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COMPETITION Brawling Bobcat: Armored Truck for the Lone Free State (2245)

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9 hours ago, Toxn said:

You'll have to correct me on this, but hitting the requirement with a single shot means something along the lines of a 4.7'/120mm calibre shell.

 

Edit: so, using the 122mm OF-462 shell as a reference, and assuming that the filler weighs the same as TNT, then the minimum you can get away with is 4.5'/115mm, with an all-up shell weight of 50.3lb/22.8kg.

 

It should be equivalent to a 3" shell's filler as I recall, but I can check.

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50 minutes ago, N-L-M said:

You could always just hose down everything with a 100 round burst :D

More or less. Rough calculations have the 57mm needing a 15-round burst to make the requirements. Which is glorious overkill :)

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43 minutes ago, Toxn said:

More or less. Rough calculations have the 57mm needing a 15-round burst to make the requirements. Which is glorious overkill :)

 

FYI: There is no requirement for the main gun to have capability.

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After review of firing trials, the Rangers approve cutting that spec significantly, to 1.6 lb or 26 oz HE fill, approximately the fill of a so called "75mm" 3 inch M48 HE shell of old.

We apologize for the inconvenience.

 

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What is "psft" in ground pressure requirements?

 

Edit:

This is pounds per square feet? But 8 psf is 380 Pa. The ground pressure of human and modern FAVs is ~55 - 70 kPa (8 to 10 psi). The very safe pressure for wheeled vehicles is 170 kPa (25 psi). In case of modern wheeled APCs is around 200 to 350 kPa (29 to 51 psi). In case of human with snowshoes it is ~700 Pa.

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On 3/24/2020 at 9:46 PM, N-L-M said:

Size is essentially unrestricted, axle load must be below 10 tons (per axle ofc)

 

Axle load with this ground pressure will be much lower. I'll count that.

 

MMP ground pressure formula (in metrics)

 

opony.png

K - constant dependent on number of axles and drive axles

g - gravity (~9,8 m/s^2)

m - weight of vehicle

n - number of axles

d - outer diameter of chosen tires

b - width of chosen tires

(o/h) - tire deflection to height ratio (usually between 0,15 and 0,35)

 

And table regarding the choice of K ratio

 

opony+%25281%2529.png

The top line - number of drive axles

The side lide - number of axles

 

Source: M. Saarilahti, Modelling of the wheel and tyre. 1. Tyre and soil contact, Soil Interaction Model. Appendix Report No. 5, s. 24-29

 

 

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As far I've counted mass restrictions for 16.9R24 tires (d = 1,333 m, b = 0,44 m), 0.35 ratio and 8 psi maximum ground pressure.

 

4x4 vehicle - 2,5 metric tons

6x6 vehicle - 3,5 metric tons

8x8 vehicle - 4,4 metric tons

10x10 vehicle - 5,2 metric tons

12x12 vehicle - 5,9 metric tons

 

 

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3 hours ago, Zadlo said:

What is "psft" in ground pressure requirements?

 

Edit:

This is pounds per square feet? But 8 psf is 380 Pa. The ground pressure of human and modern FAVs is ~55 - 70 kPa (8 to 10 psi). The very safe pressure for wheeled vehicles is 170 kPa (25 psi). In case of modern wheeled APCs is around 200 to 350 kPa (29 to 51 psi). In case of human with snowshoes it is ~700 Pa.

 

Sorry I was given a bad conversion factor by google. Good eye!

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On ‎3‎/‎30‎/‎2020 at 11:56 PM, Zadlo said:

What is "psft" in ground pressure requirements?

 

Edit:

This is pounds per square feet? But 8 psf is 380 Pa. The ground pressure of human and modern FAVs is ~55 - 70 kPa (8 to 10 psi). The very safe pressure for wheeled vehicles is 170 kPa (25 psi). In case of modern wheeled APCs is around 200 to 350 kPa (29 to 51 psi). In case of human with snowshoes it is ~700 Pa.

So I'm struggling to square the figures you've provided here with your formula.

 

If we take the maximum ground pressure (350kPa) and plug it into an 8x8 vehicle, we get something along the lines of a 15mt limit. This seems a bit incongruous when a number of modern 8x8 AFVs are pushing 30mt. Am I just applying this thing wrong?

