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2 hours ago, Xoon said:

What did you dislike about the AMX-10RC, or armored vehicles in general? 
Everything counts, even lack of space for snacks for that matter. 

Generaly speaking, I never answer to such a question because it’s the start of unrealistic discussions of technology fanboys unknowing real. But, I can say :

- never forget AMX-10RC is a very 80’s light tank. So, any improvement must be cheap provide. 

- the world famous Serge AFV belief is : an AFV chassis push, carry and tow. 

- having a good AFV is good, but without its environment, it’s useless. 

 

FCS, sights, weapons were good.

 

So, I would have :

- modified the seats to have something more confortable and armored. Maybe an harness to sleep ;

- introduced a new TC hatch with an umbrella opening (my priority) ;

- rearrange external storage to increase them ;

- suppress river crossing (both useless and dangerous) to have more storage ;

- add spall liner and mine proof plates under pilot seat and turret floor. 

 

Considering chassis, I would have add :

- 2 rear fuel drop barrels like the Leclerc ones. Fuel drums are compulsory ;

- front tools connector to push mine rollers...

 

Considering it’s environment, I would have :

- add a fourth 10RC per troop (In France, reccon tanks troops are 3 tanks troops. Leclerc : 4 MBT troops) ;

- adopted AMX-10RTT as command post and ARVs instead of VAB and ARV based on trucks.

c080b9187ce9aa61fe7302c881f145e3.jpg

 

With diminution of 10RC number, I would have transformed some of them in general purpose vehicles able to carry dedicated teams for special tasks such as EW....

When dimounting the barrel and ammo racks, you have plenty of room. 

 

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On 16/04/2018 at 9:43 AM, Alzoc said:

 

I remember reading that they payed a particular attention on mass balance around the trunnion for the Leclerc's gun, so that the strain on the electric drive of the gun would be as limited as possible.

  Reveal hidden contents

 

 

Don't know the final performance level they reached, but Nexter/GIAT commonly marketed the Leclerc as the only tank with a true fire on the move capability (describing the M1, Leo 2 and Challenger 2 as tanks that have merely acquired this capacity at limited speed and only in the frontal arc).

 

When reading on the history of it's development one have the really distinct feeling that they went full retarted on having the best stabilization possible.

The initial aluminum tracks that had awful service life were chosen for their light weight but mostly because they generated less vibrations, for example.

 

Dunno if the M1, Challenger 2 and Leo 2 still use an hydraulic drive for their guns or if their most recent versions switched to electric.

 

 

A sort of mechanical arm that would measure the angular difference?

Well that's a question for a crewman for once. Does the gunner lose the target when the gun is reloading?

@Serge Aren't you the one who knows an ex Leclerc TC?

Or was it @Laviduce?

 

The specs required a highly mobile tank capable to destroy any Warsaw pact (PAVA) tanks at long range with a high hit probability on first shot. This led to the crafting of highly precise system.
To be honnest with you there is no stabilisation on the Leclerc. The gun is slave to the ballistic computer which computes the ideal LOF from the stabilised LOS.
When reloading, the gun goes to the reloading elevation. Meanwhile the LOS is still stabilised to the direction of observation (in the limits of the mirrors amplitude). Unless you release the palm switches, the mirrors go to their mechanical neutral positions.

The gunner sight is mechanically mounted to the main armament. When the gun goes up and down; the sight bows up and down.
Since the both move along with the exact same angle, boresighting can be done automatically with a deviation measurement laser (AMX 10 RC being the first french AFV to be equiped with such device).
Crews do some alignments (what we call "harmonisation" where we keep the parallax in check), but that's not the bullshit stated by Sergei Suvorov where crews were forced to boresight everytime they move their tanks...
 

On 16/04/2018 at 4:06 PM, Alzoc said:

 

There was a shitload of concept for the Leclerc (same for any 3rd gen MBT I guess).

Take your pick:
 

  Reveal hidden contents

 

948baa2e8a4ae5304082a3e24b9f8dcc

c2a0af58e19ef91f9b4d00ae3e3d6659

dacb53df9ff04e126e9e56c34b16aae9

67403526cad3d05ca951b20ae286c18f

d9ef28c84fa495f9adc6d3d325d839a2

0068Ayuagy1fc6caf4g2vj31kw23vb2b.jpg

 

 

At the time engineers were open minded on what could replace the classical tank. Once they defined that their platform was still an AFV, they assessed every kind of compromise to take what was the most favorable and compatible to their specs guideline.
 

20 hours ago, Alzoc said:

On the mass balance topic, here's a citation of a book I (and probably other French speaking members) own.

Even if you don't speak French it's quite a nice book to have with plenty of pictures (all those pictures of the various early EPC concept comes from here), though you have the impression that nobody ever proofread it (screw grammar and the orthograph^^).

