Dual safety: new generation of mortar fuses

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Armed forces have, for many decades, opted for the highly reliable and extremely robust mechanical mortar fuses DM93 and DM111.

These have been produced in many millions in a range of different variants fired from smooth-bore mortars which do not rotate after the firing to stabilise the projectile or use rotation as a physical environmental condition as an arming criteria, for example, as with artillery fuses.

For this reason, a safety pin needed to be removed manually by the soldier immediately before loading and firing. This action was used in the past as the first safety and arming criteria with mortar fuses.

This also made the application in modern mortar breech auto-loaders problematic. Design developments of the mortar time fuse (DM93) and mortar impact fuse (DM111) now achieve compliance of STANAG 4187.

The Federal Defence Office (Bundeswehr) for equipment, IT and In-Service Support (BAAINBw) required a new generation of mechanical dual purpose fuses (time function and impact function), for the introduction of the New Generation 120mm mortar munition without the manual removal of safety and arming criteria. This was required to be physically independent from the launch acceleration, but dependent on the environmental conditions generated by firing, to conform to the safety requirements of STANAG 4187.

JUNGHANS has developed a fuse design, based on the existing fuse DM93 legacy, which uses the flow of air passing over the fuse at high velocity after firing. This “wind wheel” at the top of the fuse rotates with the airflow, and the fuse is mechanically armed.

This development posed a challenge due to the high “packing density” of the precision mechanical elements requiring waterproofing and environmental protection.

The dual purpose fuse DM183/DM193 (DM183 for illumination and smoke munition, DM193 with booster charge for HE munition) is now qualified, and the pilot lot tests for the introduction with the Bundeswehr successfully concluded.

This new “wind wheel fuse” is designed to be used throughout the standard mortar calibre range, from 60mm and 81mm through to 120mm.

In France, this fuse is already in official qualification process for 81mm mortar ammunition.

Due to the absence of the clockwork mechanism in the DM111 fuse, the adaption of the pure impact fuse was significantly less complex and can be used for all standard mortar calibres, qualification of this fuse will soon be completed.

The aerodynamic characteristics of these new fuses, in particular the design of the wind wheel, have been studied in detail in order to limit the influences on the ballistics of the munition.

The final optimised design of the wind wheel has overcome an important technical challenge in order to obtain what is only an insignificant reduction in range performance.

We are proud that we can offer our customers a new generation of mechanical mortar fuses.

The elimination of the safety pin simplifies the handling of the munition, and reduces the risk of user error, as well as also enabling use with automatically loaded mortar systems.

These new products are soon to be demonstrated to the SANDF, Armscor and Defence Industry stakeholders by Atlantis Manufacturing Management Services, the official JUNGHANS South African representative.

AMMS has an 18-year relationship with JUNGHANS and was awarded local manufacture licences for 40mm AGL High Velocity Self Destruct Fuses, which has qualified on RDM and DIEHL ammunition.

This capability has been extended resulting in modifications for 40mm medium velocity fuse application.

AMMS provides design and development of defence equipment for the Armed Services and is a supplier of equipment to ARMSCOR, SANDF and the international market.



* Extracts of the article taken from JUNGHANS Fuze News June 2014