20mm cannon, best, worst, specs, comparison to LMG, HMG etc.

[Shortround6]

I would say that while secondary fragments (from the structure) can increase the damage radius it is a might iffy thing. Fuselage and wing skin are not going to provide much in the way of worthwhile fragments and even stringers, stiffeners and rivets are going to limited as to the damage they do. The further from the blast center the less velocity they will pick up and the less damage they will do.
A direct hit on a rib, frame or longeron may provide a good pattern of secondary projectiles but a hit just a few inches away may provide few, if any.
The effect of blast on a structure is very dependent on the size of the explosive charge and the size (volume) of the structure and of course, placement in the structure.

See this hand grenade: MK3A2 concussion offensive hand grenade

226-227 grams of TNT and in the open it's 'effective casualty radius' is 2 meters. This may be different form lethal radius. In a confined space (room or bunker) it changes and it may even change if placed against a wall. It has nearly 12 times the explosive of a 20mm mine shell and almost 3 times that of 30mm mine shell.
The 20mm mine shell was very good at making big holes in fuselage and wing skins and with later fuses that allowed it to get inside it was still very good at blowing areas of skin off of wings and fuselages of fighters. Bombers presented more of a problem because their larger void spaces dissipated the force of the explosion more and the pressure wave against the skin was less.

Shells with thicker walls and more/heavier primary fragments didn't have as good a "blast" radius or effect but their fragments went further with a better chance of cutting fuel, oil, hydraulic lines, wiring, control cables, etc. With both types of shells exact hit placement changed the results considerably. Hits in wing tips or bomber vertical fins weren't likely to be critical even if impressive. A hit in a radiator or oil cooler by either is going to guarantee the loss of the engine or plane and so on. And hit at mid wing on a fighter is going to be iffy with either. What is the likelihood of each of cutting the aileron controls, or landing gear hydraulics/electrics. etc. Changing impact point by even a few inches can drastically change outcome.
With any air force having fuse failure rates heading into double digits at times, the effect of a non-detonating projectile may want to be looked at.

 

[renrich]

Just a comment relating to the debate between the cannon shell people and the kinetic energy round people like in the 50 BMG. Today, I believe that some of the ammo for the CIWS in use by the USN and others are kinetic energy projectiles and also some of the ammo for the 30 mm gun in the A10.

 

[davebender]

Artillery shells and aircraft 20mm meant for aircraft use are probably best designed differently.

To some extent that is true but some things remain the same. It takes a certain amount of explosive filler to to destroy structural elements in an airframe or to blow a hole in a fuel tank too large to self-seal. It also takes a certain amount of explosive filler to destroy field fortifications such as concertina wire and bunkers.

As for anti-aircraft missiles, they have massive warheads. For instance:
95g. MG151/20 mine shell projectile weight.
9.4kg. Sidewinder missile warhead.

Almost 100 times as large as the 20mm projectile. With a warhead this large it becomes possible to disperse fragments that will cause serious damage over a considerable distance. You don't get that option with a 20mm shell. A 20mm projectile must hit the target. If you want damage beyond a 20mm hole in the aircraft skin then it must contain enough HE filler to rip aluminum sheet metal and damage airframe structural members.

 

[tyrodtom]

Kinectic energy rounds are for use against armor, heavy armor. They use heavy metal cores, depleted uranium in some.

The WW2 designers had to fulfill conflicting requirments. The shell that would work best against a IL-2 probably wouldn't do so good against a P-51, or a Yak. B-17's and B-24 needed their own . The Americans tried to do it all with one round, the .50 cal, but they weren't faced with the wide variety of targets presented to the Germans. The .50 cal was probably a fine round for strafing airfields, convoys full of soft skinned trucks, and trains, but it had to be useless against late war tanks.

 

[renrich]

I believe the CIWS rounds which are kinetic energy projectiles are depleted uranium and are to be used against cruise missles. Perhaps though I am wrong.

 

[Shortround6]

You don't get that option with a 20mm shell. A 20mm projectile must hit the target. If you want damage beyond a 20mm hole in the aircraft skin then it must contain enough HE filler to rip aluminum sheet metal and damage airframe structural members.

have you seen the video of one round from Glacier Girls 20mm cannon hitting a 55gal drum?
The 20mm Hispano had enough HE to make a sizable hole even if not quite as much HE as the 20mm MG 151. The British seemed to be convinced that the fragments from the 20mm Hispano shell body were effective for several feet from the explosion in cutting or puncturing fuel, oil, coolant, and hydraulic lines. They did shoot up an number of Blenheim bombers on a test range with a variety of their own and captured weapons.
The British also found that Hispano rounds, either solid shot or duds, hit with enough force to break spar mounting flanges and other structural members.

The Hispano was using one or two mechanisms of damaging an aircraft, the German mine shell was emphasizing another mechanism. How effective each one ones depended on the location of the hit. Neither one was the best in all situations. Neither one was the worst in all situations.

 

[Rivet]

I'd opt for a thick shell body in design consideration of an exploding projectile. I'd found that the thicker wall of the case caused a greater initial pressure rise due to containment than a thin wall.