 

P58:

 

Comme pour la fonction mobilité, une mécanique de haute technologie est requise pour la fonction feu. Celle-ci est entièrement conçue pour faire du tir en roulant le mode normal d'engagement des cibles.

La précision de la stabilisation est donc au cœur des performances du système. Stabiliser un objet dans l'espace (en l’occurrence la tourelle et son canon) est un défi technique qui requiert de la part de l'ingénieur en mécanique le respect des trois règles d'or:

 

-La recherche des équilibres ;

-Le contrôle des élasticités et des déformations dynamiques ;

-La chasse au jeu entre les pièces.

 

Ces équilibres sont obtenus par conception du canon de 120mm et de la tourelle dont les centres de gravité sont respectivement situés sur les axes de rotation site et gisement.

 

Canon et tourelle sont mis en mouvement à l'aide de moteurs électriques transmettant leur puissance à des boîtes mécaniques de pointage dont les élasticité sont contrôlées en permanence grâce à un montage utilisant des barres de torsion.

Enfin des roulements à billes sans jeu assistent le mouvement du canon dans l'axe vertical.

Sans ces technologies mécaniques particulières, la meilleure électronique du monde ne saurait conserver le canon en direction de la cible sans une débauche de puissance peu compatible avec les contraintes d'emport dans une tourelle.

 

Google trad doesn't make too bad of a job translating it but the main points are:

 

-The gun center of gravity lay on the level of the trunnion

-The turret center of gravity is on the axis of rotation of said turret

-The elasticity of the mechanical parts driving the gun and the turret are monitered in real time reduced using torsion bars (don't know exactly how) The backlash is nearly suppressed.

-Ball bearings with minimal backlash (and same apply for most moving parts) are used.

-No hydraulics, everything is electrically driven.

 

20 hours ago, Serge said:

Yes.

The Leclerc MBT barrel is very rearward compared the manualy loaded turret. This way, artillery is naturally balanced. 

 

Yes.

Leclerc MBT was the first tank designed to achieve fire on the move at hight speed. Firing off road at 40km/h to a mobile target is basic.

Maybe Type-10 and K2 are better today. Maybe. 

 

Yes. 

Aluminium tracks can’t last as long as classical steel ones. They were found too much expensive to support for peace time. 

 

You have such a mechanical link. I don’t know the exact purpose. 

 

I was AMX-10RC tank commander. I never served with Leclerc MBT. So, I can’t help for very detailed data. 

In France, you have Leclerc, Darklabor, Totochez, Rescator. They are not bullshiting. 

Fun fact regarding the tracks. They spent quite some time to switch to steel tracks. They initially used the same arrangement as the aluminum alloy tracks (the shape of the rubber trackpads were supposed to reduce the stomping effect). Surprise, surprise, the vibrations at high speed were strong enough to be a handicap. This explains why we transition from V2 (alloy) to V5 (steel). Apparently V4 was also a disappointment.

Even with V5 or DST 840 the vibration is quite awkward compared to V2.

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Thanks a lot for your answers, and welcome to SH.

 

45 minutes ago, DarkLabor said:

To be honnest with you there is no stabilisation on the Leclerc. The gun is slave to the ballistic computer which computes the ideal LOF from the stabilised LOS.
When reloading, the gun goes to the reloading elevation. Meanwhile the LOS is still stabilised to the direction of observation (in the limits of the mirrors amplitude). Unless you release the palm switches, the mirrors go to their mechanical neutral positions.

The gunner sight is mechanically mounted to the main armament. When the gun goes up and down; the sight bows up and down.
Since the both move along with the exact same angle, boresighting can be done automatically with a deviation measurement laser (AMX 10 RC being the first french AFV to be equiped with such device).
Crews do some alignments (what we call "harmonisation" where we keep the parallax in check), but that's not the bullshit stated by Sergei Suvorov where crews were forced to boresight everytime they move their tanks...

 

So if I understand well, the gunner sight is normally linked to the gun (as it follow the gun when it move up and down) but the mirror inside it can be decoupled from it to allow to keep the LoS intact when for example the gun elevate to reload?

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1 hour ago, Alzoc said:

Thanks a lot for your answers, and welcome to SH.

 

 

So if I understand well, the gunner sight is normally linked to the gun (as it follow the gun when it move up and down) but the mirror inside it can be decoupled from it to allow to keep the LoS intact when for example the gun elevate to reload?

Just like any contemporary tank, the mirrors are decoupled from the turret/armament in order to offer a stabilised view.
As long as the gunner pushes the palmswitches, the turret is "active", the mirror will compensate the movement of the tank. When you release the palmswitches, the mirror will return to the mechanical zero. In the case of this happenning during a reload, where the gun is mechanically locked in a certain position; means that the LOS will move to realign with the gun (the LOF will certainly not move since the palmswitches are the elementary security switches for turret movements).
 

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13 hours ago, DarkLabor said:

switches, the mirrors go to their mechanical neutral positions.

