AVIATION***


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THE FIRST MAN-CARRYING AEROPLANE CAPABLE OF SUSTAINED FREE FLIGHT:
LANGLEY'S SUCCESS AS A PIONEER IN AVIATION

by

A. F. ZAHM, Ph. D.

From the Smithsonian Report for 1914, pages 217-222
(WITH 8 PLATES)







[Illustration]

(Publication 2329)

Washington
Government Printing Office
1915




THE FIRST MAN-CARRYING AEROPLANE CAPABLE OF
SUSTAINED FREE FLIGHT--LANGLEY'S SUCCESS AS A
PIONEER IN AVIATION.

By A. F. ZAHM, Ph. D.

[With 8 plates.]


It is doubtful whether any person of the present generation will be able
to appraise correctly the contributions thus far made to the development
of the practical flying machine. The aeroplane as it stands to-day is
the creation not of any one man, but rather of three generations of men.
It was the invention of the nineteenth century; it will be the fruition,
if not the perfection, of the twentieth century. During the long decades
succeeding the time of Sir George Cayley, builder of aerial gliders and
sagacious exponent of the laws of flight, continuous progress has been
made in every department of theoretical and practical aviation--progress
in accumulating the data of aeromechanics, in discovering the principles
of this science, in improving the instruments of aerotechnic research,
in devising the organs and perfecting the structural details of the
present-day dynamic flying machine. From time to time numerous aerial
craftsmen have flourished in the world's eye, only to pass presently
into comparative obscurity, while others too neglected or too poorly
appreciated in their own day subsequently have risen to high estimation
and permanent honor in the minds of men.

Something of this latter fortune was fated to the late Secretary of the
Smithsonian Institution. For a decade and a half Dr. Langley had toiled
unremittingly to build up the basic science of mechanical flight, and
finally to apply it to practical use. He had made numerous model
aeroplanes propelled by various agencies--by India rubber, by steam, by
gasoline--all operative and inherently stable. Then with great
confidence he had constructed for the War Department a man flier which
was the duplicate, on a fourfold scale, of his successful gasoline
model. But on that luckless day in December, 1903, when he expected to
inaugurate the era of substantial aviation, an untoward accident to his
launching gear badly crippled his carefully and adequately designed
machine. The aeroplane was repaired, but not again tested until the
spring of 1914--seven years after Langley's death.

Such an accident, occurring now, would be regarded as a passing mishap;
but at that time it seemed to most people to demonstrate the futility of
all aviation experiments. The press overwhelmed the inventor with
ridicule; the great scientist himself referred to the accident as having
frustrated the best work of his life. Although he felt confident of the
final success of his experiments, further financial support was not
granted and he was forced to suspend operations. Scarcely could he
anticipate that a decade later, in a far away little hamlet, workmen who
had never known him would with keenest enthusiasm rehabilitate that same
tandem monoplane, and launch it again and again in successful flight,
and that afterwards in the National Capital it should be assigned the
place of honor among the pioneer vehicles of the air.

When in March, 1914, Mr. Glenn H. Curtiss was invited to send a flying
boat to Washington to participate in celebrating "Langley Day,"[1] he
replied, "I would like to put the Langley aeroplane itself in the air."
Learning of this remark Secretary Walcott, of the Smithsonian
Institution, soon authorized Mr. Curtiss to recanvas the original
Langley aeroplane and launch it either under its own propulsive power or
with a more recent engine and propeller. Early in April, therefore, the
machine was taken from the Langley Laboratory and shipped in a box car
to the Curtiss Aviation Field, beside Lake Keuka, Hammondsport, N. Y. In
the following month it was ready for its first trial since the
unfortunate accident of 1903.

  [1] May 6, the anniversary of the famous flight of Langley's steam
  model aeroplane in 1896, is known in Washington as "Langley Day," and
  has been celebrated with aerial maneuvers over land and water.

