car sliding into a ditch

Julie Taylor

Rob Getreu is Jankel’s guest blogger. Read here his thoughts on the increasing threats of RTCs in the field

Civilian Armoured Vehicles - Mobility - The Ability To Move, Turn and Stop... Before It’s Too Late!

  My purpose in a recent series of articles has been to provide a generalised understanding of the many deliberations and concerns arising when designing CAVs. To date, I have described the various considerations for determining the user requirements, as well as the desired level of protection for a civilian armoured vehicle (CAV) and the aspects that influence the ability of the vehicle to be discreet in hostile environments. In this article, my goal is to provide a broad overview about those aspects that play an important role in influencing the safe use of mobility and manoeuvrability of CAVs. These aspects are highly technical, and in keeping with this nature of these papers, I will keep my comments at a more general and first principle basis.  Tyres play a critically vital role in a vehicle’s mobility. If you think about it, there is basically a very small area of rubber that serves to safely connect a very large and heavy piece of fast moving metal… and most importantly, the people inside… to the road.  It’s important to consider several factors, some examples of which include ensuring that the tyres are correctly rated for the weight and missions of the vehicle. Additionally, are they inflated to the manufacturer’s recommended pressures? Are they in good condition?  Sadly, time and again, I have seen catastrophic - and preventable - vehicle incidents caused by incorrect weight ratings, under or over inflation, tyres in poor condition and tyres that are past their expiration date (generally speaking, tyres have a shelf life of about five years). Poor condition of tyres includes cuts and gouges in the tyre wall and minimal tread. Tyres must be checked regularly. 

Brake System - To stop or not to stop… that is the question!

  The average weight of an uparmoured CAV is approximately 5,000kg. When thinking of the momentum of this amount of metal mass travelling at say 100kph, it’s pretty clear that suitable and fit for purpose brakes are not only essential, they’re absolutely critical. I’ve seen CAVs that are put on the road with the standard OEM brakes and these are simply not suitable. In fact, they are just not safe.  Inevitably, the profile of the braking system required should be determined through an understanding the mission profiles and operating terrain for which the vehicle is intended. Brake discs and pads need to be rated for the vehicle weight and the nature of the driving environment. In using high capacity brake pads, you may also need to think about replacing callipers and installing stainless steel braided brake lines.  By way of example, locations such as Kabul, Nairobi and Jakarta are the epitome of stop/start traffic. The pressure on the brakes (particularly the front brakes) is enormous. Brake failure due to excessive hard braking is common in these locations, and so the brake system must be rated as fit for environment. In Pretoria and Johannesburg, on the other hand, you tend see faster speeds on well built roads, with softer stops, so the brake profile will likely be different.  There are numerous brake manufacturers that have products suitable for the CAV. Ideally, you should test a variety of brake system solutions with your vehicle to ascertain which provides the best performance based on user needs.  

 Suspension System

  One of the key aspects of the CAV, which significantly differs to that of a “soft skin” (i.e. non –armoured vehicle), is the centre of gravity.  When a driver brakes a moving vehicle, the car dives down at the front. When accelerating, the vehicle arches back, i.e. “squats”. Equally, you have rolling when turning corners. These movements are natural accelerative forces, and they are acting through the centre of gravity. The taller (and heavier) the vehicle, the higher the centre of gravity; thus, the more the cornering roll, squat and dive accelerative reactions. If insufficiently managed through the vehicle’s mechanical infrastructure, these movements can be potentially dangerous.  Much of the vehicle’s control is owed to the suspension design. With the height of the average Sports Utility Vehicle (SUV) and the increased body weight of approximately 5,000kg inherent in a CAV, it is vital that the suspension system is modified to cater to the vehicle’s unique dynamics. Keeping the original OEM suspension is generally not advisable. Upgraded suspension should include springs, shocks and roll bars (also known as stabiliser bars). With these, the vehicle will exhibit more controlled weight transfer, which means less rolling, squatting and diving. All up, this means far safer road handing performance.


Mobility and Speed

  Long experience in this industry has taught me that even if a vehicle has been fitted with upgraded brakes and suspension, it is excessive speed that is the most common cause of a vehicle rollover. With the uparmoured SUV’s high centre of gravity and its increased weight, a rollover is a very real probability if drivers are less than cautious with their speed during cornering. Much though we may want it, the weight and height of the uparmoured SUV will ensure that it won’t handle like a Ferrari. It just won’t hug the corners when doing 120kph, nor will it respond well to quick and sudden changes in direction.  Some time back, I learned an important lesson. A vehicle in my fleet was travelling at 110 – 120 kph along a well maintained highway and, due to debris on the road and the driver swerving at the last moment, the vehicle experienced a catastrophic rollover. To be sure, high speeds are not recommended even in a soft skin. When you add the effects of a very heavy vehicle and high centre of gravity, high speeds can be even more perilous. Thankfully, both the driver and front passenger only sustained light injuries due to wearing seat belts and the quality of the armouring. But it served as an important lesson as to keeping speed to a safe level.



Off Road Driving…. Or not

   I am often asked about taking a CAV off road. The assumption is that since it’s a four wheel drive, surely it can safely and easily go off road. Well, yes and no. Consider for a moment 5,000kg plus driving along soft sand areas like the car in the photo to the left. It’s pretty certain that the vehicle will sink. If you have VIPs in the car, chances are that this is not what they want to experience. So no, in most cases, taking the CAV off road is probably not a good idea. Can the CAV go on compacted unsealed roads? Yes, it can, but again, should the vehicle get into soft areas on the side of the road, it will increase the likelihood that it will end up being bogged and stuck. In a hostile area, this will be a highly dangerous situation, and thus significant consideration should be given prior to choosing to drive on such a road.  

 Vehicle Testing

   An important aspect of the development of a “best practice” CAV is to actually test the vehicle with the brake and suspension system to be deployed. This will give drivers, trainers and fleet managers a better idea of the vehicle’s performance, capability and limitations.  Some operators like to base the vehicle’s performance on the local vehicle licensing bureau’s requirements for a vehicle of that weight. Personally, I like using the VSAG 12 Part 3 Vehicle Testing and Trial Log Methodology (and potentially also the PAS 301 currently in development). It provides a good broad range of considerations including axle loads, performance, handling, braking, Run-Flats and acceleration. Importantly too, it does not set specific and/or arbitrary numerical scores. What it does is provide four possible assessments (does not satisfy, partially satisfies, substantially satisfies and fully satisfies), which allows users to make their own judgments based upon their specific requirements and operating conditions. The vehicle’s overall mobility then becomes a combination of these many factors and matches better with the users’ requirements and expectations.  

 Summary

   A CAV’s ability to safely manoeuvre will be a function of a number of factors, not least being its mobility systems: tyres, brakes and suspension.  Importantly, these need to be fit for purpose for a vehicle of uparmoured weight. They need to be tested and aligned to the proposed operating conditions. Drivers, trainers, maintainers and fleet managers should also understand what to expect as to its performance so as to then anticipate and manage the operation of the vehicle in the field. Additionally, safe use with regard to speed, handling and roads used must be kept front of mind.  The bottom line? Every human and mechanical precaution must be taken when structuring and driving a CAV. Safety in mobility just can’t be overstated.  For more information from Rob contact him at rob@nefeshconsulting.com   Click here for more information on the standards a CAV should meet.
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