THE WORK OF SCIENTISTS
Sir George Cayley’s forecasts--A steam-driven model
which flew--The shape and curve of planes.
So passed the haphazard stage of flight; and now history moves to a
second and more important period, that in which men of science were
attracted to the problem. They worked upon theories, and made
experiments with models; they studied the shape which Nature has given
the birds; they sifted false notions and showed where error lay. But
they did not fly. They were merely clearers of the ground, gathering
information and classifying it, and paving the way for those daring
workers who were to follow them--men who, by putting science to the
test, were willing to risk their lives.
[Illustration: FIG. 4.--Sir George Cayley’s suggestion for an Arched
Plane.]
To England goes the distinction of the first practical attempts to solve
the problems of flight; and it is the work of Sir George Cayley, an
eminent scientist and engineer, that next merits attention. In a series
of articles, published in _Nicholson’s Journal_ during the years
1809-10, he forecasted many of the principles that go to the making of a
modern-type aeroplane. He advised the construction of machines with
fixed, outstretched wings like those of a bird; but he did more than
this, for it is admitted generally he was first to point out that, to
increase their lifting power as they were moved through the air, these
wings should not be flat, but should be curved from front to back, or
arched upward (Fig. 4). How important this suggestion was, subsequent
experimenters were to show. Sir George Cayley realised also that a
tail-plane, carried at the rear of a machine, would give it equilibrium,
and might be moved up and down to control ascent or descent; and he used
a rudder upon models, to steer them from side to side. He advised the
use of steam engines as a motive power, and of revolving propellers to
drive a craft through the air. But, like many another man, he was before
his time. He built experimental craft--one, a model glider, which would
sail down gracefully from the top of a hill; and another, a far larger
machine, which would bear a man through the air, for a distance of
several yards, if he ran forward with it against the wind. But the
difficulty of obtaining a sufficiently light and practical motor, either
of steam or other power, was an obstacle that proved insurmountable. One
light engine, which Sir George Cayley planned, was to be driven by a
series of gunpowder explosions in a cylinder; but the suggestion came to
no practical issue.
This scientist did not write or work in vain. He compiled data which was
invaluable, and interested and encouraged other men--even those, indeed,
who in due course made the conquest. One of the first to work upon Sir
George Cayley’s theories was an experimenter named Henson. He planned
an ambitious machine weighing about a ton. It was to have planes of
canvas stretched over a rigidly trussed frame of bamboo rods and hollow
wooden spars; and these planes were to contain 4500 square feet of
lifting surface, and be driven by screws operated by a steam engine of
30 h.p. (Fig. 5).
But this craft did not take practical shape, although in its appearance
and many of its details it bore a resemblance to machines which
ultimately were to fly. In the specification of the patent he took out
for his invention, Henson indicated that it was for
“Improvements in locomotive apparatus and machinery for conveying
letters, goods, and passengers from place to place through the
air.”
[Illustration: FIG. 5.--Henson’s proposed Machine.]
Explaining his theories in this same specification he wrote:
“If any light and flat or nearly flat article be projected or
thrown edgewise in a slightly inclined position, the same will
rise into the air till the force exerted is expended, when the
article so thrown or projected will descend; and it will readily
be conceived that, if the article so projected or thrown possessed
in itself a continuous power or force equal to that used in
throwing or projecting it, the article would continue to ascend so
long as the forward part of the surface was upwards in respect to
the hinder part.”
Had Henson been able to carry out his ideas, it is almost certain that
this experimental machine would have been wrecked in its tests, and
probably several more after it, seeing that he would have had to learn
to control them when in flight, and remembering also that, even with
aircraft as they are built to-day, many details have to be studied and
improved before a successful model is evolved.
All such work, of course, entails heavy expense. It was, indeed, the
cost of experiments which prevented many an early inventor from building
a full-sized machine. The designing and construction of a man-carrying
craft, and the employment of skilled workmen and mechanics, to say
nothing of repairs that may have to be made during a series of tests,
represent an expenditure that may amount to thousands of pounds. As a
rule, the inventor is not a man of wealth; and so far as flying was
concerned, at any rate in the early days,--and to a more limited extent
even at the present time,--people with money thought the difficulties so
great that they would not advance funds for the carrying out of trials.
So men with ideas had to do the best they could, and this resolved
itself generally into writing and lecturing, and endeavouring to
interest the public. But the public was not easily interested; ordinary
folk did not believe that men would ever fly, while many people declared
that it was going against Nature for us to try to imitate the birds, and
that nothing but mischief would come of so doing.
Henson, failing to make definite progress with his scheme for a
man-carrying craft--despite the fact that a company was floated to
assist him--co-operated with another enthusiast named Stringfellow in a
plan which was not so elaborate. They began to experiment with a series
of models driven by tiny and most ingenious steam engines built by
Stringfellow; and so cleverly did he construct them that the
Aeronautical Society awarded him a prize of £100. The model which won
him this recognition was a little plant which, while it weighed only 13
lbs., without water or fuel, would develop one horse-power.
