the chief problems in connection with the construction of a
full-sized apparatus was that of the construction of an engine, for it
was realised from the first that a steam power plant for a full-sized
machine could only be constructed in such a way as to make it a constant
menace to the machine which it was to propel. By this time (1898) the
internal combustion engine had so far advanced as to convince Langley
that it formed the best power plant available. A contract was made for
the delivery of a twelve horse-power engine to weigh not more than a
hundred pounds, but this contract was never completed, and it fell to
Charles M. Manly to design the five-cylinder radial engine, of which a
brief account is included in the section of this work devoted to aero
engines, as the power plant for the Langley machine.

The history of the years 1899 to 1903 in the Langley series of
experiments contains a multitude of detail far beyond the scope of
this present study, and of interest mainly to the designer. There were
frames, engines, and propellers, to be considered, worked out, and
constructed. We are concerned here mainly with the completed machine and
its trials. Of these latter it must be remarked that the only two actual
field trials which took place resulted in accidents due to the failure
of the launching apparatus, and not due to any inherent defect in the
machine. It was intended that these two trials should be the first of
a series, but the unfortunate accidents, and the fact that no further
funds were forthcoming for continuance of experiments, prevented
Langley's success, which, had he been free to go through as he intended
with his work, would have been certain.

The best brief description of the Langley aerodrome in its final form,
and of the two attempted trials, is contained in the official report of
Major M. M. Macomb of the United States Artillery Corps, which report is
here given in full:--

REPORT

Experiments with working models which were concluded August 8 last
having proved the principles and calculations on which the design of the
Langley aerodrome was based to be correct, the next step was to apply
these principles to the construction of a machine of sufficient size
and power to permit the carrying of a man, who could control the motive
power and guide its flight, thus pointing the way to attaining the final
goal of producing a machine capable of such extensive and precise aeria