Current incidents underline that the overturning, i.e. tipping, of tank firefighting vehicles is currently a hot topic in the firefighting sector. Rosenbauer, as an innovation and world market leader, has always diligently dealt with the topic of safety and accident prevention. Rosenbauer Engineering invests a great deal of time and energy into integrating the best possible accident prevention solutions into its products and of always being at the cutting edge of technology and setting new standards.
Rosenbauer see, first and foremost, their role as including informing relevant persons as to which physical forces act on a tank firefighting vehicle when cornering, and which measures for accident prevention can counteract these.
Weight and centrifugal force when cornering
The faster a vehicle turns into a curve, the greater the centrifugal force FF acting on its center of mass m. In this view, it is assumed that the vehicle does not push outward, i.e. slide, but instead holds the same line.
If the vehicle drives into a curve with a velocity v greater than vtipping limit, a torque MK is built up between the center of mass and the tipping point, which causes the vehicle to tip outward over the tipping point.
In the following, the force vectors of cornering at the tipping limit are shown on the left, and the force vectors of cornering above the tipping limit are shown on the right:
Mathematically, the following conclusions can be drawn from the pictures and formulas:
- The larger the track width b and the lower the center of mass h of the vehicle, the higher the centrifugal forces FF that can be tolerated by the vehicle, that is, the faster the vehicle can drive through a given curve, with a given curve radius r,, without tipping.
- The larger the curve radius r,, the faster the vehicle can drive through the curve without tipping.
- Since the mass m affects both the weight force FG and the centrifugal force FF of the vehicle, it has no direct effect on the maximum cornering speed vtipping limit with respect to tipping.
Verification of the tipping angle by means of a tipping test
Rosenbauer subjects every vehicle it manufactures to a tipping test. In this test, the vehicle is brought in an inclined position by means of swivel stage. This simulates cornering.
For firefighting vehicles to meet the general safety and performance requirements and to comply with European Standard EN 1846-2, they must be able to be tipped to the following static tipping angles, depending on their weight class and category:
A tipping angle of 30° simulates a centrifugal force FF, which corresponds exactly to half the weight force FG.
Supportive measures to reduce the risk of tipping
- The choice of the chassis significantly influences driving stability and driving safety:
- If requirements permit, selection of the widest possible axle track is advantageous.
- 4×2 drive variants are beneficial due to their significantly lower center of gravity compared to a 4×4 chassis.
- Twin tires are preferable to single tires. To be able to bear the same axle load, it would be necessary to use a single tire of a larger diameter compared to a twin tire. Therefore, the center of gravity of the vehicle would be increased, and the vehicle would have a “spongy” driving behavior.
- The availability of an assistance system, such as an ESP (Electronic Stability Program) with integrated roll-over protection system, offers additional benefits in terms of tipping stability.
Driving stability systems are not just limited to firefighting vehicles with OEM chassis, but are also provided by Rosenbauer for PANTHER ARFF vehicles. More detailed information can be found in the Blog post”Even more safety for the PANTHER“.
- Off-road tires are detrimental to on-road operations because of the reduced traction on asphalt and softer driving behavior. This would give the vehicle poorer road holding and “spongy” driving behaviour.
- As a superstructure manufacturer, Rosenbauer is responsible for ensuring that the center of gravity of the superstructure, including tank contents and load, is also designed and executed to be as low as possible.
- As a superstructure manufacturer, Rosenbauer installs an intelligent mechanical coupling between superstructure and driver’s cab on its premium AT (Advanced Technology) product. The driver receives notice of the rolling of the entire vehicle at an early stage, and, as a result of the relatively stiff overall composite, has a more direct steering control, which enables the employment of countermeasures. This reduces, among other things, the oscillation during a lane change maneuver.
- Even the most sophisticated vehicle design cannot prevent a driver from tipping over due to excessive cornering speed. However, design considerations such as those described above can reduce the risk of tipping, thereby maximizing the safe driving zone.