December 18, 2009

Update on the Rarefaction Wave Gun

In 2008, we covered the rarefaction reduced recoil tank gun

There is 36 page report on new computer models of a 105-mm Rarefaction Wave Gun

Currently, large-caliber guns require a heavy mount to absorb the recoil. However, the emphasis in the U.S. Army is now on lightweight and deployable vehicles. The Rarefaction wAVE guN (RAVEN) was invented by Kathe to substantially reduce the recoil and, hence, the mass of the system that absorbs the recoil, while minimally reducing the projectile velocity. This is accomplished by venting the breech through an expansion nozzle during the firing cycle. If the timing is done correctly, the rarefaction wave from the venting will not reach the projectile until muzzle exit. Therefore, the projectile does not know that the vent has opened.

A 35 mm rarefaction gun was built and tested. A 105-mm demonstrator RAVEN gun showing
significant differences from the 35-mm gun design is being designed.

Lighter and Stronger Materials
Here is a 29 page presentation that discusses the lightweight materials that are to be used in a RAVEN gun and other systems

• Combining composite and ceramic technologies with castings of any alloy – for dramatic weight reduction
• Opportunities for improved cast metal adhesion to inserts
• New opportunities ceramic inserts for improved wear resistance and lower weight

Develop and demonstrate hybrid component concepts (design, fabrication, and properties) that combine aluminum castings with both polymer matrix composites and ceramics.

• For DoD
– Weight savings over alternate steel casting design
– Meet or exceed design strength and durability

• For the Metalcasting Industry
– Provide advanced fabrication technology to expand metalcasting in high performance markets
• defense, aerospace, automotive, alternative energy

Proposed 105 mm Raven Gun design
The proposed 105-mm demonstrator is based on a modified cased telescope ammunition automatic Colt pistol cartridge. The projectile has a long boat tail extending almost to the breech. The charge is JA2 stick propellant. The figure shows a preliminary design where the breech is replaced by a piston with one of six spindles on the end. The spindle initially seals the breech. Unlike the 35-mm gun, there is no shear plug. The piston is initially held in place by recuperators exerting a small forward force (see section 5.4). Spindle A (left) takes the longest time to open the vent. The other spindles are cut away to open the vent sooner. The demonstrator has a split nozzle. The inside part of the nozzle is attached to the gun. The outside part of the nozzle is attached to the piston (not shown). As the piston moves backwards, the nozzle becomes longer. The piston is stopped by recoil brakes. Unlike the 35-mm gun, the piston is decelerated to the mount instead of the gun. Recuperators return the piston to the initial position. The gun will move forward at a slow velocity and is stopped with forecoil pads.

The 1-D code now more accurately models the nozzle when it is overexpanded. The pressure in the nozzle can be under atmospheric pressure for a significant amount of time. During this time, the nozzle produces negative thrust since the pressure on the outside of the nozzle is larger than the pressure inside the nozzle. Due partially to this effect, the 35-mm nozzle and the proposed 105-mm nozzle are larger than necessary. The nozzles can be reduced significantly in size, with only a minor effect on the recoil. There may be other reasons for a large nozzle than recoil reduction, such as blast reduction.

For both basic gun designs, the code indicates that the recoil can be reduced 50%, with only a small decrease in the muzzle velocity. The recoil can be reduced by at least 75% if a large decrease in muzzle velocity is allowed.

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