Tank suspensions; fight!

[z42]

The higher tank with torsion bars seemed to be a particularly German thing. The King Tiger was 3m (10 ft) in height, but the T-44 and M26 (shown in cutaway below) also with torsion bar suspension were notably shorter at 2.4m (8 ft) and 2.7m (9ft) tall. I think torsion bar suspension needn't lead to a higher tank if the engine, transmission and drive sprockets are placed in the rear of the tank, thus allowing for a lower turret basket.

View attachment 844653

View attachment 844654

Interestingly, it took the Germans until the postwar Leopard 1 to present a tank with torsion bar suspension and rear transmission and drive sprockets. And to its benefit, at 2.6m (8.5ft) high, the Leopard was the shortest German tank since the 2.5m (8ft) Panzer III.

The famous late war German tanks were very big and roomy in general. IIRC Germany selected big and strong men for tank duty. The Soviets selected short men for tanks and sent the big and strong men to the infantry instead.

As for the effect of torsion bars on the height of the vehicle, it seems self evident that all other things being equal, a tank that needs space in the bottom of the hull for torsion bars needs to be higher than one that doesn't. Of course in reality all other things are not equal, and there's a lot of other factors affecting the height. Like requiring a shaft under the turret if you have the transmission at the front. Or indeed if your tank crews are tall men.

Maybe with torsion bars, by suitably placing the driver the foot well can be between two torsion bars, and thus the driver position could be as low as for an equivalent tank with another type of suspension? Doesn't help with the turret basket of course.

 

[Shortround6]

The famous late war German tanks were very big and roomy in general. IIRC Germany selected big and strong men for tank duty. The Soviets selected short men for tanks and sent the big and strong men to the infantry instead.

Maybe the Germans selected large/strong men for loaders once they started putting in very large 75mm ammo and large 88mm ammo into the tanks?
Soviets used small crewmen to keep the hull size down but they also accepted a much lower rate of fire (can we say..........dismal?).
Somebody is supposed to have said (in regards to the T-54/T-55) that the soviets were going to be in trouble when they ran out of strong, left handed, circus midgets to crew their tanks with.

 

[WARSPITER]

The positioning of the transmission and final drive at the front certainly adds to the height. The Sherman is another example of this.
It also meant the glacis had to be quite large and could not be at a low angle. The only alternative was to have an almost vertical
front plate as with the Tiger A, Panzer III / IV.

 

[Admiral Beez]

The positioning of the transmission and final drive at the front certainly adds to the height. The Sherman is another example of this.

Did any nation consider routing the drive shaft beside rather than under the turret basket? I've read that modern fire trucks and construction vehicles sometimes have offset drivelines with a transfer case that allows one or two 90° changes in angle before reaching the rear axle. Presumably, more joints mean more friction and power loss.

 

[Thumpalumpacus]

Did any nation consider routing the drive shaft beside rather than under the turret basket? I've read that modern fire trucks and construction vehicles sometimes have offset drivelines with a transfer case that allows one or two 90° changes in angle before reaching the rear axle. Presumably, more joints mean more friction and power loss.

Most fire trucks [edit: I should have written crash trucks -- Thump] don't have drivetrains going through the crew-compartment. The engine(s) in the rear, one engine you will usually see a PTO box splitting the power into three or four axles. Two engines, you will see an extra gearbox combining and syncing the two engines between the engines and the PTO, can't remember what it's called but it joins the power of the two engines before sending it to the power take-off box. These were obviously offset in a twin-engined truck driving six or eight wheels, they came in at angles.

A single-engined crash truck will have the drivetrain going to the PTO, which will apportion power to each axle, which is then handled by the differential. I hope S Shortround6 will give better detail, but that's my take.

Me, I wouldn't want a power shaft in a combat compartment. It'll just get in the way. Put it underneath.

 

[Elan Vital]

The famous late war German tanks were very big and roomy in general. IIRC Germany selected big and strong men for tank duty. The Soviets selected short men for tanks and sent the big and strong men to the infantry instead.

As for the effect of torsion bars on the height of the vehicle, it seems self evident that all other things being equal, a tank that needs space in the bottom of the hull for torsion bars needs to be higher than one that doesn't. Of course in reality all other things are not equal, and there's a lot of other factors affecting the height. Like requiring a shaft under the turret if you have the transmission at the front. Or indeed if your tank crews are tall men.

Maybe with torsion bars, by suitably placing the driver the foot well can be between two torsion bars, and thus the driver position could be as low as for an equivalent tank with another type of suspension? Doesn't help with the turret basket of course.

