Evening star., 1936-03-22

dom used Tor any appreciate distance
offshore, because of their limited
range and the inaccuracy of their bear
ings as distances from the shore sta
tions increase.
Pan-American engineers eight years
ago, when international air transport
service was first undertaken, attacked
the problem of providing positive radio
flight control over the relatively great
distances required on scheduled flight
between North and South America.
They were successful in perfecting
radio direction finders. employing both
short and long wave frequencies for
distances up to 800 miles-or better
than six times the consistent range of
the standard ships radio compass or
the airway radio beam used on trans
continental lines within the United
States.
Range Is Increased.
AS one of the preparations for trans
Pacific operations the engineers we're
successful in decreasing the range of
these direction finders to the remark
able distance of 1000 miles. So the
flying clipper ships, even in midocean,
have the same positive radio guard
that surface vessels have near shore.
The signals from the airliner are
measured by their minimum at the
receiving station, where they are reg
istered on dial. The resultant read
ing gives the true bearing of the clip
per from that station. This is then
relayed to the clipper. So perfected is
the system that complete bearings can
be given from these ground stations
at l0-second intervals. Thus, single
station can tell a plane whether it is
to the left or right of its course. Two
stations can give it intersecting bear
ings to fix its position exactly. or even
one station, by directing the clipper to
fly at right angles to its course and
then make a second change of direc-
ton, can determine such fix. With
the range of the direction finders there
are always two stations ION guard" at
each stage of trans-Pacif1c flight
In addition to the radio direction
finders on the surface, a modified
form of this system has been devel-
oped for the aircraft itself, so that
each clipper carries a direction find
ing station of its own, with a range
up to 1000 miles and with which the
clipper can tune in ships or any fixed
stations to obtain bearings of its own.
Two Hours on Duty.
Now, we might see what all this
means in terms of the navigators
duties, say, on the 2,4O0-mile, 18-hour
hop from San Francisco to Honolulu.
At the present time, in addition to the
chief navigation officer, four of the
six crew members work at the navi-
cation problems in their poSt-gradu-
ate training course, on watches calling
for two hours on, two hours of duty.
Every hour one of them dons a
jacket, helmet and goggles to take a
celestial observation through either
the hatch at the rear of the bridge
or in the top of the hull structure
behind the wing. Thirty minutes of
calculations are compressed into six
minutes for the plotting of this fix.
At least every 80 minutes a drift sight
must be taken through the cabin win
dow at bomb or flare. From this dead
reckoning progress is computed and
the course position plotted. Every
Is minutes, in normal routine, radio
bearings are received from the guard
ing ground stations and the three
navigational systems co-ordinated for
the regular Commute position report.
radioed back to the fight control Office.
Meantime, occasional sights on the
sun are taken with the drift-sight in
dicator for positive check on the
ships compass. And the navigator
must keep constant check of weather
reports, write summary of weather
conditions encountered and plot fore
casted weather changes with relation
to the course being flown. From all
Of these calculations he determines
the course being made, the actual
position of the ship and provides the
bridge officers with the proper COM
pass course to follow.
So far as Is known, this is the first
time an airplane has set up a navi-
cation routine for ocean flying.
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