Dimensioning of an hydraulic system
for water bombing from an aircraft
First, we gathered information on forest fires and means to fight them.
Source : http://fr.wikipedia.org/
A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. A wildfire differs from other fire by its extensive size, the speed at which it can spread out from its original source, its potention to change direction unexpectedly and its ability to jump gaps such as roads, rivers and fire breacks. Wildfires are characterized in terms of the cause of ignitation, their physical properties such as speed of propogation, the combustible material present and the effect of weather on the fire.
Wildfires occur when all ot the necessary elements of a fire triangle come together in a susceptible area: an ignition source is brought into contact with a combustible material such as vegetation, that is subjected to sufficient heat and has adequate supply of oxygen from the ambient air, that's the fire triangle.
Source : http://www.assessco.co.uk/
The tools to combat forests fires
The best known means to extinguish a flame is water: in contact with heat, water evaporates, and the created water vapor drives the air, depriving the fire of oxidizer. Besides, water participates in the cooling (vaporization absorbs heat): the rise of the temperature of the water consumes energy, but the transition from one state to another consumes even more energy. Thus, water cools the air, smoke, objects... and prevent the fire from spreading. The extinction is therefore a combination of choking by steam and cooling.
To that end, civilian security uses water bombing aircrafts to drop water, foam or retardants on forest fires. These fluids have different chemical characteristics, which allows them to have different actions to fight the fire. The problem is that the kind of fluid influences the footprints on the ground because it has effects on how the fluid atomise.
For instance, retardants can capture the heat of a fire, the temperature decreases and the combustion is stopped when the temperature falls below the ignition point. The retardant also slows the spread of fire, because it prevents the distillation of essences of vegetation which are highly flammable. The retardant is red so that the pilots of water bombing aircrafts can see where the retardant is spread.