What you suggested in the last sentence was done a couple times yes. The Soviets (at least on T-64, T-72 and T-80), used ribbed floors so that the torsion bars would sit in the ribs and reduce their total space claim. This had the bonus of stiffening the floor.

 

[WARSPITER]

That is the reason why most countries produced rear drive after WWII. It's easier and there is more room up front
for the crew etc and thicker armour.

 

[Shortround6]

A single-engined crash truck will have the drivetrain going to the PTO, which will apportion power to each axle, which is then handled by the differential. I hope S Shortround6 will give better detail, but that's my take.

All my experience was with "city" trucks. One rear axle drive only except for the 100ft aerial platforms that used two powered axles in the back just like the rear axles of a 10 wheeler truck/tractor.

Never had a front axle driven and city trucks use high cabs so everything is under the floor or in the 'dog house'.

With the 100ft aerial platform we had one word for off pavement driving................DON'T!!!
This truck is 3 years newer than what I drove in my last 15 years.

about 68-72,000lbs on 3 axles, crappy approach and departure angles and the ground clearance underneath between the front and rear axles was not designed for off-roading.
Truck is about 11ft from ground to upper ladder rails.

Crash trucks could be (and were) completely different???

 

[Admiral Beez]

That is the reason why most countries produced rear drive after WWII. It's easier and there is more room up front
for the crew etc and thicker armour.

I wonder if there is a fork in the road where we could have seen the US Army introduce a medium tank with rear drive instead of the M4 Sherman. We need to get to the specifiers and/or designers of the M2 medium tank and tell them the new tank must be rear drive/transmission in order to reduce height. One challenge is can US-designed heavy transmissions of the time be operated reliably by a driver located in the front hull? The rear drive T-34 and British Crusader (and other cruiser tanks) predate the M2, so someone sorted it out.

 

[Elan Vital]

I wonder if there is a fork in the road where we could have seen the US Army introduce a medium tank with rear drive instead of the M4 Sherman. We need to get to the specifiers and/or designers of the M2 medium tank and tell them the new tank must be rear drive/transmission in order to reduce height. One challenge is can US-designed heavy transmissions of the time be operated reliably by a driver located in the front hull? The rear drive T-34 and British Crusader (and other cruiser tanks) predate the M2, so someone sorted it out.

The most straightforward paths would have been to specify T5 Medium around the T4 Combat Car line of thought with Christie or the VVSS (seen in a patent). There was such a design patended by Capt. Rarey. I have never seen any evidence that driving effort was a problem in the T4 especially as it was even standardized at one point, but abandonned as too expensive and heavy for the role.

I should emphasize that on M2 and M3, the height problem was made even worse by the fact the driver had to sit on the gearbox. The rear drive not only eliminated the driveshaft but also allowed a lower driver's position.

 

[WARSPITER]

US and German tanks generally had the transmission at the front as it made it easy to change gears.

The British Merrit-Brown gearbox had a light change system so having it at the rear of the tank wasn't a
problem. Cruiser tanks had constant mesh boxes so not too hard to change gear.

The crash box in the T-34 used linkages to the front and was best changed using a hammer.

 

[EwenS]

I wonder if there is a fork in the road where we could have seen the US Army introduce a medium tank with rear drive instead of the M4 Sherman. We need to get to the specifiers and/or designers of the M2 medium tank and tell them the new tank must be rear drive/transmission in order to reduce height. One challenge is can US-designed heavy transmissions of the time be operated reliably by a driver located in the front hull? The rear drive T-34 and British Crusader (and other cruiser tanks) predate the M2, so someone sorted it out.

See the T20 series intended as an M4 replacement

T20 medium tank - Wikipedia

en.m.wikipedia.org

250 of the T23 model were built but it was never standardised to become operational.

 

[z42]

Maybe the Germans selected large/strong men for loaders once they started putting in very large 75mm ammo and large 88mm ammo into the tanks?
Soviets used small crewmen to keep the hull size down but they also accepted a much lower rate of fire (can we say..........dismal?).
Somebody is supposed to have said (in regards to the T-54/T-55) that the soviets were going to be in trouble when they ran out of strong, left handed, circus midgets to crew their tanks with.

IIRC at least for the Waffen-SS the idea was that those chosen to serve would represent the finest racial specimens of the nation. And driving around a tank was higher status than being a lowly grunt, so the men chosen for the Waffen-SS tank crews were (at least per their own propaganda) the best of the best. Never mind that being tall and handsome might not correlate with being able to operate in the confined space of a tank. Oh well.

Not sure whether there was similar selection done for Heer tank crews?

