Magnetos of Bf109E-4/Trop

[[FtN|GT] Die Happy]

Originally Posted by angelangelv2

What's the point of shutting the JU door anyway?

well in former version you were able to "walk" inside the JU52, closing the door would prevent you from falling out
however the "walking" inJu52 also had some unforeseen consequences, and i am not talking about things like dropping a geballte ladung inside or firring a rifle grenade.
not to talk about of the huge amount of teamkills the pilot would have gotten...


so right now closing the door is just for the better looks

[Stray03]

Originally Posted by Commie

War Emergency Power, basically wringing as much power out of the engine as possible. Of course, doing so wasn't encouraged (hence 'Emergency') since it drastically reduced the service life of engines and made them more prone to failure.

It was common to put wire across the throttle at the point where it would go from normal power to absolute maximum. The pilot would have to push the throttle 'through the wire', as the saying goes. The broken wire would indicate to ground crews afterwards that the engine had been pushed to its limits and needed a much more thorough check for any problems.

Didn't some Aircraft also have a water/methanol mix for that?

[Von Mudra]

Yes, that they did. It's so nice to see such things represented in game

[Spencer the Great]

Originally Posted by Stray03

Didn't some Aircraft also have a water/methanol mix for that?

Some of the simpler designs let the throttle open a tad more, later on they incorporated water/methanol injection such as MW50. The Germans started using nitrous oxide to retain power at high altitudes for their interceptors. (MW50 worked better at low altitudes)

In the ever greater quest for more horsepower the opposing factions took different paths. The Germans, limited by the quality of their gasoline, were forced to increase the displacement of their existing engines, or design brand new ones for that matter to keep up with the horsepower race. (the Germans largely failed in this effort)

The Americans and English simply increased the octane of the fuel by using massive quantities of lead. The Allison V1710 is a perfect example of this. Originally designed to produce 1000 horsepower, by the end of the war they were rated for 2300 horsepower. They did not bore out the cylinders to increase displacement, they simply fueled it with higher octane gas and cranked up the boost levels accordingly. (This also applies to the British Merlin engine)

The Merlin in the spitfire was a 27 liter engine.
The P-38s P-39s etc used 28 liter engines.
The BF109 had a 36 liter engine.

36 liters-- that is a lot of motor for such a tiny airplane

[Stray03]

I thought lead was added to gasoline in order to be able to increase the compression ratio of the pistons, Thus increasing the efficiency of the engine.

Problem with gasoline engines are that since the fuel is sprayed in during the compression stage of the cycle, it can auto-ignite, which means it lights before it is supposed to, causing engine knocking.
2 ways around this:
decrease engine compression ratio which decreases power and efficiency
or
Add something to the gas which will make it less prone to auto ignition at said pressures/temps. Lead was the cheapest thing.

Diesel engines don't have that issue but are much heavier thus weren't too suitable in aircraft of that type.

[Spencer the Great]

Originally Posted by Stray03

I thought lead was added to gasoline in order to be able to increase the compression ratio of the pistons, Thus increasing the efficiency of the engine.

Close, but the engines in question were all supercharged. The compression ratios were quite low - around 6:1, with 7:1 at max. The pistons were flat topped to keep the ratio low. Power was increased by changing the gear ratio to the supercharger. In the beginning of the war, when octane was low, the supercharger overdrive ratio was low. As octane increased they were able to increase the supercharger gear ratio dramatically, producing dramatic increases in power.

My car has a compression ratio of 10.2 to 1. If I supercharged it without lowering the compression the motor would explode.





edit***

For what its worth, the BF109 actually used a hydraulic coupling instead of gears to drive its supercharger. This simplified the pilots work load, all he had to do was control the throttle. The propeller pitch was also handled automatically, props to the Germans!

What made the Merlin so good, especially in later versions was its two stage two speed supercharger. It was one of the great marvels of the war. It gave the Spitfire and Mustang an extra edge over the other guy, but it was a very complex piece of engineering with lots of tiny parts and gears. (it solved the problem of achieving maximum boost and horsepower at all altitudes , from the deck to 26,000 feet)

Finally the Americans used turbochargers on various planes, the advantage over geared superchargers was primarily in the area of simplicity and the "infinitely variable" nature of the boost developed. (did the same as the Merlin supercharger sans the the tiny parts and gears, although not without its own problems)

[Commie]

Originally Posted by Stray03

Didn't some Aircraft also have a water/methanol mix for that?

