+-------------------------------------------------+------------------------------------+
| INSECTS | BIRDS. |
+---------------------------+---------------------+-------------------+----------------+
| | Flying Surface | | |
| | referred to the | | Flying Surface |
| | Kilogramme | | referred to the|
| Names. | = 2 lb. 8 oz. 3 dwt.| Names. | Kilogramme. |
| | 2 gr. avoird. | | |
| | = 2 lb. 3 oz. 4.428 | | |
| | dr. troy. | | |
+---------------------------+---------------------+-------------------+----------------+
| | sq. | | sq. |
| | yds. ft. in. | | yds. ft. in. |
| Gnat | 11 8 92 | Swallow | 1 1 104-1/2 |
| Dragon-fly (small) | 7 2 56 | Sparrow | 0 5 142-1/2 |
| Coccinella (Lady-bird) | 5 13 87 | Turtle-dove | 0 4 100-1/2 |
| Dragon-fly (common) | 5 2 89 | Pigeon | 0 2 113 |
| Tipula, or Daddy-long-legs| 3 5 11 | Stork | 0 2 20 |
| Bee | 1 2 74-1/2 | Vulture | 0 1 116 |
| Meat-fly | 1 3 54-1/2 | Crane of Australia| 0 0 130 |
| Drone (blue) | 1 2 20 | | |
| Cockchafer | 1 2 50 | | |
| / Stag-beetle \ | | | |
| Lucanus < (female) / | 1 1 39-1/2 | | |
| cervus | Stag-beetle \ | | | |
| \ (male) / | 0 8 33 | | |
| Rhinoceros-beetle | 0 6 122-1/2 | | |
+---------------------------+---------------------+-------------------+----------------+
"It is easy, by the aid of this table, to follow the order, always
decreasing, of the surfaces, in proportion as the winged animal
increases in size and weight. Thus, in comparing the insects with one
another, we find that the gnat, which weighs 460 times less than the
stag-beetle, has 14 times more of surface. The lady-bird weighs 150
times less than the stag-beetle, and possesses 5 times more of
surface, &c. It is the same with the birds. The sparrow weighs about
10 times less than the pigeon, and has twice as much surface. The
pigeon weighs about 8 times less than the stork, and has twice as much
surface. The sparrow weighs 339 times less than the Australian crane,
and possesses 7 times more surface, &c. If now we compare the insects
and the birds, the gradation will become even much more striking. The
gnat, for example, weighs 97,000 times less than the pigeon, and has
40 times more surface; it weighs three millions of times less than the
crane of Australia, and possesses 140 times more of surface than this
latter, the weight of which is about 9 kilogrammes 500 grammes (25 lb.
5 oz. 9 dwt. troy, 20 lb. 15 oz. 2-1/4 dr. avoirdupois).
"The Australian crane, the heaviest bird weighed, is that which has
the smallest amount of surface, for, referred to the kilogramme, it
does not give us a surface of more than 899 square centimetres (139
sq. in.), that is to say, about an eleventh part of a square metre.
But every one knows that these grallatorial animals are excellent
birds of flight. Of all travelling birds they undertake the longest
and most remote journeys. They are, in addition, the eagle excepted,
the birds which elevate themselves the highest, and the flight of
which is the longest maintained."[12]
The way in which the natural wing rises and falls on the air, and
reciprocates with the body of the flying creature, has a very obvious
bearing upon artificial flight. In natural flight the body of the flying
creature falls slightly forward in a curve when the wing ascends, and
is slightly elevated in a curve when the wing descends. The wing and
body are consequently always playing at cross purposes, the wing rising
when the body is falling and vice versa. The alternate rise and fall of
the body and wing of the bird are well seen when contemplating the
flight of the gull from the stern of a steamboat, as the bird is
following in the wake of the vessel. The complementary movements
referred to are indicated at fig. 29, where the continuous waved line
represents the trajectory made by the wing, and the dotted waved line
that made by the body. As will be seen from this figure, _the wing
advances both when it rises and when it falls_. It is a peculiarity of
natural wings, and of artificial wings constructed on the principle of
living wings, that when forcibly elevated or depressed, even in a
strictly vertical direction, they inevitably dart forward. If, for
instance, the wing is suddenly depressed in a vertical direction, as at
a b of fig. 29, it at once darts downwards and forwards in a double
curve (see continuous line of figure) to c, thus converting the vertical
down stroke into a _down, oblique, forward stroke_. If, again, the wing
be suddenly elevated in a strictly vertical direction, as at c d, the
wing as certainly darts upwards and forwards in a double curve to e,
thus converting the vertical up strokes into an _upward, oblique,
forward stroke_. The same thing happens when the wing is depressed from
e to f and elevated from g to h, the wing describing a _waved track_ as
at e g, g i.
[Illustration: FIG. 29 shows how in progressive flight the wing and the
body describe _waved tracks_,--the crests of the waves made by the wing
(a, c, e, g, i) being placed opposite the crests of the waves made by
the body (1, 2, 3, 4, 5).]
There are good reasons why the wings should always be in advance of the
body. A bird when flying is a body in motion; but a body in motion tends
to fall not vertically downwards, but _downwards and forwards_. The
wings consequently must be made to strike _forwards_ and kept in advance
of the body of the bird if they are to prevent the bird from falling
_downwards and forwards_. If the wings were to strike backwards in
aerial flight, the bird would turn a forward somersault.
That the wings invariably strike forwards during the down and up strokes
in aerial flight is proved alike by observation and experiment. If any
one watches a bird rising from the ground or the water, he cannot fail
to perceive that the head and body are slightly tilted upwards, and that
the wings are made to descend with great vigour in a downward and
_forward_ direction. The dead natural wing and a properly constructed
artificial wing act in precisely the same way. If the wing of a gannet,
just shot, be removed and made to flap in what the operator believes to
be a strictly vertical downward direction, the tip of the wing, in spite
of him, will dart forwards between 2 and 3 ft.--the amount of forward
movement being regulated by the rapidity of the down stroke. This is a
very striking experiment. The same thing happens with a properly
constructed artificial wing. The down stroke with the artificial as with
the natural wing is invariably converted into an oblique, downward and
forward stroke. No one ever saw a bird in the air flapping its wings
towards its tail. The old idea was that the wings during the down stroke
_pushed_ the body of the bird in an upward and forward direction; in
reality the wings do not push but _pull_, and in order to pull they must
always be in advance of the body to be flown. If the wings did not
themselves fly _forward_, they could not possibly cause the body of the
bird to fly forward. It is the wings which cause the bird to fly.
It only remains to be stated that the wing acts as a true kite, during
both the down and the up strokes, its under concave or biting surface,
in virtue of the forward travel communicated to it by the body of the
flying creature, being closely applied to the air, during both its
ascent and its descent. This explains how the wing furnishes a
persistent buoyancy alike when it rises and when it falls (fig. 30).