The gunner sight is mechanically mounted to the main armament. When the gun goes up and down; the sight bows up and down.

Crews do some alignments (what we call "harmonisation" where we keep the parallax in check), but that's not the bullshit stated by Sergei Suvorov where crews were forced to boresight everytime they move their tanks...

Rezun said this about soviet tanks or french?

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2 hours ago, That_Baka said:

Rezun said this about soviet tanks or french?

The french ones in UAE (Gulf 2005???).
The documentary was totally bullshit with russian bias.
He also claimed that the emiratis were in love of the BMP-3 (but we know what happenned when they used them in Yemen).

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21 minutes ago, DarkLabor said:

BMP-3 (but we know what happenned when they used them in Yemen).

 Arab military is all gear no skill to use it meaning they are ridicuously bad performance benchmark for AFV .

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On 4/17/2018 at 9:30 AM, DarkLabor said:

To be honnest with you there is no stabilisation on the Leclerc. The gun is slave to the ballistic computer which computes the ideal LOF from the stabilised LOS.
When reloading, the gun goes to the reloading elevation. Meanwhile the LOS is still stabilised to the direction of observation (in the limits of the mirrors amplitude). Unless you release the palm switches, the mirrors go to their mechanical neutral positions.

The gunner sight is mechanically mounted to the main armament. When the gun goes up and down; the sight bows up and down.
Since the both move along with the exact same angle, boresighting can be done automatically with a deviation measurement laser (AMX 10 RC being the first french AFV to be equiped with such device).
Crews do some alignments (what we call "harmonisation" where we keep the parallax in check), but that's not the bullshit stated by Sergei Suvorov where crews were forced to boresight everytime they move their tanks...

 

On 4/17/2018 at 11:21 AM, DarkLabor said:

Just like any contemporary tank, the mirrors are decoupled from the turret/armament in order to offer a stabilised view.
As long as the gunner pushes the palmswitches, the turret is "active", the mirror will compensate the movement of the tank. When you release the palmswitches, the mirror will return to the mechanical zero. In the case of this happenning during a reload, where the gun is mechanically locked in a certain position; means that the LOS will move to realign with the gun (the LOF will certainly not move since the palmswitches are the elementary security switches for turret movements).
 

 

Welcome to SH, DarkLabor.  Always good to have someone who can talk specifics.

 

Could you explain more of what you mean when you say that "there is no stabilization on the Leclerc?"

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3 hours ago, Collimatrix said:

 

 

Welcome to SH, DarkLabor.  Always good to have someone who can talk specifics.

 

Could you explain more of what you mean when you say that "there is no stabilization on the Leclerc?"

Well it's just a certain nuance.
Obviously there is a stabilisation system but it is limited to the stabilisation of the line of sight (within the sights).
The turret itself has no stabilisation system.
A stabilisation system uses a set of gyroscopes located at specific points (hull, turret, armament).
The angular informations gathered by the different gyros is computed by the FCS which gives a set of corrections to the elevation and traverse mechanism (the most early stab systems where the armament remains to the same position no mater how the tank behaves). In addition the FCS adds on top of this another set of corrections related to the ideal LOF (later stab systems that introduces the concept of correction of the position of the tank).

On the Leclerc, the sight being how it is, the number of variables is kept as minimum as possible. You only compute the angular variation between the current LOS and the ideal LOF. The set of values is then dispatched to the "guidance system" (asservissements) which monitors the actual movement of the turret (traverse and elevation) and assess the need to power the electric motors or revert them into generators to brake the movement.
In itself the tank knows on its own the position of the differents elements (hull, turret and armament) with the closed loop elevation and traverse. The sight give the angle of the whole.

Hope it is clear. It's not a whole lot but we make this distinction.

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Thank you for taking the time to explain this.  Technical discussions across a language barrier are often difficult, because technical terminology rarely translates well!

It sounds like the fire control system on the Leclerc works very similarly to other, modern MBTs.  In English technical jargon it would be described as having a feed-forwards, two-plane, gun-follows-sight stabilization system, but it sounds like the literal translation of the French terminology would give an English speaker a very misleading idea of what's going on.

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On 4/16/2018 at 11:57 PM, Serge said:

- modified the seats to have something more confortable

 

I've heard that this is especially the case regarding the commander's seat (in terms of lack of comfort).

 

On 4/16/2018 at 11:57 PM, Serge said:

- rearrange external storage to increase them ;

- suppress river crossing (both useless and dangerous) to have more storage ;

 

For what purpose ?

 

More tools ?

More space for the crew personal equipment ?

Or just fitting the tools currently mounted outside (towing cable, entrenching tool, sledgehammer, ...) inside ?

 

 

On 4/16/2018 at 11:57 PM, Serge said:

- add spall liner and mine proof plates under pilot seat and turret floor. 

