Evening star., 1939-05-07
By Joseph S. Edgerfon.

liar to that around q rifle bullet in
flight, acting as an effective brake to
any further increase In speed. After
the shock wave stage Is reached, It has
been found, an increase in speed Of 10
per cent can be gained only through
an increase in horsepower Of 500 per cent.
Unless, of course, the shock wave forma
ton can be eliminated or delayed
through a change in structural form.
The necessary changes in form to delay
shock wave effects now are being sought.
When they are found, and only then,
may we expect to push airplane speeds
past 500 miles per hour in level flight.
The present worlds record of 40 miles
now is being approached here and abroad
by military aircraft.
The visitors saw motion pictures, made
at rate Of 10000 exposures second, Of
the sequence OF events in the combus-
ton chamber of an aviation engine CYL
inder Developed only within the past
few weeks to point of successful opera
ton, the tremendously high speed cam
era, slowing down motion 800 times, is
opening new field of engine study yield
ing promise of great gains In fuel econ
omy.
Working under conditions similar to
those encountered by sand hogs" who
drive tunnels under rivers and by deep
sea divers, research workers now are
beginning a program of studies in the
two newly dedicated wind tunnels.
"Scale Effect" Overcome.
The first of these, a 19-foot pressure
tunnel is the worlds latest step in the
development of improved methods for
solving aerodynamic problems in the de-
sign of large high-speed aircraft. The
EMPLOYMENT of air under pressure has
been resorted to as q method Of over
coming scale effect" in the testing of
airplane models and Of increasing COM
parative air speeds. The use Of high
density air has been proved in a smaller
form of tunnel and now can be applied
to an entirely new series of aviation
problems clamoring for solution.
The tunnel is of tubular steel con-
struction, graduated in size from the
l9-foot jet to 60-foot diameter section
in which the test chamber is housed
Here observers and operators work un-
der pressures which may reach two and
one-half atmospheres, or 40 pounds per
square inch Air under compression can
be forced through the jet at speeds OF
up to $50 miles per hour. The complete
tunnel is 271 feet long and 1913 feet wide
~ ia or Ss
driven by an 8;000-horsepower electric
motor to move the air. To make life en-
durable within the test chamber, the air,
heated by friction, must be cooled and
dried, Decomposition chambers are pro-
vided to safeguard personnel from the
dreaded 'bends" resulting from working
in compressed air.
The present program for the tunnel,
which has taken two years to complete,
calls for investigation Of the effects of
operating airplane propellers at high-tip
speeds-the shock-wave problem again
and to investigate the potentially fatal
flutter and vibration of wings, propellers
and tail surfaces driven through the air
at high speeds.
Models Tested in Free Flight.
The second new tunnel makes possible
the study of airplane models in free
fight, supported only by the flow of ali
through the test chamber in which thev
fy. In this case the whole tunnel is
mounted on bearings and can be tilted
to correspond to the angle of flight of
the model. The model is flown in the
tunnel by ''pilot" who operates switches
sctuating electromagnetic in the model