The main objects of these renewed trials were, first, to show whether
the original Langley machine was capable of sustained free flight with a
pilot, and, secondly, to determine more fully the advantages of the
tandem type of aeroplane. The work seemed a proper part of the general
program of experiments planned for the recently reopened Langley
Aerodynamical Laboratory. It was, indeed, for just such experimentation
that the aeroplane had been given to the Smithsonian Institution by the
War Department, at whose expense it had been developed and brought to
completion prior to 1903. After some successful flights at Hammondsport
the famous craft could, at the discretion of the Smithsonian
Institution, either be preserved for exhibition or used for further
scientific study. To achieve the two main objects above mentioned, the
aeroplane would first be flown as nearly as possible in its original
condition, then with such modifications as might seem desirable for
technical or other reasons.

Various ways of launching were considered. In 1903 the Langley aeroplane
was launched from the top of a houseboat. A car supporting it and drawn
by lengthy spiral springs ran swiftly along a track, then suddenly
dropped away, leaving the craft afloat in midair with its propellers
whirring and its pilot supplementing, with manual control, if need be,
the automatic stability of the machine. This method of launching, as
shown by subsequent experimentalists, is a practical one and was
favorably entertained by Mr. Curtiss. He also thought of starting from
the ground with wheels, from the ice with skates, from the water with
floats. Having at hand neither a first rate smooth field nor a sheet of
ice, he chose to start from the water.

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 1.

LANGLEY AEROPLANE (BUILT 1898-1903) READY FOR LAUNCHING AT HAMMONDSPORT,
N. Y., MAY 28, 1914.]

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 2.

LANGLEY AEROPLANE JUST RISING FROM WATER, JUNE 2, 1914, PILOTED BY
CURTISS.]

[Illustration: FLIGHT OF LANGLEY AEROPLANE WITH ITS OWN POWER PLANT OVER
LAKE KEUKA, JUNE 2, 1914, PILOTED BY CURTISS.]

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 3.

CURTISS 80-HORSEPOWER MOTOR AND TRACTOR SCREW MOUNTED ON LANGLEY
AEROPLANE.]

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 4.

ELWOOD DOHERTY CLEARING THE WATER SEPTEMBER 17, 1914, IN THE LANGLEY
AEROPLANE DRIVEN BY A CURTISS 80-HORSEPOWER MOTOR AND TRACTOR SCREW.]

In the accompanying illustrations, plates 1 and 2 show the appearance of
the Langley flying machine after Mr. Curtiss had provided it with
hydroaeroplane floats and their connecting truss work. The steel main
frame, the wings, the rudders, the engine and propellers all were
substantially as they had been in 1903. The pilot had the same seat
under the main frame, and the same general system of control as in 1903.
He could raise or lower the craft by moving the big rear rudder up and
down; he could steer right and left by turning the vertical rudder. He
had no ailerons nor wing-warping mechanism, but for lateral balance
depended upon the dihedral angle of the wings and upon suitable
movements of his weight or of the vertical rudder. And here it may be
noted that Langley had placed the vertical steering rudder under and to
the rear of the center of gravity. So placed, it served as a fairly good
aileron by exerting a turning movement about the longitudinal axis of
the machine.

After the adjustments for actual flight had been made in the Curtiss
factory, according to the minute descriptions contained in the Langley
Memoir on Mechanical Flight, the aeroplane was taken to the shore of
Lake Keuka, beside the Curtiss hangars, and assembled for launching. On
a clear morning (May 28), and in a mild breeze, the craft was lifted
onto the water by a dozen men and set going, with Mr. Curtiss at the
steering wheel, ensconced in the little boat-shaped car under the
forward part of the frame. Many eager witnesses and camera men were at
hand, on shore and in boats. The four-winged craft, pointed somewhat
across the wind, went skimming over the wavelets, then automatically
headed into the wind, rose in level poise, soared gracefully for 150
feet, and landed softly on the water near the shore. Mr. Curtiss
asserted that he could have flown farther, but, being unused to the
machine, imagined the left wings had more resistance than the right. The
truth is that the aeroplane was perfectly balanced in wing resistance,
but turned on the water like a weather vane owing to the lateral
pressure on its big rear rudder. Hence in future experiments this rudder
was made turnable about a vertical axis, as well as about the horizontal
axis used by Langley. Henceforth the little vertical rudder under the
frame was kept fixed and inactive.