[Illustration: FIG. 30 shows the kite-like action of the wing during the
down and up strokes, how the angles made by the wing with the horizon
(_a, b_) vary at every stage of these strokes, and how the wing evades
the superimposed air during the up stroke, and seizes the nether air
during the down stroke. In this figure the spaces between the double
dotted lines (c g, i b) represent the down strokes, the single dotted
line (h, i) representing the up stroke. The kite-like surfaces and
angles made by the wing with the horizon (a, b) during the down strokes
are indicated at c d e f g, j k l m,--those made during the up strokes
being indicated at g h i. As the down and up strokes run into each
other, and the convex surface of the wing is always directed upwards and
the concave surface downwards, it follows that the upper surface of the
wing evades in a great measure the upper air, while the under surface
seizes the nether air. It is easy to understand from this figure how the
wing always flying forwards furnishes a persistent buoyancy.]
The natural kite formed by the wing differs from the artificial kite
only in this, that the former is capable of being moved in all its
parts, and is more or less flexible and elastic, whereas the latter is
comparatively rigid. The flexibility and elasticity of the kite formed
by the natural wing are rendered necessary by the fact that the wing, as
already stated, is practically hinged at its root and along its anterior
margin, an arrangement which necessitates its several parts travelling
at different degrees of speed, in proportion as they are removed from
the axes of rotation. Thus the tip travels at a higher speed than the
root, and the posterior margin than the anterior margin. This begets a
_twisting diagonal movement_ of the wing on its long axis, which, but
for the elasticity referred to, would break the wing into fragments. The
elasticity contributes also to the continuous play of the wing, and
ensures that no two parts of it shall reverse at exactly the same
instant. If the wing was inelastic, every part of it would reverse at
precisely the same moment, and its vibration would be characterized by
pauses or dead points at the end of the down and up strokes which would
be fatal to it as a flying organ. The elastic properties of the wing are
absolutely essential, when the mechanism and movements of the pinion are
taken into account. A rigid wing can never be an effective flying
instrument.
The kite-like surfaces referred to in natural flight are those upon
which the constructors of flying machines very properly ground their
hopes of ultimate success. These surfaces may be conferred on artificial
wings, aeroplanes, aerial screws or similar structures; and these
structures, if we may judge from what we find in nature, _should be of
moderate size and elastic_. The power of the flying organs will be
increased if they are driven at a comparatively high speed, and
particularly if they are made to reverse and reciprocate, as in this
case they will practically create the currents upon which they are
destined to rise and advance. The angles made by the kite-like surfaces
with the horizon should vary according to circumstances. They should be
small when the speed is high, and vice versa. This, as stated, is true
of natural wings. It should also be true of artificial wings and their
analogues.
_Artificial Flight_.--We are now in a position to enter upon a
consideration of artificial wings and wing movements, and of artificial
flight and flying machines.
We begin with artificial wings. The first properly authenticated account
of an artificial wing was given by G.A. Borelli in 1670. This author,
distinguished alike as a physiologist, mathematician and mechanician,
describes and figures a bird with artificial wings, each of which
consists of _a rigid rod in front and flexible feathers behind_. The
wings are represented as striking _vertically downwards_, as the annexed
duplicate of Borelli's figure shows (fig. 31).
Borelli was of opinion that flight resulted from the application of an
inclined plane, which beats the air, and which has a wedge action. He,
in fact, endeavours to prove that a bird wedges itself forward upon the
air by the perpendicular vibration of its wings, the wings during their
action forming a wedge, the base of which (c b e) is directed towards
the head of the bird, the apex (a f) being directed towards the tail
(d). In the 196th proposition of his work (_De motu animalium_, Leiden,
1685) he states that--
"If the expanded wings of a bird suspended in the air shall strike the
undisturbed air beneath it with a motion _perpendicular to the
horizon_, the bird will fly with a _transverse motion_ in a plane
parallel with the horizon." "If," he adds, "the wings of the bird be
expanded, and the under surfaces of the wings be struck by the air
_ascending perpendicularly to the horizon_ with such a force as shall
prevent the bird gliding downwards (i.e. with a tendency to glide
downwards) from falling, it will be urged in a horizontal direction."
[Illustration: FIG. 31. Borelli's bird with artificial wings.
r e, Anterior margin of the right wing, consisting of a rigid rod.
o a, Posterior margin of the right wing, consisting of flexible
feathers.
b c, Anterior; and
f, Posterior margins of the left wing same as the right.
d, Tail of the bird.
r g, d h, Vertical direction of the down stroke of the wing.]
The same argument is restated in different words as under:--"If the
air under the wings be struck by the flexible portions of the wings
(_flabella_, literally fly flaps or small fans) with a motion
perpendicular to the horizon, the sails (_vela_) and flexible portions
of the wings (_flabella_) will yield in an upward direction and form a
wedge, the point of which is directed towards the tail. Whether,
therefore, the air strikes the wings from below, or the wings strike
the air from above, the result is the same,--the posterior or flexible
margins of the wings _yield in an upward direction_, and in so doing
urge the bird in a _horizontal direction_."
There are three points in Borelli's argument to which it is necessary to
draw attention: (1) the direction of the down stroke: it is stated to be
_vertically downwards_; (2) the construction of the anterior margin of
the wing: it is stated to consist of _a rigid rod_; (3) the function
delegated to the posterior margin of the wing: it is said _to yield in
an upward direction_ during the down stroke.
With regard to the first point. It is incorrect to say the wing strikes
vertically downwards, for, as already explained, the body of a flying
bird is a body in motion; but as a body in motion tends to fall
downwards and forwards, the wing must strike downwards and forwards in
order effectually to prevent its fall. Moreover, in point of fact, all
natural wings, and all artificial wings constructed on the natural type,
invariably strike downwards and forwards.
With regard to the second point, viz. the supposed rigidity of the
anterior margin of the wing, it is only necessary to examine the
anterior margins of natural wings to be convinced that they are in every
case flexible and elastic. Similar remarks apply to properly constructed
artificial wings. If the anterior margins of natural and artificial
wings were rigid, it would be impossible to make them vibrate smoothly
and continuously. This is a matter of experiment. If a rigid rod, or a
wing with a rigid anterior margin, be made to vibrate, the vibration is
characterized by an unequal jerky motion, at the end of the down and up
strokes, which contrasts strangely with the smooth, steady fanning
movement peculiar to natural wings.
As to the third point, viz. the upward bending of the posterior margin
of the wing during the down stroke, it is necessary to remark that the
statement is true if it means a slight upward bending, but that it is
untrue if it means an extensive upward bending.
Borelli does not state the amount of upward bending, but one of his
followers, E.J. Marey, maintains that during the down stroke the wing
yields until its under surface makes a backward angle with the horizon
of 45 deg. Marey further states that during the up stroke the wing
yields to a corresponding extent in an opposite direction--the posterior
margin of the wing, according to him, passing through an angle of 90
deg., plus or minus according to circumstances, every time the wing
rises and falls.
That the posterior margin of the wing yields to a slight extent during
both the down and up strokes will readily be admitted, alike because of
the very delicate and highly elastic properties of the posterior margins
of the wing, and because of the comparatively great force employed in
its propulsion; but that it does not yield to the extent stated by Marey
is a matter of absolute certainty. This admits of direct proof. If any
one watches the horizontal or upward flight of a large bird he will
observe that the posterior or flexible margin of the wing never rises
during the down stroke to a perceptible extent, so that the under
surface of the wing, as a whole, never looks backwards. On the contrary,
he will perceive that the under surface of the wing (during the down
stroke) invariably looks forwards and forms a true kite with the
horizon, the angles made by the kite varying at every part of the down
stroke, as shown more particularly at c d e f g, i j k l m of fig. 30.