 

So, it would be a  kind of lightened version of the SEPAR kit ?

 

On 4/16/2018 at 4:06 PM, Alzoc said:

 

There was a shitload of concept for the Leclerc (same for any 3rd gen MBT I guess).

Take your pick:
 

  Reveal hidden contents

 

948baa2e8a4ae5304082a3e24b9f8dcc

c2a0af58e19ef91f9b4d00ae3e3d6659

dacb53df9ff04e126e9e56c34b16aae9

67403526cad3d05ca951b20ae286c18f

d9ef28c84fa495f9adc6d3d325d839a2

0068Ayuagy1fc6caf4g2vj31kw23vb2b.jpg

 

 

 

Notice the difference in weight between the TC 2 (53 metric tons, two-man turret) and the TC 3 (58 metric tons, three-man turret) concepts.

 

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1 hour ago, Sovngard said:

I've heard that this is especially the case regarding the commander's seat (in terms of lack of comfort).

Both commander and gunner’s seats are identical.

The only difference is the commander adjustment’s got a rear stopper to reduce the setting by 3 cm. Why ? To avoid to pierce fuel tanks. Without the stopper, the seat can protrude from the turret basket. 

My goal is to protect the crew from shrapnel. So, I would have manufactured seats with ballistic materials. 

 

We have to remain that in France, people above 185cm were not permitted to become tankist, but tank commanders.

So my knees suffered a little bit against the gunner’s seat. 

 

Quote

For what purpose ?

 

More tools ?

More space for the crew personal equipment ?

Or just fitting the tools currently mounted outside (towing cable, entrenching tool, sledgehammer, ...) inside ?

Look at any tank at war. You never have enough place.

The only external storage you have (on the RC standard, not the RCR), is a basket designed to carry 4 of the old butyl waterproof tank crew pack. During the Gulf war, crewmen stored MREs between the hull and the add-on armor.

In the French troop, you have a truck per troop to carry burden. But, in the real life you must be as autonomous as possible. 

My solution would have been a mixt between the TML-105 storage for the front and the sides and a Merkava like rear basket. 

amx2.jpg

 

Quote

So, it would be a  kind of lightened version of the SEPAR kit ?

SEPAR is too much heavy. 

I’m just thinking about internal layer on some dedicated places. AMX-10RC can’t be burdened. It’s very dangerous considering its steering system.

In 2002, Australian SAS LRPV received 4cm thick anti-mine composite floor plates. This kind of solution would have been acceptable. 

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2 minutes ago, Serge said:

SEPAR kit is so heavy, 10RCR is beyond its limits. 

It was designed during Afghanistan but it’s no more used.

 

Well the 10 RCR will be put out of service in a few years anyway.

I doubt we will see any more upgrades on the platform.

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Just now, Alzoc said:

 

Well the 10 RCR will be put out of service in a few years anyway.

I doubt we will see any more upgrades on the platform.

The arrival of Jaguar will not come instantly, there is still room for "operational emergencies"...

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8 minutes ago, DarkLabor said:

The arrival of Jaguar will not come instantly, there is still room for "operational emergencies"...

 

True.

 

What I said is simply that I doubt that the government will be willing to spend money on upgrades for a vehicles on it's way out.

Especially now that they finally understood that keeping old vehicles in services cost more in the long run than accelerating the delivery of the new ones.

 

There seem to be a will from the actual government to increase the defence budget but 5 years is a short time to make up for the lack of investment over decades and we don't know what will be the stance of the next government.

We'll see I guess.

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8 minutes ago, Mighty_Zuk said:

So will they be scrapped or just sent to get dust in some remote long term storage?

 

With the habits of the French army, I would say sent to long term storage.

I guess that the first to be retired would be cannibalized for the maintenance of those still in service.

After some time it's possible that they will end in the open market.

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1 hour ago, Mighty_Zuk said:

So will they be scrapped or just sent to get dust in some remote long term storage?

I think scrapped. 

They will be very old. The upgrade capability is poor and the barrel is not NATO compatible. It fires a light 105mm shell. 

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On 4/16/2018 at 5:57 PM, Serge said:

Generaly speaking, I never answer to such a question because it’s the start of unrealistic discussions of technology fanboys unknowing real. But, I can say :

- never forget AMX-10RC is a very 80’s light tank. So, any improvement must be cheap provide. 

- the world famous Serge AFV belief is : an AFV chassis push, carry and tow. 

- having a good AFV is good, but without its environment, it’s useless. 

 

FCS, sights, weapons were good.

 

So, I would have :

- modified the seats to have something more confortable and armored. Maybe an harness to sleep ;

- introduced a new TC hatch with an umbrella opening (my priority) ;

- rearrange external storage to increase them ;

- suppress river crossing (both useless and dangerous) to have more storage ;

- add spall liner and mine proof plates under pilot seat and turret floor. 

