Bronezhilet

The hatch receded a bit. The blue line you photoshopped is the top of the add-on modules, so the hatch takes about 2 cm from the total thickness, so that mechanism would be ~45 mm. The white line in the next picture is the edge of the side armour modules, which stay straight (this picture also shows the receding hatch).

 
Luckily I took a photo of the actual add-on modules on the same day:

With the very scientific method of measuring my thumb nail I can determine that the modules are 65-70 mm thick.
 
The side modules in this picture are 40-45mm thick.

*cracks fingers*

Something that has interested me for a while, are shape stabilised projectiles. As in, projectiles that are stable due to their shape. Everybody has heard of rotation stabilised and fin stabilised projectiles, but shape stabilised is kind of different. I guess most of you here have seen shape stabilised projectiles without actually knowing how and why they work.

Geek sidenote: Fin stabilised projectiles are actually fin and rotation stabilised.

As I said, shape stabilised projectile have a stable flight path due to their unique shape.

Figure 1: A 84mm Carl Gustav shape stabilised HEAT-round

Note the slightly ogive front and the stand-off, which are characteristic of shape stabilised projectiles (SSP). Both features are absolutely crucial for the SSP to work.
I'm going to throw you guys into the deep end by showing a .gif of the airflow in front of an SSP.
Here's a link because I can't embed .gifv apparently
The first thing you should notice is the air circulating in some-sort of pocket, and that this airflow is subsonic. Before I continue, here's the airflow in front of a blunt projectile: Clicketyclick
While that projectile has a subsonic airflow in front of it as well, it is not circulating.

Here's the airspeed of both projectiles as a normal picture:

Figure 2: Airspeed in front of an SSP


Figure 3: Airspeed in front of a blunt projectile

It's clear that an SSP has a ogive-shaped subsonic airpocket in front of the projectile. This basically emulates the ogive of a normal rotation stabilised projectile. In other words, it makes it more aerodynamic. But does that airpocket stabilise the projectile?
No it does not.

So why is this projectile stabilised? The key is in what happens when it starts to tumble. Right now, there is nothing stopping the projectile from tumbling, and that's the interesting thing. There is literally nothing stopping the projectile from tumbling, except...


the projectile itself.

Lets take a look at what happens when an SSP starts to tumble. (If I remember correctly, I rotated the projectile 10 degrees)
First off, the airflow in front of the projectile. It's fairly obvious that the airflow has changed. Lets check that again, but this time as a picture.

Figure 4: Airflow in front of a tumbling SSP

Again, it's obvious that the airflow has changed. The subsonic pocket has mainly shifted to one side and the air itself isn't really circulating in the pocket. This change causes a huge change in the Cd of the projectile. Let me show you why.

Figure 5: Pressure in front of a tumbling SSP

Next, the pressure in front of an SSP flying straight.

Figure 6: Pressure in front of an SSP flying straight

Please note the approximate pressure in front of both projectiles. The tumbling projectile has, on one side, twice the pressure as the projectile that's flying straight. Very interesting. What's even more interesting is that the pressure occurs on the opposite of the side it's turning to! The projectile is turning upwards, but the pressure builds up at the bottom. This pressure forces the projectile to start turning down again, forcing the projectile in a state where the pressure on all sides is equal.

Voila, a shape stabilised projectile.


But... why does it work?

The subsonic airpocket is created by the stand-off and that little flange, or whatever you want to call it. The dimensions and placement of both are equally important. The stand-off and its side create the airpocket and the flange give the airpocket the required shape. The stand-off size can vary, but the flange size and placement is very important. If the flange is too far forward or too far back, the airpocket will be either too small or too big. Why does the size of the pocket matter? Because of this:

Figure 7: Subsonic pocket in front of an SSP

I changed the parameters slightly and made all airflow above Mach 1 red. Whatever is not red, is trans- or subsonic. The interesting thing to note here, is the pocket extends to the edge of the projectile (if I made the projectile better it should be exactly on the edge). (Sidenote: Here's the same picture of an SSP at a 10° angle)
While the airpocket does not start at the flange, the flange determines where the pocket starts. If, at this velocity, the flange was further back, there would be supersonic flow hitting the front of the projectile, massively increasing drag. If the flange was further forward, the airpocket would be further forward too. This would mean the airpocket would not end at the edge of the projectile, but further out. Creating an airpocket which is wider than the projectile. This would allow the projectile to tumble a bit, because pressures wouldn't change much unless there is supersonic flow hitting the projectile.