Yep, but that's engine boosting as opposed to just beating the shit out of the engine

Germans had the MW50 water/methanol mix for medium-low altitude work that could be used with the DB605 series engines (and the Fw190D-9's Jumo 213), but that was late '44 onwards with later models of the Bf109G.

The Bf109E that's in FH2 at the moment only received extra power boosting in the form of the GM-1 nitrous oxide system for a specialized high-altitude version, the Bf109E-7/Z. Not many of them were built as far as I know.

[Stray03]

Originally Posted by Spencer the Great

Close, but the engines in question were all supercharged. The compression ratios were quite low - around 6:1, with 7:1 at max. The pistons were flat topped to keep the ratio low. Power was increased by changing the gear ratio to the supercharger. In the beginning of the war, when octane was low, the supercharger overdrive ratio was low. As octane increased they were able to increase the supercharger gear ratio dramatically, producing dramatic increases in power.

My car has a compression ratio of 10.2 to 1. If I supercharged it without lowering the compression the motor would explode.

Excuse my ignorance when it comes to Superchargers since I don't know all that much about them. But they are designed to increase pressure of air entering the cylinders right?

When we consider compression ratios we are talking about the difference in the volume of air of the cylinders correct?

So Assuming you have a compression ratio of 10 you'd (in an Ideal cycle) be increasing the pressure from atmospheric pressure of 101.3kPa to a pressure of 2544.5kPa and the temperature from lets say 20 C to about 463C.

Lets say you Had a compression ratio of 8 now and you want to have the same effect your intake pressure would have to be 138kPa or 1.36 times atmospheric pressure. This increase of initial pressure would be supplied by a Supercharger right? thus giving you The performance Of a larger engine from a smaller one?

Now say we started with a 138kPa and kept the C ratio of 10.
this would increase pressure to 3466.4kPa a full 922kPa more.

So from this I'd have to assume that an 8:1 engine with a supercharger compressing air to 138kPa (that manages to keep the temperature of the air it is pressurizing at the same as the environment) will have the same autoIgnition Properties as a 10:1 engine pulling in air at atmospheric pressure at sea level.

Which is also why placing the same supercharger on a 10:1 may destroy
the engine.

So Adding a supercharger doesn't change the compression ratio of the engine but it does increase pressure levels which means you get (in this example) the same amount of Fuel and air molicules in an 8-1 engine running said supercharger as you would have in a stock 10:1.

Therefore more power per cycle. But still same issue with autoignition which is solved with higher octane gasoline which was at that time solved with lead.

In the beginning of the war, when octane was low, the supercharger overdrive ratio was low. As octane increased they were able to increase the supercharger gear ratio dramatically, producing dramatic increases in power.

What I said explains that too.

Here is something more official I guess
About.com: http://www.turborick.com/gsxr1127/gasoline.html
section 6.2 and 6.3

[Anlushac11]

The Allison V-1710 was a Vee configuration with 1,710 cubic inches.

The Compression ration was 6.65:1

This pic shows the block and the big round thing is the supercharger, the two holes on the end of the supercharger is the carburetor mounting pad.
http://airpower.callihan.cc/images/E...lisonV1710.jpg

To build a reverse rotation V-1710 for use in P-38's the crankshaft could be swapped and installed reversed with a different idler gear.

[Spencer the Great]

That is a lot to digest stray! I have an exam soon so I'll try and tackle that question afterwords. In general your understanding is quite good!

This is a cut away of a two stage two speed Merlin. The air comes in on the left hand side, from the bottom. It flows through the supercharger wheels, through the intercooler, (the big gray mass in the upper left) then it follows thought the manifold between the "V" and is distributed the cylinders. The exhaust exits through little stacks.

It had a smaller displacement than the Allison and the engine was physically smaller. The large supercharger system on the left hand side was considerably larger and more complex than the one on the Allison. The Allison V1710 was designed from day 1 to use a turbocharger in series with the mechanical supercharger. As a result engineers spent very little time perfecting the mechanical supercharger on the Allison. This is in marked contrast to the English and Germans who devoted large amounts of resources on their mechanical superchargers.

Only one fighter in the world was powered with a turbocharged Allison(s) during WWII, and that was the P-38 lightning. The large pipe work interfered with optimum aerodynamic shape and special alloys needed for the turbine limited production. The system to control the waste gate often froze and caused the engine to either over boost and explode, or not make enough power at all. (the P-47 had a turbo as did the US heavy bombers but they used radial engines)

The Allison was the most underrated of any of the V12s produced during WWII. Although it lacked high altitude performance when "straight piped" it served well in low level attack planes like the P-39 Airacobras sent to the Soviet Union.