Features of the British Chieftain tank gun
It is no secret that during the Iran-Iraq war one of the Iranian tanks The Chieftain Mk.5P was captured and handed over in full working order to the Soviet Union, allowing domestic researchers to study this British aircraft in detail.
As a result, Soviet testers wrote many fascinating reports on this tank, one of which concerned the features of its gun. This document no longer has any practical value today, but it does have technical value, so it is highly recommended reading.
Main features of a tank gun
The British main battle tank is armed with the 120mm L11 cartridge-loading rifled gun, which was developed specifically for the second-generation Chieftain tank and has undergone several upgrades. Let's examine the design and layout features of this gun's modification, designated L11A5.
The L11A5 cannon consists of the following main components: the barrel with the breech, the breech with a semiautomatic opening and closing mechanism, the cradle with a guard, and recoil mechanisms. The cannon is mounted in the turret using trunnion-type cradle assemblies.
The barrel is a monoblock, consisting of a chambered tube with 32 grooves of constant rifling angle of 9°54' (1/18 of a knuckle). It is connected to the cradle via cylindrical guides in the breech. A heat-protective jacket is attached to the outside of the tube.
The middle section features a thickening for mounting the receiver and eight inclined threaded holes for the barrel's ejector. The muzzle thickening has a mounting platform for a device (presumably a mirror) for the integrated sight alignment with the gun.
The breech is rectangular in shape with a vertical wedge.
The tube-to-breech connection is quick-release, with a sector-shaped stop thread in both the breech and the tube. A locking plate prevents the barrel from unscrewing from the breech. A wedge breech locks the barrel and opens when the barrel is rolled (using a cam).
A distinctive feature of the gun is its caseless obturation of the powder gases in the barrel bore, achieved through the use of a special obturation device consisting of an insert in the breech face and a sleeve mounted on the breech face of the tube (figure). Reliable obturation is ensured by the deformation of the sleeve under the action of the powder gases and its tight fit against the chamber seat and the breech obturation ring.
Obturator device: 1 - wedge; 2 - obturator socket; 3 - obturator ring; 4 - obturator coupling
The ignition of the powder charge is carried out by ignition tubes installed in a special socket of the wedge using a loading mechanism located on the breech.
The recoil parts are connected to the recoil devices using a swivel secured to the front cylindrical part of the breech with two bolts.
The breech mechanism is of the copying type and consists of a copying element located on the cradle bracket, a closing spring (torsion) and an axis on which a crank (interacting with the wedge) and a cam (interacting with the copying element and the manual breech mechanism) are located.
The welded and cast cradle is mounted in the turret on gimbal bearings using trunnion bushings. The inner cylindrical portion of the cradle contains front and rear bronze bushings that guide the barrel during recoil and recoil. The cradle also contains mounting sockets for the recoil and recoil brake cylinders, a fluid expansion compensator, and a guard housing the loader's follower and safety device.
On the cheeks of the cardan suspension of the cradle, needle bearings of the trunnion assemblies are installed and devices for installing the gun in the embrasure of the turret and adjusting the axial play are located.
The hydropneumatic recoil devices consist of two recoil brakes symmetrically positioned relative to the bore axis, a recuperator located below and to the right of the cradle, and a fluid expansion compensator. The recoil brake is of the camber type. The recoil brake cylinders are secured to the cradle sockets using a bayonet connection, and the piston rods are attached to a swivel mounted on the breech.
The cavities of both recoil brakes are connected to a brake fluid expansion compensator, consisting of a cylinder and a piston compressed by a spring. The compensator piston is connected to a gauge that allows one to monitor the fluid level in the recoil brakes.
The recuperator is hydraulic and consists of two communicating cylinders connected by a channel. One cylinder houses a piston with a piston rod. As the piston moves during retraction, fluid flows through the channel into the other cylinder, moving a floating piston that separates the gas and the working fluid, thereby storing recuperation energy.
In the cover of the other (high-pressure cylinder) there is a control rod indicating the position of the floating piston, and its gas cavity is connected to a pressure gauge, which can be used to directly judge the gas pressure in the recuperator.
