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, [1]Delagrange,

Herring and others.

[1] 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

as follows:

"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

the h.p.

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

be changed.

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.[2]

[2] Aeronautics.