 

Considering chassis, I would have add :

- 2 rear fuel drop barrels like the Leclerc ones. Fuel drums are compulsory ;

- front tools connector to push mine rollers...

 

Considering it’s environment, I would have :

- add a fourth 10RC per troop (In France, reccon tanks troops are 3 tanks troops. Leclerc : 4 MBT troops) ;

- adopted AMX-10RTT as command post and ARVs instead of VAB and ARV based on trucks.

 

With diminution of 10RC number, I would have transformed some of them in general purpose vehicles able to carry dedicated teams for special tasks such as EW....

When dimounting the barrel and ammo racks, you have plenty of room. 

 

 

9 hours ago, Serge said:

Both commander and gunner’s seats are identical.

The only difference is the commander adjustment’s got a rear stopper to reduce the setting by 3 cm. Why ? To avoid to pierce fuel tanks. Without the stopper, the seat can protrude from the turret basket. 

My goal is to protect the crew from shrapnel. So, I would have manufactured seats with ballistic materials. 

 

We have to remain that in France, people above 185cm were not permitted to become tankist, but tank commanders.

So my knees suffered a little bit against the gunner’s seat. 

 

Look at any tank at war. You never have enough place.

The only external storage you have (on the RC standard, not the RCR), is a basket designed to carry 4 of the old butyl waterproof tank crew pack. During the Gulf war, crewmen stored MREs between the hull and the add-on armor.

In the French troop, you have a truck per troop to carry burden. But, in the real life you must be as autonomous as possible. 

My solution would have been a mixt between the TML-105 storage for the front and the sides and a Merkava like rear basket. 

amx2.jpg

 

SEPAR is too much heavy. 

I’m just thinking about internal layer on some dedicated places. AMX-10RC can’t be burdened. It’s very dangerous considering its steering system.

In 2002, Australian SAS LRPV received 4cm thick anti-mine composite floor plates. This kind of solution would have been acceptable. 

 

Might as well make a new bloody vehicle with all those changes. Maybe something like a 105mm armed VBCI or the Vextra 105? Or maybe just build a totally new vehicle from the ground up specifically for urban/sub-urban combat. Could probably give it MRAP capabilities stock and not have to worry about a damn 2 ton upgrade package... 

 

Thinking about it, the newest Centauro sounds like a pretty good fit, just add some extra boxes to the hull sides/turret bustle and you’re pretty close to those requirements. 

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This design was used by French tanks and nobody else.     For some reason, volute spring suspensions are completely absent from this section. This is the best image of a Vertical Volute Spring Suspension (early Shermans) that I could find. It's kind of similar to the first image, except the spring is a volute spring, and it's vertical instead of horizontal. Later Shermans used horizontal volute springs.     Of course, as the book points out, these suspension elements are very easy to damage externally and knocking out one part of the suspension will typically take out the rest of the assembly, so independent suspensions are the way to go. The best way to do this are torsion bars. The bar is attached to a lever that holds your road wheel. As pressure is applied to the road wheel, the bar subtly twists, remaining elastic enough to reset once the pressure is off. This image is kind of weird, but the part in the center is the part on the far left, zoomed in, showing you where the lever and the opposite side's torsion bar are attached. As you can see, road wheels in a torsion bar suspension are going to be a little off on one side, unlike what you're used to on cars and such.     Now, since torsion bars are metal bars on the floor, they are going to make your tank taller. If you want a tank that's as short as possible at the expense of width, you may want to consider a Christie like suspension. Here, much like in torsion bars, the pressure is transferred inside the tank, but instead of a bar to absorb it, it's a spring in a vertical (or angled) tube. In most tanks with this kind of suspension, the springs are on the inside, but if you want to make the tank roomier on the inside, you can have them on the outside too. If you're really fancy, you can put a spring within the spring like in this diagram.     Since this is a Soviet tank book, you gotta have a huge T-34 diagram. Here it is.     The T-34 uses Christie springs, which you can see in the diagram. The road wheel configuration is a mix of the externally dampened and internally dampened "Stalingrad type" road wheels. The former have more rubber for absorbing hits from terrain, but the latter use less rubber. When you're in Stalingrad and you have to make tanks with a rubber deficit, that's the kind you want. When road wheels from other factories were available, they would go in the front and then the back to absorb most of the impact from harsh terrain features, and the steel-rimmed wheels went in the middle. The diagram shows how both types of wheels work.   Rubber can't really take too much punishment, so the KV, being a heavy tank, went with internally dampened road wheels from the very beginning, with a ring of rubber on the inside around the axle.     And finally, idlers. If you don't have big Christie type wheels, you gotta have idlers so your saggy track doesn't fall off. This diagram shows the rubber coating on an idler, and also how the rear idler can adjust to tighten the track. A loose track makes more noise, gets worn more, and is liable to slip off.     Keep those tracks tight, and you'll be zooming towards glorious victory in no time flat!     Now, the book ends and my own stuff begins. I mentioned rubber, but not what a headache it was to tank designers. In hot weather, the rubber in your tracks and wheels tends to fall apart. If you go fast enough, tires that don't have proper ventilation are going to melt too. There was a lot of pre-war panic in the USSR about the German PzIII being able to do 70 kph on tracks, but once the Soviets started building SU-76Is on the PzIII chassis they found out that the speed had to be limited to a whopping 25 kph to keep the wear to a reasonable level.
    • By Collimatrix
      Tank design is often conceptualized as a balance between mobility, protection and firepower.  This is, at best, a messy and imprecise conceptualization.  It is messy because these three traits cannot be completely separated from each other.  An APC, for example, that provides basic protection against small arms fire and shell fragments is effectively more mobile than an open-topped vehicle because the APC can traverse areas swept by artillery fires that are closed off entirely to the open-topped vehicle.  It is an imprecise conceptualization because broad ideas like "mobility" are very complex in practice.  The M1 Abrams burns more fuel than the Leo 2, but the Leo 2 requires diesel fuel, while the omnivorous AGT-1500 will run happily on anything liquid and flammable.  Which has better strategic mobility?  Soviet rail gauge was slightly wider than Western European standard; 3.32 vs 3.15 meters.  But Soviet tanks in the Cold War were generally kept lighter and smaller, and had to be in order to be moved in large numbers on a rail and road network that was not as robust as that further west.  So if NATO and the Warsaw Pact had switched tanks in the late 1950s, they would both have downgraded the strategic mobility of their forces, as the Soviet tanks would be slightly too wide for unrestricted movement on rails in the free world, and the NATO tanks would have demanded more logistical support per tank than evil atheist commie formations were designed to provide.
       

