Evening star., 1936-03-22
BY FREDERICK NOONAN.


those tiny islands out in the middle
of 65,000,O00 square miles of Pacific?"
Literally hundreds have asked us that
question in one form or another.
A steamship can take its time at
such task or in making any land
fall. If clouds or fog make accurate
navigation difficult, it can lie-to or
creep along until conditions improve.
An airplane, on the other hand. must
arrive at its destination and proceed
with its landing within a few hours
Of its schedule. The contrast has
struck no one with more force than it
has struck me. Until the clipper
flights started last year. my only trip
across the Pacific was made 20 years
ago as navigation officer on a square
rigger, one of the last of the old sail
ing clipper ships.
On a surface vessel the navigator s
Sob is comparatively simple-a sex
tant's sight at the sun and a little
trigonometry at high noon, another
sight at sundown, an occasional read
Ing of the ships log whirling at the
rail, then bearing or two to plot
from a coastline radio compass sta
ton should the ship run into fog
near shore. That much suficeS. be-
cause even a fast surface vessel
travels only five or six hundred miles
in full day The flying clipper ships
go that far in three or four hours.
Even if our problems were as simple
as those of a steamers officers, we
would therefore have some six times
as much navigating work to do.
Complexities in Air Cited.
But it isn't even that easy. Fun
damentally we use the same three
methods to find our way as they do
observations of sun and stars, esti-
nations of our movement in relation
to the oceans surface. the directional
guidance Of radio. But each of these
takes on its own new complexities
when used from the air.
Celestial navigation is a case in
point. 1t is still the mainstay in
our technique, as it was in that Of
the old sailing clipper ships. AS most
people know. it consists of measuring
the angle above the horizon of the
sun or a star at an exactly known
time, and from that angle computing
ones latitude and longitude by means
Of mathematical formulae.
1t is not overly simple even on
surface ships. In the air it becomes
complicated from the fact that the
observer is not at sea level, the proper
point from which to measure the
angles above the horizon, but any
where up to four miles above it
Sometimes, too, haze or clouds will
entirely obscure the horizon from an
airplane navigator. But we have de-
Veloped for our use a specially de-
signed instrument, an octant instead
Of sextant, whose "level-bubbles
create an artificial horizon" at the
planes level. That means extra "cor-
receives" to allow for the altitude
point.
Then the speed of the airplane
Itself demands greater speed in work
ing up ones data into a position
fix" A ships mate might thumb
through his tables for half an hour
TO get the ships noon position. The
ship would still be within few miles
of the fixed point" when he had
finished. But in the same interval
an airplane would have Travelled 10
or 80 miles-and 70 or 80 miles Is
o long way to be off course.
Plotting Time Reduced.
To cut this time, our flight officers
responsible for navigation have spent
long months in training and in re-
search to abstract from tables and
elmanacS the material which would
be OF use in each particular region
of the Pacific. We worked out in
advance the correctives we had to
make for altitude. We devised special
tables to cut down on other mathe-
matical manipulations. In many cases
we prepared graphs to replace these
tables. Then each flight officer was
required to spend hours on practice
rouunes. AS consequence, the
average time needed for computing
sights and plotting positions has been
cut from 80 minutes to 6.
Routine navigation is done by
means of dead reckoning'-a proc
ess for keeping track of ones prog
ress over the ocean by straight COM
pass reading in relation to the surface
speed being made. A ships officer
gets an accurate measure of the YES
EelS speed by use of a log, which
trails from a cable attached to the
rail on the stern. He gets the ships
heading from the master compass
EirAA a ho 70 nj. u. -
currents and since the drift of the
ship due to wind is small, it then is
comparatively simple for him to plot a
very nearly accurate course from such
data alone
But even this dead reckoning sys-
tenn, which, before the ocean transport
operations of the clipper ships, was
relied upon for most trans-ocean
nights, is far more complicated from
the air than 1t Is from the deck of a
steamer.
An airplane's crew knows only its
speed through the air in the direction
In which it is pointing. Head winds,
cross winds, tail winds are constantly
on hand to make the speed and direc-
ton Of the planes progress over the
ocean something entirely different. To
find the latter the airplane's naviga-
tor must take periodic sights at some
fixed point on the oceans surface.
That means, first of all, the fixing of
some point on the surface to sight at.
This problem is solved, at night, by
the use Of high-powered flares, which
drop from the plane and burn for sew.
sral minutes after striking the water.
For daytime targets, Pan american
, developed glass bombs filled with alum
mum powder. A split second after
one Of these has shattered after strik-
ing the water, the aluminium has
spread out In a big shining patch,
distinctly visible against the oceans
green or blue. A new instrument,
which, by simple triangulation, affords
an almost instantaneous check on the
ground speed, has been developed,