The authors who have adopted Borelli's plan of artificial wing, and who
have endorsed his mechanical views of the wing's action most fully, are
J. Chabrier, H.E.G. Strauss-Durckheim and Marey. Borelli's artificial
wing, it will be remembered, consists of a rigid rod in front and a
flexible sail behind. It is also made to strike vertically downwards.
According to Chabrier, the wing has only one period of activity. He
believes that if the wing be suddenly lowered by the depressor muscles,
it is elevated solely by the reaction of the air. There is one
unanswerable objection to this theory: the birds and bats, and some if
not all the insects, have distinct elevator muscles, and can elevate
their wings at pleasure when not flying and when, consequently, the
reaction of the air is not elicited. Strauss-Durckheim agrees with
Borelli both as to the natural and the artificial wing. He is of opinion
that the insect abstracts from the air by means of the inclined plane a
component force (composant) which it employs to support and direct
itself. In his theology of nature he describes a schematic wing as
consisting of a rigid ribbing in front, and a flexible sail behind. A
membrane so constructed will, according to him, be fit for flight. It
will suffice if such a sail elevates and lowers itself successively. It
will of its own accord dispose itself as an inclined plane, and
receiving obliquely the reaction of the air, it transfers into tractile
force a part of the vertical impulsion it has received. These two parts
of the wing, moreover, are equally indispensable to each other.
Marey repeats Borelli and Durckheim with very trifling modifications, so
late as 1869. He describes two artificial wings, the one composed of a
rigid rod and sail--the rod representing the stiff anterior margin of
the wing; the sail, which is made of paper bordered with cardboard, the
flexible posterior margin. The other wing consists of a rigid nervure in
front and behind of thin parchment which supports fine rods of steel. He
states that if the wing only elevates and depresses itself, "the
resistance of the air is sufficient to produce all the other movements.
In effect (according to Marey) the wing of an insect has not the power
of equal resistance in every part. On the anterior margin the extended
nervures make it rigid, while behind it is fine and flexible. During the
vigorous depression of the wing, the nervure has the power of remaining
rigid, whereas the flexible portion, being pushed in an upward direction
on account of the resistance it experiences from the air, assumes an
oblique position which causes the upper surface of the wing to look
forwards." The reverse of this, in Marey's opinion, takes place during
the elevation of the wing--the resistance of the air from above causing
the upper surface of the wing to look backwards.... "At first," he says,
"the plane of the wing is parallel with the body of the animal. It
lowers itself--the front part of the wing strongly resists, the sail
which follows it being flexible yields. Carried by the ribbing (the
anterior margin of the wing) which lowers itself, the sail or posterior
margin of the wing being raised meanwhile by the air, which sets it
straight again, the sail will take an intermediate position and incline
itself about 45 deg. plus or minus according to circumstances.... The
wing continues its movements of depression inclined to the horizon; but
the impulse of the air, which continues its effect, and naturally acts
upon the surface which it strikes, has the power of resolving itself
into two forces, a vertical and a horizontal force; the first suffices
to raise the animal, the second to move it along."[13] Marey, it will be
observed, reproduces Borelli's artificial wing, and even his text, at a
distance of nearly two centuries.
The artificial wing recommended by Pettigrew is a more exact imitation
of nature than either of the foregoing. It is of a more or less
triangular form, thick at the root and anterior margin, and thin at the
tip and posterior margin. No part of it is rigid. It is, on the
contrary, highly elastic and flexible throughout. It is furnished with
springs at its root to contribute to its continued play, and is applied
to the air by a direct piston action in such a way that it descends in a
downward and forward direction during the down stroke, and ascends in an
upward and forward direction during the up stroke. It elevates and
propels both when it rises and falls. It, moreover, twists and untwists
during its action and describes figure-of-8 and waved tracks in space,
precisely as the natural wing does. The twisting is most marked at the
tip and posterior margin, particularly that half of the posterior margin
next the tip. The wing when in action may be divided into two portions
by a line running diagonally between the tip of the wing anteriorly and
the root of the wing posteriorly. The tip and posterior parts of the
wing are more active than the root and anterior parts, from the fact
that the tip and posterior parts (the wing is an eccentric) always
travel through greater spaces, in a given time, than the root and
anterior parts.
[Illustration: FIG. 32.--Elastic Spiral Wing, which twists and untwists
during its action, to form _a mobile helix or screw_. This wing is made
to vibrate by a direct piston action, and by a slight adjustment can be
propelled vertically, horizontally or at any degree of obliquity.
a b, Anterior margin of wing, to which the neurae or ribs are affixed.
c d, Posterior margin of wing crossing anterior one.
x, Ball-and-socket joint at root of wing, the wing being attached to
the side of the cylinder by the socket.
t, Cylinder.
r r, Piston, with cross heads (w, w) and piston head (s).
o o, Stuffing boxes.
e, f, Driving chains.
m, Superior elastic band, which assists in elevating the wing.
n, Inferior elastic band, which antagonizes m. The alternate
stretching of the superior and inferior elastic bands contributes to
the continuous play of the wing, by preventing dead points at the end
of the down and up strokes. The wing is free to move in a vertical and
horizontal direction and at any degree of obliquity.]
The wing is so constructed that the posterior margin yields freely in a
downward direction during the up stroke, while it yields comparatively
little in an upward direction during the down stroke; and this is a
distinguishing feature, as the wing is thus made to fold and elude the
air more or less completely during the up stroke, whereas it is made to
expand and seize the air with avidity during the down stroke. The
oblique line referred to as running diagonally across the wing virtually
divides the wing into an active and a passive part, the former elevating
and propelling, the latter sustaining.
It is not possible to determine with exactitude the precise function
discharged by each part of the wing, but experiment tends to show that
the tip of the wing elevates, the posterior margin propels, and the root
sustains.
The wing--and this is important--is driven by a direct piston action
with an irregular hammer-like movement, the pinion having communicated
to it a smart click at the beginning of every down stroke--the up stroke
being more uniform. The following is the arrangement (fig. 32). If the
artificial wing here represented (fig. 32) be compared with the natural
wing as depicted at fig. 33, it will be seen that there is nothing in
the one which is not virtually reproduced in the other. In addition to
the foregoing, Pettigrew recommended a double elastic wing to be applied
to the air like a steam-hammer, by being fixed to the head of the
piston. This wing, like the single wing described, twists and untwists
as it rises and falls, and possesses all the characteristics of the
natural wing (fig. 34).
[Illustration: FIG. 33 shows the Spiral Elastic Wings of the Gull. Each
wing forms a mobile helix or screw.
a b, Anterior margin of left wing.
c d, Posterior margin of ditto.
d g, Primary or rowing feathers of left wing.
g a, Secondary feathers ditto.
x, Root of right wing with ball-and-socket joint.
l, Elbow joint.
m, Wrist joint,
n,o, Hand and finger joints.]
