Tech Briefs

Successful development of mobile weapon systems must incorporate operation on sloped terrain.

When firing artillery, there is typically a maximum angle that the platform cannot exceed relative to the Earth plane. This is due to the large recoil forces involved and the risk of destabilizing the platform the weapon is mounted to. Mobile systems are particularly sensitive to this as the attitude of the platform relative to Earth is constantly changing. A simple solution is to add pitch and roll sensors directly to the platform. However, many mobile systems already have an assortment of sensors that can be used to calculate the platform attitude.

Excessive cant

U.S. Army weapon systems are designed to be deployed and operated wherever a need arises. This design requirement necessitates operation on a myriad of terrain types. This includes hills, mountains and ravines — locations where level ground is rare or unavailable. It follows that successful development of mobile weapon systems must incorporate operation on sloped terrain.

Sloped terrain presents challenges for firing large caliber weapons. When a weapon is fired, the forward momentum of the discharge is equally reflected to the weapon in the form of a recoiling impulse. That recoiling force can be minimized via a recoil system, which applies a lesser counter force over a calculated distance to spread the impulse over a greater period of time. However, even with sophisticated recoil systems, large caliber guns can impart significant forces into the weapon mount and, subsequently, the weapon platform. The figure below illustrates a large platform cant combined with a low firing angle tangential to that cant. Firing in this configuration could destabilize the platform, resulting in a vehicle rollover.

Sloped terrain can also impact non-firing operations. Traversing on a level platform requires force to accelerate the inertia of the mass and overcome any frictional losses. When canted, a gravitational component is added. That additional load increases with the cant angle and is reflected to the traversing mechanism requiring additional force to overcome. There are also instances when cant must be minimized in order to perform certain maintenance procedures, such as boresighting the gun tube.

Due to the challenges presented by operation on uneven terrain, determination of the weapon cant is essential. Computer controlled indirect weapon systems typically have an attitude sensing device that is aligned to the gun tube and enables precise pointing of the weapon. This device provides the attitude of the gun tube relative to Earth using a series of rotations (yaw, pitch, and roll) called Euler angles. In addition, these systems often incorporate sensors to indicate the angles of the traversing and elevating actuators relative to the platform. The weapon attitude and actuator sensor data can be used to calculate the attitude of the platform relative to Earth, as well as the maximum cant and heading values.

This work was done by Joshua Stapp for the Army Armament Research, Development and Engineering Center. ARDEC-0001