Why so few planes that fired thorugh the propeller hub?

[Ivan1GFP]

Hello GregP,

Perhaps I didn't explain the concept of Point Blank Range very well, but I believe you are not using the term correctly. The problem is that there is common usage and the technically correct meaning.

Ivan, I believe point blank means the bul;let will hit where it is aimed exactly. So a point blank range of 5800 yards doesn't say anything about rise and fall, it says the bullet will hit the belt at 500 yards if aimed exactly there.

PBR does take into account the maximum height of the bullet's trajectory:

PBR is the maximum range at which a shooter can aim directly at his target without adjusting the elevation.
PBR is a function of the gun / ammunition and the target size.
Take for an example a common .30-06 rifle.

If my target is a basketball, my bullet cannot rise or fall more than about 5 inches or so if I aim at the center. To get the maximum PBR, I adjust the zero on the rifle so that the maximum height of the bullet is never more than 5 inches. At some point, the drop of the bullet will be 5 inches from my line of sight. THAT will be at the maximum PBR. As a guess, I would figure that to be around 250 yards or so.

If my target is a person, the US army figured out with the M1903 rifle that the maximum PBR was 550 yards (probably with around a 300-something yard zero). The bullet would not go higher than the target's head or drop below the target's feet within 550 yards.

Aeroplanes are much bigger than people, so I am assuming the distance to be considerably more than 550 yards. I didn't try to figure out how far, but my GUESS was around 750 yards or so. Perhaps I guessed wrong?

To find the bullet rise between the gun muzzle and the impact point at 500 yards, you have to go to the ballistics characteristics of the round with the length of the barrel or, more correctly, the distance between the chamber and the gas port known. However, if you are interested in hits, the rise doesn't matter if you can hit the target ... unless you are shooting under something. That's rare in combat.

Actually barrel length, chamber length, gas port locations and internal ballistics considerations are pretty much irrelevant. All that is important is the Muzzle Velocity and the flight characteristics typically represented by a Ballistic Coefficient and ballistic model. Most people use the G1 model which is based on a 1 inch diameter projectile that looks pretty much like we expect a "bullet" to look. This was the Krupp standard bullet. That is why you get things like ballistics coefficients that change with velocity range: because the modern rifle bullet really doesn't follow that kind of flight path. Interestingly enough, a typical aircraft cannon shell DOES bear a pretty good resemblance to a Krupp standard bullet. The modern boat tailed spitzer bullet is better represented by the G7 model.

As for the differening ballistic characteristic of armament in fighters, if you shoot anywhere NEAR the point blank range, it doesn't matter. If you shoot closer or farther away by a significant amount, it does. That;s why the Zero allowed the pilot to select the MG, the cannon, or both ... to account for shooting at bombers from a distance. He could turn off the MG and just use the cannon.

You are assigning a tactical reason to the armament configuration of the A6M. I have no knowledge of why this was done. I do know that the FW 190 series had guns selectable as well and there were less ballistics differences between the cannon and MG. (This ballistics similarity is the point I have been arguing all along.) I have always thought that the gun selection and trigger on the A6M was much less than optimal. The throttle is just not the right place to put the trigger IMO.

Regards.
- Ivan.

 

[Greyman]

Aeroplanes are much bigger than people, so I am assuming the distance to be considerably more than 550 yards. I didn't try to figure out how far, but my GUESS was around 750 yards or so. Perhaps I guessed wrong?

The Brits gave 600 yards in their instruction during the war (.303 gunnery).

 

[Ivan1GFP]

The Brits gave 600 yards in their instruction during the war (.303 gunnery).

Velocity of the .303 is also a bit lower: 2450 fps versus 2600 for the 7.92 and 2800 for the US .30 Cal.
Not sure it makes much of a difference but it is a difference. Besides, Instructions tell you what to do, they don't necessarily tell you what the weapon is capable of.

- Ivan.

 

[Greyman]

In terms of bullet drop the .30 generally seems to travel about 50 extra yards to equal the same drop distance of the .303

 

[swampyankee]

I remember reading somewhere (this means I've no clue as to a citation) that the US 0.50 in MG bullet was modified to increase dispersion, as they felt that increased dispersion would make it a more effective anti-personnel weapon. Was the ammunition used in aircraft installations the same as that used in ground installations?

 

[fastmongrel]

I remember reading somewhere (this means I've no clue as to a citation) that the US 0.50 in MG bullet was modified to increase dispersion, as they felt that increased dispersion would make it a more effective anti-personnel weapon. Was the ammunition used in aircraft installations the same as that used in ground installations?

