I was looking at some pictures of the MBT-70 and I was impressed with how short the thing was. Clearly, moving the driver under the turret armor allows a lot of hull height to be lost.

Alas, there are issues with the counter-rotating driver's seat. Because the driver wasn't centerline they experienced some disorientation. This was fairly widely reported.

Less widely reported, but no less obvious is the fact that a counter-rotating driver's position in the turret requires more volume than a fixed one because the driver is rotating relative to the interior of the turret. Therefore there must be room for the driver's legs as they sweep around in a circle. This problem increases if one wishes to have the driver in a supine position to reduce the height of the driver's station, as the circle they describe in the turret will be that much wider.

So, what can be done?

For starters, something has to be done about the gun breech. In all current designs it occupies most of the center-line of the turret, which is right where the driver needs to be. Non-recoiling mounts have been tried a number of times; not to any great success but perhaps the reduction in hull height would finally make them worth it.

The gun could simply be moved to one side or the other of the turret, though this would tend to torque the turret during firing .

Conceivably, the hydraulics and springs of the recoil system could be shoved out the front of the turret, and only the very breech would intrude. This configuration would make the gun more vulnerable, but would allow enough room for the driver to sit center-line and furthermore would allow a considerable increase in gun depression.



Thoughts?

I'm personally not certain of its worth. As you've tried to explain, there are too many issues behind moving him into the turret. After all, even RRoan kept her driver in a traditional supine position in RRoantank.

One problem I might see is that a shorter tank is not necessarily a better one. A shorter vehicle means that surface area of the tracks is smaller and thus the ground pressure for the same mass is going to be greater. Also the ratio between the length of the tracks and their width will be smaller thus making your tank less maneuverable.

True, though not necessarily you think so.

Here are some comments based on the S-tank and its short tracks.

But it will also be lighter du to being shorter and due to having a smaller protected volume, So the net difference won’t be too bad. Note that compared to the S-tanks turret-less design you will not save that much weight but the S-tank had way shorter tracks than its body for reasons I will mention later. And since it is even more extreme in its short trackedness It can still serve as a example of what short tracks result in.

Actually the reason the S-tank had so short tracks was because a turret less design needed to be more maneuverable (they are useful during normal turns and during clutch brake 180 “skids”) There are however maneuverability downsides to shorter tracks to, the biggest problem for the S-tank (And the one that has be criticized in the Swedish military) was crossing wide ditches (worsened by the pointy front, but helped by the suspension) the only way to cross them was to hit them with high speed and an angle. Other than that the strv 103 did fine with its short tracks and it was almost impossible to throw a track now matter what you did with them (parially due to the suspension) still compared to the Centurions also employed by Sweden at that time the difference is staggering.

By "height" I meant length from the ground to the top of the commander's cupola, but I suppose hull length can be trimmed somewhat as well.

Was what I think purp was on about.

As to what can be done turret wise, you could perhaps do something with an oscillating turret. But that would probably be best on a lighter vehicle (the one on the AMX-50 became so damned high)

Why do you need to counter-rotate the driver?

Would it not be easier to provide cameras and a counterrotating periscope mechanism so they can see whats in front even if they are facing 90 degrees off axis?

I suspect it would be nauseating to "look" in one direction while facing another.

Prevents the driver from suffering desorientation. I can imagine that after a while, a driver would seriously mess forwards and backwards up, even though the camaras show otherwise.

If the driver is located centreline of the turret ring, and if his seat is fixed to the chassis, and if he only uses cameras for orientation, then I do not see any problems. But it would still use up space, at the place where most of the tank's internal systems are placed. And it would be somewhat overcomplicated too.

A turretless tank would be a good alternative, IMO.

The hull is about six inches shorter than the Abrams' hull... which is exactly the height savings you would get by using hydraulic suspension instead of torsion bar. The driver placement doesn't have anything to do with it.

This is all wildly overcomplicated and totally unnecessary. A supine driver in the hull and gunner+commander below the turret ring coupled with a hydraulic transmission will get you the smallest possible profile (unless you put all the crew in the hull, but then you're sacrificing side armor).

Horrific disorientation due to the mismatch between what the eyes and inner ear are reporting.

Um, no. There's no effing way the torsion bars are six inches in diameter. There's also no way that they're pushing the hull up by six inches either; they're not completely wasted height as there are auxiliary items nestled in-between them. Also, if that were true then why isn't the challenger 2 any shorter than an abrams? If you measure the height of the engine decks, maybe, but that's nonsense for painfully obvious reasons.


If you look at this cross-section:

http://www.fprado.com/armorsite/MBT_70_PIC...yout_big-01.png

You can clearly see that the hull was supposed to be lower even than a supine position would have allowed.

Doesn't help the driver much.

Really the only way you can pull this off is if the driver is in the rotational centre of the turret. How you do this while leaving enough room for the gun to operate AND still reduce the tanks size IDK.

It just isn't a very good configuration. It also maximizes the chance of losing the entire crew if the turret is penetrated. And guess where top attack weapons usually hit...

Available internal height in the MBT-70s hull is actually the same as the Abrams. Supine driver really does fit there.

The engine is the single biggest driver in hull height, as you need to fit a lot in.

The torsion bars aren't six inches... but their housing is. If you like, I can start quoting Hunnicutt as I believe he had a few sentences on exactly this issue in Abrams.

I scaled the available height in that picture (~775-790mm), which is, by coincidence, just about the exact same height that the driver of the Abrams occupies from the base of his seat to the top of his helmet. Recline him a few more degrees and the driver will be plenty comfortable.