My Beaut Aussie Cent

[Fabrice Le Roux]

Good refs, Stephen,
Worth checking by direct measurement as you say. Problem with the PRO is the exorbitant photocopying charges, but may be worth a visit. Bet TM has the relevant docs tucked away in some cardboard box!

Spent several hours measuring the TM's AVRE 105 "44BA17" in July. Very illuminating, eg had failed to appreciate that the later six-hole idlers (very similar to Chieftain/Chally pattern)are assymetric, the outer wheel being much thicker than the inboard. Though the holes appear to be bored from the horizontal, as opposed to perpendicular to the dished face as per your Comet units.

AVRE 165's at Duxford and Gillingham are next recce targets, but the TM archive is always worth the trip.

Cheers, Fabrice

[David Skeldon]

Hi,
Found these photos of the extra armour.

David

[Stephen White]

David

Thanks for the pics, very useful. I've found another source (next post) which says that the original glacis is 76mm thick and that with the applique, the thickness increased to 120mm, putting the applique at 44mm. I'll go with that until I can measure directly.

Regards. Stephen

[Stephen White]

Looking for suggestions for Christmas? Here's an idea. This arrived in the post from Australia:





It's just been published. Bruce Cameron commanded the last Centurion troop in action in Vietnam before Australia pulled out its tanks. He's written the definitive history of the Royal Australian Armoured Corps in Vietnam. It is certainly not a dry history. Bruce has spent more than a decade collecting photos and anecdotes from fellow crewmen and the two books cover the whole period of Australian armour in Vietnam. The publisher's blurb is quite long, so here's the link to one bookseller:

http://regimental-books.com.au/canister ... -2071.html

Here's a page to get a flavour of the action:



Armour was very successful in Vietnam, contrary to the expectations of many. If you tire of reading yet another account of Tigers at Kharkov or Shermans in Normandy, this is something different. Bruce Cameron has written it is such a way that the experience of tank warfare in the jungle really comes across. It's a cliche to say that I haven't been able to put it down.

Although I got my copy from Aus, I gather from the author that it is to be stocked by the Tank Museum Shop. It's a great read.

Regards.

Stephen

[Stephen White]

Started collecting some figures for the Cent crew and two options for the .30 cal flex MG (commnader's machine gun). The gun was designated L3A2 .30 cal Browning M1919A4 (flexible) in British and Australian service. There are two sources in one sixth, the Soldier Story metal version and a plastic kit by Dragon:







Getting the right clothing for an Australian Vietnam tank crew is a bit of a challenge - Vietnam doesn't feature much in the one sixth figure business.

Regards

Stephen

[Fabrice Le Roux]

Hi Stephen,

Looks like Dunstan may wrong about the applique. It is instructive to see how such small errors just get slavishly repeated .

The painted (metal?) .30 Flex gets my vote. The thicker barrel with twelve cooling holes per row matches the pics. The Dragon kit has ten holes per row, plus different muzzle. Not wrong, just not as fitted to any Cents.

A small additional detail, one of your photos shows a blurry open mag box in foreground with what appears to be metal-linked ammo, rather than the canvas linked ammo in the plastic kit (and sometimes as used by the Britsh Army). This is supported by the photo of "Sleepy" in the section on the .30 Cal Flex MG on page 5 of Steel Thunder site.

I am now wondering if 31/32 Armoured Engineers kept .30 Cal on the AVRE 165 in to the 1980s or if they switched to GPMGs? Any thoughts.

Cheers, Fabrice

[Graham Conabeare]

.30 cal all metal can be found @ Monkey depot

http://www.monkeydepot.com/Rifle_Soldie ... 8-w153.htm

[Stephen White]

Fabrice

Thanks on a number of counts. Not sure about when GPMG replaced .30 as commander's mg - we certainly had turret mounted .30 in our Ferrets into the eighties and I suspect the Sapper AVREs were the same. Haven't been able to find anything on ARSSEPEDIA but did find the illustrated parts list:

http://www.ferret-afv.org/manuals/brown ... s_list.pdf

Some good material if anyone is thinking of making one.......

Regards

Stephen

[Stephen White]

Idlers: which one?

The Cent went through at least three and possibly four types of idler wheel during the period when Mk 5s were in service. To model a particular tank, you really need photos to establish which type were fitted. I've even seen examples of two different types on the same tank, which must have been wearing for the driver, having to make small corrections to direction all the time.

The first and original pattern are known as the "long spoke" type:



These were found to crack in service. In Vietnam, the RAEME craftsmen were not at first able to get access to the British modified idlers and resorted to welding reinforcements on the spokes:



A modified type was then introduced and can be seen on tanks in Vietnam from 1969:



The spokes on the two halves are set apart and so the kit idler might need to be replaced.

The final version reverted to a pattern which had been found to be unsatisfactory on the earlier Comets, as it packed with mud and caused track throwing but clearly the Cent design overcame the problem:



Fabrice - last one for your AVRE?

Photos courtesy of Col Filtness' excellent Steel Thunder web site.

Stephen

[Fabrice Le Roux]

Hi Stephen,

Bear with my inept picture uploading!

It seems choosing which idler pattern to reproduce depends on the location and period of the vehicle being modelled. 1980s BAOR AVREs of 32 Armoured Engineers appear to be fitted with the six hole type. If you come across a cross section in your travels it could be very informative.
Might steering problems indicate a difference in diameter?
The spoked pattern idlers has rims of equal width as the sectioned example at TM shows:

sectioned short spoke type idler

Anyone contemplating reducing the thickness of the spokes of the kit would be well advised to clear it with Mark, as I suspect you might end up with the same cracking issue the 1:1 long spoke pattern had. Perhaps scratch building in steel would be a better option here.
cont..

