Evening star., 1939-05-07
"A. P. Photo.

| which in turn. move the control surfaces
With this tunnel, for the hrst time. it
will be possible to tell whether an air
plane is q good airplane" before the
actual ship is even built. An airplane
may be scientifically sound In all re-
spects and yet not be good airplane
from the standpoint of the man who
must fly it.
Hitherto, this has been matter which
could be determined only by completing
and flying the airplane. With airplanes
now growing in size and costliness, this
method fast is becoming impracticable
To be able to gain the same results with
model will indeed prove a boon to the
designer and manufacturer. It should
be more than welcome to the poor test
pilot who has to pit himself against a
new and untried airplane of hitherto
unpredictable flight characteristics.
THE new free-flight tunnel" N. A..
c. A. officials explained, gives promise
of the development Of new design stand
ads for stability and control that will
result in marked improvement in the
Sa1eIy OF 1uture aircraft.
Seaplane Hull With Glass Bottom.
As the introduction Of heavy glass
window in the cylinder Of an engine
permits the photographing Of the COM
bustion of fuel within, so the building
of a seaplane hull with glass bottom
permits the similar Photographic study
of water flow lines along its under sur
face. This means has been resorted to
in the N. A. c. A. tank to give q new
and direct approach to development of
hull form providing the least resistance
and the best take-off.
The take-off of large flying boat is
critical performance. In large boats
now in operation 5000 horsepower or
more may be required to break the hull
free from the surface while only half
that power is required for cruising speed
in flight. The possible solution? Hydro
foils which may be retracted in flight
and lowered for take-of and landing
much as are the wheels of land plane.
Here is another promising N. A. c. A.
study now in progress.
The most serious strains imposed upon
modern large transport airplanes result,
not from turns and maneuvers, as in
the case of military aircraft, but from
air turbulence or gusts. The N. A. G. A.
now has accelerometer records for TO-
100000 miles of commercial airplane
flight, including the trans-Pacific opera
tions of Pan-American Airways. These
records are being supplemented by tests
in progress in the new gust tunnel at
Langley Field, tunnel in which the
test model, in free flight, passes through
a sharply defined rising current Of air.
Plane Reactions Varied.
Different airplanes respond differently
to the same gust and the distribution of
loads or strains varies. In the absence
Of exact knowledge Of the spots where
these strains occurred, 1t is necessary to
build aircraft with excessively heavy
structures so no possible point Of strain
may be overlooked. The new studies,
however, make it possible to determine
the exact points where reinforcement is
necessary and obviate the addition of
excess structure at, points where it is
not required. The results now are being
applied to actual design and will make
possible substantial saving in weight,
which can be applied to improvements
in range and useful load.
Experience during the past year In op-
Grafton Of the N. A. c. A. free-spinning
wind tunnel makes it possible to deter
mine within few minutes whether .
new airplane possesses dangerous spin.