Soviet fighters gun convergence (harmonization)

[greybeard]

Hi all!

I was unable to find any value neither on the Internet nor on books I bought so far. The only hint is a practical range of fire on the La-5 flight manual, indicated as from 50 to 500 m, which lets figure some intermediate convergence (275 m?)... Too bad!

I wonder if someone has reliable info; also, I put in the object both "philosophies", because would be interesting too knowing if Soviets simply converged to a point or tried to control bullets spread to get higher hit probability along the longest possible path of bullets trajectory.

Thanks for any help,
GB

 

[Shortround6]

We may be having a bit of language problem here.

Most times "convergence" means at what point the bullets/shells will meet/cross paths in the horizontal plane. as in the lower diagram of this chart.

It might mean at what point the rounds cross the line of sight, as in the upper diagram but that meaning is much less common.
For the P-38 you have this diagram

at 350-400 yds the bullet paths have 'converged" vertically but since they only started out about 7 in apart it has no practical significance.

For most fighters with fuselage mounted guns I don't think it makes much difference if like guns are set to converge or not (are set parallel). Unlike guns (different calibers) do need to be set up for a common impact point in regards to the line of sight due to trajectory.

LA-5 with two cowl mounted 20mm guns might be set up either way horizontally and given the closeness of the guns to the line of sight the practical difference in any set up is going to be minimal.

 

[pbehn]

From the little I have read I believe soviet pilots and or units had quite a lot of scope to change things as they liked.

 

[greybeard]

Thanks for replies.

I agree that, given the general layout of Soviet fighter guns on the deck, horizontal convergence could be quite conceivably "infinite" (that's to say they were aimed parallel). Nevertheless, I guess that a vertical convergence (or, like for the P-38, boresighting) had to exist, otherwise how ground personnel should have performed some kind of weapons calibration? None of these documents survived the war?

 

[Shortround6]

Most guns are going to be set up with elevation to bring the path of the projectiles up to the line of sight. It is a question of how soon this happens as this affects how high above the the line of sight the projectiles will get and how far out it will be before they come back down through the line of sight. Unless you have a really crappy muzzle velocity you will be able to keep the rounds on a fighter fuselage sized target out to 500-600yds without much trouble. either a foot or two above or below the the line of sight.
However making the guns parallel to the line of sight doesn't work. ALL projectiles will fall 16 ft in the first second of flight. So aiming the guns upwards slightly can give a very useful increase in range without affecting the practical area of impact.
At 500-600yds the time of flight becomes more important than the actual trajectory.

The Russian 12.7mm is probably very close to the US .50cal in trajectory. The Russian 20mm is not quite as good as the Hispano. Good velocity but lousy shape on the projectile, at a few hundred yds it probably makes little difference but at 400yds and up?
But that starts getting into quality of gun sights, pilot training, range estimation, etc. making as much or more difference than the ballistics of the projectile.

 

[tomo pauk]

...
The Russian 12.7mm is probably very close to the US .50cal in trajectory. The Russian 20mm is not quite as good as the Hispano. Good velocity but lousy shape on the projectile, at a few hundred yds it probably makes little difference but at 400yds and up?
But that starts getting into quality of gun sights, pilot training, range estimation, etc. making as much or more difference than the ballistics of the projectile.

MV of the Shvak was some 10-12% lower than of the Hispano, coupled with shell that was 2/3rds of the weight it will not excell ballaistically as it was with the Hispano. Similar was the thing with the MG 151/20.
But indeed, it the disadvantages will show up at far greater distances than it is prudent for the pilot to shoot at it's aerial target.

 

[CharlesBronson]

The gun convergence depends many times in the tastes of each pilot, the figures you might find on internet are merely an average.