Google+ Panzerserra Bunker- Military Scale Models in 1/35 scale: Sherman V “Crab” - Mine Flail Tank
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terça-feira, 31 de maio de 2011

Sherman V “Crab” - Mine Flail Tank

      Hi, Tankers...
            This is my new project: The Sherman V (M4A4) Crab mine flail tank.
Sherman Crab mine flail tank
      To do this beast, I'll use the kit Dragon 6041+ Legend Products LF 1139, in 1/35 scale.
History:
      A mine flail is a vehicle-mounted device that makes a safe path through a mine-field by deliberately detonating land mines in front of the vehicle that carries it. They were first used by the British during World War II. The mine flail consists of a number of heavy chains, ending in fist-sized steel balls, (flails) that are attached to a horizontal, rapidly-rotating rotor mounted on two arms in front of the vehicle. The rotor's rotation makes the flails spin wildly and violently pound the ground. The force of a flail strike above a buried mine mimics the weight of a person or vehicle and causes the mine to detonate, but in a safe manner that does little damage to the flails or the vehicle.
      The idea is commonly attributed to a South African soldier - Captain Abraham du Toit. A test rig was constructed in South Africa and results were so encouraging that du Toit was promoted and sent to England to develop the idea.
    Before du Toit left for England, he described his idea to Captain Norman Berry, a mechanical engineer who had been sent to South Africa in 1941 to evaluate the system. Captain Berry later served in the British Eighth Army during the Western Desert Campaign. He had become an enthusiast for the mine flail idea; he lobbied senior officers to authorize development of a flail and carried out his own experiments with mine flails in the spring of 1942. Later Major L. A. Girling was given the task of developing a similar device after it had been independently re-invented by another South African officer. When Captain Berry heard of this, he handed over his work to Girling (who had had no idea he was duplicating du Toit's current work in England, as that was still highly secret). Dr.David Gustanski made the device that connected to the side of the tank and made the flail go up and down.
      Development by Girling's team in Egypt continued over the summer of 1942 and resulted in the "Matilda Scorpion" (the name came from a senior officer's remark on the tank's appearance).

