Sabot-ed FLAK shells

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stg 44
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Sabot-ed FLAK shells

#1

Post by stg 44 » 06 Dec 2016, 19:07

https://books.google.com/books?id=6-UDD ... el&f=false
Germany experimented with sabot shells for FLAK, a 70mm subcaliber projectile for the 88mm gun and a 88mm subcaliber projectile for the 105mm gun (among other projects), but never really seemed to both to try and put them into production. What if they had managed to get them into production in 1942 to improve accuracy and range? Late in the war the Brits managed to find a rather complex way to have a sabot effect by relining a 113mm gun down to their 94mm projectile on a 113m cartridge without excessive barrel wear, but that took a lot longer to make operational in 1944.
Would this 'buff' have made the late war 88mm and 105mm guns still viable against the higher flying US bombers and made them more accurate against British night bombing?

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Re: Sabot-ed FLAK shells

#2

Post by maltesefalcon » 07 Dec 2016, 05:58

Saboted ordinance makes sense for kinetic weapons like anti armour shells. The reduced overall weight and streamlined projectile allow a flatter trajectory, increased velocity and heavier penetration.

Flak projectiles are high explosive fragmentation weapons. The increase in range and velocity would be more than offset by the reduced payload. Not only that, with unguided shells, they would only be incrementally more accurate.

So not really a benefit IMHO.


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Re: Sabot-ed FLAK shells

#3

Post by thaddeus_c » 08 Dec 2016, 03:07

how much is payload really being reduced if an 88mm shell is used in 105mm gun? my understanding was they were switching to 128mm guns not for larger payload but rather increased range?

still think the suggestion posted on this forum several times for subcaliber shells with tracer rounds would have been most effective (feasible) scenario for Germany.

would like to see estimate on declining accuracy of bomb raids for every 5,000 ft. higher?

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Re: Sabot-ed FLAK shells

#4

Post by maltesefalcon » 08 Dec 2016, 03:25

Lets assume they sabot the 105mm to the standard 88 x571mm shell.
A Flak 105mm fires a 105 x 767mm shell.

So a 105 has a shell volume 1.89 times larger, with comensurate payload.

To answer the question above about payload reduction the answer would have to be quite a lot frankly.

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Re: Sabot-ed FLAK shells

#5

Post by T. A. Gardner » 08 Dec 2016, 03:35

The big problem for the Germans by the beginning of 1944 with flak isn't the rounds, its the fire controls. Their radar has the snot being jammed out of it. If they can't optically spot the target then they're using blind fire and box barrages. The hit rate skyrockets to about 1 in 5 to 10,000 rounds. What they needed most was a way to accurately range on a target. That, they no longer had in service.

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Re: Sabot-ed FLAK shells

#6

Post by Sheldrake » 08 Dec 2016, 10:17

T. A. Gardner wrote:The big problem for the Germans by the beginning of 1944 with flak isn't the rounds, its the fire controls. Their radar has the snot being jammed out of it. If they can't optically spot the target then they're using blind fire and box barrages. The hit rate skyrockets to about 1 in 5 to 10,000 rounds. What they needed most was a way to accurately range on a target. That, they no longer had in service.
1. The long time of flight mitigates against accuracy against aircraft which change course every 30 secs except on the bomb run itself.

2. Is it more difficult and expensive to manufacture a sabot round?

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Re: Sabot-ed FLAK shells

#7

Post by Aber » 08 Dec 2016, 11:47

Sheldrake wrote:
1. The long time of flight mitigates against accuracy against aircraft which change course every 30 secs except on the bomb run itself.

2. Is it more difficult and expensive to manufacture a sabot round?
And helmets on, for all those on the ground around the battery. IIRC Horrocks was a victim of friendly anti-aircraft fire in North Africa.

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Re: Sabot-ed FLAK shells

#8

Post by stg 44 » 08 Dec 2016, 15:05

Aber wrote:
Sheldrake wrote:
1. The long time of flight mitigates against accuracy against aircraft which change course every 30 secs except on the bomb run itself.