I know some MG tripods were built so that the gun could move automatically side to side during firing to increase the width of the stream of fire but never heard of bullets being modified.

 

[Shortround6]

Quality control of Military ammunition ( and especially war time ammunition) is NOT the same as commercial ammo and commercial ammo has gotten a lot better from the 1930s to the last 2-3 decades. There were minimum standards however. Ammo might have to group 3-4 minutes of angle, fired from heavy test barrels in heavy receivers mounted on concrete or heavy timber benches. They were testing ammo, not guns. Some batches were better than others, sometimes much better. My father and his friends had one lot number of early 1950s 30-06 AP that would group better than 2 min of angle out of any of 5 different accurized M-1s. This does NOT mean that the lots produced before and after it were "designed" to be less accurate. BTW this group of shooters had a number of members who worked for Winchester at the time, a few of which shot for the Winchester team and had access or knew men who worked in the under ground test tunnel.

As far as shooting at airplanes goes, it rather depends on the airplane, Most single engine fighters are not more than 6 feet tall once the landing gear is retracted, tail fins and P-47s excepted Bombers on the other hand???

Point blank range against stationary "tanks" is roughly the muzzle velocity + 10%. smaller or larger tanks change the distance and type of projectile will affect distance. WW II Heat rounds with poorer than normal ballistic co-efficient are a bit shorter while APDS. and APDSFS are quite a bit longer.

Once again, the American .50, the Russian 12.7mm and the German 15mm mg 151/15 were in a class of their own and the mg 151/15 was used to a large (thousands) extent. The 20mm Hispano comes close and just about every common WW II aircraft gun is worse, some much worse.

I rather doubt the Japanese were using the 20mm guns in the Zero for long range fire, at least the early ones. It had about the worst MV of ANY WW II 20mm gun. It would need the best estimate of range and speed, the most elevation of the gun and the greatest lead on a moving target. It also had the 60 round drums which means they didn't get too many "chances to guess" before they were out of ammo. Not to say a few pilots didn't try but it doesn't seem like a sound tactical practice.

 

[Ivan1GFP]

Quality control of Military ammunition ( and especially war time ammunition) is NOT the same as commercial ammo and commercial ammo has gotten a lot better from the 1930s to the last 2-3 decades. There were minimum standards however. Ammo might have to group 3-4 minutes of angle, fired from heavy test barrels in heavy receivers mounted on concrete or heavy timber benches. They were testing ammo, not guns. Some batches were better than others, sometimes much better. My father and his friends had one lot number of early 1950s 30-06 AP that would group better than 2 min of angle out of any of 5 different accurized M-1s. This does NOT mean that the lots produced before and after it were "designed" to be less accurate. BTW this group of shooters had a number of members who worked for Winchester at the time, a few of which shot for the Winchester team and had access or knew men who worked in the under ground test tunnel.

I have heard that AP ammunition steel cores would wreck the barrel of a rifle. This was a before and after test on a M1 Garand that was about to be re barreled anyway. How did these rifles fare?
3-4 MOA was NOT being met with 7.62 NATO ammunition for quite some time even with the test rifles. Typical accuracy out of the Army's new M14 rifle was around 6 MOA for a while with service ammunition and special lots of ammunition had to be made up for rifle acceptance testing.

As far as shooting at airplanes goes, it rather depends on the airplane, Most single engine fighters are not more than 6 feet tall once the landing gear is retracted, tail fins and P-47s excepted Bombers on the other hand???

Height wise I agree, but at the many different angles you can approach a typical fighter, on the average, it is a whole lot bigger than a 6 foot diameter circle.

Point blank range against stationary "tanks" is roughly the muzzle velocity + 10%. smaller or larger tanks change the distance and type of projectile will affect distance. WW II Heat rounds with poorer than normal ballistic co-efficient are a bit shorter while APDS. and APDSFS are quite a bit longer.

How many and which WWII tank guns actually used HEAT, APDS or APDSFS ammunition????

- Ivan.

 

[Aozora]

How many and which WWII tank guns actually used HEAT, APDS or APDSFS ammunition????

- Ivan.