After a few more flights with the Langley aeroplane, kept as nearly as
possible in its original condition, its engine and twin propellers were
replaced by a Curtiss 80-horse motor and direct-connected tractor
propeller mounted on the steel frame, well forward, as shown in the
photographs. It was hoped in this way to spare the original engine and
propeller bearings, which were none too strong for the unusual burden
added by the floats. In 1903 the total weight of pilot and machine had
been 830 pounds; with the floats lately added it was 1,170 pounds; with
the Curtiss motor and all ready for flight it was 1,520 pounds. But
notwithstanding these surplus additions of 40 per cent and 85 per cent
above the original weight of the craft, the delicate wing spars and ribs
were not broken, nor was any part of the machine excessively
overstrained.

Owing to the pressure of other work at the factory, the aeroplane
equipped with the Curtiss motor was not ready for further flights till
September. In the absence of Mr. Curtiss, who had gone to California in
August, a pupil of his aviation school, Mr. Elwood Doherty, volunteered
to act as pilot.

During some trials for adjusting the aeroplane controls and the center
of gravity, Mr. Doherty, on the afternoon of September 17, planed easily
over the water, rose on level wing, and flew about 450 feet, at an
elevation of 2 or 3 yards, as shown by the accompanying photographs of
that date. Presently two other like flights were made. Mr. Doherty found
that with the forewings at 10° incidence, the rear ones at 12°, and the
pilot's seat on the main frame about midway between the wings, the flier
responded nicely to the movements of the pilot wheel. A slight turn of
the wheel steered the craft easily to right or left, a slight pull or
push raised or lowered it. The big double tail, or rudder, which
responded to these movements, was the only steering or control surface
used. The breaking of the 8-foot tractor screw terminated these trials
for the day. The waves indicate the strength of the wind during the
flights.

On September 19, using a 9-foot screw, Mr. Doherty began to make longer
flights. A pleasant off-shore breeze rippled the water, but without
raising whitecaps. A dozen workmen, lifting the great tandem monoplane
from the shore, with the pilot in his seat, waded into the lake and set
it gently on the water. A crowd of witnesses near at hand, and many
scattered about the shores, and on the lofty vine-clad hills, stood
watching expectantly. When some of the official observers and
photographers, in a motor boat, were well out in the lake, a man in
high-top boots, standing in the water, started the propeller, and
stepped quickly out of the way. Then with its great yellow wings
beautifully arched and distended, the imposing craft ran swiftly out
from the shore, gleaming brilliantly in the afternoon sun. At first the
floats and lower edges of the rudders broke the water to a white surge,
then as the speed increased they rose more and more from the surface.
Presently the rear floats and the rudders cleared the water, the front
floats still skipping on their heels, white with foam. The whole craft
was now in soaring poise. It quickly approached the photographers,
bearing on its back the alert pilot, who seemed to be scrutinizing every
part of it and well satisfied to let it race. Then it rose majestically
and sailed on even wing 1,000 feet; sank softly, skimmed the water, and
soared another 1,000 feet; grazed the water again, rose and sailed 3,000
feet; turned on the water and came back in the same manner; and, as it
passed the photographers, soared again nearly half a mile. The flights
were repeated a few minutes later, then, owing to squally weather, were
discontinued for 11 days.

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 5.

FLIGHT OF LANGLEY AEROPLANE ABOVE LAKE KEUKA SEPTEMBER 17, 1914, PILOTED
BY E. DOHERTY AND DRIVEN BY A CURTISS MOTOR AND TRACTOR SCREW.]