[Illustration: FIG. 34.--Double Elastic Wing driven by direct piston
action. During the up stroke of the piston the wing is very decidedly
convex on its upper surface (a b c d, A A'); its under surface (e f g h,
A A') being deeply concave and inclined obliquely upwards and forwards.
It thus evades, to a considerable extent, the air during the up stroke.
During the down stroke of the piston the wing is flattened out in every
direction, and its extremities twisted in such a manner as to form two
screws, as seen at a' b' c' d', e' f' g' h', B, B'. The active area of
the wing is by this arrangement considerably diminished during the up
stroke, and considerably augmented during the down stroke; the wing
seizing the air with greater avidity during the down than during the up
stroke. _i, j, k_, elastic band to regulate the expansion of the wing;
l, piston; m, piston head; n, cylinder.]
He also recommends an elastic aerial screw consisting of two blades,
which taper and become thinner towards the tips and posterior margins.
When the screw is made to rotate, the blades, because of their
elasticity, assume a great variety of angles, the angles being least
where the speed of the blades is greatest and vice versa. The pitch of
the blades is thus regulated by the speed attained (fig. 35).
The peculiarity of Pettigrew's wings and screws consists in their
elasticity, their twisting action, and their great comparative length
and narrowness. They offer little resistance to the air when they are at
rest, and when in motion the speed with which they are driven is such as
to ensure that the comparatively large spaces through which they travel
shall practically be converted into solid bases of support.
After Pettigrew enunciated his views (1867) as to the screw
configuration and elastic properties of natural wings, and more
especially after his introduction of spiral, elastic artificial wings,
and elastic screws, a great revolution took place in the construction of
flying models. Elastic aeroplanes were advocated by D.S. Brown,[14]
elastic aerial screws by J. Armour,[15] and elastic aeroplanes, wings
and screws by Alphonse Penaud.[16]
[Illustration: FIG. 35.--Elastic Aerial Screw with twisted blades
resembling wings (a b c d, e f g h).
x, End of driving shaft.
v,w, Sockets in which the roots of the blades of the screw rotate, the
degree of rotation being limited by steel springs (z, s).
a b, e f, tapering elastic rods forming anterior or thick margins of
blades of screw.
d c, h g, Posterior or thin elastic margins of blades of screw. The
arrows m, n, o, p, q, r indicate the direction of travel.]
Penaud's experiments are alike interesting and instructive. He
constructed models to fly by three different methods:--(a) by means of
screws acting vertically upwards; (b) by aeroplanes propelled
horizontally by screws; and (c) by wings which flapped in an upward and
downward direction. An account of his helicoptere or screw model
appeared in the _Aeronaut_ for January 1872, but before giving a
description of it, it may be well to state very briefly what is known
regarding the history of the screw as applied to the air.
[Illustration: FIG. 36.--Cayley's Flying Model.]
The first suggestion on this subject was given by A.J.P. Paucton in
1768. This author, in his treatise on the _Theorie de la vis
d'Archimede_, describes a machine provided with two screws which he
calls a "pterophores." In 1796 Sir George Cayley gave a practical
illustration of the efficacy of the screw as applied to the air by
constructing a small machine, consisting of two screws made of quill
feathers, a representation of which we annex (fig. 36). Sir George
writes as under:--
"As it may be an amusement to some of your readers to see a machine
rise in the air by mechanical means, I will conclude my present
communication by describing an instrument of this kind, which any one
can construct at the expense of ten minutes' labour.
"a and b, fig. 36, are two corks, into each of which are inserted four
wing feathers from any bird, so as to be slightly inclined like the
sails of a windmill, but in opposite directions in each set. A round
shaft is fixed in the cork a, which ends in a sharp point. At the
upper part of the cork b is fixed a whalebone bow, having a small
pivot hole in its centre to receive the point of the shaft. The bow is
then to be strung equally on each side to the upper portion of the
shaft, and the little machine is completed. Wind up the string by
turning the flyers different ways, so that the spring of the bow may
unwind them with their anterior edges ascending; then place the cork
with the bow attached to it upon a table, and with a finger on the
upper cork press strong enough to prevent the string from unwinding,
and, taking it away suddenly, the instrument will rise to the
ceiling."
Cayley's screws were peculiar, inasmuch as they were superimposed and
rotated in opposite directions. He estimated that if the area of the
screws was increased to 200 sq. ft., and moved by a man, they would
elevate him. His interesting experiment is described at length, and the
apparatus figured in _Nicolson's Journal_, 1809, p. 172.
Other experimenters, such as J. Degen in 1816 and Ottoris Sarti in 1823,
followed Cayley at moderate intervals, constructing flying models on the
vertical screw principle. In 1842 W.H. Phillips succeeded, it is stated,
in elevating a steam model by the aid of revolving fans, which according
to his account flew across two fields after having attained a great
altitude; and in 1859 H. Bright took out a patent for a machine to be
sustained by vertical screws. In 1863 the subject of aviation by
vertical screws received a fresh impulse from the experiments of Gustave
de Ponton d'Amecourt, G. de la Landelle, and A. Nadar, who exhibited
models driven by clock-work springs, which ascended with graduated
weights a distance of from 10 to 12 ft. These models were so fragile
that they usually broke in coming in contact with the ground in their
descent. Their flight, moreover, was unsatisfactory, from the fact that
it only lasted a few seconds.
[Illustration: FIG. 37.--De la Landelle's Flying-machine. m, n, o, p;
q, r, s, t, Screws arranged on vertical axes to act vertically upwards.
The vertical axes are surmounted by two parachutes, and the body of the
machine is furnished with an engine, propeller, rudders and an extensive
aeroplane.]
Stimulated by the success of his spring models, Ponton d'Amecourt had a
small steam model constructed. This model, which was shown at the
exhibition of the Aeronautical Society of Great Britain at the Crystal
Palace in 1868, consisted of two superposed screws propelled by an
engine, the steam for which was generated (for lightness) in an
aluminium boiler. This steam model proved a failure, inasmuch as it only
lifted a third of its own weight. Fig. 37 embodies de la Landelle's
ideas.
All the models referred to (Cayley's excepted[17]) were provided with
rigid screws. In 1872 Penaud discarded the rigid screws in favour of
elastic ones, as Pettigrew had done some years before.
[Illustration: FIG. 38.--Helicoptere or Screw-Model, by Penaud.]
Penaud also substituted india-rubber under torsion for the whalebone and
clock springs of the smaller models, and the steam of the larger ones.
His helicoptere or screw-model is remarkable for its lightness,
simplicity and power. The accompanying sketch will serve to illustrate
its construction (fig. 38). It consists of two superposed elastic screws
(a a, b b), the upper of which (a a) is fixed in a vertical frame (c),
which is pivoted in the central part (d) of the under screw. From the
centre of the under screw an axle provided with a hook (e), which
performs the part of a crank, projects in an upward direction. Between
the hook or crank (e) and the centre of the upper screw (a a), the
india-rubber in a state of torsion (f) extends. By fixing the lower
screw and turning the upper one a sufficient number of times the
requisite degree of torsion and power is obtained. The apparatus when
liberated flies into the air sometimes to a height of 50 ft., and
gyrates in large circles for a period varying from 15 to 30 seconds.
