Weird tank gun trajectories

[Rokko]

There's something I've a few times (it doesn't happen often to me) during tank duells for instance. Sometimes you see a tank round aimed at another tank go UNDER the tank and hit the ground behind it. I really can't imagine how this could be possible (given a completely flat surface, happened during a testing scenario once). I'm not sure at which ranges this will happen ingame, but it strikes me as fairly odd.

Has anyone ever experienced something alike?

[womble]

Yes, actually, now you mention it. I've been doing some 15-on-15 armour testing, and I think I've seen that sort of behaviour: dirt plumes directly and immediately behind a target, like the shot passed clean through centre of mass and buried itself. I've assumed they're just display SNAFUs; we've been told that WeGo replay display is sometimes a bit off, though realtime is accurate, so I suppose if I ran the tests in RT I shouldn't see these anomalies.

Edit: and this is at 2000m where the shot is dropping at a "sharp" enough angle that minutely high shots can actually hit the engine deck.

[Rokko]

Well I never play WeGo and the distance was more like 700m and I could clearly see where the shoot went, so it was almost certainly not a plunging shot (especially not a such a distance).

[Amizaur]

Why not ?

I see that people usually tend to overestimate the descend angles of tank rounds. They are really not that high as you may think.

At a range of 1000m the descend angle of typical tank AT round would be in order of 7-14 mils and at 2000m it's 15-33 mils (that's 0.4-0.8deg at 1000m and 0.86-1.9deg at 2000m.

Data taken from ballistic tables of Russian D-10 100mm gun (900m/s muzzle velocity - the smaller angle) and ZIS-5 76mm gun (680m/s muzzle velocity - higher angle).

So - it's really small angle, it's almost horizontal. With such trajectory, almost horizontal with very gentle descend - a shell that didn't hit the front lower hull can easily fly below the tank and hit the ground tens of meters behind it. With a descenting trajectory of -1deg a shell that flew under a tank at height of 50cm would fly further 57m before it meets the dirt - assuming absolutely flat ground (0.5m * 1/sin(1deg) = 57,3m).

With such low angle it's also obvious that any accidental hits of top armor against a tank target would be ineffective on a flat ground (really any hit at 2deg impact angle would glance even from very thin top armor). Penetration of top armor is only possible if firing from well above the target, or the target is on downhill slope.

[womble]

At 2000m, the 800m/s (ish) 76mm round takes 2.5s to cover the distance to the target. s=ut+1/2 at^2, so with a=g=10m/s, the shell drops 31m. Since the firing Sherman's gun is only 2.5m off the ground, it has to lob it up somewhat. Assuming it spends half its time going up and half coming down, it's falling from 15m, 1000m out, so it drops 15mm per metre of forward travel (neglecting air resistance). The Panther is about 9m long, so it drops 135mm from front to back. The round is 76mm tall, obviously, so the difference between the top just missing the underside of the front of the target and the height of the bottom of the shell as it clears the rear end of the tank is 210mm.

The Panther's ground clearance is 560mm, so there's room there for the shell to fly under, but it won't be going 10s of metre past the rear of the tank very often; any shell that did would have paint from the bottom edge of the nose on it. This fits with what I saw, in terms of possibilities: the dirt plumes were within a tank length of the rear of the 'missed' Panther in all cases.

Anyone have any guesses as to how fast a 76mm round was going after 2000m of flight?

[Vanir Ausf B]

For APCBC it should be 1878.7 fps or 572.6 mps if I did the math right.

[Amizaur]

At 2000m, the 800m/s (ish) 76mm round takes 2.5s to cover the distance to the target.

I believe the values from ballistic tables, but we may also try to estimate it this way .

I would take 3s as the shell is slowing down considerably at such range. But let's continue with 2.5s.

s=ut+1/2 at^2, so with a=g=10m/s, the shell drops 31m.

right

Since the firing Sherman's gun is only 2.5m off the ground, it has to lob it up somewhat. Assuming it spends half its time going up and half coming down, it's falling from 15m,

Not really. The drop lasting 2.5s would be 31m (s=1/2*a*t^2 = 31.25). As you noticed, the shell is falling only half of this time - 1.25s.

But height of a 1.25s drop is not half of 2.5s drop - the time is squared in the formula.

1/2*1.25^2*10 = only 7.8m. Your resulting angle would have to be halved, and your resulting length of shell travel would have to be be doubled

1000m out, so it drops 15mm per metre of forward travel (neglecting air resistance).

Half of that - 7.8mm. On average.

But the trajectory is close to a parabola so the trajectory angle would be higher at the start and at the end, than the "average" on ascending and descending part of trajectory. So it's actually bit closer to your initial doubled results .

