PT-91 Twardy - Development

Development

Starting from July 1991 T-72 modernization programs were implemented by the Bumarcombine which had been producing T-72s under Soviet license. The modernized main battle tank was designated PT-91 Twardy. From base modification it differs in increased protection, fire control system and engine. In 1993 the Polish Defense Ministry ordered 20 PT-91 tanks to be used for field trials and Armed Forces tests.

The main battle tank's protection from high-explosive anti-tank (HEAT) projectiles and missiles is increased by the new Erawa dynamic armor developed by the Poland Military-Technical Institute. This protection consists of 394 tiles with explosives, detonating in case of a direct hit. The tiles cover 9m2 on the tank. 108 tiles are placed on the turret, 118 on the hull and 84 on each side's anti-HEAT screens. The Twardy uses steel anti-HEAT screens instead of the rubber used on the T-72. Erawa's main difference from the Soviet analogs is that Erawa's containers fit almost without gaps while on the Soviet modernised T-72 gaps reach 10 – 15 mm noticeably decreasing defense effectiveness. There are two Erawa modifications: Erawa-1 and -2, differing in weight of the explosives.

Experiments showed that the Erawa dynamic defense decreases the high-explosive jet impact depth by 50 - 70% and penetrator (APFSDS) projectiles by 30 - 40%. Furthermore, explosive containers don't detonate when hit by shot of up to 30 mm calibre, shell or mine fragments, or when covered in burning napalm or petrol.

The Twardy is armed with the same 125 mm smoothbore gun 2A46 used in the T-72, fitted with an automatic reloading mechanism which reduced the tank crew by one as it replaced the gun loader, and gave a rate of fire of 8 to 10 rounds per minute. Additional armament comprises the 7.62 mm PKT coaxial general-purpose machine gun and 12.7 mm NSVT anti-aircraft heavy machine gun. The PT-91 has a thermosmoke device generating smoke screens from fuel and 24 grenade launchers fitted with smoke or anti-personnel frag grenades.

The modernization of the fire control system started by replacing the earlier used Soviet two plane stabilizer 2Є28M with a new stabilizer developed in Slovakia. It has an electronic information block showing the tank's technical condition. Furthermore it informs the commander when effective sighted fire becomes ineffective because of an excessively high cross-country speed or other reasons.

The Drawa fire control system, developed by Polish engineers, contains the gunner's day sight PCD and the TES thermovision night sight developed by the Israeli company ELOP, the commander's combined day-night passive observation and aiming sight POD-72, a ballistic computer, a laser rangefinder and a data system processing information for the ballistic computer. The sighting of the ballistic computer depends on the target's speed, weather conditions, projectile temperature and projectile type.

The driver uses the control and diagnostic complex US-DK-1 controlling the tank's main systems and displaying information on a monitor. The driver's night sight was replaced by the Radomka passive night sight.

The modernized tank's increased weight led the developers to add a more powerful engine. It is a 12-cylinder S-12U diesel engine, a modernized version of the Soviet V-46-6 produced in Warsaw by PZL-Wola (850 hp instead of 780). The main improvement is the modernized fuel and air injection system. This caused a noticeable decrease in the tank's road endurance. The latest Twardy variants have the 1000 hp S-1000 engine with a turbocharger.