2. Is it more difficult and expensive to manufacture a sabot round?
And helmets on, for all those on the ground around the battery. IIRC Horrocks was a victim of friendly anti-aircraft fire in North Africa.
AFAIK the sabot would separate well away from the crew; especially given normal battery layout that staggered guns. The report from the barrels was such that crew stayed away from the business end and the guns did not usually fire at a straight 90 degrees straight up where the sabot could fall back on them. But the way the Germans did their sabot they had two small rings (one around the base and one further up the shell) that flew apart in small pieces once outside the barrel so it wouldn't fall directly down in one heavy piece like normal AT gun sabot.

http://s57.photobucket.com/user/Mathos/ ... 0.jpg.html

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Re: Sabot-ed FLAK shells

#9

Post by T. A. Gardner » 08 Dec 2016, 20:56

Sheldrake wrote:
T. A. Gardner wrote:The big problem for the Germans by the beginning of 1944 with flak isn't the rounds, its the fire controls. Their radar has the snot being jammed out of it. If they can't optically spot the target then they're using blind fire and box barrages. The hit rate skyrockets to about 1 in 5 to 10,000 rounds. What they needed most was a way to accurately range on a target. That, they no longer had in service.
1. The long time of flight mitigates against accuracy against aircraft which change course every 30 secs except on the bomb run itself.

2. Is it more difficult and expensive to manufacture a sabot round?
Not being able to accurately aim at the aircraft and predict the flight time for accurate fuzing means it doesn't matter if you shave a second or so off the flight time. When you can't optically see the target due to cloud cover or night, and are relying on radar to provide information for fire control, and that radar is being overwhelmed with jamming, flight time of the shell is irrelevant.
The second the Germans are forced to go to predictor box barrages is the second they're firing thousands of shells into a box of empty sky hoping like hell the plane(s) will fly through it.

On two, I'd think it is a bit more difficult considering you're still making a basic round like before then having to make the sabot and install it.

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Re: Sabot-ed FLAK shells

#10

Post by maltesefalcon » 09 Dec 2016, 03:31

Still the bulk of sabot rounds tend to use a very dense and narrow penetrator like tungsten or depleted uranium with an aluminum sabot.

The principal does not yield many advantages in HE rounds.

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Re: Sabot-ed FLAK shells

#11

Post by stg 44 » 09 Dec 2016, 03:35

maltesefalcon wrote:Still the bulk of sabot rounds tend to use a very dense and narrow penetrator like tungsten or depleted uranium with an aluminum sabot.

The principal does not yield many advantages in HE rounds.
Only if you're going for AT rounds. What you're describing is an APDS or APFSDS round, which is quite different than what I am talking about here.
There were discarding sabot HE rounds that just use normal FLAK shells that the Germans developed historically by the end of the war, I included link with pictures earlier.
Image
Image

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Re: Sabot-ed FLAK shells

#12

Post by maltesefalcon » 15 Dec 2016, 04:14

No one is disputing the fact that sabot rounds were developed and tested.
But there does not seem to be much widespread use (or interest) from either side.
For one there were relatively few 10.5 cm guns, compared to 8.8 cm.

Besides lets consider the reduced shell size one more time. If you can put a shell with even a 25% bigger blast radius into use, you double the lethal "sphere" volume. This mitigates the reduced accuracy somewhat.

I think the Germans realized it too and the project was a dead end.

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Re: Sabot-ed FLAK shells

#13

Post by stg 44 » 23 Mar 2017, 21:45

Found some info about experiments with German sabot that the British conducted post-WW2 that folded into the Green Mace program:
https://en.wikipedia.org/wiki/Green_Mace
Effectively they used HE-FSDS rounds with impact fuses and later proximity fuses of sufficiently small size fired from a smoothbore barrel...with ring sabot rounds:
Image
Effectively it would use the center ring sabot to stabilize the dart shell and use the fins to ride the bore to keep the tail in place, leaving a minimal 3-4 piece ring to separate from the dart shell in flight, leaving tiny pieces to fling off away from crews and if they did fall on someone they were so light and small that they wouldn't case any significant damage, especially if the person was wearing a helmet. The goal was to achieve direct hits or near enough later with the proximity fuse so a large blast radius was unnecessary, which minimized the necessary explosives for such a shell, as 500g of explosives would be enough to shoot down a bomb with a direct hit.

The Germans hit on the idea that direct hits were just as achieve-able as putting an 88 round with a mechanically timed fuse within blast radius of a bomber if not even much more so (Ian Hogg's book on German artillery talks about it), so maximizing muzzle velocity and limiting drag was the best option, which was most achievable with dart sabot rounds. British testing easily achieved 5000fps, which is over 1500mps. Bombers operated around 6000m by night and by day around 7000m so such a dart shell could reach a bomber in 5-6 seconds or less, while a standard 88mm shell took 30 seconds, which would let a maneuvering bomber move out of the way of a mechanically timed shell or change speed so that box barrages would miss or be marginally effective. Cutting shell flight time to 1/6th and increasing the rate of fire (no need to slow down and set predicted flight times on mechanical timed fuses) is a massive increase in hit probability, plus it eliminates the chance of setting the wrong flight time or timed fuse malfunction. It dramatically cuts down on materials needed and simplifies the construction of the shell without the mechanically timed fuse and could use what lighter FLAK rounds did to self detonate before falling back to earth: a tracer element which enabled crews to see where they were shooting as a chemical fuse. Much more simple (they were already using tracer elements in the base of shells to see where they were doing, so it adds no more chemical material use compared to using a regular FLAK shell) and less expensive than a normal 88 shell, even an impact fused one. It also increases gun life, because they don't have to worry about the rifled liner on the barrel to maintain accuracy (after several thousand sells the gun would have to be relined to make sure the rifling was still able to engage with the shell), as smooth bored barrels don't need to be relined, just be mindful about material failure after 30,000 shells or some such number.