       
      So instead of wading into a deep and subtle subject, I am going to write about something that is extremely simple and easy to describe in mathematical terms; the top speed of a tank moving in a straight line.  Because it is so simple and straightforward to understand, it is also nearly meaningless in terms of the combat performance of a tank.
       
      In short, the top speed of a tank is limited by three things; the gear ratio limit, the power limit and the suspension limit.  The tank's maximum speed will be whichever of these limits is the lowest on a given terrain.  The top speed of a tank is of limited significance, even from a tactical perspective, because the tank's ability to exploit its top speed is constrained by other factors.  A high top speed, however, looks great on sales brochures, and there are examples of tanks that were designed with pointlessly high top speeds in order to overawe people who needed impressing.
       

      When this baby hits 88 miles per hour, you're going to see some serious shit.
       
      The Gear Ratio Limit
       
      Every engine has a maximum speed at which it can turn.  Often, the engine is artificially governed to a maximum speed slightly less than what it is mechanically capable of in order to reduce wear.  Additionally, most piston engines develop their maximum power at slightly less than their maximum speed due to valve timing issues:
       

      A typical power/speed relationship for an Otto Cycle engine.  Otto Cycle engines are primitive devices that are only used when the Brayton Cycle Master Race is unavailable.
       
      Most tanks have predominantly or purely mechanical drivetrains, which exchange rotational speed for torque by easily measurable ratios.  The maximum rotational speed of the engine, multiplied by the gear ratio of the highest gear in the transmission multiplied by the gear ratio of the final drives multiplied by the circumference of the drive sprocket will equal the gear ratio limit of the tank.  The tank is unable to achieve higher speeds than the gear ratio limit because it physically cannot spin its tracks around any faster.
       
      Most spec sheets don't actually give out the transmission ratios in different gears, but such excessively detailed specification sheets are provided in Germany's Tiger Tanks by Hilary Doyle and Thomas Jentz.  The gear ratios, final drive ratios, and maximum engine RPM of the Tiger II are all provided, along with a handy table of the vehicle's maximum speed in each gear.  In eighth gear, the top speed is given as 41.5 KPH, but that is at an engine speed of 3000 RPM, and in reality the German tank engines were governed to less than that in order to conserve their service life.  At a more realistic 2500 RPM, the mighty Tiger II would have managed 34.6 KPH.
       
      In principle there are analogous limits for electrical and hydraulic drive components based on free speeds and stall torques, but they are a little more complicated to actually calculate.
       

      Part of the transmission from an M4 Sherman, picture from Jeeps_Guns_Tanks' great Sherman website
       
      The Power Limit
       
      So a Tiger II could totally go 34.6 KPH in combat, right?  Well, perhaps.  And by "perhaps," I mean "lolololololol, fuck no."  I defy you to find me a test report where anybody manages to get a Tiger II over 33 KPH.  While the meticulous engineers of Henschel did accurately transcribe the gear ratios of the transmission and final drive accurately, and did manage to use their tape measures correctly when measuring the drive sprockets, their rosy projections of the top speed did not account for the power limit.
       
