benefits of direct injection.

[Crumpp]

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking.

The Allies did not have any direct injection engine technology to use.....

They could not make direct injection workable or practical using their fuel metering technology. Bosch's design, up until recently was the pinnacle of direct injection technology. It requires very high fuel pressures and the German system used a high pressure pump for each cylinder.

As already pointed out, post war, the turbine was supreme so why would any nation waste resources for a post war piston engine aircraft?????

[Crumpp]

Great Wartime article Viper. Thanks for posting that.

http://www.flightglobal.com/pdfarchi...0-%200569.html

http://www.flightglobal.com/pdfarchi...0-%200563.html

http://www.flightglobal.com/pdfarchi...0-%200562.html

An article definitely written to contain the public relations damage from intelligence on German fuel metering technology.

Rolls Royce's basic message is the German engines are not as efficient as they could be and only somewhat more efficient than the our engines.....

AND we can make a carburetor heat system that will overcome icing....