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Posted

Looking at 'Mr Hewes' on Youtube, who restores Chieftains as well as Centurions, I think he would underline that Centurions are more difficult to service. He likes them, but nobody else in his team does. :D

Im wondering if the high fuel consumption is down to unfamiliarity with driving it.

Posted
1 hour ago, Junior FO said:

Measured values vs.  regulation values pages 3-4

The measured M47 had considerable differences to it's book values. Engine HP, but also some of the armour, notably on the side and back, gun depression, turret yaw/elevation speed and even a 10cm difference in chassis length.

Interesting report, appreciate the translation. The M47's TM does list gross horsepower and torque values:

Rh06WQS.jpg

 

Also, the January 1952 edition of the TM indeed says the maximum gun depression is -5 degrees, but this was corrected to -10 degrees in the first change to the manual (the preliminary manuscript of which was published in April 1952). Interesting that the Swiss apparently had the old information.

XIVNtQE.jpg

Posted

great report, thank you!

 

vwY-1_VicMo.jpg?size=1332x1904&quality=9

 

is this also from some of your research ?

from reddit, but can't see link in comments

 

Posted
6 hours ago, Junior FO said:

Switzerland held trials with 2 Centurion Mk. III (leased) and 2 M47 (bought) from late1952 to early 1953. The 2 M47's seem to have gone to Germany in return for their 4 Cents.

https://ufile.io/dgbbm1s0

Full report

https://ufile.io/cmwlnc2e

Extra details on mobility portion, details on slope tests, road tests, track performance etc.

 

Measured values vs.  regulation values pages 3-4

The measured M47 had considerable differences to it's book values. Engine HP, but also some of the armour, notably on the side and back, gun depression, turret yaw/elevation speed and even a 10cm difference in chassis length.

M47 paper HP value of 820 seems to have been raw HP. The measured brake HP for both tanks was much closer than paper values with 590 ( manual 650) for the Cent III and 680 (manual 820) for the M47.

Measured Petrol usage was higher for the Cent III 500l/100km road compared to it's book value of 400l, while the M47 used considerably less than it's book value with 550l/100km road vs it's book value of 700l.

 Regarding climbing there might be a mistake in the table for the M47. It failed the 68° climb test (see second document) and due to the reason for the failure, slippage in the hydraulic transmission, it seems unlikely it succeeded elsewhere nor are additional climb tests mentioned anywhere.

 

Maintainability

Cent III

Cent III notably more difficult to service.

Carburettor needs 3 hours and nothing can be adjusted, sparkplugs need 2 hours etc. Magnetos, Petrolpump, Oilpump, Starter difficult to get to.

Waterpump, clutch, transmission, brakes easy to access, transmission is easy to remove. Removing all modules takes 3 men 15 hours with many small connectors that need to be removed/loosened. Mounting everything takes 3 men 30 hours and needs skilled workers, again due to number and complexity of connectors.

Rear drive wheel deals with dirt very well, but can form ice and throw track due to build up.

The raodwheels are under very heavy pressure with 2100kg, which should result in a lot of wear on the rubber. Rubber is compressed down to 37mm/125mm from 53mm/115mm. (I saw a document with UK expected 6 month war usage, I think it was 25 wheels or so per tank, of course can't find it anymore)

Ventilation with air from the engine room is adequate with closed hatches, but inadequate without. (Using coax with open hatches led to some cases of CO poisining early in Swiss service. UK regs do state hatches need to be closed)

heater might as well not exist with open hatches.

M47

Easy to service.

Motor can be removed very quckly and can be connected to tank via cables allowing test running even when outside of the tank. Removing all modules takes 3 men only about an hour, remounting takes 3 men about 3 hours.

Carburettor can be adjusted without having to dismount motor. Sparkplugs easy to replace, Magnetos easily accessible.

Petrol pump and starter and dynamo difficult to access.

Rear drive wheel with bad shape. Not very good dirt performance and bad with Ice/snow build up. Reverse turn in slight slope with deep snow throws track.

Rubber on inner wheels get very hot after a while, with 70C° at external temp of 18C°.

Rubber track pads erode quickly with 2cm thick profile pretty much gone after 1000km. Steel track tear up roads badly due to agressive profile and very high ground pressure of 90kg/cm2.

 

Mobility

Centurion III page 18

Rollresistance, speeds in different geaes and brakepower, turn radius in different gears.

A perpendicular to 55% is determined as being fine. (but in actual test Cent is noted as having a tendency to slide, which seems to contradict this, see below)

Graph on page 19 with acceleration and rollout performance.