It is also possible to change the size of the airpocket by changing the front of the projectile itself. If the radius connecting the front and the stand-off is too big, the airflow inside the pocket would disrupt the circulation. The same would happen if the radius is too small. The angle of the front is important as well, but I haven't expermented that much with it so I don't know how important it exactly is, but it has an effect on the airflow.

By the way, if the flange did not exist at all, the airpocket would start at around a third to half of the stand-off. Which would completely ruin the airpocket. Without a flange, the stand-off itself would have to be way bigger and longer to create the same kind of airpocket.

But Bronezhilet, I hear you cry, if the airspeed changes, the pocket changes as well!

I'm glad you brought that up, because you are right.

A shape stabilised projectile only works properly within a certain flight envelope. If the projectile is moving too fast, the airpocket would compress allowing supersonic flow to hit the front of the projectile. Which in turns increases drag. By a lot. If the projectile is moving too slow the airpocket widens, allowing the projectile to tumble a bit before it would stabilise.

I've been brainstorming with Colli a bit, and we've come to the conclusion that is why some projectiles are both shape stabilised and fin stabilised. When the projectile is moving too slow for shape stabilisation, the fins would keep it pointing in the right direction.



And that concludes today's lesson. Thank you for reading.

some update

105mm m900 m833 m774 m735


m900 - penetrator length 603 mm, volume 206344,9906mm³ (density 18,6/~3,830kg/real 3,830kg)
m833 - penetrator length 427 mm, volume 196634,2908mm³ (density 18,6/~3,657kg/real 3,668kg)
m774 - penetrator length 345 mm, volume 178942,0578mm³ (density 18,6/~3,328kg/real 3,364kg)
m735 - core length 309,5 mm, volume 119354,6819mm³ (density 18,5/~2,208kg/real 2,210kg)

Spielberger doesn't use the decimal point, so not only does he use a Nazi naming system, he uses the wrong version of it.

Unt some mit very interesting ideas about ze lower races, ja?

But it's on Warisboring, so its trash. 
 

The German IADS might have had better IADS than the Japs, but it had some serious, serious flaws. When the British intelligence figured them out, the whole Kammhuber Line came crashing down.
 
When I can find the time and energy I should make a topic about it, since it's quite an interesting subject.

Ah that is correct. But that's because the engine bay doesn't have an AFSS. 
As for the AFSS in the crew compartment:

Which follows on to this:
      
tl;dr:
- Where there's an AFSS the chance of a sustained fire is zero.
- Sustained fires can only happen in locations where there is no AFSS and where there the fuel is actually in a form in which it can form a sustained fire.
 
And with that in mind the only place where sustained fires can happen are the REFC, LEFC and EHY. All of which are in the engine bay.
 
Furthermore, all this is based on calculated probabilities, with the actual calculation not mentioned in the paper:

 
Also, only steel/aluminium armours were considered in the paper, for as far as I can see. While currently we obviously have NERA and ERA which will result in different terminal ballistics.
 
Reading further on in the paper, there is some data that's outright wrong, based on actual tests I've attended. But for (hopefully) obvious reasons I can't discuss the tests nor the results of the tests. And the more I read this paper, the more I'm raising my eyebrows. Here are a few quotes:
(!!!)(!!)  
...these aren't things I want to read in a report.

This is FUTURE TEXAS, son. We measure our armour in fractions of 16ths of a mile and like it.

Some genuine fucking advice, mate. The Americans lied all the time. The Soviets lied all the time. This does not mean that the reality is "actually our side is the liar culture and their side was the truth culture". Everyone fucking lied. Every society in the 20th Century (and many other centuries, but especially that one and this one), had a penchant for lies.

Just because the Americans lied about My Lai does not mean the Nazis didn't lie about kill counts. Or Auschwitz, and be careful how close one takes you to the other.

