In the seventies of the last century the Belgian PRB company invented a radical new way to look at the mortar and mortar shell. One searched for a weapon with a low signature, meaning a low noise signature upon firing, no smoke and muzzele flash, and no hot weapon barrel that emitted a clearly recognisable infra red signature.
The design was called the jet shot at first, which was later renamed the Fly-K, a name used up till this day.
The warhead consists of a wound 3x3mm square wire, notched on the inside every 3mm, thus forming the fragmentation sleeve, placed in a green PVC cilinder. In the fragmentation sleeve a 140 gram cilinder TNT is placed with a booster charge of three small cilinders hexogen (red) in the center.
The fragmentation warhead is screwed into the lower -aluminium- part of the warhead which houses the impact fuze and the tail with the propulsion charge.
The impact fuze consists of (Picture 2, from top to bottom) : the detonator (1), below that the spring loaded rotating safety shutter (2) which houses the stab detonator. This level of the fuze also houses the reduction gear that slows down the rotating movement of the safety shutter upon arming.
Below that the inertia activated firing safety (3) is placed which keeps the safety shutter (2) rotated out of line with the booster (1) and the firing pin (4) when in safe position.
Upon firing, inertia moves down the firing safety (3), releasing the rotating safety shutter (2), rotating the stab detonator in line with the firing pin (4) and the booster (1), the rotating movement delayed by the reduction gearbox. Upon impact (look at the picture upside down) the firing pin is swung forward into the stab detonator, riding the weak firing pin spring. This will detonate the fragmentation warhead.
Below the fuze, the tail is screwed into the lower part of the warhead. The tail houses the piston (7) which has a tapered base, the firing cap (5) in the center of the piston, and the propulsion charge (6) in top of the piston. The mortar shell is placed over a spigot pin in the barrel, this spigot pin is a shaft with four half round profiles at 90 degrees each (picture 3 section A-A). These profiles center the fring pin below the firing cap (5), but leave enough space left to allow a bushing with an internal cone to be screwed over the end of the tail. Four half round indentations –fitting the profiles- have been machined into the internal cone of this bushing, allowing the spigot to exactly fit the tailpiece.
Upon activation of the firing cap (5) by the firing pin in the spigot, the gasses of the propulsion charge send the piston down the tail with high speed until the cone at the base of the piston gets stuck in the internal cone of the bushing over the end of the tail.
This propels the grenade away from the spigot without the propulsion gasses leaving the tailpiece, meaning no noise, no flash, no smoke, and no heat signature of the weapon, as the hot powder gasses are trapped in the tail of the mortar shell. The sound the Fly –K makes upon firing is like an air gun and does not exceed 52Db, which translates to a soft spoken voice in noise level.
This makes the Fly-K especially suitable for usage by special forces as it is very difficult for an enemy to determine from what position the shells are fired. Another advantage is that the weapon only weighs 4,5 kg , compared to -for instatce- 21 kg for the 60mm mortar. The 51mm Fly-K mortar is 311mm long.
A weakness of the weapon is the range which cannot be adjusted by additional charges , making the ranbge of the wepon somehow limited; 200 meters minimum, and 700 meters maximum. Also, the explosive charge is quite light, the ammunition is expensive and cannot be fired from another mortar.
This caused the weapon slip into oblivion by the turn of the century, to be reintroduced 30 years later -when the PRB patents expired- nearly unchaned by the Rhreinmetal company as the 51mm LGI Fly-K.
Rheinmetal also introduced a 60mm 12 spigot launcher, allowing firing 12 shells to be fired in a rapid succesion.
Available are a practice shell, High explosive, smoke and illunmination. A infra red illumination shell is under development (info 2005).
At the moment the only countries using the 51mm Fly-K are France and the United Arab Emirates (info 2010). China does what it’s best in; copying the 51 mm Fly-K as the QLT89.
Russia went a step further and redesigned the Fly-K into an own design ; the 82mm Burevestnik 2B25 silent mortar with the 82mm 3VO35 high explosive shell.
