Armored Vehicles and The Center of Gravity

Armored Vehicles and The Center of Gravity

By Tony Scotti on January 16th, 2020

This article will discuss the Vehicle’s Center of Gravity (CG).

First, some basic definitions:

The Center of Gravity. The Center of Gravity (CG) is the point on the vehicle where all the weight is balanced. It is measured from the ground to a point in the vehicle’s height and width. All forces acting on a vehicle act through the CG.

The height of the center of gravity. The height of the CG relative to the wheelbase determines weight transfer between the front and rear. CG height to track width determines the weight transfer from side to side.

Weight above the center of gravity. In an armored vehicle, the weight above the CG is an important vehicle characteristic. It determines the vehicle’s tendency to roll over and is a significant factor in the vehicle’s emergency maneuvering capability.

Additional weight on the tires affects the contact patch. All vehicles are supported by a cushion of air contained in four flexible rubber tires. Each of these four small patches of rubber is known as the “contact patch.” These are the only points of contact between the armored vehicle and the road. It is these four patches that create the traction which makes the vehicle – go – stop and turn – that send the feedback back to the driver, and it is these four patches the driver has to manage. Consider them to be a source of information needed to control the vehicle. The contact patch is sensitive to weight – all modifications made by the armorer affect the contact patch. The next newsletter will cover armored vehicles and tires. An article:

http://vehicledynamics.com/the-tire-contact-patch/

The Problem

In an emergency maneuver – either accident avoidance or vehicle violence – the driver will be required to apply 80 to 100 % of the vehicle’s weight pushing on the vehicle’s CG. The concerns:

1. The CG height – The higher the CG, the more weight will be transferred to the vehicle’s tire contact patch.

2. The weight above the center of gravity. The majority of the vehicle’s weight comes from the windshield. The heavier the windshield and the greater the distance from the CG to the windshield, the more weight is transferred to the contact patch.

Questions on CG Height

Has the armorer computed the CG height? Although this may seem complicated, there are some simple methods that can be used to determine CG.

Questions on Weight Transfer

Have the spring and shock absorbers been modified to compensate for the additional weight and weight transfer? Not just add stiffer springs and more shocks – has the manufacturer computed/measured the weight transfer and thoughtfully compensated for the additional weight transfer?

Questions – Braking

An increase in weight also decreases brake life. The energy the brakes must absorb and dissipate is a function of the vehicle’s weight and changes in speed. What has the manufacturer done to compensate for the additional energy the brakes must absorb?

Ask the armored vehicle manufacture if the vehicle has been tested to the PAS 301 Standards. PAS 301 is a standard that describes test methods that may be completed on a civilian armored vehicle (CAV) to assess its automotive characteristics for payload, acceleration, maximum speed, through gear acceleration, handling, braking, and run-flat.