That said the issue then is making sure you're aiming at targets. Jamming was an issue for radar, but there was still optical observation even by night via searchlights. While hardly foolproof if there was cloud cover, it was better than nothing. By day if they could see a bomber box they view and track it, lighting it up with rapid fire sabot rounds and probably doing a pretty good job of hitting it with only a 5-6 second flight time for the shells to the box and trying to fire as fast as possible to saturate the target. With the few combat tests with the 88mm Double Fuse (contact and timed) shells at the end of the war (with 30 second flight time regular shells) they were able to achieve more kills by at least 3-400%. That was in April 1945 with worn out guns, jammed radar, and suboptimal manpower. Now had they done that with better crews and a shell 5-600% faster their efficiency would likely dramatically increase and the kill rate could have increased substantially more than 3-400%. In 1943-44 it might have been enough to shut down the daylight bombing offensive and done major damage to the RAF night raids.

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Re: Sabot-ed FLAK shells

#14

Post by Yoozername » 23 Mar 2017, 23:08

The payload for (heavy) AA is actually fragmentation due to the reduced effects of explosives in thin air. So, having a thicker walled projectile, and enough HE to fragment that metal, is the ideal. A sabot round would typically be giving up metal. Unless increased altitude and reduced time of flight really matters, I don't think there is much payoff. I would think that larger fragments may be better than what is typically effective against infantry. Taking out engines and flight systems is a good payoff especially if the plane does not return to base. Of course, metal is MUCH denser than explosives and the weight is mostly metal. The 88mm was actually a fairly thick walled projectile. 90% of its weight is actually metal.

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Re: Sabot-ed FLAK shells

#15

Post by stg 44 » 24 Mar 2017, 00:26

Yoozername wrote:The payload for (heavy) AA is actually fragmentation due to the reduced effects of explosives in thin air. So, having a thicker walled projectile, and enough HE to fragment that metal, is the ideal. A sabot round would typically be giving up metal. Unless increased altitude and reduced time of flight really matters, I don't think there is much payoff. I would think that larger fragments may be better than what is typically effective against infantry. Taking out engines and flight systems is a good payoff especially if the plane does not return to base. Of course, metal is MUCH denser than explosives and the weight is mostly metal. The 88mm was actually a fairly thick walled projectile. 90% of its weight is actually metal.
The problem the Germans found is that there is a half second variation in time fuzes, which means that it would travel something like 61m in that time frame, well outside the 9m lethal radius. So even without factoring in the delay to set the timed fuse with an automatic fuse setting fed data by a gunnery computer, which adds in yet another element of delay and inaccuracy for the burst time and slows down the rate of fire, it is incredibly unlikely to actually burst a shell near a bomber even in formation within the lethal radius. You can certainly throw a fair bit of shrapnel into a bit of air space and do superficial damage to a bomber and wound crew members, but the chance of actually shooting down a bomber with a box barrage is actually worse than achieving a direct hit with an impact fuse if just firing as fast as possible. So shrapnel range is effectively meaningless and less effective at achieving bomber kills, which was actually proven in combat trials in 1945. The issue though was by going for direct hits you miss out on the shrapnel damage, but that was usually pretty easily repairable and wounding/killing crew members with it was generally lucky. IIRC in the one combat trial I was able to find data on they managed to achieve something like 1400 shells per kill with standard 88mm impact rounds, while at the time they were averaging 16,000 rounds per kill with an 88mm shell set for mechanically timed burst.

Now if you reduce the flight time of the shell to 5-6 seconds (or say at most 10) instead of the standard 30 seconds for an 88mm shell to reach 7000m you're going to make your AAA guns much more accurate and reduce errors in aiming due to maneuvering bomber formations while facing less deviations in the trajectory of the shell due to say cross winds and temperature differences. Having a lighter, small, faster shell with extra lift from the tail wings actually then also saves a lot of construction material while making it much more accurate.

Here is a report that the German General of FLAK wrote about the practice for US forces post-war:
http://downloads.sturmpanzer.com/FMS/NARA_FMS_D031.pdf

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