Environmental Engineering Reference
In-Depth Information
of a hill on a map with height contour curves. In this case it has a
maximum power (gram-metres/second) at the velocity factor
three. Reading the corresponding angle on the horizontal axis gives
7½ degrees. To make the best possible sail, take the least steep
path from the top of the hill, which gives the path a-c. Obviously
it means that the sail should be slightly twisted with large angles
near the centre and smaller ones further out. The curved path a-c
could not be followed at that time using materials such as wood
and iron. Today with glass fibre this is possible. Consequently, from
about the velocity factor 1.4 it is necessary to compromise with
a straight line hitting the horizontal diagram axis near the rotation
centre at 25 degrees.
The research procedures for these findings were as follows:
(1) Initially it is assumed that the flow pressure perpendicular to
the plane is proportional to the area of the plane.
(2) Secondly, it is determined that the pressure perpendicular
to the plane is proportional to the velocity of the wind flow
squared.
(3) After that, the pressure perpendicular to a plane profile from
a flow directed from diferent angles of 1 to 90 degrees on
the plane is measured. The surprise was that these results
did not fit with the values calculated in advance using New-
tonian physics. They were not proportional with the width
of the impacting air stream. It must be concluded that the
resulting pressure mysteriously turned out to have other
directions than perpendicular to the plane.
To determine the directions of the resulting pressure on the
plane from the air streams coming from diferent angles, the
rotational axis of the plane is turned in every case until the plane
or profile is balancing back and forth in a regular manner. Then the
resultant pressure diference would be lying right over the shaft,
and the optimum bevel angle could be measured.
Repeating the same with a curved profile and a bent profile it was
concluded that the pressure resultant under certain circumstances
(bevel and shape) lies to the “favourable” side of the perpendicular
direction to the chord of the sail, sometimes to the “unfavourable”
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