Matilda mine flail Scorpion
      This was a Matilda tank fitted with a rotor, mounted on two arms, roughly 6 feet (1.8 m) in front of the tank. The rotor carried 24 flails and was driven at 100 rpm by a 105 horsepower (78 kW) Ford V8 engine. This second engine was fitted in an armoured box mounted on the right side of the tank, the outside box included space for a crewman who operated the device. Although the mine sweeping process was slow, the Scorpions raised such a huge dust cloud when used in the desert that they obscured themselves from German gunners. The cloud also blinded the drivers; the crews had to resort to wearing their gas masks in order to breathe.
      Twenty-five Matilda Scorpions, operated by the 1st Army Tank Brigade's 42nd Royal Tank Regiment and 44th Royal Tank Regiments, were available by October 1942 and took part in the Second Battle of El Alamein. German minefields around El Alamein contained around three million mines and had been named the Devil's gardens by the German commander, Erwin Rommel. Breaching these minefields was vital to the Allied battleplan.
      During the battle, the Scorpions were less successful than hoped. While reasonably effective at mine clearing, the hastily developed flail system was unreliable and broke down frequently. Also, there were frequent engine failures as the air filters were overwhelmed by the volume of dust produced by flailing or the engines overheated because of the desert environment. Much of the mine clearing that was critical to the Commonwealth victory still had to be carried out by hand. One unexpected effect was that the noise, dust and terrifying appearance of an approaching flail tank caused several Axis infantry units to surrender without resistance.
      After the battle, a Mark II version of the Scorpion was produced by removing the main gun as that was thought to be redundant. Controls for the flail were moved into the turret so the flail operator could be moved inside the tank, taking the place of the gunner. Engine air filters were improved and unreliable components strengthened. Mark III and Mark IV Scorpions were later developed that were based on the M3 Grant.
George Bradford drawing
M3 Grant Scorpion
      This larger tank was a more suitable mount for a flail than the Matilda and many became available for modification as, by this time, they were being replaced on the battlefield by the M4 Sherman. A small number of these Grant Scorpions were produced and were used during the remainder of the North African campaign and later during the Allied invasion of Sicily.
      Meanwhile, in Britain, du Toit (as unaware of developments in North Africa as they were of his), working with AEC Limited, had developed the Matilda Baron. The Baron's problem was that, like the Scorpion, the rotor was powered by external, auxiliary engines that made it too wide to cross a Bailey bridge and which had to be removed if it was to be transported by rail. Curran Brothers of Cardiff constructed 60 Barons, but they were only used for demonstrations and training.
Matilda Baron in training field
Valentine Scorpion
      A number of experimental flail tanks were produced, including the Valentine Scorpion, based on the Valentine tank and several designs based on the M4 Sherman – the Sherman Mark IV and Mark V Scorpions and the "Sherman Lobster".
Sherman Lobster
     Eventually one of these, the Sherman Crab, went into full production at the request of General Hobart and saw active service.
Gen. Hobart in front a mine flail tank
       Du Toit himself had became a strong advocate of a concept called the Parambulator Mine Flail - a self contained device with its own engine, that could be pushed ahead of any tank that was available. However, the consensus of opinion favored special-purpose tanks with a permanently mounted flail system and he returned to South Africa in 1943.
Sherman V Crab I (early)
Crab in the beach, starting your job...
       Unlike the Scorpion, the Crab's flail was powered by the main engine. In Britain, the time and resources were available to carry out the major modifications to the Shermans' transmission that were needed to add a power take off. For this reason, the M4A4 version was chosen to be converted into the Crab: the powerful multibank engine Chrysler (425 HP) had enough power for the vehicle and for the flail device.
Chrysler A57 Multibank being installed
      This removed a major problem of the Scorpion - the outside auxiliary engine with its vulnerable operator. The Crab's rotor carried 43 flails and was driven at 142 rpm by a driveshaft running down the right hand side of the tank.
      An innovation was the addition of cutters to the rotor that cut barbed wire and stopped the flail from becoming tangled. This feature made the Crab very effective at tearing up barbed wire obstacles. In the initial Crab design, the flail arms were raised and lowered hydraulically to set the height of the flail. The Mark II version of the Crab, developed as "Contouring Crab", switched to a counterweighted jib that naturally assumed the right height in balance to the force exerted by the rotating flail. This ensured mines buried under a dip in the ground would not be missed. The addition of a gearbox was required to maintain the correct flail speed when the tank was traveling slower, such as while climbing. A blast shield between the flail and the tank gave added protection from detonating mines. The hull machine gun was removed as the blast shield and flail blocked its field of fire. The Crab weighed 32 tons,  around two tons more than a normal Sherman.