This being said, I'll still keep my kit in the kinetic camp. I'd had the opportunity to heft a MK 108 that came out of a Me-163B that disintegrated over Ohrduf on April 29, 1945. You could lift two M-2 Brownings and change for the effort of lifting that one cannon. The initial weight of the weapon, amount of cartridges in number vs. weight, effect of recoil on point of aim....I believe I'll stick with Browning's stuff, thank you.

 

[davebender]

shell that would work best against a IL-2 probably wouldn't do so good against a P-51, or a Yak.

Aircraft wings cannot be armored. Hence HE is effective against all aerial targets.

 

[tyrodtom]

Aircraft wings cannot be armored. Hence HE is effective against all aerial targets.

I would think most pilots trying to shoot down a single engine plane would be mostly aiming at the part of the aircraft with most of the vital parts, pilot, engine, gas and oil tanks. Those were all armored to differing degrees on the IL-2, and a great deal more so than a P-51 or Yak. Hartman even talks about targeting the oil cooler from below, can't remember him targeting the wings on a IL-2, from behind a wing isn't a very prominent target. Though, the main spars probably wouldn't take many 20mm hits to fail, but hitting them wouldn't be easy.

 

[P-40K-5]

didn't the MG151/20 use a Minegeschloss round also?

 

[Shortround6]

A wing spar is a whole lot bigger than an oil cooler. the problem is getting the shells to the spar. The wing surface/skin is going to deflect/destabilize/detonate a fair amount of of 20mm HE rounds before they get to the spar. Wing may look like swiss cheese but no 20mm shell may have gone off in contact with the spar.

 

[davebender]

Hence the reason for a relatively large HE filler. A burst of 20mm mine shells which hit nothing but aircraft skin will still cause a lot of sheet metal damage.

 

[Shortround6]

Yes it will but that is often superficial damage. Early 20mm mine shells ( and Hispano shells) would explode on the fuselage skin making some rather impressive holes but not damaging much of the structure or anything inside, The victim maybe out of the fight that day but was often repairable.
Both sides developed fuses that offered a small amount of delay. Here is were things get difficult. How much delay? we are talking a few thousands of a second. What allows the shell to penetrate 2-3 feet into a fuselage might allow it it pass completely through a wing. Or if timed for 2-3 feet of penetration at 350yds it may pass through the fuselage of a small plane at 150yds when the shell is moving hundreds of feet per second faster. What angle of impact is the fuse designed for? a 90 impact and a 30 degree impact will slow the shell somewhat differently, the 30 degree impact means the shell has to move at least twice the metal. Shallower impacts get much trickier. The delay must be a compromise that works better than a surface explosion but will seldom be ideal in many circumstances.

Steel fragments traveling at thousands of feet per second can do a fair job of ripping up thin aluminium sheet too.

 

[P-40K-5]

wouldn't mine shells be more effective hitting the area around the engine cockpit?

 

[tyrodtom]

In the IL-2 case the aft fuselage, and most of the wing is wood, and a lot of aircraft on the Russian side used a lot of wood.

No one shell, or fuse setting is going to work efficently on everything that flys.

 

[Shortround6]

wouldn't mine shells be more effective hitting the area around the engine cockpit?

On which plane? They may burst on the surface of the IL-2 and not penetrate the armor.

On more normal planes they would be more effective but not guaranteed.

They may burst on/in the cowling (generally heavier metal than rear fuselages or outer wing skins) of more normal planes but still inches away form the actual engine. Cockpits are also iffy. While certainly more effective than hits in the extremity of the plane a hit in the cockpit of a 109 or Spitfire maybe more effective that a hit in the cockpit of a P-47 which may kill the pilot or be several feet away from him, It may damage vital parts or controls or it may explode in sort of a void space with nothing important nearby. German Mine shells had difficulty damaging things on the other side of armor plate. That doesn't mean they didn't make a mess of radios, IFF gear, oxygen equipment and other stuff behind the cockpit but not behind armor.

 

[P-40K-5]

well are we talking a single shell hit here? cause it would seem that more then one would hit any givin area. no?

 

[icepac]

1. Hispano 20mm (typhoon, tempest, spit V and later....etc)

2. Shvak 20mm (la5, la7....etc)

3. type 99-2 (J2m3, N1K2J...etc)

3. HO5 (ki84...other japanese planes)

4. MG151 (me109, fw190, me110....etc)

 

[davebender]

Most pilots and aerial gunners weren't good enough to hit a specific part of moving aircraft. So they aim for center mass and hope some of the rounds hit home. Aircraft wings offer the greatest surface area so by the law of averages that's where many of the rounds will hit.

The accuracy problem is much worse when firing wing mounted weapons. Convergence and wing flexing practically guarantee the rounds will impact over a large area.

 

[P-40K-5]

really? well guess all them 109 vs B-17 gun footage film when they were accurately hitting the engines were just lucky shots?
I doubt very much they would concentrate on hitting a B-17's upper/middle fuse. goes for any fighter attacking heavy bombers.