The key to becoming a good historian, speaking as someone who frankly is a pretty decent one, is to recognize lies. And you're not looking at truth, with this Korner dude.

Ah yes, "hit by projectile" a surefire way to determine the cause of destruction to be the 'long 8,8' since that thing is unique in the sense that it's the only thing on the battlefield that fires projectiles!
 
The rest of the guns fire... what exactly?

We're trying, but that one dude just wont leave.

We're trying, but that one dude just wont leave.

So another side note: this game also works really well in reverse...
 
Discussing, let's call it the A42 "Cataphract", as developed by the British in 1943:
 
Designer: "Overall its dimensions were comparable to Tiger 1, but about 60cm longer and 30cm narrower. For all that, the turret ring diameter was 160cm. The vehicle weighed around 45 tonnes, ten tonnes less than Tiger, but had a lopsided armour scheme with equivalent (or better) frontal protection and about half the armour everywhere else."
 
Wehraboo: "Typical poor British design: over-emphasising some aspects at the expense of others. This reminds one of Churchill, which paid a heavy tank's bill on weight and mobility (not to mention an over-long hull which makes turning difficult), but only has good protection from the front for the trouble."
 
D: "The tank carried a high-velocity gun in the 75-76mm class, with good armour penetration (able to knock out all but the heaviest tanks). On the other hand, it had a less powerful HE round than existing 75mm guns like KwK40 and M3."
 
W: "This is also typically British. They put can-openers on their tanks and then forgot the most common mission for them: infantry support! It is less of an issue for specialist vehicles such as Archer, but for a mass-production tank it's a crippling defect."
 
D: "The drivetrain was complex, bulky and very unreliable, but provided nice-to-have capabilities like neutral steering and good gun stability over rough terrain. The engine was underdeveloped and needed a massive amount of work (including derating) before it could be used for any length of time successfully. Overall, the time-to-failure was something like a few hundred kilometres, and they didn't foresee being able to improve this (although the lifespan of individual components could have been improved)."
 
W: "This is Covenanter all over again - a bunch of 'clever' ideas that amounted to a mess. At least then they had the good sense to keep it as a training vehicle instead of sending it into battle. They should have stuck to well-proven transmission and suspension components, and used a surplus aero-engine or something rather than bodging it."
 
D: "Due to the issues with the suspension, drivetrain, turret ring diameter and turret design, the vehicle had almost no upgrade potential. The armour could not be thickened appreciably without causing even worse reliability problems, and the gun could not be replaced by a larger-bore weapon without designing an entirely new turret (and even then it would have been a squeeze for the crew)."
 
W: "This was the problem with Cromwell too - forcing the British to make iterative new vehicles when it should have been upgrading existing ones. The Germans, Russians and Americans all realised this with PzIV, T-34 and M4. Each was able to be reworked with new weapons, turrets, armour, and even engines without stopping the whole production line to produce a completely new vehicle."
 
D: "Speaking of the turret, there were technically two hatches (a commander's hatch and an escape hatch directly in the rear), but the placement made it so that only the loader could use the rear hatch and only the commander and gunner could use the commander's hatch. The hatches were very small (around 40cm diameter), but the commander's hatch was well-appointed with periscopes, a mounting for a scissors periscope and a geared azimuth indicator to show the turret's rotation in relation to the hull. The gunner had a single coaxial sight with a single level of magnification (2.5x), but later production was slated to have a selectable 2.5/5x sight. The FoV was around 28' for the 2.5x, and 14' for the 5x."  
 
W: "Again, the British talent for wonky engineering on show. The hatch is a mix of good ideas (they cottoned on to the use of periscopes quickly, after all), dubious ones (a simple ring indicator would have worked just as well) and terrible ones (Comet hatch syndrome strikes again). The gunner's sights were good and workmanlike (3x and 21' FoV is more typical for the British), but the Americans had already introduced modern conveniences such as a second unity/fixed magnification sight mounted to the roof at that point. This tank should have had these, it would made the gunner's life much easier!"
 