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3 hours ago, TokyoMorose said:

I was tempted to mount ye old M135 demolition cannon as a secondary mount to meet the HE requirement while being under armor. I am quite certain the 165mm HEP round would satisfy even the most ardent of rangers.

 

:thispleasesme:

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2 hours ago, Toxn said:

If we take the maximum ground pressure (350kPa) and plug it into an 8x8 vehicle, we get something along the lines of a 15mt limit. This seems a bit incongruous when a number of modern 8x8 AFVs are pushing 30mt. Am I just applying this thing wrong?

 

A bit wrong. For standard 8x8 wheeled APC using 14.0R20 tires the acceptable weight for this ground pressure (I mean 350 kPa) is almost 24 mt (precisely 23,8 mt). For newer vehicles using 16.0R20 tires it is 28,5 mt. On the other side for 13mt SKOT using smaller tires (13.0R18) the ground pressure is 250 MPa.

 

But there's one assumption. This numbers are related to situation where the vehicle goes through untreated, wet terrain f.e. ploughed-up cornfield. On unpaved road the problem exists only when the ground pressure is higher than 400 kPa.

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3 hours ago, Zadlo said:

 

A bit wrong. For standard 8x8 wheeled APC using 14.0R20 tires the acceptable weight for this ground pressure (I mean 350 kPa) is almost 24 mt (precisely 23,8 mt). For newer vehicles using 16.0R20 tires it is 28,5 mt. On the other side for 13mt SKOT using smaller tires (13.0R18) the ground pressure is 250 MPa.

 

But there's one assumption. This numbers are related to situation where the vehicle goes through untreated, wet terrain f.e. ploughed-up cornfield. On unpaved road the problem exists only when the ground pressure is higher than 400 kPa.

Thanks. What are the dimensions on the 16.0R20 tires, just so I can double-check my math?

 

Edit: the tires I used are 345/80R20s, which have a total diameter of just over a metre and are 34cm wide.

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On 4/1/2020 at 1:10 PM, Toxn said:

Thanks. What are the dimensions on the 16.0R20 tires, just so I can double-check my math?

 

Edit: the tires I used are 345/80R20s, which have a total diameter of just over a metre and are 34cm wide.

 

16.0R20 has 1.343 meter of diameter and are 43,8 cm wide.

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Greetings all, I've been pulled on as a judge for this one, so none of the following should be construed as competition so much as... encouragement.

 

This is the Mogcat:

T2nIhi4.jpg

TX2sjkE.jpg

ZpEzqkh.jpg

 

It's designed to exactly nail the minimum specs, while being relatively easy to produce and long-legged. It sports a 3"/76mm main gun, a bunch of machineguns and the sort of conveniences you'd expect from a late-40s design (gunner's panoramic sight, wet ammo racks, internal firefighting equipment and smoke launchers). It's otherwise very bare-bones, and comes in at all of 10.3st/9.3mt.

 

I'll add further specs as this goes along, but for the moment all you have to know is that this is the minimum, lowest bar that I can think of. This thing is intended to be the product of unimaginative minds working at what passes for the ordinance department in the Lone Free State - men who spent their lives designing incremental improvements on machineguns and recoilless guns, and think that their lightweight 3" gun is a world-beating novelty.

 

For what it's worth; what I would like to see is something that grabs the requirements by the balls and works out a way to wring something that can beat @N-L-M's Norman design in a reasonably fair fight out of the thin gruel that the Provisional Government has put out. Remember that the Texans don't know what they don't know - their official line is that the arrival of Deseret light tanks is some sort of shocking revelation. But they aren't stupid - the smarter engineers will already be looking at what they could do with their given automotive and gun tech, and what was achieved in the pre-war era, and are probably staying up late at night worrying about their conclusions.

 

Update 1:

I had a think last night, and decided to swap out the turret crew to a commander-loader and gunner configuration instead of the T-34-esque commander-gunner and loader configuration (now included with the rest of the pictures).

 

Here's a bonus picture of the vehicle in travel configuration - turret rearward and gun in cradle:

cLqzQnA.jpg

 

Update 2:

Here's some more stats on the vehicle, in the prescribed units...