Petrol usage with Swiss driver 700l/100km road, with English driver 550l/100km. On flat (25km, hightdiff 275m) average is about 440l/100km, on "Mountain" stretch (19km, hightdiff 600m) 620l/100km.

General notes

Due to breadth of the vehicle, but especially due to each gear having a fixed turn radius, somewhat difficult to drive and high average consumption.

Before each curve, the driver has to estimate which gear will be needed. This leads to drivers erring on the side of caution, especially if road is can not be fully overseen. This in turn leads to drivers often going into low gears and low average speeds when navigating curves.

Long delays when changing gears also leads to drivers opting for lower gears when climbing slopes, since he would otherwise have problems recovering from choosing a too high a gear initially.

Good visibility for driver when seat fully elevated though a centered driver position would be prefered. When buttoned up visibility is unsatisfactory. The 2 movable episcopes are not practical since both of the drivers hands are occupied.

Good cross country mobility, even in swampy or snowy conditions. It feels as if the Motor is providing more power than its rating.

Track configuration is not good for sideways stability which is shown when driving canted or in snow/icy conditions. This is due to low 20kg/cm2 pressure which is good for summer and helps prevent road damage but insufficent for winter.

Nothing good can be said about the cooling system. 95C° even on cool days means temperatures in Summer conditions must be expected to be very high even though system allows a max temperature of about 115C°.

No mechanical faults, factory new vehicles.

Gears

4% climb 5-4th

15% climb 3->2nd

can't go from 2nd into first gear as delay is too long. One needs to come to a complete stop. Same for going from 1st into 2nd gear. At 12% a good driver can still go from 2nd into 3rd gear without losing too much speed.

 

 

 

 

More later.

 

Well, I can't read Swiss :(

Posted
12 hours ago, Wiedzmin said:

is this also from some of your research ?

from reddit, but can't see link in comments

 

Many people apprently do. The comment is there, it was not deleted, just for some reason hidden by reddit from everyone.

 

 

 

 

image.png.7ee20206041a4eabb857ebef59f35070.png

 

I'll post the links in this thread and direct people here instead:

https://mega.nz/file/GThCCYIS#Um8-V3PiijW7ijJhgV3N7GseXzs6KPXGNTEbOPQOITg

https://mega.nz/file/OfYglRyB#C00b8hHINNS7qQ0OMqOsMdhHE75-G5LO6T1lVEjRzho

https://mega.nz/file/6bZXCAab#0goUQu4S6dveHm_ALrK4oRkoUJjFHD_aq-l2HWApSh8

Posted
20 minutes ago, Stuart Galbraith said:

But have we anyone that translate American to English? :)

 

American is the accurate and proper English best spoken by Hoosiers, those esteemed and elite citizens native to the phenomenal U.S. state of Indiana :P

Posted (edited)

Linguistic bragging rights aside, for some reason I am unable to translate the full report from Swiss to Hoosier, er, uh, English.

Edited by Rick
Posted

You have to copy  and paste individual sections, and paste the english take together on notepad to get it to work. Its cleary working here, perhaps there isnt a field for Hoosier. :)

 

Posted

I wanted to compare the performance of 20pdr APDS with that of it's predecessor, the 17pdr.

There doesnt seem to be a significant proportional difference, except for very thin plates (60, 40 and 30mm) at very high obliquity. I've noticed that these plates used in this trial are VERY hard. 150kg/mm^2 is about 416 BHN and others are ever harder (200kg/mm^2). I've seen such hardness levels only in the outer hardened layer of face-hardened armor, which is what I believe these plates to be. This has probably decreased their effectiveness at deflecting shells at high obliquity and inflated the effectiveness of the 20pdr against them. Homo plates of same thickness would probably be defeated only at lower obliquites.

 

20pdrvs17pdr.thumb.png.2dbe72df78d78c1cad7c8f0fcb41e4df.png

Posted

Ive a very vague recollection that when Bob Griffin wsa looking into this, he said he found in the records (which were still somewhat classified at the time) something like the ability to penetrate 230mm at 2000 yards. Perhaps the case that all the 20 pounder did was sustain similar penetration performance to 17pdr out another 1000 yards. Which would perhaps explain the desire to move onto the 105mm.

Posted
6 hours ago, Stuart Galbraith said:

But have we anyone that translate American to English? :)

 

Sorry, you’re out of luck there.

Posted (edited)

It is interesting to compare this data with data posted in this thread here.