[Fabrice Le Roux]

The later type is only superficially similar to the unsuccessful Comet pattern. The Comet design had a shallow groove which undercut the rim, preventing incompressible debris from exiting easily and hence lifting the track horns. Stephen included a diagram on page 4 of his Comet build illustrating this. The lack of the depth in the centre groove persisted in the two-part, bolted, short-spoke Centurion idler design, though I suspect the spokes themselves were the weakest link. The six hole design suffers from none of these problems, the groove is much deeper and has no obstructions to the flow of debris, plus there is more metal in the wall of the casting hence it is stronger. It should be noted that the casting is convex in profile rather than concave like the Comet. This adds to the strength. This pic of the Cent ARV at War&Peace demonstrated the way mud gets freely extruded by this design:

Centurion ARV idler CU

Ther is one other very distinctive change that appears in the six hole pattern, but goes on to be included in the Chieftain and Challenger MBTs. That is that the inboard rim of the idler is much thinner than the outboard. The thinner rim does not cover the sprocket holes in the track links whereas the outer does.
cont..

[Fabrice Le Roux]

To wrap up. This view of the TM BARV idler shows difference well:

Cent BARV idler CU

As to why this design was adopted may relate to track failure on cambered roads. This problem is mentioned in one of the references. I hope to look at the papers in the Public Record Office, Kew, in due course.

The position of the steel return roller behind the idler was inboard of the track horns with the earlier pattern, so there was apparently no problem with that part of the track system. The provision of a narrow inboard rim on the idler would permit the track to twist slightly between the idler and first roadwheel, thus conforming to the road camber and reducing the load/wear on the track pins. This is just a hunch and some bright spark may already have better info!

This is also very arcane for a Tuesday morning.

Thanks for reading.
cheers Fabrice

have edited out a few typos!

[Stephen White]

Fabrice, phew! Good technology.

The steering problem associated with having different idlers on the same vehicle was, bizarrely, due to there being a slight difference in outer diameter between the second and third types. There is at least one Cent in Australia on display with two dissimilar idlers.

The sectioned idler in your first post is the second ie modified type, which was introduced in response to the problem of cracking spokes. I'm not clear whether it too had problems but at some point it was replaced with the final dished type late in the Cent's career. Nevertheless, your point about seeking advice from Mark before modifying the kit idler is valid. I'm not sure if I'll machine some new idlers - the kit idler is based on the second type but until I've got better photos of my chosen vehicle, I can't confirm which type to fit. I'm in contact with one of the veterans of Binh Ba, Roger Foote, who has some really good photos of Buku Boom Boom in action at Binh Ba, which should show the detail.

All the best

Stephen

[Fabrice Le Roux]

Stephen,

Going back to the reference photos you posted about 24A "Buku Boom Boom" at Binh Ba, the center hub of the long spoke idler is quite prominent, even in photos where you are too far away to see the detail of the spokes. It just catches the light differently to the short spoke type.

In the photo you cross-referenced by the shutter detail of the village house, probably showing 24A, the tank in the shot has a prominant idler hub, so could well have carried long spoke idlers.

Of course the other undated photos of "BBB" clearly show the early idler present...but you were trying to confirm vehicle details as of the day of the 1969 Binh Ba action. Other photos, notably 1971 "Lolita" Mk5, show the short type in Vietnam. It will be handy if you can locate dated photos that bracket the action and confirm which type were on 24A.

I can recommend a non-ferrous foundry near Hersham, if you wanted to bite the bullet and cast a robust 1/6th long spoke idler in bronze from a pattern (wood/plastic/alu)? You would only have to make the pattern once (even if it was in two parts) and it would look the proverbial dog's...

Cheers, Fabrice

[Stephen White]

Bingo on the glacis plate - how thick is the applique armour? This is from a 1956 report in the National Archives:

"Following a request by DRAC for an investigation to improve the immunity of the glacis plate of Centurion tanks Marks 3 & 7, a scheme was prepared in which a singles 44mm plate could, after removal of certain fittings, be welded in position to increase the overall thickness from 76mm to 120mm."

So the applique was 44mm as we thought. When the test establishments did some proof firing with 20 pdr APDS at Shoeburyness, they found a surprising result:

"The critical velocities obtained for the 3in thick plate with and without applique armour were the reverse of those expected in that the CV of the two plates in contact was higher than that of a single plate of equal thickness."

The improvement in performance with the applique armour was very significant:

"From the limited results of these tests it is apparent that immunity against kinetic energy projectiles will be obtained at considerably reduced ranges eg against 20 pr shot the estimated minimum ranges are:

76mm (normal glacis) 20 pdr APDS 4,400 YDS
76mm + 44mm applique plate 850 yds"

Some further tests were condudted with a space armour array but it was found to obscure the drivers view and didn't improve protection. It was thought that the spaced armour would increase protection against HEAT and HESH but the standoff wasn't sufficient to be effective:

"Further tests of a spaced armour array revealed the vulnerability of all three variations of glacis to 90mm heat and 120mm HESH".

This was a portent of things to come in that when Cent was subjected to RPG fire using H/EAT in Vietnam, the armour was penetrated on a number of occasions.

Regards

Stephen