Penaud next directed his attention to the construction of a model, to be
propelled by a screw and sustained by an elastic aeroplane extending
horizontally. Sir George Cayley proposed such a machine in 1810, and
W.S. Henson constructed and patented a similar machine in 1842. Several
inventors succeeded in making models fly by the aid of aeroplanes and
screws, as, e.g. J. Stringfellow in 1847,[18] and F. du Temple in 1857.
These models flew in a haphazard sort of a way, it being found
exceedingly difficult to confer on them the necessary degree of
stability fore and aft and laterally. Penaud succeeded in overcoming the
difficulty in question by the invention of what he designated an
automatic rudder. This consisted of a small elastic aeroplane placed aft
or behind the principal aeroplane which is also elastic. The two elastic
aeroplanes extended horizontally and made a slight upward angle with the
horizon, the angle made by the smaller aeroplane (the rudder) being
slightly in excess of that made by the larger. The motive power was
india-rubber in the condition of torsion; the propeller, a screw. The
reader will understand the arrangement by a reference to the
accompanying drawing (fig. 39).
Models on the aeroplane screw type may be propelled by two screws, one
fore and one aft, rotating in opposite directions; and in the event of
only one screw being employed it may be placed in front of or behind the
aeroplane.
When such a model is wound up and let go it descends about 2 ft., after
which, having acquired initial velocity, it rises and flies in a forward
direction at a height of from 8 to 10 ft. from the ground for a
distance of from 120 to 130 ft. It flies this distance in from 10 to 11
seconds, its mean speed being something like 12 ft. per second. From
experiments made with this model, Penaud calculates that one horse-power
would elevate and support 85 lb.
[Illustration: FIG. 39.--Aeroplane Model with Automatic Rudder.
a a, Elastic aeroplane.
b b, Automatic rudder.
c c, Aerial screw centred at f.
d, Frame supporting aeroplane, rudder and screw.
e, India-rubber, in a state of torsion, attached to hook or crank at
f. By holding the aeroplane (a a) and turning the screw (c c) the
necessary power is obtained by torsion. (Penaud.)]
D.S. Brown also wrote (1874) in support of elastic aero-biplanes. His
experiments proved that two elastic aeroplanes united by a central shaft
or shafts, and separated by a wide interval, always produce increased
stability. The production of flight by the vertical flapping of wings is
in some respects the most difficult, but this also has been attempted
and achieved. Penaud and A.H. de Villeneuve each constructed winged
models. Marey was not so fortunate. He endeavoured to construct an
artificial insect on the plan advocated by Borelli, Strauss-Durckheim
and Chabrier, but signally failed, his insect never having been able to
lift more than a third of its own weight.
[Illustration: FIG. 40.--Penaud's Artificial Flying Bird.
a b c d, a' b' c' d', Elastic wings, which twist and untwist when made
to vibrate.
a b, a' b', Anterior margins of wings.
c d, c' d', Posterior margins of wings.
c, c', Inner portions of wings attached to central shaft of model by
elastic bands at e.
f, India-rubber in a state of torsion, which provides the motive
power, by causing the crank situated between the vertical wing
supports (g) to rotate; as the crank revolves the wings are made to
vibrate by means of two rods which extend between the crank and the
roots of the wings.
h, Tail of artificial bird.]
De Villeneuve and Penaud constructed their winged models on different
types, the former selecting the bat, the latter the bird. De Villeneuve
made the wings of his artificial bat conical in shape and comparatively
rigid. He controlled the movements of the wings, and made them strike
downwards and forwards in imitation of natural wings. His model
possessed great power of rising. It elevated itself from the ground with
ease, and flew in a horizontal direction for a distance of 24 ft., and
at a velocity of 20 m. an hour. Penaud's model differed from de
Villeneuve's in being provided with elastic wings, the posterior margins
of which in addition to being elastic were free to move round the
anterior margins as round axes (see fig. 24). India-rubber springs were
made to extend between the inner posterior parts of the wings and the
frame, corresponding to the backbone of the bird.
A vertical movement having been communicated by means of india-rubber in
a state of torsion to the roots of the wings, the wings themselves, in
virtue of their elasticity, and because of the resistance experienced
from the air, twisted and untwisted and formed reciprocating screws,
precisely analogous to those originally described and figured by
Pettigrew in 1867. Penaud's arrangement is shown in fig. 40.
If the left wing of Penaud's model (a b, c d of fig. 40) be compared
with the wing of the bat (fig. 18), or with Pettigrew's artificial wing
(fig. 32), the identity of principle and application is at once
apparent.
In Penaud's artificial bird the equilibrium is secured by the addition
of a tail. The model cannot raise itself from the ground, but on being
liberated from the hand it descends 2 ft. or so, when, having acquired
initial velocity, it flies horizontally for a distance of 50 or more
feet, and rises as it flies from 7 to 9 ft. The following are the
measurements of the model in question:--length of wing from tip to tip,
32 in.; weight of wing, tail, frame, india-rubber, &c., 73 grammes
(about 2-1/2 ounces). (J. B. P.)
_Flying Machines_.--Henson's flying machine, designed in 1843, was the
earliest attempt at aviation on a great scale. Henson was one of the
first to combine aerial screws with extensive supporting structures
occupying a nearly horizontal position. The accompanying illustration
explains the combination (fig. 41).
[Illustration: FIG. 41.--Henson's Aerostat.]
"The chief feature of the invention was the very great expanse of its
sustaining planes, which were larger in proportion to the weight it
had to carry than those of many birds. The machine advanced with its
front edge a little raised, the effect of which was to present its
under surface to the air over which it passed, the resistance of
which, acting upon it like a strong wind on the sails of a windmill,
prevented the descent of the machine and its burden. The sustaining of
the whole, therefore, depended upon the speed at which it travelled
through the air, and the angle at which its under surface impinged on
the air in its front.... The machine, fully prepared for flight, was
started from the top of an inclined plane, in descending which it
attained a velocity necessary to sustain it in its further progress.
That velocity would be gradually destroyed by the resistance of the
air to the forward flight; it was, therefore, the office of the
steam-engine and the vanes it actuated simply to repair the loss of
velocity; it was made, therefore, only of the power and weight
necessary for that small effect." The editor of Newton's _Journal of
Arts and Sciences_ speaks of it thus:--"The apparatus consists of a
car containing the goods, passengers, engines, fuel, &c., to which a
rectangular frame, made of wood or bamboo cane, and covered with
canvas or oiled silk, is attached. This frame extends on either side
of the car in a similar manner to the outstretched wings of a bird;
but with this difference, that the frame is immovable. Behind the
wings are two vertical fan wheels, furnished with oblique vanes, which
are intended to propel the apparatus through the air. The rainbow-like
circular wheels are the propellers, answering to the wheels of a
steamboat, and acting upon the air after the manner of a windmill.
These wheels receive motions from bands and pulleys from a steam or
other engine contained in the car. To an axis at the stern of the car
a triangular frame is attached, resembling the tail of a bird, which
is also covered with canvas or oiled silk. This may be expanded or
contracted at pleasure, and is moved up and down for the purpose of
causing the machine to ascend or descend. Beneath the tail is a rudder
for directing the course of the machine to the right or to the left;
and to facilitate the steering a sail is stretched between two masts
which rise from the car. The amount of canvas or oiled silk necessary
for buoying up the machine is stated to be equal to one square foot
for each half pound of weight."
