building. We went into camp about the middle of July, and were soon
joined by Mr. E. C. Huffaker, of Tennessee, an experienced aeronautical
investigator in the employ of Mr. Chanute, by whom his services were
kindly loaned, and by Dr. A. G. Spratt, of Pennsylvania, a young man who
has made some valuable investigations of the properties of variously
curved surfaces and the travel of the center of pressure thereon. Early
in August Mr. Chanute came down from Chicago to witness our experiments,
and spent a week in camp with us. These gentlemen, with my brother and
myself, formed our camping party, but in addition we had in many of our
experiments the valuable assistance of Mr. W. J. Tate and Mr. Dan Tate,
of Kitty Hawk.

* * * * *

It had been our intention when building the machine to do most of the
experimenting in the following manner:--When the wind blew 17 miles an
hour, or more, we would attach a rope to the machine and let it rise as
a kite with the operator upon it. When it should reach a proper height
the operator would cast off the rope and glide down to the ground just
as from the top of a hill. In this way we would be saved the trouble of
carrying the machine uphill after each glide, and could make at least 10
glides in the time required for one in the other way. But when we came
to try it we found that a wind of 17 miles, as measured by Richards'
anemometer, instead of sustaining the machine with its operator, a total
weight of 240 lbs., at an angle of incidence of three degrees, in
reality would not sustain the machine alone--100 lbs.--at this angle.
Its lifting capacity seemed scarcely one-third of the calculated amount.
In order to make sure that this was not due to the porosity of the
cloth, we constructed two small experimental surfaces of equal size, one
of which was air-proofed and the other left in its natural state; but we
could detect no difference in their lifting powers. For a time we were
led to suspect that the lift of curved surfaces little exceeded that of
planes of the same size, but further investigation and experiment led to
the opinion that (1) the anemometer used by us over-recorded the true
velocity of the wind by nearly 15 per cent.; (2) that the well-known
Smeaton coefficient of .005 V^2 for the wind pressure at 90 degrees is
probably too great by at least 20 per cent.; (3) that Lilienthal's
estimate that the pressure on a curved surface having an angle of