The USDA forest service in the United States and the CEREN in France test the airtankers according to the Cup & Grid method. They measure the coverage level on the ground. These coverage level are expressed in l/m2 or in GPC ( 1 GPC = 0.4 l/m2) . They are presented graphically and each colour corresponds to a coverage level.
By studying the data of the USDA Forest Service, Dominique Legendre discovered a physical law (2) establishing a relationship between the coverage levels and certain characteristics of the drop systems:
• Liquid velocity at exit of aircraft
• Surface of hatches
• Aircraft speed
He developed the NaSCa software able to predict the drop pattern of any delivery system.
What’s the meaning of the lines?
Unlike the lines of Nasca in Peru that inspired the name of the software, the origin of the coloured curves of Nasca is known. Each coloured line corresponds to a particular coverage level. The line defines the area in which the coverage level will be greater than a given value. For example, in the above drop, the entire area surrounded by the magenta line receives more than 3 GPC (more than 1.2 l/m2).
The advatages of
If we compare the Nasca prediction and the Cup&grid test drop patterns for the same configuration, we see that Nasca is very close (irregularities taken a part) to the actual drop.
If Nasca predicts a certain level of recovery, the actual value will never be higher. This precision makes it possible to know the maximum performance of a configuration.
During the design phase, the main elements of the drop systems can be dimensioned and it is possible to avoid the conception of an inefficient or under dimensioned system.
During the flight tests, only a few drop tests are necessary to refine the working hypotheses. Once these settings are validated, Nasca can predict the system performances in all configurations. This feature significantly reduces the cost of flight testing.
AFF North America 2020