F.H. Wenham, thinking to improve upon Henson, invented in 1866 what he
designated his aeroplanes.[19] These were thin, light, long, narrow
structures, arranged above each other in tiers like so many shelves.
They were tied together at a slight upward angle, and combined strength
and lightness. The idea was to obtain great sustaining area in
comparatively small space with comparative ease of control. It was hoped
that when the aeroplanes were wedged forward in the air by vertical
screws, or by the body to be flown, each aeroplane would rest or float
upon a stratum of undisturbed air, and that practically the aeroplanes
would give the same support as if spread out horizontally. The
accompanying figures illustrate Wenham's views (figs. 42 and 43).
[Illustration: FIG. 42.--Wenham's system of Aeroplanes designed to carry
a man.
a, a, Thin planks, tapering at each end, and attached to a triangle.
b, Similar plank for supporting the aeronaut.
c, c, Thin bands of iron with truss planks a, a, and
d, d, Vertical rods. Between these are stretched five bands of holland
15 in. broad and 16 ft. long, the total length of the web being 80 ft.
This apparatus when caught by a gust of wind, actually lifted the
aeronaut.]
[Illustration: FIG. 43.--A similar system, planned by Wenham.
a, a, Main spar 16 ft. long;
b, b, Panels, with base board for aeronaut attached to main spar.
e, e, Thin tie-band of steel with struts starting from main spar. This
forms a strong light framework for the aeroplanes, consisting of six
webs of thin holland 15 in. broad. The aeroplanes are kept in parallel
plane by vertical divisions of holland 2 ft. wide.
c, c', Wing propellers driven by the feet.]
[Illustration: FIG. 44.--Stringfellow's Flying Machine.]
Stringfellow, who was originally associated with Henson, and built a
successful flying model in 1847, made a second model in 1868, in which
Wenham's aeroplanes were combined with aerial screws. This model was on
view at the exhibition of the Aeronautical Society of Great Britain,
held at the Crystal Palace, London, in 1868. It was remarkably compact,
elegant and light, and obtained the L100 prize of the exhibition for its
engine, which was the lightest and most powerful so far constructed. The
illustration below (fig. 44), drawn from a photograph, gives a very good
idea of the arrangement--a, b, c representing the superimposed
aeroplanes, d the tail, e, f the screw propellers. The superimposed
aeroplanes (a, b, c) in this machine contained a sustaining area of 28
sq. ft., in addition to the tail (d). Its engine represented a third of
a horse power, and the weight of the whole (engine, boiler, water, fuel,
superimposed aeroplanes and propellers) was under 12 lb. Its sustaining
area, if that of the tail (d) be included, was something like 36 sq.
ft., i.e. 3 sq. ft. for every pound. The model was forced by its
propellers along a wire at a great speed, but so far as an observer
could determine, failed to lift itself, notwithstanding its extreme
lightness and the comparatively very great power employed. Stringfellow,
however, stated that it occasionally left the wire and was sustained by
its aeroplanes alone.
The aerial steamer of Thomas Moy (fig. 45), designed in 1874, consisted
of a light, powerful, skeleton frame resting on three wheels; a very
effective light engine constructed on a new principle, which dispensed
with the old-fashioned, cumbrous boiler; two long, narrow, horizontal
aeroplanes; and two comparatively very large aerial screws. The idea was
to get up the initial velocity by a preliminary run on the ground. This
accomplished it was hoped that the weight of the machine would gradually
be thrown upon the aeroplanes in the same way that the weight of certain
birds--the eagle, e.g.--is thrown upon the wings after a few hops and
leaps. Once in the air the aeroplanes, it was believed, would become
effective in proportion to the speed attained. The machine, however, did
not realize the high expectations formed of it, and like all its
predecessors it was doomed to failure.
[Illustration: FIG. 45.--Moy's Aerial Steamer.]
Two of the most famous of the next attempts to solve the problem of
artificial flight, by means of aeroplanes, were those of Prof. S.P.
Langley and Sir Hiram S. Maxim, who began their aerial experiments about
the same time (1889-1890). By 1893-1894 both had embodied their views in
models and large flying machines.
Langley, who occupied the position of secretary to the Smithsonian
Institution, Washington, U.S.A., made many small flying models and one
large one. These he designated "aerodromes." They were all constructed
on a common principle, and were provided with extensive flying surfaces
in the shape of rigid aeroplanes inclined at an upward angle to the
horizon, and more or less fixed on the plan advocated by Henson. The
cardinal idea was to force the aeroplanes (slightly elevated at their
anterior margins) forwards, kite-fashion, by means of powerful vertical
screw propellers driven at high speed--the greater the horizontal speed
provided by the propellers, the greater, by implication, the lifting
capacity of the aerodrome. The bodies, frames and aeroplanes of the
aerodromes were strengthened by vertical and other supports, to which
were attached aluminium wires to ensure absolute rigidity so far as that
was possible. Langley aimed at great lightness of construction, and in
this he succeeded to a remarkable extent. His aeroplanes were variously
shaped, and were, as a rule, concavo-convex, the convex surface being
directed upwards. He employed a competent staff of highly trained
mechanics at the Smithsonian Institution, and great secrecy was observed
as to his operations. He flew his smallest models in the great lecture
room of the National Museum, and his larger ones on the Potomac river
about 40 m. below Washington.
While Langley conducted his preliminary experiments in 1889, he did not
construct and test his steam-driven flying models until 1893. These
were made largely of steel and aluminium, and one of them in 1896 made
the longest flight then recorded for a flying machine, namely, fully
half a mile on the Potomac river. The largest aerodrome, intended to
carry passengers and to be available for war purposes, was built to the
order and at the expense of the American government, which granted a sum
of fifty thousand dollars for its construction.
[Illustration: FIG. 46.--Langley's Flying Machine. a, Large aeroplane;
b, Small aeroplane; c, Propelling screws.]
Langley's machine shown in fig. 46 was a working model, not intended
to carry passengers. In configuration the body-portion closely
resembled a mackerel. The backbone was a light but very rigid tube of
aluminium steel, 15 ft. in length, and a little more than 2 in. in
diameter. The engines were located in the portion of the framework
corresponding to the head of the fish; they weighed 60 oz. and
developed one horse-power. There were four boilers made of thin
hammered copper and weighing a little more than 7 lb. each; these
occupied the middle portion of the fish. The fuel used was refined
gasoline, and the extreme end of the tail of the fish was utilized for
a storage tank with a capacity of one quart. There were twin screw
propellers, which could be adjusted to different angles in practice,
to provide for steering, and made 1700 revolutions a minute. The
wings, or aeroplanes, four in number, consisted of light frames of
tubular aluminium steel covered with china silk. The pair in front
were 42 in. wide and 40 ft. from tip to tip. They could be adjusted at
different angles. The machine required to be dropped from a height, or
a preliminary forward impetus had to be given to it, before it could
be started. Fixity of all the parts was secured by a tubular mast
extending upwards and downwards through about the middle of the craft,
and from its extremities ran stays of aluminium wire to the tips of
the aeroplanes and the end of the tubular backbone. By this trussing
arrangement the whole structure was rendered exceedingly stiff.
