StuG III Thread (and also other German vehicles I guess)

[Walter_Sobchak]

On 4/7/2017 at 4:30 PM, EnsignExpendable said:

Too late, Trumpeter already release a scale model of the early, mid, and late production versions.

Has it been introduced into world of tanks yet as a premium?

[SH_MM]

8 hours ago, EnsignExpendable said:

The tank is being repaired with peak German efficiency!

 

 

Worker, project manager, assistant project manager - seems pretty German to me.

[Xlucine]

10 hours ago, EnsignExpendable said:

The tank is being repaired with peak German efficiency!

 

 

the extra men are there to help open the engine cover

[Walter_Sobchak]

In case you have never given much thought to the suspension bogies of the Ferdinand/Elefant, here is a diagram.  

 

I keep staring at this and I still don't quite get it.  It's like looking at an M.C. Escher painting. 

 

[Collimatrix]

It's one of the worst tank suspensions ever designed, so far as I can tell.  Tank suspension is a combination of desirable traits and unavoidable trade-offs.  This screws up pretty much all of them.

 

Suspensions with high unsprung mass tend to improve ride quality, as some of the the energy of going over bumps is absorbed in oscillation of the unsprung elements.  Suspensions with low unsprung mass have better bump-following ability and maintain traction better when going over uneven terrain.  Low unsprung mass is considered the way to go when designing a cross-country vehicle like, oh, I don't know, a goddamned tank.  High unsprung mass is for luxury vehicles.  The Porsche torsion bar suspension has extremely high unsprung mass, since the springing medium moves with the road wheels and because there's a whole lot of additional levers and packaging that are adding to the mass of the suspension units.

 

The road wheels in the Porsche suspension design are sprung as pairs, not independently as in (most) other torsion bar designs.  This does give some inherent advantages in resisting pitching oscillations, but there are plenty of ways to have independent road wheel suspension and to damp out pitching oscillations at the same time.

 

This design is just about the worst possible for getting a large amount of road wheel travel out of a torsion bar with the technology available at the time.  A torsion bar, like any other spring, has an elastic limit; i.e. the point beyond which bending it will cause permanent distortion.  The range of motion of a tank's suspension needs to be small enough that it is not causing permanent distortion to its suspension, or the crew is going to have to replace a lot more torsion bars than they do already.

 

The modern solution to this problem has been to make the torsion bars out of fancy prestressed VIM/VAR steels that have extremely high microstructure cleanliness, and can thus take a hell of a twisting.  But back in the 1940s they didn't have those, so there were two workable solutions:

1)  Limit the travel range of the suspension to something less than ideal (sanely designed tanks)

2)  Spread out the strain from the suspension loads over an absolutely enormous amount of spring (panther)

 

The Porsche design does the exact opposite.  The arm that twists the torsion bar is splined to the middle of the torsion bar, instead of to one of the ends.  This divides the torsion bar into two half length torsion bars, which doubles the spring constant (k) and halves the amount of swing arm deflection before hitting the elastic limit of the steel.  The designer could compensate for this by making the swing arms longer to introduce some leverage into the equation, but that is a band-aid fix for a stupid problem that shouldn't exist in the first place, and further increases the unsprung mass and overall mass of the suspension.

 

The two advantages I can see for this suspension design are that it would be relatively easy to fix in the field; just unbolt the unit and put a new one on, and that it would provide good resistance to pitching oscillation.  Of course, HVSS, VVSS and Horstmann suspension also share those advantages, and they're much simpler.

[Walter_Sobchak]

29 minutes ago, Collimatrix said:

 

 

The Porsche design does the exact opposite.  The arm that twists the torsion bar is splined to the middle of the torsion bar, instead of to one of the ends.  This divides the torsion bar into two half length torsion bars, which doubles the spring

 

Good lord.  This is why I couldn't figure out the drawing.  I kept thinking to myself that they can't possibly be twisting the bar from the middle.

[Xlucine]

It isn't as bad as that - it's a bar-in-tube design. In the second paragraph they describe one end of the torsion bar splined to the housing, while the other end is splined into a tube that is free to rotate ('journalled') in the housing. The tube extends to the end of the arm on axle B, and then has an arm splined upon it connecting to the arm on axle B.

 

What I can't work out is how it worked, given their comment that the torsion bar housing rested on the bump stop while the vehicle was stationary. If you lift axle A, then as it's already against the rubber block the whole assembly will pivot around the hull pivot bearing and lift the hull. I believe axle B is not free to rotate in the rocker arm (begging the question of why have the arm on axle B part of the rocker arm casting instead?). Lifting axle B instead, it seems to me that a similar situation will occur - if the rocker arm and torsion bar housing came apart then that would produce an anticlockwise rotation in the torsion bar (viewed from the fixed end), but that would also unnecessarily lift the hull.

 

The answer might lie in the comment that the rubber block 'rests lightly' upon the torsion bar housing. If there was still some give left in the rubber block then lifting axle A would both compress the rubber block and rotate the torsion bar slightly clockwise (in the same frame of reference as before), and lifting B would have a similar effect. The end result would be a suspension with decent independent wheel travel (as the whole assembly can pivot around the hull pivot bearing), and only a couple of millimetres of actual sprung travel. You could achieve a similar effect without the torsion bar or lever arms and a larger rubber block, so I suspect porsche may have found the most wasteful way to conserve rubber humanly possible. It resists pitching oscillations because they are not actually possible, beyond very small displacements!