      As a tank moves, power from the engine is wasted in various ways and so is unavailable to accelerate the tank.  As the tank goes faster and faster, the magnitude of these power-wasting phenomena grows, until there is no surplus power to accelerate the tank any more.  The system reaches equilibrium, and the tank maxes out at some top speed where it hits its power limit (unless, of course, the tank hits its gear ratio limit first).
       
      The actual power available to a tank is not the same as the gross power of the motor.  Some of the gross horsepower of the motor has to be directed to fans to cool the engine (except, of course, in the case of the Brayton Cycle Master Race, whose engines are almost completely self-cooling).  The transmission and final drives are not perfectly efficient either, and waste a significant amount of the power flowing through them as heat.  As a result of this, the actual power available at the sprocket is typically between 61% and 74% of the engine's quoted gross power.
       
      Once the power does hit the drive sprocket, it is wasted in overcoming the friction of the tank's tracks, in churning up the ground the tank is on, and in aerodynamic drag.  I have helpfully listed these in the order of decreasing importance.
       
      The drag coefficient of a cube (which is a sufficiently accurate physical representation of a Tiger II) is .8. This, multiplied by half the fluid density of air (1.2 kg/m^3) times the velocity (9.4 m/s) squared times a rough frontal area of 3.8 by 3 meters gives a force of 483 newtons of drag.  This multiplied by the velocity of the tiger II gives 4.5 kilowatts, or about six horsepower lost to drag.  With the governor installed, the HL 230 could put out about 580 horsepower, which would be four hundred something horses at the sprocket, so the aerodynamic drag would be 1.5% of the total available power.  Negligible.  Tanks are just too slow to lose much power to aerodynamic effects.
       
      Losses to the soil can be important, depending on the surface the tank is operating on.  On a nice, hard surface like a paved road there will be minimal losses between the tank's tracks and the surface.  Off-road, however, the tank's tracks will start to sink into soil or mud, and more power will be wasted in churning up the soil.  If the soil is loose or boggy enough, the tank will simply sink in and be immobilized.  Tanks that spread their weight out over a larger area will lose less power, and be able to traverse soft soils at higher speed.  This paper from the UK shows the relationship between mean maximum pressure (MMP), and the increase in rolling resistance on various soils and sands in excruciating detail.  In general, tanks with more track area, with more and bigger road wheels, and with longer track pitch will have lower MMP, and will sink into soft soils less and therefore lose less top speed.
       
      The largest loss of power usually comes from friction within the tracks themselves.  This is sometimes called rolling resistance, but this term is also used to mean other, subtly different things, so it pays to be precise.  Compared to wheeled vehicles, tracked vehicles have extremely high rolling resistance, and lose a lot of power just keeping the tracks turning.  Rolling resistance is generally expressed as a dimensionless coefficient, CR, which multiplied against vehicle weight gives the force of friction.  This chart from R.M. Ogorkiewicz' Technology of Tanks shows experimentally determined rolling resistance coefficients for various tracked vehicles:
       

       
      The rolling resistance coefficients given here show that a tracked vehicle going on ideal testing ground conditions is about as efficient as a car driving over loose gravel.  It also shows that the rolling resistance increases with vehicle speed.  A rough approximation of this increase in CR is given by the equation CR=A+BV, where A and B are constants and V is vehicle speed.  Ogorkiewicz explains:
       
       
      It should be noted that the lubricated needle bearing track joints of which he speaks were only ever used by the Germans in WWII because they were insanely complicated.  Band tracks have lower rolling resistance than metal link tracks, but they really aren't practical for vehicles much above thirty tonnes.  Other ways of reducing rolling resistance include using larger road wheels, omitting return rollers, and reducing track tension.  Obviously, there are practical limits to these approaches.
       
      To calculate power losses due to rolling resistance, multiply vehicle weight by CR by vehicle velocity to get power lost.  The velocity at which the power lost to rolling resistance equals the power available at the sprocket is the power limit on the speed of the tank.
       
      The Suspension Limit
       
      The suspension limit on speed is starting to get dangerously far away from the world of spherical, frictionless horses where everything is easy to calculate using simple algebra, so I will be brief.  In addition to the continents of the world not being completely comprised of paved surfaces that minimize rolling resistance, the continents of the world are also not perfectly flat.  This means that in order to travel at high speed off road, tanks require some sort of suspension or else they would shake their crews into jelly.  If the crew is being shaken too much to operate effectively, then it doesn't really matter if a tank has a high enough gear ratio limit or power limit to go faster.  This is also particularly obnoxious because suspension performance is difficult to quantify, as it involves resonance frequencies, damping coefficients, and a bunch of other complicated shit.
       
      Suffice it to say, then, that a very rough estimate of the ride-smoothing qualities of a tank's suspension can be made from the total travel of its road wheels:
       

       
      This chart from Technology of Tanks is helpful.  A more detailed discussion of the subject of tank suspension can be found here.
       
