Ground Pattern Performance of the
Ayres Turbo Thrush with Standard Fire Door

The proper amount of gum-thickened retardant (expressed as coverage levels in gallons per 100 square feet) differs depending on the fuel model. Table 1 shows the coverage needed for specific fuel models using both the National Fire Danger Rating System (NFDRS) and Fire Behavior Fuel Model descriptions.

Table 1—Retardant coverage levels needed for specific fuel models.

The results of drop tests allow managers to estimate the length of line a specific airtanker produces at various coverage levels. Table 2 can be used to determine the maximum line length for water at each coverage level. Table 3 can be used to determine the maximum line length for foam at each coverage level. Table 4 can be used to determine the maximum line length for gum-thickened retardant at each coverage level.

Table 2—Water tests producing the longest line. All tests were conducted at airspeeds of 79 to 100 knots (91 to 115 mph).

The ground drop characteristics for the Ayres Turbo Thrush were derived through controlled test drop procedures on flat ground (Figure 3). This information is to serve only as a guide in assisting field personnel to determine the proper drop height, air speed, and door opening for delivering water, foam, or gum-thickened retardant. Actual coverage may vary depending on terrain, wind, weather, and pilot proficiency.

Figure 3—Drop test of the Ayres Turbo Thrush.