[Illustration: FIG. 47.--Langley's Aerodrome in flight.]
In the larger aerodrome (fig. 47) the aeroplanes were concavo-convex,
narrow, greatly elongated and square at their free extremities, the
two propellers, which were comparatively very large, being placed
amidships, so to speak. At the first trial of this machine, on the 7th
of October 1903, just as it left the launching track it was jerked
violently down at the front (being caught, as subsequently appeared,
by the falling ways), and under the full power of its engine was
pulled into the water, carrying with it its engineer. When the
aerodrome rose to the surface, it was found that while the front
sustaining surfaces had been broken by their impact with the water,
yet the rear ones were comparatively uninjured. At the second and last
attempt, on the 8th of December 1903, another disaster, again due to
the launching ways, occurred as the machine was leaving the track.
This time the back part of the machine, in some way still unexplained,
was caught by a portion of the launching car, which caused the rear
sustaining surface to break, leaving the rear entirely without support
and it came down almost vertically into the water. Darkness had come
before the engineer, who had been in extreme danger, could aid in the
recovery of the aerodrome. The boat and machine had drifted apart, and
one of the tugs in its zeal to render assistance had fastened a rope
to the frame of the machine in the reverse position from what it
should have been attached, and had broken the frame entirely in two.
Owing to lack of funds further trials were abandoned (see _Annual
Report of the Smithsonian Institution_, 1904, p. 122).
[Illustration: FIG. 48.--Sir H. Maxim's Flying Machine.]
Sir Hiram S. Maxim, like Langley, employed a staff of highly skilled
workmen. His machine (fig. 48) consisted of a platform, on which stood
a large water-tube boiler, a number of concavo-convex aeroplanes
arranged in tiers like shelves, each making a slight upward angle with
the horizon, two very large vertical screws placed aft and propelled
by steam engines, tanks for the storage of water, naphtha, &c. The
boiler was especially noteworthy. The water was contained in about
2000 bent copper tubes, only 3/8 in. in external diameter, heated by
over 7000 gas jets arranged in rows. The fuel was naphtha or gasoline.
Steam could be got up in the short space of half a minute. The
steam-generating appliances, which weighed only 1000 lb. in all, were
placed in the front of the machine. The motive power was provided by a
pair of two-cylinder, compound engines, poised about 8 ft. from the
ground, and about 6 ft. apart. Each of them was independently
governed, and furnished together 363 horse-power in actual effect, an
amount which, considering that their total weight was only 600 lb.,
gave the extraordinary efficiency of over 1 horse-power for every 2
lb. weight. The high and the low pressure cylinders were 5 and 8 in.
in diameter respectively, and the stroke was 12 in. When going at full
speed these engines conferred 425 revolutions per minute on the two
gigantic propellers that drove the machine along. These were in
appearance like two-bladed marine propellers except that they were
square instead of rounded at the ends, and were broad and thin. They
were built from overlapping strips of American pine, planed smooth and
covered with glued canvas. They weighed 135 lb. each, the length of
each blade being close upon 9 ft. and the width at the ends 5-1/2 ft.
The pitch was 16 ft. They were carefully stayed by steel wires to
their shafts, or the first revolution would have snapped them off
short. The material of which the framework was built was thin steel
tubing, exceedingly light. All the wires and ties were of the best
steel, capable of standing a strain of 100 tons to the square inch.
The body of the machine was oblong in shape, with the fore-part cut
away like a water-chute boat, and a long counter at the stern over
which the propellers revolved. It had canvas stretched all over it.
High overhead, like a gigantic awning, was the slightly concavo-convex
main aeroplane, tilted towards the front at an imperceptible angle,
and stretched taut. Its area was 1400 sq. ft., increased by side wings
to 2700 sq. ft. There were also side aeroplanes arranged in tiers, and
large aeroplanes in front, which were pivoted and served for vertical
steering. The machine was strengthened in every direction by vertical
and other supports and securely wired together at all points. It was
furnished with four strong flanged wheels and ran along a light
broad-gauge (9 ft.) railway track, 1800 ft. long, in the hope that
when the speed reached a certain point it would leave the rails, but
it was prevented from rising more than an inch or so by four arms, or
outriggers, furnished with wheels, which projected from its sides and
ran under an inverted wooden upper or safety track outside the railway
track proper.
At a trial carried out in 1894 at Bexley, Kent, only the main
aeroplane, the fore and aft rudders, and the top and bottom side
planes were in position. After everything had been got in readiness,
careful observers were stationed along the track, and the machine was
connected to a dynamometer. The engines were then started and the pump
set so as to deliver over 5000 lb. of water per hour into the boiler.
The gas was then carefully turned on until the pressure amounted to
310 lb. per sq. in., and the dynamometer showed a thrust of more than
2100 lb. A small safety-valve placed in the steam pipe had been
adjusted so as to blow off slightly at 310 lb. and with a strong blast
at 320 lb. The signal being given to let go, the machine darted
forward at a terrific pace, and the safety-valve ceased to blow. More
gas was instantly turned on, and before the machine had advanced 300
ft., the steam had mounted to 320 lb. per sq. in., and the
safety-valve was blowing off a steady blast. When the machine had
travelled only a few hundred feet, all four of the small outrigger
wheels were fully engaged, which showed that the machine was lifting
at least 8000 lb. The speed rapidly increased until when the machine
had run about 900 ft. one of the rear axletrees, which were of 2 in.
steel tubing, doubled up and set the rear end of the machine
completely free. When the machine had travelled about 1000 ft., the
left-hand forward wheel became disengaged from the safety track, and
shortly after this the right-hand wheel broke the upper track--3 in.
by 9 in. Georgia pine--and a plank became entangled in the framework
of the machine. Steam had already been shut off, and the machine
coming to rest fell directly to the ground, all four of its wheels
sinking deeply into the turf without leaving other marks. Before
making this run the wheels which were to engage the upper track were
painted, and the paint left by them on the upper track indicated the
exact point where the machine lifted. The area of the aeroplanes was
very nearly 4000 sq. ft. and the total lifting effect was fully 10,000
lb. The planes therefore lifted 2.5 lb. per sq. ft., and 5 lb. for
each pound thrust. Nearly half of the power of the engines was lost in
the screw slip. This showed that the diameter of the screws was not
great enough; it should have been at least 22 ft.
In 1897 M.C. Ader, who had already tested, with indifferent results, two
full-sized flying machines, built a third apparatus with funds furnished
by the French government. This reproduced the structure of a bird with
almost servile imitation, save that traction was obtained by two
screw-propellers. The steam engine weighed about 7 lb. per horse-power,
but the equilibrium of the apparatus was defective.