      The Real World Rudely Intrudes
       
      So, how useful is high top speed in a tank in messy, hard-to-mathematically-express reality?  The answer might surprise you!
       

      A Wehrmacht M.A.N. combustotron Ausf G
       
      We'll take some whacks at everyone's favorite whipping boy; the Panther.
       
      A US report on a captured Panther Ausf G gives its top speed on roads as an absolutely blistering 60 KPH on roads.  The Soviets could only get their captured Ausf D to do 50 KPH, but compared to a Sherman, which is generally only credited with 40 KPH on roads, that's alarmingly fast.
       
      So, would this mean that the Panther enjoyed a mobility advantage over the Sherman?  Would this mean that it was better able to make quick advances and daring flanking maneuvers during a battle?
       
      No.
       
      In field tests the British found the panther to have lower off-road speed than a Churchill VII (the panther had a slightly busted transmission though).  In the same American report that credits the Panther Ausf G with a 60 KPH top speed on roads, it was found that off road the panther was almost exactly as fast as an M4A376W, with individual Shermans slightly outpacing the big cat or lagging behind it slightly.  Another US report from January 1945 states that over courses with many turns and curves, the Sherman would pull out ahead because the Sherman lost less speed negotiating corners.  Clearly, the Panther's advantage in straight line speed did not translate into better mobility in any combat scenario that did not involve drag racing.
       
      So what was going on with the Panther?  How could it leave everything but light tanks in the dust on a straight highway, but be outpaced by the ponderous Churchill heavy tank in actual field tests?
       

      Panther Ausf A tanks captured by the Soviets
       
      A British report from 1946 on the Panther's transmission explains what's going on.  The Panther's transmission had seven forward gears, but off-road it really couldn't make it out of fifth.  In other words, the Panther had an extremely high gear ratio limit that allowed it exceptional speed on roads.  However, the Panther's mediocre power to weight ratio (nominally 13 hp/ton for the RPM limited HL 230) meant that once the tank was off road and fighting mud, it only had a mediocre power limit.  Indeed, it is a testament to the efficiency of the Panther's running gear that it could keep up with Shermans at all, since the Panther's power to weight ratio was about 20% lower than that particular variant of Sherman.
       
      There were other factors limiting the Panther's speed in practical circumstances.  The geared steering system used in the Panther had different steering radii based on what gear the Panther was in.  The higher the gear, the wider the turn.  In theory this was excellent, but in practice the designers chose too wide a turn radius for each gear, which meant that for any but the gentlest turns the Panther's drive would need to slow down and downshift in order to complete the turn, thus sacrificing any speed advantage his tank enjoyed.
       
      So why would a tank be designed in such a strange fashion?  The British thought that the Panther was originally designed to be much lighter, and that the transmission had never been re-designed in order to compensate.  Given the weight gain that the Panther experienced early in development, this explanation seems like it may be partially true.  However, when interrogated, Ernst Kniepkamp, a senior engineer in Germany's wartime tank development bureaucracy, stated that the additional gears were there simply to give the Panther a high speed on roads, because it looked good to senior generals.
       
      So, this is the danger in evaluating tanks based on extremely simplistic performance metrics that look good on paper.  They may be simple to digest and simple to calculate, but in the messy real world, they may mean simply nothing.
    • By Collimatrix
      Since we've got the new AFV design competition going and not everyone has solidworks, I thought I would share this information from Technology of Tanks so those who do not have CAD/CAM programs could come up with a reasonable accounting of what a tank ought to weigh:
      -Armor usually contribute between 35% and 51% of the total mass of the vehicle. The lower figure is typical for light tanks, the higher for MBTs. If the armor were reduced to the minimum necessary for structural purposes it would still be about 20% of the total mass. The highest figure on record is 57% for the armor of the IS-3.
      -The tracks contribute about 8% to 10% of the mass of the vehicle in the case of steel link tracks. On a fast track-laying combat vehicle the tracks are getting slung around over all sorts of rocks and whatnot, so they need to be tough, which means that they're heavy. Band tracks weigh 25%-50% less than steel link tracks, but band tracks can only be used on lighter vehicles. The heaviest vehicle I know of that uses band tracks is the Turkish Tulpar IFV at 32 tonnes.
      -Suspensions contribute about 8% to 10% of the total mass of the vehicle. Hydropneumatic suspensions are the lightest, but not by an enormous margin. Higher performance suspensions weigh more.
      -The power pack, that is the engine and the transmission together, account for about 12% of the vehicle's mass.
      -Guns typically contribute 3% to 7% of the total mass of the vehicle, although cramming the very largest gun possible into the very smallest tank possible can bring this up to about 10%.
      -Ammo generally weighs less than the gun. Fuel weighs about the same as ammo.
      On any fictional or notional tank design, I'll be looking to see if the weight of the components are within these bounds. If they're not there had better be a damned good explanation.
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