 

There's a ferdinand at the tank museum for a recent tiger wank exhibition, so if I can make it there I'll see if the rubber block (if it's still present) has much travel left before the suspension bottoms out.

[Collimatrix]

I see; you're right.  It is a bar in tube.  Sort of.  The tube is half-length.  One end of the tube is attached to the inner torsion bar.  The other end of the tube is attached to the articulated arm ("Axle radius arm") that's attached to the road wheel axle ("Bogie wheel axle B").

[EnsignExpendable]

Pasholok posted a description of how it works sent to the British Military Mission, since presumably they also couldn't figure out how: http://yuripasholok.livejournal.com/3759556.html

 

I guess I should get around to translating that.

[EnsignExpendable]

1 hour ago, Collimatrix said:

 

The two advantages I can see for this suspension design are that it would be relatively easy to fix in the field; just unbolt the unit and put a new one on, and that it would provide good resistance to pitching oscillation.  Of course, HVSS, VVSS and Horstmann suspension also share those advantages, and they're much simpler.

 

You're right, we need to interleave Porsche bogeys so that it's harder to remove. 

[EnsignExpendable]

 

[SH_MM]

No offense, but if the Tiger I is among the worst weapons, what about most British tanks of WW2?

[Scolopax]

I have that book somewhere.  A lot of odd things in it, some decidedly worthy of the title and many others not so much.

 

Some guy going through it all for those curious.  Would recommend to probably just mute it.

 

 

 

 

2 hours ago, Xlucine said:

There's a ferdinand at the tank museum for a recent tiger wank exhibition, so if I can make it there I'll see if the rubber block (if it's still present) has much travel left before the suspension bottoms out.

Did they ship the American one over there or something?  I was aware that there was only the one (formerly) at Aberdeen and the other at Kubinka.

[Khand-e]

1 hour ago, SH_MM said:

No offense, but if the Tiger I is among the worst weapons, what about most British tanks of WW2?

 

Most members here already mock the hell out of most British tank designs for reference.

[Xlucine]

12 minutes ago, Scolopax said:

I have that book somewhere.  A lot of odd things in it, some decidedly worthy of the title and many others not so much.

 

Some guy going through it all for those curious.  Would recommend to probably just mute it.

  Reveal hidden contents

 

 

 

Did they ship the American one over there or something?  I was aware that there was only the one (formerly) at Aberdeen and the other at Kubinka.

 

they've got the US one on loan

http://www.tankmuseum.org/year-news/bovnews53855

[Walter_Sobchak]

6 hours ago, Scolopax said:

I have that book somewhere.  A lot of odd things in it, some decidedly worthy of the title and many others not so much.

 

 

I've got that book too, i think it was a gift.  It's worth about five minutes of entertainment.  This might shock you all, but I wouldn't put the Tiger on the list of worst weapons ever.  It was a flawed design that poorly suited the needs of WWII Germany, but to call it one of the worst weapons ever?  I think the author is trying too hard to shock.  He also has the AK-47 in the book, so it's pretty obvious he is trying to be contrarian.

[EnsignExpendable]

I translated Pasholok's document on the Porsche suspension, can you mech nerds tell me if my terminology is right? https://docs.google.com/document/d/1N6LSr2AgrtxubFqXi1edh_sC6UIsmWkasYV3FQ4_Fbk/edit?usp=sharing

[Collimatrix]

4 hours ago, EnsignExpendable said:

I translated Pasholok's document on the Porsche suspension, can you mech nerds tell me if my terminology is right? https://docs.google.com/document/d/1N6LSr2AgrtxubFqXi1edh_sC6UIsmWkasYV3FQ4_Fbk/edit?usp=sharing

 

I'll make sure to look at this tonight.

[Xlucine]

14 hours ago, EnsignExpendable said:

I translated Pasholok's document on the Porsche suspension, can you mech nerds tell me if my terminology is right? https://docs.google.com/document/d/1N6LSr2AgrtxubFqXi1edh_sC6UIsmWkasYV3FQ4_Fbk/edit?usp=sharing

 

It looks good to me, thank you. I'm pleased they agree with me about the extreme limits on the actual sprung travel of the torsion bar

[Collimatrix]

Yep, seems fine to me too.

 

It sounds like there isn't actually that much range of motion in that thing.

[EnsignExpendable]

"German tank knocked out during the battle for Prokhorovka, 1943"

 

 

Sure it is

[ApplesauceBandit]

6 minutes ago, EnsignExpendable said:

"German tank knocked out during the battle for Prokhorovka, 1943"

 

Sure it is

 

Must have been from the alternate Wehriverse where Germany had Tiger IIs by '43 and won the war as a result.

[EnsignExpendable]

But the photo clearly shows that it was immobilized in the harsh Russian July winter.

[Collimatrix]

That's not snow, that's salt.  The Germans wanted to make sure nothing ever grew there again, Carthage-style.

[DogDodger]

The Soviets were good enough to import some of Belgium's snow so their American friends wouldn't be so cold during the Battle of the Bulge.