Venturi-type and rotary-slinger spreaders are used to distribute dry formulations of herbicides, fertilizers, and seed. Fixed-wing aircraft use venturi spreaders while helicopters use rotary spreaders. Venturi spreaders clamp to the gate box at the base of the hopper. Gate boxes are 25-, 38-, or 41-inches wide. Agitators and positive metering systems are available. Rotor spreaders are self-contained units that hang below the helicopter. A recent approach for helicopters is to use saddle tanks with an auger and forced-air boom. Additional information is covered in the chapter on Aerial Seeding.
Vanes in the spreader can be adjusted to control the swath pattern, and the pattern should be tested for even distribution of materials upon initial spreader installation. Agitators are available to assist the flow of material from the hopper. Positive metering systems are valuable for metering pelleted herbicides or hard slick grass seed in fixed-wing aircraft. Chaffy grass seed can be especially difficult to meter and operator “know-how” is valuable.