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 6.

LANGLEY AEROPLANE IN FLIGHT SEPTEMBER 19, 1914; CLIMBING.]

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 7.

LANGLEY AEROPLANE IN FLIGHT OCTOBER 1, 1914; NATURAL POISE.]

[Illustration: Smithsonian Report, 1914.--Zahm.

PLATE 8.

LANGLEY AEROPLANE IN FLIGHT OCTOBER 1, 1914. HAMMONDSPORT, N. Y., IN
BACKGROUND.]

On October 1, 1914, the aeroplane was launched at 11 a. m. in an
off-shore breeze strong enough to raise whitecaps. Hovering within 30
feet of the water, and without material loss of speed, it made in quick
succession flights of the following duration, as observed by four of us
in a motor boat and timed by myself: 20 seconds, 20 seconds, 65 seconds,
20 seconds, 40 seconds, 45 seconds. As the speed through air averaged
about 50 feet per second, the through air lengths of these flights were,
respectively, 1,000 feet, 1,000 feet, 3,250 feet, 1,000 feet, 2,000
feet, 2,250 feet. As the aeroplane was now well out from shore among the
heavy billows and white caps, Mr. Doherty landed it upon the water and
turned it half about for the homeward flight. Thereupon the propeller
tips struck the waves and were broken off, one casting a splinter
through the center of the left wing. The pilot stopped the engine,
rested in his seat, and was towed home by our motor boat. The flights
were witnessed and have been attested by many competent observers.

As to the performance of the aeroplane during these trials, the pilot,
Mr. E. Doherty, reports, and we observed, that the inherent lateral
stability was excellent, the fore-and-aft control was satisfactory, and
the movement of the craft both on the water and in the air was steady
and suitable for practical flying in such weather. Apparently the
machine could have flown much higher, and thus avoided touching the
water during the lulls in the breeze; but higher flying did not seem
advisable with the frail trussing of wings designed to carry 830 pounds
instead of the 1,520 pounds actual weight.

At the present writing the Langley aeroplane is in perfect condition and
ready for any further tests that may be deemed useful. But it has
already fulfilled the purpose for which it was designed. It has
demonstrated that, with its original structure and power, it is capable
of flying with a pilot and several hundred pounds of useful load. It is
the first aeroplane in the history of the world of which this can be
truthfully said.

If the experiments be continued under more painstaking technical
direction, longer flights can easily be accomplished. Mr. Manly, who
designed the Langley engine and screws and who directed the
construction and tests of the large aeroplane up to December 8, 1903,
reports that he obtained from the propulsion plant a static thrust of
450 pounds, and that he once ran the engine under full load for 10 hours
consecutively. This thrust is nearly 100 pounds more than that commonly
obtained at Hammondsport with the same plant, and 20 pounds more than
the static thrust obtained with the Curtiss motor on the day when it
flew the aeroplane with 1,520 pounds aggregate weight. Hence, by
restoring the engine and propellers to their original normal working
condition they should be able to drive the aeroplane in successful
flight with an aggregate weight of nearly 1,600 pounds, even when
hampered with the floats and their sustaining truss work. With a thrust
of 450 pounds, the Langley aeroplane, without floats, restored to its
original condition and provided with stronger bearings, should be able
to carry a man and sufficient supplies for a voyage lasting practically
the whole day.

Dr. Langley's aerotechnic work may be briefly summarized as follows:

1. His aerodynamic experiments, some published and some as yet
unpublished, were complete enough to form a basis for practical pioneer
aviation.

2. He built and launched, in 1896, the first steam model aeroplane
capable of prolonged free flight, and possessing good inherent
stability.

3. He built the first internal-combustion motor suitable for a practical
man-carrying aeroplane.

4. He developed and successfully launched the first gasoline model
aeroplane capable of sustained free flight.

5. He developed and built the first man-carrying aeroplane capable of
sustained free flight.


[Illustration]




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