Variability
To understand the variability between drops and within the experiment, replicate drops were made where the height, flow rate, speed, volume, and material dropped were constant. The effects of humidity, wind, and temperature were low enough to be assumed to be negligible. Basically, three drop types were tested with two replicates each (table 5).
The winds were equal to or less than 5 miles per hour, the temperature was between 70 and 90 °F, and the relative humidity was between 29 and 56 percent. Lids were placed on all the cups within 10 minutes, minimizing the liquid lost to evaporation.
| Drop Test | Height (feet) | Speed (knots) | Flow rate (gallons per second) | Volume (gallons) | Material |
|---|---|---|---|---|---|
| 201 and 202 | 150 to 160 | 131 | 250 | 900 | H2O |
| 203 and 204 | 145 to 160 | 130 to 133 | 250 | 871 to 877 | GTS-R |
| 205 and 206 | 155 to 160 | 133 to 137 | 500 | 821 to 958 | GTS-R |
Analysis of Variance (ANOVA) Results
The anaysis of variance (ANOVA) results (appendix A) demonstrate how differences between factors can be compared. For instance, the mean continuous line length at 0.5 gpc for water is greater than the mean, continuous line length for GTS-R retardant (p-value of 0.000388). It also shows that the line length associated with the low flow rate of 250 gallons per second is longer at 0.5 gpc than the length associated with the high flow rate of 500 gallons per second (p-value of 0.0000955).
Figure 15 illustrates some differences within the replicates. The scatterplots show gpc levels by row, presenting a horizontal profile of the drop. Drops 201 and 202 are fairly similar. They have two distinct peaks, tapering off on either end. The line length charts indicate similar line lengths except for 2 and 8 gpc.
Figure 15—Comparison of line lengths at different
gpc
levels for drops 201 and 202.
The scatterplots for drops 203 and 204 (figure 16) are not quite as similar as the scatterplots for drops 201 and 202, but the line length chart for drop 203 is similar to that for 204, except for 2 gpc.
Figure 17 shows similar profiles for drops 205 and 206. Drop 205 has more points at coverage levels higher than 4 gpc. The line lengths are similar with discrepancies
Figure 16—Comparison of line lengths at different
gpc levels for drops 203 and 204.
Figure 17—Comparison of line lengths at different
gpc levels for drops 205 and 206.
