THE DESIGN WHICH FULFILS THE CONDITIONS.
In constructing any sort of machine it is usual to first obtain the
most important device and then to build up the accompanying parts to
that. We have now succeeded in evolving the thing we set out to look
for, i.e., a plane which will fly and lift with the minimum of head
resistance, and which is absolutely stable laterally and
longitudinally by reason of its construction and without any
interference from the pilot or the employment of balancing devices of
any description. We have now to fit the propelling apparatus, car, and
chassis on to this.
Fortunately, the design is one that lends itself easily to
manipulation, which is not always the case with models. The short span
of the planes, for instance, with the dihedral angle, at once suggests
girder construction (see Figs. 29, 30), which is, perhaps, the
strongest of all devices, being an M strut girder, familiar to us in
numberless bridges.
[Illustration: FIG. 29. AND FIG. 30.]
The photo which forms the frontispiece of this book, and which, by the
way, makes the car look much too large owing to its position nearest
the camera, represents a 6-foot model which was exhibited at the
Olympia Show, in order to show the construction of a full-sized
machine made to the design of the paper model. This has since been
considerably simplified, though the broad lines have been retained, by
doing away with the struts and supports at the rear. The whole of the
back plane is now supported by two curved members, which start from
the girder of the leading edge and curve down to the T-section
longitudinals which form the rigid part of the chassis. These
longitudinals and the skids end at the leading edge of the back plane
and the laminated skids and wheels are placed there. The machine is
built without a wire and without a casting. It was made entirely of
wood, but is so designed that it can be made entirely out of steel
tube by using the ordinary screw connexions. If built of timber, the
joints are made with strips of steel bolted and screwed on to the
wood. The girders forming the leading edge of each plane have sockets
formed in the upright struts of the M into which the ribs fit (see
Fig. 30), and these are solid pieces on edge tapering to the trailing
edge, where they are clipped to a slight spar which holds them
together. This construction, while very strong, is yet sufficiently
flexible to bend considerably before it reaches breaking point.
Longitudinal rigidity is secured by means of the triangular duct which
forms a complete girder from end to end. A sufficient number of
uprights fill the space between the plane and the two T-section
longitudinals which form the rigid bottom of the machine. On these
latter the floor is placed and the car is built up, enclosing all the
obstructions and putting the pilot in a place of safety, enclosed on
all sides in the middle of the strongest part of the machine, with the
strongest portion of that part between him and the ground. The centre
of gravity is situated behind the pilot in the back of the car, near
the floor, and here is space for the oil and petrol tanks. The engine
is in front of the pilot, who is thus able to control it and watch it,
and at the same time is free from the danger of having it fall upon
him in case of an accident. As the machine turns horizontally and
vertically on its centre of gravity, the front part of the car forms a
sort of baffle or blinker for the rudder and elevator to act against.
Both these are at the tail of the machine, where they have the most
leverage, and these two are controlled by the one lever, which is
pushed forward or pulled backward to raise or lower the elevator, and
turned bicycle fashion to move the rudder. As the machine balances
itself, there is no need for any balancing device either automatic or
controlled.
[Illustration: FIG. 31. ]
The propellers may be two or more, and those in front find a very firm
fixing in the intersection of two strong struts, which join the
wingtips to the bottom of the car, and the supports which run from the
centre of these to the strong joint formed by the intersection of the
longitudinal and lateral girder. At the back there may be two
propellers fixed as in the front, or one large one at the rear of the
car. They are all worked from the one engine and the thrust is
slightly above the centre of gravity. Each propeller is placed just
under the leading edge of a plane, Fig. 31, the idea being that a
certain amount of air is always thrown out by centrifugal force all
round a revolving propeller, and this air, which, ordinarily, is lost,
must, when thrown upwards, exert a lift on the under surface of the
plane. Also, when thrown towards the car, it must, by impinging on the
slanting surface of the car, tend to impel it forward, Fig. 32. Where
four propellers are used, the back pair should be of greater pitch
than the front pair, as they must to a certain extent, work in the
stream from the front pair. There are several ways of coupling the
propellers to the engine, but in the model they are shown coupled up
by belts, which seems to be the most efficient and lightest device.
[Illustration: FIG. 32.]
In order to cool the engine and keep the air in the car clear, a
ventilating pipe is led from the front of the car to the engine, and
the air, rushing through this at the speed of the machine, plays over
the engine and is conducted out through a large opening and discharged
at the back.
The whole of this part of the machine is rigid and braced together by
means of struts, though whether made of steel tube or timber, there
must always, from the nature of the construction, be a certain amount
of elasticity which makes for strength, a great advantage over a
construction braced rigidly by non-elastic wires, which snap instead
of giving to a sudden strain.
Under the two rigid T-section longitudinals there are a number of
elastic laminated wood springs set at an angle, and the lower ends of
these are pivoted on to a long elastic skid. This skid is made in
laminations, with alternate joints, and starts from the point where
the two planes intersect in the front of the machine, which is one of
the strongest joints in the whole construction. From this point it
bends out in a semicircle to protect the propeller and the front of
the machine and car, this portion of it being very elastic by reason
of the laminations having free play one upon the other. At the bottom
of the semicircle the skid is joined to the slanting skids or springs
depending from the bottom of the machine, and here the laminations are
bolted together making the skid stiffer. The skid runs the whole
length of the machine like the runner of a sledge. On this skid the
wheels are sprung with a steel spring lever arrangement, Fig. 33. The
shock of landing is, therefore, taken first on the wheels, and should
it be sufficiently heavy to cause the skids to touch the ground there
is still the series of laminated wood springs to absorb any vibrations
and prevent any possible shock to the car. The car is so secure from
vibration by reason of these precautions that the whole lower half of
the front of it may be made of protected glass, to enable the pilot to
get a clear view of his surroundings.
[Illustration: FIG. 33.]
The dimensions of the full-sized machine are estimated to be as
follows:--
Span 20 feet
Length 43 feet
Parachuting area 500 square feet
Efficient lifting area 360 square feet
Weight (all up) 800 lb.
It will be understood that though only 360 square feet is counted as
efficient for lifting, the whole 500 square feet is efficient as
parachuting surface in descending. The weight of the machine compares
very favourably with existing machines, and the load 2-1/4 lbs. per
square foot, gives plenty of margin for passenger carrying.
The chief advantages claimed for this machine are:--
(1) Speed.
(2) Stability.
(3) Strength of construction.
(4) Shock absorbing capacity.
It is a practical impossibility for the machine to turn over or be
blown over, and it will recover its balance if started at any angle.
If allowed to dive vertically, either tail first or head first, it
will recover its position in six times its own length, purely by its
own balance, without any effort of the pilot.
LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED,
GREAT WINDMILL STREET, W., AND DUKE STREET, STAMFORD STREET, S.E.