199 A Fast -Acting, Self -Energized, Low -Cost Valve for Air Cannons  

Lee E. Brown* 

Abstract  

A novel pneumatic valve has been developed to control pressurized air  for an air cannon. It offers very  rapid opening time, is self -energized when opened, self -locking when closed, and is of relatively low cost.   The valve uses a variation on the classic four -bar linkage which enables the valve to be self -locking against  pressure when closed, yet self -energized and opens very rapid ly when the valve mechanism is tripped. The  valve has been tested and has been us ed in the field to test munitions fuzes .  Background   Air cannons have long been used for dynamic testing of electronics and mechanisms.  These air cannons  are used to simulate high- G environments such as artillery fire  or high- speed impacts.  They can also be  used to propel electromechanical devices past objects of interest, such as testing munitions fuz es against  specific types of targets.  The use of air instead of chemical propellants greatly simplifies these kinds of  tests and greatly reduces the cost of such testing.   The key component in any air cannon is the means by which the high pressure air is controlled. A very  rapid rise in pressure is needed to accelerate the projectile to the desired muzzle velocity within the shortest  possible barrel length.   The oldest means  of obtaining a very rapid pressure rise is through the use of a burst disk. A burst disk is  a membrane designed to fail at  a specified air pressure and thus achieve a sudden release of air into the  cannon’s chamber . Burst disks are capable of controlling very high pressures  and are usually designed  with scoring or grooves that give fairly repeatable failure pressures.   The drawback to burst disks is that they must be replaced after each shot which is time consuming. High  pressure burst disks are often precision machined elements which adds to the cost per shot.  At lower  pressures  metal or plastic foils are employed; however , they tend to operate with less consistency and thus  higher variations in projectile velocity.   More recently, electromechanical pneumatic valves have been tried in lieu of burst disks. These valves  avoid the per -shot expense of burst disks but the initial purchase price of  valves capable of handling high  pressures can be quite high.  Electromechanical valves also offer substantially longer pressure rise times   than do burst disks and longer barrels are necessary unl ess some sort of ret arding mechanism is used to  hold the projectile in the chamber  until peak pressure is achieved.   Requirements   In the spring of 2015 Electronics Development Corporation undertook the development of a 75-mm bore  air cannon  to be used for t he testing of munitions fuzes.  The design goal for the 75- mm air cannon is to  propel a 1- kg projecti le with a muzzle velocity of at least 75 m/s. It must use the shortest possible barrel  length and be very easy to operate. Low cost, both for cost of acquisition and cost per shot is also a factor.  

* Electronics Development Corporation, Columbia, MD;   lee.brown@elecdev.com  

Proceedings of the 45th Aerospace Mechanisms Symposium, NASA Johnson Center, 2020