Base bleed or base burn (BB) is a system used on some

artillery Artillery consists of ranged weapons that launch Ammunition, munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during sieges, and l ...

shells to increase range, typically by about 20%–35%. It expels gas into the low-pressure area behind the shell to reduce base drag (but does not produce thrust, unlike rocket-assisted projectiles). Being percentage-based, the range extension is more useful on longer-range artillery where an increase of approximately can be achieved, and it also was found that the reduced turbulence gave the projectiles a more consistent trajectory, resulting in tighter grouping, and efficient shelling more than away. Base bleed technology was developed in Sweden in the mid-1960s but took some time to spread and find its niche between cheaper classical ordnance and even more expensive rocket-assisted projectiles. It is now a fairly common option.

Function

Most (50–60%) of the drag on an artillery shell derives from the nose portion of the shell. Artillery shells travel through the air at supersonic speeds; as the shell pushes the air out of its way, it creates

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

s that bleed off the shell's kinetic energy and therefore reduce its airspeed. Shaping the shell properly effectively reduces this component of drag; however, in regular flat-base artillery shells, the other large component is the so-called "base drag", caused by the low-pressure ("suction") area created directly behind the shell as it travels through the air. Base drag can be reduced --without significantly extending the base of the shell or profiling it (as is done with sabot projectiles) by adding a small ring of metal extending just past the base, and placing a small

gas generator A gas generator is a device for generating gas. A gas generator may create gas by a chemical reaction or from a solid or liquid source, when storing a pressurized gas is undesirable or impractical. The term often refers to a device that uses a ...

to the rear part of the shell. The gas generator provides little to no

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

, but fills the vacuum in the area behind the shell with an inflow of gas, dramatically reducing drag. This means that, at a cost of only very little space to fit the gas generator in the casing, * a longer effective firing range can be achieved with the same amount of propellant * less propellant is needed to achieve the same effective range as with normal munitions * heavier shells can be fired to the same effective range

History

The principles were developed in Sweden in the mid-1960s by the Försvarets forskningsanstalt (abbreviated FOA) and the Artillery bureau at the Kungliga Materielförvaltningen (later the Försvarets Materielverk (FMV)) while working on a

rocket-assisted projectile A rocket-assisted projectile (RAP) is a cannon, howitzer, Mortar (weapon), mortar, or recoilless rifle round incorporating a rocket motor for independent propulsion. This gives the projectile greater speed and range than a non-assisted Ballistics ...

called "reatil". Their goal was to increase the range of coastal artillery.Grenander By 1966, it had been concluded that a small slow-burning charge at the base of the projectile would alleviate the low pressure behind the shell, hence increasing the range by lessening the difference between the pressure due to

aerodynamic drag In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers, two solid surfaces, or b ...

on the nose of the shell and the low pressure behind the base. The first full-scale tests took place in 1969 with modified 10.5 cm steel shells, with excellent results, and the Swedish patent was granted to FOA in 1971 although both application and patent were classified. Since the development was done, the patent was transferred to FMV for procurement to the armed forces of Sweden. The concept was quickly implemented into the ''7.5 cm sjömålsgranat m/66'' (7.5 cm anti-ship shell m/66) used in the 7.5 cm tornpjäs m/57 fixed coastal artillery gun, and then rapidly into all anti-ship shells in the Swedish military. Since FMV was to contract a company in the US to manufacture the gas generator for the ''12 cm sjömålsgranat m/70'' (12 cm anti-ship shell m/70), used in the 12 cm TAP m/70 fixed coastal artillery gun, the classification ''secret'' was removed from the patent. Shortly thereafter the international rights were sold, eventually ending up with the Space Research Corporation (SRC), then owned by aeronautical engineer

Gerald Bull Gerald Vincent Bull (March 9, 1928 – March 22, 1990) was a Canadian engineer who developed long-range artillery. He moved from project to project in his quest to economically launch a satellite using a space gun, huge artillery piece, to which ...

. By the end of the 20th century, the technology was generally available world-wide.

References

Bibliography

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External links

Army researchers add power, range to artillery
Picatinny Arsenal {{DEFAULTSORT:Base Bleed Artillery ammunition Swedish inventions

Function

History

See also

References

Bibliography

External links