       Great attention was paid to marking the cleared path through the mine field. Crabs carried a pair of bins filled with powdered chalk that slowly trickled out to mark the edges of the safe route. They were also equipped with a hopper that periodically dropped smoke grenade markers and a system that automatically fired illuminated poles into the ground at intervals. A pair of lit masts were mounted at the back for station-keeping when several Crabs were flailing together in echelon. Dust clouds reduced visibility to a minimum and careful control was essential to make sure the tanks' paths didn't drift apart, leaving an uncleared strip of ground between them.
      In North-West Europe, Crabs were operated by the Lothian and Border Horse, the 22nd Dragoons and the Westminster Dragoons, all of whom were part of the 79th Armoured Division's 30th Armoured Brigade; In Italy, they were operated by the 51st Royal Tank Regiment.  A flail squadron of the Royal Armoured Corps, as established on 29 March 1944, comprised seven ordinary Shermans (Squadron HQ and a four-tank pilot troop) and four troops of four flail-equipped tanks. In July 1944, the new establishment removed the pilot troop and one of the flail troops; on the plus side, the squadron gained an Armoured recovery vehicle. In 1945, in light of experience, each gained a fifth flail tank. Scorpion regiments had been formed of 3 flail troops.
Crab in action
      In combat, the usual tactic was to use Crabs in groups of five. Three would go forward in echelon formation, clearing a broad path through the minefield. The other two would hang back on the flanks and give fire support, but were ready to move forward to replace one of the flailing tanks if it was disabled. The Crab had disadvantages; flailing did not remove all mines. A Teller mine buried up to 5 inches deep would be set off, but the resulting explosion would destroy a single flail chain, which would have to be replaced at some point.
      The Crab could only move at two km/h when flailing and the gun had to point to the rear so the tank could not fire even if the gunner could see his target. As with the Scorpion, flailing raised a huge cloud of dust. Despite all this, it was an effective and valuable vehicle during and after D-Day, especially as the Germans made extensive use of minefields to slow the Allied advance through France and the Low Countries. By the final months of the war, German minefields had ceased to be a major problem and it was proposed that the surviving Crabs should have their flail equipment removed and be converted back to regular Shermans - an idea that was bitterly resented by the Crab crews, who considered themselves to be a highly-trained elite. In the end, this never occurred and the Crabs spent the last part of the war clearing old minefields behind Allied lines.
The flail device
      The Sherman Crab saw limited use by the American army; the Crab Mark I was designated the Mine Exploder T3 Flail and the Crab Mark II the Mine Exploder T4. The flail idea was also copied by the Japanese, who produced a vehicle called the Mine Clearing Tank G that was based on a Type 97 Chi-Ha tank. In the 1950s, the British Army used heavily armoured Churchill tanks fitted with flails - this was the Churchill Flail FV3902 or Toad.
Sherman Crab with periscopes for driver and MG gunner
Specs:
Sherman Mk.V (M4A4) Crab I
George Bradford drawing

Type: Mine flail Crab Mark I
Manufacturer: Detroit Tank Arsenal
Engine: Chrysler A57  Multibank 30, with 20.5 liters of displacement; 425hp@2600rpm gasoline
Transmission: 5 marchs ahead Syncromesh + 1 reverse
Lenght: 840 cm
High: 300 cm
Width: 362 cm 
Fuel capacity: 705 liters - gasoline
Autonomy: 161 km.
Ground clearance: 41 cm
Fording: 170 cm
Diameter of turn: 21 m
Weight: 34.000 kg
Armament: main gun M3 75 mm; 2 MGs M1919 Browning .30 + 1 MG  .50 Browning
Ammo: 74 rounds 75 mm; 17 box . 30 e 5 box  .50
Max. speed: 32 Km / h (road)

The kits:
            The kits are the Dragon 6041 plus Legend Products LF 1139. The Dragon kit is the old M4A4 with 60 lb rockets (Tulip).The Dragon kit was used because it was a shelf queen and the set of rockets were separated for further conversion.
The players
        The Dragon kit accuses the age, although it is fun to build. The plastic is soft and free of aggressive burrs. The Legend kit has a very sturdy box, with a beautiful picture on the cover:
Legend picture
            I started the project with a research on the vehicle in question and one thing that struck me was precisely the aspect "buried" the vehicle. The weight of the device altered the center of gravity of the Sherman, causing the first bogie suspension stay almost flat by excess weight concentrated at the front, and the second and third bogie were gradually forced less.
Notice the bogies...
      And most interesting is that I did not find this feature on any scale model.

Notice the suspension of the Crab
Ok! It was enough for me to try to modify the suspension of Sherman to show this effect. As the suspension arms this kit come separately, the task was made relatively easily: cut up the arms in the traces 1 and 2. Then, cut the excess (3) and, using a ruler as a support, glue the set horizontally. Notice the arms in horizontal near a arms unchanged:
The arms under surgery
        Repeat this process in the internal and external portions of the set of arms:
first set of arms (flat)
... and we set the wheels in his arms. Comparison between the flat bogie (front) compared with the normal bogie  (rear):
Front and rear bogies
            To make the intermediate bogie with arms at the precise angle, we will use the two bogies already obtained (the flat and normal) as a reference, gluing them to the chassis of the tank. When the chassis lay down in the suspension in a flat surface, the intermediate space for the second bogie will be appear. This intermediate bogie will be cutted according to the remaining space. See below: The images are self-explanatory ...


