Long bursts more effective than multiple short ones?

[Laurwin]

Fuel tanks could also ignite from multiple hits.

With bombers exploding from hits, this could happen from the bombload being ignited. Explosion would be spectacular... and dangerous.

Often happened vs nightfighters because of the angle of the Schräge Musik cannons.

In principle greybeard is about right, I think. There was an American training video made by Disney, to US Naval aviators in WW2. It's on youtube. And most importanltly it was narrated by the infamous John Thach. He is the tactical innovator behind the Thach Weave manouver.

Thach recommends in the video, to always aim for the frontal engine (vs an enemy fighter aircraft). Unless that is, you can confidently pop some bullets directly into the cockpit of the enemy.

The reasoning being, that once you have solid aiming point in the engine, first bullets, even if only a few of them, will hit the vulnerable engine. Any engine will lose performance, once damaged, I think.

Other bullets in the burst will sweep across the other vulnerable parts such as the cockpit. The only reliably effective cockpit armor vs heavy machine guns or cannons, is armor steel or titanium. Neither of which, exist to protect the pilot in the plexiglass canopy, out of which the pilot is observing the world around him.
Yes, the radial engine would act as sort of armor, blocking shots from the front, to the pilot. But engine might get knocked and lose power so it's not exactly a win-win scenario here...

Oftentimes there would be fuel stores just in the centerline fuselage, behind the cockpit. (such arrangement exist in me109 and fw190, also spitfires for the Allies)

Basically when you hit the engines with a good solid burst, you will have a chance of damaging any of the following three: engine, pilot, internal fuel tanks.

You can also damage the control surfaces more to rear, the tailplane, if it was a longer burst.

Although despite Thach's advice about aiming, it was also specifically very effective to aim for the wingroots of A6M zeroes, as they had vulnerable fuel stores there (of course every respectable IL-2 player knows this already!)

[Pursuivant]

Originally Posted by Laurwin

With bombers exploding from hits, this could happen from the bombload being ignited. Explosion would be spectacular... and dangerous.

Fuel-air explosions could also be spectacular, but that required AvGas vapor plus O2 rich air, plus a spark. To prevent this, aircraft fuel tanks are (and were) blanketed with CO2 - usually cooled engine exhaust.

To get a fuel tank to blow up, you need a strong primary explosion to vaporize and heat the fuel while exposing it to air, or you need prior damage which allows air to get into the system or fuel to leak from the tank and vaporize.

So, in some cases, a "long" burst might be more effective at setting a plane's fuel systems on fire since the first hits tear open the fuel tank, letting air in and splashing the fuel around to vaporize it, then subsequent hits provide the spark or explosive heat needed for the vaporized fuel to explode rather than burn.

[MaxGunz]

If you have leaked fuel inside the plane then a big rush of oxygen and a spark is all you need for a fire or an explosion. There's enough oxygen in those tanks to last a pilot for hours, not minutes.

Russians ducted cooled exhaust gases into the fuel tanks to not have oxygen right over the fuel. The US has at least one that put CO2 in the tank. But no one was filling the wings and fuselage with exhaust or CO2.

[MaxGunz]

I'd also like to know how except from dead six a long burst is supposed to hit the same part, especially when many spread-out guns are shooting?

Sure, you might keep it all 2 meters close but it's chance. Concentrate on the nose is not 'a part' that gets hit. It is many with some just 1 hit criticals, like carbuerettors, fuel lines, etc.

Most long bursts I've seen, over half the shots never hit. Get used to hosing, your choice of planes becomes limited.

[Pursuivant]

Originally Posted by MaxGunz

If you have leaked fuel inside the plane then a big rush of oxygen and a spark is all you need for a fire or an explosion.

True, but you'll notice in most cases O2 cylinders/globes were positioned well away from fuel tanks. I'm not saying that damage to an 02 cylinder and to a fuel tank couldn't set up a situation where you could get a big fuel explosion, but it was unlikely.

Typically, fuel explosions occurred when air got into a partially empty fuel tank, or when there was a leak in a fuel tank which was near an arcing electrical connector.

The latter case was a common problem with the B-24 Liberators or PB4Y Privateers where removable "Tokyo Tanks" in the bomb bay could leak, filling the bomb bay with AvGas vapor. Due to the number of electrical connections which also ran through the bomb bay, the fuel vapor sometimes ignited, and a number of B-24s were lost due to in-flight explosions.

Originally Posted by MaxGunz

Russians ducted cooled exhaust gases into the fuel tanks to not have oxygen right over the fuel. The US has at least one that put CO2 in the tank. But no one was filling the wings and fuselage with exhaust or CO2.

The cooled exhaust gas trick was used by most nations. It's fair to say that after about 1940 most Western combat aircraft would have some variant of the system.

A number of bombers had additional fuel-protection systems such as CO2 fire extinguishers which could send compressed CO2 into fuel tanks.