I The standard K4s Pacific type of locomotive was
offered as the subject for consultation on streamlining
to improve its speed and appearance. The Pennsylvania
Railroad Company operate some 2,500 of these loco
motives, so it was natural that the specifications for the
I new designs should stipulate that in streamlining,
- everything in the existing locomust be clearedWhen
comparing the new design with, say, the Silver
Jubilee, this point should be kept in mind.
The first stage in the solution of the problem at which
results began to appear was the testing of clay models,
seven feet long, in the wind tunnel of New York
University's Aerodynamic Laboratory. This was a
process which was carried on over a period of months;
clay was the substance chosen for modelling because
it was easy to make alterations where the tests proved
that these were needed.
The development of streamlining again presented in the form of a
Railroad Company, a concern which builds as well as
t runs its locomotives.
Observations of the air flow were made by the use of
silk threads and smoke bombs, as well as by photo
graphs and sketches taken while the tests were in
progress. Twenty-four models were built and dis
carded in favour of four, from which the final design
was selected. Comparative tests were made for wind
resistance with the model of one locomotive, with
tender and one coach.
Under these conditions, at wind tunnel speeds of
100 m.p.h., air resistance was reduced from 890 h.p.
in the standard model to 600 h.p. with the streamlined
design. This represents, at maximum speeds, of 90 to
100 miles per hour, by reduction of air pressure, a
saving in speed of nearly 300 h.p.
It is interesting to compare the two locomotives side
by side and notice the different factors which have
contributed to this success.
Since the specifications stated that the existing loco
motive must be covered as it stood by the new model,
the obvious method of achieving a streamline by cut
ting back the smoke box was scratched. Instead,
therefore, the streamlining was achieved by doming
out the front, removing the lamp and setting it in the
centre of the dome. This part of the work was carried
out in sheet steel.
Special methods of providing for smoke lift were also
worked out which will be dealt with later.
Meanwhile, wherever desirable, other features of the
standard form were retained. Changes were not made
for the sake of making them. The separation between
the front end of the boiler and the skirting in front of
the pilot and round the cylinders was retained. This
178 was proved to give uniformity of pressure in the air