which the height of the arms?? how much should I cut??
The intermediate bogie with intermediate angle done...
Voiláa
Simple, is not it??
      Another detail: In the normal M4A4, the air intakes on the rear deck are facing forward (... and I built in accordance with the Dragon's instructions and the photo of the Legend kit). But they are wrong!!!
engine air intakes: wrong way...
Legend´s pic: wrong too..
     The correct way: air intakes facing backwards, to absorb minus dust that raised when the device is working:
Notice the air intakes
..again..
      Correcting the air intakes:
Fixing the defect
Done!
      While the hull and suspension stabilized in their buildings, let's play with the turret: time to open the Legend's box and use the resin parts. And I got scared: The resin seems immature, stained, inhomogeneous ... This is the mantlet canvas:
Turret: left side
Turret: right side
And doing a dry-run: Only when the turret is on the hull is the thing that looks like a tank ...
Almost a tank...
But now I had a huge disappointment: the resin parts of my kit came all warped, twisted and stained. The problem of staining was not aesthetic, but the uniformity of mixing the resin, causing irreparable twists parts. Look defective parts below: Twists impossible to be restored with the old resource of a hot water bath ....Legend, shame on you !!!
Defective parts
defective parts beyond repair
          Luckily, most of defective and irreparable parts was rectilinear. Although given a job from hell, it was possible to reproduce all the damaged parts with plasticard and lots of patience, but it was a disappointment with a prestigious brand like the Legend ...
Twisted resin parts and plasticard  ones
Notice the resin non-homogeneous. Thankfully, these parts were not crooked ...
Scratch, scratch and scratch to fix the Legends's errors
Plasticard as lifeboats
Scratch, metal, resin and plastic are building the new parts. The crab is growing...
The flail fork
 More details in metal. The kit's photo-etched is fantastic...
Metal parts...
       Making details with copper wire:
      Now is the time for monk's patience: install the 43 flail chains. The kit provides the chains (great), but the resin balls are horrible. I decided to replace them by bijoux balls, which are more suitable size and weight for the kit. I had to make the individual hooks, pass wires through the spheres and then soldering them with electronic welding, flail by flail, cutting the excess ...





      Then, on a block of wood, I made a template for the exact length of each flail set and I was doing that following the sequence: hook in wire - welded the sphere - cut the chain with template. I did this sequence to save chain. With this sequence, although delayed, no waste of chain and all flails was made with same size:


Building flails...
         Flais done, it's time to scratch the straps that attach the chains in to rotating roll. Another monk work ...
flail straps made with copper wire
           The hflail strap ready and cutted in the correct size. Just do another forty-two ...

     And installing (with care) in the roll device...Pfeww!!

The flails in position..
     Done. Notice the periscopes in the hatches of driver and gunner:
The flail chains done
      To relax, making the rear guides with rigid copper wires ..
     And in the tank's rear. Almost ...

      As in the original vehicle, the front portion got very heavy ... The kit's snout tends to fall on the floor. I filled the aft baggage compartment with lead and made a counterweight to the flail device:
counterweigh
     And the Crab is ready for painting...
      Primmer:
       Green:

       Ups and downs in the basic ton of green...Future to prevent silvering...
     Decals from my spare parts box. Glorious British 79th!  Hobart´s Funnies !!!


Weathering:
      Dragon's link-by-link...A real nightmare!!!!!
I hate link-by-link
      Making the cargo in the rear deck: Tracing-paper with white-glue
And Joan is ready for duty!!!!
Sherman Mk V Crab - Joan - Mine flail tank

Sherman Mk V Crab - Joan - Mine flail tank - rear view


Sherman Mk V Crab - Joan - Mine flail tank - left side - Notice the feeling of weight in front
Sherman Mk V Crab - Joan - Mine flail tank - right side - Notice the feeling of weight in front

Well, Gents...This is the funny Crab !!!  Thanks for following !!!

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