HELICOPTER MODELS.
§ 1. There is no difficulty whatever about making successful model
helicopters, whatever there may be about full-sized machines.
§ 2. The earliest flying models were helicopters. As early as 1796 Sir
George Cayley constructed a perfectly successful helicopter model (see
ch. iii.); it should be noticed the screws were superimposed and
rotated in opposite directions.
§ 3. In 1842 a Mr. Phillips constructed a successful power-driven
model helicopter. The model was made entirely of metal, and when
complete and charged weighed 2 lb. It consisted of a boiler or steam
generator and four fans supported between eight arms. The fans had an
inclination to the horizon of 20°, and through the arms the steam
rushed on the principle of Hero's engines (Barker's Mill Principle
probably). By the escape of steam from the arms the fans were caused
to revolve with immense energy, so much so that the model rose to an
immense altitude and flew across two fields before it alighted. The
motive power employed was obtained from the combustion of charcoal,
nitre and gypsum, as used in the original fire annihilator; the
products of combustion mixing with water in the boiler and forming
gas-charged steam, which was delivered at high pressure from the
extremities of the eight arms.[47] This model and its flight (fully
authenticated) is full of interest and should not be lost sight of, as
in all probability being the first model actuated by steam which
actually flew.
The helicopter is but a particular phase of the aeroplane.
§ 4. The simplest form of helicopter is that in which the torque of
the propeller is resisted by a vertical loose fabric plane, so
designed as itself to form a propeller, rotating in the opposite
direction. These little toys can be bought at any good toy shop from
about 6_d._ to 1_s._ Supposing we desire to construct a helicopter of
a more ambitious and scientific character, possessing a vertically
rotating propeller or propellers for horizontal propulsion, as well as
horizontally rotating propellers for lifting purposes.
[Illustration: FIG. 51.--INCORRECT WAY OF ARRANGING SCREWS.]
§ 5. There is one essential point that must be carefully attended to,
and that is, _that the horizontal propulsive thrust must be in the
same plane as the vertical lift_, or the only effect will be to cause
our model to turn somersaults. I speak from experience.
When the horizontally revolving propellers are driven in a horizontal
direction their "lifting" powers will be materially increased, as they
will (like an ordinary aeroplane) be advancing on to fresh undisturbed
air.
§ 6. I have not for ordinary purposes advocated very light weight wire
framework fabric-covered screws, but in a case like this where the
thrust from the propeller has to be more than the total weight of the
machine, these might possibly be used with advantage.
§ 7. Instead of using two long vertical rods as well as one long
horizontal one for the rubber strands, we might dispense with the two
vertical ones altogether and use light gearing to turn the torque
action through a right angle for the lifting screws, and use three
separate horizontal rubber strands for the three propellers on a
suitable light horizontal framework. Such should result in a
considerable saving of weight.
[Illustration: FIG. 52.--CORRECT MANNER. A, B, C = Screws.]
§ 8. The model would require something in the nature of a vertical fin
or keel to give the sense of direction. Four propellers, two for
"lift" and two for "drift," would undoubtedly be a better
arrangement.
FOOTNOTE:
[47] Report on First Exhibition of Aeronautical Society of Great
Britain, held at Crystal Palace, June 1868.