Enhanced RAMAC performance in subdetonative propulsion mode with semi-combustible projectile

Investigations are carried out at ISL to determine the experimental conditions required to accelerate a projectile in the mass range from 1.5 to 2kg up to a muzzle velocity of 3km/s while keeping the maximum acceleration below 40,000g. Therefore, two smooth-bore ram-accelerators denoted RAMAC 30-II and RAMAC 90, in caliber 30 and 90mm respectively, are being operated in the thermally choked propulsion mode. Different matenal configurations for the projectile afterbody have been investigated, while keeping an aluminum nose cone. Besides afterbodies made of aluminum or magnesium alloy only, a third configuration is presented relying on a short magnesium part fitted to the base of an alurninum afterbody. This configuration denoted as "semi-combustible" is designed so that magnesium particles are steadily injected and burnt-out within the combustion zone at the base, therefore providing an additional heat release and consequently a significantly greater forward thrust. Experimental results achieved in both 30 and 90mm along a 300-caliber-long ram-section and using up to three different gaseous mixtures are presented. To date, for a given semi-combustible projectile and an injection velocity into the ramsection of 1380m/s, a maximum muzzle velocity of 2380m/s has been achieved in RAMAC 30-II and 2180m/s in RAMAC 90, the initial projectile mass being 69g and 1608g respectively