skip to main page contentUSDA Forest Service logoPrivacy | Legal Table of Contents

Back | Next | Cover Page | Cover Page		 Forest Service Technology & Development logo
Technology &
Development Center

How to Conduct Drop Tests of
Aerial Retardant Delivery Systems

Drop Test Procedures

Drop test procedures have been developed by the U.S. Department of Agriculture, Forest Service’s aerial delivery project to quantify retardant drop patterns produced by rotary and fixed-wing airtanker retardant delivery systems (figure 1). More information on the history of drop testing can be found in the publication Drop Testing Airtankers: A Discussion of the Cup-and-Grid Method (0057–2868–MTDC). Drop testing serves as the most accurate means of measuring retardant ground patterns. Tests are performed under controlled conditions, over flat terrain during low winds with steady and closely monitored flight speed, altitude, and attitude. Data from drop testing are used to quantify performance of retardant delivery systems, to define performance requirements set by the Interagency Tanker Board (IAB), to establish a relationship between drop parameters (particularly flow rate) and drop pattern (coverage levels), and to compare the performance of different retardant delivery systems. Actual performance in the field may vary.

[photo] Drop Test
Figure 1—Airtanker dropping water over a grid of cups during a drop test.

Before the drop test, metal stakes are arranged in a grid pattern and pounded into a level section of ground. A plastic cup is attached to the top of each stake. This cup holds a second cup that is cradled inside and held in place by a rubberband. Each cup holder is numbered according to its column and row location within the grid.

As the aircraft passes over, it releases the load of retardant. A lid is placed on each cup that is hit and the cup’s location number is written on the lid. These cups are removed from the grid and taken to a weighing area. The weight of retardant contained in each cup and the cup’s location are recorded. These data are used to report drop pattern characteristics.

back to main page content
Top

Back | Next

Table of Contents

Cover Page
UsableNet Approved (v. 1.4.1)
Visitor hit counter hit counter hit counter hit counter hit counter hit counter since November 10, 2004