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

[Kryten]

dont get too hung up on the notion of mine shells being super shells because of the name, the actual amount of explosive you can fit in 20mm round is not a great deal and the difference between the he and mine shells is not much, put 20g of rdx on a car bonnet and its more likely to leave a big dent than a hole, fragmentation is everything with cannon fire, look at the modern HE rounds developed for AFV's for instance!

 

[tyrodtom]

You've got to do more than just hit the surface area of the wing to destroy a aircraft, hit a main spar, wing tank, if any are there.

Let's face it most pilots were probably happy if they got hit's anywhere, but some were good enough to aim and hit specific targets. The biggest targets in any aircraft is crew, engine/s, and fuel. In most fighters all three was in the fuselage, in bombers it was different. Plus in bombers you had the load as a big target too. I wonder if that's why a lot of Luftwaffe pilots targeted engines ( not a small target on any 4 engine bomber ) If you were targeting engines you were also putting rounds near the fuel tanks, and not putting rounds near the bombs. I think maybe they felt if they set off the bombs, they would likely die too.

 

[P-40K-5]

Its was pointless to target the mid-fuse section on a -17. rounds would likely not bring it down. as opposed to hitting the engines/wings/tail.
two main areas of attack on a -17 would be head-on, and from behind. with, sad to say, the tailgunner belly turret gunner being targets.
head-on obviousely being the flight crew.

now as far as fearing the bombs would explode, perhaps, but on a few occasions the did experiment with dropping 250kg bombs into the middle
of a -17 formation from 200m above or so. It was very sucsessful, but abandoned. the weight penalty vs manouvering wasn't worth it to the pilots.

 

[davebender]

B-17 bombers are large targets and they cruised at about 180mph when loaded. Very different from trying to hit a maneuvering Spitfire traveling at 350+ mph. A job tailor made for the very powerful but low velocity 3cm Mk108 cannon.

 

[P-40K-5]

the Mk108 is powerful thats for sure. heres some footage of a single round hitting a spitfire wing.
now imagine two more hits!

View: https://www.youtube.com/watch?v=nPWlYhfhLrI

 

[pinsog]

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.

We have all seen the famous, slow motion footage from a German fighters gun camera, where he is pumping rounds into the B17 from directly behind, point blank range. Obviously the tail gunner and ball turret gunner are out of action. He is simply planted on the B17's tail pumping rounds into the 2 port side engines, or at least attempting to. Even from that range, with no one shooting back at him, a large portion of his cannon shells go under the left wing missing the B17 completely. Several go into the engines, and as I recall they both start smoking, but you could have hit the German from the tail gunner position with a pellet gun, and yet a good many of the cannon shells miss the left wing/engine area.

Surely someone here can find and post that gun camera footage I'm referring to. I'm too computer illiterate to do it myself.

 

[P-40K-5]

don't have that, but I do have this one:


View: https://www.youtube.com/watch?v=ROjPFv4MpPM

this is with the MG151/20 btw.

 

[Rivet]

I thought of the footage of the rear attack when considering this thread , Pinsog. As poor a showing of accurate delivery as the footage of P-40K-5's is good. I'd wager the Me-109 pilot attacking was using his fuselage armament.

In conversation with Walter Horten and Paul Opitz at the Eight Airforce museum in Savannah, Ga. in 1998 it was mentioned by them that it was the waist gunners whose field of fire they wished to avoid.

 

[davparlr]

don't have that, but I do have this one:

very impressive video. I could not tell if the B-17 was a G model or before. This does show the deadly danger to both attacked and attacker of head on attacks. Against the G the fighter would be facing four or five .50s from the attacked plane with a very little angular rate. This would be a high risk attack to both sides. I suspect these B-17s were earlier models.

 

[P-40K-5]

not 100% sure, but I think there were some muzzle flashes from the nose of one oth the B-17s.
I have some more videos. I'll post it up in a little while. thanks.

 

[P-40K-5]

heres some more. again, the cannon is a MG151/20. not sure what kind of shell rounds were used I think the twin engine plane at the 1:15 mark is a JU88:


View: https://www.youtube.com/watch?v=DMKJTxKeAI4

 

[Jabberwocky]

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.

For most pilots, yes, a lot of it would of been luck. There were a lot of other factors. Ignoring pilot skill, things affecting the likelihood of hitting a target include the aircraft they were flying and its armament, the aspect and speed of the target, the altitude they were operating at, the range they opened and closed fire, the relative angle and rate of closure.

The gun camera footage kept by Luftwaffe operational research groups was primarily that of successful attacks.

Working off the US assessment of German operational gun cam records, at 100 m, the likelyhood of a German fighter observably hitting a B-24/B-17 on any single pass (front, sides, rear) was about 40%. Rear attacks were notably more likely to result in hits, but even then, single shot hit probability of hitting a heavy bomber target was just 25%.

Of these close in attacks, around one third were considered "good" (ie concentrated on target, within the limits of typical dispersion) while the other two thirds wandered over the target.

At 100 m, a rear aimed pass would typically result in 18-20 rounds observed as hitting the target - typically these are 20/30 mm HE/API hits, as pure AP and smaller rounds (7.9 and 13 mm) were much harder to observe. A nose-on pass would typically put 5 20/30 mm observable rounds on target at 100 m.

The Luftwaffe estimated that it usually required 18 20mm mine rounds or 4 30 mm mine rounds to cripple or kill a US heavy bomber.

At a more usual firing distance of 500 m, the likelyhood of a fighter hitting the target on any single pass drops well below 10%. Notably though, the number of observed rounds hitting drops significantly, around 8 per pass from the rear and just two per pass from the front.

 

[P-40K-5]

awesome info, thanks!

 

[davebender]

I don't think it's a matter of hitting a bomber on a single pass but inflicting enough damage to destroy it. During the first half of the war it was common for bombers to be attacked multiple times before damage was enough to cripple the aircraft. Greater fighter aircraft firepower is the solution to this problem.

 

[P-40K-5]

yep. greater firepower. like the 2 x Mk108 'Kannonboot' under the wings the nose Mk108. or the 2 x rocket tubes. on a -109. I wonder how effective those
rockets actually were..

 

[davebender]

It's my understanding all WWII era aircraft rockets were inaccurate except for the late war German folding fin R4/M.

 

[P-40K-5]

It's my understanding all WWII era aircraft rockets were inaccurate except for the late war German folding fin R4/M.

sorry, I meant if it actually hit, or exploded very close to a B-17.

 

[johnbr]

I read ed one hit the bombs of a B17 and the explosion took out 3 other B17's.

 

[davebender]

The 21cm Werfer-Granate 21 artillery rocket had a 90 lb warhead. That's 4 1/2 times the size of a modern day Sidewinder Missile warhead. A tank cannot withstand that sort of firepower. An aluminum aircraft would likely become confetti.

 

[Shortround6]

you had two problems with those old big rockets. one was accuracy, best considered dismal. The second was fusing. Since the chance of a direct hit was so low the common method (no proximity fuse) was a time fuse. The method of employment was to fire a number of rockets from a distance so they would explode in the bomber formation and cause the formation to break up so the individual bombers were be easier targets for the guns of the fighters. Fire enough of them and you will get a hit. Heck, you can roll 7s at craps a number of times in a row but that is not the way the smart money bets