Another AFV design question

Why is is it that most tanks are designed in 3 compartmants with the engine in the rear, the gun, gunner, commander, (loader) in the middle and then the front with the driver, radio operator. If the engie is in the back why on *most* tanks are the drive sprockets on the front???

This means the transmission has to go all the way through the vehicle and more impartantly goes under the main weopen which adds to height, surley there are massive advantages in driving the rear sprockets?? dispensing eith all kinds of prop shafts, getting rid of a whole shed load of weight, making less sensitive componants, creating more space for amunition/fuel.

Kev

 

The Commander, Gunner and Loader are normally in the center of the vehicle. This is because that is where the turret is.

The driver and in older (including WW2) designs the radio operator are in the front. Normally this is the same compartment as the 'fighting compartment' where the turret is.

The engine is (on most designs) at the rear with the drive from the gerarbox direct to the rear sprockets. These are the drive sprockets. The tanks that do have front drive are disadvantaged by the transmission taking up space but are at an advantage because the steering system is simplified.

That is the most common design for tanks, but as with many things there are as many designs as there are tanks.

 

Hi Kev,

Except for Churchills, the purpose for using forward drive sprockets was to lay down track faster than could be done by rear sprockets - when braking tracks, this ensured a slightly speedier turn.

The Churchill, by contrast, mounted a sophisticated gearbox which eliminated the necessity of braking a track. When turning to the port, laying the starboard track was speeded up while correspondingly slowing down that on the left side - and vice versa. Perhaps even more significant, when in neutral the Churchill could turn on its own axis - one track being laid backward the other at the same speed forward.

In Africa, when we received a few Shermans (pending subsequent delivery in Italy of Na75s) tests showed, at equivalent speeds, Churchills effectively turned almost twice as fast as did the American built tank.

Also significant, the absence of a drive shaft made for an easier bale-out by the chaps in the forward compartment.

Sadly, the designer of the Churchill gearbox did not live long enough to see it become the post-war standard.

Cheers, Gerry

 

Hi Kev,

Except for Churchills, the purpose for using forward drive sprockets was to lay down track faster than could be done by rear sprockets - when braking tracks, this ensured a slightly speedier turn.



So there are handling benefits to have forward driven sprockets? Would it also effect the suspension?? from sprockets the slack run is under the wheels while the tight run is on the track return rollers?? Rear drive would mean that when you poor on the gas the tight run is on the wheels which would be pulled up and compresssed??? or would be negliable.

Why are front sprockets faster???

Both UK and US school of thought seem to favor front sprockets while German and Soviet have a mixture.

Had a read in my books about the Churchil drive, not much explanation, do you know techincial details? SDounds like it had some sort of limted slip clutch that allowed the tracks to run at different speeds? Instead of just simple clutches like a bulldozer?

Kev

 

Not WW2, but don't Israeli tanks, or didn't they?? have their engines in the front to provide extra protection for the crew because a round would also have to penetrate the engine to kill the crew?

Thought I heard that somewhere.

 

Hi Kev
So there are handling benefits to have forward driven sprockets? Would it also effect the suspension?? from sprockets the slack run is under.


The slack is never on the ground. I well recall, during training at 51st RTR, Warminster, for our instructor asking for volunteers to put a foot between track links - a few did, I wasn't brave enough!
Why are front sprockets faster???

Given equal sprocket speeds, the front one lays the track a few seconds faster than does the rear mounted one.
Had a read in my books about the Churchill drive, not much explanation, do you know technical details?

The co-ordinated speeding up/slowing down of tracks was done through a series of epicyclic gears. The story I heard (not confirmed) was that the chap who designed the gearbox suffered a serious mental breakown which contributed to his early death. On my return home in May I will dig out more specific info for you.

All the best,

Gerry

 

thanks Gerry

 

A frontal engine would seem to give thebest of both worlds with all the advantages of a compact power train and front drive.

 

Your gearbox is in the front anyhow, you lose that and your motor is useless.

Also you have your driver up there too, also pretty sensitve bit of equipment.

Kev

 

no I think the "Merk" is the only one VP. Cant think of any other one. What about the French AMX range?

 

driver's gotta be there, no choice, the engine's such a big target that any kind of strike on it could disable a small but significant part, hence rear-mounting makes big sense, much easier to place extra armour round a gear/transfer box without too much weight gain. I'm trying to think of an MBT other than the Merkava that went for front-engined?? anything other than conversions spring to mind?


Surely its the outer hull thats armoured not indiviual componants. Any breech to the front hull is gonna take out some vital componant, gearbox, engine, driver, etc. To protect a rear engine front drive power train has got to involve more armour than front drive/front engine. I seen no disadvantage of having the motor up there rather than having it in the stern and lots of advantages. Off the top of my head..

No prop shaft along the thinner more vulrenble armoured belly
better weight distubution with main armourment in the rear compartment and power train out front
Reduced power loss
Less weight
less complexity (increased reliability)
Lower turret profile since no power prop shafts beneath the basket.
More internal volume for fuel/rounds/armour
increase frontal Protection for crew (at least not inc driver)
Production savingsd

Disadvantages

Less volume for power train
More difficulty maintainance due to Less space
Non standard design. bespoke componants for increased cost of manufacture.

dunno I think the design has merits.

Kev

 

Maybe not then, but there is a big disadvantage now. Front mounted engine interferes with thermal imaging and targeting systems due to the heat signature off your own engine.

But like I say, that's now not then.

 

Not an MBT but is the CVRT, scimitar/sabre etc. front engined?? been looking at pics and can't decide if it's in the front or low at the back??


Yes it is. up front next too the driver. Amazing little thing those, I couldnt beleive how small it was at Bovy next too all that other kit, must be really hard to hit

 

But, when it is hit.... the armour is aluminium alloy (aluminium burns at high temps) and the driver and commander sit on the fuel tanks. As a slight improvment all CVR(T)s have now been changed from petrol to diesel engines, and diesel is less combustable than petrol.

However in doing so they took away the major advantages of the CVR(T)s in the recce role..... they were so quiet you could drive really close to the enemy without being detected by the noise, and they were really fast. Now you can hear the them a mile off and they are slower without their petrol Jaguar engines.

Oh well, that's progress for you.