Quote

84 mm APDS M3 - v1000=1308m/s

287mm@0°

226mm@30° (LOS 261mm)

162mm@45 (LOS 229mm)

92mm@60° (LOS 184mm)

Note: assuming the distance is in yards, the muzzle velocity required to obtain the s.v. of 1308m/s is 1487m/s (4880fps)!

 

Quote

Armor Field Forces Boart No. 2 [Ft Knox]

Report of Project No. 1406 Mar 14, 1950

Test of Medium Tank, M26E1, with 90mm gun T54E4

This is a strange little test, done by Ft Knox “…to confirm, by test, the results obtained by Aberdeen Proving Ground; to make a further study of the fightability characteristics of the tank mounting this gun; and to perform limited armor penetration tests for comparison with the 20 pounder gun, Mark I (Centurion III), and the 105mm gun, T5E2 (Heavy Tank, T29).”

 

The refs show the pilot M26E1/T54 mating was approved 14Jun45, the gun being approved for development the same date. The ammo development appr 13Sep45.

 

The tank differed from the M26 in turret fittings only, introducing the gun in combination mount T126. Coax is .50. The use of the longer fixed piece ammo [replacing the semi fixed of the Super Pershing of 1945 fame] reducd stowage from 70 to 41 rds. The T54E4 was developed to replace the T15E2 in the T26E4 [“Super-Pershing”] to overcome disadvantages of separated ammo. A bore evacuator is also fixed. The shorter fixed 90mm round was obtained by increasing the chamber diameter and reinforcing it with a long breech ring. The completed tank was shipped to Ft Knox Feb49 for limited service testing.

 

20 rds fired at 2000 yds for accuracy testing, no significant variance from accepted standards for 90mm guns.

 

Penetration test at 1000 yds vs. 4 inch homogeneous armor, Brunel 230 at 48-60 degrees. Penetration achieved at 49.4 but not greater inclination. Performance approx equal to 105mm T5E2 and “possibly somewhat inferior “ to 20 pdr.

 

Data: 90mm T54E4 is 66 calibers long; ME is 1713 ft-tons, Max Ch Press 40,000 psi. Rifling 1:32 calibers, 32 grooves. Test ctg was AP-type 3200 fps M.V. [T48E1 HVAP for 90mm T54].

 

Penetration testing:

Comparisons to other guns via previous firing data, as not available for shoot-off:

105mm HVAP vs. 4-inch plate 47 degrees at 1500 yds = complete penetration

20pdr APDS vs. 6-inch plate 46.3 degrees at 750 yds. = complete penetration

 

noted hits by 90mm T48E1 HVAP, all at 1000yds:

 

1 - 59.2 % tube wear 60.3 degree impact no pen; no bulge in rear; 3” gouge.

2- 61.2 59 same exc ½” bulge

3- 61.8 52.1 same; hit high on plate

4- 62.5 49.8 no pen; 3.5” gouge, bulge 1” high 6”

diameter

5- 63.2 49.4 complete penetration

6- 63.8 50.5 no pen; 3.5” gouge; 1x6” bulge

 

[Edit to add pics, I am unable to upload:]

http://www.afvnews.ca/pics/pic71095.jpg

http://www.afvnews.ca/pics/pic71094.jpg

Souce: NARA RG127/E162/ box 21.

 

Note: the s.v. at 1000yrds for the 90mm M304 HVAP shell fired from the long 90mm at 3750fps is 3270fps.

In the Swiss trials the 28.1.53 test with 90mm M304 HVAP at s.v. of 1002m/s(3287fps) shows one PP against 100mm/55° plate and one CP against the same plate at 50°, which fits with the data above.

 

Edit: Hold one, here is another interesting tidbit: the 20pdr APDS projectile in the 1952/53 document is NOT the Mk.3 shot. The core has the same shape, but the carrier is different. 

Quote

image.png

 

Edited by Peasant
Posted

This APDS is of Canadian line, developed by J. A. Caddy. Sabot is one-piece, shot is tappered, hence a bit worse ballistic properties (velocity drop, dispersion) than Mk. 3 with L. Permutter four-pieces petal sabot.

Posted
7 minutes ago, Junior FO said:

Swiss seems to have bought the Mk.3 only in 1956. See attached buying letter from later 1955.

https://ufile.io/36gbrp5i

Very nice. I guess we can say with a fair degree of certainty, that these trials were carried out using only the Mk.I APDS shot.

Posted (edited)

It seems that the design of 20pdr APDS evolved considerably between each model. Here is a comparison of 20pdr APDS Mk.3 and Mk.4:

Quote

Comparsion.png

 

Edited by Peasant

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