ina in the summer of 1900 and proved at any rate the correctness
of the principles of the front elevator and warping wings, though its
designers were puzzled by the fact that the lift was less than they
expected; whilst the 'drag'(as we call it), or resistance, was also
considerably lower than their predictions. The 1901 machine was, in
consequence, nearly doubled in area--the lifting surface being increased
from 165 to 308 square feet--the first trial taking place on July 27th,
1901, again at Kill Devil Hill. It immediately appeared that something
was wrong, as the machine dived straight to the ground, and it was only
after the operator's position had been moved nearly a foot back from
what had been calculated as the correct position that the machine would
glide--and even then the elevator had to be used far more strongly than
in the previous year's glider. After a good deal of thought the apparent
solution of the trouble was finally found.

This consisted in the fact that with curved surfaces, while at large
angles the centre of pressure moves forward as the angle decreases, when
a certain limit of angle is reached it travels suddenly backwards and
causes the machine to dive. The Wrights had known of this tendency from
Lilienthal's researches, but had imagined that the phenomenon would
disappear if they used a fairly lightly cambered--or curved--surface
with a very abrupt curve at the front. Having discovered what appeared
to be the cause they surmounted the difficulty by 'trussing down' the
camber of the wings, with the result that they at once got back to
the old conditions of the previous year and could control the machine
readily with small movements of the elevator, even being able to follow
undulations in the ground. They still found, however, that the lift was
not as great as it should have been; while the drag remained, as in
the previous glider, surprisingly small. This threw doubt on previous
figures as to wind resistance and pressure on curved surfaces; but
at the same time confirmed (and this was a most important result)
Lilienthal's previously questioned theory that at small angles the
pressure on a curved surface instead of being normal, or at right angles
to, the chord is in fact inclined in front of the perpendicular. The
result of this is that the pressure actually tends to draw the machine
forward into the wind--hence the small amount of drag, which had puzzled
Wilbur and Orville Wright.

Another le