Better airtanker firefighting: a challenge for fluid dynamics

Airtanker firefighting is a fascinating tool operated to fight wildland fires. Airtankers are based on aircraft or helicopters and they are developed considering empirical methods. Their performance is currently discovered after drop tests made above a grid of cups distributed on a plane field with no vegetation (the cup & grid method) developed during the 90's. Dropping a liquid from an aircraft is a priori easy to achieve because the released liquid directly falls down to the ground due to gravity. However, the liquid deposit on ground is not uniform, thus creating preferential paths for the fire to propagate. The fluid dynamics processes that govern this practice is characterized by rich and varied physical phenomena, and controlling the resulting fluid distribution of the drop pattern raises many scientific issues. The liquid column penetration in the air, its large scale column fragmentation and an intense surface atomization process give shape to the rainfall produced by the airtanker and the final product deposition onto the canopy. The respective roles of these mechanisms will be described in order to discuss the parameters of importance for improving airtanker drop performance for more efficient firefighting.