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and weather (I think that's all).
Organisation, however, is most
important. If you keep changing
chemicals, the whole pattern of work
will be disrupted, so grouping crops
that require the same cover on a
regular basis can get rid of not only
dead ferrying time, but also
unnecessary cleaning of tanks. Very
often, you can expect to top up with
fuel after every delivery, to get the
maximum spread.
To minimise weight, liquid solutions
will be more concentrated than
normal, and exposing yourself and
ground staff to the spray must be
regarded as a possibility, either by
ingestion, skin contact (sometimes
through the eyes) or inhalation.
Remember, whatever it is kills
things, so it will be toxic—the larger
the LD50 value, the less it will be, but
below 10 is regarded as extremely
toxic (LD50 indicates a dose that will
kill 50% of test animals within a
certain period, and refers to acute
toxicity). Minimise skin
contamination with rubber gloves
and boots (unlined), and clean
clothing which includes long
trousers and sleeves, which is just
what you need on a hot day,
especially with coveralls on top
(wear trouser legs outside boots). It's
not essential to use anything
waterproof unless you actually
expect to get drenched, or are
working in a mist. Cover cuts and
abrasions. Flaggers can avoid
exposure to whatever is being
sprayed by simply keeping out of the
way of each pass.
Acute poisoning refers to a single
dose, while chronic poisoning arises
from many non-poisonous doses
over time.
Spray Drift
This is the movement of whatever
you're spraying to areas it was not
intended for. It's undesirable, not
only because it reduces the chemical
used on the job, but it also causes
damage in non-target areas due to
concentrated amounts accumulating
downwind, sometimes more than
that applied to the target (it's also
trespassing). Spray Drift is affected
by greater wind velocity at height,
volatility of the solution, temperature
inversions combined with spray
pressure, nozzle spray angle and air
movement around the aircraft. You
can reduce the chances of it by
releasing large droplets close to the
target, by:
· Flying as low and slow as
possible.
42 The Helicopter Pilot’s Handbook
· Locating nozzles away from
rotor tips.
· Placing the spray boom as far
forward as possible.
· Orienting nozzles backward and
spacing for uniform patterns.
· Using low nozzle pressures.
· Using larger orifices in the
nozzles.
· Spraying when winds are light
and the air is cool, about 4 a.m.
· Using herbicides that do not
produce damaging vapours.
· Using buffer zones, particularly
around water
You can also modify the solution
with additives that produce more
viscosity (adjuvants), or with an invert
emulsion system, which will apply a
mayonnaise-like material. They both
have disadvantages, though, in either
needing specialised equipment or
mixing techniques.
If you're trying to increase the
volume of solution over a particular
area, you're better off tinkering with
the nozzles than reducing speed or
raising spray pressure. This will help
to avoid small droplets, or 'fines',
that are more likely to drift. There
are some crops, however, that
require good coverage and small
droplets, which is the opposite. This
is where you need to be a bit of a
chemist as well as a pilot to satisfy
the customer.
Vapour drift is a similar effect arising
from evaporation.
Accurate records are essential, not
only as aids to the business but also
for later complaints of drifting. It's
helpful to note such items as nozzle
size and spacing, wind velocity and
weather conditions, rate of
application and time on task,
together with a diagram (which you
should have made anyway, for
planning purposes—many pilots use
an aerial photograph and keep a log
of the tracks flown with a marker).
Seeding
When a pipeline, or similar, has been
laid, the countryside has to made to
look attractive again as soon as
possible. A large hopper full of grass
seed is used to do this, and you will
get to do a series of runs over the
pipeline to spread it.
The hopper is basically a large
fibreglass bucket that weighs about
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The Helicopter Pilot’s Handbook(28)
