Tuesday, June 22, 2010
Russian NxRA for LAVs
"The change in geopolitical situation in the world, less probability of global military con-flicts and, quite on the contrary, increased number of local and asymmetrical conflicts require complete revision of the armed forces structure, including the structure of the Armor, practically in all world powers. These changes do not imply the use of large numbers of main battle tanks, but rely on a wide range of types and a great number of light-armored vehicles (LAV). Recent military conflicts (Afghanistan, Iraq, Yugoslavia, Middle East) have clearly shown that light-armored vehicles are the most efficient solution for such situations, provided the vehicles feature sufficient all-round protection, high mobility and firepower. The world and European markets of weapons and military equipment have immediately responded to these changes. Thus, for the last decade the sales of tanks has dropped by more than 30%, and the forecast for the near future is unfavorable. At the
same time, the sales of light-armored vehicles, and in the first turn of infantry fighting vehicles (IFV), self-propelled guns and other LAV has been growing steadily, and the highest growth (up to 40%) in the nearest future is expected in the sales of IFVs. One of the most critical requirements to LAV is the desired level of protection. It is actually the criterion which determines the final profile of the vehicle, and it is the focus of main efforts of LAV designers. It should be mentioned that high level of protection is required not only from IFV,
but also from other LAV including APC, armored cars etc.
Nowadays requirements to protection of LAV abroad are defined by appropriate standards. One of them is STANAG 4569 «Protection Level for Occupants of Logistic and Light Armoured Vehicles» which defines 5 levels of protection for LAV. The highest one –Level 5 –implies protection against 25mm APDS rounds and HE-round fragments. This standard was adopted in May 2004, but has already become obsolete, and many of
LAV designers are pursuing much more challenging goals. The requirement of all-round protection of LAV against 30mm cannon projectiles, RPG and ATGM penetrating up to 400-450mm of RHA is becoming typical.
Among the up-to-date protection systems able to counter these threats, explosive reactive armor (ERA) is the most cost-effective solution. ERA effect is based on the use of explosion energy which destroys the shaped-charge jet when throwing of a metal plate obliquely either after or towards the jet at the optimum obliquity. In many countries this type of protection as applied to LAV is developing rapidly, and we can see several generations of ERA, that have already been implemented or are in the process of implementation on different LAV. Russia is no exception here. It was among the first to show the possibility of using ERA on LAV. And today Russia offers a variety of solutions that can provide LAV with protection not only against single-warhead RPG and ATGM penetrating up to 500…600mm of RHA, but also against tandem rounds.
As long ago as in 1988 Russia made first attempts to fit LAV with ERA kits (that had been by that time widely used for tank protection).Fig. 1 show the first ERA kits “Contact” with 4S20 ERA elements on Cobra-S (upgraded BMP-1) IFV. However, live tests of those kits revealed their complete non-applicability to LAV. When an ERA box and a grenade detonated together, with the total amount of explosives about 1.1-1.2kg, the
thin main armor of the vehicle was simply broken through that disabled the vehicle (Fig. 2). However, in 1999 the engineers of “NII Stali” company in Russia succeeded in designing a functional ERA kit for BMP-3 IFV on the basis of 4S20 tank ERA element. The weight of that ERA kit was 4 tons (Fig. 3). The kit offered protection of the main vehicle surfaces against PG-9VS grenades piercing up to 500mm of RHA, at course angles of ±180. At the same time protection of BMP-3 IFV against small-arms and artillery ammunition
also improved. The experience gained during the design of that ERA kit showed that a new ERA element
specially adapted for LAV is required.
In 2006 a new ERA element (4S24) for LAV was accepted for service of the Russian Army. 4S24 ERA element contained twice less explosive than 4S20 element, which resulted positively both for ERA survivability, and for the survivability of the main armor. The use of 4S24 ERA elements together with unconventional solutions that enhanced fire safety of ERA elements when perforated by 7.62...14.5mm bullets, resulted in creation of ERA packages, adapted to such LAV as BMP-2 IFV, BTR-90 APC etc., which by their multi-
hit ability, fire resistance and other parameters exceeded the first ERA kits for BMP-3 IFV by several times. (Figs. 4, 5)
In the process of designing such protection systems a number of technical challenges was solved, such as non-transfer of detonation inside the ERA box, blast damping, increase of ERA survivability and fire safety. The plastic explosives used in the first generations of ERA featured high sluggishness. Detonation of the explosive compound took place only 3…5μs after the impact of the shaped-charge jet. As a result the jet lead-
er managed to get through the ERA (Fig.6). With the velocity of 9…10km/s and weight of 5…10
gram, the slipped leader could pierce 50…80mм of steel armor that is sufficient to disable LAV. A flow of fragments formed during the penetration process, overpressure inside the vehicle (100…150atm) and the noise level of about 150…200dB could disable both the occupants and the internal equipment.