AFAIK no WW 2 tank gun used HEAT or APDSFS but a few, such as the 6 and 17 pdrs, used APDS and APCBC Great Britain's Gun Penetration Tables - World War II Vehicles, Tanks, and Airplanes

 

[Juha]

AFAIK no WW 2 tank gun used HEAT or APDSFS but a few, such as the 6 and 17 pdrs, used APDS and APCBC Great Britain's Gun Penetration Tables - World War II Vehicles, Tanks, and Airplanes

At least GB, Germany, Soviet Union and Finland had HEAT tank ammo.

 

[Aozora]

At least GB, Germany, Soviet Union and Finland had HEAT tank ammo.

Doh! For some reason I was thinking of HESH. Yes there were primitive HEAT rounds used during WW2, but HEAT was more effective when used in unrotated projectiles such as Panzerfausts, Panzerschrecks and PIATs and the like.

Waaay OT - Come to think about it didn't the Petard Spigot mortar used on some of the Churchill AVRE's use HESH?

 

[fastmongrel]

Waaay OT - Come to think about it didn't the Petard Spigot mortar used on some of the Churchill AVRE's use HESH?

Not during the war it was simply a blast weapon and known as the "Flying Dustbin". HESH didnt get into service till after the war, the later 165mm AVRE gun used HESH rounds.

 

[Ivan1GFP]

At least GB, Germany, Soviet Union and Finland had HEAT tank ammo.

Can you comment on which guns had them and when? I had only heard of APDS used in a 6 pounder and 17 pounder.

- Ivan.

 

[Juha]

Hello Ivan
GB: 95mm
Germany: at least 75mm round, others for field artillery and A/T units at least
Soviet Union: at least 76,2mm
Finland: at least 114mm, in fact GB 4.5" field howitzer round modied to take German 105mm HEAT round, used in BT-42. see e.g. BT-42 - Wikipedia, the free encyclopedia

Juha

Forgot the time, Germans were the first ones, introduced the 75mm HEAT round mid-1940 just after the Battle of France.

 

[silence]

Forgot the time, Germans were the first ones, introduced the 75mm HEAT round mid-1940 just after the Battle of France.

Didn't they bring it in to make the short-barrel Pz MkIV more effective in tank-vs-tank combat?

 

[fastmongrel]

The Italians used Effeto Pronto shells which I think were HEAT but I cant read Italian

High Explosive Anti-Tank - Wikipedia

 

[Rufus123]

I am obviously a super novice on the topic of aircraft but I find the subject interesting and have wonder why things are the way they are hence my strange questions.

One of the reasons I was curious over firing through the hub and it sounding like a good idea was filling a void at all ranges.

I have thought that 3 cannon with one in the hub might be better than 4 in the wings for this reason. At very close range there could be a gap in the shell strikes if the pilot did a perfect job of aiming. If the aim was slightly off to the right or left the wing gun would strike where to pilot was trying to aim. I do realize that the individual hits will be spread out because both aircraft are moving. I have wondered if when using three cannon if the wing guns should be parallel rather than converge creating a wider damage zone at all ranges of fire.

 

[Juha]

Didn't they bring it in to make the short-barrel Pz MkIV more effective in tank-vs-tank combat?

Originally yes, and of course also the early StuG IIIs, but later also KwK 40, the long barrel 75mm gun of later PzKpfw IVs and the 88mm L/56 of Tiger got HEAT rounds to be used on longer ranges where they had better penetration power than traditional APCBC shells, at least in theory, but how common was their use, I cannot recall.

Juha

 

[douvie]

In the discussion between whether "centre fire (hub)" was better than "wing platform" configuration, I have read in several books and mags, that most German Ace pilots believed that the "wing platform" configurations were more effective for the following reasons:

1). There was more "lead" thrown at the target with a wing platform arrangement.
2). It was more difficult to bring the weapons to bare with the hub arrangement, especially in dog fight situations.

Another thing not mentioned in the discussions so far, is that a relative number of Hurricanes and Spitfires did have 2 40mm wing-mounted cannons in addition to 6 machine guns on the Hurricane and the 4 machine guns on the Spitfires.

Also, I'll get the quote if necessary, many German pilots complained that if they fired too long the 30mm cannon would cause them to lose airspeed. RAF pilots had a similar experience if they fired the 40mm cannons too long.

I've got the info I just need to get it scanned in.

 

[tyrodtom]

What would the German aces know about wing platform armament, except from being on the receiving end of it ?

They had no fighters with wing armament alone, all were centerline armed, some with added wing guns.

Some FW190 had fuselage guns, wing root cannons, and cannons further out on the wings, but the majority of it's firepower would be considered centerline.