And yes, while it may make sense to select slightly shorter men than average for things like tanks and fighter aircraft, if you make the selection criteria too strict you run the risk of running out of people who qualify for those roles.

 

[Admiral Beez]

Interestingly, on the Ferdinand/Elefant heavy casemate tank destroyer, the torsion bar suspension was installed longitudinally rather than transversely. And yet still the thing was almost 10ft tall and nearly 2ft taller than the contemporary ISU-122.

 

[WARSPITER]

The Elefant was certainly different. The gun was large and the ammo was stored vertically facing down.
Under this was the electric drives at the rear and two petrol engines to power generators to feed the electric drives - these were in
the centre under the gun with the driver and radio operator positioned in front of them. All in all, a tall vehicle as the drive system
was positioned directly under the gun and casemate.

The suspension system itself was all outside the vehicle but was also prone to failures with the vehicle weight making it very hard
to repair without the correct equipment.

 

[Admiral Beez]

The Elefant was certainly different.

The Germans would have been better off skipping all the Tigers, Panthers, Elefants, and casemate tank destroyers and instead taken the same money and resources to produce 10x as many 7.5 cm KwK 40 L/43 armed Panzer IVs, with earlier introduction of the Ausf. H with its better armour and longer, high velocity 7.5 cm KwK 40 L/48 gun. With the right AP round this gun will kill any T-34 or Sherman at reasonable range.


View: https://m.youtube.com/watch?v=NhDPhtuWxU0&pp=ygUJUGFuemVyIGl2

 

[Admiral Beez]

See the T20 series intended as an M4 replacement

Yes, but I'm asking for a rear drive medium tank instead of the M4, and M3 for that matter.

 

[EwenS]

Yes, but I'm asking for a rear drive medium tank instead of the M4, and M3 for that matter.

Read the article I linked and look at the photos.

T20 medium tank - Wikipedia

en.m.wikipedia.org

These had the transmission moved to the rear, driving sprockets at the rear. No drive shaft through the fighting compartment just as you are asking for, giving a lower profile.


View: https://www.youtube.com/watch?v=8STbWUhy408

 

[z42]

The Germans would have been better off skipping all the Tigers, Panthers, Elefants, and casemate tank destroyers and instead taken the same money and resources to produce 10x as many 7.5 cm KwK 40 L/43 armed Panzer IVs, with earlier introduction of the Ausf. H with its better armour and longer, high velocity 7.5 cm KwK 40 L/48 gun. With the right AP round this gun will kill any T-34 or Sherman at reasonable range.

As a counter-point, towards the middle of the war the Pz IV was on its last legs as a usable platform. It was just too small for the gun and armor required for a competitive middle-late war tank. The middle-late war versions had lots of problems, e.g. front suspensions bottoming out and resulting very poor ride quality.

They would have needed a new medium tank design in the 35-40 ton range, in order to have a small edge over the hordes of T-34's and Shermans coming their way. The Panther was maybe the closest they got, but alas, too little too late.

As for casemate tank destroyers, considering that from the middle of the war onwards they were on the defensive, I don't think it was a bad idea per se. Particularly if you can use the chassis that are too small for a competitive medium tank (Pz III & IV).

Yes, but I'm asking for a rear drive medium tank instead of the M4, and M3 for that matter.

I read that one reason why the Sherman was the way it was, that is narrow, short and high, was that it allowed them to pack more of them into transport ships. That being said, a rear drive version with torsion bars wouldn't have necessarily changed that basic constraint, although it would have allowed it to be somewhat lower profile.

 

[EwenS]

I read that one reason why the Sherman was the way it was, that is narrow, short and high, was that it allowed them to pack more of them into transport ships. That being said, a rear drive version with torsion bars wouldn't have necessarily changed that basic constraint, although it would have allowed it to be somewhat lower profile.

AFAICT narrow/short/high M4 was a function of the design evolution of US medium tanks from M2 of 1939 to M3 to M4, all with the same basic chassis, engine & transmission layout.

Where size did come into play was with the adoption of a successor to the M4. That emerged, after the failure of the T20-23 series, in the shape of the T26 (standardised as the M26) which finally entered production in Nov 1944 and saw 20 vehicles sent to Europe for trials in Jan 1945. The first big test for the M26 would have been in Operation Olympic, the invasion of Japan in Nov 1945. It was larger both dimensionally and weight wise which would have reduced numbers carried in a ship and caused difficulties with lifting capacity of cranes required for loading / unloading.

But size was only one reason for the delay in introducing a successor. Various other factors played a part.