What, by the way, is meant by a horse-power? The answer is as follows:
in the early days of engineering, when it was found necessary to
establish some well-recognised unit of power, a large number of
experiments were carried out with horses, which were made to raise a
weight from the ground by means of an arrangement of pulleys and ropes.
The experiments showed this: that a horse can exert sufficient power to
raise 33,000 lbs., or about 15 tons, to a height of 1 foot in the space
of one minute. This, therefore, was called “one horse-power.”
In Stringfellow’s days, it must be remembered, there was no petrol
engine; an engine so extremely light for the power that it will give,
and with its liquid fuel and oil carried conveniently in tanks--an
engine which, as Sir Hiram Maxim puts it, will give one horse-power of
energy “for the weight of a barn-door fowl.”
The question of motive-power was, indeed, the great obstacle for the
pioneers. When a man builds an aeroplane he must drive it through the
air; and to drive it through the air he requires an engine. But he knows
that his planes, owing to the small density or sustaining power of the
air through which they pass, will raise only a limited load. And the
machine itself, even if it is built of wood and canvas, represents an
appreciable weight; to say nothing of that of the pilot. So, if his
engine is heavy in proportion to the power it gives, and its fuel
weighty, he may be prevented altogether from rising from the ground; or
if he does rise, he may be able only to carry sufficient fuel for a
flight of a short distance.
[Illustration: FIG. 6.--Henson and Stringfellow’s Model.]
Henson and Stringfellow built in 1845 a model which weighed about 30
lbs. (Fig. 6); and although its stability was not perfect, it was an
interesting machine--a forecast of the monoplane of the future. Here one
saw the lifting planes take shape; the body between the wings; the
tail-planes at the rear; and, above all, a suggestion of the means by
which machines would be driven through the air: the fitting to the
model, that is to say, of revolving propellers or screws. When an
inventor has fitted an engine to an aircraft, means must be devised for
using its power to drive the machine through the air; and to make the
wings flap like those of a bird, has been found so complicated, owing to
the mechanism necessary to imitate natural movements, that much of the
power is wasted. Inventors such as Henson and Stringfellow, realising
this difficulty, made wings that were outstretched and immovable, like
those of a bird when it is soaring, and relied upon screw
propellers--which they set spinning at great speed by means of their
engines--to thrust their craft forward through the air.
[Illustration: FIG. 7.]
In an early and simple form, the aerial propeller was as shown in Fig.
7. Here are two curved blades, so shaped that, when the propeller is
made to revolve quickly, these blades will act powerfully upon the air.
What the propeller does is to screw itself forward through the air, as
one might revolve a corkscrew and drive it into a cork, or force a
gimlet into a piece of wood. Each time you twist the gimlet for
instance, as you drive it inwards, it forces itself a certain distance
through the wood; and in a like manner the air-propeller, each time it
revolves, tends to bore its way through the air (Fig. 8) and so push, or
draw with it, the flying machine to which it is attached. But with air,
seeing that its density is small, it is necessary to use a large screw,
and to turn it fast, before power can be obtained.
[Illustration: FIG. 8.]
In 1845, Stringfellow, who was now working alone--Henson having
abandoned the tests and gone abroad--met with a definite success. He
obtained actual flights with a steam-driven model in the form of a
monoplane, weighing 8-1/2 lbs. These tests attracted attention among
scientists, but they led to nothing else--that is to say, no full-sized
machine was the result. But Stringfellow’s model interested many people
in the problems of flight. It showed, indeed, although in miniature,
that a flying machine could be built and driven through the air; and so
this patient experimenter did not labour in vain.
Following Stringfellow, upon the list of those who forged links in the
aerial conquest, came Francis Herbert Wenham. His interest in flying, as
with many other men, was aroused by watching the birds. Wenham, an
engineer by profession, made a voyage up the Nile; and his study of the
movement of birds, as they flew near his yacht, caused him to take up
aviation in earnest, and carry out experiments for the Aeronautical
Society. Wenham was interested largely in the lifting power of planes,
and sought efficient shapes. He recommended the building of arched
surfaces, so arranged that they had considerable span, but were narrow
from front to back; and he suggested also that they should, when fitted
to a machine, be placed one above another. Thus Wenham was the inventor
of the biplane, as we know that craft to-day.
In explaining this point he wrote:
“Having remarked how thin a stratum of air is displaced between
the wings of a bird in rapid flight, it follows that, in order to
obtain the necessary length of plane for supporting heavy weights,
the surfaces may be superposed, or placed in parallel rows with an
interval between them” (Fig. 9).
[Illustration: FIG. 9.--Superposed Lifting Planes.]
To illustrate his theory, he built a model which had six long, narrow
planes, arranged one above the other, rather like the slats of a
Venetian blind. Wenham’s experiments were highly important, because they
cleared a great deal of ground, and removed many misunderstandings. By
showing that a long, narrow plane was more efficient--would, that is to
say, carry a greater load through the air than one which was deep from
front to back, owing to the fact that it is the front section of an
inclined plane that provides the most “lift”; and by illustrating how,
in a full-sized machine, such a row of planes could be arranged one
above another, Wenham directed men’s thoughts towards a definite goal.