To analyze the accuracy parameters of the L11A5 cannon, we will use the classification of firing errors adopted in tank design. The firing accuracy of the cannon-projectile system is assessed using three types of errors: the technical dispersion error of the projectiles, the technical preparation error when firing from a stationary position, and the vibration dispersion error of the projectiles when firing on the move.
When firing from a stationary position, the accuracy of a tank gun depends on the degree of its dynamic balance when firing.
It is known that a system is dynamically balanced if the sum of the moments of the active forces during firing (the gas pressure forces on the base of the projectile and the recoil resistance forces) is close to zero. This means that the dynamic balance of a gun depends on the relative position and interaction of those components and systems that determine the disturbing loads that arise during firing.
The dynamic balance of the L11A5 tank gun, as can be seen from the description of its design, is ensured by the location of the trunnion axis, passing through the center of mass of the recoil parts, in the plane of the barrel bore axis, the location of two recoil brakes symmetrically relative to the barrel axis and the trunnion axis, and the connection of their working cavities with one compensator for thermal expansion of the liquid.
On the bottom right there is one recuperator, the moment from which, when firing, is compensated by the static moment from the weight of the barrel.
However, due to the absence of free (low-braking) recoil in the initial section, a possible reason for the dynamic balance of the gun when firing may be the uneven operation of the recoil brakes.
It should be noted that the L11A5 cannon's stabilization in various firing conditions is enhanced by a thermal protective casing installed on the barrel and a special device for integrated sight alignment with the cannon, with a mirror on the muzzle of the barrel (this also allows for the thermal deflection of the barrel to be taken into account during alignment).
In order to evaluate the accuracy of the L11A5 cannon, firing at the shield was carried out with two types of projectiles:
— an armor-piercing sub-caliber projectile in a group of 5 shots at a range of 2000 m;
— an armor-piercing high-explosive projectile in a group of 6 shots at a range of 800 m.
The coordinates of the average point of impact (API) and the magnitude of the dispersion of projectiles in the vertical (Vv) and horizontal (lateral dispersion Vb) planes (table) show that, despite the fact that shooting errors are statistical parameters that can be reliably assessed only as a result of a large number of experiments, the obtained results confirm the estimated value of the error in technical dispersion, determined at the level of Vv = Vb = 0,15 - 0,18 mrad.
Estimating the firing preparation error based on the results is impossible due to limited data. Given the aforementioned design features of the L11A5 cannon and the relatively high level of technology abroad, it is possible, in accordance with accepted industry methods, to preliminarily estimate the firing preparation error of the L11A5 cannon based on average values of 0,2 mrad for the BPS and 0,25 mrad for the BFS.
The vibration dispersion of shells when firing on the move is determined by the angular vibrations of the barrel in the cradle and the bending vibrations of the tube from the overloads acting on the gun when the tank is moving.
The amplitude of the tube's flexural vibrations depends primarily on its flexural rigidity, which for the L11A5 gun, with a cantilever tube length of 5420 mm, is 2820 N/cm. This value is significantly lower than the flexural rigidity of other foreign and domestic guns.
However, it is also worth noting the design solutions that have a positive effect on the accuracy of firing on the move, namely, the placement of the quick-release connection of the barrel with the breech outside the cradle and the use of a device for adjusting the axial play in the gun-to-turret connection, which reduces the possibility of additional vibrations of the barrel relative to the cradle, and the cradle relative to the turret when the tank is moving.
When evaluating the performance characteristics of the L11A5 cannon, along with the positive aspects (the presence of a quick-release connection of the barrel with the breech, built-in control of the recoil devices, built-in control of the alignment), some negative aspects should also be noted.
These include the presence of a high-precision obturator, which is very sensitive to mechanical impacts and contamination, the small capacity of the cartridge magazine, and the lack of a firing mechanism. Furthermore, the ease of barrel replacement through the hatch at the rear of the turret is questionable, as this requires a special device to move the breech out of the barrel's path.
Overall, the L11A5 cannon is designed to a modern standard, taking into account the requirements for firing accuracy, and a number of design solutions are of practical interest and can be used in domestic tank construction.
Final World
The L11A5 gun is a highly ballistic tank gun designed to meet modern requirements for tank guns.
Source:
"The Main Features of a Tank Gun." V.P. Blizgarev, V.N. Kasyanov. "Questions of Defense Technology," Issue No. 5 (111), 1983.
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