As is known, there was a time (certainly as late as WW2 and possibly later ), when the turrets of tanks merely rested on their turret rings and were not held in place by anything other than their weight. Since nowadays a hermetic seal must presumably be necessary in order to prevent chemical and biological weapon's material from entering the tank, when is it thought that the method of merely resting the turret on the ring was last used ( and on what tanks ? ) ? BG
so how did snorkling tanks work then? The PIV and a few others could actually opperate fully submerged or submerged up their turret ring. So the the weight must be enough to create a watertight seal? FNG
turret seals its simple to use any one of several types of seal to seal the ring. the tonnage of the turret is more than enough to keep it tight. if fact most seals will fail if there is too much pressure on them. next time you get to look at the crank seals of a motor you are looking at the same basic design. as a backup there is also the over pressure system that is a basic part of any ABC system.
Tanks that were meant to wade ashore for D-Day had their turret rings sealed with a caulking "gunk" to prevent ingress of water. IIRC Warrior for the Working Day by Peter Elstob (a novel based on his own experiences) described how much tank crews hated sealing turret rings because the stuff was so sticky and viscous. If that were true then how do turrets turn? There is room between the bearings of the turret race for water (especially at any depth and therefore pressure) to force its way in.
I'm not sure there are any turrets that just sit on top by virtue of their own weight, or at least I can't think of any. All modern tanks I've heard anything about use a ball or roller bearing to retain the turret, as far as I'm aware it was standard practice even in WWII tank. The only tanks that spring to mind that I know don't are the M3 Stuart which uses some kind of fixed rollers rather than a ball bearing ring, and the FT17 which I think rides on top of some kind of bearing but even it still has some mechanical restraints to prevent it being dislodged by enemy fire/rough terrain or whatever. For submerged operation the Tiger (and presumably other German tanks) has an inflatable rubber seal built into the turret ring, I think it's mentioned in the Bovington Tiger restoration. I believe modern tanks use a similar system.
. this doesn't seems right , rought driving would shake anything loose , the weight would keep it in place only stationary , on the move it would actually make it worst the repeated shocks of a few tons landing back into place would shear anything if it wasn't secured . if this is true , my notions of mechanics are to be seriously revised .
. By the way talking of turret rings , I've read that the ring diameter was one of the main limitating factor for upgrading a machine , the PZKW 4 was supposedly designed with an oversized turret ring for this eventuality .
Turret ring fixing I have read nothing here that persuades me that I am wrong in believing that turrets merely rested on their rings, with an appropriate ball race or some other means of easing the traverse. It is correct that turret ring diameter limited the ways of up-gunning a tank, since a larger and more powerful gun would have had a longer breech - which required a more spacious turret. Another fact that underlines the seeming lack of any means of retaining the turret, is the need for a counterbalance at the rear of the turret to offset the barrel length weight. Sure, it is probable that a balance weight would still be needed, even if the turret were secured in place on the ring, but the need for a balance would proportionately be much greater if, as I believe to be the case, no fixing to the ring is employed. BG
a counter balance is needed regardless of securing as if you have a lot of weight on the front it would wear the bearings at the front faster than at the back putting undue and unnecesery strain on the turret ring shortening it's life span FNG
Well I suppose it technically could be done like that however I would be very surprise to ever see it in practice. One of the earliest turreted AFVs is the FT 17 a US version was made, the M1917 see here 5th from the top. The turret apparently does sit on a bearing of some description but the turret is retained by the 7 little "ears" that hook under the hull roof. Here is how it's usually done It's a cross section of the turret ring on the Cromwell. As you can see the turret rides on the ball bearings but they also trap the turret, there is no way to just lift the turret off without breaking something first. Turret balance is a whole other issue. If you use a ball bearing ring race then you are right there is no need to balance the turret, provided it stays on level ground. Put the tank on a slope and the turret will rotate to point the gun down hill unless the gunner or traverse mechanism constantly holds it in position, if it's too far out of balance, well, you better hope your target is down hill I suppose. If you need further convincing just have a look for various wrecked tanks and pay particular attention to those that have been rolled or flipped over as a result of poor driving, or railway loading accidents, or simply being bulldozed out of the way. Note that the turret is usually still in place on the vehicle, if it weren't fixed in some manner it should have fallen off as the tank went over.
AFAIK it's not a barrier to upgrading necessarily but it is a barrier to upgunning a tank. The bigger and stronger the turret ring, the bigger the turret can be made and the bigger and more powerful the gun that can be installed. I'm sure I'll be corrected if I'm wrong, but since the PzIV started out with a pretty large bore gun to begin with it needed a large turret ring from the off, I'm not too sure it was designed with any sort of upgradability in mind.
. thanks Simon , the upgrading could be only on barrel lenght , by the late 30ies 75mm was huge as for the recoil force I would think the power of a gun is proportionnal to its propeling powder charge ( explosive pressure ) by its caliber diameter a large , low velocity shell could have a lower recoil that a smaller bore with a heavier charge and a higher muzzle speed , the "grain" of the load would matter too, if the barrel is long a slower burning charge might be required giving a quite different recoil . .
Actually there is a need to counter-balance. Bearing useful life (L50) depends upon loading - if the front of the turret ring is more heavily loaded than anywhere else the bearings will fail that much quicker. In addition to which unequal loadings will affect the rotational inertia and cause slippage and/ or lag. Correct balance is essential. It's not so much the strength of the turret ring as internal size. There needs to be enough room inside the turret to allow for full recoil, and for loading a round into the breech (i.e. internal gun length, breech length + round length) even if the gun is elevated.
. that make sense , the self propelled guns got rid of the turret limitations and the same chassis got massive increase in caliber .
Turret retaining mechanism. Hi Gryle, Thanks for the useful and convincing turret ring diagram. I guess that this does confirm the existence of some sort of mechanism for the purposes of retaining the turret on it's ring. Funnily enough, though, your comments re those tanks that have had accidents etc. and still retain their turrets - it was the fact that there are so many tanks seem to easily lose their turrets that gave me to believe that perhaps NO such mechanism is employed. Cheers BG
The turret retaining ring is designed to take a steady known load in particular directions - heavy shock loading (such as an internal explosion or getting hit with a large-calibre AT round) will overload the ring and break it. There's only so much that mechanical design can cater for. If the retaining ring was designed to stay in place during such loading then it would be far larger and far heavier - thus losing some internal capacity in the vehicle and adding weight.
