Northrop Grumman has carried out successful ground tests of a Solid Fuel RamJet (SFRJ) tactical engine that the company is developing for the US Army. Part of the Army's XM1155 Extended-Range Artillery Projectile (ERAP) program, the engine is designed to boost the effective range of a 155 mm artillery shell to over 62 miles (100 km).
Even in an age of missile-firing drones and laser weapons, artillery is still the cornerstone of fire support for infantry and other ground forces. The problem is that artillery pieces have a relatively short effective range. Worse, the shells that they fire can only follow a ballistic trajectory, which means that once the projectile leaves the gun muzzle, there's no way of altering its course, so it isn't very effective against a target that's actively avoiding the fall of shot.
There are a number of ways of overcoming this being explored and one of the more promising is the SFRJ. A ramjet is also known as a flying stovepipe because it is basically an empty tube into which fuel is sprayed. That may seem pointless, but when that tube is moving at high speed, especially in the supersonic range, its forward motion compresses the incoming air before burning the fuel, producing thrust without the need for moving parts.
A solid-fuel ramjet is a version that, as the name implies, uses a solid fuel lining the engine instead of injecting liquid jet fuel. The same compression and combustion occurs, producing thrust. It's technology that's being developed for a number of uses, including boosting hypersonic missiles and enhancing the performance of artillery.
Firing a SFRJ-equipped shell accelerates the engine to its operational velocity so it can ignite. Once it is running, it not only increases the range of the projectile, it also changes its flight characteristics because the engine keeps the shell from slowing down due to air resistance. In addition, it allows the shell to be steered in flight, making it more precise and capable of hitting a moving target.
The Phase One XM1155 ERAP ground tests included the firing of multiple rounds and determined that the SFRJ's survivability and the performance met predictions. The eventual goal is to produce a shell that can be used against stationary and moving high-level targets in all weather conditions and any terrain.
"Successful completion of the rigorous tests of the Solid Fuel Ramjet demonstrates maturation of the technology to survive the very challenging gun-launch environment and significantly extend the range of the US military’s current field artillery with a high level of confidence," says Pat Nolan, vice president, missile products, Northrop Grumman.
Source: Northrop Grumman
