EVOLUTION OF TWOSURFACE FLYING MACHINE.
By Octave Chanute.
I am asked to set forth the development of the "two-
surface" type of flying machine which is now used with
modifications by Wright Brothers, Farman, Delagrange,
Herring and others.
 Now dead.
This type originated with Mr. F. H. Wenham, who
patented it in England in 1866 (No. 1571), taking out
provisional papers only. In the abridgment of British
patent Aeronautical Specifications (1893) it is described
"Two or more aeroplanes are arranged one above the
other, and support a framework or car containing the
motive power. The aeroplanes are made of silk or canvas
stretched on a frame by wooden rods or steel ribs.
When manual power is employed the body is placed
horizontally, and oars or propellers are actuated by the
arms or legs.
"A start may be obtained by lowering the legs and
running down hill or the machine may be started from
a moving carriage. One or more screw propellers may
be applied for propelling when steam power is employed.
On June 27, 1866, Mr. Wenham read before the
"Aeronautical Society of Great Britain," then recently
organized, the ablest paper ever presented to that society, and
thereby breathed into it a spirit which has continued to
this day. In this paper he described his observations of
birds, discussed the laws governing flight as to the
surfaces and power required both with wings and screws,
and he then gave an account of his own experiments with
models and with aeroplanes of sufficient size to carry
the weight of a man.
Second Wenham Aeroplane.
His second aeroplane was sixteen feet from tip to tip.
A trussed spar at the bottom carried six superposed
bands of thin holland fabric fifteen inches wide, connected
with vertical webs of holland two feet apart, thus
virtually giving a length of wing of ninety-six feet and
one hundred and twenty square feet of supporting surface.
The man was placed horizontally on a base board
beneath the spar. This apparatus when tried in the wind
was found to be unmanageable by reason of the fluttering
motions of the fabric, which was insufficiently stiffened
with crinoline steel, but Mr. Wenham pointed out that
this in no way invalidated the principle of the apparatus,
which was to obtain large supporting surfaces without
increasing unduly the leverage and consequent weight
of spar required, by simply superposing the surfaces.
This principle is entirely sound and it is surprising that
it is, to this day, not realized by those aviators who are
hankering for monoplanes.
Experiments by Stringfellow.
The next man to test an apparatus with superposed
surfaces was Mr. Stringfellow, who, becoming much impressed
with Mr. Wenham's proposal, produced a largish
model at the exhibition of the Aeronautical Society in
1868. It consisted of three superposed surfaces aggregating 28
square feet and a tail of 8 square feet more.
The weight was under 12 pounds and it was driven by a
central propeller actuated by a steam engine overestimated
at one-third of a horsepower. It ran suspended
to a wire on its trials but failed of free flight, in
consequence of defective equilibrium. This apparatus has
since been rebuilt and is now in the National Museum
of the Smithsonian Institution at Washington.
Linfield's Unsuccessful Efforts.
In 1878 Mr. Linfield tested an apparatus in England
consisting of a cigar-shaped car, to which was attached
on each side frames five feet square, containing each
twenty-five superposed planes of stretched and varnished
linen eighteen inches wide, and only two inches apart,
thus reminding one of a Spanish donkey with panniers.
The whole weighed two hundred and forty pounds. This
was tested by being mounted on a flat car behind a
locomotive going 40 miles an hour. When towed by a line
fifteen feet long the apparatus rose only a little from the
car and exhibited such unstable equilibrium that the
experiment was not renewed. The lift was only about one-
third of what it would have been had the planes been
properly spaced, say their full width apart, instead of
one-ninth as erroneously devised.
Renard's "Dirigible Parachute."
In 1889 Commandant Renard, the eminent superintendent
of the French Aeronautical Department, exhibited
at the Paris Exposition of that year, an apparatus
experimented with some years before, which he termed
a "dirigible parachute." It consisted of an oviform body
to which were pivoted two upright slats carrying above
the body nine long superposed flat blades spaced about
one-third of their width apart. When this apparatus
was properly set at an angle to the longitudinal axis of
the body and dropped from a balloon, it travelled back
against the wind for a considerable distance before
alighting. The course could be varied by a rudder. No
practical application seems to have been made of this
device by the French War Department, but Mr. J. P.