The angle you would get from "on average" drop of 7.8m/1000m would be arctg (7.8/1000) = 0.45deg. The real angle on the end of trajectory - because of parabolic shape - would be around 3 times larger.

The Panther is about 9m long, so it drops 135mm from front to back.

That would be half of that, so 68mm.

The round is 76mm tall, obviously, so the difference between the top just missing the underside of the front of the target and the height of the bottom of the shell as it clears the rear end of the tank is 210mm.

143mm now.

The Panther's ground clearance is 560mm, so there's room there for the shell to fly under, but it won't be going 10s of metre past the rear of the tank very often; any shell that did would have paint from the bottom edge of the nose on it.

This fits with what I saw, in terms of possibilities: the dirt plumes were within a tank length of the rear of the 'missed' Panther in all cases.

417mm/68mm = roughly 6 tank lenghts. So 55m. But it would be less as the trajectory is not linear but parabolical, and the descent angle is higher than that.

From the tables, descent angle of 85mm shell with initial velocity of 792m/s and retaining 608m/s at 2000m (BR-365) - so close enough to estimate the US 76mm shell. (I don't have any ballistic tables of German or US tank ammo, sadly).

From those tables, the angle of descend of this shell when shooting at 2000m is 22mils or 1deg 19min.

With this angle, and the clearing of 560-76mm = 484mm, the shell could theoretically travel further (assuming for simplicity that the trajectory is now straight)

1/sin(1,31deg)*484mm = 21m.

It's about 12m behind the rear of the Panther. Does it sound right now ?

[womble]

It's about 12m behind the rear of the Panther. Does it sound right now ?

That's what I was assuming would be about the max realistic (i.e. not "missed by a coat of lacquer") distance. It still fits.

[Amizaur]

From 1000m it would be much smaller angle and even longer distance possible.

So, the "weird tank gun trajectories" are actually correct .

[dieseltaylor]

From Troop Leader by Bill Bellamy page 133:

Below us and about 1,000 yards away was the village, screened by

trees, and just short of these, to my left front near a slight jink in the

road, was a patch of bushes. There was something about them

which worried me and I called to Allen to traverse on to them and

tell me if he saw anything suspicious. After a few seconds he said he

thought he might have seen movement and as it was such an

obvious place for an anti-tank gun I told him to fire. It is difficult to

separate the next series of events one from another. As Allen fired, so

there was a brilliant flash from the bushes and simultaneously an

incredible roar and a whooshing noise which seemed to envelop us.

People always describe AP (armour-piercing) shots as sounding like

an approaching express train and this to some extent described the

noise that we heard at that moment. The shot, because that was

what it turned out to be. came from a German 75mm anti-tank gun.

It went diagonally from left to right, across the front of my glacis

plate, missing us by inches, then struck the ground at the front of

Bill Pritchard's tank, passed straight under it. emerged at the rear

and ricocheted over Alan Howard's turret before disappearing noisily

into the rear areas.

[Michael Emrys]

From Troop Leader by Bill Bellamy page 133:

And what was the dénouement of that incident?

Michael

[Sergei]

But why is it odd? In a large take you're going to see some shots go over, some under. Some very narrowly over, some very narrowly under so that they impact the ground under the tank or even behind it.

Think of the space between the ground and the vehicle's bottom as a pipe. If the pipe is directed toward the firing gun, there is a chance that a shot falling short of the target will go straight through that 'pipe'.

In CMSF I have seen multiple times ATGM's passing the 'five-hole' of the target. THAT would be a lot harder to accomplish in real life, because a missile with its fins would very likely touch either side of the 'pipe' and spin out of control. Though it still might not harm the target.

[womble]

But why is it odd? In a large take you're going to see some shots go over, some under. Some very narrowly over, some very narrowly under so that they impact the ground under the tank or even behind it.

Think of the space between the ground and the vehicle's bottom as a pipe. If the pipe is directed toward the firing gun, there is a chance that a shot falling short of the target will go straight through that 'pipe'.

In CMSF I have seen multiple times ATGM's passing the 'five-hole' of the target. THAT would be a lot harder to accomplish in real life, because a missile with its fins would very likely touch either side of the 'pipe' and spin out of control. Though it still might not harm the target.

~What has been established in this thread is precisely that it is not odd, though the OP (and, on first look, others) thought it was. The thread is done. People are now just chatting.

[dieseltaylor]

75mm ATG destroyed on probably 2nd shot as orange explosion noted which apparently is generally a hit. However they did not take the village until the following day.

Apropos tracking and firing whilst they were covering down the main village street on the following day - from outside the village - an SP crossed the road inside the village. According to Bellamy it was in sight for at most 3 seconds but one of the gunners nailed the front idler and disabled it. Very good shooting indeed according to Bill.