 

Description

The Mogcat is a 6x6 armoured scout car designed for mobility and extended operations. The design boasts an innovative engine, drivetrain, suspension package and gun, all built with an eye to ruggedness and light weight. The Mogcat's 3-inch cannon is able to provide useful anti-armour (APHE and HEAT-FS) and anti-infantry (HE, canister and shrapnel shell) firepower, while the plethora of machineguns it sports allows it to tackle dismounted infantry and light vehicles with confidence. The combination of purpose-built drivetrain components, long operational range and firepower makes the Mogcat a strong contender for the present production contract.

 

Major dimensions and mass

Crew: 3 (driver, commander-loader, gunner)

Length: 16'/9" (hull), 19"/4' (gun forward)

Width: 6'/7"m

Height: 9'/6"m (top of commander’s cupola)

Unloaded weight:  8.7 ton

Loaded weight:  10.3 ton

Ground pressure: 4900lb/ft2 (unloaded, muddy ground) to 5785lb/ft2 (loaded, muddy ground)

Axle loading: 3.4t/axle loaded

 

Mobility

Engine: 4-cylinder turbodiesel, 732cu displacement, 200-280HP

PWR: 19.4HP/t loaded, detuned

Ground clearance: 17.7"

Max road speed: 60mph

Max offroad speed: 20mph

Operational range (on road/offroad): 850mi/500mi

 

Protection

 

Armour:

2" LOS on hull front (1" RHA @ 60°)

0.8" LOS on hull sides with 30° angle (0.8" RHA @ 90°, 0.5"mm @ 45°)

0.6" RHA on hull rear

0.5" LOS on hull bottom (0.4" RHA @ 45°)

2" LOS on turret front (1.8" RHA @ 30°)

2" CHA mantlet

0.8" LOS on turret sides with 30° angle (0.6" RHA @ 25°)

0.6" RHA on turret rear

0.4" RHA on roof

0.4" RHA on turret floor

2" RHA turret neck ring and splash guard

0.4" Aluminium turret basket, skeletonised

 

3.2" smoke dischargers (2 reloads).

Fuel tanks on driver’s sides improve protection against threats from the front.

Ammunition stowage in wet racks in turret bustle, turret floor and driver’s compartment.

Internal fire control system (BCF canisters in engine compartment and fighting compartment, driver has access to removable CO2 extinguisher).

 

Firepower

 

Turret ring diameter: 4'/5"

Main gun: 3" L/40 medium-pressure gun, 12" recoil travel

Ammunition stowage: 50 rounds main gun ammunition stowage

+30/-10 degree elevation.

Ammunition:

3"x15.2" cartridge (3.7" base, 19lb max all-up weight)

APHE: 13.9lb, 2425ft/s, 3.5" RHA penetration at 1000m

HEAT-FS: 15.4lb, 2295ft/s, 9.8" penetration

HE: 13.7lb (1.35lb fill), 2460ft/s, 0.4" RHA penetration

APFSDS (spindle-type, 15L/D ratio, maraging steel penetrator): 1.5lb, 5900ft/s, 6.5" RHA penetration at 1000 yards.

Secondary weapons:

.30 cal coaxial MG (600 rnds)

.30 cal gunner's MG (600 rnds)

.50 cal commander’s MG (500 rnds)

 

Additional features

 

Long-range transistor radio.

Vehicle intercom system.

Ancillaries (fire tables, gunner’s quadrant, traverse markings etc) for indirect fire missions.

Commander has access to panoramic sight (x1) and telescopic sight (x4) for target acquisition and lay-on.

Turret traverse is electric (30 degrees per second rotation).

Fume extractor on main gun

Large hatches in hull rear allow easy servicing of engine and gearbox.

Storage lockers in hull rear flanking the engine for personal/supplies stowage.

Hydraulic jacks on the hull bottom between the first and second wheels and at the rear make changing tires easier.

 

Update 3: I reworked all the images.

0hj3Z5n.jpg

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2 hours ago, Kal said:

Hedgehog

Wombat

Malkara

 

Return of the JAFT HedgehogWombatMalkara

The design was originally based on Unimog components (although everything except the tires has been changed at this point) and a moggie is an unremarkable cat...

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I am curious, what would be needed to penetrate the Norman at 1-2Km range?

Speaking about both HEAT and KE.


Would a 120mm be sufficent?
Or would a 150mm be needed?

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