Looking at the practicality of a vehicle and its outward appearance, the countless calculations behind a successful civilian and military product are often overlooked. Safety and reliability are the first objectives to be achieved, but it is precisely safety that requires a large and demanding series of tests that must be concluded within precise parameters dictated by the type of vehicle. For this reason, based on the use (ordinary, tactical, logistic) there are specific categories of vehicles that are apparently very similar.
Among these tests is the localization of the center of gravity, an essential element to be able to catalog the specific prerogatives of a tactical vehicle.
In vehicular mechanics the concept of center of gravity, center of mass and gravity are coincident. While being able to count on different detection methods to find the position of the center of gravity of a vehicle, it is based on instruments or even on special test benches. When tilting a vehicle sideways to find the height of the center of gravity, it is essential to consider the greater load on the suspension oriented downstream, so to record certain data it becomes necessary to block the compression of the springs by leveling the vehicle as if it were level. Even the lifting (scale type) of the vehicle with ropes determines a vertical inclination line that starts from the lifting hook to reach a point on the underbody where the center of gravity falls. There are even very sophisticated instruments that determine the position of the masses in real time with the vehicle in motion, revealing and locating the center of gravity.
The tests can last even more than a year and, as far as defense is concerned, they are entrusted to CEPOLISPE (Multifunctional Experimentation Center - opening photo and following), the former Motorization Technical Center based in Montelibretti where there is a tilting platform tilt table. Here there is a lot of synergy between Army engineers and colleagues from various military manufacturing companies. The prototypes that do not pass the tests are sent back to the houses for the reported updates, while those that pass the distinct tests based on the type have the purchase approval.
TARDEC
The production of tactical vehicles for the American Armed Forces includes similar tests carried out in Warren, Michigan at the Tank Automotive Research, Development and Engineering Center (last photo), an important experimentation center for new technologies applied to Defense. Here is a modern platform called VIPER II (Vehicle Inertia Parameter Evaluation Rig) to replace the previous one VIPER I less updated.
The platform is able to measure all the specific parameters of a rotated tactical vehicle, i.e. the height of the vehicle's center of gravity, the moments of inertia of pitch, roll and yaw.
To understand the importance that these parameters play in the automotive sector, I summarize their physical characteristics:
Pitch: oscillating movement in the longitudinal direction that occurs during braking and acceleration.
Yaw: oscillation of the vehicle around its vertical axis which can be generated by the vehicle dimensions, steering angle and grip.
Roll: oscillation of the vehicle around its longitudinal axis; side lying.
Sponge: quantity that determines the dynamic behavior of a vehicle when it is subject to the influence of external forces (braking, steering, etc.). Hence the concept of inertia, that is the tendency of a body to maintain its state of motion.
The range of vehicles that can access these tests before marketing start from a Ptt of 1,5 tons up to 45 and a good 3,80 meters in width and 15 in length, including vehicles with five axles.
Although the TARDEC is also open to tests for civil vehicles, military vehicles follow a much higher test path even if they derive from civil production. A higher range is usually required from military vehicle platforms and for this reason we are talking about reinforced structures, that is, able to travel with armor or maximum loads uneven surfaces or roughness of any kind without deforming and above all maintaining manageability. Without prejudice to the almost always symmetrical appearance on both sides of a vehicle, the anti-mine structures are wider than the shape of a civil analogue and also for this reason all the inertia, roll-inclination, yaw and pitch values must be recalculated. .
The structure appears as a large computerized platform where the vehicle is positioned and is able, thanks to hydraulic jacks, to change inclination by rotating and swinging. The vehicle is monitored in its static position by signaling to the many sensors pointed in the underbody all the variations of forces and resistances acting on the empty or loaded structure (even a full tank of fuel affects the results). The difference is minimal and this platform is able to faithfully simulate a real dynamic and operational condition. However, from what is learned, the structure VIPER II it does not allow you to analyze tank trailers or tanks for structural reasons.
Photo: Italian Army / US Army
