per would have been to the lift
(108 lbs.) as the sine of 13 degrees is to the cosine of 13 degrees,
or.22 X 108/.97 = 24+ lbs.; but this slightly exceeds the total pull
of 23 pounds on our scales. Therefore it is evident that the average
pressure on the surface, instead of being normal to the chord, was so
far inclined toward the front that all the head resistance of framing
and wires used in the construction was more than overcome. In a wind of
fourteen miles per hour resistance is by no means a negligible factor,
so that tangential is evidently a force of considerable value. In a
higher wind, which sustained the machine at an angle of 10 degrees the
pull on the scales was 18 lbs. With the pressure normal to the chord the
drift proper would have been 17 X 98/.98. The travel of the centre of
pressure made it necessary to put sand on the front rudder to bring
the centres of gravity and pressure into coincidence, consequently the
weight of the machine varied from 98 lbs. to 108 lbs. in the different
tests= 17 lbs., so that, although the higher wind velocity must have
caused an increase in the head resistance, the tangential force still
came within 1 lb. of overcoming it. After our return from Kitty Hawk
we began a series of experiments to accurately determine the amount and
direction of the pressure produced on curved surfaces when acted upon by
winds at the various angles from zero to 90 degrees. These experiments
are not yet concluded, but in general they support Lilienthal in the
claim that the curves give pressures more favourable in amount and
direction than planes; but we find marked differences in the exact
values, especially at angles below 10 degrees. We were unable to obtain
direct measurements of the horizontal pressures of the machine with
the operator on board, but by comparing the distance travelled with the
vertical fall, it was easily calculated that at a speed of 24 miles per
hour the total horizontal resistances of our machine, when bearing
the operator, amounted to 40 lbs., which is equivalent to about 2 1/3
horse-power. It must not be supposed, however, that a motor developing
this power would be sufficient to drive a man-bearing machine. The extra
weight of the motor would require either a larger machine, higher speed,
or a greater angle of incidence in order to support it, and therefore
more power. It is probable, however, that an engine of 6 horse-power,
weighing 100 lbs. would answer the purpose. Su