Holland, the inventor of the submarine boat which bears
his name, proposed in 1893 an arrangement of pivoted
framework attached to the body of a flying machine
which combines the principle of Commandant Renard
with the curved blades experimented with by Mr. Phillips,
now to be noticed, with the addition of lifting screws
inserted among the blades.
Phillips Fails on Stability Problem.
In 1893 Mr. Horatio Phillips, of England, after some
very interesting experiments with various wing sections,
from which he deduced conclusions as to the shape of
maximum lift, tested an apparatus resembling a Venetian
blind which consisted of fifty wooden slats of
peculiar shape, 22 feet long, one and a half inches wide,
and two inches apart, set in ten vertical upright boards.
All this was carried upon a body provided with three
wheels. It weighed 420 pounds and was driven at 40
miles an hour on a wooden sidewalk by a steam engine
of nine horsepower which actuated a two-bladed screw.
The lift was satisfactory, being perhaps 70 pounds per
horsepower, but the equilibrium was quite bad and the
experiments were discontinued. They were taken up
again in 1904 with a similar apparatus large enough to
carry a passenger, but the longitudinal equilibrium was
found to be defective. Then in 1907 a new machine was
tested, in which four sets of frames, carrying similar sets
of slat "sustainers" were inserted, and with this
arrangement the longitudinal stability was found to be very
satisfactory. The whole apparatus, with the operator,
weighed 650 pounds. It flew about 200 yards when
driven by a motor of 20 to 22 h.p. at 30 miles an hour,
thus exhibiting a lift of about 32 pounds per h.p., while
it will be remembered that the aeroplane of Wright
Brothers exhibits a lifting capacity of 50 pounds to
Hargrave's Kite Experiments.
After experimenting with very many models and
building no less than eighteen monoplane flying model
machines, actuated by rubber, by compressed air and by
steam, Mr. Lawrence Hargrave, of Sydney, New South
Wales, invented the cellular kite which bears his name
and made it known in a paper contributed to the Chicago
Conference on Aerial Navigation in 1893, describing
several varieties. The modern construction is well
known, and consists of two cells, each of superposed surfaces
with vertical side fins, placed one behind the other
and connected by a rod or frame. This flies with great
steadiness without a tail. Mr. Hargrave's idea was to
use a team of these kites, below which he proposed to
suspend a motor and propeller from which a line would
be carried to an anchor in the ground. Then by actuating
the propeller the whole apparatus would move
forward, pick up the anchor and fly away. He said:
"The next step is clear enough, namely, that a flying
machine with acres of surface can be safely got under
way or anchored and hauled to the ground by means of
the string of kites."
The first tentative experiments did not result well and
emphasized the necessity for a light motor, so that Mr.
Hargrave has since been engaged in developing one, not
having convenient access to those which have been produced
by the automobile designers and builders.
Experiments With Glider Model.
And here a curious reminiscence may be indulged in.
In 1888 the present writer experimented with a two-cell
gliding model, precisely similar to a Hargrave kite, as
will be confirmed by Mr. Herring. It was frequently
tested by launching from the top of a three-story house
and glided downward very steadily in all sorts of breezes,
but the angle of descent was much steeper than that of
birds, and the weight sustained per square foot was less
than with single cells, in consequence of the lesser support
afforded by the rear cell, which operated upon air
already set in motion downward by the front cell, so
nothing more was done with it, for it never occurred to
the writer to try it as a kite and he thus missed the
distinction which attaches to Hargrave's name.
Sir Hiram Maxim also introduced fore and aft superposed
surfaces in his wondrous flying machine of 1893,
but he relied chiefly for the lift upon his main large surface
and this necessitated so many guys, to prevent distortion,
as greatly to increase the head resistance and
this, together with the unstable equilibrium, made it
evident that the design of the machine would have to
How Lilienthal Was Killed.
