[Azimech]

Originally Posted by Sternjaeger

double ignition gives an overall better burn performance, but it's more relevant on small engines than on large bore ones. A 100RPM drop on a 1650HP engine is negligible compared to the same drop on a 150HP. Besides don't give credit to stuff just because you read it on the internet dude, there are several inaccuracies in that "report", which by the way is on the detonation issue..
In a high performance military aeroplane redundancy has priority, especially considering the huge amount of power available.

Why don't you point out exactly which inaccuracies you've seen in that report?

it's probably because you don't know how to read them. And that's also why many planes now have backup generators.

Backup generator, APU's etc... not much room to put them in a fighter back then. I know of multi-engined planes having multiple generators.

Why don't you send me an electric schematic of an aircraft of that period with the request to explain it to you? I haven't learned modern high-voltage AC systems but that old stuff is pretty transparent.

...so how can they freeze? And even if they did, batteries are not used during flight, it's all fed through the generator. Another thing, they're not continuously charged since they could overcharge. The circuit overload is controlled by means of breakers that... hang on a minute, have a read for yourself: this is the P-51 Pilot's manual, not some random guy's dissertation on detonation
P-51 Mustang Pilot's Manual

browse words like "battery" and read about how the electrical circuit works.. also read the engine turn off procedure and see how you want to switch the plane off. Magnetos go OFF.

First of all, of course you switch mags off, but the sequence differs per engine or situation. I never suggested leaving the plane with mags still on.

I read nothing new in that P51 manual. Very standard tech for that period. I hoped to find something new but that small portion about the electrical system is not interesting. The only thing I like is the automatic manifold pressure regulator, That means in the future P51 drivers in IL2 or SOW will have less risk of wrecking their virtual engine. Maybe the Rolls Royce Merlins have it as well...

Overcharging happens when a voltage regulator fails, not before. A voltage regulator back then was an electromechanical device which dynamically relayed overvoltage into one or more resistors, changing the power into heat. Now i've seen a lot of those old things broken and even nowadays the electronic versions often break before the alternator itself does. Usually those old flight systems operated at 14V or 28V while the battery provided 12V or 24V. The extra 2V or 4V was, and is still used, to charge the battery. A battery won't charge to it's full capacity if input voltage is the same as battery rated voltage.
Now if the voltage regulator fails, you might wreck your battery very soon because electrolysis increases in an enormous rate, producing a lot of heat. But, the battery is a buffer, it usually keeps the increase in voltage within around 50% but it's capacity starts to drop rapidly. Some batteries can burst. If a battery bursts or when it cooks dry, it's capaciting effect stops and the peak voltage can grow with 200% or even 400%! I've seen it happen. One guy touched the lead of a running alternator which normally produced 6 volts, he got a jolt and jumped in the air. I've also seen a very hot and deformed battery which got us all nervous, the alternator provided 18 volts instead of 14 regardless if the mechanical voltage regulator was connected or not. I had to pick four regulators off the shelf, the first three were broken.

That's what those switches are for, Battery on/off is for switching power when you park or want to start, generator off for the safety of your electrical system. The generator provides the power to the plane's systems when running enough RPM, the battery is the buffer which compensates for peaks & jolts which cannot be compensated for by a failing voltage regulator, and heavy undervoltage situations. These can distort the functions or be harmful or even fatal to delicate systems like radio, navigation, instruments or radar.

Remember that generators provide DC and they start to provide a meaningful voltage at higher RPM's than the later DC rectified alternators. The fact that the P51's generator only starts at 1500 RPM while a modern alternator does that at 850, is the perfect proof. It also means that an engine that runs too slow while a lot of electrical systems are running can create a system's wide voltage drop, possibly more than the 2V or 4V, which is more than the margin the electronic equipment was designed for. The battery compensates for those moments, adding up where the generator fails to provide.
Another problem which generators have is the fact they can be used as an electric motor, with the battery providing it's power. A problem alternators don't have. This was the time before the invention of the high-power diode. The voltage regulator had a built-in function to disconnect the generator from the system when generator voltage output dropped below that of the battery.

again, it's all down to the plane. See what a Pilatus Porter pilot thinks of generator failures

I think ANY pilot would get nervous if his generator fails