By his work, and chiefly by his sifting of data, an outline was obtained
of that aeroplane of the future which was actually to fly.
While Wenham was experimenting, an inventor named Penaud, in France,
testing a series of models, made one which was driven by the twisting of
elastic, and flew quite well. Penaud’s work in this respect is
interesting, because small elastic-driven machines, such as he designed,
were used afterwards in demonstration, and are flown to-day. For a
miniature aeroplane, elastic is an ideal motive force--light and yet
providing ample power, and with only one disadvantage: it unwinds itself
rapidly, and then the model must descend.
In experiments of permanent value, after the discoveries of Wenham,
important work was that of Horatio Phillips. Like Wenham, he devoted his
attention mainly to a study of lifting planes, and tested many shapes
and curves. Sir George Cayley, it may be remembered, had suggested a
curved and not a flat plane; but Phillips went one better than this, for
in 1881 he devised a plane with what has been termed a dipping front
edge.
[Illustration: FIG. 10.--The Phillips Wing-Curve.]
The shape and curve of a plane, is of vital importance. A machine may be
built, and an engine and propellers fitted, but the question is: Will
the planes support through the air the load they have been given to
carry? Phillips made many experiments, and in the end he produced a
wing-shape which he patented. He pointed out that an advantage might be
gained in lifting effect if the main curve or camber was situated near
the front edge of the plane, and not in the centre (Fig. 10). The theory
Phillips worked upon was this--and it is interesting if it can be
expressed clearly. Taking a plane curved as he recommended, with this
“hump” towards the front, and forcing it through the air as would be the
case were an aeroplane in flight, the rush of wind which meets the edge
of the plane is split into two currents--one sweeping above and one
below. The air current below the plane, following its curve, is thrust
downward, and in being so thrust down imparts a lift to the plane; while
the current thrown above the plane--rushing up and over the “hump”
which, as has been shown, is situated close to the front edge--will
sweep rearwards in such a way that there is a partial vacuum or air
space between the fast-moving wind current and the curved-down section
of the plane behind the “hump.” The value of such a vacuum is this: it
has a raising effect upon the surface of the plane, which is thus not
only pushed up from below, but drawn from above.
[Illustration: FIG. 11.--Suction above a Cambered Surface.]
How a vacuum is caused, by air passing over such an arched surface as
Phillips recommended, may be shown in a simple experiment. Take a sheet
of paper and curve it in the way shown in Fig. 11, allowing the rear
portion to hinge in such a way that it will move freely up and down.
Then, if the sheet of paper is held between the finger and thumb and one
blows across the top edge, the hinged flap at the rear will be found to
raise itself--drawn up by the influence of the vacuum, such as Phillips
describes.
Apart from his theory as to the dipping front edge of a plane, Phillips
agreed with a suggestion made by Wenham; and this was that a plane, in
order to be most effective in its “lift,” should be narrow from front to
back. This theory meant that, as a plane moved forward, it was the
curving front section which gripped and acted up the air; and that, if
the plane was carried too far towards the rear, its lifting influence
fell away, while the surface that was superfluous acted as so much
resistance to the machine’s progress through the air.
[Illustration: FIG. 12.--Phillips’s Experimental Craft.]
In furtherance of his views, Phillips built the strange-looking machine
which is seen in Fig. 12. It resembled, more than anything else, a huge
Venetian blind; and he adopted this form so as to introduce as many
narrow planes as possible. There were, as a matter of fact, fifty in the
machine, each 22 feet long and only 1-1/2 inch wide. The craft, as can
be seen, was mounted on a light carriage which, having wheels fitted to
it, ran round and round upon a railed track. A steam engine was used as
motive power, driving a two-bladed propeller at the rate of 400
revolutions a minute. The machine was so arranged on its metals that,
although the rear wheels could raise themselves and show whether the
planes exercised a lift, the front one was fixed to its track--thus
preventing the apparatus from leaping into the air, overturning, and
perhaps wrecking itself. Tests with the machine were successful. The
lifting influence of the planes, when the engine drove them forward, was
sufficient to raise the rear wheels from the track; and they did so even
when a weight of 72 lbs., in addition to that of the apparatus, had been
placed upon the carriage. In his main object, then, Phillips succeeded;
and that was to show the lifting power of his planes. But his apparatus
had not the makings of a practical aeroplane. He gained for himself,
nevertheless, a name that has lived and will live. Even to-day, in
discussing the wing-shape of some machine, draughtsmen will speak of the
“Phillips entry.” Other workers did not pin themselves exactly to his
shapes or theories, but these paved the way for a series of further
tests.
Science was forging link by link indeed the chain that would lead to an
ultimate conquest. Sir George Cayley suggested an arched plane; Wenham
devised a machine in which narrow planes should be fitted one above
another; and Phillips laid down the rule for a curve or camber of
special shape, which should exercise most “lift” when thrust through the
air. But still men lacked many things; all the links in the chain were
far from being in their place; and one of the greatest flaws was that no
man, even supposing he was able to build a machine that would fly, had
learned as yet to balance that machine when it was in the air.