I was only able to find one movie showing a silent Spicgot mortar in action (the Russian 82mm Burevestnik 2B25) :
https://www.youtube.com/watch?v=leePXmJe5C0
Regards, DJH
The design was called the jet shot at first, which was later renamed the Fly-K, a name used up till this day.
The warhead consists of a wound 3x3mm square wire, notched on the inside every 3mm, thus forming the fragmentation sleeve, placed in a green PVC cilinder. In the fragmentation sleeve a 140 gram cilinder TNT is placed with a booster charge of three small cilinders hexogen (red) in the center.
The fragmentation warhead is screwed into the lower -aluminium- part of the warhead which houses the impact fuze and the tail with the propulsion charge.
The impact fuze consists of (Picture 2, from top to bottom) : the detonator (1), below that the spring loaded rotating safety shutter (2) which houses the stab detonator. This level of the fuze also houses the reduction gear that slows down the rotating movement of the safety shutter upon arming.
Below that the inertia activated firing safety (3) is placed which keeps the safety shutter (2) rotated out of line with the booster (1) and the firing pin (4) when in safe position.
Upon firing, inertia moves down the firing safety (3), releasing the rotating safety shutter (2), rotating the stab detonator in line with the firing pin (4) and the booster (1), the rotating movement delayed by the reduction gearbox. Upon impact (look at the picture upside down) the firing pin is swung forward into the stab detonator, riding the weak firing pin spring. This will detonate the fragmentation warhead.
Below the fuze, the tail is screwed into the lower part of the warhead. The tail houses the piston (7) which has a tapered base, the firing cap (5) in the center of the piston, and the propulsion charge (6) in top of the piston. The mortar shell is placed over a spigot pin in the barrel, this spigot pin is a shaft with four half round profiles at 90 degrees each (picture 3 section A-A). These profiles center the fring pin below the firing cap (5), but leave enough space left to allow a bushing with an internal cone to be screwed over the end of the tail. Four half round indentations –fitting the profiles- have been machined into the internal cone of this bushing, allowing the spigot to exactly fit the tailpiece.
Upon activation of the firing cap (5) by the firing pin in the spigot, the gasses of the propulsion charge send the piston down the tail with high speed until the cone at the base of the piston gets stuck in the internal cone of the bushing over the end of the tail.
This propels the grenade away from the spigot without the propulsion gasses leaving the tailpiece, meaning no noise, no flash, no smoke, and no heat signature of the weapon, as the hot powder gasses are trapped in the tail of the mortar shell. The sound the Fly –K makes upon firing is like an air gun and does not exceed 52Db, which translates to a soft spoken voice in noise level.
This makes the Fly-K especially suitable for usage by special forces as it is very difficult for an enemy to determine from what position the shells are fired. Another advantage is that the weapon only weighs 4,5 kg , compared to -for instatce- 21 kg for the 60mm mortar. The 51mm Fly-K mortar is 311mm long.
A weakness of the weapon is the range which cannot be adjusted by additional charges , making the ranbge of the wepon somehow limited; 200 meters minimum, and 700 meters maximum. Also, the explosive charge is quite light, the ammunition is expensive and cannot be fired from another mortar.
This caused the weapon slip into oblivion by the turn of the century, to be reintroduced 30 years later -when the PRB patents expired- nearly unchaned by the Rhreinmetal company as the 51mm LGI Fly-K.
Rheinmetal also introduced a 60mm 12 spigot launcher, allowing firing 12 shells to be fired in a rapid succesion.
Available are a practice shell, High explosive, smoke and illunmination. A infra red illumination shell is under development (info 2005).
At the moment the only countries using the 51mm Fly-K are France and the United Arab Emirates (info 2010). China does what it’s best in; copying the 51 mm Fly-K as the QLT89.
Russia went a step further and redesigned the Fly-K into an own design ; the 82mm Burevestnik 2B25 silent mortar with the 82mm 3VO35 high explosive shell.
I was only able to find one movie showing a silent Spicgot mortar in action (the Russian 82mm Burevestnik 2B25) :
https://www.youtube.com/watch?v=leePXmJe5C0
Regards, DJH
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