Largely with the view of studying the problem of maintaining
equilibrium, several experimenters, including Otto Lilienthal, Percy
Pilcher and Octave Chanute, cultivated gliding flight by means of
aeroplanes capable of sustaining a man. They depended mainly on the
utilization of natural air currents, trusting for stability and balance
to movements in their own bodies, or in portions of their machines which
they could control. They threw themselves from natural or artificial
elevations, or, facing the wind, they ran or were dragged forwards
against it until they got under way and the wind caught hold of their
aeroplanes. To Lilienthal in Germany belongs the double credit of
demonstrating the superiority of arched over flat surfaces, and of
reducing gliding flight to regular practice. He made over 2000 glides
safely, using gravity as his motive power, with concave, batlike wings,
in some cases with superposed surfaces (fig. 49). It was with a machine
of the latter type that he was upset by a sudden gust of wind and killed
in 1896. Pilcher in England improved somewhat on Lilienthal's apparatus,
but used the same general method of restoring the balance, when
endangered, by shifting the weight of the operator's body. He too made
several hundred glides in safety, but finally was thrown over by a gust
of wind and killed in 1899. Chanute in America confined his endeavours
to the production of automatic stability, and made the surfaces movable
instead of the man. He used several different forms of apparatus,
including one with five superposed pairs of wings and a tail (fig. 50)
and another with two continuous aeroplanes, one above the other (fig.
51). He made over 1000 glides without accident.
[Illustration: FIG. 49.--Lilienthal's Gliding Machine.]
Similar experiments were meanwhile conducted by Wilbur and Orville
Wright of Dayton, Ohio, in whose hands the glider developed into a
successful flying machine. These investigators began their work in 1900,
and at an early stage introduced two characteristic features--a
horizontal rudder in front for steering in the vertical plane, and the
flexing or bending of the ends of the main supporting aeroplanes as a
means of maintaining the structure in proper balance. Their machines to
begin with were merely gliders, the operator lying upon them in a
horizontal, position, but in 1903 a petrol motor was added, and a flight
lasting 59 seconds was performed. In 1905 they made forty-five flights,
in the longest of which they remained in the air for half an hour and
covered a distance of 24-1/2 m. The utmost secrecy, however, was
maintained concerning their experiments, and in consequence their
achievements were regarded at the time with doubt and suspicion, and it
was hardly realized that their success would reach the point later
achieved.
[Illustration: FIG. 50.--Chanute's Multiple Gliding Machine.]
[Illustration: FIG. 51.--Chanute's Biplane Gliding Machine.]
Thanks, however, to the efforts of automobile engineers, great
improvements were now being effected in the petrol engine, and, although
the certainty and trustworthiness of its action still left something to
be desired, it provided the designers of flying machines with what they
had long been looking for--a motor very powerful in proportion to its
weight. Largely in consequence of this progress, and partly no doubt
owing to the stimulus given by the activity of builders of dirigible
balloons, the construction of motor-driven aeroplanes began to attract a
number of workers, especially in France. In 1906 A. Santos Dumont, after
a number of successful experiments with dirigible cigar-shaped gas
balloons, completed an aeroplane flying machine. It consisted of the
following parts:--(a) A system of aeroplanes arranged like the capital
letter T at a certain upward angle to the horizon and bearing a general
resemblance to box kites; (b) a pair of very light propellers driven at
a high speed; and (c) an exceedingly light and powerful petrol engine.
The driver occupied a position in the centre of the arrangement, which
is shown in fig. 52. The machine was furnished with two wheels and
vertical supports which depended from the anterior parts of the
aeroplanes and supported it when it touched the ground on either side.
With this apparatus he traversed on the 12th of November 1906 a distance
of 220 metres in 21 seconds.
[Illustration: FIG. 52.--Santos Dumont's Flying Machine.]
About a year later Henry Farman made several short flights on a machine
of the biplane type, consisting of two main supporting surfaces one
above the other, with a box-shaped vertical rudder behind and two small
balancing aeroplanes in front. The engine was an eight-cylinder
Antoinette petrol motor, developing 49 horse-power at 1100 revolutions a
minute, and driving directly a single metal screw propeller. On the 27th
of October 1906 he flew a distance of nearly half a mile at
Issy-les-Molineaux, and on the 13th of January 1908 he made a circular
flight of one kilometre, thereby winning the Deutsch-Archdeacon prize of
L2000. In March he remained in the air for 3-1/2 minutes, covering a
distance of 1-1/4 m.; but in the following month a rival, Leon
Delagrange, using a machine of the same type and constructed by the same
makers, Messrs Voisin, surpassed this performance by flying nearly 2-1/2
m. in 6-1/2 minutes. In July Farman remained in the air for over 20
minutes; on the 6th of September Delagrange increased the time to nearly
30 minutes, and on the 29th of the same month Farman again came in front
with a flight lasting 42 minutes and extending over nearly 24-1/2 m.
But the best results were obtained by the Wright brothers--Orville
Wright in America and Wilbur Wright in France. On the 9th of September
1908 the former, at Fort Myer, Virginia, made three notable flights; in
the first he remained in the air 57-1/2 minutes and in the second 1 hour
3 minutes, while in the third he took with him a passenger and covered
nearly 4 m. in 6 minutes. Three days later he made a flight of 45 m. in
1 hour 14-1/3 minutes, but on the 17th he had an accident, explained as
being due to one of his propellers coming into contact with a stay, by
which his machine was wrecked, he himself seriously injured, and
Lieutenant Selfridge, who was with him, killed. Four days afterwards
Wilbur Wright at Le Mans in France beat all previous records with a
flight lasting 1 hour 31 minutes 25-4/5 seconds, in which he covered
about 56 m.; and subsequently, on the 11th of October, he made a flight
of 1 hour 9 minutes accompanied by a passenger. On the 31st of December
he succeeded in remaining in the air for 2 hours 20 minutes 23 seconds.
Wilbur Wright's machine (fig. 53), that used by his brother being
essentially the same, consisted of two slightly arched supporting
surfaces, each 12-1/2 metres long, arranged parallel one above the other
at a distance of 1-4/5 metres apart. As they were each about 2 metres
wide their total area was about 50 sq. metres. About 3 metres in front
of them was arranged a pair of smaller horizontal aeroplanes, shaped
like a long narrow ellipse, which formed the rudder that effected
changes of elevation, the driver being able by means of a lever to
incline them up or down according as he desired to ascend or descend.
The rudder for lateral steering was placed about 2-1/2 metres behind the
main surfaces and was formed of two vertical pivoted aeroplanes. The
lever by which they were turned was connected with the device by which
the ends of the main aeroplanes could be flexed simultaneously though in
opposite directions; i.e. if the ends of the aeroplanes on one side were
bent downwards, those on the other were bent upwards. By the aid of
this arrangement the natural cant of the machine when making a turn
could be checked, if it became excessive. The four-cylinder petrol
engine was placed on the lower aeroplane a little to the right of the
central line, being counterbalanced by the driver (and passenger if one
was carried), who sat a little to the left of the same line. Making
about 1200 revolutions a minute, it developed about 24 horse-power, and
was connected by chain gearing to two wooden propellers, 2-1/2 metres in
diameter and 3-1/2 metres apart, the speed of which was about 450
revolutions a minute. The whole machine, with aeronaut, weighed about
1100 lb., the weight of the motor being reputed to be 200 lb.
[Illustration: PLATE I.