[MikeyD]

I recall another combat anecdote (from God-knows-where) about an 88 round passing directly beneath a Sherman, the round scraping the bottom of the tank just below the drivers feet. In US manuals tankers are taught the technique of 'skipping' rounds off terrain, usually to achieve airbursts over trenches using delay fuses. AP with burster charge has a delayed base fuse (you'd want your round to penetrate before exploding) so its not unreasonable for an AP round that found itself rattling between the road and the underbelly might detonate on the far side.

[John Kettler]

I recall another combat anecdote (from God-knows-where) about an 88 round passing directly beneath a Sherman, the round scraping the bottom of the tank just below the drivers feet. In US manuals tankers are taught the technique of 'skipping' rounds off terrain, usually to achieve airbursts over trenches using delay fuses. AP with burster charge has a delayed base fuse (you'd want your round to penetrate before exploding) so its not unreasonable for an AP round that found itself rattling between the road and the underbelly might detonate on the far side.

MikeyD,

As the proud owner (methinks, status of most of library unknown) of a 1944 issue FM 17-12, TANK GUNNERY, I confirm that U.S. tankers were indeed taught ricochet or grazing fire. That the British were taught and used this is readily confirmed by reading Wilson's FLAMETHROWER TANK. This is a valuable form of direct fire that I've pushed for in every way I know how. It was taught, it was used by both the Allied and Axis tankers, and I believe ought to be in CMx2 games. The Allies had ex-Syrian 75mm graze action fuzes fitted to HE shells fired by the Grants at Gazala--well before CMFI, let alone CMBN. Source of the last, Jarrett, ARMOR IN THE WESTERN DESERT. Jarrett is the guy who provided the Grants with an effective AP shell--by turning down spin-armed PzGr 39 shells' driving bands so they'd fit the Grant's cannon. He's about as authoritative as it gets when it comes to ordnance groggery.

Regards,

John Kettler

[John Kettler]

Amizaur,

How closely do those ranges you quoted come to usable max range range for the weapons? The reason I ask is a concept from naval warfare called danger space. This is the region where if any part of the target is subtended by the descending shell's trajectory, the target will be hit. This is explained and shown here.

http://www.kbismarck.org/forum/viewtopic.php?f=36&t=2631

Typically, shots fired at long and extreme ranges will hit the deck armor, while those fired from lesser ranges will hit the belt armor, which is vertical. The likelihood of such a hit isn't great, but naval gunnery isn't looking for a first round kill, but successively refined range brackets until the target is straddled, whereupon the guns go to maximum rate volley fire in order to smother the target with fire and pulverize it. The land analog would be a Pakfront or similar. The difference is that most WW II antitank weapons lacked the kind of rangefinding equipment standard on warships as small as a destroyer. Exceptions would be 88s, U.S. 90 mm and whatever units had at their disposal 1-2 meter rangefinders or similar. Otherwise, it simply wasn't possible to use a weapon to its full range potential. In turn, this resulted in the very small descent angles quoted, all but eliminating the possibility of turret roof and hull deck hits. The D-10s, you will note, has a maximum range of some 14,000 meters. At that kind of range, you'd see something like a 20 degree descent angle, just as in the Bismarck example. The only way to get that kind of range is to mass fires, preferably from an elevated position at least as high as a destroyer's main rangefinder and with the advantage of a fully kitted out fire control party. To show what can be done with the right equipment and training, the Germans got 5000 meter kills in Russia on massed armor targets, ranges so extreme the Russians thought they'd blundered into an antitank minefield! And that was by no means the upper limit!

http://www.battlefront.com/community/showthread.php?t=62704

This site says the Tiger I had the AP sight running out to 4000 meters and the HE to 6000!

http://www.fprado.com/armorsite/tiger1.htm

I hope this sheds some light on a complex topic.

Regards,

John Kettler

[Jaksteri]

I came here to see simple explanation, not to read a bloody novel about muzzle velocities and projectile physics.

[dieseltaylor]

Well to some of us it is simple : )

However I afraid you can't stop people posting so you might aswell live with it and accept the good with the bits you do not like.

[Jaksteri]

It was a joke, genius.

[dieseltaylor]

Thats why we use smilies! : )

But thanks for the recognition - nobody else realises I am a genuis!!

[Michael Emrys]

...nobody else realises I am a genuis [sic]!!

Which is as good a testament to common sense as will ever be found!

Michael

[Childress]

That 'sic!!' was just cruel.

[Michael Emrys]

That 'sic!!' was just cruel.

But admit it, you chuckled or at least smiled. And the exclamation points were in the original.

Michael

[Childress]

No one's posts amuse me me more than yours, Michael. With the possible exception of Redwolf when he's soaring on whimsy.