D: "The tank used almost no components common to other models besides the engine (which, again, needed massive reworking), and was difficult to service in almost every respect due to the complexities and placement of the drivetrain and suspension components. This, along with a chronic shortage of spare parts (because production of vehicles was prioritised over the production of spares) meant that commanders in the field would have to rely heavily on rail to move the tanks up to the front. There were no road transporters large enough to carry them, and next to no engineering vehicles able to unditch them."
 
W: "This is madness from the perspective of fighting a mobile war - something that the Germans excelled at but the allies had to painfully learn. A tank is only useful when it's moving under its own power. More than that - when winning an industrial war, it is rational production that counts. Look at the effort the Germans made under Speer to rationalise production of aircraft and tanks. This rationalisation probably prolonged the war by a year, giving the Wehrmacht the material to push back against the hordes of Russian vehicles being thrown at it."
 
D: "It was made by Germans."
 
W: "Oh its amazing! A wonder weapon! The ancestor of all modern tanks!"
 

I occasionally play this mental game where I imagine describing, let's call it the Schwer-mittel panzerkampfwagen 44 "Cougar", to the typical wehraboo.
 
"It had a low profile, only 10cm taller than the PzIV. But the vehicle is much more heavily armed and armoured (equivalent or better to a Tiger frontally, only a little thinner on the side)."
"Fantastic. Really good, compact design. The Germans were known to be good at efficient layouts."
 
"The drivetrain was extremely compact and reliable, with a better power-to-weight ratio than PzIV, as well as a slick automatic gearbox that reduced workload on the driver and improved offroad mobility."
"Wonderful, truly a vehicle for mobile warfare. Didn't Guderian say, after all, that the principle weapon of the tank was its engine and radio?"
 
"The vehicle had lots of vision devices, a large, roomy interior and nice-to-haves like panoramic gunner's sights and an azimuth indicator in the commander's cupola."
"Brilliant. We know that the crew which sees the target and fires first usually wins. This all adds up to an improvement in firepower!"
 
"Over 2000 were produced in less than a year, making it a relatively common sight on the battlefield when compared to older heavies such as Tiger."
"That's great! Wars are won by industrial production as much as by feats of arms - look at the miracles that Speer accomplished."
 
"It had lots of upgrade potential. Prototypes were produced with guns and armour equivalent to Tiger II, but without completely sacrificing either mobility or reliability."
"This is what made the Germans so formidable during the second world war - their ingenuity and ability to improve on existing designs. If only it had been fielded for longer, it would have had the potential to turn the tide of the war."
 
"It was made by Americans."
"Oh, it's absolute shit then."

Man, millions and millions of automatic gearboxes in past eighty years all around the Globe have been equipped with torque converter. If you never heard about the most common coupling solution in automatic gearboxes, it means without any doubt that you have zero clue about transmissions and since differentials are rather difficult topic to grasp I think you shall not argue about them. Even what you just wrote is simply stupid. 

Indeed.  Most of the early work on what would become the HK and CETME family of rifles was initially done in France by ex-Mauser employees.  They later moved to Spain, which they seem to have preferred for its relaxed economic protectionism, drier climate, and slightly fascist dictatorship.

And, like fuckin clockwork, we get the "I was just trolling" response.

It's like pottery.

Hi,
Just a head's up of a new book just published by the Tank Museum at Bovington. It is Richard Ogorkiewicz's autobiography which he had just completed before his death and which was brought to publication thorough the determination of David Willey, Curator of the museum. I received the book out of the blue  as a gift, through I think, the good offices of 
Richard's wife. The book is entitled "Observer of Cold War tank development", it is 78 pages long and richly illustrated and is full of interesting facts and personal anecdotes. 
Once available for general sale, it looks likes it will be a purchase well made.
Cheers
Marsh

Interesting link was posted on otvaga.
https://david-2.livejournal.com/603749.html
   "Raam Segol" soft-kill APS from late 1990s.
 

 
 

 
 

Well... not exactly an armored fighting vehicle, but still!

Well... not exactly an armored fighting vehicle, but still!

Well... not exactly an armored fighting vehicle, but still!

Well... not exactly an armored fighting vehicle, but still!