condition in which the air is at ground level is warmer than the air at higher altitudes.
Under a lapse condition, particles in the atmosphere tend to fall vertically with a
minimum amount of dispersion. The reverse of this condition is known as a
temperature inversion. In an inversion condition, the air at the earth's surface is colder
than the air above it. The result is that the cool air is trapped under the warmer air and
air movement is lateral rather than vertical. Aerial distribution should be avoided under
an inversion condition since the pesticide particles will not penetrate the inversion layer
and may fall laterally far from the point of dispersal.
c. Formulation. Both liquids and granules can be dispersed from fixed and
rotary wing aircraft.
d. Droplet/Particle Size. The size of the spray droplet will affect the distance
that a pesticide will travel before reaching the ground.
e. Dust in the Atmosphere. Liquid chemical droplets adhere to dust particles
in the atmosphere and may be carried for great distances. Therefore, aerial dispersal
should be avoided under dusty conditions.
3-5. ROTARY WING AIRCRAFT AND INSECTICIDE DISPERSAL
The Army's helicopter slung, pesticide dispersal unit (PDU) can disperse liquid
and granular formulations from rotary wing aircraft. The aircraft themselves must be
provided by the requesting unit. Helicopter-mounted spray equipment is used for areas
up to 1,500 acres. If areas exceeding this size must be sprayed, the requesting unit
should submit a request for Air Force support through normal request channels. The Air
Force has C-130 aircraft that are equipped for aerial spraying missions over large areas
using liquid formulation only.
HELICOPTER SLUNG PESTICIDE DISPERSAL UNIT (PDU),
a. General. The helicopter using PDU (see figure 3-13) is designed to be used
in three configurations -- low volume (LV) liquid spray, ultra low volume (ULV) liquid
spray, and dry system. During operation, the PDU is suspended from the helicopter by
a nylon strap. All configurations consist of a hopper containing the pesticide, a self-
contained gasoline-powered engine, and a hydraulic pump. In the LV configuration,
liquid pesticide is pumped by a hydraulic motor-driven centrifugal pump from the hopper
to 34 boom spray nozzles. In the ULV spray configuration, liquid pesticide is pumped
by the centrifugal pump from the hopper to boom rotary atomizers; the rotary atomizers
are hydraulically driven. In the dry system configuration, granular pesticide (only) drops
from the hopper to the slinger where it is dispersed by hydraulic motor-driven vanes.