In 1895, Otto Lilienthal, the father of modern aviation,
the man to whose method of experimenting almost all
present successes are due, after making something like
two thousand glides with monoplanes, added a superposed
surface to his apparatus and found the control of
it much improved. The two surfaces were kept apart
by two struts or vertical posts with a few guy wires, but
the connecting joints were weak and there was nothing
like trussing. This eventually cost his most useful life.
Two weeks before that distressing loss to science, Herr
Wilhelm Kress, the distinguished and veteran aviator
of Vienna, witnessed a number of glides by Lilienthal
with his double-decked apparatus. He noticed that it
was much wracked and wobbly and wrote to me after
the accident: "The connection of the wings and the
steering arrangement were very bad and unreliable. I
warned Herr Lilienthal very seriously. He promised
me that he would soon put it in order, but I fear that he
did not attend to it immediately."
In point of fact, Lilienthal had built a new machine,
upon a different principle, from which he expected great
results, and intended to make but very few more flights
with the old apparatus. He unwisely made one too
many and, like Pilcher, was the victim of a distorted
apparatus. Probably one of the joints of the struts
gave way, the upper surface blew back and Lilienthal,
who was well forward on the lower surface, was pitched
headlong to destruction.
Experiments by the Writer.
In 1896, assisted by Mr. Herring and Mr. Avery, I
experimented with several full sized gliding machines,
carrying a man. The first was a Lilienthal monoplane
which was deemed so cranky that it was discarded after
making about one hundred glides, six weeks before
Lilienthal's accident. The second was known as the
multiple winged machine and finally developed into five
pairs of pivoted wings, trussed together at the front and
one pair in the rear. It glided at angles of descent of
10 or 11 degrees or of one in five, and this was deemed
too steep. Then Mr. Herring and myself made computations
to analyze the resistances. We attributed much
of them to the five front spars of the wings and on a
sheet of cross-barred paper I at once drew the design for
a new three-decked machine to be built by Mr. Herring.
Being a builder of bridges, I trussed these surfaces
together, in order to obtain strength and stiffness. When
tested in gliding flight the lower surface was found too
near the ground. It was taken off and the remaining
apparatus now consisted of two surfaces connected together
by a girder composed of vertical posts and diagonal
ties, specifically known as a "Pratt truss." Then
Mr. Herring and Mr. Avery together devised and put
on an elastic attachment to the tail. This machine
proved a success, it being safe and manageable. Over
700 glides were made with it at angles of descent of 8
to 10 degrees, or one in six to one in seven.
First Proposed by Wenham.
The elastic tail attachment and the trussing of the
connecting frame of the superposed wings were the only
novelties in this machine, for the superposing of the
surfaces had first been proposed by Wenham, but in
accordance with the popular perception, which bestows
all the credit upon the man who adds the last touch
making for success to the labors of his predecessors, the
machine has since been known by many persons as the
"Chanute type" of gliders, much to my personal gratification.
It has since been improved in many ways. Wright
Brothers, disregarding the fashion which prevails among
birds, have placed the tail in front of their apparatus and
called it a front rudder, besides placing the operator in
horizontal position instead of upright, as I did; and also
providing a method of warping the wings to preserve
equilibrium. Farman and Delagrange, under the very
able guidance and constructive work of Voisin brothers,
then substituted many details, including a box tail for
the dart-like tail which I used. This may have increased
the resistance, but it adds to the steadiness. Now the
tendency in France seems to be to go back to the monoplane.
Monoplane Idea Wrong.
The advocates of the single supporting surface are
probably mistaken. It is true that a single surface
shows a greater lift per square foot than superposed
surfaces for a given speed, but the increased weight due
to leverage more than counterbalances this advantage by
requiring heavy spars and some guys. I believe that
the future aeroplane dynamic flier will consist of superposed
surfaces, and, now that it has been found that by
imbedding suitably shaped spars in the cloth the head
resistance may be much diminished, I see few objections
to superposing three, four or even five surfaces properly
trussed, and thus obtaining a compact, handy, manageable
and comparatively light apparatus.