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checked by the banking action of the plan it will
again swing back； and again carry with it the
frame； thus setting up an oscillation； which is extremely
dangerous。
The tail E； with its unchanged angle； does not；
in any degree； aid in maintaining the frame on
an even keel。 Being nearly horizontal while in
flight； if not at a negative angle； it actually assists
the forward end of the frame to ascend。
APPLICATION OF THE NEW PRINCIPLE。Extending
the application of the suggested form； let us see
wherein it will prevent this pendulous motion at
the moment the power ceases to exert a forwardly…
propelling force。
_Fig。 21。 Synchronously moving Planes。_
In Fig。 21 the body A is shown to be equipped
with the supporting plane B and the tail a； so
they are adjustable simultaneously at the same
angle； and the weight D is placed below； similar to
the other structure。
At every moment during the forward movement
of this type of structure； the rear end of
the machine has a tendency to move upwardly；
the same as the forward end； hence； when the
weight seeks； in this case to go on； it acts on the
rear plane； or tail； and causes that end to raise；
and thus by mutual action； prevents any pendulous
swing。
LOW WEIGHT NOT NECESSARY WITH SYNCHRONOUSLY…MOVING WINGS。
A little reflection will convince
any one that if the two wings move in harmony；
the weight does not have to be placed low；
and thus still further aid in making a compact
machine。 By increasing the area of the tail； and
making that a true supporting surface； instead of
a mere idler； the weight can be moved further
back； the distance transversely across the planes
may be shortened； and in that way still further
increase the lateral stability。
CHAPTER V
DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS
THERE are three distinct types of heavier…than…
air machines； which are widely separated in all
their characteristics； so that there is scarcely a
single feature in common。
Two of them； the aeroplane； and the orthopter；
have prototypes in nature； and are distinguished
by their respective similarities to the soaring
birds； and those with flapping wings。
The Helicopter； on the other hand； has no antecedent
type； but is dependent for its raising
powers on the pull of a propeller； or a plurality
of them； constructed； as will be pointed out hereinafter。
AEROPLANES。The only form which has met
with any success is the aeroplane； which； in
practice； is made in two distinct forms； one with
a single set of supporting planes； in imitation of
birds； and called a monoplane； and the other having
two wings； one above the other； and called
the bi…plane； or two…planes。
All machines now on the market which do not
depend on wing oscillations come under those
types。
THE MONOPLANE。The single plane type has
some strong claims for support。 First of these
is the comparatively small head resistance； due
to the entire absence of vertical supporting posts；
which latter are necessary with the biplane type。
The bracing supports which hold the outer ends
of the planes are composed of wires； which offer
but little resistance； comparatively； in flight。
ITS ADVANTAGES。Then the vertical height of
the machine is much less than in the biplane。 As
a result the weight； which is farther below the
supporting surface than in the biplane； aids in
maintaining the lateral stability； particularly
since the supporting frame is higher。
Usually； for the same wing spread； the monoplane
is narrower； laterally； which is a further
aid to prevent tilting。
ITS DISADVANTAGES。But it also has disadvantages
which must be apparent from its structure。
As all the supporting surface is concentrated
in half the number of planes； they must
be made of greater width fore and aft； and this；
as we shall see； later on； proves to be a disadvantage。
It is also doubted whether the monoplane can
be made as strong structurally as the other form；
owing to the lack of the truss formation which is
the strong point with the superposed frame。 A
truss is a form of construction where braces can
be used from one member to the next； so as to
brace and stiffen the whole。
THE BIPLANE。Nature does not furnish a type
of creature which has superposed wings。 In this
particular the inventor surely did not follow nature。
The reasons which led man to employ this
type may be summarized as follows：
In experimenting with planes it is found that
a broad fore and aft surface will not lift as much
as a narrow plane。 This subject is fully explained
in the chapter on The Lifting Surfaces of
Planes。 In view of that the technical descriptions
of the operation will not be touched upon
at this place； except so far as it may be necessary
to set forth the present subject。
This peculiarity is due to the accumulation of
a mass of moving air at the rear end of the plane；
which detracts from its lifting power。 As it
would be a point of structural weakness to make
the wings narrow and very long； Wenham many
years ago suggested the idea of placing one plane
above the other； and later on Chanute； an
engineer； used that form almost exclusively； in
experimenting with his gliders。
It was due to his influence that the Wrights
adopted that form in their gliding experiments；
and later on constructed their successful flyers
in that manner。 Originally the monoplane was
the type generally employed by experimenters；
such as Lilienthal； and others。
STABILITY IN BIPLANES。Biplanes are not naturally
as stable laterally as the monoplane。
The reason is； that a downward tilt has the benefit
of only a narrow surface； comparable with the
monoplane； which has broadness of wing。
To illustrate this； let us assume that we have
a biplane with planes five feet from front to rear；
and thirty…six feet in length。 This would give
two planes with a sustaining surface of 360 square
feet。 The monoplane would； probably； divide
this area into one plane eight and a half feet from
front to rear； and 42 feet in length。
In the monoplane each wing would project out
about three feet more on each side； but it would
have eight and a half feet fore and aft spread
to the biplane's five feet； and thus act as a greater
support。
THE ORTHOPTER。The term orthopter； or ornithopter；
meaning bird wing； is applied to such
flying machines as depend on wing motion to support
them in the air。
Unquestionably； a support can be obtained by
beating on the air but to do so it is necessary to
adopt the principle employed by nature to secure
an upward propulsion。 As pointed out elsewhere；
it cannot be the concaved type of wing；
or its shape； or relative size to the weight it must
carry。
As nature has furnished such a variety of data
on these points； all varying to such a remarkable
degree； we must look els