FLIGHT
12
JULY 4TH, 1943
Full-size mock-up of the " Air Horse." The first machine to be built will be used for pest destruction.
Cierva "Air Horse
A Three-rotor Helicopter with Three Tons Pay Load : Specially
Designed for Pest Destruction
H
ITHERTO one has been accustomed to think of
helicopters mainly as small aircraft. The limiting
factor of helicopter size appears to be. rotor diameter, and in the present state of the art at any rate,
really large size implies a multiplicity of rptors. Consequently it is not surprising that the ufiBjieli£opter designed by the Cierva Autogiro Co., KfaTTand ncwsbeing
built under a recent agreement witkCunliffe-Owen) Aircraft at the Southampton Airport for
l
is based on a three-rotor arrangement.
To Dr. Ripper, of Pest Control, Ltd., goes the credit
for having foreseen the advantages of the helicopter type
of aircraft for the destruction of pests. His patent has
as its chief claim the utilization of the slipstream from
a helicopter rotor for circulating the chemically laden
spray so as to ensure that the poison reaches the undersurfaces of foliage, where the majority of the insects
appear to concentrate. The Cierva company adapted an
existing Sikorsky R.4 for experimental work. Artificial
foliage was coated with a substance which would be discoloured by the spray from the helicopter, and it was
found that the downwash from the rotor very effectively
coloured the underside of the leaves, thus proving Dr.
Ripper's contention.
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Rotor Loads
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The Cierva company has now been entrusted with the
task of building a very large helicopter (15,000 lb loaded
weight) for pest destruction at home and in many parts
of the Empire. If the scheme works as expected (and
there is every reason to believe that it will) the undertaking may be of very great
importance to the Empire,
especially in these days of
food shortage, when maximum yield of crops is so
vital.
It is very fitting that the
Cierva Autogiro Co., Ltd.,
* should be the pioneers in
this work, for that firm can
A Merlin XXXII installed in
the mock-up. Rotor drive is
divided into primary and secondary transmission. An axialflow fan with variable-pitch
blades gives the desired massflow through the radiator under
ali conditions.
be regarded as the mother of rotating-wing aircraft, and it
has had, in conjunction with its licensees, G. and J. Weir,
Ltd., long experience in the development of this type of
aircraft.* Full use of this accumulated knowledge has
been made in the design of the '' Air Horse,'' as the new
helicopter has been named. The only innovation introduced is the three-rotor arrangement, and as this should
basically make for stability there is every prospect of
success with this seemingly ambitious project. At a loaded
weight of 15,000 lb, the average loading of each rotor will
be only 5,000 lb., which is within the range of presentday experience.
Operating' Height a n d Range
The' working conditions of a helicopter designed specifically for pest destruction are somewhat unusual. Forward speed is unimportant, but great load-carrying
capacity is required, and a remarkable feature is that the
useful load is consumed at a very high rate. Thus every
flight will usually begin at maximum weight, and a landing will be made a comparatively short time later at
almost empty weight. Furthermore, the height above the
ground will be almost zero (within a rotor diameter or so
of the top of the crop being sprayed), although that above
sea level may be fairly great in some parts of the Empire.
While flight at zero height is an aerodynamic advantage, owing to the so-called ground effect, it introduces a
risk in that an engine stoppage will leave little time for
* An account of the development work done on helicopters by G. and J.
Weir, Ltd., was published in our issue of Mas; 1 lth, 1944.