Landships II

Mark Hansen · Legend

A weighty problem...

Centurion · Legend

Is that the longtitudinal centre line or the lateral one?

Mark Hansen · Legend

That's the longitudinal centre line. Fore and aft the weight is fairly well balanced.

Centurion · Legend

Sounds like the difference between male and female sponsons on a composite? I think the answer must partly depend on the characteristics of the tank in question, for example does it have suspension or unsprung rollers? In general when a tank turns it has to overcome a friction drag on the tracks on the side of the turn with the slowest moving tracks which must be influenced by the weight on that side (especially if turning is made by stopping the tracks on one side). I would have thought that if the weight was greater on say the port side then turns to port would be slightly more difficult and vice versa.

Mark Hansen · Legend

It is indeed the difference on a composite! I was wondering whether this would increase the steering problems on a Mk V* (as if it didn't have enough!) which had been converted to a composite. Also whether a standard Mk V would also have steering difficulties from having mismatched and therefore unbalanced sponsons. The figures I used were from "The Devil's Chariots" converted to metric figures (never have been really comfortable with imperial; metric was introduced while I was in primary school).

Pody · Lieutenant

Hello Mark!

When serving in our forces(Bundeswehr)the M113 tank has been converted from a
450 Kg Petrol-engine to a 730 Kg Diesel aggregate. These 280 kg had a severe
result in maneuverability of said tank. The engine compartment is in the front on
the right side, the driver sits to the left of the engine.
With the petrol-engine the M113 drove nearly straight ahead due to the ratio of
62 track-pads left to 63 track-pads on the right track.
With the diesel engine you had to jerk permanently on the right steering stick to
compensate for the tanks tendency to drive in the ditch. I hated this piece of sh..

Later the differential-gearboxes where adjusted to compensate for this faulty
driving behaviour.

Best regards,

Pody

Centurion · Legend

Pody and Mark

An interesting observation that suggests that the asymetric weight distrubution affects traveling in a straight line. In the case of the Mark V* the extra ground contact made it difficult to do anything but travel in a straight line so the asymetric effect in a composite configuration might be less noticable when going straight but and make turning in one direction easier and more fificult in the other. One wonders if it would be even noticable if applied to a Mark V* Tapole (one of which was assembled at CW) as turning this was almost impossible anyway.

Mark Hansen · Legend

Thanks Pody and Centurion

I thought it might make a difference but not being a tanker or engineer, I didn't know for sure. It seems as if it might have affected a standard Mk V more than a V*.

The Mk V* tadpole - is there a photo of it anywhere? That and the Mk IV testbed for the Mk V* are two tanks I would really like to see, even if only in a photo.

Centurion · Legend

Mark

Looking at the number of photos of tanks with roof loads piled on any whichway I suspect that the old rhomboids of all Mks were not very sensitive to asymetric loading unless it was particulary gross. If they were male tanks would be prone to develop left or right handedness depending on which sponson had fired most rounds. And looking at the cutaway of a Mk V it looks as if the internal weight distribution must be skewed given that the radiator and water tank are on the starboard side (unless there was some internal 'ballast' weights to compensate which would be a solution to the composite issue as well)

I'd like to see those photos, if they exist, as well. There is only a text reference to the MkV*Tadpole - I suspect it was another of Johnson's semi unofficial experiments just like the Mk IV cut and shunt. I did post my attempt at a drawing - here it is again (but I suspect I've got the gearing coverplates wrong).

http://img.villagephotos.com/p/2005-11/1114252/mkvstartadpole.jpg

Centurion · Legend

Looking at the subject of weight distribution further there are some interesting questions about the effect of changes in the longitudinal centre of gravity. The trench crossing ability of a tank would depend not only on the length of the tracks but also on how far over a gap the forward part of the tank could protrude before the vehicle began to tilt forward and start the process of ditching. An article written by a member of the Tank Corps in 1919 suggests that one reason why the gun carriers were so infrequently used to actually carry guns is that with a heavy artillery piece loaded the centre of gravity was too far forward and this caused the carriers to ditch too readily. When I see photos of Mk Vs with a crib and two trench bridges carried well forward I wonder if this had any adverse effect on the tanks� performance.
However I suspect that fuel consumption may have had a more noticeable impact. The external fuel tank at rear of the Mk IV and V when full must have had a considerable weight and an impact on the position of the CoG. However as fuel was consumed (and those tanks were real gas guzzlers) the tank would become lighter and the CoG would move forward. Is there any evidence of an increased incidence of ditching the longer the tank had been in action?