It is possible to reduce or completely prevent the breakthrough of the jet leader by using high-sensitive explosives, but in this case the problems of ERA element inflammation when perforated by small arms bullets and ERA element detonation under the impact of 30mm and heavier ammunition become more urgent. These problems have been solved in ERA with 4S24 elements (Fig.7).
The engineers of “NII Stali” have shown, that in ERA elements (regarded as conventional) only 10…15% of the detonation energy is spent on destroying the shaped charge jet. The rest of the energy is spent uselessly and has a parasitic effect on the protected object and close environment. Besides, this type of ERA elements has little efficiency against 30mm ammunition and is completely ineffective against APDS rounds of 35…50mm cannons. The experts of “NII Stali” think that further efforts in development of LAV protection should be focused on reducing the amount of energy released in the protection system that has a parasitic effect on the main armor. According to the latest research of “NII Stali”, one of the ways of further development is the shift from conventional ERA to so called energetic materials. Reactive armor, both abroad and in Russia, is
seen as the protection system based on materials able to absorb a part of the shaped-charge jet energy and give it back in the form of moving bulge that interacts with the shaped charge jet.This type of protection is qualified abroad as reactive armor of NERA type (non-energetic reactive armor). In Russia this type of protection was used in tank armoring as long ago as in late 1960s and is known in literature as “bulging or reflecting plates”. However, it’s very difficult to use this type of reactive armor for LAV per se, because its sluggishness is 10…20μs and more, which in its turn causes the breakthrough of a considerable part
of the jet leader which is able to penetrate 100-150mm of RHA (Fig.8).
An attempt to raise the efficiency of the reactive armor led “NII Stali” to creation of so called
energetic materials. Energetic materials are a new class of protective materials, which stands
between conventional ERA and reactive armor. R&D conducted in “NII Stali” has shown that
when the shaped charge jet impacts the energetic material enclosed between metal plates, in the interaction zone which is as small as 60-120mm, a chemical reaction takes place with release of a considerable amount of energy. The energy release rate is comparable to that of the best plastic explosives. It’s about 5000m/s in the
interaction zone, and decreases to sonic speeds with the distance from the epicenter. It prevents the shift of the process to the stage of the steady-rate detonation. The efficiency of such systems is much higher than that of other reactive armor systems discussed above, because all the energy released in the local zone is direct-
ed to destruction of the shaped charge jet. On X-ray photos it is clearly seen (Fig.9) that the area in which the process is going on and bulging of reactive armor elements is taking place is very limited.
This type of reactive armor is called NxRA abroad, which means it doesn’t use any explosives; it’s used in a variety of different armor systems (SLERA, LRA, IRA etc.). The use of this approach in reactive armor
designs with multi-row cluster order of energetic elements with different levels of energy release allows control of the interaction process and adaptation to particular parameters of the shaped charge jet, which results in increased protection. Energetic materials can be based on different formulations. Due to selective sensibility to the shaped charge jet energy, the energetic materials are effective against tandem-warhead rounds and
long-rod penetrators of APFSDS.
The ideas of such hybrid reactive armor abroad are implemented only for protection against single-warhead chemical energy projectiles and kinetic-energy projectiles of small-caliber guns. Russian designers are pursuing more ambitious goals for hybrid reactive armor, and they are very close to creation of really multipurpose systems that provide protection against the complete range of threats, including tandem projectiles.
Table shows the evolution of the main characteristics of reactive armor for LAV, that has been developed or is under development in “NII Stali”.For the last decade the Russian company has managed to reduce the amount of detonating explosive by four times, and in the near future may give it up completely, which allows significant
increase of multi-hit ability of reactive armor systems. Moreover, in such systems the level of protection does not go down, but tends to increase. The long experience of “NII Stali” in LAV protection enables the company to work out new technical solutions and to adapt those which already exist to all types of light-armored vehicles with maximum efficiency.