Diagram of a base bleed unit. The top diagram shows the bottom of the shell and the location of the gas vents. The bottom diagram is a cut-away view showing the gas generator mechanism.

Base bleed is a system used on some artillery shells to increase their range, typically by about 30%. Artillery (from French artillerie) is a military Combat Arm which employs any apparātus machine

Most of the drag on an artillery shell comes from the nose of the shell, as it pushes the air out of its way at supersonic speeds. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a Shaping the shell properly can reduce this greatly. Another powerful source of drag is the vacuum left behind the shell due to its blunt end, at the base. This is difficult to remove, because the shell needs to be "nose heavy" in order to have proper ballistics, and it cannot easily be shaped into a more aerodynamic form. Ballistics ( gr βάλλειν ('ba'llein' "throw" is the science of Mechanics that deals with the motion behavior and effects of Projectiles

Base bleed is one way to reduce this drag without extending the base of the shell. Instead, a small ring of metal extends just past the base, and the area in the rear of the shell is filled with a small gas generator. The gas generator provides little net thrust, but simply fills the area behind the shell with pressure, dramatically reducing the drag due to the vacuum. Thrust is a reaction force described quantitatively by Newton 's Second and Third Laws. The only downsides are a small loss of accuracy due to the somewhat more turbulent airflow, and a small loss in explosive payload due to some of the shell being taken up by the engine. In Fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic Stochastic property changes

Since base bleed extends the range by a percentage it is only really useful on longer range artillery. Until recently the loss in explosive was not considered worthwhile for the small gains in range. However, the introduction of much longer range systems based on the GC-45 howitzer has changed the equation somewhat, as 30% extra range on these systems represents 5 to 10km. The GC-45 ( Gun Canada 45- Calibre) is a 155 mm Howitzer designed by Gerald Bull 's Space Research Corporation (SRC in the 1970s Base bleed shells are starting to become more common in units equipped with modern artillery of this type.

The field was largely pioneered by Gerald Bull. Gerald Vincent Bull ( March 9, 1928 - March 22, 1990) was a Canadian engineer who developed long range Artillery.

See also

rocket assisted projectile (RAP) / velocity enhanced long range artillery projectile (VLAP)

External links

• Preliminary investigation of effectiveness of base bleed in reducing drag of blunt-base bodies in supersonic stream: formerly classified NASA report from 1951